Crystal Spectra of Metal Coordination Compounds. III. Nickel Complexes with Salicylaldehyde and Its Imines

Polarized single crystal absorption spectra are reported for three nickel complexes: bis-N-methylsalicylaldiminato-nickel (II), bis-salicylaldiminato-nickel (II), and diaquo-bis-salicylaldehydato-nickel (II). The analysis of the bands of an orthorhombic form of bis-N-methyl-salicylaldiminato-nickel (II) (described for the first time) results in the assignment of the two visible absorption bands to 1Ag→1B1g and 1Ag→1B3g, respectively. This assignment is discussed in relation to the simple crystal field model and a possible refinement of the model has been suggested. The analysis of the band observed with bis-salicylaldiminato-nickel (II) is consistent with the assignment of those in bis-N-methylsalicylaldiminato-nickel (II). The analysis of the visible absorption band of diaquo-bis-salicylaldehydato-nickel (II) shows that the theoretical assignment is incorrect although an unambiguous assignment cannot be made from the crystal spectrum.