Manganese(II) Oxazolidine Nitroxide Chelates: Structure, Magnetism, and Redox Properties

Abstract

The mononuclear oxazolidine nitroxide complex [Mn II(L)2](ClO4)2 (1) (L ,4-dimethyl-2,2-di(2-pyridyl)oxazolidine N-oxide) has been synthesized and investigated using single-crystal X-ray diffraction, variable-temperature magnetic susceptibility measurements, and electrochemistry. The structural analysis reveals bond lengths compatible with a linear L –MnII–L arrangement where the ligands are in the neutral ligand form and the central MnII ion is high spin (S = 5/2). Although analysis of the variable-temperature magnetic susceptibility data suggests a strong antiferromagnetic metal– radical interaction, the radical–radical intramolecular interaction could not be determined unambiguously from such fits. The resultant isolated S = 3/2 ground state is confirmed by low-temperature magnetization versus field measurements. Electrochemical studies reveal similar square schemes and redox intermediates to the previously reported analogues [FeII(L)2][BF4]2 and [CoII(L )2][NO3]2

Use of the TCNQF42− Dianion in the Spontaneous Redox Formation of [FeIII(L−)2][TCNQF4⋅−]

“…The crystallographic bond lengths and angles (Tables and ) are used to assign the redox level of the tridentate ligand and TCNQF 4 . For the cationic Fe species in 1 , the nitroxide N−O (N3−O1) bond length is 1.4177(19) Å, which is clearly appropriate for the hydroxylamino anionic form of the ligand (L − ) . The Fe−O (1.8551(12) Å) and Fe−N (1.9869(16) and 1.9553(15) Å) bond lengths are consistent with earlier studies on [Fe III (L − ) 2 ](BPh 4 ), so we can confidently assign the cationic species as [Fe III (L − )] + where the Fe III ion is low‐spin.…”

“…− radical anion, where the C≡N band in LiTCNQF 4 is located at 2223 cm −1 (Figure b) and at 2205 cm −1 for (Pr 4 N)TCNQF 4 , similar to that observed in 1 . The equivalent C≡N band in Li 2 TCNQF 4 is located at 2119 cm −1 …”

“…and [Fe II (L . ) 2 ][BF 4 ] 2 were synthesised as described previously . Li 2 TCNQF 4 was prepared according to literature methods .…”

“…The manganese analogue, [Mn II (L . ) 2 ](ClO 4 − ) 2 , can in principle undergo similar redox chemistry but some reactions are of an irreversible nature …”

An Introduction to Molecular Magnetism: SANZMAG-1 (Southampton-Australia-New Zealand Workshop on Molecular Magnetism)

“…[1,2] The issue also contains several Focus and Research articles detailing the magnetic properties of novel molecular complexes, clusters, coordination polymers and solid state materials. [3][4][5][6][7][8][9][10][11][12] We would like to thank all of the organisers and participants in this inaugural SANZMAG conference which allowed for its success and we look forward to the next instalment. We also sincerely thank all of the authors who have made such an effort to contribute to this issue.…”