Bis-o-semiquinonato complexes of transition metals with 5,7-di-tert-butyl-2-(pyridine-2-yl)benzoxazole

Bis-o -Benzosemiquinonato Cobalt(II) and Nickel(II) Complexes with Neutral N-Heterocyclic Carbene Ligand: Synthesis, Structure and Magnetic Properties

“…In accordance with IR‐spectroscopy data the IR‐spectra of 1 and 2 contain a set of typical vibration bands (1450‐1300 cm −1 ) corresponding to one‐and‐half C … O bonds that confirms radical‐anion nature of o ‐quinonato ligands in the investigated complexes …”

“…The magnetic moment of 1 in the range 300–60 K region (4.02‐4.09 µ B ) is slightly bigger than the theoretical spin‐only value 3.87 µ B for system with S =3/2 with g=2.0, and it is close to the expected theoretical value of 4.06 µ B for complexes of high spin Co(II) (d 7 , S =3/2) in a quartet spin state taking into account g Co ≈2.1 which is usual for cobalt(II) compounds: for example, g Co =2.09 for five‐coordinate cobalt(II) compound [Co( 2 L N ) 2 (tBu‐py)] based on N‐phenyl‐ o ‐phenylenediamine H 2 ( 2 L N IP ), g Co =2.08 and 2.06 for Co(3,6‐SQ) 2 L complexes with L is 5,7‐di‐ tert ‐butyl‐2‐(pyridine‐2‐yl)benzoxazole and 2,6‐dimethyl‐N‐(thiophen‐2‐ylmethylene)benzenamine respectively; g Co =2.2 was calculated for binuclear cobalt(II) complex [Co II (L S AP ) 2 ] 2 based on 6‐amino‐2,4‐di‐ tert ‐butyl‐thiophenolate ligand L S AP …”

“…The second synthetic way (Scheme , equation Ib) is the redox‐substitution of o ‐benzosemiquinonato ligand with NHC from cobalt coordination sphere in tris(3,6‐di‐ tert ‐butyl‐ o ‐benzosemiquinonato)cobalt(III) (3,6‐SQ) 3 Co. This method is often used for the synthesis of o ‐benzosemiquinonato cobalt complexes with neutral ligands because (3,6‐SQ) 3 Co exchanges easily one o ‐benzosemiquinonato ligand . However this reaction proceeds sluggishly in comparison with previous method by the reason of equilibrium between (3,6‐SQ) 3 Co and (3,6‐SQ) 2 Co+3,6‐Q and the competitive reactions between 3,6‐Q and neutral ligand.…”

“…The six‐membered rings C(1‐6) and C(1 A‐6 A) of chelating ligands demonstrate quinoid‐type distortion that also points to the radical‐anion nature of these ligands. The Co(1)‐O(1), Co(1)‐O(2) and Co(1)‐O(1 A), Co(1)‐O(2 A) bond length (2.0001(8), 2.0582(8) respectively) are typical for Co(II) high‐spin complexes …”

Magnetism and variable temperature and pressure crystal structures of a linear oligonuclear cobalt bis-semiquinonate

“…There are very few examples available in the scientific literature with which to compare our exchange model, which makes it difficult to provide context for the exchange parameters obtained here. In the few studies available, Co(II)-SQ exchange values range from J = 0, 62 to J = −7 cm −1 , 13 to J = −594 cm −1 , 63 although it should be noted that the Hamiltonians used in the literature are not exactly the same in all cases.…”