2-cyanoguanidine: a versatile hydrogen-bonding ligand in copper(II)-2,2'-bipyridine-2-cyanoguanidine complexes

The copper(II)2,2'-bipyridine (bipy)-2-cyanoguanidine (cnge) complexes, [Cu(bipy)(cnge)(2)(FBF3)(2)] 1, [Cu(bipy)(cnge)Cl-2]. H2O 3, and [Cu(bipy)(2)(cnge)][BF4](2) . H2O 5, have been synthesised and structurally characterised. Their copper(II) co-ordination geometries vary from cis-distorted tetragonally elongated octahedral (for 1) through square pyramidal(for 3) to trigonal bipyramidal (for 5). That ill 1 comprises one bidentate chelating bipy and two monodentate cnge as equatorial ligands plus two BF4- anions as axial ligands, that in 3 comprises one bidentate chelating bipy, one monodentate cnge and one chlorine in equatorial positions with the other chlorine in the axial position, and that in 5 comprises two bidentate bipy ligands which straddle equatorial and axial sites and an equatorially located monodentate cnge ligand. The weak Cu-FBF3- co-ordinate bond in 1 is supported by an intramolecular N-H ... F hydrogen bond from an adjacent cnge amino moiety. A similar intramolecular N-H ... Cl interaction occurs in 3. Intermolecular hydrogen bonds exist in all three complexes; they include pairs of N-H ... N donor-acceptor interactions between centrosymmetrically related cnge ligands (in 3) and double N-H ... F contacts(in 5) as well as more conventional single N-H ... X (X = F, Cl, O or N) interactions.