ch 19. d-block metals
DESCRIPTION
Ch 19. d-Block Metals. D H vap (in kJ/mol) for Metals. T m Ba 725°C W 3410°C Au1064°C. T m across TM. Quick Review of Redox Rxns. To balance a half-reaction: 1. Identify and balance redox atoms 2. Add e as needed 3. Add H + or OH - to balance charge - PowerPoint PPT PresentationTRANSCRIPT
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Ch 19. d-Block Metals
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Hvap (in kJ/mol) for Metals
Tm
Ba 725°C
W 3410°C
Au 1064°C
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Tm across TM
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Quick Review of Redox RxnsTo balance a half-reaction:
1. Identify and balance redox atoms2. Add e as needed3. Add H+ or OH- to balance charge4. Add H2O as needed
Ex:
Balance HMnO4 Mn2+ in acidic soln
5e + HMnO4 + 7H+ Mn2+ + 4 H2O
Balance VO43 V2O3 in basic solution
4e + 2VO43 + 5H2O V2O3 + 10 OH E = 1.37V at pH = 14
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Quick Review of Redox Rxns
Nernst relation
E = E - (0.059V / n) log Q
What is E (VO43 / V2O3) at pH = 12 ?
E = E - (0.059V / 4) log [OH]10
= E + (10) (0.059V / 4) ( pOH)
= +1.37 V + (0.148) (2)
= +1.66 V (E increases with decr pH because OH is produced)
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Quick Review of Redox RxnsLatimer diagrams
1. Reverse direction, reverse sign
2. n E are additive, not E
Mn3+ Mn2+ Mn
E = (1) (1.5V) + 2(1.18V) / 3 = 0.28V
3. E is independent of stoichiometry
1.5 -1.18
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Quick Review of Redox Rxns
e- + Fe3+ → Fe2+
E = 0.77 V
e- + Fe(OH)3 + 3H+ → Fe2+ + 3 H2O
E = E0 - 3(0.059) pH
e- + Fe(OH)3 → Fe(OH)2 + OH-
E = E0 - 0.059 pH
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TM redox trends
Electronegativity increases for TM going across the rows, therefore elements become more difficult to oxidize. A different way of stating this is that later TM elements are stronger oxidants at a given oxidation state.
This is shown by the increasing upward slope for oxidation reactions in Frost diagrams.
TM Frost diagramsat pH=0
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TM Pourbaix diagrams
Pourbaix diagrams show increasing E for M/M2+ and M2+/M3+ equilibria
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Early vs late TMs
2 e + CoO2 Co2+ E = 1.66V
2 e + TiO2+ Ti 2+ E = - 0.14V
Note that CoO2 is unstable in H2O because:
2 e + 4 H+ + CoO2 Co2+ + 2 H2O E = 1.66
2 H2O O2 + 4 e + 4 H+ E = -1.23
2 CoO2 + 4 H+ 2 Co2+ + O2 + 2 H2O E = +0.43
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TM redox trends
More valence e- going across the rows means higher oxidation states are possible, but later TM are too electronegative to be oxidized to their group number.
3 4 5 6 7 8 9 10 11 12
Sc Ti V Cr Mn Fe Co Ni Cu Zn
+3 +4 +5 +6 +7 +6 +4 +2,3 +2,3 +2
Highest oxidation states accessible in aqueous solution
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TM redox trendsWithin a triad, 2nd and 3rd row TM are usually similar.
Example:
Group 6 = Cr, Mo, W triad
Cr3+ is v. stable, unlike Mo3+ and W3+
Cr6+ is a strong oxidizer, unlike Mo6+ and W6+
Generally can get higher ox states for 2nd and 3rd row TMs
Larger ions can have higher CN; CN = 6 is generally the max in 1st row TM complexes, but CN = 7-9 common for 2nd and 3rd row TM
[Cr(CN)6]3 (Oh) vs [Mo(CN)8]3 (D4d square anti-prism)
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PolyoxometallatesMetal atoms linked via shared ligands, usually corner or edge-shared Td or Oh
Common for groups 5 (V Nb Ta) and 6 (Cr Mo W)
pH dependence:
high pH Al(OH)4 VO4
3 MoO42 no M-O-M
decr pH,
decr chg / vol
lower pH Al2O3 (s) V2O5(s) MoO3(s) extensive M-O-M
polyoxometallates
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Vanadates
2 H2VO4- + H+ H3V2O7
- + H2O pKa ~ 4
metavanadate chains, (VO3) NaVO3
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Polyoxometallates
decavanadate has edge-sharing Oh
6 MoO42 + 10 H+ Mo6O19
2 + 5 H2O
M6O19n ; M = Nb,Ta (group 5); Mo,W (group 6)
There are 6 edge-sharing Oh, each Oh has 1 unique O 1
4 shared O 4 x ½
1 center O 1 x 1/6
total O / M 3 1/6 = M6O19
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Keggin structure
[PMo12O40]3 Keggin structures
Td site at cluster center, can also be As,Si,B,Te,Ti
PO43- + 12 WO4
2- + 27 H+ H3PW12O40 + 12 H2O
http://en.wikipedia.org/wiki/Keggin_structure (ref Fig below)
X2M18O62n−
Dawson structure
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Ferrodoxins
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Clusters (M-M bonding)
[Re2Cl8]2- D4h
Re-Re = 2.24 Å
< ClReRe = 104°
[Mo2(CH3CO2)4]
Mo-Mo = 2.11 Å
2 Mo(CO)6 + 4 CH3COOH [Mo2(O2CCH3)4] + 4 H2 + 12 CO
Re(m) has Re-Re = 2.74 Å and Tm=3180°C ; Mo(m) Mo-Mo = 2.80Å
“NaReCl4” isroyal blue, diamagnetic
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M-M bonding interactions
[M2X8]n common in groups 6-9 (Mo, W, Re, Ru, Rh)
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Electronic configurations
Cluster ions config b.o. b.l.
[Mo2(SO4)4]4 Mo(II) d4 σ242 4 2.11 Å
[Mo2(SO4)4]3 Mo(II) d4 σ241 3.5 2.17 Å
Mo(III) d3
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Electronic configurations
Cluster ions config b.o. b.l.
[Mo2(HPO4)4]2 Mo(III) d3 σ24 3 2.22 Å
[Ru2Cl2(O2CCl)4] Ru(II) d6
Ru(III) d5 σ242**2 2.5 2.27 Å
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Electronic Configurations
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Larger Metal Clusters
[Re3Cl12]3-
ZrCl Zr-Zr bondlengths
intrasheet 3.03 Å
Intersheet 3.42 Å
In Zr (m) 3.19 Å
3 Zr(s) + ZrCl4(g) 4 ZrCl (s)
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MoCl2 and [Mo6Cl14]2-
[Mo6Cl14]2- MoCl2
4 of the 6 Cl bridge to other Mo6 clusters
For each Mo6:
8 Cl capping faces
4 (½ Cl) bridging
2 Cl unique
12 Cl / Mo6 cluster
Similar for M = Mo, W, Nb,Ta
HCl (aqu)
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Groups 8-11
Noble metals : groups 8 – 11 except Fe, Co, Ni
metallic forms can exist under environment conditions (see Pourbaix diagrams)
Group 11 metals (Cu, Ag, Au) can even exist in strong acid, for example Au does not react with HCl (conc)
Au (s) [AuCl4]- (aq) + NO (g)
[Au(CN)2]- (aq)
NO3 oxidant, Cl forms stable complex
3 HCl / 1 HNO3
“aqua regia”
O2 / CN
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Group 11+1 state = d10 no LFSE
- usually CN = 2 linear (VSEPR)
- often disproportionate
2 Cu+ Cu (s) + Cu2+ E = +0.36 at pH = 0
1.2 at pH = 14
- soft LA Kf I > Br > F
R3P > R3N
S2- > O2
+3 state = d8
- usually D4h square planar (ex AuCl4-)
Ni(II) Cu(III)
Rh(I) Pd(II) Ag(III)
Ir(I) Pt(II) Au(III)
sometimes Td
AuF3
AuCl
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Group 12 (Zn, Cd, Hg)Not noble metals; Zn, Cd are readily oxidized
pH = 0 Fe/Fe2+ E0 = + 0.44V
Cu/Cu2+ E0 = 0.34V
Zn/Zn2+ E0 = + 0.76V
Why the aperiodic change from group 11 to 12 ?
B–H approach:
Cu Zn
M (s) M (g) + 338 +131 kJ/mol
M (g) M2+ (g) + 2 e +2704 +2639
M (s) M2+ (g) + 2 e +3012 +2770
Zn(m) is used for anodic protection (sacrificial anode)
www.boatzincs.com/shaft.html
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Group 12Group 12 has d10s2 filled orbitals, much weaker M–M bonding, and lower IE
MP Cu 1080°C Zn 420 C
Cd 320
Hg - 39
Zn2+ common CN = 4 (6)
Cd2+ common CN = 6 (4)
Hg2+ common CN = 2 (linear)
Hg2+ is stable in aqu solution
HgCl – mercurous chloride (calomel) is [Hg2]2+ 2Cl
Raman band at 171cm1 Hg–Hg stretch
Diamagnetic (Hg+ would be d10s1)
XRD
bondlengths
Hg (m) 300 pm
Hg22+ 250-270 pm
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Hg catenation
Hg32+ linear ion (catenation)
(6-x) Hg + 3 AsF5 2 Hg3 x/2 AsF6 + AsF3
Superconductor Tc ~ 4 K
Hg3NbF6 2D hex Hg plane
SO2(l)
Gray = Hg, white = F, black = Nb
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f-block elementsRelatively constant electroneg across block (shielding keeps Z* = Z-σ nearly constant), so chemistry is very consistent across f-block
Ions – have only f valence e
Ce = [Xe]4f2 6s2
Ce3+ = [Xe]4f1 Ce4+ = [Xe]
All Ln have 3+ as their most stable oxidation state
Ce4+ is relatively stable (f) E0 (Ce4+/ Ce3+) = +1.76V strong oxidant
Eu2+ “ “ “ (f7) E0 (Eu2+/ Eu3+) = + 0.35V mild reductant
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Actinide Frost
Diagrams
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Pourbaix f-block
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Ligand interactionsf-block metal – ligand interactions:
Ligands have less influence on f orbitals
f–f electronic transitions are sharp, relatively independent of ligand type, and long-lived (slow non-radiative energy transfer) luminescence
d–d transition forbidden (Laporte selection rules)
Eu(III) 1 % gives bright orange-red luminescence
Gd2O2S: Pr
Gd(III) = f7 colorless (spin forbidden transitions)
Pr(III) = f2 green
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Actinidesactinides +3 oxidation state common, but high ox states also:
Th4+ (f); U3+ U6+ all common
ArO22+ linear cation for U, Np, Pu, Am
UO22+ uranyl cation (bright yellow)
High CN common (8-10)
[UO2(NO3)2(OH2)4]
ThO2
ThCl4