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, Le and Lm, having ethylene and methylene spacers between donor groups, with bite angles Le ≈ 100° and Lm ≈ 80°, dictate pseudotetrahedral and trigonal-bipyramidal geometries in six high-spin Ni­(II)-halide complexes, [Ni­(Le)­X2] and [Ni­(Lm)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.