Synthesis, Structure, and Magnetism of Mono- and Binuclear Manganese(II) Compounds of Nitronyl Nitroxide Substituted Phosphine Oxides

Complexes of manganese (II) -containing aminoxyl radical substituted phosphine oxide ligands are reported. The compounds (o-nitronyl nitroxide-phenyl) diphenylphosphine oxidebis (hexafluoroacetylacetonato) manganese (II), 3, and bis (p-nitronyl nitroxide-phenyl) diphenylphosphine oxidebis (hexafluoroacetylacetonato) manganese (II), 4, prepared by addition of the free radical phosphine oxides to Mn (hfac) (2), were structurally characterized. Complex 3 is mononuclear, containing an O, O-chelating ortho-substituted radical phosphine oxide ligand, while in 4 the para-substituted ligands bridge two Mn (hfac) (2) units to yield a binuclear molecular rectangle. The magnetic behavior of both systems is dominated by a strong antiferromagnetic Mn (II) -aminoxyl interaction (J = -213 (3), -218 (4) cm (-) (1) with H = -JS (Mn). S (rad) ) to give effective S = 2 ground state units. The S = 3 excited state is populated at high temperatures. At low temperatures a decrease in chi (M) T in both complexes is attributable primarily to inter- or intramolecular antiferromagnetic interactions rather than zero-field splitting (ZFS) of the S = 2 ground state. For the bimetallic compound, the magnetic data indicate that ligand-mediated interactions between the Mn (II) spin carriers are weak. The powder EPR spectra of both systems have been recorded and successfully simulated, giving a ZFS parameter D = 0. 112 cm (-) (1). Crystals of 3 are triclinic, space group P with a = 10. 6672 (19) Å, b = 13. 270 (6) Å, c = 15. 363 (3) Å, alpha = 93. 84 (2) degrees, beta = 108. 054 (16) degrees, gamma = 105. 69 (3) degrees, and Z = 2. Crystals of 4 are monoclinic, space group P2 (1) /a with a = 12. 463 (6) Å, b = 19. 315 (3) Å, c = 17. 084 (9) Å, alpha = 90 degrees, beta = 98. 49 (2) degrees, gamma = 90 degrees, and Z = 2.