Preparation, crystal structure and single-crystal polarized spectra of bis(1,2,6,7-tetracyano-3,5-dihydro-3,5-diiminopyrrolizinido)zinc(II)–tetrahydrofuran (1/4)

Abstract

The complex bis( 1,2,6,7-tetracyano-3,5-dihydro-3,5-diiminopyrrolizinido)zinc( II), as its tetrahydrofuran (thf) adduct, Zn (CllN,H,),4thf, has been synthesized 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-Nimino 2.070(8) A] and t w o thf units in the apical positions [Zn-O,,, 2.249(7) A]; the other two thf molecules are equatorially linked to the imino hydrogens. The electronic absorption spectra have been derived through a Kramers-Kronig transformation of the single crystal polarized specular reflectance spectra and then resolved via Gaussian deconvolution. They show an extensive mixed polarization, since their prominent components are distributed along different molecular directions.The low-energy band (a) is polarized mainly along the in-plane molecular short axis (y). the next band (B) along the long axis (x) and the third band (N) along z. The interpretation is based on the only available theoretical model, that is INDO/S molecular orbital calculations, carried out on the analogous Nil' complex (D2,,). The agreement between the observed and predicted transitions is qualitatively quite good, in the sense that several spectroscopic states have been calculated within the energy range investigated, of symmetry mainly B,,(y) at low energy, B,,(x) at intermediate energy and Bl,(z) at high energy. While crystal optics may contribute slightly t o polarization mixing, there is evidence for vibronic coupling between states of different symmetry; the proposed assignment (D,) is thus based on the extrapolation of the above calculations by using the vibronic coupling, with the frequent occurrence of the type B , , x b, , x B,,.

Polarized Specular Reflectance Spectra of Fe(β-dtpy)2·4THF: AD2hModel of Porphyrins

“…Description of the Structure. The molecular structure of the title compound is shown in Figure : it closely resembles that of the homologous zinc complex Zn(β-dtpy) 2 ·4THF already reported . In both cases the metal atom is surrounded by four imino nitrogens from two β-dtpy ligands and by two THF oxygen atoms in a tetragonally elongated octahedral geometry, while other two THF molecules are equatorially linked to the imino hydrogens.…”

“…[49][50][51][52] A disadvantage of the D 4h symmetry of porphrinic systems is the degeneracy of many orbitals and the in-plane transitions involving these. We recently reported on a zinc complex, Zn-(β-dtpy) 2 ‚4THF, where dtpy ) 1,2,6,7-tetracyano-3,5-dihydro-3,5-diiminopyrrolizinde, 53 which has a spectrum very similar to that of the phthalocyanines but has the advantage of D 2h symmetry with no orbital degeneracies. The morphology of the crystals, however, did not allow for complete separation of the three polarizations.…”

On the Spectral Similarities between 1,2,6,7-Tetracyano-3,5-dihydro-3,5-diiminopyrrolizinato Complexes and Phthalocyanines – X-ray Crystal and Molecular Structure of Two Mixed Monopyrrolizinato Nickel(II) Complexes with the 2,4-tert-Butylacetylacetonide Ligand

“…In this case, the reason for the absence of any solvatochromism, despite the well-known tendency of square-planar Cu II complexes to increase the metal-coordination number, might be that the Cu-N eq distances do not lengthen significantly, due to the large Jahn-Teller effect normally observed in these type of compounds, [3,18] on going from square-planar to tetragonally elongated hexa-coordination. 2 We previously [1][2][3][4] reported the solution optical spectra of ML 2 complexes, but, for the reasons given below, most of these data actually referrred to ML species. Here, the correct spectra of the pertinent ML 2 species are presented for the first time ( Figure 5 and Table 3).…”

“…Materials: Our procedures were followed for the synthesis of LH [20] and ML 2 (M ϭ Co, [1] Ni, [2] Cu, [3] Zn [4] ), while M(DPM) 2 (M ϭ Co, Ni, Cu, Zn), [21] Co(DPM) 3 [21] and Na[CoPc(CN) 2 ] [22] were prepared as described in the literature. Commercial H 2 Pc, NiPc, CuPc, and ZnPc were purified by sublimation.…”

“…Our attention was mainly concentrated on the structurally characterized bispyrrolizinates ML 2 (ML 2 ϭ Fe, [1] Co, [1] Ni, [2] Cu, [3] Zn, [4] and Pd [5] ). An important feature of these species is the surprisingly strict similarity of their optical spectra (due to the πǞπ* transitions), especially in the low-energy region (Q band), with those of metal-phthalocyanines (-tetraazatetrabenzoporphyrins, MPc).…”