Supramolecular assembled networks in crystal structure built up of copper(II) dipicolinates with pyrazine- and pyridinecarboxamides connected through hydrogen bonds

Abstract

New copper(II) dipicolinate complexes containing pyrazine- or pyridinecarboxamides, namely {[Cu(pca)(dipic)(H2O)]·H2O} (1), [Cu(nia)(dipic)(H2O)] (2), {[Cu(mnia)(dipic)(H2O)]·2H2O} (3), {[Cu(inia)(dipic)]n·2nCH3OH} (4) {[Cu(hmnia) (dipic)(H2O)]2·2[Cu(hmnia)(dipic)(H2O)2]·4H2O} (5) and [Cu(denia)(dipic)(H2O)] (6) (dipic = dipicolinate, anion derived from pyridine-2,6-dicarboxylic acid, pca = pyrazinecarboxamide, nia = nicotinamide, mnia = N-methylnicotinamide, inia = isonicotinamide, hmnia = N-(hydroxymethyl)nicotinamide and denia = N,N-diethylnicotinamide) were synthesized, structurally characterised by single-crystal X-ray diffraction analysis and their properties were studied using IR, UV–Vis and EPR spectroscopic techniques. The Cu(II) compounds are of square-pyramidal (1–4 and 6) or square-bipyramidal geometry (5), in which copper(II) centres are coordinated by N donor atom of a nicotinamide or its derivatives, one N donor atom and two O donor atoms of dipicolinate anions and the coordination sphere around the Cu(II) atoms is completed by terminal aqua ligands (besides 4). The complex 4 is a polymer, in which are dipicolinate ligands bridging via O atoms of their carboxylate groups neighbouring Cu(II) atoms. The compound 5 is made up of two different types of complex molecules, dinuclear [Cu(hmnia)(dipic)(H2O)]2 and mononuclear [Cu(hmnia)(dipic)(H2O)2], and lattice solvent molecules in the ratio of 1:2:4. Copper(II) atoms in the dinuclear complex molecules of 5 [Cu(hmnia)(dipic)(H2O)]2 are interconnected through carboxamide O donor atoms of bridging N-(hydroxymethyl)nicotinamide ligands. In most cases are complex molecules to each other and solvent molecules linked together via NH⋯O and OH⋯O hydrogen bonds and form 2D or 3D supramolecular networks. The X-band EPR spectra of six copper(II) complexes were recorded at room and low temperature (98 K). The g-factor relation g// > g⊥ > 2.0023 is consistent with the dx2-y2 ground electronic state.