Studies on the metalamide bond. VIII. The crystal structure of [N,N′-bis(2′-pyridinecarboxamido)-trans-1,2,-cyclohexane] nickel(II)

[N,N′-bis(2′-pyridinecarboxamido )-trans-1,2-cyclohexane] nickel(II) C₁₈H₁₈N₄Ni, is monoclinic, space group I2/a, with a = 13.652(8), b = 12.127(6), c = 10.739(5) Å, β = 106.0(1)°, Z = 4. The structure was refined to R = 0.088 for 811 photographic reflexions using least-squares calculations. The molecule has space group imposed C2(2) symmetry and the nickel atom is four-coordinate with the ligand acting as distored square-planar N₄-tetradentate [NiN(amide) 1.868(7), NiN(pyridine) 1.944(8) Å, N(amide)Ni;N(amide) 86.2(4)°, N(pyridine)Ni;N(pyridine) 107.0(4)°]. The amide nitrogen atom is best described as having a flattened pyramidal geometry. Steric interactions are further alleviated by rotations with the non-planar amide chelate ring. The cyclohexane ring adopts a skew-chair conformation in which the methine hydrogens are in transconfiguration. The molecules are packed in the lattice in layers parallel to (101).