Theoretical studies on metal–metal interaction and spectroscopic properties of a series of hetero-binuclear d8–d10 complexes containing iridium(i) and gold(i)

Abstract

The ground and triplet excited state geometries, metal-metal (Ir–Au) attractive interaction, electronic structures, absorptions, and phosphorescence of three d⁸–d¹⁰Ir(I)–Au(I) complexes [Ir(CO)ClAu(µ-dpm)₂]⁻ (1), [Ir(CNCH₃)₂Au(µ-dpm)₂]²⁻ (2), and [Ir(CNCH₃)₃Au(µ-dpm)₂]²⁻ (3) [dpm = bis(diphosphino)methane] were investigated theoretically. Their ground and triplet excited states geometries were fully optimized at the MP2 and UMP2 (6-31G for H/C/N/O atoms, LANL2DZ for Ir/Au/P/Cl) levels, respectively, and the calculated geometries are well consistent with the X-ray results. The calculated results indicated that a weak Ir–Au interaction exists in the ground state of 1–3, moreover the interaction of 1 and 2 is strengthened by excitation, on contrast, the Ir–Au attractive interaction of 3 in the excited state becomes little lower than that in the ground state. By adding one more CNMe group on complex 2, the bond type of HOMO can be changed from σ*[d_z²(Ir/Au)] to σ[d_z²(Ir/Au)]. Under the TD-DFT level with PCM model, the absorptions and phosphorescence of 1–3 were calculated based on the optimized ground and excited states geometries, respectively. The lowest-lying absorptions of 1 and 2 are all attributed to σ*[d_z²] → σ[p_z] and that of 3 is assigned to σ[d_z²] → π[p_z] with MC/MMLCT transition characters. The phosphorescence of 1, 2, and 3 are assigned to σ[p_z] → σ*[d], σ[p_z] → σ*[d], and π[p_z] → σ[d] transitions, respectively. The calculated results also indicated that with the increase of the Ir–Au bond distance both in the ground and the excited state, the absorptions and the emissions are red-shifted correspondingly.