Indian Journal of Chemistry Vol. 43A, Januury 2004, pp. 92-97

Synthesis and characterization of transition metal complexes containing oxime, amido

and thioamido groups

A A EI- Asmy*, M E Khali ra & M M Hassani an

Chemistry Dcpa rt ment . Faculty o f Science, Mansoura Uni vcrsity, Mansou ra, Egy pt

Receil'eli I I May 2000; rel'iseli 20 NOl'elllber 2003

New t r~lI1 s i tio n metal complexes of a-ox im inoaccto-o­anisidide-4-phcnylthioscmi ca rbazo nc CH.10AAT) havc bccn prepared and lheir gcometrics arc ass igncd. All the inves ti gated co mpl exes are mononuclca r cxcept the Cu(lI ) ions which form bin uclear complexes Wil h lhc chlori de and acetate salts. The li gand aClS as binegative tri de ntate in the CoC II ), Ni(II ), Zn(lI ) and Pd (lI ) comp lcxes, lrinegati ve tridcntate in the Fe( lIl ) and CoCIII ) complexcs and trincgali ve pent aden tate man ner in lhe Cu(lI ) co mplcxes. The Cu(lI ) and Pd(lI ) complexes possess a square­pla nar stereochemistry whil c Ni( lI ) complex has an oc tahcdral Slruclure. Co(lI ) salt s form diamag neli c and paramagnetic complexes. The prolonat ion constants o f thc ligand and lhe stability constants of ilS Co(ll ), Ni (lI ) and Cu(lI ) complexes are ca lcul alcd pH-metr ica ll y. Moreovcr, H.10I\AT has becn app li ed for the delermin ati on of Ni ( II ), Co(l l), Cu( lI ) and Pd( lI ) ions in thc 0. 1-3.5 pp m range.

Coordinati on compounds conta ining ONS do nors are of considerable importance due to the ir anti mic ro­bia l acti viti es l.2. Thiosemi carbazones have acti vity

. II 3 . d ' 4 d b I ' 5 A aga ll1st sma pox', virus Iseases an tu e rcu OS IS . great allenti o n is a lso due to the ir carc inos tati c prop­e rt ies aga inst a spec tru m of transpl aced neoplasm6

. u­O ximinohydrazones have antiparas iti c, fun g ic idal and bacte ri c idal pro perti es 7. The coordi nati on of u­ox iminoaceto-o/p-an iside thi osemi carbazones were fo und through the nitrogens o f ox imino and azome­thine groups as well as the thio l sulphur ato m whi ch fo rm bri dge between the meta l io ns8

. Recent publica­tions o n complexes of u-ox iminoacetoacety lpyrid ine9

and its 4-thiosemi carba-zone deri vati ve 10 were re­po rted.

Expel-imental All chemi cal s were o f ana lyti cal grade-hi gh purity

materi a ls . T he ox ime de ri vati ve was sy nthes ized accord i ng to the we ll know n method I I • The thi osemicarbazone-ox ime derivati ve was prepared by mi xing equimolar amounts of the ox ime derivative

(1 S.5g, 0 .05 mol ) and 4-pheny lthiosemicarbazide (S.4g, 0.05 mo l) in 30 mL absolute EtOH. The mi xture was stirred under reflu x fo r 3 h on a water bath. The product thus formed o n coo ling was filt ered off, c rys ta lli zed fro m EtOH and d6 ed in a des iccator over anhydrous CaCI2. The purity of the fo rmed compound was monitored by TLC us ing silica ge l and ch arac te ri zed by e lemental ana lysis and infrared spec tra.

Preparation of COlli pIe xes

T he solid complexes were prepared by ml xll1g equimol ar amounts of the meta l salt s and the li gand in abso lute EtOH (in case of the chl o ride sal ts) and in EtOH-H 20 mi xture ( 1: I by vo lume) for the acetate salts. The solu tio n mixture was heated under refl ux on a wate r bath fo r 0 .5-4 h. The same procedure was appli ed with PdCI2 but 0.5g C H}COONa was added. In each case, the react io n product was filte red immedi ate ly, washed severa l times with hot EtOH foll owed by die thyl ether and dri ed in a des iccator over anhydrous CaCI2.

All measurements were carri ed out as prev ious ly reported !2. The anal ytical and phys ical data are g iven in Table I . A ll the co mplexes are soluble in DM F and DMSO.

Results and discussion

The I.R. spectrum of H}O AAT showed medium intensity bands at 3510 and 1365 c m' ! ass igned to the stretching and bending vibratio ns o f the ox ime 01-1 group . The strong band at 1670 cm'! is attri buted to

v (C=O) w hile the two bands at 9S0 and 16 15 cm' ! are

ass ig ned to the v(NO) and v(C= N) of oximino grou p, respect ive ly . The thioamide (IV) band appeared at 7S0 cm' ! while the strong band at 1600 c m'! may be

ass igned to v(C=C) of the benzene ring and v(C=N) o f the thiosemi carbazone moiety 13. Also, the !HNMR spectrum of H)OAAT, in {h-DMSO, shows ch aracte ri stic sig nals at 11.34, 9 .05, 8.6S and 8.27 ass ig ned to the proto ns of OH , .H, N2H and ~ H , respectively. Fro m these data , o ne can conclude that H30 AAT in its so lid state may ex ist in keto/thi oketo form (Structure 1)

NOTES 93

Structure I

The active coordination sites of H,OAAT have been evalu ated by analysis of the l.R spectra of the ligand and its metal complexes.

Characterizatioll of [CII2(OAAT)X( H20 h J2H20 As reported earli er'J, o-ox iminoacetoacetanilide-4-

phenylthio-semicarbazone reacted with CuCl 2 giving binuclear complex, its o-methoxy substituent (the in­vestigated ligand) fo rmed the same type of chelates but with CuCl2 and Cu(AcOh salts .

The I.R spectra of the investigated complexes showed that H,OAAT behaves as a trinegative anion binding in a pentadentate manner with the two copper atoms via three of the C=N nitrogens, the eno lic (C­O) oxygen and the thi ol (C-S) sulphur with di splace­ment of two hydrogen atoms from the amide and thi o­amide groups through enoli zation and thioenoli zation processes. The third hydrogen atom is liberated from the oxi me OH group. This mode o f compl exation is

supported by: the di sappearance of bands due to 8 (OH ) ox ime, v(C=O), v(NH), v(N2H) and v(C=S)

vibrations, the appearance of new bands fo r the v(C-

0 ) and v(C-S) and multiple shoulders in the region 1650- 1620 cm·1 for the v(C=N) observed as a result of eno lization and thioenolization, the shift of v(NO) to a higher wavenumber and the appearance of new bands at 470, 430 and 320 cm·1 for the v(M-N)1 4, V(M-S)I S and V(M-0)16 vibrations, respecti ve ly .

x = cr or AcO-

Structure 2

The electronic spectra of the complexes, in DMF soluti on, exhibit two bands at 25000 and 15100 cm·l. The first may be due to L-M charge transfer i7

, while

the second is assigned to the 2T2g f- 2E g transition. The band pos itions are similar to those reported fo r planar copper(lI) complexes l8. The room temperature magnetic moments per one copper ion for the two complexes (Table 1) are in the range reported for the presence of one unpaired electron and measured for compounds only hav ing covalent character.

The ESR spectrum of the solid [Cu2(OAAT)Cl(H20 h ]2H20 complex at room tem­perature (298 K) shows an isotropic signal at go = 2.081 corresponding to the presence of the two copper atoms in a square-planar geometryl 8.

DT A, DTG and TG analyses have been used to follow the thermal decompositi on of [Cu2(OAAT)(AcO)( H20)2]2H20 . The TG thermo­gram is characterized by three weight loss stages; the first is correlated with the elimination of the two hy­

drated water molecul es in the SO-1 20°C range. The second with the loss of the two coordinated water

molecules at ISO-2 10°C range with a weight of 5.7%. The DT A thermogram in the region 140-3 1 SoC is ch aracterized by a series of exothermic and endo­

thermic peaks . The peak at 180°C is attributed to the elimination of coordinated water. The peak in the

DT A curve at 263°C is ass igned to the loss of the acetate group (a loss of 9 .2% in the TG graph in the region 240-27SoC confirms thi s phenomenon). The TG curve also shows two main decomposition stages, the 260-32SoC stage is probab ly assigned to the e limination of two ph-NH moieties with a weight loss of 26.0%. The second stage is concerned with the de­composition and ox idation of the res idual part in the temperature range 3IS-460°C giving CO/C02 and NO/N02 leav ing CuO as an end product.

Characterizatioll of Ni( HOAAT)4H20 and ZII( HOAA)H20

Other che lation mode is depicted from the analysis of the T.R spectra of the complexes isolated with Ni (AcOh and Zn(AcO)2 salts. The ligand in these complexes behaved as a binegative tridentate mole­cule coordinating via the ox ime and thiosemicarba­zone azomethine nitrogens and the thiol sulphur. Thi s behavior is supported by : i) the disappearance of

v(C=S), v(N2H) and 8(OH) bands, ii ) the increase in intensity of the v(C=C) at 1600 cm-I owing to its

94 INDIAN J C HEM , SEC A, JANUARY 2004

Table 1 - Analytical and physica l data o f H)OAAT and its complexes

Compound Co lour m.p. DC

H)OAAT Bcige 176

lCu2(OAAT)CI(H20) 2]2 H2O Brown 205

[Cu2(OAAT)(AcO)( H20h ]2H2O Brow n >300

[Ni(HOAAT)( H2OhlH20 Brown >300

[Co(OAAT)(H20 h l Brown >300

[Co(HOAAT)(H20)31 Brown >300

[Fe(OAAT)] Brown >300 >300

[Zn( HOAAT)( H2O)] Orange >300

[PcI(HOAAT)( H2O)1 Red >300

overlap with the new azomethine groups created as a result o f thioenoli zation process (thi s band is observed with many shoulders) and iii ) the shi ft of the NO band to a hi gher wavenumber.

The I HNMR spectrum o f the Zn(IJ) complex shows the absence of signals due to OH and N2H protons which is a furth er support for the deprotona­tion and thi oenoli zation processes.

The e lectronic spectrum of the Ni([I) complex in OMF solu tion showed two broad bands centered at 26000 and 16100 cm-I (the third o ne is not observed due to limitations in our instrument. The observed

bands are assigned to the JA ]g 4 "T,g (P) and "A 2g 4

3T I g (F) transitions, respectively . These bands together

with the calculated 10 Oq , 8 and ~ values suggest that the Ni(II) complex has an octahedral configuration. The measured magnetic moment (3.2 8M) lies within the va lues reported for octahedral Ni(ll) complexes.

M = Ni(II ); X = H,O Zn(II ); X = zcro

Structure 3

1\ a In )lcff Found (Caled), %

(B.M) C H M

56.3 5.4 (56. 1 ) (5.0)

13 1.63 36.0 4.3 2 1.1 (36.0) (4.0) (2 1.2)

6 1.62 38.5 3.7 19.8 (38.5) (3.9) (20.4 )

9 3.2 1 42.3 4.5 10.8 (4 1.9) (4.9) ( 11.4 )

5 0.0 44.3 4.8 12.0 (43.6) (4.7;. ( 11.9)

4 3.27 44.1 5.1 12.0 (43.5) (4.7) ( 11.8)

7 2.38 49.5 3.6 12.5 (49.3) (3.7 ) ( 12.7)

5 0.0 47.9 4.4 14.4 (48.2) (4.3} ( 14.6)

4 0.0 43.1 3.3 20.6 ( 42 .6) (3.7) (20.8)

The TG thermogram in the temperature range 20-750°C for [Ni (HOAAT)(H20)3]H20 displays 3.7%

weight loss at 100- 140°C cOtTesponding to the e limi­nation of one hydrated water molecule, 10.25%

wei ght loss at 140-205°C most probab ly ass igned to the elimination of the other three water molecules (the re latively high temperature supports the opinion that these water molecules are strongly coordinated to the meta l ion . The DT A curve exhibits an endo thermi c

peak at 202°C. The third step with 14 .9% loss is con­cerned with the beginning of decomposi ti on of the complex and e limin ati o n of the benzene nuc leus at

2 10-320°C with an exothermic effect at 313°C in its OTA curve. Fina lly , the fourth step is attributed to the decomposition of the res idual part of the complex in

the range 320-750°C g iving volatile carbon and nitro­gen oxides leav ing NiO res idue (14.5 %) .

Characterization of M L.nH20 Moreover, H30AAT behaved as a binegati ve tri­

dentate ligand in its complexes with Co(Il) and Pd(Il ) but the oxime group does not take part in coordina­tion. The carbonyl band shifts to lower wavenumber by 18 cm- I as wel l as the azomethine of the thiosemi­carbazone moiety and thiol sulphur bands. Structure (4) is suggested for thi s type of com r;lexes on the ba­sis of: the hi gher shift ( 140 c m- I

) of v (N-O) with the increase in its intensity indi cating that the OHox imc is deproto nated and not parti ci pate in chelatio n. This

NOTES 95

observation is noticed on comparing the I.R. spectra of these complexes with the spectra of the other in­vestigated complexes.

The Co(lT) complex isolated from the acetate salt exhibits two bands at 17100 and 21300 cm'! in its electronic spectrum in DMF solution which are attrib­

uted to the 4T' g --7 4A 2g (V2) and 4T'g --7 4T, / P)(V3) transi tions, respecti vel y, in an octahedral structure(22). The ligand field parameters are calculated to be 950 cm'! (B), 0 .98 (~) and 1050 cm'! (10 Oq) . The calcu­

lated v, value (8605 cm'!) as well as the V2/v, (2.17) are in agreement with the values reported for an octa­hedral structure. The subnormal magnetic moment value (3.2 BM) may be due to partial oxidation of the Co(J1) to Co(JII) in the presence of the ligand.

M = Pd(ll) ; X = zero M = Co(ll) ; X = H20

Structure 4

The electronic spectrum of the Pd(J1) complex shows one band at 19320 cm' ! due to the !A!g --7 ! B !g

transItIon in a planar configuration. Its diamagnetic character is further support for the proposed struc­ture! 7.

Finally, the ligand behaved in a trinegative triden­tate manner coordinating via the oxygen of the eno­lized carbonyl, the sulphur of the thiol (C-S) and the nitrogen of the azomethine thiosemicarbazone in the Co(ll) and Fe(JlI) complexes.

Structure 5

The electronic spectral bands observed for the OMF so lution of the Co (III) complex at 16200 and

26400 cm' ! are assigned to the 'A' g --7 'T'g and 'A' g --7

'T2g transitions, respectively , in a low spin octahedral configuration (Structure 5). Its diamagnetic character supports the proposed structure.

Table 2- Molar absorp ti vity (c), specific absorptivity (a) , San-dell 's sensiti vity index (S), Beer's law and Ringbom ranges for M2+/H30AAT at pH=8

Property Cu2+ C02+ Ni2+ Pd2+

Allla , (nm) 400 345 385 398

c( 1 mol" cm") 65064 44764 32872 11764

a(ml cm" ~,g " ) 1.02 0 .76 0.56 0.11

S(~lg cm" )x 10.4 1.02 7.6 5.6 1.00

Beer' s range(pJml) 0.1-1.0 0 .1, 1.0 0.1-1.0 0.5-3 .5

Ringbo m 0.25-0.5 0 .2-0.8 0.3-0.75 0.5,3.5

range(~LlIllI)

Metal/ligand rati o 1:1 1:2 1:1 1:2

Stability constants 11.1 3 10.57 5.64 9.21 (log K)

The lower value of the magnetic moment (2.38 BM) measured for [Fe(OAAT)h may be attributed to antiferromagnetic exchange l2 due to either direct metal-metal interaction or super exchange through S­bridge

It is observed that the ligand reacts with the CoOl) salts in two different manners. Its reaction with CO(ACO)2 gave paramagnetic complex but with CoCI2

it gave complex with diamagnetic character. The li­gand in the last reaction acts as an oxidizing agent which completely oxidized the Co(JI) to Co(IH). Therefore, one can conclude that the oxidation pro­cess must be carried out in a strong acidic medium. The liberation of HCI gas during the complex forma­tion from the chloride salt makes the medium suitable for the oxidation. Tn case of the acetate salt, the me­dium (acetic acid) is insufficient for complete oxida­tion .

The pH-metric titrations of 5x 1O,3M H30AAT with 0.0 I M NaOH , in the presence of 0.1 M HCI and in a

50% water-dioxane mixture at f1. = 0.1 were carried out using the procedure developed by Calvin and

Bjerrum. The nA, !L and pL values were calculated at

different pH using the Iriving-Rossotti equations. Plotting !LA against pH gives the proton-ligand for­

mation curve. The protonation constants, log KI Hand log K2H, are found to be 10.9 and 9.0, respectively. The metal-ligand stability constants were obtained from the curves drawn between Ii and pL. The calcu­lated log K values are 12.8,9.15 , 8.25, 6.4 and 5 .8 for the Cu(II) , Co(ll), Ni(ll), Zn(II) and Cd(Il) com­plexes, respectively . The variation in stability may be due to the di fference in the effective electric fi eld strength (F*) of the metal ion, F* = Z/r2. The values

'-0 0\

Table 3 - Spectrophotometric determination of the studied metal ions in presence of interfering species using the proposed procedure

Absorbance (')

Series Sample taken* ppm Amax At atpH 8 A 2 pH 1.5 AJpH 1.5 in t;.A Found using Error ±% Copper samples presence of N20 J proposed procedure

i) 0.5 Cu(II) 370 0.22 0.22 0.22 0.00 0.22 0.5 0.00 ii) 1.0 Cu(U) 0.43 0.43 0.43 0.003 0.427 0.495 1.00 iii) 0.5 Cu(U)+ 5 Zn(II) 0.508 0.21 0.22 0.0 0.22 0.494 1.0 iv) 0.5 Cu(II)+ 10 Pb(II) 0.40 0.21 0.22 0.0 0.22 0.5 0.0 v) 0.5 Cu(U)+ 10 Cd(II) 0.38 0.23 0.22 0.0 0.22 0.5 0.0 vi) 0.5 Cu(II)+5 Zn(II) 0.83 0.21 0.22 0.0 0.22 0.5 0.0

+10 (Cd(II)+Pb(II») II Cobalt samples i) 0.5 Co (II) 345 0.30 0.30 0.50 0.0

z S2

ii) 0.5 Co(II)+ 5Zn(II) 0.56 0.30 0.50 0.0 > iii) 0.5 Co(II)+lOPb(II) 0.46 0.295 0.49 2.0 z

'-

iv) 0.5 Co+IOCd(II) 0.47 0.31 0.48 4.0 n ::c

v) 0.5 Co(II)+5 Zn(II) 0.92 0.29 0.49 2.0 m +10 (Cd(fl)+Pb(Il») 3:

III Nickel samples en m

i) 0.25 Ni(II) 400 0.25 0.25 0.25 0.0 n . "\ 0.25 Ni(U)+5 Zn(II) 0.52 0.245 0.247 1.2

> 11)

'-

iii) 0.25 Ni(II)+ 10 Pb(II) 0.41 0.247 0.247 1.2 > z iv) 0.25 Ni(U)+ IOCd(II) 0.42 0.26 0.26 4.0 c v) 0.25 Ni(II)+5 Zn (II) 0.87 0.245 0.245 2.0 >

;:0

+ 1O(Cd(II)+Pb(II») -< N

IV Palladium samples 0 0

i) 1.0 Pd(II) 400 0.24 0.24 0.27 0.27 0.0 1.0 0.0 .j>.

ii) 1.0 Pd(II)+ 5 Zn(II) 0.48 0.235 0.26 0.26 0.0 0.98 2.0 iii) 1.0 Pd(II)+ 10 Pb(II) 0.42 0.24 0.25 0.25 0.0 0.98 2.0 iv) 1.0 Pd(II)+IO Cd(II~ 0.41 0.24 0.26 0.26 0.0 0.99 1.0 v) 1.0Pd(II)+ 5Zn(1I)+ 0.85 0.237 0.265 0.26 0.0 0.995 0.5

10 (Cd(II)+PbII») V Simultaneous determination i) 0.5 Cu(II)+ 1.0 Pd(II)+0.5 Co(lI)** 370 0.77 0.77 0.46 0.245 0.215 0.49.1.01.0.55 1.0. 0.3. 3.00 ii) 0.5 Cu(II)+l Pd(II)+0.25 Ni(II)*** 370 0.70 0.70 0.465 0.25 O.2iS 0.49, i .01,0.55 1.0, 1.0, 3 iii) 0.5 Cu(II)+0.5 Co(II)+ 5 Zn(II) 370 1.01 0.53 0.22 0.22 0.5, 0.0,0.55 0.0, 0.0, 2.00

+10 Cd(rI)+Pb(rI) iv) 1.0 Pd(rI)+0.5 Cu(II)+5 Zn(lI) 370 1.07 0.46 0.465 0.245 0.22 0.5, 1.01. 0.0 0.0, 1.0,0.00

10 (Cd(U)+Pb(U»)

(') mean of five replicas

NOTES 97

of log KI for the metal complexes are plotted also against the ionic potential (Z2/r); the observed linear relationship proves that the nature of the metal-ligand bond in the complexes is ionic.

The reaction of H30AA T with Cu(II), Co(II) , Ni(II) and Pd(JT) was followed spectrophtometrically in pH range 2-1]. The UV absorption spectra of H30AA T is Lharacterized by two di stinct absorption bands at 225 and 300 nm. The variation of intensity of the band at 225 nm in the pH 2-5 is correlated with the intermolecular charge transfer involving intermo­lecular hydrogen bonding. At pH 10 and 11 , the inten­sity and position of the band at 300 nm are changed whcih is assigned to the probable keto/enol or thio­keto/thioenol equilibrium on the anilide and thiosemi­carbazone moieties.

The effect of pH on the development of color for different metal complexes has been studied. The re­sults obtained indicate that the color development de­pends mainly on the pH of the solution. The maxi­mum absorbance is achieved in the 6-8 pH range.

Job's method of continuous variation was applied to establish the stoichiometric ratio of the formed complexes. The mole fractions of the metal ion and H30AA T were varied continuously keeping their combined concentration at lxlO·s mol L· I and meas­uring the absorbance at Amax for each system against reagent blank. The results are summarized in Table 2. The logarithmic values of the stability constants are 11.13 and 6.44 for ]: 1 Cu(II) and Ni(II); 10.54 and ] 0.57 for 1:2 Pd(H) and Co(II) complexes , respec­tively.

Beer's law was obeyed over the ranges 0.5-3 .0 p.g/ml for the Cu(II) and Pd(II) and 0.1-l.0 p.g/ml for the Co(II) and Ni(lI) ions . The molar absorptivity (c:)

being ranged from 1.17 to 6.5x104 L mor l cm-I (Ta­ble 2) . The interferences of AI(III), Cr(IlI), Fe(III), Mn(H), Mg(II) , Hg(II) , La(lII) , Ca(Il), Zn(II) , Cd(II) and Pb(II) were tolerated. Furthermore, the reagent is successfully used for the analysis of some synthetic mixtures and certified samples (Table 3).

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