The disproportionation of [Ni(tacn)]2+ in Ni2+ and [Ni(tacn)2]2+ crystallographically demonstrated (tacn = 1,4,7-triazacyclononane)

Bite-Angle-Regulated Coordination Geometries: Tetrahedral and Trigonal Bipyramidal in Ni(II) with Biphenyl-Appended (2-Pyridyl)alkylamine N,N'-Bidentate Ligands

Two simple biphenyl-appended (2-pyridyl)alkylamine N-bidentate ligands, L^e and L^m, having ethylene and methylene spacers between donor groups, with bite angles L^e ≈ 100° and L^m ≈ 80°, dictate pseudotetrahedral and trigonal-bipyramidal geometries in six high-spin Ni(II)-halide complexes, [Ni(L^e)X₂] and [Ni(L^m)₂X](ClO₄) (where X = Cl^-, Br^-, I^-), respectively. The structures in the solid state, determined using X-ray crystallography, and in solution, determined using spectroscopic methods (UV-vis-NIR and paramagnetic ¹H NMR), which complement each other, are described.