Novel Cobalt Bis-o-semiquinonato Complexes with Bidentate N-Donor Ligands

Two new cobalt bis-o-semiquinonato complexes, (Pyz-Phen)Co(3,6-DBSQ)(2) (I) and (Bpyz)Co(3,6-DBSQ)(2) (II) (Pyz-Phen = pyrazino[2,3-f][1,10]phenanthroline, Bpyz = bipyrazine, 3,6-DBSQ = 3,6-di-tert-butyl-o-benzoquinone radical anion), were synthesized. According to X-ray diffraction data, both complexes have a trigonal-prismatic geometry of the inner coordination sphere. The distribution of C-O and Co-O bond lengths, which reflects the valence state of the metal and the ligands, indicates that the complexes are formed by cobalt(II) surrounded by two semiquinone radical anions. The results of magnetochemical measurements show that the pyrazino[2,3-f][1,10]phenanthroline complex is a derivative of low-spin divalent cobalt, whereas its bipyrazine structural analogue is a high-spin cobalt(II) derivative.