Manganese (II) coordination complexes involving nitronyl nitroxide radicals

Three new complexes involving nitronyl nitroxide and PhCOO- or N-3- ligands have been synthesized and structurally and magnetically characterized. The se compounds are formulated as Mn(L)(4)(X)(2). nH(2)O, L = 2-(p-pyridyl)-4, 4,5,5-tetramethylimidazoline-1-oxyl-3-oxide (PNN) or 2-(p-pyridyl)-4,4,5,5- tetramethylimidazoline-1-oxyl (PN) and X = PhCOO- or N-3-. Compound A [Mn(P NN)(2)(PhCOO)(2)(H2O)(2)] presents the following structural parameters: tri clinic, space group P (1) over bar (No. 2), a = 6.859(1) Angstrom, b = 11.2 71(2) Angstrom, c = 13.978(6) Angstrom, alpha = 88.88(2)degrees, beta = 89. 38(2)degrees, gamma = 78.28(2)degrees, Z = 1. The complex has a centrosymme tric distorted octahedral geometry in which the manganese ion is bound to t wo radical ligands through the nitrogen atom of the pyridine rings, two ben zoate groups, and two water molecules. The two compounds B [Mn(PNN)(4)(N-3) (2)] and C [Mn(PN)(4)(N-3)(2)] are isostructural with the following structu ral parameters: B; triclinic, space group P (1) over bar (No. 2), a = 7.177 (4) Angstrom, b = 13.767(3) Angstrom, c = 13.928(4) Angstrom, alpha = 90.20 (2)degrees, beta = 102.94(4)degrees, gamma = 91.86(4)degrees, Z = 1; C, tri clinic, space group P (1) over bar (No. 2), a = 7.004(2) Angstrom, b = 13.8 85(1) Angstrom, c = 14.036(2) Angstrom, alpha = 90.34(1)degrees, beta = 101 .42(2)degrees, gamma = 92.92(1)degrees, Z = 1. They adopt a centrosymmetric tetragonally distorted octahedral geometry in which the manganese ion is b ound to four radical ligands through the nitrogen atom of the pyridine ring s, and the azido groups occupy the apical positions. For all three compound s A, B, and C intramolecular ferromagnetic interactions between the Mn(II) ion and the nitronyl nitroxide radicals are observed, but at very low tempe ratures, intermolecular antiferromagnetic interactions dominate.