STRUCTURE AND SPECTROSCOPY OF THE COPPER(II) COMPLEX OF THE UNSYMMETRIC ENCAPSULATING LIGAND 13-DITHIA-6,10,16,19-TETRAAZABICYCLO[6.6.6]ICOSANE (AMN(4)S(2)SARH)

The copper(II) complex of the N4S2 encapsulating ligand -dithia-6,10,1 6,19-tetraazabicyclo-[6.6.6]icosane, [Cu(AMN(4)S(2)sarH)](3+), is repo rted. Crystals of the complex are monoclinic, of space group P2(1)/a ( Z = 4, a = 16.463(3) Angstrom, b = 11.073(3) Angstrom, c = 17.138(3) A ngstrom, beta = 106.20(1)degrees, R = 0.053 (3449 F)). The coordinatio n about the copper(II) atom is a distorted version of a 4 + 2 elongate d octahedron with the pronounced tetragonal distortion arising from lo ng Cu-N and Cu-S axial bonds of 2.447(5) and 2.600(2) Angstrom, respec tively. The presence of longer Cu-S bonds (2.436(2), 2.600(2) Angstrom ) cis to shorter Cu-N bonds (2.012(5), 2.029(5) Angstrom) results in a tilting of the capping groups in relation to the pseudo-3-fold axis o f the metal complex, the two caps being eclipsed with respect to one a nother. The randomly orientated frozen solution EPR spectrum and low-t emperature (similar to 10 K) absorption spectrum are indicative of an orthorhombically distorted complex with a pronounced tetragonal elonga tion, consistent with the crystal structure determination and room-tem perature magnetic moment of 1.75 mu(B). Computer simulation of the ran domly orientated frozen solution X-band EPR spectrum yielded g(z) = 2. 189, g(x) = 2.048, g(y) = 2.074, and A(z) = 160.5 x 10(-4) cm(-1). Lig and nitrogen hyperfine coupling was not resolved on the M(I) = -1/2 pa rallel resonance at S-band microwave frequencies, presumably a consequ ence of the low symmetry around the Cu(II) ion. From the analysis of t he absorption spectrum, angular-overlap-model ligand-field parameters of e(sigma)(N) = 6000, e(sigma)(S) = 6100 cm(-1) (for the shortest Cu- N and Cu-S bonds), zeta = 600 cm(-1) and k = 0.69 were obtained, resul ting in calculated g values in very good agreement with those found fr om EPR measurements.