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)···Au(I) contact. The addition of Br(-) ions to a DMSO solution of [1](PF(6))(2) caused a red-shift in the fluorescence emission band from 396 nm to 496 nm. Similarly, the addition of Br(-) ions to [1](PF(6))(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)···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.