june, 1965
TRANSCRIPT
m
THE THERMAL DISSOCIATION OF SOME PMTAMMINS
AND HEXAMMINBCHROMIUM(III) COMPLEXES
CHAK TAN JOE, B. A,
A THESIS
IN
CHEMISTRY
Sumitted to the Graduate Faculty of Texas TeahnoXegioal College in Partial Fulfillment of the Requirements for
the Degree of
MASTER OF SCIENCE
APPROTED
June, 1965
^ Jl«3»v.
13 I J ^ ^ ACKNO\VLii.D&i...i:.KTS
k\o 53 C 2 ^ r* Grateful acknowledgement is made to Dr. Wesley Vv.
Wendlandt for his supervision and advioe on tne pro
blem, and to the United States Air Foree, Air Force
Office of Scientific Research, for financial cssistance
that made thia investigation possible. I also wish to
express my thanks to my eolleagues for their helpful
suggestions and enoouragement*
11
ri
TAii^i; OF GCIiTii^iTS
.•i.GK;^0;VLi:.D{>i..Sy T3 i i
LIST OF TABLES v
LIST OF FIGURriS vi
I. INTRODUCTIOIJ 1
statement of Problem 1
Review of Literature 2
II. s^j^ii^dl^A^vilAh PROCEDURE 4
Preparation of Complexes 4
Materials • 4
Method of Preparation. • . . . . . • 4
Analyt ioa l Proeediires • . . . . . • • 13
Analys is for Metal 13
Analys is for Ammonia 13
Analys is for Anions 14
Instrumental iMethods 14
Thermogravimetric Analys is 14
D i f f e r e n t i a l Thermal Analys is and
&as j^^volution Analys is 19
Thermomanometrie Analys is 23
Determination of Stoiohiometry of i)ecom -
p o s i t i o n and Vacjuum P y r o l y s i s 25
I I I . ElO'JrLIi.iENTAL R.u.DljLa?S MiH DloCuS^lOiiS 3I
i o ia ly t ioa l Resul t s 31
i l l
Bisoussion of The Thermogravimetrie
Analysis Curves in Air 32
i)iseussion of The Thermogravimetrie
Analysis in Yaouum •,,, • 41
Bisoussion of The Differential Thermcd
Analysis and Gas Evolution Curves... 41
Diacussion of The Thermomanometrie
Analysis Curves • 55
jJisoussion of The Stoiohiometry Deter
mination. 60
lY. GONOLUblONS 66
Llo'i O'M' HJ^H^ERSNGES 69
iv
LIST OF TABLES
Table Page
I. Analytioal Results of The Pentammine and
Hexammineohromium(III) Complexes • 31
II. AnalytiOiil Results of The Hexaureaehromium(III)
Complexea.. • • • 32
III. Thermogravimetrie Data for Compounds Run in
An Air Atmosphere.• 33
IV. X-Ray Diffraction Data for Chromium Nitride.••• 38
V. Analytioal Data Obtained for The Isolated
Intermediates in The DTA Study..•• 43
VI. Determination of The Stoiehiometry of Reaction
by Helium Pyrelisis • • 62
VII. Determination of The Stoiehiometry of Reaotion
by Vaouum Pyrelysis ..••.••....••• 64
I J I S T Or f±\Jr{]kUijo
Figure jr'age
1. Schematic Illustration of Thermogravimetric
Analysis Apparatus 15
2. Apparatus for Thermogravimetrie Analysis in
Vacnium IB
3. Schematie Illustration ot DTA-&i. Apparatus.... 20
4. 3ehematie Illustration of DTA Fumaoe and
Sample Holder. 21
5. Sehematie Diagram of Thei^omanometric >inaly8is
Apparatus ^4
6. Wheatstone Bridge Circuit for Thermomanometrie
Analysis. • •...•..•. 26
7. Helium I'yrolysis Apparatus • 29
8. Yacsuum Pyrolysis Apparatus. 30
9. Thermogravimetrie Curves of Some Hexamiaine-
chromium(III) Complexes 33
10. Thermogravimetrie Curves of Some Ghloropti/i-
tammineehromixim(III) Complexes 37
11. Thermogravimetric Analysis Curves of Some
1 entammineehromixuidll) Complexes........ 39
12. Therraogravimetric Analysis Curves of Some
Hexaureachromi'um( III} Complexes • 42
Vi
13. Differential Thermal Analysis Cuonres of Some
Hexammineehromium(III) Complexes 44
14. &&S Evolution Curves of Hexammineehromium(III)
Complexes •.•.•••.••.••..••. ..*.• 45
15. Differential Thermal Analyaia Curves of Some
Chloropentammineehromiiuidll) Complexes.•• 43
16. Gaa Evolution Curves of Some Chleropentammine-
ehromium(III) Complexea...... «.. 49
17. Differential Analyaia Curves of Some Pentammine-
ohromiumdll) Complexea.... ••.•••••....... 51
18. Gaa Bvolutien Curves of Some Pentammine-
ohromiumdll) Complexes....«••.........••. 52
19* Differential Thermal Analysis Curves of Some
Hexaureaohromium(III) Complexea...•.••••.• 53
20. Gaa Evolution Analyais Curves of Some Hexaurea«^
ehromium(III) Complexes. •..•......••• 54
21* Thermomanometrie Azialyaia Curves of Some Hexa-
mmineehromium(III) Complexea ..•••• 56
22* Thermomanometrie Analyaia Curves of Some
Pentammineohromium( III) Complexea .....•••• 59
vii
I. INTRODUCTION
STATEMENT OF PROBLEM
The ohromium(III) ammine eomplexes which have the
general formulae, [Gr(im^)^X^ and [Orim.^)^xiY^
(where X and Y repreaent the halide ion), deeompose
thermally aeoording to the reaotionai
[Or(NH3)^]X3 g; > [Gr(NH3) 5X3^1 * 3NH3
[Or(NH3)jX]X2 gj; > 1[0r(NH3) XYgl • SNH^
Very little work haa been done previoualy on the thermal
diaaooiation reaotiona for these complexes* Therefore,
it is the purpose of this investigation to elueiadate the
theraial dissoeiation reaotions by subjecting these ohre-
mium(III) hexammine and pentammine complexea to the methoda
of thermogravimetric analyaia, differential thermal ana
lyaia» gas evolution analyaia, thermomanometrie analyaia,
and atoiohiometry determination.
Further atudy was extended to include the hexaurea-
ehromium(III) oomplexea by the aame methoda*
REVIEW OF LITERATURE
Late in the last eentury, Jorgensen published a
series of papers conoeming the pentammineehromiumdII)
(1) and hexammineohromiumdil) (2) eomplexes. He found
that chloropentammineehromiumdil) ohloride, [Cr(NH,)KCl] Clpt
formed the aquopentammineohromium(III) ohloride complex,
[0r(NH,)cH20lCl,, upon prolonged standing in water (3).
He also found that the aquopentamminechromiumdil) salts
[0r(liH,)eH2O]X-, lest the water molectile from the coor
dination sphere on heating to about lOO^C.
In 1925 f Sehlesinger and Womer (4)> upon heating
chloropentammineehromiumdil) chloride in an air, carbon
dioxide, or ammonia atmosphere, were able to obtain tri-
ehlorotriammineehromium, [Gr(NH^),Cl^^, as the decomposition
product. They found that further heating of the latter
oompound yielded black chromium nitride, CrN, as the de
composition product (5). They also found that if the
ohloropentammineohromiumC III) chloride was heated in a
stream of dry hydrogen eiiloride a vigorous reaction took
place at 270^0 with the evolution of heat. The green tri-
ehlorotriammineehromium, whieh was formed, was isolated if
the temperature was not allowed to rise above 270 *0.
About the same time, Sehlesinger and Riokles (6) were
able to prepare three mixed halide ohromium triammines,
having the formulas, [cr(NH^)^Br3] , [cr(m^)3ClBr2] , and
2
3
[Cr(NH^)^BrCl2l» by the thermal deocxposition of the appro
priate pentammine. The general method for the preparation
of these triammines was as follows:
[Cr(NH3)^XlY2 ^^7^^ J^270^G} Cr(NH3)^AY2 ^ ZHYi^
( where X and Y were chlorine and bromine ).
They were, however, not able to prepare the iodo-, nitrate-,
or nitritetriammineohromium complexes by this method*
In I960, Pesehko and Block (7)» on their atudy of the
thermal stability of ohloropentamminechromiumdll) ohloride,
were able to isolate [0r(NH~)-Cl3] at about 250*>C in air.
An equated product of this compound was found to be
[Cr(NH ).(H20)2]C1- rather than the expected \OT{im^)^{E^O)^ '
Cl«. Therefore they suggested that the oomplex, having
the formula [0r(NH^)^Cl^], was really an ionio species with
the eomposition, [Cr(!m^)^Cl2]LCr(NHj)2Cl^.
Wendlandt and Bear (8) studied the thermal deaquation
of some aquopentaimaineehromium(III) complexes. They found
that deaquation of these eomplexes took place at about 115^0.
Wendlandt and Robinson (9) also studied the thermal deaqua
tion of some diaquotetramminechromium(III) eomplexes. They
found that the deaquation took place stepwise prior to the
evolution of stmmonia*
II. EXPx^IMENTAL ritOG DURE
PREPARATION OF OOBILPLUA.^3
Materials:
The anhydrous ammonia was obtained from the Matheson
Co., Joliet, Illinois.
The ohromiumCIXIi chloride hexahydrate was obtained
from the Mallinekrodt Chemioal Works, St. Louis, Mo. It
was used for the preparation of the anhydrous chromium(III)
chloride, the starting material in the preparation of most
of the pentammine- and hexamminechromium(III) complexes.
All of the other chemicals used in this study were of Re
agent Grade Q\iality.
Method of Preparation:
Hexammineohromiumdil) Complexes
Hexammineohromium(III) nitrate, [Cr(H.i .)/l (1^0^),, was
prepared by the method of Oppegard and Bailar (10).
Anhydrous ohromium(III) chloride was prepared by
passing carbon tetraohloride over hot chromium oxide at
about 600* 0 (11). The apparatus used for this preparation
consisted of a furnace, a 500-ml. distillation flask, D,
whieh was inserted inside the furnace, and a 250-iiil. dis-
tillation flaak, B, having its moutix enclosed by a separa-
tory funnel, A, and its side-tube connected to the mouth
of the flask D by glass tubing. The side-tube oi fiasK: D
was then connected to a condenser and a receiver. Thirty-
seven grams of the chromiumdII) chloride 6-hydrate, OrGl^ •
6H2O, was placed in distillation flask, D, and 100 lul. of
carbon tetrachloride in the separatory funnel A. The fur
nace was heated to 90*C and the carbon tetrachloride dis
tillation was started, one drop from the separatory funnel
every two seconds was a suitable rate. The hydrated salt
melted at approximately 150^0 and soon formed a spongy mass
which filled the flask. At approxima-tely 200°C, a condensate
of water and carbon tetrachloride began to collect in the
receiver. At higher temperatures, phosgene was present in
the eifluent gas, and anhydrous chromium(III) chloride was
formed. The reaction was completed when the temperature
of the furnace was approximately 650^0. The entire product
was left in the flask as a loose mass of glistening violet
crystals, which could be easily removed from the flask.
For the preparation of hexamminechromium(III) nitrate,
about 800 ml. of liquid amaionia was introduced into a one-
liter Dewar flask, along with 0.5 g* of clean sodium metal,
and 0.2 g. of ironClI) ammonium sulfate. After the blue
color of the sodium had disappeared, ^0 g. (approximately
0.3 mole) of anhydrous chromlum(III) chloride was added in
2-g. portion, while the solution was constantly stirred*
After the addition had been completed (1 to 2 hours), the
brown preeipitate was allowed to settle, and the clear,
slightly colored supernatant liquid was deeanted or si
phoned from the Dewar flask.
The residue was transferred to a large evaporating
dish and allowed to stand with oocasional stirring until
the odor of ammonia was no longer detected and a bright
yellow, freely flov/ing powder remained. The impure he
xammineohromiumdil) ohloride obtained was quickly dissolved
in a mixture of 150 ml. of water and 10 ml. of concentrated
hydrochloric acid at 50®C, and filtered. The filtrate was
immediately treated with ^0 ml. of concentrated nitric aoid
and cooled to room temperature. Pure hexammine chromiumdII)
nitrate precipitated out on standing. The bright yellow,
crystalline salt was collected on a Buchner funnel and
washed first with cold distilled water containing a little
nitric aoid, then with alconol, and finally with ether.
The product was then dried in a IIQOC oven for two hours
before being placed in the desiccator over barixim oxide.
Hexammineohromiumdil) chloride, [Gr(NK ,) ] Cl^ , was
precipitated by adding to a warm solution of hexammine
ohromiumdil) nitrate an excess of a 1:2.5 solution of con
centrated hydrochloric acid and ethanol (12)* The preci
pitate obtained was purified by recrystallization and dried
in a 110«C oven for two hours before being plaeed in the
desiccator.
Hexamminechromium(III) bromide, CCr(NH )jBr and p t 3' ******
7
hexamminechromiumdll) iodide, [Or(Lili,)/lI,, were prepared
by the same general method of adding solutions of concen
trated hydrobromie and hydroiodic acid, respectively, to
a warm saturated solution of hexammineohromiumdil) nitrate.
PentammineehromiumdII) Complex
Chloropentammlneohromiuiiidll) chloride, [Cr(NH,)cGlJ Clp,
was prepared by the method described by Christensen (13).
Ten grams of anhydrous chromiumdII) chloride (11; was in
troduced in 2 g. portion to a Dewar flask which contained
150 ml. of liquid ammonia. After the addition of the an
hydrous ChromiumdII) chloride was completed, the red pre
eipitate was allowed to settle, and the clear, slightly
colored supernatant liquid was decanted. The residue was
transferred to a large evaporation dish and allowed to
stand with occasional stirring until the odor of ammonia
was no longer detectable. The residue was then ground with
40 ml. of cooled water, filtered, and washed with a small
amount of cooled water until all of the red filtrate waa
washed away. The residue, which contained the impure ohlo
ropentamminechromiumdll) chloride, was transferred to a
beaker and boiled with 50 ml. of concentrated hydrochloric
acid. After cooling, the mixture was filtered and the red
residue waa q\iickly dissolved in 100 ml. of distilled water
at 50^0. After the addition of a few drops of concentrated
sulfuric acid, the solution was filtered by using a sintered-
8
flaaa fonmal* Then 200 ml* of eoneentrated hydreehlerla
aoid waa added to the aolutiont and a bright red, erya-
talline aalt waa preeipltated* The produet waa waahed
firat with cold diatiXled water eontaining a little hydro-
oblerio aeid and then with alcohol. The produet waa heated
in a XXO^O oven for two hour a and then plaeed in the deai-
eeator over bariiua oxide.
OhXaropentammineohromium(III) bromide, \]0r(NH,)K0l}-
Br2t ohleropentammineehromium(III) iodide, [Cr(NH,)K01] l2t
and ohloropentamminechromiumdll) nitrate, [Cr(NH.)KGX] (N0-)2
were prepared by the same general method of adding aolutiona
of eoneentrated hydrobromie aeid, l^droiodie acid and nitrie
aeid, reapeetively, to a aaturated aolution of ehloropentam-
mineebromium(III) chloride* The red produeta obtained were
purified ^ reoryataXlization from 95% ethanol*
Hitratopentammineehromium(III) nitrate, [cr(NH.}.(N0^)l-
(H0«)2t waa prepared by the method deaoribed by Mori (14) •
uaing aquopentammineehromium(III) nitrate ammonium nitrate,
[Cr(NH5)5H20](H03)3 • NH^NOj*
One hundred grama of potaaaiumdil) sulfate 12-hydrate
( 0*2 mole )» pulverized to pass through a 60-meah aieve,
waa mixed in a flai^ with 250 ml. of 15 M aqueoua ammonium
nitrate* Then 250 g* of ammonium nitrate waa added, and
the flaak waa Xooaely atoppered with a oork eontaining a
thermometer* The mixture was then cooled to below 40*C,and
a vigoreua eurrent of air paaaed thre\&gh it for 30 minutea*
9
The aolution was poured alowly into a mixture of 100 g* of
eraeked lee and 250 ml. of concentrated nitrie aeid, the
temperature being maintained below 30*G by means of an iee
bath. The red suapenaion was kept in the iee bath for one
hoxir, with oeeaaional stirring to complete orystalliaatien*
The resulting orange crystals were eelleoted on a Buchner
funnel and dissolved in 200 ml* of water. The suspension
was filtered, and the filtrate was treated with a filtered
solution of 200 g* of ammonium nitrate in 200 ml* of water.
The mixture was stirred and eooled with iee. The orange
erystals that formed were removed by filtration and washed
firat with 200 ml* of a filtered, aaturated ethanolie aolu
tion of ammonium nitrate and then with 200 ml* of a 1:1
mixture of ethanol and diethyl ether*
For the preparation of nitratopentafflmlneehromium(III)
nitrate, [Cr(NH,)eNOJ](N03)2» four and two-tenths grama of
aqaepentammineehromiumdll) ammonium nitrate was diaaolved
in 50 ml* of distilled water, and 20 ml* of eoneentrated
nitrie aeid was added. The mixture was cooled in an ice
bath, and then 20 ml. of 95^ ethanol was added* After
several minutes, the orange leaflets of aquopentammineehro-
mium(III) nitrate thua formed were eollected on a filter
and waahed with 95^ ethanol* Thia eompeund was heated in
an oven at 60**C for eight houra to give the fleah-eolored
nitratopentammineehromium( III) nitrate *
BromopentammineohromiumdII) bromide, [cr(NH3)cBrlBr2f
waa prepared by diaaolving 4.2 g* of aquopentammineehro-
10
mium(III) nitrate ammonium nitrate in 8 ml* of water eontain
ing 2 ml* of 15 M aqueoua ammonia* Ten millilitera of 43%
hydrobromie aoid and 10 ml. of 95% ethanol were added, and
the mixture was eooled to 0«C* The preeipitate waa eelleoted
on a filter, waahed with 95% ethanol, and then diaaolved
in 20 ml* of water. The resulting solution waa filtered,
treated with 20 ml* of 48% hydrobromie aeid, and eooled to
O^C. The eryatalliaed aquopentaamineehromium(III) bromide
waa removed by filtration and waahed with 95% ethanol*
Theae eryatala were diaaolved in 20 ml* of water and 5 ml*
of 48% hydrobromie aeid was added* The mixture was digested
on a at earn bath for 30 minutes, and three 50 ml. portions
of 48% hydrobromie aeid were added at intervala of several
mlnuLtea* The mixture waa eooled to room temperature and
filtered* The preeipitate of bromopentammineehromiumdll)
bromide waa waahed with 95% ethanol and air dried*
lodepentammineehromium(III) iodide, [0r(NH3)el]l2t was
prepared by the acune general method deaoribed above* Foxur
and two-tentha grama of aquopentammineehromium(III) nitrate
ammonium nitrate waa diaaolved in 8 ml* of water eontaining
2 ml* ef 15 M aqueoua ammonia* Ten millilitera of 48% taydro-
iedio aeid and 10 ml. of 95% ethanol were added, and the
mixture waa eooled to 0*0* The aqoopentammineehromiumdll}
iodide ao obtained waa purified by diaaolving it in 20 ml*
of water and reeryataXliaatien from 20 ml* of 47% hydroiodie
aoid* The eryatala were then diaaolved in 20 mX* of water.
11
and 5 ml. of 47% hydroiodie aoid was added. The mixture
was digested on a steam bath for 30 minutes, during whieh
time three 50 ml. portions of 47% hydroiodie aeid were added
at intervals of several minutes. After cooling and filter
ing, the orange-colored precipitate of iodopentajmminechro-
mium(III) iodide was waahed with 95% ethanol and air dried.
HexaureachromiumdII) Complexes
Hexaureachromium(III) chloride (15)» [Cr(C0N2H.)^]-
Cl, • 3H2O, waa prepared by the reaction of urea with green
ohromium(III) chloride hexahydrate (15).
The green chromium(III) chloride hexahydrate, CrGl^ -
• 6H2O, was prepared by mixing 100 g. of chromic acid (CrO^)
and 400 ml. of concentrated hydrochloric acid in a round
bottle flaak.. The mixture was boiled gently in a fume hood
until chlorine evolution ©eased and the solution was of a
clear, green color. The solution was concentrated in an
evaporating dish on a steam batn until it beeame Yerj via-
oous and aolidified to a orystalline mass on cooling. The
eryatala were dried first on a porous plate and then over
concentrated sulfuric aoid in a desiccator. Half of the
erude produet was dissolved in 50 ml. of distilled water,
filtered, and the eooled solution was saturated with hydro
gen ohloride. The resulting solution was allowed to stand
for a few hoiirs, then filtered quickly onto a sintered-
glaas funnel. The solid produot was transferred to a de-
12
siocator and dried for two days* The dried crystals were
stirred with dry acetone, filtered into a Buchner funnel,
and waahed with successive quantities of acetone.
For the preparation of [Cr(G01T2H.)g] 01, * 3H2O, 10 g.
of green chromiumdII) chloride hexahydrate was plaeed into
an evaporating dish and heated until it dissolved in its
own "water * of orystallization. One or two drops of dilute
hydroehlorio aeid was added, along with 10 ml. of water
and 25 g. of urea. The solution was evaporated on the steam
bath until a eruat formed on the surface. The residue
was eooled and dissolved in water at 50°C. The hexaurea-
chromiumdll) chloride was filtered off from the solution
in the form of fine green needles* The compound was waahed
with acetone and air dried before being placed in a desie-
eator.
Hexaureachromiuadll) iodide, C0r(G0IT2H^)g]I,, and
hexaureaohromiiam(III) nitrate, [priOO}i^.)/\i^O^)^, were
prepared by the same general method of adding to a warm
solution of [Cr(G0N2H^)g]Cl^ • 3H2O solutions of 47% hydro
iodie aoid and concentrated nitric acid, respectively. The
products obtained were dried in a 110*C oven for four hours
before being placed in the desiccator.
AKi-LYgjCAL rRGCi DUHL
Analysis for Metal
For the analyaia of the ohromium content of the com
plexes employed in this atudy, it was neccessary to decom
pose the complexes thermally to their oxides, i.e. CrpO^.
The samples to be analyzed were intimately mixed with oxalic
acid and then alowly heated to the decomposition temperature.
The mixture, after the removal of the original halide iona
as hydrohalide, was then heated in a muffle furnace at 700^0.
Analysis for Ammonia
The ammonia content of the penta- and hexamminechro
miumdll) oomplexea were analyzed by means of the Xjeldahl
method for the determination of ammonia (16).
About 50 mg of the sample to be analyzed was dissolved
in 50 ml. of distilled water at 60«C. The solution was
tranaferred to a 125 ml. Kjeldahl flaak and then 30 ml. of
6 N sodium hydroxide was added rapidly to it. The mixture
was heated to boiling and the distillate condensed into 30
ml* of 6 N sodium hydroxide was added rapidly to it* The
mixture was heated to boiling and the distillate condensed
into 30 ml. of 4% borio aeid* The distillation was oom-
pleted after two-thirds of the volume of the original solu
tion was distilled* The solution obtained was then titrated
13
14
with standard 0.1004 N hydroehlorio aeid from blue to a
greenish-yellow color of bromocreaol green indicator that
was exactly matched by a reference solution of the same
volume and eoncentration of borio acid and indicator.
Analysis for Anions
For the determination of the halide anions, the com
plex were dissolved in distilled water and titrated with
standard 0.0214 N silver nitrate solution. Fluorescein
was used as an absorption indicator.
INSTRIJI/IENTAL METHODS
Thermogravimetric Analysis
(1) In an Air Atmosphere
The thermogravimetric analysis study of the eomplexes
in an air atmosphere was carried out on an automatic recor
ding thermobalance as previously described by Wendlandt et.
al* (17). The schematic diagram of the instrument is shown
in Figure 1.
The automatic recording thermobalance consisted of a
chainomatic analytioal balance to which a Fisher Recording
Balance accessory was attached. A Moseley, Model 53, X-Y
reeorder was used to reeord the baleuice attachment voltage
output. The weight was reoorded on the vertioal Y axis
while the temperature, as detected by a Chromel-Alumel
thermocouple, was recorded on the horizontal X axis.
FURNACE
rs
V FURNACE CONTROL
BALANCE \ .
o CO
O CO
C O
RECORDER
BALANCE CONTROL
FIGURE 1 SCHEMATIC ILLUSTRATION OF THERIvIOGRVI:,!r.THIC
ANALYSIS APPARATUS
16
A Hevi-Duty furnace, with a rating of 750 watts and a
maximum temperature of 1000*»C, was used. A ceramic rod of
an outside diameter of 2 mm was mounted on the top of the
left balanoe arm. On the top of this rod was placed a
nickel orueible holder on which a size 00000 porcelain oru-
oible waa seated. A Chromel-Alumel thermoeouple was placed
immediately above the crucible.
The temperature rise of the furnace was controlled by
gradually increasing the input voltage to the furnace win
ding by means of a six revolution-per-day syohronous motor
connected to the shaft of a Powerstat autotransformer (18).
A second Powerstat controlled the input voltage to the motor-
driven Powerstat. With an input voltage of 120 volts to the
motor-driven Powerstat, which was set at 30 volts, a heating
rate of about 5 C per minute was obtained*
To run a sample for the thermogravimetric analysis,
about 70 ml. of sample was weighed out into the clean and
dried crucible. The crucible was placed into the nickel
crucible holder and the balance was allowed to come to equi
librium* The heating cycle was started and the weight change
recorded up to a temperature about 500*C.
(2) In a Vacuum Atmosphere
The thermogravimetrie studies were carried out also in
a vacuum atmosphere using a vacuum thermobalance. An Aina-
worth automatic recording balanoe was used. This balanoe
17
was obtained from William Ainsworth and Sons, Ine., Denver,
Colorado*
A schematie diagram of the instrument is shown in
Figure 2*
The furnace used was made by insulating a 23 em long
Vyoor tube with asbestos paper. A thermocouple well in the
bottom of this furnace tube was extended 3 em into the fur
nace area. The tube was wrapped with 30 ft. of Niohrome
resistance wire (1.05 ohms per ft.) to give a total resis
tance of about 21 ohms. The wrapping was then covered with
approximetely a 1 em thick layer of asbestos insulation.
The sample holder consisted of a 0.5 g* platinum cru
cible 3 mm in diameter by 7 mm high. The crucible was sus
pended by 3 inch long segment of platinum wire whioh was
attached to the lower end of a 60 cm long, 2 mia in diameter
Pyrex rod, while the upper end of this rod was attached to
the bottom of the left balanoe pan. This rod was inserted
inside a 2.5 em in diameter Pyrex tube whioh contained a
ground glass joint to which the f\xmace was attached. An
outlet from this Pyrex tube was connected to a conventional
high vaouum system*
To run an TGA curve in vaouum, 10 to 20 mg of sample
was weight out into the tared orueible, whieh was then sus
pended inside the furnace chamber. The system was evacuated
by means of a vacuum pump and tne high vacuum system* After
the system eame to equilibrium and the desired vacuum was
18
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w
CO C.*3
I
J wo 2 ; ^ pc; c> 1 3 0 C^
o
EC4
3-< (D kvyyyyyyyy.
^
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31
JZ
^
5 P
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19
obtained, the furnace heating cycle was begun. A heating
rate of 5* 0 per minute was normally employed* The weight
loss of the sample was reoorded on one pen of the recorder
while the temperature was recorded by another pen. Both
funotlona were recorded against time.
Differential Thermal Analysis and Sas Evolution
Analysis ( DTA-GE )
The apparatus used for this study waa the same as that
previously described by Wendlandt (19) • The Instrument
consisted of a basio DTA unit which was able to detect the
gases evolved during the process of pyrolyais by means of a
thermal conduotlvity cell. Thus it was able to plot the
DTA curves suid gas evolution (GE) curves as a function of
temperature. A schematie diagram of the apparatus is shown
in Figure 3.
The furnace eonsiated of a nickel tube, 2.40 cm in
diameter by 15 cm long, to which was welded a flange to
support the sample holder, as shown in Figure 4. The fur
nace tube was insulated first with asbestos paper, then
wound with 20 ft. of Niohrome resistance wire (1.05 ohm per
ft.)* The heater winding was covered with approximately a
1 cm thick layer of asbestos insiilation*
The thermocouples, whieh were held in place in the
sample holder by two holed eeramle rods of 3 mm in diameter,
were made by spot-welding No. 26 gauge Chromel-Alumel wire*
H •• X. *". 20
.>!. • ' '
E H
i O - J
d
O . I
O M • ^
OQH
o
o
II O
I X
o M El
o
»
0)
E H
P4
S! M CD
I < EH Q
&• O
O
E H
3 H 4
o M
o CO
to
M
' i * •• • •
21
REPKRENCE
1IGKEL TUBE
2-HOLg INSULATOR TUBES
He
IlviCONEL GUP
SAI.'PLE
FURNACE <VII\DING
U l III U" RliMCx SEAL
a& I ^~33^
FIGURE 4 SCHEMATIC ILLUSTRATION OP DTA FURNACE
AND SAiMPLE HOLDER
22
Two small Inoonel cups were seated at the ends of ^hese
insulator rods in such a raanner that they made intimate
contact with the thermocouple junction. The cups, with
a capacity of 0.27 lal.i were obtained from The Robert L.
Stone Co., Austin, Texas. A neoprene "0** ring, 3.5 em in
diameter, was employed to provide a gas-tight seal between
the sample holder and the fumaoe assembly.
The furnace temperature control unit was the same as
described for the thermobalance. ii small squirrel-cage
type blower was employed to cool the furnace down to room
temperature after each run.
The DTA part of the apparatus consisted of a Leeds
and Northrup Model 9335B d.o. microbolt amplifier and a
Houston Instrument Corp. X-Y Recorder. The thermistor
thermal conductivity cell, T/C, containing two matched
8000 ohm thermistors, was obtained from the P gmd M Scien
tific Corp., New Castle, Del. The oell bridge eireuit was
conventional in design and was powered by a Zener diode
stabilized 12 volt d.o. supply, Model T-lOO, also obtained
from The F and M Scientific Corp. The output from the bridge
circuit was fed into the Y-axis of a Lioseley Model 135 R » Y
reeorder, while the X axes of both recorders were connected
to the reference thermoeouple in the sample holder through
a O^C iee-water reference junction*
To run a DTA-GB curve, about 40 mig of sample was placed
into the sample cup. The reference cup was filled with appro
ximately the aame amount of alumina. After loading, the sam-
23
pie holder assembly was inserted into the fumaoe ehember
and locked in place by four bolts and wind-nuts* Then
helium ga^ was allowed to flush throu^ the aystem for a
few minutea at a flow rate of 200 ml* per minute, and later
reduced to 100 ml. per minute* The bridge oirout was ba
lanced with 9*5 ma of eurrentt while the T attenuation of
the &S reeorder was aet at 10 mv* per inch* The DTA d*o*
amplifier was ao adjuated that a one inoh defleotion on
the X a^a of the DTA reoorder oorresponded to lOC^v^T*
After allowing a few minutes for the ayatem to stabliae,
the fvirnaoe power supply was adjusted to a heating rate of
lO^C per nisu.te»
Thermomanometrie Analyaia
A aehematie diagram ef the apparatua waa shown in
Figure 5*
The apparatus eonaiated of a horisontal Pyrex glaaa<»
tube aample holder of whieh one aide was attached to a
vaouum ayatem by an ^ O" ring aeal* On the other aide ef
the tube waa a thermeeouple^well, whioh oontaiaed a QbromeX-
Alumel thezmoooupla* The sample holder was put inaide of
a fomaee whose eonstruotion waa aimilar to the vacuum TdA
fojmaoe* The fuxnaee eontreXler waa designed in the aame
way aa mentioned in the T&A apparatus* A gXaaa aampling
bulb waa oennected by a gXaaa Joint near the aample holder*
Two maaometera measured the preaaore of the ayatem*
24
CO
E H
Pi
CO M CO
o M P: W a o
o
EH
o
M O
o M EH
O CO
M
25
one measured the pressure of the vacuum line, the other
measured the pressure in the sample holder. This mano
meter was connected, as shown in Figure 6, to the Whet,t-
stone bridge eireuit by means of two Ni chrome resistance
wires. The increase in resistance of one arm of the Wheat-
stone bridge eireuit, due to the dropping of Hg-oolumn,
ereated an unbalance of the circuit. This unbalance of the
bridge was recorded as the pressure change on the Y axis
of the X-Y recorder.
To make a thermomanometrie analyais run, a sample was
weighed into a porcelain boat and placed inside the sample
holder. The system was evacuated and stopcock A was closed
while B was kept open. The stopcoek to the gaa sampling
bulb oould be opened if gas collection and analysis was
desired. The furnace power supply was then adjusted for
a heating rate of 10*»C per minute and the change in pressure
of the system recorded on the recorder. A plot of pressure
change in the aystem versus temperature was thus obtained*
Determination of Stoiohiometry of Decomposition by
Helium and Vaouum Pyrolysis
In order to determine quantitatively the amount of
ammonia evolved during pyrolysis, two apparatus were set up,
as shown in Figures 7 and 8.
A sehematie diagram of the apparatus for the deter
mination of ammonia in a helium atmosphere is shown in
^(
X-Y RECORDER
DC POWER SUPPLY
iEALING WAX
RESISTANCE WIRE
: . — H g COLUMN
FIGURE 6 WHEATSTONE BRIDGE CIRCUIT FOR THERMOS.ANOMETRIC
ANALYSIS
27
Figure 7. The first U-tube, which contained barium oxide,
BaO, was used to absorb the HgO which was evolved during
pyrolysis. The second U-tube which was packed with mag
nesium perohlorate, Mg(C10.)2 , was used for the purpose of
abaorbing ammonia*
The furnace and its temperature control were of the
same type as described previously for the vacuum TGA. A
glass tube, of about 3 cm in diameter by 20 cm long, was
packed with Drierite for the purpose of absorbing moisture
in the helium gaa stream before it entered the pyrolysis
furnaoe.
To make a run lor the determination of amraonia evolve
during the deeomposition, about 0.1 to 0.2 g. of sample
was weighed into a saoiple boat. The sample boat v/as then
plaeed inside the sample holder. A stream of helium gas,
with a flow rate of about 20 ml. per minute was SLllowed to
flush through the aystem for a few minutes. The U-tube
eontaining magnesium perohlorate was then weighed and re-
placed in the ayatem. The power supply of the furnace was
turned on and the sample was heated at a rate of 5 C per
minute* The atopcocks of the U-tube containing magnesium
perohlorate were then opened* The aimiionia gas which was
evolved at a higher temperature was absorbed by the mag
nesium perohlorate. The heating was stopped at about 500^0.
A few minutes after the power supply of the furnace was
turned off, the stopcooks of this U-tube were elosed. The
28
U-tube waa removed and weighed. The increase in weight
was equal to the amount of ammonia evolved during pyro
lyais. The residue in the sample boat was also weighed.
A sehematie diagram of the apparatus used for the
determination of ammonia in a vacuum is shown in Figure 8.
The apparatua was very similar to that mentioned above,
exoept that a vaouum pump was used to evaouated the system
prior to the pyrolyais of the compound.
6
29
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ii I"
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EH
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30
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I I I . £;AP^RIMI:.WTAL RL3ULTS AND DloLiU^^IUiS
AICALYTICAL XX SULTS
The r e s u l t s of the ana lys i s of the pentammine- and
hexammineehromi\im(III) eomplexes and the hexaureachro-
mium(III) complexes are shown, r e s p e c t i v e l y , in Tables
I and I I .
TABLE I
ANALYTICAL K.c:;: ULTS OP Jlhr.
i-ENTAMMINE AND HLXA;nv!lNLGHRO.cJUM(III) 00- fhj^Asi.5
Compound Theoretioal Found
%Cr %NH, viCr ^ h .
{GT{mi^)^-\Br^ 13.20 25.93 13.60 25.60
tCr(NH3)g'lCl3 19.96 3S.21 19.64 39.03
rCr(NH3)^]l3 9.72 19.10 9.37 19.21
(Crdraj)^"] (NOj)^ 15.29 30.03 15.40 29.69
[Cr(NHj)^Cl]Cl2 21.36 34.09 21.49 33.37
[Cr(NH3)3Cil Brg 15.65 25.37 15.83 25.31
rGr(NH3)3Clll2 12.22 19.97 12 .14 19.42
[Cr(NH5)5l]l2 10.04 16.44 10.06 16.25
lCr(NH3)5Cl](N03)2 17 .53 28.71 17 .48 17 .91
rCr(NH^)5BrJBr2 13.30 22.59 13.36 21.95
^r(NH3)^(N03)J (NO^)^ 16.09 26.35 It).20 26.47
31
32
T A B L L il
A>iALYTICAL RLSUij'rS OF T}ii:i
iij:.uLiajRi:«AGiiRC. IUiri( III; GCj.PijEiujS
Compound
[Cr(GOK2H^)gJCl3 • 3H2O
LCr(C0N2H^)^1Br5
LCr(C0N2H^)g]l5
\Cr(00N2H^)g](N03)3
Theoret ioal
%Cr
9.08
7 .98
6.57
3 .69
%anion
18.41
36.78
48.01
Found
%0r
9.08
7.67
6 .53
3 .62
%anlon
18.34
36 .4
47.63
DISCUSSION OF THE THERift.;GRAVIivlETRIC
ANALYSIS (TGA) GURVLS IN AIR
The TGA curves (in air) of the pentammine- and
hexamminechromiumdll) complexes showed that the nitrate
deocmpoded violently at about 200®G, while the rest of
the complexes began to evolve gases in the 180^0 to
250*0 temperature range, with a constant loss in weight
observed up to 420«C. The ehromium(III) oxide, CrgO,,
whieh was formed between 460^0 to 480'C, was the residue
at higher temperatures. Table III shows a suimnary of the
analytioal results ef the TGA study of the pentammine-
ohromiumdll), hexamminechromiumdll) and hexaureachro-
m i u m d i l ) complexes*
TABLE I I I
THERIviOGRAVIi-iETRI C
DATA FOR GOivlPOUNDS RU. IN AIR
33
Compound Deeomposition
Product Theoretioal Found
\pT{m^)^'\ci^
lCr(NH3)g]Br3
[Cr(NH3)g]l3
lpr(NH3)g] (1)03)3
L0r(NH3)3Cilci2
Ior(NH3)5Cl]Br2
|_Cr(NH3)5Cl]l2
lCr(NH3)3Cl|(N03)2
[Cr(NH3)5l]l2
gr(NH3)3BrlBr2
[Cr(NH3)3NO^( 1^03)2
[cr(CON2H^)g]Cl3 • 3H2O
Ccr(NH3)3(
Cr203
Cr203
Cr203
C^2^3
^^2^3
C^2^3
Cr203
Cr203
^^2^3 Cr203
Cr^O,
[CrCCONgH^
; Cr(C0N2H^
CrCl,
CrgOj
3I3]
^hl *>5
CI3
01^
30.28
29.17
19.29
14.21
22.34
31.21
22.36
17.74
25.62
14.68
20.17
23.52
90.56
59.01
27.65
13.27
80.3
29.0
19.5
14.4
22.5
32.2
23.6
17.7
26.2
14.9
20.1
23.5
90.1
58.2
26.8
13.0
34
TABLE III CONTINUED
ICr(C0N2H^)g]Br3 [Gr(C0K2H^)3Br3J 72.48 73.1
CrBr3 44.71 44.9
Cr203 11.66 11.9
[cr(C0N2H^)g]l3 f_Cr(C0N2H4)3l3] 77.28 76.1
Crl3 54.56 53.8
Cr203 9.53 9.6
[cr(C0N2H^)^(N03)3 0r203 12.70 - -
The TGA eurves of the hexamminechromiumdll) eomplexes
are shown in Figure 9. The hexamminechromiumdll) chloride
began to lose weight at a temperature of 200<»C. A alight
diseontinuity in the weight loss curve was observed near
300®C, whioh corresponded to the loss of three moles of
ammonia per mole of oomplex. This was followed by further
loss of weight up to 430«C. From 430^0 to 440*>C addition
al weight loss took plaoe to give Cr203 aa the residue*
The TGA cxirve of hexamminechromiumdll) bromide showed
that this compound was stable up to 250<'C. At this tem
perature, the compound began to lose weight. A stable re
sidue, which was not identified, was formed at 410^0. This
unknown oompound was converted to CrgO, upon further heating
to 480^0.
.•4%* i
fV^ ' !*
II
EH
M
S . LCr(NH3)Q](N0
10 mg
35
100 200 300 400 >te" TEJ/5PERATURE, C
1*^41.,JfpIOURE 9 ' {ERMOaRAVIMETRIC CURVES OF SOME ' • 7 •
4 ' '
V , 1 r
HmKCJINECtoOMIUMdII) COMPLEXES
S'>
36
The hexamminecnrofflium(III) iodide began to deeompose
at 190®C, and lost moat of its weight before 290* 0. A
horizontal plateau, which was found from 290*>G to 430«C,
indicated that a stable intermediate compound was obtained
in this temperature range. This intermediate oompound was
converted to 0r203 between 430«C to 450*0.
For the hexammineohromiumdil) nitrate, tne TGA curve
ahowed that thia oompound started to lose weight alowly
from 170^0 to 210*0. Upon reaching 210 «»C, this compound
formed the stable, green ohromium oxide, OTJ^T,*
The TGA eurves ef the chloropentammineehromiumdil)
complexes are shewn in Figure 10. The ohloropentammine
chromiumdll) chloride complex was foiind to lose weight at
235^0. At 435**C, an unknewn residue was found, which was
converted to chromium oxide from 470° to 480°C. resehko
and Block (7) indicated that CrOCl was the stable oompound
whioh oorresponded to the presence of tne horizontal level
before the formation of OrpO^. This unknown residue waa
isolated as a black colored suostance and it gave a poor
X-ray pattern which was later Identified as GrlT. The -rsLy
data for this compound are given in Table IV.
The ehloropentammineciiromium(III) bromide and iodide
oomplexea had the same general weight loss curves. They were
similar to that found for the ohloride complex. The bromide
deeomposed at 270°C, a .d formed a stable intermediate in the
temperature range from 410*>C to 460^0. This intermediate
37
Lcr(lIH„).Cl3Cl 3 ' 5
[Cr(NH^)^Cl3
LCr(NH3)5Cl]l2
[Cr(NH3)5Cl](N03)
10 mg
J . L i 100 400 500
FIGURE 10
200 300
T E I P ' E R A T U R E / C
THER!.:OGRAVII:ETRIC CURVES OF 30!.:E
G::LOROPENTA::I.IINECHROI;IUI.:(III) CO:.TLEXES
38
was eonverted to Ox^Q^ at 480*C.
The ohloropentamminechromiumdll) iodide lost weight
steadily from 230*0 to 340^0. At 340*C the slight weight
ohange eontinued before Cr20, was formed at 520®C.
The TGA eurve of ohloropentamminechromiumdll) nitrate
indicated a alight weight loss from 170< G to 195°C. At
the latter temperature, a large loss of weight resulted
giving a residue of CrgO, at 480°C*
TABLE lY
X-RAY DIFFRACTION DATA FOR CrN
d Spaeing ( in A* )
Found Theoretical(a) l/l^
2.06 2.07 100
2.33 2.39 50
1.45 1.46 50
(a)J Index to the X-Ray Powder Data File,
Amerioan Soeiety of Testing ivlaterials (1961).
The TGA eurves of bromopentammineehromiumdll)
bromide, iodopentammineohromium(III) iodide, and ni tra
topentammineehr omiumdl I) nitrate are shown in Figure 11*
39
M
TELPERATURE, G
FIGURE 11 THER'-OGRAVIMETRIC AIIALYSIS CURVES OF
SOME PS::TAI.I::iNECHRor.!iui.:(iii) coi.TLiiXES
40
The bromide began co lose weight at 2. 5 0 and formed a
stable residue between 415°G and 480*C whioh was converted
to the oxide, Cr203, at 510*0. For the iodide, the
weight loss occurred between 160^C and 330«»G, iorming
ohromium oxide, Cr^e^, at 330^0.
The TGA curve of nitratopentammlnechromiujndll)
nitrate indicated a slight ohange from 150' O to 190^0*
At the latter temperature, a large weight ohange resul
ted, giving a residue at 280*C.
The TGA curves of the hexaureachromium(III) complexes
are shown in Figure 12. The first weight loss, from 25°C
to 95°C, corresponded to the loss of the three moles of
hydrate-bound water. The weight loss from 170^G to 325°G
corresponded to the loss of three moles of urea per mole
of couplex with the formation of [Cr(C0N2H,)3Cl3| . The
remaining three moles of urea were evolved between 325*
and 4400C. The CrCl, reacted rapidly with air and formed
ohromium oxide at 480*0. The TGA curve of the hexaurea-
ohromiumdll) chloride, whioh was obtained by the de
hydration of its hydrate in an 110^0 oven for three hours,
showed the same pattern of decomposition above a tempera
ture of 170*C.
The hexaureachromiumdll) bromide showed a continous
weight loss between 200*0 and 430*C which corresponded to
the evolution of the six urea molecules* The chromiumdII)
bromide residue then reacted rapidly with air to form
41
ohromium oxide at 490«0*
The fQk ottirve ef hexaxuraachromiumdil) iodide ahowed
that thia eompeund evolved three molea of urea between
230«0 to 375*0, with the foimation of [0r(CON2H.)3l3]
at 275*0* Another three molea of urea ware evolved up to
330*0* The weight XeveX above 480*0 oorreaponded to
ohromium oxide, 0r20«*
The fOA curve ef hexaureaehromiua(III) nitrate
ahowed a aXia^t weight loss from room tuiperature to
200*0, and deoompoaed violently in the temperature range
between 205*0 and 250*0* The residue, at 460*C, was the
green ohromium oxide*
DISCUSSION OF THE
THSRMOGRAVIMETRIC ANALYSIS IN VACUUM
A few attempta were made for theae atudiea* However,
the eurvea obtained were poorly defined and gave ao
poaitive information*
DISCUSSION OF THE DIFFERENTIAL
THERMAL ANALYSIS AND GAS EVOLUTION (DTA-GE) CURVES
When gaaea were evolved during pyrolyaia, the ia-
fonaatien obtained from the OS ourvea waa generaXXy in
agreement with the DTA eurvea* However, the GE eurvea
provided further information about whether or not a phaae
ohaage luid taken place* Therefore, unleaa there waa a
4L
100 200 300 400 TEMPERATURE, ''C
500
FIGURE 12 THERI/OGRAVIMETRIC ANALYSIS CURVES OF
SOME HEXAUREACHROMIUM(III) COMPLEXES
43
phase change upon heating, a detailed discussion of the
DTA curves only will be given. The intermediates iso
lated in the DTA-G^ studies are summarized in Table V.
TABLE V
ANALYTIGAI. DATA OLTAINED FOR THE
ISOLATED Ix:T.DRI..LDI.cTi.S IN THE DTA STUDY
Original
Compound
[prm^^Br^ lCr(NH3)3GlJci2
[Cr(NH3)3GllBr2
\Cr(NH3)g]l3
[cr(NH3)3Clll2
Intermediate
Compound
^r{Wd^)^BT^
[cr(NH3)3Gl3l
jCr(NK3)3ClBr2]
iCr(ivH3)3l3l
LCr(NH3) 30112!
%NH3
TheoretiecO.
14.90
24.39
17.12
10.56
13.02
Found
14.47
24.12
16.98
10.15
12.63
The DTA-GE eurves of the hexammine ohromium (III)
eomplexes are shown in Figures 13 and 14.
For the hexamminechromiumdll) chloride, the first
endothermic peak with a peak meucimum temperature at 280*0,
corresponded to the evolution of three moles of ammonia
per mole of oomplex with resulting formation of [Cr(NH3)3-
01J. The seoond peak, at 368^0, was believed to be due
to the evolution of the additional three moles of ammonia .
44
H
ce
p«
o o
2i M
o P: w o
. 'f^.., ^
I - .
45 :r. y:.
36N0<I6aH HaoHooau
.. t
46
However, pure CrCl3 was not isolated as the residue. In
stead, a Lixtui-e of green CrCl^ and black Grll, due to the
reaction of some of the Cr0l3 with ammonia at high tem
peratures, was obt ained*
The DTA curve of the hexammineohromiumdil) bromide
gave an endothermic peak with a peak maximum temperature
of 290*0. This peaic was due to the evolution of three
molea of ainrionia. The seoond endothermie peaK, at 373*0,
was believed to be due to the evolution of the other three
moles of ammonia. A mixture of the CrBr, and CrN was
found in the residua*
The DTA eurve of the hexamminechromiumdll) iodide
had the same general pattern of endothermie peaks as
was obtained for the bromide and chloride complexes.
The first endothermic peak, at 230^0, corresponded to
the evolution of three moles of ammonia with the formation
of the intermediate, [Cr(NH3)3l3l • The other three moles
of ammonia were evolved at the peak temperature of 335*0.
The BfA curve shown in Figure 13 revealed that the shape
of the first endothenaie peak was symmetrieal to that of
the second*
The DTA-GL curves for the hexamminechromiumdll)
nitrate, as shown in Figures 13 and 14» showed a sharp
exothermic peak at 210*0. The residue was found to be the
green ohromium oxide.
The DTA and GB curves for the ohloropentammine-
47
chromiumdII) eomplexes €u:e shown in Figures 15 and 16,
respectively*
For the chloropentammineehromiumdil) cnloride
oomplex, the first endothermie peak with a peak temperature
of 295®C, corresponded to the evolution of two molea of
ammonia with the formation of the intermediate, [Cr(NH3)^-
013! • However, the possible evolution of the other three
moles of ammonia oecurred at the peak with the maximum
peak temperature of 375^0. No pure CrCl, waa found due
to the partial reaction of CrCl, with ammonia to form CrN
at the higher tei3iperatures.
The DTA curve for ohloropentamrriineehroraium(III)
bromide ahowed that the endothermie peak, with a peak
maximum temperature at 300*0, oorresponded to the evolu
tion of three moles of ammonia and the formation of
[Cr(NH,)^ClBr2l • The other endothermic peaks, in the
temperature range from 330*0 to 410°C, clearly showed that
the other three moles of ammonia were evolved at 360*0,
335®C, and 395^0, respectively.
The DTA ciirve for the ohloropentamminechromiumdll)
iodide showed that the evolution of two moles of ammonia
took place at the maximujii peak temperature of 290*0, with
the formation of the rather unstable intermediate, [Cr(NH^)^-
CII2] • A broad endothermic peak from 325° to 350*0. follow
ed Immediately after the first peak. It was believed that
the other three moles of ammonia were liberuted in this
latter temperature range*
48
o 3
^* o CO
1x4 en o CO
1 1 1 t • t 1
i o 1 « ! ' ^
o o
1 i
lO rH
M
a
M
o g o M
P4
o o o
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<1
49
CO
o o
M
o p; o w z
EH
w p o o
o
aeN0dS3H HaaH003H
TEXAS TECHNOLOG4-••^^^CK. T£xas^^
50
The DTA eurve of the ehloropentaamineohromium(III)
nitrate waa noted by the appaeu anee of a aharp exothar-
mie peak at 200«C*
In Figarea 17 and 18, the DTA and GE ourvea of the
bromopentammineehromiumdll) bromide, iodopentammine-
ohromium(III) iedide and nitratopentammineehromium(III)
nitrate are ahown*
The DTA curve of bremepentammineehromiumdil)
bromide indicated the evolution of two moles of NH, by
an endothermie peak with a peak maximum temperature of
290^0* Similarly, the DTA eurve for iedopentamminaehro-
mim(III) iodide ahowed the evolution of two molea ef
ammonia by the endothermie peak with a peak maximum
temperature of 295*0* The remaining three molea of
ammoaia were believed to be releaaed from the {prdTH.}.-
Br*] at the 380*0 peak* While for the unatable inter
mediate, lOrCNH.}.!.]* three molea of ammonia were be
lieved to be releaaed at the peak temperature of 320*0*
Similar to the other eompXex nitratea, a aharp
axothermio peak at X95*C oharaeterised the DTA eurve for
nitratopentammineehromiumdll) nitrate* The green reaidue
obtained waa Or203*
The DTA and Qf& ourvea for the hexaureaehromiumdlX}
oomplexea were ahowa in Figurea X9 and 20, reapeetively*
The DTA eurve for hexaureaohromiumdll) ohloride in-
dieated the evolution or deoompoaition of three molea of
|*-:|^-'i
51
M ^
:'• , / • ,
.*jU>V# •',•
•i
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CO
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M EH
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itii'-ii 'ilr 1
52
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CO
Pi ^ -4 o o
M
o o to
o o ««
w P: 3 EH ^ r '•^
w PH - W EH
O O OJ
o o
:3 M »_
o P: DT: o w z M
« ^ H *<-» W P* (x«
o CD trl > P: :=) O
:^
o M EH P .-1 O > Ul rO < cb
CO H
W CD rh h «
3s::0cis5H H^ai oo' ^
53
S CO
CO
o CO M
cn
03
I O
5 H
a EH
:^ M
pa
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K:: .51-M u*-f (il* ' u ' . i , .
iW; ',.4 "i"
f-W-
54
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s
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k.
M
aSN0dS3H HaOHOOaH
CO
o o
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e
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S&-. : • > • ( ; , ; '
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55
tturea per aele ef oomplex took plaoe at theld5*0 peak* The
reaaiader of the eurve waa poorly defined. The hexamrea^
obromlundlX) bromide, however, waa believed to evolve
three meXea ef urea at the higher peak temperature ef
215*0* The hexaureaohromiumdll) iodide waa believed to
reieaae the ooordiaated urea aoleouXea in the peak from
210*0 to 290*0* A atable reaidae waa found at 400*0;
the DTA eurve of the hexaureaehromium(XII} nitrate
waa eliaraoterlsed by the appearenee ef aa endethermie
peak at 195*0 followed immediately by an exothendo peak
at 2X5*0«
DI80USSI0N OF THS THMM(»CANCatSTRIQ ANALYSIS OURVES
In Fifure 21, the thermomanometrie (TliA) ourvea
for the hexaamiaeehromiurndXI) ohloride, bromide and
iodide are ahowa* The ohloride bei^a to evolve a gaa at
200*0* The iaereaae la preaaure of the ayatem in the tem
perature raoige from 200*0 to 310*0 waa eauaed by the evelu-
tiea ef three molea of the eoordiaated aoaoaia* Further
iaereaae la preaaure waa eauaed by the evolutiea of the
ether three molea of ammoaia ia the temperature raage from
310*0 to 389*0* A atabXe reaidue, probably OrOX^, waa
ebaerred ia fhe raage from 985* to 429*0* A charaeteriatie
preaaure drop, prebubXy due to the reaotiea betweea Or01«
aad ammeaia* wuii noted bet»e«a 425* aad 470*0* A mixture
of bla^ OrV aad ef wiate m ^ O l waa feuad iaalda the fur-
.^AAibiAriiM
56
— o X t o o 3
o O
o CO
O CO
>
o
E*
o
o
EH
Cvj
§
CO
PH
O o CO
M CO
:=)
M
O P: X o M
X
P« <3
57
naee chamber after eooling. In order to confirm the
formation of CrN in the reaotion, a mixture of pure an
hydrous CrCl3 ana NH3 was introdueed into the evaouated
system and heated to 425^0. A significant pressure drop
in the aame temperature range was found, as shown in
Figure 20, whieh confirmed the formation of the black
CrN and white NH.Cl.
The gases, eollected at the end of the pyrolyais,
were analyzed by the mass spectrometer. Both ammonia
and nitrogen were found, whereas chlorine was not present*
Ths TMA curve of the hexammineohromiumdil) bromide
shewed an inerease in pressure in the temperature range
from 250* to 290*G, probably resulting from the evolution
of three moles of ammonia. Further increase in pressure
between 290* and 370 °C was believed due to the evolution
of three moles of ammonia. A mixtui e of CrN and ammonium
bromide was found Inside of the sample holder. The mass
spectrometer results indicated the presence of both NH,
and No* Therefore, It was possible to assume that the
released ammonia reacted promptly with tne chromiumdII)
bromide*
The TMA curve of hexamminechromiumdll) iodide
ahowed an increase In pressure in trie temperature range
of 250°C to 280*0 and from 280*C to 350*0, which was
believed to due to the evolution of ail six moles of ammonia.
A decrease of pressure at 415*0 was noted for the reaotion
58
of Crl3 and ammonia and xhe formation of the blaok CrN.
The TMA curves of the ehloropentat^Liiinecnromiuadll)
ohloride, bromopentamaineehromium(III) bromide, iodo-
pentamminechromiumdll) iodide, and ehloropentaomine-
ehromiua(III) chloride wre ahown in Figure 22* The
preaaure ohange for the ehloropentamalneehromiumdll)
ohloride in the temperature range from 250*0 to 315*C
oorreaponded to the loss of three molea of sLomonia, while
another three moles of ammonia were releaaed between
315*C to 400*0. Interaction of aamonia with CrCl3 waa
indioated at higher temperatures.
The Tdk curve for the ehloropentaxominechromiiuidll)
ahowed the evolution of all aix molea of a..aonia between
275^0 to 390*0* No pure residue was isolated due to the
immediate reaction of ammonia with CrClBr2 at higher tem
peratures*
i'or the TiMA eurve of bromopentammineehromiumdll)
bromide, the preaaure ohange between 260*0 to 3b0*C,
oorresponded, probably, to the evolution of all aix molea
of armonia* Likewise, the preaaxure ohaage in the tempera
ture range from 270*0 to 34 *C of the TUA eurve for iodo-
pentaomineehromiumdll) iodide was oharaeterised by the
evolution of all six moles of aamonia* The residue, the
product of interaction between the ohromium halidea and
ammoniaf was not iaolated in tne pure form*
59
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o o -"^
oo o« ro •» [xl
£ 5 trt
S w P4 *^- H
EH
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w »- H
OF
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P. <3
DISCISSIONS 0¥ THE STOICHIOi. TRY D^J'SRMINAXIO!.
The analytioal results for the deteriaination of the
stoiohiometry of the helium pyrolysis are shown in Table
VI.
For the hexammineohromiumdil) bromide, the ammonia
to ohromium ratio which was determined by this study,
showed inconsistent values, varying from 4.48 to 6.3.
A few ratios were found to be near 6, while a few other
ratios were near 5*2. If the former value of 6 was the
desired one, it is possible to assume that all six moles
of fiuamonia were released upon heating. However, because
of the ineonsistent result, no ijositive conclusions can
be made.
For the chloropentammineehromiumdil) chloride, the
aiamonla to chromium ratio gave more consistent results.
The average value found was about five. This would in
dicate that all five moles of aamionia were evolved L.-pon
heating. The green residue whieh was obtained after he
ating up to 500*0 was very hygroscopic. In some cases a
small amount of black substance was mixed with the green
residue*
The aiainonia to chromium ratio determination in ehlo«
ropentammineohromiumdll) bromide, [cr(NH3)cCl] Brgi also
showed the evolution of five moles of aiamonia* The resi
due was also very hygroscopic*
60
61
The ammonia to ohromium ratio for hexammineehromium-
(III) nitrate showed that only a small amount of ammonia
was evolved as the decomposition product*
The analytical results for the stoiehiometry deter
minations in vaouum for the hexamminechromiumdll) bro
mide, ohloropentamminechromiumdll) c; loride, hexammine-
ehromium(III) ohloride and bromopenta'aminechromiumdll),
as shown in Table VII, was 5.11 3.5f 4.5 and 4.2, respec
tively. The residues contained chromium halides together
vrith a small amount of blaok substance. The a jnonium
halides were found in the sample holder along with the
other deeomposition products. Therefore it was assumed
that when a pentammine- or hexamminechromiumdll) halide
was pyrolyzed in a vacuum, the decomposition products
were chromium halide, chromium nitride, ammonium halide,
and probably nitrogen.
62
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IV. CONCLUSION
The reaulta of the DTA study ahowed that the general
reaotion for the thermal dissociation of the hexammine-
ehromiumdll) halide eomplexes wast
[Cr(NH5)^]X5 j^ ^ LOrCNHj)^!,! ^ 3NH5
(where X ia ehlorlde, bromide or iodide)
Continued heating eaused the evolution of the remaining
three molea of ammonia aeoording to the reactions
\OT(m^)^X^~] ^ ^ CrXj i- 3NH3
Some of the ammonia evolved reacted immediately with
the ohromium halide to fozm a mixture of ehromium ni
tride, ammonium halide and unreaoted ohromium halide*
However, the hexammineohromiumdil) iodide gave iodine
and probably hydrogen iedide in addition to those prodiusts
mentioned above*
On heating in air^ the hexamminechromium(III)
halide formed ohromiumdil) oxide at about 480*0. The
hexammineohromiumdil) ohloride released three moles of
ammonia from the ooordination aphere with the aub-
aequent formation of triehlorotriammineehromium(III) at
a temperature of 500*0* Similar intermediates for the
66
67
thermal deoompeaition of hexammineehromium(III) bromide
and iodide were not obaerved from the air TOA atudiea*
Farther atudy by vaouum pyrolyais ahowed that all
aix melea of ammonia were evolved from the ooordination
aphere of the hexamminechromiumdll) halide oomplexea*
The ehromiumdil) halide whieh formed reacted immediate
ly with the ammonia to yield the deeempoaltio i preduets,
ehromium halide, ehromium nitride and probably nitrogen*
Thia ia in agreement with the DTA atudiea*
The pentamyoaineehromiiuadll) oomplexea deeomposed,
in a helium atmoaphere, to form the trihalotriaramine-
ehromiumdll) oomplexea by the evolution of two moles
of ammonia* The reaction is summarized as follows:
[pHm^)^x]i^ ^ > [Qr{m^)^XX2\ • 2NH5
(where X and Y are ohloride, bromide and iodide)
Theae pentammineehromiumdII) eomplexes when heated
in air, alao yielded ehromiumdil) oxidea. However, the
aequenee of reaotions for the deoompoaition coiild not be
determined*
On heating in a vaouum, these pentammineehromium(III)
oomplexea deeompoaed to form a mixture of ohromium halide,
ehromium nitride, ammonium halide and probably nitrogen*
A poaaible reaotion for thia type of thermal diasoeiation
is propoaed aa an interaetion between the evolved ammonia
68
and the ehromium halide* The exothermic natui*e ef the
thermal deoompoaition of the pentammine chromlum(III)
nitrate prevented a detail investigation of its deeomposi
tion produets*
The thermal diasoeiation ef the hexaureaehromium(III)
oomplexea in air wa» found to proeeed according to the
following reaotiona s
[0r(C0N2H^)g]X3 ^ j > [Cr(CON2H^)3X3] • JCONgH^
[QT{GO^^^)yl^ A ^ CrXj H- JOONgH^ axr
LIST OF REFERENCE
1* S. M* Jorgensent **Beitrage Zur Ohemie der Chromam-moniakverbindunger**» Journal f* prakt* Ohemie, Vol. 20, ld79f pp. lOT*
2* 3* M* Jorgenaenf '*Beitrage Zur Chemie der Chromam«' moaiakverbiadunger**, Journal f* prakt* Chemie, Vol. 30, 1884, pp. 1.
5« 3. M. Jergenaen, **Ueber daa Verbaltnias awiaehen Xiuteo- und Roaeoaalsen'*, Jo\irnal f. prakt. Chemie* Vol. 29, 1884, pp. 409.
4* H* I. Sohleainger and R* K* Werner, *«Studie8 on Complex Gompounda* I* Removal of Ammonia From The Coordinat On Sphere'*, J* Amer* Cham* Soe** Vol* 51# 1929,pp. 3520.
5. C. £. Ufer "Uber daa Stiekatoffehrom**, Ann* Chem** Vol. 112, 1859f pp. 281.
6* H* I. Sohleainger and D. H. Rieklea, **3tudie8 on Oomplex Iona* II* The Preferential Removal of Bromide Ion From The Coordination Sphere**, J. Amer* Chem* Sec, Vol. 52, 1930, pp. 3523*
7. N. D. Peaehko and B. P. Block, "The Thermal Stability of Metal Amminea-I Pentaomiineohloroohro-mium(III) Chloride**, J* Inors* Nuol* Chem* Vol. 15, I960, pp. 71.
8* W. W. Wendlandt and John L. Bear, »*The Thermal Deoompoaition of Some Aquopentammineehromium(III) Complexea**, J. Inorg* Chem. Vol. 22, 1962, pp. 77.
9. W* R* Robinaon, **The Thermal Deaqtuation of Some Chromium and Cobalt (III) Complexea, M. S* Theals, 1962, Texas Teehnologieal College*
10. A. L. Oppegard and J. C. Bailar Jr., Inorganie Sratheaia III* L. F* Audrieth, MeGraw-Hill Book Co*, New York, 1950, pp* 153.
11. 0. B* Heiaig, E. Fawkes, and R. Hedin, Inorganie Syntheaia II, W. C. Femaliua, MoGraw-Hlll Book Co., New York, 1946, pp. 193.
69
70
12* P. Pascal, Nouyeau Traits De Chimie Minerale Maasen Et Gie, 1959, pp. 430.
13. 0* T* Christenaen, Z. Anorg* Cnem* 4, 189:?, PP. 229.
14. M* Mori, Inorganie Syntheaia* T. Moeller, teaGraw-Hill Book Co*, New York, Vol V. pp. 131.
15. A* King, Inorganie Preparations* New Yorkf D* Van Nestrand Co., Inc., 1936, pp. 104; pp. 48*
16* H. H. Willard, N. H. Furman, 0. E* Brieher, Elementa QiP Qiia ' 'i - irii Ani^iyiQ, D. Yan Nostrand Ceo, Ine., 1958, pp. 161.
17* W. W. Wendlant, T. D. George and G. R. Horton, **The Thermal Deeompoaition of Therium(I7), Uranium and the Rare Earth Metaldll) Oxalate**, J* Inorg* Nuol. Chem.* Vol, 17, 1961, pp* 274.
18. W. W. Wendlandt, ••Reaotion Kinetics by Differential Thermal Analysis**. J. Chem. Ed. Vol. 28, 1961, pp. 571.
19. W. W. Wendlandt, **A New Apparatua for Simultaneoua Differential Thermal Analysis and Gas Evolution". Anal. Chem. Aeta. 27, 1962 pp. 309.
r