Steric effects and five-co-ordination in first-row transition-metal compounds. Compounds with a linear tetra-amine ligand

Compounds of MnII, CoII, NiII, CuII and ZnII of the type M(chelate)X2[where chelate =NN′-di-(3-aminopropyl)piperazine; X = one of a variety of anions] are reported. Square-pyramidal five-co-ordinate cations in the compounds [M(chelate)X]X and [M(chelate)X]Y are characterised for the following: where M = CoII, X = Br and I; where M = NiII, X = Cl, Br and possibly NCS; and where M = CuII, X = Cl, Br, I, NCS, and Y = ClO4, PF6. In addition, a five-co-ordinate species Cu(chelate)Cl2 in which the ligand is only terdentate with a free NH2, also is characterised. Four co-ordinate planar [MN4]2+ species also are characterised for NiII, CuII and perhaps CoII. No significant structural data is available for the MnII, FeII, or ZnII species. The structural assignments for the solid compounds rely on X-ray data (powder-pattern correlations with a known three-dimensional structure), i.r. and electronic spectra, and magnetic measurements. Structural studies of solutions in non-aqueous solvents also are reported. These rely on electronic spectra. Specific ion-pairing limits the use of conductivity data. The origin of the five-co-ordinate structures in these compounds is discussed in terms of the peculiar steric effects of the ligand, which is the precursor of a class of homologous ligands, each of which is expected to give five-co-ordinate compounds of these metals.