Self-assembly of extended structures through non-coordination intermolecular forces: Synthesis, crystal structures, and properties of metal complexes with 5-methyl-2-pyrazinecarboxylate

Abstract

Three new complexes of 5-methyl-2-pyrazinecarboxylate (Hmpca) with cobalt(II), [Co(mpca)(2)(H2O)(2)], nickel(II), [Ni(mpca)(2)(H2O)(2)] and iron(III) [Fe(mpca)(2)(OH)](2) center dot 2H(2)O, have been synthesized and characterized by spectroscopic techniques, X-ray crystallography and low-temperature magnetic measurements in the range 5-300 K. The molecular structures of [Co(mpca)(2)(H2O)(2)] (1) and [Ni(mpca)(2)(H2O)(2)](2) comprise mononuclear complexes of cobalt(II) and nickel(II), with distorted octahedral coordination environments. In both cases, the mononuclear entities are linked through hydrogen-bonding and pi-pi stacking interactions to form two-dimensional network structures. The molecular structure of [Fe(mpca)(2)(OH)](2) center dot 2H(2)O (3) consists of a symmetric bis(mu-hydroxido)-diiron(III) core. The geometry around the two iron(III) ions is pseudo-octahedral due to the coordination of two mpca(-) ions in a bidentate chelating manner and of two bridging hydroxide ions. Adjacent dinuclear Fe-2(OH)(2) molecules are linked together via hydrogen-bonding and pi-pi stacking interactions, thus forming a two-dimensional network. Variable-temperature magnetic susceptibility data suggest that weak intermolecular antiferromagnetic interactions are effective in 1 and 2, while intramolecular antiferromagnetic interactions (J = -21.2 cm(-1)) between the two iron(III) ions are operative in 3. The spectroscopic and magnetic properties of the complex [Cu(mpca)(2)(H2O)] center dot 3H(2)O (4) are in agreement with the earlier reported mononuclear structure. (C) 2006 Elsevier Ltd. All rights reserved.