title: Pentacoordinate nickel(II) complexes double bridged by phosphate ester or phosphinate ligands: spectroscopic, structural, kinetic, and magnetic studies.
abstract: The bis(phosphatediester)-bridged complexes [[Ni([12]aneN(3))(mu-O(2)P(OR)(2))](2)](PF(6))(2) [[12]aneN(3)=Me(3)[12]aneN(3), 2,4,4-trimethyl-1,5,9-triazacyclododec-1-ene; R=Me (1), Bu (2), Ph (3), Ph-4-NO(2) (4); [12]aneN(3)=Me(4)[12]aneN(3), 2,4,4,9-tetramethyl-1,5,9-triazacyclododec-1-ene; R=Me (5), Bu (6), Ph (7), Ph-4-NO(2) (8)] were prepared by hydrolysis of the phosphate triester with the hydroxo complex [[Ni([12]aneN(3))(mu-OH)](2)](PF(6))(2) or by acid-base reaction of the dialkyl or diaryl phosphoric acid and the above hydroxo complex. The acid-base reaction was also used to synthesise the phosphinate-bridged complexes [[Ni([12]aneN(3))(mu-O(2)PR(2))](2)](PF(6))(2) [[12]aneN(3)=Me(3)[12]aneN(3), R=Me (9), Ph (10); [12]aneN(3)=Me(4)[12]aneN(3), R=Me (11), Ph (12)]. The molecular structures of complexes 2, 3 and 12 were established by single crystal X-ray diffraction studies. The eight-membered rings defined by the nickel atoms and the bridging ligands show distorted twist-boat, chair and boat-boat conformations in 2, 3 and 12, respectively. The experimental susceptibility data for compounds 2, 3 and 12 were fitted by least-squares methods to the analytical expression given by Ginsberg. The best fit was obtained with values of J=-0.11 cm(-1), D=-9.5 cm(-1) and g=2.20 for 2; J=-0.97 cm(-1), D=-9.3 cm(-1) and g=2.21 for 3; and J=-0.14 cm(-1), D=-11.9 cm(-1) and g=2.195 for 12. The magnetic-exchange pathways must involve the phosphate/phosphinate bridges, because these favour antiferromagnetic interactions. The observation of a higher exchange parameter for compound 3 is a consequence of a favourable disposition of the O-P-O bridges. The kinetics for the hydrolysis of TNP (tris(4-nitrophenyl)phosphate) with the dinuclear nickel(II) hydroxo complex [[Ni(Me(3)[12]aneN(3))(mu-OH)](2)](PF(6))(2) was studied by UV-visible spectroscopy. The proposed mechanism for TNP-promoted hydrolysis can be described as one-substrate/two-product, and can be fitted to a Michaelis-Menten equation.
authors.affiliation: Departamento de Química Inorgánica, Universidad de Murcia, 30071 Murcia, Spain.
authors.forename: M Dolores
authors.initials: MD
authors.lastname: Santana
authors.forename: Gabriel
authors.initials: G
authors.lastname: García
authors.forename: A Abel
authors.initials: AA
authors.lastname: Lozano
authors.forename: Gregorio
authors.initials: G
authors.lastname: López
authors.forename: José
authors.initials: J
authors.lastname: Tudela
authors.forename: José
authors.initials: J
authors.lastname: Pérez
authors.forename: Luis
authors.initials: L
authors.lastname: García
authors.forename: Luis
authors.initials: L
authors.lastname: Lezama
authors.forename: Teófilo
authors.initials: T
authors.lastname: Rojo
mesh_terms: D004952:Esters / Q000737:chemistry*; D006572:Heterocyclic Compounds, Bridged-Ring / Q000138:chemical synthesis / Q000737:chemistry; D007700:Kinetics; D008024:Ligands; D008280:Magnetics; D008956:Models, Chemical; D008968:Molecular Conformation; D009532:Nickel / Q000737:chemistry*; D009942:Organometallic Compounds / Q000138:chemical synthesis / Q000737:chemistry; D010720:Phosphines / Q000737:chemistry*
chemical_list: D004952:Esters; D006572:Heterocyclic Compounds, Bridged-Ring; D008024:Ligands; D009942:Organometallic Compounds; D010720:Phosphines; D009532:Nickel