SYNTHESIS, STRUCTURE, AND SPECTROSCOPY OF AN ENCAPSULATED NICKEL(II) COMPLEX OF THE UNSYMMETRICAL MACROBICYCLIC LIGAND 13-DITHIA-6,10,16,19-TETRAAZABICYCLO[6.6.6]ICOSANE (AMN(4)S(2)SAR)

The nickel(II) complex of the encapsulating ligand dithia-6,10,16,19-t etraazabicyclol[6.6.6]-icosane, [Ni(AMN(4)S(2)sar)](2+), is reported. Crystals of the complex are monoclinic, space group P2(1)/c, with Z = 4, a = 9.167(6) Angstrom, b = 19.885(4) Angstrom, c = 13.068(8) Angstr om, beta = 95.37(3)degrees, and R = 0.055. The low-temperature (simila r to 10 K) Single-crystal absorption spectrum and ligand field analysi s of the complex are reported. The spin-forbidden (3)A(2g) --> (1)E(g) ,(1)A(1g) transitions were observed at low temperature, and from the s pectroscopic analysis, a significant differential nephelauxetic effect is shown to occur resulting in much lower values for the Racah B and C parameters for these spin-forbidden transitions in relation to the s pin-allowed transitions.