CRYSTAL-STRUCTURES AND MAGNETIC-PROPERTIES OF MERCURY(II) BROMIDE COMPLEXES WITH PYRIDYL-SUBSTITUTED N-OXYL N'-OXIDES (NITRONYL NITROXIDES)

The crystal structures have been determined and magnetic properties in vestigated for four novel HgBr2 complexes with pyridyl-substituted 'ni tronyl nitroxides', 4,4,5,5-tetramethyl-2-(4-pyridyl)-(L-1), -2-(2-pyr idyl)-(L-2), -2-(3-pyridyl)-(L-3) and -2-(6-methyl-2-pyridyl)-2-imidaz oline N-1-oxyl N-3-oxide (L-4). Complex 1, [HgBr2L1], is mononuclear, in which mercury(lr) has planar trigonal co-ordination core, from two bromide atoms and one nitrogen atom of the pyridyl group. In 2, [HgBr2 L2] the Hg-II atom has distorted-tetrahedral four co-ordination involv ing two bromide atoms and chelating by oxygen and nitrogen atoms of th e L-2 ligand. Complex 3, [(HgBr)(3)L-2(3)]. is a zigzag polymeric chai n with a distorted T-shaped HgBr2L3 unit and self-assembly involving c oordination by an oxygen atom of the nitroxide groups. Complex 4, [(Hg Br2)(3)L-2(4)], is a quasi-linear chain with HgBr2L4 moieties and HgBr 2 cores. Cryomagnetic susceptibility measurements (4-300 K) showed tha t 1 and 3 exhibit a weak intermolecular alternating one-dimensional an tiferromagnetic exchange interaction, while 3 and 4 possess weak one-d imensional antiferromagnetic and ferromagnetic exchange interactions r espectively. A simple spin-polarization model has been used to justify the observed ferromagnetic exchange interaction between the spins of the radical NO group in complex 4.