CHEMISTRY OF IRIDIUM CARBONYL CLUSTER COMPLEXES - SYNTHESIS AND CHARACTERIZATION OF MIXED-METAL CARBONYL CLUSTERS VIA CAPPING REACTIONS WITH HGCL2 AND AU(PPH3)CL - CRYSTAL-STRUCTURES OF [N(PPH3)2][IR6(MU-3-CO)3(CO)12(MU-3-HGCL)].0.5C6H12 AND [NME3(CH2PH)][IR6(MU-CO)3(CO)12[MU-3-AU(PPH3)]].C4H8O

The new anionic carbonyl clusters [Ir6(CO)15(HgCl)]- (1) and [Ir6(CO)15[Au(PPh3)]]- (2) have been obtained by reaction of [Ir6(CO)15]2- with HgCl2 or Au(PPh3)Cl in tetrahydrofuran solution. The complexes have been characterized by IR(nu-CO) and NMR studies (C-13, P-31, Hg-199) and fast atom bombardment mass spectroscopy. The molecular structures of complexes 1 and 2 have been determined by single-crystal X-ray diffraction. The salt [N(PPh3)2][Ir6(mu-3-CO)3(CO)12(mu-3-HgCl)].0.5C6H12 (1a) crystallizes in the triclinic space group P1BAR, with unit cell dimensions a = 14.115 (5) angstrom, b = 14.619 (3) angstrom, c = 17.762 (5) angstrom, alpha = 71.21 (2)-degrees, beta = 66.43 (2)-degrees, gamma = 64.61 (2)-degrees, and Z = 2; R = 0.039 and R(w) = 0.044 for 4513 observed reflections. The salt [NMe3(CH2Ph)][Ir6(mu-CO)3(CO)12[mu-3-Au(PPh3)]].C4H8O (2a) crystallizes in the triclinic space group P1BAR, with unit cell dimensions a = 13.582 (2) angstrom, b = 14.513 (2) angstrom, c = 14.624 (4) angstrom, alpha = 110.07 (2)-degrees, beta = 91.75 (2)-degrees, gamma = 98.37 (1)-degrees, and Z = 2; R = 0.033 and R(w) = 0.043 for 6011 observed reflections. The heptanuclear cluster 1 has an octahedral iridium core, with the mercury atom, which bears a terminally bonded chlorine ligand, capping a triangular face [Ir-Hg average value 2.792 angstrom, Hg-Cl 2.346 (5) angstrom]. Two terminal CO groups are bound to each iridium atom, while the three face-bridging carbonyl groups connect vertex-sharing faces. Average distances are Ir-Ir 2.797 angstrom, Ir-CO(t) 1.86 angstrom, Ir-CO(b) 2.23 angstrom (t = terminal, b = bridging). The structural analysis of 2 shows that the AuPPh3 group caps one face of the Ir6 octahedral framework [Ir-Au average 2.838 angstrom, Au-P 2.272 (3) angstrom], maintaining the stereogeometry of the CO ligands of the parent metal carbonyl anion [Ir6(CO)15]2- of idealized D3 symmetry. Average distances are Ir-Ir 2.796 angstrom, Ir-CO(t) 1.87 angstrom, Ir-CO(b) 2.08 angstrom. The mu-CO groups in 2 are bent, so to assume a ''semitriple'' coordination mode. Very little difference in the ligands' environments is present in the two clusters.