Hydrogen-bonded supramolecular architectures in (N-(methylpyridin-2-yl)-amidino-O-alkylurea)copper(ii) halides

Abstract

Methanolysis and ethanolysis of N-(methylpyridin-2-yl)-2-cyanoguanidine in the presence of copper(II) chloride or bromide yielded four products of identical stoichiometry, Cu(L³ⁱ)X₂ [L³ⁱ = L^3m {N-(methylpyridin-2-yl)-amidino-O-methylurea} or L^3e {N-(methylpyridin-2-yl)-amidino-O-ethylurea}; X = Cl or Br]. Recrystallisation gave the four L³ⁱ-containing copper(II) halides, [Cu(L^3m)Cl₂], 1, [Cu(L^3e)Cl₂], 2, [Cu(L^3e)(OH₂)Cl]Cl, 3 and [Cu(L^3m)Br₂]·MeOH, 4, structural analysis of which showed their crystal engineering to depend on just three of the four N–H donors of the co-ordinated tridentate ligand. In all four compounds, two of the N–H donors are used, in conjunction with halide acceptors, to generate the same R¹₂(6) hydrogen-bonded supramolecular synthon. Whereas in 1, 2 and 3 the synthons form part of hydrogen-bonding assemblies generating centrosymmetric dimers, in 4 they are used to generate a hydrogen-bonded 1-D chain. The dimers in 1 and 2 are identical but for the pendant O-alkyl group, the two centrosymmetrically related [Cu(L³ⁱ)X₂] monomers being linked by pairs of R¹₂(6) hydrogen-bonding assemblies. The dimer in 3 is simply an extended version of those in 1 and 2, in which the halide anion, instead of being co-ordinated to the copper centre, is hydrogen-bonded to a co-ordinated water molecule of the [Cu(L^3e)(OH₂)Cl]⁺ cationic monomer. The extended architectures of the structures depend on hydrogen-bonding interactions involving the third N–H donor, which lead to 1-D chains (in 2), 2-D sheets (in 1 and 4) or, with the assistance of a water hydrogen atom, 3-D networks (in 3). In the absence of further hydrogen-bonding, weak Cu⋯N co-ordinate and π–π stacking interactions form the basis of the forces linking the chains and sheets into 3-D networks.