Studies on the metalamide bond XI. The structure of aqua[N, N′-bis(2′-pyridinecarboxamido)-trans-1, 2-cyclohexane] copper(II) dihydrate

Aqua[N, N′-bis(2′-pyridinecarboxamido)-trans-1, 2-cyclohexane] copper(II) dihydrate, C₁₈H₂₄N₄O₅Cu, is monoclinic, space group P2₁/c, with a = 9.094(10), b = 17.620(7), c = 12.141(7) Å, β = 91.9(1)°, Z = 4. The structure was refined to R = 0.088 for 2787 photographic reflexions using least-squares calculations. The copper atom is five-coordinate with the ligand acting as an essentially planar N₄-tetradentate which encompasses the base of a distorted square-based pyramid [average CuN(amide) 1.934(5), CuN(pyridine) 2.026(5) Å, N(amide)CuN(amide) 83.5(2)°, N(pyridine)CuN(pyridine) 110.2(1)°]. The copper atom is displaced by 0.19 Å from the N₄-plane towards the apical water molecule [CuO 2.338(5) Å]. Both amide nitrogen atoms are approximately 50% pyramidally distorted. The cyclohexane ring adopts a chair conformation in which the two methine hydrogen atoms are in a trans configuration. The coordinated and the two lattice water molecules are involved in a hydrogen-bond network which includes the carboxyl oxygen atoms of the amide groups of neighbouring chelate molecules. The chelate molecules pack in layers parallel to (101).