The non-isomorphous crystal structures of NHC-Au-Cl and NHC-Au-Br (NHC is 1,3-dibenzyl-4,5-diphenylimidazol-2-ylidene).

Gold monochloride and monobromide can be transformed into monomeric complexes by ligands such as CO, PPh3 or Me2 S, and such ligand-stabilized gold monochloride compounds have been investigated as catalysts, luminescent materials and anticancer drugs, especially when coordinated to a lipophilic benzyl-substituted N-heterocyclic carbene (NHC) ligand. The triclinic structures of NHC-Au-Cl {chlorido(1,3-dibenzyl-4,5-diphenylimidazol-2-ylidene)gold, [AuCl(C29 H24 N2 )]} and NHC-Au-Br {bromido(1,3-dibenzyl-4,5-diphenylimidazol-2-ylidene)gold, [AuBr(C29 H24 N2 )]}, determined by X-ray crystallography at 100 K, have one and four molecules, respectively, in their asymmetric units. The chloride compound shows an almost linear C-Au-Cl fragment [179.76 (8)°], with an Au-C distance of 1.976 (3) Å and an Au-Cl distance of 2.3013 (6) Å, while the bromide compound shows surprisingly large geometry deviations, from 1.969 (12) to 2.016 (10) Å for the Au-C distance and from 2.4279 (14) to 2.4796 (12) Å for the Au-Br distance, in the four independent molecules.