Ch 19. d-block Metals

Transcription

1 Ch 19. d-block Metals

2 H vap (in kj/mol) for Metals T m Ba 725 C W 3410 C Au 1064 C 2

3 T m across TM 3

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 H 2 O as needed Ex: Balance HMnO 4 Mn 2+ in acidic soln 5e + HMnO 4 + 7H + Mn H 2 O Balance VO 4 3 V 2 O 3 in basic solution 4e + 2VO H 2 O V 2 O OH E = 1.37V at ph = 14 4

5 Quick Review of Redox Rxns Nernst relation E = E - (0.059V / n) log Q What is E (VO 4 3 / V 2 O 3 ) at ph = 12? E = E - (0.059V / 4) log [OH ] 10 = E + (10) (0.059V / 4) ( poh) = V + (0.148) (2) = V (E increases with decr ph because OH is produced) 5

6 Quick Review of Redox Rxns Latimer diagrams 1. Reverse direction, reverse sign 2. n E are additive, not E Mn 3+ Mn 2+ Mn E = (1) (1.5V) + 2( 1.18V) / 3 = 0.28V 3. E is independent of stoichiometry 6

7 Quick Review of Redox Rxns e - + Fe 3+ Fe 2+ E = 0.77 V e - + Fe(OH) 3 + 3H + Fe H 2 O E = E 0-3(0.059) ph e - + Fe(OH) 3 Fe(OH) 2 + OH - E = E ph 7

8 TM redox trends TM Frost diagrams at ph=0 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. 8

9 TM Pourbaix diagrams Pourbaix diagrams show increasing E for M/M 2+ and M 2+ /M 3+ equilibria 9

10 Early vs late TMs 2 e + CoO 2 Co 2+ E = 1.66V 2 e + TiO 2+ Ti 2+ E = V Note that CoO 2 is unstable in H 2 O because: 2 e + 4 H + + CoO 2 Co H 2 O E = H 2 O O e + 4 H + E = CoO H + 2 Co 2+ + O H 2 O E =

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 Sc Ti V Cr Mn Fe Co Ni Cu Zn ,3 +2,3 +2 Highest oxidation states accessible in aqueous solution 11

12 TM redox trends Within a triad, 2 nd and 3 rd row TM are usually similar. Example: Group 6 = Cr, Mo, W triad Cr 3+ is v. stable, unlike Mo 3+ and W 3+ Cr 6+ is a strong oxidizer, unlike Mo 6+ and W 6+ Generally can get higher ox states for 2 nd and 3 rd row TMs Larger ions can have higher CN; CN = 6 is generally the max in 1 st row TM complexes, but CN = 7-9 common for 2 nd and 3 rd row TM [Cr(CN) 6 ] 3 (O h ) vs [Mo(CN) 8 ] 3 (D 4d square anti-prism) 12

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 VO 4 3 MoO 4 2 no M-O-M decr ph, polyoxometallates decr chg / vol lower ph Al 2 O 3 (s) V 2 O 5 (s) MoO 3 (s) extensive M-O-M 13

14 Vanadates 2 H 2 VO H + H 3 V 2 O H 2 O pk a ~ 4 metavanadate chains, (VO 3 ) NaVO 3 14

15 Polyoxometallates decavanadate has edge-sharing Oh 6 MoO H + Mo 6 O H 2 O M 6 O n 19 ; 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 = M 6 O 19 15

16 Keggin structure [PMo 12 O 40 ] 3 Keggin structures Td site at cluster center, can also be As,Si,B,Te,Ti PO WO H + H 3 PW 12 O H 2 O (ref Fig below) X 2 M 18 O 62 n Dawson structure 16

17 Ferrodoxins 17

18 Clusters (M-M bonding) NaReCl 4 is royal blue, diamagnetic [Mo 2 (CH 3 CO 2 ) 4 ] Mo-Mo = 2.11 Å [Re 2 Cl 8 ] 2- D 4h Re-Re = 2.24 Å < ClReRe = Mo(CO) CH 3 COOH [Mo 2 (O 2 CCH 3 ) 4 ] + 4 H CO Re(m) has Re-Re = 2.74 Å and T m =3180 C ; Mo(m) Mo-Mo = 2.80Å 18

19 M-M bonding interactions [M 2 X 8 ] n common in groups 6-9 (Mo, W, Re, Ru, Rh) 19

20 Electronic configurations Cluster ions config b.o. b.l. [Mo 2 (SO 4 ) 4 ] 4 Mo(II) d 4 σ 2 π 4 δ Å [Mo 2 (SO 4 ) 4 ] 3 Mo(II) d 4 σ 2 π 4 δ Å Mo(III) d 3 20

21 Electronic configurations Cluster ions config b.o. b.l. [Mo 2 (HPO 4 ) 4 ] 2 Mo(III) d 3 σ 2 π Å [Ru 2 Cl 2 (O 2 CCl) 4 ] Ru(II) d 6 Ru(III) d 5 σ 2 π 4 δ 2 δ * π * Å 21

22 Electronic Configurations 22

23 Larger Metal Clusters [Re 3 Cl 12 ] 3-3 Zr(s) + ZrCl 4 (g) 4 ZrCl (s) ZrCl Zr-Zr bondlengths intrasheet 3.03 Å Intersheet 3.42 Å In Zr (m) 3.19 Å 23

24 MoCl 2 and [Mo 6 Cl 14 ] 2- HCl (aqu) [Mo 6 Cl 14 ] 2- MoCl 2 4 of the 6 Cl bridge to other Mo 6 clusters For each Mo 6 : 8 Cl capping faces 4 (½ Cl) bridging 2 Cl unique 12 Cl / Mo 6 cluster Similar for M = Mo, W, Nb,Ta 24

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) NO 3 oxidant, Cl forms stable complex 3 HCl / 1 HNO 3 Au (s) [AuCl 4 ] - (aq) + NO (g) aqua regia O 2 / CN [Au(CN) 2 ] - (aq) 25

26 Group state = d 10 no LFSE - usually CN = 2 linear (VSEPR) - often disproportionate 2 Cu + Cu (s) + Cu 2+ E = at ph = at ph = 14 AuCl - soft LA K f I > Br > F R 3 P > R 3 N S 2- > O 2 +3 state = d 8 - usually D 4h square planar (ex AuCl 4- ) AuF 3 sometimes Td Ni(II) Cu(III) Rh(I) Pd(II) Ag(III) Ir(I) Pt(II) Au(III) 26

27 Group 12 (Zn, Cd, Hg) Not noble metals; Zn, Cd are readily oxidized ph = 0 Fe/Fe 2+ E 0 = V Cu/Cu 2+ E 0 = 0.34V Zn/Zn 2+ E 0 = V Zn(m) is used for anodic protection (sacrificial anode) Why the aperiodic change from group 11 to 12? B H approach: Cu Zn M (s) M (g) kj/mol M (g) M 2+ (g) + 2 e M (s) M 2+ (g) + 2 e

28 Group 12 Group 12 has d 10 s 2 filled orbitals, much weaker M M bonding, and lower IE MP Cu 1080 C Zn 420 C Cd 320 Hg - 39 Zn 2+ common CN = 4 (6) Cd 2+ common CN = 6 (4) Hg 2+ is stable in aqu solution Hg 2+ common CN = 2 (linear) HgCl mercurous chloride (calomel) is [Hg 2 ] 2+ 2Cl Raman band at 171cm 1 Hg Hg stretch Diamagnetic (Hg + would be d 10 s 1 ) XRD bondlengths Hg (m) 300 pm Hg pm 28

29 Hg catenation Hg 3 2+ linear ion (catenation) SO 2 (l) (6-x) Hg + 3 AsF 5 2 Hg 3 x/2 AsF 6 + AsF 3 Superconductor T c ~ 4 K Hg 3 NbF 6 2D hex Hg plane Gray = Hg, white = F, black = Nb 29

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]4f 2 6s 2 Ce 3+ = [Xe]4f 1 Ce 4+ = [Xe] All Ln have 3+ as their most stable oxidation state Ce 4+ is relatively stable (f ) E 0 (Ce 4+/ Ce 3+ ) = +1.76V strong oxidant Eu 2+ (f 7 ) E 0 (Eu 2+ / Eu 3+ ) = V mild reductant 30

31 Actinide Frost Diagrams 31

32 Pourbaix f- block 32

33 Ligand interactions f-block metal ligand interactions: Ligands have less influence on f orbitals Gd 2 O 2 S: Pr 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 Gd(III) = f 7 colorless (spin forbidden transitions) Pr(III) = f 2 green 33

34 Actinides actinides +3 oxidation state common, but high ox states also: Th 4+ (f ); U 3+ U 6+ all common ThO 2 ArO 2 2+ linear cation for U, Np, Pu, Am UO 2 2+ uranyl cation (bright yellow) High CN common (8-10) ThCl 4 [UO 2 (NO 3 ) 2 (OH 2 ) 4 ] 34