CHIRAL METAL-COMPLEXES .35. UNUSUAL TERDENTATE BEHAVIOR IN THE CRYSTAL-STRUCTURE OF CHLORO[N,N'-DI(2-PICOLYL)-N-(2-PYRIDINECARBOXAMIDE)-1,2-DIAMINOCYCLOHEXANE]PALLADIUM(II) PERCHLORATE HEMIHYDRATE

An improved method of synthesis for the tetradentate ligand rac-N,N'-di(2-picolyl)-1,2-diaminocyclohexane, (rac-picchxn), is described. The controlled reaction of 2-pyridinecarboxylic acid with this compound results in the potentially pentadentate N5 ligand N,N'-di(2-picolyl)-N-(2-pyridinecarboxamide)-1,2-diaminocyclohexane, (rac-picchxnam). A palladium(II) complex of this ligand was isolated and its crystal structure determined by X-ray diffraction. [Pd(picchxnam)Cl]ClO4.1/2H2O, C24H28N5O5.5Cl2Pd, crystallises in the monoclinic space group Pn (non-standard No. 7) with a = 12.006(2), b = 8.207(2), c = 13.477(2) angstrom, beta = 100.80(1)-degrees, Z = 2. The structure was refined to R = 0.039 by least-squares techniques for 2066 reflections. The ligand coordinates as a terdentate through the two picolyl pyridine-N atoms and the secondary amine-N atom. This results in a five-membered chelate ring and an unusual eight-membered ring which contains the tertiary amide nitrogen atom. The pyridinecarboxamide group does not coordinate, but is non-planar and is orientated away from the PdN3Cl square-plane. The Pd-Cl, Pd-N(amine) and Pd-N(pyridyl) distances are 2.309(3), 2.079(7), 2.091(8) and 2.029(8) angstrom, respectively.