Single crystal electronic spectra of a series of trans nickel(II) complexes with N,N′-diethyl- and N,N′-dimethylethylenediamine

We have measured the polarized crystal spectra at 10 K. of Ni(s-Et2en)2X2, where X = Cl, Br, NCS, and H2O (with Cl, Br, and I counterions) and *-Et2en is N, N'-diethylethylenediamine, and of Ni(s-Me2en)2X2, where X = NCS and NO3, and.s-Me2en is N,N′-dimethylethylenediamine. Transition energies were calculated for D4h symmetry using symmetry adapted functions and a normalized spherical harmonic Hamiltonian. When the differences between calculated and observed band positions are minimized, the ligand-field and angular overlap parameters listed in Table 2 are obtained. The criteria for the band assignments are discussed. The principal conclusions are: (1) The π interactions between Ni(II) and the axial ligands are small in contrast to tetragonal Cr(III) complexes. (2) Equatorial and axial parameters are relatively independent, in contrast to tetragonal Cu(II) complexes. (3) The more basic,s-Et2en exerts a stronger ligand field than,s-Me2en. (4) The σ-bonding strength of the axial ligands follows the spectrochemical series. (5) DQ for the axial ligands in the ethyl complexes is lower than anticipated, probably due to steric hindrance of the bulky ethyl groups. (6) B values are all near 850 cm−1, except for an anomalously low value for Ni(s-Et2en)2(NCS)2.