Luminescent heterobimetallic complexes. Electronic structure, spectroscopy, and photochemistry of [AuPt(dppm)2(CN)2]ClO4 and the X-ray crystal structure of [AgPt(dppm)2(CN)2(CF3SO3)]

Abstract

The d10-d8 heterobimetallic complexes [AuPt(dppm)2(CN)2]ClO4 and [AgPt(dppm)2(CN)2(CF3SO3)] (dppm = bis(diphenylphosphino)methane) were prepared by literature methods. The X-ray crystal structure of [AgPt-(dppm)2(CN)2(CF3SO3)] has been determined. Crystal data for [AgPt(dppm)2(CN)2(CF3SO3)]: monoclinic, space group P21, a = 10.453(2) Å, b = 16.372(4) Å, c = 14.846(6) Å, and β = 92.17(2)°. The intramolecular Pt⋯Ag distance is 3.002(1) Å. The absorption spectra of [AuPt(dppm)2(CN)2]ClO4 and [AgPt(dppm)2(CN)2(CF3SO3)] exhibit intense 1(dσ* → pσ) transitions at 323 nm and 317 nm, respectively. The results of extended Hückel molecular orbital calculations suggested that the dσ* orbital in each case is mainly composed of the Pt (5dz2) orbital. In acetonitrile and at room temperature, [AuPt(dppm)2(CN)2]ClO4 exhibits a broad emission (lifetime = 18 μs) at 570 nm. The emitting state has been suggested to be 3(dδ*pσ). The effect of solvent on the emission properties has been investigated. The [AgPt(dppm)2(CN)2(CF3SO3)] complex shows metal-perturbed intraligand emission in glass solution at 77 K. The rate constants of quenching of the excited state of [AuPt(dppm)2(CN)2]+ by pyridinium acceptors have been treated by Marcus quadratic, Rehn-Weller, and Agmon-Levine equations and the excited state reduction potential of [AuPt(dppm)2(CN)2]+, [Au-Pt]2+ + e- → [Au-Pt]+*, is estimated to be about -1.73 to -1.80 V vs SCE. The photoreactions of [AuPt(dppm)2(CN)2]+ with halocarbons were investigated by Stern-Volmer quenching, flash photolysis, and steady-state photolysis experiments. An electron transfer mechanism is suggested. © 1994 American Chemical Society.