Homoleptic organometallic anions of Ti, Zr, Hf, and Nb.

Reactions of C(6)H(5)Li and 4-CH(3)C(6)H(4)Li with halides of Ti, Ir, Hf, and Nb lead to the formation of homoleptic organometallic anions of these metals. Owing to their thermal instability and their sensitivity towards H(2) O and O(2) , these compounds are characterized by single-crystal structure determinations at low temperature, whereas other physical data could only be obtained occasionally. Three pentacoordinate complex anions Ti(C(6)H(5))(5), Ti(4-CH(3)C(6)H(4))(5), and Zr(C(6)H(5))(5) have square-pyramidal structures that display only slight deviations from the ideal geometry, in contrast to the already known structures of Ti(CH(5))(5). The hexacoordinate complex anions Zr(C(6)H(5))(6), Zr(4-CH(3)C(6)H(4))(6), Nb(C(6)H(5))(6), and Nb(4-CH(3)C(6)H(4))(6) all have trigonal-prismatic structures, in accord with the known hexamethyl complex dianions. In contrast, the hexacoordinate complex anion Hf(C(6)H(5))(6)(-) has an octahedral or close to octahedral structure, in contrast to the known trigonal-prismatic structures of Ta(C(6)H(5))(6) and [Ta(4-CH(3)C(6)H(4))(6) (-). A qualitative explanation for this structural variability is given.