Intra- and inter-molecular hydrogen bonding interactions in [Cu(en)(py) 2(FBF 3) 2] {en = 1,2-diaminoethane, py = pyridine}

Abstract

The crystal and molecular structures of [Cu(py) 2(en)(FBF 3) 2] (py = pyridine; en = 1,2-diaminoethane) 1 have been determined at 298 and 120 K. It comprises discrete molecular units based on cis-distorted tetragonally elongated octahedral copper(II). Strong equatorial bonds are formed by one bidentate en {Cu … N = 2.017 Å} and two monodentate py {Cu … N = 2.020 Å} ligands, while two monodentate tetrafluoroborate anions form weak axial bonds {Cu … F = 2.567 Å} The location of the anion, which exhibits no disorder even at room temperature, is supported by an intramolecular NH … F hydrogen bond {N … F = 3.193 Å, N … H = 0.88 A, H … F = 2.42 A, NHF = 146}. A literature search has revealed similar intramolecular NH … X interactions in all other structurally characterised copper(II) complexes containing equatorially coordinated 1,2-diaminoethane and axially located tetrafluoroborate or perchlorate {[Cu(en) 2(FBF 3) 2] 2 and [Cu(en)L(H 2O)(OClO 3)](ClO 4) (L = 2,2′-bipyridine 3 or 1,10-phenanthroline 4);. Temperature has limited effect on the structure of 1, the weaker interactions being affected most. The most significant changes are contractions in the Cu … F axial interaction (1.22%), the intramolecular hydrogen bonds (2.64%) and the intermolecular hydrogen bonds (1.96%) which link the molecules to give a two-dimensional motif.