Coordination behavior of L-aspartic acid: ternary nickel(II) complexes with imidazoles. Crystal and molecular structure of (L-aspartate)tris(imidazole)nickel(II).

Two ternary compounds of formula Ni(L-asp)B, (L-asp = L-aspartate ion; B = imidazole and 2-methylimidazole)were prepared and characterized by means of magnetic and spectroscopic measurements. For one of them, the Ni(L-asp)(im),complex, the crystal structure was also determined. The compound crystallizes in the monoclinic space group P2, with fourformula units in a cell of dimensions a = 22.001 (2) A, b = 8.631 (1) A, c = 8.514 (1) b;, and p = 95.07 (1)°. X-ray diffractiondata were collected with a Philips PW 1100 automated four-circle diffractometer by using Mo Ka radiation. The structurewas solved by the heavy-atom method and refined by full-matrix least-squares procedures to a final R factor of 0.0514 for205 1 independent reflections. The structure consists of two crystallographically independent but chemically equivalentNi(L-asp)(im), molecules in which each Ni atom is coordinated in a distorted octahedral geometry by one L-aspartate ion,acting as a tridentate ligand, and by three imidazole molecules. Infrared and ligand field spectroscopies and magnetic measurementsall agree with the observed crystal structure.