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

[Image: see text] 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))X(2)] and [Ni(L(m))(2)X](ClO(4)) (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 (1)H NMR), which complement each other, are described.