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Chemistry 481(01) Spring 2014

Chemistry 481(01) Spring 2014. Instructor: Dr. Upali Siriwardane e-mail: upali@latech.edu 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,)

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Chemistry 481(01) Spring 2014

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  1. Chemistry 481(01) Spring 2014 • Instructor: Dr. Upali Siriwardane • e-mail: upali@latech.edu • 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

  2. Chapter 19. The d-block metals The 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 trends 19.6 Noble character Representative compounds 19.7 Metal halides 19.8 Metal oxides and oxo compounds 19.9 Metal sulfides and sulfide complexes 19.10 Nitrido and alklidyne complexes 19.11 Metal-metal bonded compounds and clusters

  3. 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

  4. Origin Found 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 metal First row metals are harder than 2nd, 3rd row metals Metal oxides are generally reduced with carbon Except Ti (why? carbide?): TiO2 + C + Cl2TiCl4 + 2 CO TiCl4 + 2 Mg  Ti + MgCl2 Metal 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-bands As d-band is filled, bonding becomes stronger, until half-filled, then more d-electrons are antibonding Therefore metal-metal bond strength is maximum in the mid-TM (group 7) Cs (group 1) 6s1 mp 29 °C Ba (group 2) 6s2 mp 725 °C W (group 6) 4f146d46s2 mp 3410 °C (refractory) Au (group 11) 5d106s1 mp 1064 °C **Hg (group 12) 5d106s2 mp -39 °C Tl (group 13) 5d106s26p1 mp 303 °C ** relativistic effects

  5. Precious Metals Platinum 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 record Noble 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

  6. Oxidation states • Maximum oxidation state is always equal to the group number CrVIO42- (chromate), MnVIIO4- (permanganate) but MnVIO42- (manganate), FeVIO42- (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-)

  7. Coordination number and Oxidation State Coordination number increases down a group e.g., Cr(CN)63- but Mo(CN)84- Low oxidation state compounds may be ionic (to increase coordination number) High oxidation state compounds usually covalent (multiple bonding)

  8. 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

  9. behavior in water low 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)

  10. Condensation to Polyoxometallates 2 CrO42- + 2 H+ = O3CrOCrO32- + H2O 3d metals tend to share vertices 2nd and 3rd row TMs can also share edges polyoxomolybdates, polyoxotungstates 6 MoO42- + 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-

  11. Sulfides Sulfides tend to be more covalent Layered 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 cofactors Imido (RN) and alkylidene (RR´C) are isolobal with oxo and sulfido

  12. Multiple Bonds involving d-orbitals Metal 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.

  13. 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.

  14. Nitrido complexes MNX4 Where MN has a triple bond and X a halogen Square pyramidal, strong trans influence of multiply-bonded ligand Isolobal with RC, alkylidyne

  15. Metal-metal bonds The geometry of [ZrCl3(PR3)2]2 is edge-sharing bioctahedral. The oxidation state of Zr is III (d1), but the material is diamagnetic. Why?

  16. 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

  17. 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 (σ2π2δ2)

  18. 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 (σ2π4)

  19. Bonding in [Re2Cl8]2-, d4-d4 Quadruple metal-metal bonds are possible with a d4-d4 electronic configuration (σ2π4δ2). 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: Metal-metal triple bond (σ2π4δ2)

  20. Bonding in [Re2Cl8]2-, d4-d4 Quadruple metal-metal bonds are possible with a d4-d4 electronic configuration (σ2π4δ2). 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: Metal-metal triple bond (σ2π4δ2)

  21. Small metal clusters The 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.

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

  23. Rh6(CO)16 cluster The 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.

  24. 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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