SYNTHESIS AND CHARACTERIZATION OF EDGE-SHARING BIOCTAHEDRAL COMPLEXES OF ZIRCONIUM(III) AND HAFNIUM(III) THAT CONTAIN LONG METAL METAL SINGLE BONDS - ZR2I6(PME3)4, HF2I6(PME2PH)4, AND ZR2I6(PME2PH)4

The reduction of MI4 (M = Zr, Hf) with 1 equiv of Na/Hg amalgam, followed by addition of 2 equiv of phosphine, produces in moderate yields the edge-sharing bioctahedral complexes Zr2I6(PMe3)4 (1), Hf2I6(PMe2Ph)4 (2), and Zr2I6(PMe2Ph)4 (3). Each compound was characterized by single-crystal X-ray diffraction studies. Zr2I6(PMe3)4 (1) crystallizes from p-xylene in the monoclinic space group P2(1)/n with unit cell dimensions a = 9.752 (2) angstrom, b = 14.909 (2) angstrom, c = 11.420 (2) angstrom, beta = 96.32 (2)-degrees, V = 1650.3 (6) angstrom 3, and d(calc) = 2.501 g/cm3 for Z = 2. The structure was refined to R = 0.040 and R(w) = 0.050 for 1512 reflections having I > 3-sigma (I). Hf2I6(PMe2Ph)4 (2) crystallizes from toluene in the triclinic space group PIBAR with unit cell dimensions a = 11.083 (2) angstrom, b = 11.455 (2) angstrom, c = 10.081 (2) angstrom, alpha = 106.12 (1)-degrees, beta = 112.17 (1)-degrees, gamma = 84.70 (1)-degrees, V = 1138.4 (3) angstrom 3, and d(calc) = 2.438 g/cm3 for Z = 1. The structure was refined to R = 0.037 and R(w) = 0.051 for 2855 reflections having I > 3-sigma (I). Zr2I6(PMe2Ph)4 (3) is isomorphous to 2 with unit cell dimensions a = 11.132 (2) angstrom, b = 11.503 (2) angstrom, c = 10.118 (2) angstrom, alpha = 106.17 (1)-degrees, beta = 112.21 (1)-degrees, gamma = 84.86 (1)-degrees, V = 1151.9 (3) angstrom 3, and d(calc) = 2.157 g/cm3 for Z = 1. The structure was refined to R = 0.024 and R(w) = 0.039 for 2794 reflections having I > 3-sigma (I). Each of the three complexes has a metal-metal distance of approximately 3.4 angstrom. Molecular orbital calculations on the model complex Zr2I6(PH3)4, at the Fenske-Hall level, were conducted to evaluate the bonding between the metal centers. The calculations indicate that the HOMO is metal-metal bonding and mainly composed of metal d(z)2 and d(x)2-y2-sigma-type orbitals.