An alternating copolymer containing trigonal planar homocoordinated copper(I) ions: catena-poly[[[bis[mu-(E)-1,2-bis(1-ethyl-1H-benzimidazol-2-yl)ethene-kappa2N3:N3']dicopper(I)]-mu-(E)-1,2-bis(1-ethyl-1H-benzimidazol-2-yl)ethene-kappa2N3:N3'] bis(perchlorate) acetonitrile disolvate].

The structure of the title salt, {Cu(2)(C(20)H(20)N(4))(3)(2) x 2 CH(3)CN}(n), consists of linear [Cu(I)(2)L(3)] polymer chains [L is (E)-1,2-bis(1-ethyl-1H-benzimidazol-2-yl)ethene], which extend along the c cell direction, interspersed with disordered perchlorate ions and acetonitrile solvent molecules. In a given chain, each Cu(I) ion exhibits distorted trigonal planar coordination to three L ligands; two of these are linked to adjacent Cu(I) ions to form dimeric units containing 14-membered rings that adopt a twisted-loop configuration, stabilized by pi-pi interactions between the ethene fragments of the two ligands. The dimeric units exhibit diad symmetry (twofold axis sites in I2/a) and are linked by a third, centrosymmetric, S-shaped L ligand (inversion centers in I2/a) to form the copolymer chain. When viewed along the b cell direction, the 14-membered rings appear as vacant ellipses that form channels parallel to the b axis. The walls of the channels are formed by the benzimidazole fragments of the dimeric units. This study of a novel alternating copolymer containing homocoordinated Cu(I) ions demonstrates further the usefulness of bis(benzimidazoles) as versatile bidentate ligands.