Studies on the MetalAmide Bond. XIII. The crystal and molecular structure of the β-form of aqua[N,N′-bis(2′-pyridinecarboxamido)-1,3-propane] copper(II) dihydrate

β-Aqua [N,N′-bis(2′-pyridinecarboxamido)1,3-propane]δ-copper(II) dihydrate, C₁₅H₂₀N₄O₅Cu, is monoclinic, space group P2₁/n, with a = 6.939(9), b = 12.615(16), c = 19.472(20) Å, β = 97.15(8)°, Z = 4. The structure was refined to R = 0.086 for 2492 photographic reflexions by full-matrix least-squares procedures. The Cu atom geometry is a distorted square-based pyramid, with the ligand encompassing the base [average CuNδ-(amide) 1.954(5) Å, average CuN(pyridine) 2.065(5) Å, N(amide)CuN(amide) 93.7(2)°, N(pyridine)CuN(pyridine) 101.1(2)°], from which the Cu atom is displaced 0.24 Å towards an apical water molecule [CuO 2.268(4) Å]. A close contact between α-pyridyl H atoms (1.86 Å) causes folding of 26.2° between the two nearly planar picolinamide units, with the central six-membered chelate ring adopting a boat conformation. Enforced steric strain in the molecule results in non-planar distortions in the pyridine rings, although the coordinated amide groups remain planar. The coordinated and lattice water molecules are involved in a hydrogen-bonding network incorporating the amide oxygen atoms and giving rise to sheets perpendicular to b.