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

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Abstract
The copper(II)–2,2′-bipyridine (bipy)–2-cyanoguanidine (cnge) complexes, [Cu(bipy)(cnge) 2 (FBF 3 ) 2 ] 1, [Cu(bipy)(cnge)Cl 2 ]·H 2 O 3, and [Cu(bipy) 2 (cnge)][BF 4 ] 2 ·H 2 O 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 in 1 comprises one bidentate chelating bipy and two monodentate cnge as equatorial ligands plus two BF 4 - 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–FBF 3 - 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.

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