THE SYNTHESIS AND MAGNETIC-PROPERTIES OF 2 DIFFERENT WATER-CONTAININGLAYERED POLYMERIC NI(II) COMPLEXES WITH A 3-IMIDAZOLINE NITROXIDE - THE LOW EFFICIENCY OF EXCHANGE INTERACTIONS THROUGH THE OH-BRIDGES OF WATER-MOLECULES

The layered polymeric complexes NiL2(H2O)2 (1) and NiL2(H2O)(C3H6O) (2 ), where L is the stable nitroxide ylidene)-2,2,5,5-tetra-methyl-3-imi dazoline-1-oxyl and C3H6O is the acetone molecule, have been synthesiz ed. Polymeric layers in 1 are formed by centrosymmetric NiL2(H2O)2 mol ecules due to H-bonding of N-O group oxygens with coordinated water of adjacent NiL2(H2O)2 molecules. The synthesis of 1 allowed the complet ion of the investigation of the magnetic properties of a series of iso structural complexes NiL2(ROH)2, where R is H or the hydrocarbon group , as well as to establish that exchange interactions in the heterospin exchange cluster [GRAPHICS] are essentially weaker than those in the [GRAPHICS] cluster. Among the complexes with nitroxides, 2 has a uniqu e structure. In 2, paramagnetic ligands are in the cis-position and se rve different functions : one L is bidentate and the other is bridging tridentate. The distorted octahedral environment of Ni in 2 is formed in the equatorial plane by the enamineketone O and N atoms of the bid entate L and by O atoms of water molecule and the enamineketone group of the tridentate L. The axial positions are occupied by the enamineke tone N of the tridentate L and by the N-O oxygen of adjacent molecule. The bridging tridentate Ls link the [NiL2(H2O)] fragments in infinite chains which are combined in layers by means of H-bonding between coo rdinated water molecules of one chain and N-O oxygens of the bidentate Ls of an adjacent chain (acetone molecules are positioned between the layers and are H-bonded to the water molecules). In 2, the strong ant iferromagnetic exchange in the (Ni2+-O-N) fragment results in full cou pling of one of the unpaired Ni2+ electrons with the unpaired electron of coordinated O-N group.