Studies on the metalamide bond. X. An evaluation of molecular distrotions enforced by steric hindrance in the crystal structure of [N,N′-bis(6′methylpyridine-2′-carboxamido)-1,2-benzene]copper(II)

The structure of [N.N′-bis(6′methylpyridine-2′carboxamido) 1,2-benzene] copper(II) has been determined by photographic methods and refined to R 0.106 for 2090 unique by least-squares procedures. The monoclinic cell, with space group P2₁/c, has a = 10.44(3), b = 14.57(4), c = 11.76(2) Å, β = 104.1(2)°, Z = 4. The ligand acts as a tetradentate through the four N atoms forming a highly distorted square-plane about the Cu atom [Average CuN (amide) 1.934(7) Å, average CuN(pyridine) 2.079(7) Å, N(amide)CuN(amide) 81.3(2)°, N(pyridine)CuN(pyridine) 117.3(2)°. Amide oxygen atoms of neighbouring molecules coordinate also to form chains parallel to a and completing a tetragonally distorted six-coordination 9CuO(amide) 2.693(6) and 2.798(6) Å]. There is a significant tetrahedral distortion in the N₄ geometry of the Cu atome caused by a serve steric interaction between the methyl groups in the ′-positions of the pyridine rings (CH₃...CH₃ separation 3.35(2) Å. A full analysis of out-of-plane distortions an torsion angles shows that steric strain is relatively uniform throughout the molecule, and that no one atom or bond may be viewed as the major distortion site. A small folding effect in the pyridine rings is observed. The molecular structure parameters are compared with those of the unsubstituted analogue previously reported.