A first series of nickel(II)complexes TrpyNi(II)X of the new tripyrrolic ligand 2,15-dimethyl-3,4,8,9,13,14-hexaethyltripyrrin with X = Cl, Br and I was prepared and characterized by spectroscopic and structural means. The coordination geometry found for the four-coordinate, paramagnetic bromo- and iodo-derivatives in the solid state can best be described as distorted trigonal-bipyramidal with one ligand missing in the trigonal plane. For the chloro derivative, this empty site is occupied in the crystal by a water ligand. As proton NMR studies on the paramagnetic TrpyNiCl reveal, an equilibrium exists between the four- and five-, but not a six-coordinate form, and for pyridine-N-oxide as the fifth ligand thermodynamic data of the ligand association could be obtained by a temperature dependent NMR titration study.
