Manganese(II) complexes with croconate and 2-(2-pyridyl)imidazole ligands: Syntheses, X-ray structures and magnetic properties

The mixed-ligand complexes of manganese(II) of formula [Mn(pyim)(2)(C5O5)] (1) and [Mn(pyim)(H2O) (C5O5)](n) center dot 2.5nH(2)O (2) [pyim = 2-(2-pyridyl) imidazole and C5O52- = croconate (dianion of 4,5-dihydroxy4-cyclopentene-1,2,3-trione)] have been prepared and their structures determined by X-ray crystallographic methods. Compound 1 is a tris-chelated mononuclear complex where the manganese atom is six-coordinate: four nitrogen atoms from two pyim molecules and two oxygen atoms from a croconate group build a somewhat distorted octahedral surrounding around the metal atom. The resulting neutral mononuclear units are linked to each other through double bridges which are constituted by the imidazole N-H and the metal-coordinated croconate-oxygen atom, the metal-metal separation through this supramolecular pathway being 7.6856(11) angstrom. Compound 2 is a croconato-bridged manganese(II) uniform chain with an intrachain metal-metal distance of 7.5118(9) angstrom. A bidentate pyim group, a water molecule and four oxygen atoms from two bis-bidentate croconate ligands build an irregular seven-coordination polyhedron around each manganese atom in 2. The investigation of the magnetic properties of 2 in the temperature range 1.9-295 K has shown the occurrence of a weak antiferromagnetic interaction [J = -0.066 cm (1) with the Hamiltonian defined as H = -J Sigma S-i(i) . Si+1] through the bis-bidentate croconate. The ability of the bis-chelating croconate to mediante magnetic interactions between paramagnetic first-row transition metal ions is discussed and compared to that of the related oxalate ligand. (C) 2008 Elsevier B.V. All rights reserved.