PREPARATION, CRYSTAL-STRUCTURE AND SINGLE-CRYSTAL POLARIZED SPECTRA OF ANO-3,5-DIHYDRO-3,5-DIIMINO-PYRROLIZINIDO)ZINC(II) TETRAHYDROFURAN-(1 4)/

The complex ano-3,5-dihydro-3,5-diiminopyrrolizimido)zinc(II), as its tetrahydrofuran (thf) adduct, Zn(C11N7H2)(2).4thf, has been synthesize d and its crystal structure determined. The zinc atom, which lies on a crystallographic symmetry centre, co-ordinates four imino groups in a square-planar arrangement [Zn-N-imino 2.070(8) Angstrom] and two thf units in the apical positions [Zn-O-thf 2.249(7) Angstrom]; the other two thf molecules are equatorially linked to the imino hydrogens. The electronic absorption spectra have been derived through a Kramers-Kron ig transformation of the single crystal polarized specu[ar reflectance spectra and then resolved via Gaussian deconvolution. They show an ex tensive mixed polarization, since their prominent components are distr ibuted along different molecular directions. The low-energy band (Q) i s polarized mainly along the in-plane molecular short axis (y), the ne xt band (B) along the long axis (x) and the third band (N) along z. Th e interpretation is based on the only available theoretical model, tha t is INDO/S molecular orbital calculations, carried out on the analogo us Ni-II complex (D-2h). The agreement between the observed and predic ted transitions is qualitatively quite good, in the sense that several spectroscopic states have been; calculated within the energy range in vestigated, of symmetry mainly B-2u(y) at low energy, B-3u(x) at inter mediate energy and B-1u(z) at high energy. While crystal optics may co ntribute slightly to polarization mixing, there is evidence for vibron ic coupling between states of different symmetry; the proposed assignm ent (D-2h) is thus based on the extrapolation of the above calculation s by using the vibronic coupling, with the frequent occurrence of the type B-2u x b(1g) x B-3u.