Steric effects in pyrrole-based mixed complex systems

Abstract

New systems of the type M(pyrenNR 2)Br, M(pyrtnNR 2Br (M = Cu, Ni), M(pyr)(pyrenNR 2) (M = Cu, Ni), Cu(pyr)(pyrtnNR 2) (where Hpyr is pyrrole-2-aldehyde, pyrenNR 2 is Schiff base of pyr and NR 2CH 2 Ch 2NH 2and pytrnNR 2 is Schiff base of pyr and NR 2CH 2 CH 2CH 2Nh 2 are reported. The first two systems are shown to have planar geometry in which pyrenNR 2 and pyrtnNR 2 act as tridentate ligands. On the basis of magnetic, spectral and X-ray powder diffraction studies on pure crystal and on solid solutions of nickel(II) and copper(II) species, it is concluded that M(pyr)(pyrenNR 2 has a 4-coordinate grossly planar geometry in which the NR 2 group of pyrenNR 2 fails to occupy a coordination position due to steric reasons. Models demonstrate that this steric difficulty should considerably decrease on replacement of pyrenNR 2 by pyrtnNR 2. Indeed the species Cu(pyr)(pyrtnNR 2) have electronic spectra strongly suggestive of pentacoordination.