First complexes of a 4-alkyl-3,5-di(2-pyridyl)-4H-1,2,4-triazole: Synthesis, X-ray crystal structures and magnetic properties of dinuclear cobalt(II), nickel(II) and copper(II) complexes of 4-isobutyl-3,5-di(2-pyridyl)-4H-1,2,4-triazole

Abstract

The reaction of the new, bis(bidentate), potentially dinucleating ligand 4-isobutyl-3,5-di(2-pyridyl)-4H-1,2,4-triazole (ibdpt) with M(ClO4)2·6H2O (M = CoII, NiII or CuII) in a1:1 molar ratio in MeCN affords the dinuclear complexes [CoII2(ibdpt)2(MeCN)2(H2O)2](ClO4)4 (1), [NiII2-(ibdpt)2-(MeCN)4](ClO4)4 (2) and [CuII2(ibdpt)2(MeCN)2-(ClO4)2]-(ClO4)2·2MeCN (3). Complex 1 is obtained as a mixture of the red-orange polymorph 1a and the yellow-orange polymorph 1b, the main difference between the two forms being the hydrogen bonding patterns between the H2O co-ligands and the ClO4– counterions. The mononuclear complex [CuII-(ibdpt)2(ClO4)2] (4) was initially obtained as a minor by-product in the preparation of complex 3 but can also be deliberately prepared from Cu(ClO4)2·6H2O and ibdpt in MeCN using a metal-to-ligand molar ratio of 1:2. All five complexes have been structurally characterised by X-ray diffraction. In the dinuclear complexes 1–3 the (N,N1,N2,N)2double bridging coordination mode is realised while the mononuclear complex 4 features the common trans-(N,N1)2 coordination mode. In all cases the metal centres reside in distorted octahedral N4X2 coordination spheres with axially bound co-ligands (X = H2O, MeCN or ClO4–). The dinuclear complexes 1–3 readily lose solvent when taken out of their mother liquors giving rise to partially desolvated materials. Magnetic studies have been carried out on crystalline samples of the resulting complexes that analysed as CoII2-(ibdpt)2(ClO4)4-(MeCN)(H2O) (5), NiII2(ibdpt)2(ClO4)4(MeCN) (6) and CuII2-(ibdpt)2(ClO4)4(MeCN) (7). It was found that in these complexes the two 1,2,4-triazole bridges facilitate antiferro-magnetic coupling between the two metal centres (J =–3.76 cm–1, –13.0 cm–1 and –105 cm–1, respectively). The coordination compounds described in this paper are the first to incorporate a 4-alkyl-substituted 3,5-di(2-pyridyl)-4H-1,2,4-triazole ligand.