Revisiting Ir(CO)3Cl

We return to an old puzzle - the short metal-metal separation and electrical conductivity of the apparently unoxidized one-dimensionally stacked structure of a d(8) Ir(I) complex, Ir(CO)(3)Cl. One would expect neither a short Ir-Ir distance of 2.84 angstrom, nor metallicity in an unoxidized stacked square-planar d(8) array. We build up dimer, trimer, one-dimensional polymer and model 3-dimensional structures, in both molecular and extended structure plane wave calculations. The short Ir-Ir separation in the polymer, with a substantial contribution of 6p(z)-5d(z)2 bonding to it, is obtained without any oxidation. There is computational evidence for an important level crossing, in the polymer. The metallicity remains unexplained, but likely arises from partial oxidation. And that remains an outstanding experimental issue. (C) 2015 Elsevier Ltd. All rights reserved.