X-Ray structure of a ternary complex, copper(II)–lnosine 5′-monophosphate–benzimidazole. The first example for the absence of direct metal–nucleotide interaction

Abstract

The unprecedented absence of direct metal–nucleotide interaction has been observed in the X-ray structure of the ternary metal nucleotide system [Cu(bzim)(H2O)5]2+[IMP]2–·3H2O [IMP = inosine 5′-monophosphate(2–), bzim = benzimidazole). The complex crystallizes in the space group P21 with a= 7.013(2), b= 13.179(9), c= 14.565(9)A, β= 94.82(4)°, and Z= 2. The structure was solved by the heavy-atom method and refined by full-matrix least squares on the basis of 1 761 observed (I 3σi) reflections to final R and R′ values of 0.034 and 0.036 respectively. The CuII has a distorted octahedral co-ordination with a nitrogen of the bzim ligand [Cu–N 1.947(5)A] and three oxygens of water molecules in the basal plane [mean Cu–O 2.017(3)A] and two more water oxygens at axial positions [Cu–O 2.194(6) and 2.732(5)A]. The nucleotide base stacks with the bzim ligand at an average distance of 3.5 A and an angle of 22°. In the lattice, N(7) of the base is linked to a lattice water through a hydrogen bond, while all the phosphate oxygens are involved in hydrogen bonds with co-ordinated as well as lattice water molecules. The co-ordination behaviour of IMP to CuII is compared in structures containing different π-aromatic amines in order to assess the influence of the ternary ligand in complex formation. The present results indicate that, apart from the commonly observed phosphate binding, other modes of co-ordination are possible, these being influenced mainly by the π-accepting properties of the ternary ligand.