Ch 19. d-Block Metals
2
∆Hvap (in kJ/mol) for Metals
Tm Ba 725°C W 3410°C Au 1064°C
3
Tm across TM
4
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 4. Add H2O as needed Ex: Balance HMnO4 → Mn2+ in acidic soln 5e− + HMnO4 + 7H+ → Mn2+ + 4 H2O Balance VO4
3− → V2O3 in basic solution 4e− + 2VO4
3− + 5H2O → V2O3 + 10 OH− E° = 1.37V at pH = 14
5
Quick Review of Redox Rxns
Nernst relation E = E° - (0.059V / n) log Q What is E (VO4
3− / 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)
6
Quick Review of Redox Rxns Latimer 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
7
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
8
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 diagrams at pH=0
9
TM Pourbaix diagrams
Pourbaix diagrams show increasing E° for M/M2+ and M2+/M3+ equilibria
10
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
11
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
12
TM redox trends Within 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)
13
Polyoxometallates Metal 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
14
Vanadates
2 H2VO4- + H+ H3V2O7
- + H2O pKa ~ 4
metavanadate chains, (VO3)− NaVO3
15
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
16
Keggin structure
[PMo12O40]3− Keggin structures
Td site at cluster center, can also be As,Si,B,Te,Ti
PO4
3- + 12 WO42- + 27 H+ H3PW12O40 + 12 H2O
http://en.wikipedia.org/wiki/Keggin_structure (ref Fig below)
X2M18O62n−
Dawson structure
17
Ferrodoxins
18
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” is royal blue, diamagnetic
19
M-M bonding interactions
[M2X8]n− common in groups 6-9 (Mo, W, Re, Ru, Rh)
20
Electronic configurations Cluster ions config b.o. b.l.
[Mo2(SO4)4]4− Mo(II) d4 σ2π4δ2 4 2.11 Å
[Mo2(SO4)4]3− Mo(II) d4 σ2π4δ1 3.5 2.17 Å
Mo(III) d3
21
Electronic configurations Cluster ions config b.o. b.l.
[Mo2(HPO4)4]2− Mo(III) d3 σ2π4 3 2.22 Å
[Ru2Cl2(O2CCl)4]− Ru(II) d6
Ru(III) d5 σ2π4δ2δ*π*2 2.5 2.27 Å
22
Electronic Configurations
23
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) ∆
24
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)
25
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−
26
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
27
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
28
Group 12 Group 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 171cm−1 Hg–Hg stretch
Diamagnetic (Hg+ would be d10s1)
XRD
bondlengths
Hg (m) 300 pm
Hg22+ 250-270 pm
29
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
30
f-block elements Relatively 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
31
Actinide Frost
Diagrams
32
Pourbaix f-block
33
Ligand interactions f-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
34
Actinides actinides +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