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

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)center dot 6H(2)O (M = Co-II, Ni-II or Cu-II) in a 1:1 molar ratio in MeCN affords the dinuclear complexes [Co-2(II)(ibdpt)(2)(MeCN)(2)(H2O)(2)](ClO4)(4) (1), [Ni-2(II)-(ibdpt)(2)(MeCN)(4)](ClO4)(4) (2) and [Cu-2(II)(ibdpt)(2)(MeCN)(2)-(ClO4)(2)](ClO4)(2)center dot 2MeCN (3). Complex 1 is obtained as a mixture of the red-orange polymorph la 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 [Cu-II(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)center dot 6H(2)O 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',N-1,N-2,N'')(2)double bridging coordination mode is realised while the mononuclear complex. 4 features the common trans-(N',N')2 coordination mode. In all cases the metal centres reside in distorted octahedral N4X2 coordination spheres with axially bound coligands (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 Co-2(II)-(ibdpt)(2)(ClO4)(4)(MeCN)(H2O) (5), Ni-2(II)(ibdpt)(2)(ClO4)(4)(MeCN) (6) and Cu-2(II)(ibdpt)(2)(ClO4)(4)(MeCN) (7). It was found that in these complexes the two 1,2,4-triazole bridges facilitate antiferromagnetic 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. ((c) Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2005).