POTENTIAL FOR REDOX ISOMERISM BY QUINONE COMPLEXES OF IRON(III). - STUDIES ON COMPLEXES OF THE FE-III(N-N)(DBSQ)(DBCAT) SERIES WITH 2,2'-BIPYRIDINE AND N,N,N',N'-TETRAMETHYLETHYLENEDIAMINE COLIGANDS

Iron complexes of the Fe-III(N-N)(DBSQ)(DBCat) series, where N-N = bpy , tmeda, and DBSQ and DBCat are semiquinonate and catecholate ligands derived from 3,5- and 3,6-di-teut-butyl-1,2-benzoquinone, have been in vestigated to assess the potential for isomerism to Fe-II(N-N)(DBSQ)(2 ) species in the manner of related complexes of Mn and Co. Crystallogr aphic characterization is provided for Fe(bpy)(3,6-DBSQ)(3,6-DBCat) [m onoclinic, C2/c, a = 10.809(1) Angstrom, b = 30.149(6) Angstrom, c = 1 2.275(2) Angstrom, beta = 114.52(1)degrees, and Z = 4], Fe(tmeda)(3,6- DBSQ)-(3,6-DBCat) [monoclinic, P2(1)/c, a = 14.531(3) Angstrom, b = 13 .328(3) Angstrom, c = 19.781(3) Angstrom, beta = 106.63(2)degrees, and Z = 4], and Fe(tmeda)(3,5-DBSQ)(3,5-DBCat). 2C(3)H(5)OH [monoclinic, P2(1)/n, a = 11.884(2) Angstrom, b = 14.856(2) Angstrom, c = 25.115(5) Angstrom, beta = 93.15(2)degrees, and Z = 4]. All three complex molec ules are monomeric and octahedral. Intermolecular stacking for Fe(bpy) (3,6-DBSQ)(3,6-DBCat) appears responsible for an anomalous drop in mag netic moment at low temperature; the complexes containing tmeda ligand s have S = 2 magnetic moments that result from strong Fe(III)-semiquin one radical antiferromagnetic exchange. Electronic spectra of all thre e complexes show strong solvatochromic effects, little temperature dep endence, and no bands in the infrared that appear characteristically f or related Co(III) and Mn(III) complexes that exhibit redox isomerism. The absence of isomerism for the iron complexes is explained in terms of thermodynamic changes that contribute to equilibria of the Co(N-N) (DBQ)(2) and Mn(N-N)(DBQ)(2) series.