514 RORERT FARINA AND RALPHG. WILKTNS
Inorganic Chemistry
infrared-active modes are Raman inactive, and vice mode. In spectra of the M ( a c a ~ ) ~complexes X~ the single, rather broad M-X stretching band is generally The coincidence of bands in the infrared and Raman spectra (Table I), especially those in the lownot resolved. Only in infrared spectra of the solid dichlorides and of Hf (acac)& in dichloromethane were frequency region which have been assigned to M-0 and M-X stretching modes, indicates that the M ( a ~ a c ) ~ X two ~ M-X bands observed, and even in these cases the frequency separation between the symmetric and asymcomplexes exist in solution as the cis isomer. The metric components was only ca. 10 cm-I. Similar cis structure was suggested for the zirconium and hafsmall-frequency separations and lack of resolution nium complexes by nmr chemical shift data, and this have been reported in infrared studies of other cisstereochemistry has been ell established for the dihalometal acetylacetonates. 19,36, 37 analogous 35 and tin19,39-41 compounds. Infrared and Raman spectra afford no clue to the Infrared and Raman spectra of the cis isomers stereochemistry of the seven-coordinate M (acac)3X should show two 31-X stretching vibrations-a complexes because of the low symmetry of the possymmetric, Raman-polarized mode and an asymmetric sible geometrical isomers. versa.
(37) R. C. F a y and R. X. Lowry, Inovg. Nztcl. C h m . L P ~ ~ 3, c ~117 s, (1967). (38) I
