Studies on the metal-amide bond XV. The Molecular structure of chloro{[N-methyl-N-(2′-pyridinecarboxamide)N′-(2′-pyridinecarboxamido)]-1,2-ethane}palladium(II) determined by x-ray diffraction and high-resolution NMR studies

Chloro{[N-methyl-N-(2′-pyridinecarboxamide)-N′(2′-pyridinecarboxamido)]-1,2-ethane}palladium(II), C₁₅H₁₅N₄O₂ClPd, is tetragonal, space group I4₁/a with a = 14.340(8), c = 31.226(10) Å, Z = 16. The crystal structure was refined to R = 0.078 for 1886 photographic reflexions by least-squares calculations The ligand acts as an N₃-tridentate to the Pd atoms via the two pyridine and one deprotonated amide nitrogen atoms [Pd-N(amide) 1.98(1) Å; average Pd- N(pyridine) 2.05(1) Å]. The N-methylated amide group is not coordinated but part of an unusual eight-membered chelate ring. A square-planar coordination is completed by the chlorine atoms [Pd-Cl 2.293(4) Å]. The coordinated picolinamide unit is almost co-planar with the coordination plane, whereas the N-methyl picolinamide unit is non-planar. The plane of this amide group is approximately perpendicular to the plane of the pyridine ring, the latter making an angle of 64.9° with the coordination plane. This unusual molecular geometry is shown to be retained in solution. The complex proton n.m.r. spectrum of the compound in CDCl₃ only may be stimulated a rigid structure similar to that found in the solid state. The hydrogen atoms of the central ethane link are closely eclipsed; observed vicinal coupling constants for the protons show a close correlation with those calculated using the HCCH torsion angles derived from the X-ray analysis. Observed chemical shifts are explained in terms of close intramolecular contacts in the structure as determined.