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 [Ag3(L1)3](BF4)3 (4), whereas the digold complex [Au2(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) · 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 [Ag2(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⋯Cl interactions. Complex 4 consists of a triangular Ag3 ring with very short Ag–Ag contacts 2.777(1) Å, the Au–Au distance in 5 is 3.206(2) Å 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.