LIGATION-INDUCED CHANGES IN METAL METAL-BONDING IN LUMINESCENT BINUCLEAR COMPLEXES CONTAINING GOLD(I) AND IRIDIUM(I)

Treatment of [Ir(CO)ClAu(mu-dpm)2](PF6) (dpm is bis(diphenylphosphino)methane) with 2 or 3 equiv of methyl isocyanide and ammonium hexafluorophosphate yields [Ir(CNCH3)2Au(mu-dpm)2](PF6)2 or yellow [Ir(CNCH3)3Au(mu-dpm)2](PF6)2, respectively. Red crystals of [Ir(CNMe)2Au(mu-dpm)2](PF6)2.CH2Cl2 form in the monoclinic space group P2(1)/c (No. 14) with a = 20.337 (4) angstrom, b = 12.633 (2) angstrom, c = 22.523 (5) angstrom, and beta = 100.29 (1)-degrees at 130 K with Z = 4. Refinement of 4998 reflections and 450 parameters gave R = 0.057 and R(w) = 0.055. The structure consists of a nearly planar Ir(CNCH3)2P2 unit that is connected to a very linear AuP2 unit through two dpm bridges. The Ir-Au distance is 2.944 (1) angstrom. The complex in dichloromethane solution shows a strong absorption at 492 nm (epsilon = 5100 M-1 cm-1), which is assigned as the allowed sigma*(d(z)2d(z)2) --> sigma-(p(z)p(z)) transition and photoemission at 540 nm (fluorescence) and 668 nm (phosphorescence). Yellow crystals of [Ir(CNCH3)3Au(mu-dpm)2](PF6)2 form in the monoclinic space group C2/c with a = 30.511 (8) angstrom, b = 13.393 (4) angstrom, c = 28.859 (8) angstrom, and beta = 99.10 (2)-degrees at 130 K with Z = 8. Refinement of 7605 reflections and 462 parameters gave R = 0.0698 and R(w) = 0.0534. The structure is similar to that of [Ir(CNCH3)2Au(mu-dpm)2](PF6)2 with an isocyanide added to the iridium along the Au-Ir axis. As a result, the Ir-Au distance has shortened to 2.817 (1) angstrom. The contraction is interpreted as resulting from the conversion into a species with an Ir --> Au dative bond. The electronic absorption spectrum shows that the proximity-shifted band characteristic of [Ir(CNMe)2Au(mu-dpm)2](PF6)2 is no longer present. Rather shoulders at 332 (epsilon = 6700 M-1 cm-1) and 298 (epsilon = 11000 M-1 cm-1) are seen. In dichloromethane at 23-degrees-C, there is a broad emission at 580 nm (with a lifetime of 1.2-mu-s), which shifts to 628 nm at -196-degrees-C, that is assigned to an excited triplet state.