New structural motifs of silver and gold complexes of pyridine-functionalized benzimidazolylidene ligands

Reaction of 1,3-bis(picolyl)benzimidazolium chloride ([HL1]Cl) with Ag2O yields mononuclear complex [Ag(L1)Cl] (2), further reaction of 2 with Au(Et2S)Cl afforded [Au(L1)Cl] (3). Treatment of 2 with AgBF4 gave the trinuclear silver cluster [Ag-3(L1)(3)](BF4)(3) (4), whereas the digold complex [Au-2(L1)(2)](BF4)(2) (5) can be easily obtained from the carbene transfer reaction of 4 with Au(Et2S)Cl. A one-dimensional coordination polymer {[Ag(L2)](BF4)center dot CH3CN}(n) (8) was isolated from the reaction of [Ag(L2)Cl] (7, L2 = 1-benzyl-3-picolylbenzimidazolylidene) with additional Ag+ in good yield. The dinuclear [Ag-2(L3)(2)](PF6)(2) (12, L3 = 1,4-di(N-benzylbenzimidazolylidene)but-2-yne) is a 18-membered macrocycle. All these complexes have been structurally characterized. Complex 2 shows a dimeric structure because of intermolecular Ag center dot center dot center dot Cl interactions. Complex 4 consists of a triangular Ag-3 ring with very short Ag-Ag contacts 2.777(1) angstrom, the Au-Au distance in 5 is 3.206(2) angstrom showing very weak Au-Au interaction and the macrocyclic cations in 12 are aligned one above another to form channels filled with hexafluorophosphate anions. The complexes 2-5, 8, and 12 are intensely luminescent upon irradiation of uv light, and their emission properties are briefly described. (C) 2009 Elsevier B.V. All rights reserved.