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

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 · 2H2O, 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 π–π stacking interactions to form two-dimensional network structures. The molecular structure of [Fe(mpca)2(OH)]2 · 2H2O (3) consists of a symmetric bis(μ-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 Fe2(OH)2 molecules are linked together via hydrogen-bonding and π–π 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)] · 3H2O (4) are in agreement with the earlier reported mononuclear structure.

The present paper describes the synthesis and characterization of several metal complexes with the ligand 5-methyl-2-pyrazinecarboxylate: [Co(mpca)2(H2O)2], [Ni(mpca)2(H2O)2], [Cu(mpca)2(H2O)] · 3H2O and [Fe(mpca)2(OH)2] · 2H2O. In all cases, the X-ray crystal structure analysis reveals extended structures formed by non-covalent intermolecular forces, such as hydrogen-bonding and/or π–π stacking interactions.Figure optionsDownload as PowerPoint slide