Preparation and structure of bis(mu-acetato)dichlorodicarbonyldiiridium(II) complexes with Group 15 ligands and ESR and density functional theory studies of electronic structure of their cationic radicals

bis(mu -Acetato)dichlorodicarbonyldiiridium(II) complexes with Group 15 com pounds as axial ligands, [Ir-2(mu -O2CMe)(2)Cl-2(CO)(2)L-2] (L = PPh3: 1, P Cy3: 2, P(OPh)(3): 3, AsPh3: 4, SbPh3: 5) were synthesized. The Ir-Ir dista nces of complexes 2-5 (2.6200(9)-2.6936(7) Angstrom) were longer than those of the complexes with MeCN, py or dmso ligands at the axial sites. Cyclic voltammograms of 1 - 5 show a chemically reversible one-electron oxidation wave of which E-1/2 (vs. Fc(+) - Fc) values were between 0.22 for 2 and 0.7 5 V for 3 depending on the axial ligands. Oxidation by electrolysis and/or radiolysis of 1, 2 and 4 gave their cationic radicals. The ESR spectra of 1 (+.), 2(+.) and 4(+.) at 77 K were pseudo-axially symmetric with g tensors of g(perpendicular to) = 2.15 and g(parallel to) = 1.96, 2.18 and 1.95, and 2.20 and 1.96, respectively. Their hyperfine coupling indicates that their odd electron is delocalized equivalently onto the two axial phosphorous or arsenic atoms. The odd electron densities were estimated from the hyperfin e coupling tensors as rho approximate to 0.1 on the P atoms of 1(+.) and 2( +.) and rho approximate to 0.15 on the As atoms of 4(+.). These results ind icate that their singly occupied molecular orbital (SOMO) is the sigma (IrI r) orbital with sigma (IrP)* or sigma (IrAs)* character. DFT calculations f or model complexes, [Ir-2(mu -O2CH)(2)Cl-2(CO)(2)(PH3)(2)](+.) (6(+.)) and [Ir-2(A-O2CH)(2)Cl-2(CO)(2)(AsH3)(2)](+.) (7(+.)), gave electronic structur es consistent with the ESR results. (C) 2001 Elsevier Science B.V. All righ ts reserved.