title: Role of π-acceptor effects in controlling the lability of novel monofunctional Pt(II) and Pd(II) complexes: crystal structure of [Pt(tripyridinedimethane)Cl]Cl.
abstract: The kinetics and mechanism of substitution reactions of novel monofunctional [Pt(tpdm)Cl](+) and [Pd(tpdm)Cl](+) complexes (where tpdm = tripyridinedimethane) and their aqua analogues with thiourea (tu), L-methionine (L-met), glutathione (GSH), and guanosine-5'-monophosphate (5'-GMP) were studied in 0.1 M NaClO(4) at pH = 2.5 (in the presence of 10 mM NaCl for reactions of the chlorido complexes). The reactivity of the investigated nucleophiles follows the order tu > l-met > GSH > 5'-GMP. The reported rate constants showed the higher reactivity of the Pd(II) complexes as well as the higher reactivity of the aqua complex than the corresponding chlorido complex. The negative values reported for the activation entropy as well as the activation volume confirmed an associative substitution mode. In addition, the molecular and crystal structure of [Pt(tpdm)Cl]Cl was determined by X-ray crystallography. The compound crystallizes in a monoclinic space group C2/c with two independent molecules of the complex and unit cell dimensions of a = 38.303(2) Å, b = 9.2555(5) Å, c = 27.586(2) Å, β = 133.573(1)°, and V = 7058.3(8) Å(3). The cationic complex [Pt(tpdm)Cl](+) exhibits square-planar coordination around the Pt(II) center. The lability of the [Pt(tpdm)Cl](+) complex is orders of magnitude lower than that of [Pt(terpyridine)Cl](+). Quantum chemical calculations were performed on the [Pt(tpdm)Cl](+) and [Pt(terpyridine)Cl](+) complexes and their reactions with thiourea. Theoretical computations for the corresponding Ni(II) complexes clearly demonstrated that π-back-bonding properties of the terpyridine chelate can account for acceleration of the nucleophilic substitution process as compared to the tpdm chelate, where introduction of two methylene groups prevents such an effective π-back bonding.
authors.affiliation: Faculty of Science, University of Kragujevac, Radoja Domanovica 12, P.O. Box 60, 34000 Kragujevac, Serbia.
authors.forename: Biljana
authors.initials: B
authors.lastname: Petrović
authors.forename: Živadin  D
authors.initials: Ž
authors.lastname: Bugarčić
authors.forename: Anne
authors.initials: A
authors.lastname: Dees
authors.forename: Ivana
authors.initials: I
authors.lastname: Ivanović-Burmazović
authors.forename: Frank W
authors.initials: FW
authors.lastname: Heinemann
authors.forename: Ralph
authors.initials: R
authors.lastname: Puchta
authors.forename: Stephan N
authors.initials: SN
authors.lastname: Steinmann
authors.forename: Clemence
authors.initials: C
authors.lastname: Corminboeuf
authors.forename: Rudi
authors.initials: R
authors.lastname: van Eldik
mesh_terms: D018360:Crystallography, X-Ray; D019277:Entropy; D007700:Kinetics; D008958:Models, Molecular; D015394:Molecular Structure; D010165:Palladium / Q000737:chemistry*; D010984:Platinum / Q000737:chemistry*; D011789:Quantum Theory; D013056:Spectrophotometry, Ultraviolet; D017550:Spectroscopy, Fourier Transform Infrared
chemical_list: D010984:Platinum; D010165:Palladium