A copper(I) dimer [Cu(L)(CH3CN)]2(BF4)2 with the new chelating and bridging tridentate ligand 1-(2-pyridylmethyl)-2-(2-pyridyl)benzimidazole (L)

Reaction of 1,2-phenylenediamine with 2-pyridinecarboxaldehyde gave the new compound 1-(2-pyridylmethyl) -2-(2-pyridyl)benzimidazole (L) which reacted with [Cu(CH3CN)(4)](BF4) to form the title complex. Although the imine/2-(2-pyridyl) ('alpha-diimine') coordination setting in L appears well suited for forming a five-membered chelate ring, the crystal structure analysis of the bis (methanol) solvate revealed that the system rather opts for the formation of a partially saturated eight-membered chelate ring involving both pyridyl groups with a twist angle of 61.8 degrees between the benzimidazole and 2-(2-pyridyl) moieties. In addition, L acts as a tridentate ligand, effecting dimerization of two chelate rings through the imine nitrogen centers of the imidazole groups. This dimerization gives rise to a ten-membered dimetalla ring. Tetracoordination at copper(I) is complemented by acetonitrile. The preference for this structure is attributed to the formation of unstrained metal centers with N-Cu-N angles between 105 degrees and 118 degrees and Cu-N distances of 2.03-2.05 Angstrom. (C) 2000 Elsevier Science S.A. All rights reserved.