title: Structural investigations of palladium(II) and platinum(II) complexes of salicylhydroxamic acid.
abstract: Complexes of salicylhydroxamic acid (shaH) with palladium(II) and platinum(II) were investigated. The synthesis of [Pt(sha)(2)] was attempted via a number of methods, and ultimately (1)H NMR investigations revealed that salicylhydroxamate would not coordinate to chloro complexes of platinum(II). However, [Pt(sha-H)(PPh(3))(2)] was successfully synthesized and the crystal structure determined (orthorhombic, space group Pca2(1) a = 17.9325(19) A, b = 11.3102(12) A, c = 18.2829(19) A, Z = 4, R = 0.0224). The sha binds via an [O,O] binding mode, in its hydroximate form. In contrast the palladium complex [Pd(sha)(2)] was readily synthesized and crystallized as [Pd(sha)(2)](DMF)(4) in the triclinic space group P(-)1,a = 7.066(1) A, b = 9.842(2) A, c = 12.385(2) A, alpha = 99.213(3)(o), beta = 90.669(3), gamma = 109.767(3)(o), Z = 1, R = 0.037. The unexpected [N,O'] binding mode of the salicylhydroxamate ligand in [Pd(sha)(2)] prompted investigation of the stability of a number of binding modes of salicylhydroxamic acid in [M(sha)(2)] (M = Pd, Pt) by density functional theory, using the B3LYP hybrid functional at the 6-311G* level of theory. Geometry optimizations were carried out for various binding modes of the ligands and their relative energies established. It was found that the [N,O'] mode gave the more stable complex, in accord with experimental observations. Stabilization of hydroxamate binding to platinum is evidently afforded by soft ligands lying trans to them.
authors.affiliation: Centre for Heavy Metals Research, School of Chemistry, The University of Sydney, New South Wales 2006, Australia.
authors.forename: Matthew D
authors.initials: MD
authors.lastname: Hall
authors.forename: Timothy W
authors.initials: TW
authors.lastname: Failes
authors.forename: David E
authors.initials: DE
authors.lastname: Hibbs
authors.forename: Trevor W
authors.initials: TW
authors.lastname: Hambley
mesh_terms: D018360:Crystallography, X-Ray; D004791:Enzyme Inhibitors / Q000737:chemistry; D006877:Hydroxamic Acids / Q000737:chemistry*; D008024:Ligands; D009682:Magnetic Resonance Spectroscopy; D008666:Metalloendopeptidases / Q000037:antagonists & inhibitors; D008968:Molecular Conformation; D015394:Molecular Structure; D009942:Organometallic Compounds / Q000138:chemical synthesis / Q000737:chemistry*; D010165:Palladium / Q000737:chemistry*; D012457:Salicylamides / Q000138:chemical synthesis / Q000737:chemistry*
chemical_list: D004791:Enzyme Inhibitors; D006877:Hydroxamic Acids; D008024:Ligands; D009942:Organometallic Compounds; D012457:Salicylamides; D010165:Palladium; C005703:salicylhydroxamic acid; D008666:Metalloendopeptidases