Steric effects in pyrrole-based mixed complex systems

Abstract

New systems of the type M(pyrenNR₂)Br, M(pyrtnNR₂Br (M = Cu, Ni), M(pyr)(pyrenNR₂) (M = Cu, Ni), Cu(pyr)(pyrtnNR₂) (where Hpyr is pyrrole-2-aldehyde, pyrenNR₂ is Schiff base of pyr and NR₂CH₂ Ch₂NH₂and pytrnNR₂ is Schiff base of pyr and NR₂CH₂ CH₂CH₂Nh₂ are reported. The first two systems are shown to have planar geometry in which pyrenNR₂ and pyrtnNR₂ 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)(pyrenNR₂ has a 4-coordinate grossly planar geometry in which the NR₂ group of pyrenNR₂ fails to occupy a coordination position due to steric reasons. Models demonstrate that this steric difficulty should considerably decrease on replacement of pyrenNR₂ by pyrtnNR₂. Indeed the species Cu(pyr)(pyrtnNR₂) have electronic spectra strongly suggestive of pentacoordination.