The preparation and characterization of three binuclear Ti(II1) complexes, [ ( ?~~-c~H~)~T i ]~( B i l~n ) , ZTi]2(BiB~Im), and [ (a5-C,H5),Ti(pz)l2, where BiImZ-is the dianion of 2,2'-biimidazole, BiBzImZ-is the dianion of 2,2'-bibenzimidazole, and pz-is the anion of pyrazole, are reported. The first two air-sensitive compounds are thermally quite stable due to the bis-bidentate nature of the bridging anions, BiIm2-and BiBzIm2-. Antiferromagnetic exchange interactions are present in the first two complexes where J = -25.2 cm-' for the BiIm2--bridged Ti(1II) complex and J = -19.2 cm-I for the BiBzIm2--bridged complex, as indicated by magnetic susceptibility data taken from 270 to 4.2 K. In contrast, the bis(pyrazo1ate)-bridged dimer acts as a normal paramagnet down to 4.2 K with no signs of an antiferromagnetic interaction. An explanation for this difference is presented in terms of the structure of the two types of complexes. Frozen-glass EPR spectra of all three binuclear Ti(" complexes are characteristic of triplet-state ( S = 1) spectra with appreciable zero-field splittings. The triplet-state spectra of the three complexes are fit to theoretical equations to give the zero-field splitting parameters D (axial) and E (nonaxial), e.g., for [(qS-CsHS)2Ti]2(BiIm) it is found that ID1 = 0.0214 cm-I and IEl = 0,0018 cm-I. Excellent agreement between actual Ti-Ti distances from crystal structures and the calculated distances based on the observed D values is obtained. The 77 K X-band EPR glass (toluene-benzene, 4:l) spectrum of the analogous monomeric complex (N-methylbibenzimidazolato)bis(~5-cyclopentadienyl)titanium(III) shows both titanium hyperfine ( A = 11 .O G) and nitrogen superhyperfine ( A = 2.2 G) structure. The nitrogen superhyperfine structure indicates that the two coordinated nitrogen atoms of the N-methylbibenzirnidazolate are essentially equivalent and demonstrates that appreciable unpaired electron density is found on these two nitrogen atoms in agreement with the observed superexchange interaction in the BiImZ-and BiRzIm2-complexes.

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