Chemistry 481(01) Spring 2014

Chapter 19-1Chemistry 481, Spring 2014, LA Tech

Instructor: Dr. Upali Siriwardane

e-mail: [email protected]

Office: CTH 311 Phone 257-4941

Office Hours:

M,W 8:00-9:00 & 11:00-12:00 am;

Tu,Th, F 10:00 - 12:00 a.m.

April 10 , 2014: Test 1 (Chapters 1, 2, 3,)

May 1, 2014: Test 2 (Chapters 6 & 7)

May 20, 2014: Test 3 (Chapters. 19 & 20)

May 22, Make Up: Comprehensive covering all Chapters

Chemistry 481(01) Spring 2014


Chapter 19. The d-block metalsThe elements

19.1 Occurrence and recovery 19.2 Physical properties

Trends in physical properties 19.3 Oxidation states across a series 19.4 Oxidation states down a group 19.5 Structural trends19.6 Noble character

Representative compounds19.7 Metal halides 19.8 Metal oxides and oxo compounds 19.9 Metal sulfides and sulfide complexes 19.10 Nitrido and alklidyne complexes19.11 Metal-metal bonded compounds and clusters


The d-block• Consists of groups 3-12• Organized into triads (by groups) and series (by row) e.g., Ti, Zr, Hf are the group 4 triad, e.g., Sc-Zn are the 3d series• Group 3 and group 12 rarely have partly-filled d-shells their behavior is more like the main group (s- and p-blocks)• Group 4-11 often have partly-filled d-shells (transition metals, TM) their behavior dictated by the d-shell• Also divided into early TM (groups 4-5), mid-TM (groups 6-8) and late

TM (groups 9-11)• Atomic radii decrease from left to right as the effective nuclear charge

increases• Atomic radii increase from the 3d series to the 4d series• Lanthanide contraction: the f-block occurs between the 4d series and

5d series, giving rise to the f-electrons do not screen the increased nuclear charge well therefore 2nd and 3rd row transition elements of the same triad are more similar (atomic radius) than the first row element

• Ionization energies increase across the row and decrease down a group


OriginFound in nature as oxides (hard metal cations) or sulfide (soft metal cations)Late TM are soft; early TM are hard (oxophilic)Higher oxidation states are harder than lower oxidation states, for the same metalFirst row metals are harder than 2nd, 3rd row metalsMetal oxides are generally reduced with carbon

Except Ti (why? carbide?): TiO2 + C + Cl2 TiCl4 + 2 CO TiCl4 + 2 Mg Ti + MgCl2Metal sulfides are “roasted” in air to give the metal (Ni) or metal oxide (ZnO) that is then reduced with C Elements exhibit metallic bonding: filling of the s- and d-bandsAs d-band is filled, bonding becomes stronger, until half-filled, then more d-electrons are antibondingTherefore metal-metal bond strength is maximum in the mid-TM (group 7)

Cs (group 1) 6s1 mp 29 °CBa (group 2) 6s2 mp 725 °CW (group 6) 4f146d46s2 mp 3410 °C (refractory)Au (group 11) 5d106s1 mp 1064 °C**Hg (group 12) 5d106s2 mp -39 °CTl (group 13) 5d106s26p1 mp 303 °C** relativistic effects


Precious MetalsPlatinum group: found together in nature:

4d: Ru, Rh, Pd; 5d: Os, Ir, Pt

All rare; Rh most expensive (demand for catalytic converters and catalysts)

Jan 2008, all time record price for Rh: $7,300/troy ounce (about 31 g) $250,000/kg Rh

Pt: $1,731/troy ounce, also a recordNoble metals: Cu, Ag, Au used in coins and jewelery aqua regia (3:1 HCl/HNO3) will dissolve Au• 3 HCl + HNO3 Cl2 + NOCl + 2 H2O


Oxidation states• Maximum oxidation state is always equal to the

group number CrVIO42- (chromate), MnVIIO4

- (permanganate)

but MnVIO42- (manganate), FeVIO4

2- (ferrate)• Max. oxidation state may not be achieved (group

8: OsO4, Os(+8), but no +9 in group 9)• Stability of high oxidation states increase down

the group• Lower oxidation states found in organometallic

compounds with π-acid ligands (like CO)• Higher oxidation states found in compounds with

strong π-donors (like oxo, O2-)


Coordination number and Oxidation StateCoordination number increases down a group

e.g., Cr(CN)63- but Mo(CN)8

4-

Low oxidation state compounds may be ionic (to increase coordination number)

High oxidation state compounds usually covalent (multiple bonding)


Color and Oxidation States

Color: metal ions in lower than max. oxidation state are highly colored, because of low energy d-d transitions in the visible

Metal ions in max. oxidation state are often colorless

(ReO4-) but this is not always the case: MnO4

- is bright purple due to ligand-to-metal charge transfer

+2, +3 are common in coordination chemistry


behavior in waterlow oxidation states: M(H2O)n

m+ ; n usually 6, m usually 2 as pH increases, the water molecules become deprotonated as oxidation state increases, coordinated water becomes more acidic

VII(H2O)62+

VIVO(H2O)42+ (vanadyl)

VVO2(H2O)4+ (vanadate)


Condensation to Polyoxometallates 2 CrO4

2- + 2 H+ = O3CrOCrO32- + H2O

3d metals tend to share vertices2nd and 3rd row TMs can also share edgespolyoxomolybdates, polyoxotungstates 6 MoO4

2- + 10 H+ = Mo6O192- + 5 H2O

an octahedron of Mo atoms, with bridging O (edge-sharing octahedra)

heteropolyoxometallates – contain a central tetrahedral p-block element (P, Si, etc)

e.g. PMo12O403-


SulfidesSulfides tend to be more covalentLayered disulfides MoS2

Mo is 6-coordinated, bridging sulfur with some S-S bonding

FeS2 has discrete S22- ions

Cubanes such as Fe4S4(SR)42- are biological

cofactorsImido (RN) and alkylidene (RR´C) are isolobal

with oxo and sulfido


Multiple Bonds involving d-orbitalsMetal d orbitals can also be used to form multiple

bonds to ligands. Non-transition elements without low-lying d orbitals cannot form δ bonds, therefore all of their multiple bonds are of π-type.

The V-O bond order in VOCl3 is 3, as a result of two dπ-pπ overlaps.


Multiple delocalized bonding involving d-orbitals

[(H3N)5CrOCr(NH3)5]4+, in which the Cr-O-Cr unit

is linear because of dπ-pπ-dπ overlap.


Nitrido complexesMNX4

Where MN has a triple bond and X a halogenSquare pyramidal, strong trans influence of

multiply-bonded ligandIsolobal with RC, alkylidyne


Metal-metal bondsThe geometry of [ZrCl3(PR3)2]2 is edge-sharing

bioctahedral.The oxidation state of Zr is III (d1), but the material

is diamagnetic. Why?


Bonding in [ZrCl3(PR3)2]2, d1-d1

The dσ-dσ overlap of the dxy orbitals generates a σ-bond between

the two metal centers


Bonding in [NbCl4(R2PPR2)2]2, d2-d2

Nb(III) has a d2 electronic configuration. In the same edge-sharing bioctahedral geometry, it also forms a π-

bond (dπ-dπ), with shared electron density above and below the intermetallic axis. The Nb-Nb bond order is 2.

The metal-metal bond is a δ-bond (dδ-dδ), formed by parallel overlap of the remaining d orbital:

Metal-metal triple bond (σ2

π2δ

2)


Bonding in [W2Cl9]3- and W2(OR)6], d3-d3

metal-metal triple bond (σ2π4) is found in the d3-d3 complexes [W2Cl9]3- and W2(OR)6. In both cases, linear

combinations of three d orbitals (dxy, dxz, dyz) form one M-M σ- and two M-M π-bonds (see McCarley, Inorg.

Chem. 1978, 17, 1263). The W-W distance in [W2Cl9]3- is only 2.40 Å, compared to 2.75 Å in tungsten

metal.

Metal-metal triple bond (σ2π

4)


Bonding in [Re2Cl8]2-, d4-d4

Quadruple metal-metal bonds are possible with a d4-d

4 electronic configuration

(σ2π

4δ

2). The first quadruple bond was identified in [Re2Cl8]

2- (F. A. Cotton,

Science, 1964, 145, 1305). It is a deep blue, air-stable, diamagnetic ion with a

curious tetragonal prismatic

structure:


π4δ

2)


Bonding in [Re2Cl8]2-, d4-d4 Quadruple metal-metal bonds are possible with a d

4-d

4 electronic configuration (σ

2π

4δ

2). The first quadruple

bond was identified in [Re2Cl8]2-

(F. A. Cotton, Science, 1964, 145, 1305). It is a deep blue, air-stable,

diamagnetic ion with a curious tetragonal prismatic

structure:


π4δ

2)


Small metal clustersThe simplest metal cluster contains the M3 unit, held together by

metal-metal bonds (rather than solely by bridging ligands). An example is Ru3(CO)12. The trigonal arrangement

of metal atoms is reminiscent of the close-packing of spheres in bulk metal. The cluster Rh6(CO)16 has an

octahedral arrangement of metal atoms (with 12 terminal CO ligands and 4 triply-bridging CO ligands). The

metal organization is analogous to the packing of two trigonal M3 units in adjacent layers in bulk metal.


Wade’s RulesThe metal-metal bonds in metal clusters cannot be described as localized two-center M-M bonds.


Rh6(CO)16 clusterThe total number of valence e- available for bonding is (9x6) + (2x16) = 86. First, we need to

determine the number of e- involved in metal-ligand bonding. The cluster contains 12 terminal

CO ligands and 4 bridging CO ligands. Each of the 12 terminal CO ligands requires 2 e- to form

a M-C σ-bond, and 2 e- to form a M-C π-bond, for a total of 48 e-. Each of the 4 bridging CO

ligands requires 6 e- to form one σ- and two π-bonds to the cluster, for a total of 24 e-. The

metal-ligand bonding therefore requires 48+24 = 72 e-, leaving 86-72 = 14 e-, or 7 electron pairs,

remaining for the framework (M-M) bonding. Thus the metal framework in Rh6(CO)16 should

have a octahedral structure.


3-center two electron bond

Boron and hydrogen compounds are called boranes. Diborane

B2H6 is the simplest borane. The model determined by

molecular orbital theory indicates that the bonds between boron

and the terminal hydrogen atoms are conventional

2-center, 2-electron covalent bonds while bridging H are held

together by two 3-center-2-electron.

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Chemistry 481(01) Spring 2014