FERROMAGNETIC BEHAVIOR OF 2 MANGANESE(II) COMPLEXES WITH PYRIDINE-SUBSTITUTED NITRONYL NITROXIDE RADICALS

Two compounds of formulae (Mn(dtbz)(2)(NITpPy)(2)(H2O)(2) (1) and Mn(tnp)(2)(NITpPy)(2)(H2O)2 . 3H(2)O (2), where dtbz=3,5-dinitrobenzoate, tnp=2,4,6-trinitrophenolate, NITpPy=2-(4-pyridal)-4,4,5,5-tetramethyl-4,5-dihydro-1H-imidazolyl 3-oxide, have been synthesized. Mn(dtbz)(2)(NITpPy)(2)(H2O)(2) (1) has been characterized by X-ray crystallography. It crystallizes in the triclinic space group P $($) over bar$$ 1 with a=10.136(2), b=10.338(1), c=10.691(1) Angstrom, alpha=78.92(1), beta=88.27(1), gamma=86.35(1)degrees and Z=1. The structure of this compound is mononuclear with the manganese(II) ion octahedrally coordinated and bound to the nitronyl nitroxide radicals through the nitrogen atom of the pyridine ring. The variable-temperature magnetic susceptibility of both compounds suggests that the manganese ion and the radicals are ferromagnetically coupled with J=2.08 and 1.07 cm(-1) for compounds 1 and 2, respectively, due to the orbital orthogonality between the pi* molecular orbital of the NITpPy radical (which contains the unpaired electron and the pyridine nitrogen lone pair) and the metal orbitals d(xy), d(yz) and d(xz).