Synthesis and catalytic activity of manganese(II) complexes of heterocyclic carboxylic acids: X-ray crystal structures of [Mn(pyr) 2] n, [Mn(dipic)(bipy) 2]·4.5H 2O and [Mn(chedam)(bipy)]·H 2O (pyr=2-pyrazinecarboxylic acid; dipic=pyridine-2,6-dicarboxylic acid; chedam=chelidamic acid(4-hydroxypyridine-2,6-dicarboxylic acid); bipy=2,2-bipyridine)

Abstract

Reactions of manganese(II) acetate with 2-pyrazine carboxylic acid, 2,6-pyridinedicarboxylic acid and chelidamic acid (4-hydroxypyridine-2,6-dicarboxylic acid) yielded [Mn(pyr) 2] n ( 1), [Mn(dipic)]·1.5H 2O ( 2) and Mn(chedam)]·H 2O ( 6), respectively. Reaction of 2 with 2,2′-bipyridine and 1,10-phenanthroline results in the synthesis of [Mn(dipic)(bipy)]·2H 2O ( 3), [Mn(dipic)(bipy) 2]·4.5H 2O ( 4) and [Mn(dipic)(phen) 2]·2H 2O ( 5). Complex 6 reacted with 2,2′-bipyridine and 1,10-phenanthroline to give [Mn(chedam)(bipy)]·H 2O ( 7) and [Mn(chedam)(phen) 2]·3H 2O ( 8), respectively. Molecular structures for 1, 4 and 7 were determined by X-ray crystallography. In 1 the structure is essentially polymeric with each pyrazine carboxylate anion coordinated to the manganese ion in a bidentate fashion using one carboxylate oxygen atom and the adjacent nitrogen. The second nitrogen is uncoordinated. For 4 the asymmetric unit consists of one tridentate dipicolinate ligand, two bidentate bipyridine molecules, four full-occupancy water molecules and one half-occupancy water molecule. The structure of 7 contains monomeric [Mn(dicarboxylate)(bipy)H 2O] units in which the Mn(II) ions have very irregular six-coordinate geometry. Spectroscopic, magnetic and physical data for the complexes are presented. All of the manganese complexes catalytically disproportionate hydrogen peroxide in the presence of imidazole.