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

Abstract

Complexes of manganese(II)-containing aminoxyl radical substituted phosphine oxide ligands are reported. The compounds [(o-nitronyl nitroxide-phenyl)diphenylphosphine oxide]bis(hexafluoroacetylacetonato)manganese(II), 3, and bis{[(p-nitronyl nitroxide-phenyl) diphenylphosphine oxide]bis(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&onemacr; 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.

Two novel cyclic dimer M2L2 complexes constructed from 2-[(4-carboxyl)phenyl]-4,4,5,5-tetramethylimidazoline-1-oxyl-3 oxide: Crystal structure and magnetic properties

“…The strong antiferromagnetic interaction is probably due to the smaller angle of Mn-O-N (126.60(16)°), which results in the effective overlap of the magnetic orbitals. The determined J value is comparable to the reported analogous literature values [24,32,33].…”

Syntheses, Structures, and Magnetic Properties of Cobalt(II) Complexes with Pyridyl‐substituted Nitroxide Radicals

“…In the field of molecular‐based magnetic materials, the coordination of paramagnetic metal ions with organic radicals in terms of the “metal‐radical” strategy has attracted reasonable attention in recent years 1–3. The interest in this approach is mainly due to the account of nitronyl nitroxide radicals, which present exceptional stability and ease of chemical modification 4–6. Therefore, considerable efforts have been directed towards the preparation and characterization of different metal‐radical complex architectures with appropriate organic radicals and co‐ligands 7–9.…”

Synthesis, Structure, and Magnetic Property of Manganese(II) Complex of 1,2-closo-Carboranyl Biradical with S = 3/2 Ground State

“…The direct overlap between the magnetic orbitals of paramagnetic transition-metal ion and organic radical ensures significant magnetic exchange interaction. Because of the great advantage of the chelate effect that enforces the coordination of nitroxide, most organic radical ligands in spin-cluster complexes bear coordination subunits such as pyridine, 1 bipyridine, 2 ethylenediamine, 3 imidazole, 4 triazole, 5 phosphine oxides, 6 and so on. Recently, we have reported the synthesis and magnetic property of ortho-carboranyl biradical (OCB-BNN; Chart 1) having a weak through-space dipole intramolecular antiferromagnetic interaction.…”