Ch 19. d-Block Metals

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