Hydrogen-bonded supramolecular synthons in complexes of copper(ii) halides with polymethylene-linked bis(amidino-O-alkylurea) ligands

Abstract

Elegant supramolecular architectures are formed by copper(II) halide complexes of polymethylene-linked bis(amidino-O-alkylurea) ligands (L^2m: C₂-linked, alkyl = methyl; L^3m: C₃-linked, alkyl = methyl; L^2e: C₂-linked, alkyl = ethyl; L^3e: C₃-linked, alkyl = ethyl). The tetradentate ligands co-ordinate copper(II) to give square planar [CuL]²⁺ complex cations, which, owing to their versatile hydrogen-bonding capacity, form diverse hydrogen-bonded supramolecular synthons with the anions. Structural analysis of a series of four chlorides, [CuL^2m]Cl₂·2H₂O 1, [CuL^2e]Cl₂·MeOH·3H₂O 2a, [CuL^3m]Cl₂·MeOH·0.5H₂O 5a and [CuL^2m]₄[CuCl₄]Cl₆·5H₂O 9, and a single bromide, [CuL^3m]Br₂·MeOH·0.3H₂O 7a, has revealed two conserved supramolecular synthons, one of which is present in four structures, the other of which is present in three structures. The basic building block in 2a, 5a, 7a and 9 is a hydrogen-bonded 1-D chain of alternating [CuL]²⁺ cations and halide anions. A slightly modified motif, including a water molecule, occurs in 1. The chains are linked into 2-D sheets by hydrogen-bonding contacts involving the anions and solvate (water and/or methanol) molecules, either directly (1) or via formation of ribbons (2a, 5a, 7a and 9). When linked directly the cations in adjacent chains are parallel, but when linked via ribbons they are alternating. 3-D frameworks result from a combination of elongated axial Cu⋯Cl contacts and complex hydrogen-bonding contacts involving the anions and solvate molecules.