Bromide ion binding by a dinuclear gold(i) N-heterocyclic carbene complex: a spectrofluorescence and X-ray absorption spectroscopic study

Abstract

Fluorescence and X-ray absorption spectroscopy were used to investigate the anion binding properties of a luminescent, dinuclear Au(I) N-heterocyclic carbene (NHC) complex ([1]²⁺) with a short Au(I)⋯Au(I) contact. The addition of Br⁻ ions to a DMSO solution of [1](PF₆)₂ caused a red-shift in the fluorescence emission band from 396 nm to 496 nm. Similarly, the addition of Br⁻ ions to [1](PF₆)₂ caused a decrease in the energy of the Au L₃-edge in the X-ray absorption spectrum, consistent with the formation of an association complex between the cation [1]²⁺ and Br⁻ ions. Solution-based structural studies of the association complex were carried out using extended X-ray absorption fine structure (EXAFS) modelling of the Au(I)⋯Au(I) core of the cation. These studies indicate that the association complex results from Au(I)⋯Br⁻ interactions, with the Br⁻ ions occupying two partially occupied sites at ∼2.9 and 3.9 Å from the Au(I) atoms.