AN OPTICALLY-ACTIVE NICKEL(II) SCHIFF-BASE COORDINATION COMPOUND 1,2CYCLOHEXYLENEBIS(SALICYLIDENEIMINATO)NICKEL(II)

The Schiff base between trans-(1R,2R)-1,2-cyclohexanediamine, [(-)(D)- chxn] and 2 mol of salicylaldehyde has been used as a ligand for nicke l(II). The coordination compound has been studied by UV/VIS absorption and circular dichroism spectroscopy in solution, and the crystal stru cture has been resolved by X-ray diffraction methods. The spectroscopi c properties are related to the molecular structure found in the cryst al. The crystal system is monoclinic, the unit cell dimensions are a = 10.964(2), b = 12.735(3), c = 12.329(2) Angstrom, beta = 95.26(3)degr ees, the volume is 1714.2(6) Angstrom(3) and space group is P2(1) with Z = 4. The final residual is 3.6% for 2785 observed reflections. Two symmetry-independent molecules in the crystal lattice are related by a non-crystallographic two-fold axis. They are involved in an extensive network of stacking interactions. The Ni-Ni distance is 3.403 Angstro m. The two N and O atoms of the tetradentate ligand chelating each cen tral Ni-II ion form slightly distorted square-planar environments, the Ni-N distances ranging from 1.848(4) to 1.866(4) Angstrom, and Ni-O d istances from 1.835(3) to 1.852(3) Angstrom. The out of plane distorti on gives rise to an overall chiral surrounding of the metal ion. The d -d and charge transfer transitions shaw circular dichroism, and the la tter is shown to be consistent with the observed tetrahedral distortio n which originates in the (R,R) absolute configuration of the ligand.