The dichloroplatinum(II) and dichloropalladium(II) complexes of 1,4-diazacycloheptane: Preparative, structural and conformational studies

The preparation and purification of [Pt(hpip)Cl-2] and [Pd(hpip)Cl-2] (hpip = homopiperazine = 1,4-diazacycloheptane) are described. Crystal structures of [Pt(hpip)Cl-2] and [Pd(hpip)Cl-2] have been determined by X-ray diffraction methods and refined to R values of 0.023 (932 F) and 0.023 (948 F). The crystals of [Pt(hpip)Cl-2] are orthorhombic, space group Pbcm, a 7.7019(8), b 9.8080(12), c 12.1944(14) Angstrom, and those of [Pd(hpip)Cl-2] are monoclinic, space group P2(1)/m, a 6.1001(9), b 11.527(2), c 6.458(1) Angstrom, beta 106.30(2)degrees. The seven-membered rings of the Ligands in both complexes adopt boat-like conformations in which the five-membered chelate ring has an eclipsed N-C-C-N group and the six-membered chelate ring adopts a chair conformation. Molecular mechanics methods were used to investigate whether this conformation was a crystallographic artefact but it was found to be real. An alternative conformation in which the six-membered chelate ring adopts a skew-boat conformation was also investigated. It was found to be less stable than the conformation observed in the crystal structures, but to a degree that depends on whether non-bonded interactions involving the metal atom were included or not.