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, sp ace 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 seve n-membered rings of the Ligands in both complexes adopt boat-like conf ormations in which the five-membered chelate ring has an eclipsed N-C- C-N group and the six-membered chelate ring adopts a chair conformatio n. Molecular mechanics methods were used to investigate whether this c onformation was a crystallographic artefact but it was found to be rea l. 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 structur es, but to a degree that depends on whether non-bonded interactions in volving the metal atom were included or not.