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

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)center dot center dot center dot 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 L-3-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)center dot center dot center dot Au(I) core of the cation. These studies indicate that the association complex results from Au(I)center dot center dot center dot Br- interactions, with the Br- ions occupying two partially occupied sites at similar to 2.9 and 3.9 angstrom from the Au(I) atoms.