Intramolecular antiferromagnetic exchange in tris(o-semiquinone) complexes of vanadium(III), chromium(III), and iron(III)

Preparation and Properties of Two Tris o-Semiquinone Complexes

“…It decomposed upon prolonged exposure to oxygenated solvents such as benzene, methylene chloride, and thenaol, but is stable indefinitely in w-pentane. The solution magnetic moment of this complex at room temperature is 3.8 BM, an unusual value, but similar to the room temperature data of Pierpont and Hendrickson [5,8]. A tris o-quinone adduct of iron(O) would probably be expected to exhibit a rather lower magnetic moment in the region of 2.8 BM consistent with the spin only value for 2 unpaired electrons.…”

“…Cr(DBSQ)3, is prepared from the o-quinone and hexacarbonylchromium, a method similar to that employed for analogous complexes of other 0-quinones [5], This compound is stable in w-pentane but exposure to air causes slow decomposition. Removal of traces of free quinone from the compound is very difficult.…”

“…Brown et al, have reported well defined 3,5-di-£-butyl-o-semiquinato complexes of cobalt(III) which were isolable as solids and characterized by a variety of spectral techniques [3]. Floriani et al, have prepared complexes from 9,10-phenanthrene quinone which appear to contain the 9,10-phenanthrenesemiquinone anion ligand [4], In a recent communication, Pierpont, Hendrickson et al, demonstrated that for several neutral tris chelates prepared from a metal carbonyl (V, Cr, Fe) and an o-quinone (tetrachloroquinone, 9,10-phenanthrene quinone) the resulting species are correctly formulated as neutral tris o-semiquinone complexes, [M(o-semiquinone)3] [5]. Their formulation was based on magnetic properties and X-ray structural work.…”

Transition metal complexes with bulky 4,6-di-tert-butyl-N-aryl(alkyl)-o-iminobenzoquinonato ligands: Structure, EPR and magnetism

“…In [90] the vanadium complex with tetrachloro-o-benzoquinonato ligands was described to be a tris-semiquinonato complex of V(III), V(oCl 4 SQ) 3 , with doublet spin state. The EPR spectrum of this complex in Et 2 O solution at ambient temperature consists of eight HFS components with g iso = 2.0079 and HFS constant A i ( 51 V) = 4.1 G ( 51 V, I = 7/2, 99.8%).…”

“…For cobalt complex 89, the exchange between organic radical centers in each M(ISQ) 3 fragment is weak antiferromagnetic while coupling of two of these fragments is weak ferromagnetic (Table S6, Chart 10). Chromium (90) and nickel (92) complexes are diamagnetic. Copper compound 91 (Scheme 22) contains two uncoupled copper(II) centers [114].…”