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 structural ly 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 comprise s 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 eq uatorial positions with the other chlorine in the axial position, and that in 5 comprises two bidentate bipy ligands which straddle equatori al and axial sites and an equatorially located monodentate cnge ligand . The weak Cu-FBF3- co-ordinate bond in 1 is supported by an intramole cular N-H ... F hydrogen bond from an adjacent cnge amino moiety. A si milar intramolecular N-H ... Cl interaction occurs in 3. Intermolecula r hydrogen bonds exist in all three complexes; they include pairs of N -H ... N donor-acceptor interactions between centrosymmetrically relat ed 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.