Luminescent copper(I) halide butterfly dimers coordinated to [Au(CH3imCH2py)2]BF4 and [Au(CH3imCH2quin)2]BF4

The coordination chemistry of copper(I) halides to the homoleptic, N-heterocyclic carbene Au(I) complexes [Au(CH(3)imCH(2)quin)(2)]BF(4) and Au(CH(3)imCH(2)py)(2)]BF(4) was explored. The reaction of CuX (X = Cl, Br, I) with either [Au(CH(3)imCH(2)quin)(2)]BF(4) or [Au(CH(3)imCH(2)py)(2)]BF(4) produces trimetallic complexes containing Cu(2)X(2)-butterfly copper clusters coordinated to the two imine moieties. The triangular arrangement of the metals places the gold(I) center in close proximity (approximately 2.5-2.6 A) to the centroid of the Cu-Cu vector. The Cu-Cu separations vary as a function of bridging halide with the shortest Cu-Cu separations of approximately 2.5 A found in the iodo-complexes and the longest separations of 2.9 A found in the bridging chloride complexes. In all six complexes the Au-Cu separations range from approximately 2.8 to 3.0 A. In the absence of halides, the dimetallic complex [AuCu(CH(3)imCH(2)py)(2)(NCCH(3))(2)](BF(4))(2), containing a long Au-Cu distance of approximately 4.72 A is formed. Additionally, as the byproduct of the reaction of CuBr with [Au(CH(3)imCH(2)quin)(2)]BF(4) the deep-red, dimetallic compound, AuCuBr(2)(CH(3)imCH(2)quin)(2), was isolated in very low yield. All of these complexes were studied by NMR spectroscopy, mass spectrometry, and the copper containing species were additionally characterized by X-ray crystallography. In solution the copper centers dissociate from the gold complexes, but as shown by XANES and EXAFS spectroscopy, at low temperature the Cu-Cu linkage is broken, and the individual copper(I) halides reposition themselves to opposite sides of the gold complex while remaining coordinated to one imine moiety. In the solid state all of the complexes are photoluminescent, though the nature of the excited state was not determined.