title: Spectroscopic properties, catalytic activities and mechanism studies of [(TpPh)Co(X)(CH3OH)m] . nCH3OH: bicarbonate dehydration in the presence of inhibitors.
abstract: Two inhibitor-containing 'half-sandwich' cobalt(II) complexes [(TpPh)Co(X)(CH3OH)m] x nCH3OH ((TpPh) = hydrotris (3-phenylpyrazolyl)borate; 1: X- = N3-, m = 1, n = 2; 2: X- = NCS-, m = 0, n = 0) have been synthesized and used as the catalysts in the bicarbonate dehydration reaction. The structures of 1 and 2 were determined by X-ray diffraction analysis, which shows that N3- and NCS- coordinate to the Co(II) ions of 1 and 2, respectively, with the Co-N bond lengths of 1.992(6) A and 1.901(3) A. The coordination geometries of the Co(II) complexes in solution are five-coordinated trigonal bipyramid as revealed by the spectroscopic measurements. The dehydration kinetic measurements of HCO3- are performed by the stopped-flow techniques at pH < 7.9. The apparent dehydration rate constant k(obs) varies linearly with Co(II) complex and H+ concentrations, respectively, and the catalytic activity of 2 is lower than that of 1. The aqua Co(II) complex must be the reactive catalytic species in the catalyzed dehydration reaction and the rate-determining step is the substitution of the labile water molecule by HCO3-. The k(obs) values increase with increasing reaction temperature, and the large negative entropy of activation also indicates the associative activation mode. The inhibition ability of NCS- is stronger than that of N3-, which can be rationalized by the decreases in the Co-N(N3-/NCS-) bond lengths and effective atomic charges of the Co(II) ions based on the X-ray crystallographic data and theoretical calculations in this work.
authors.affiliation: Department of Chemistry, Nankai University, Tianjin 300071, PR China.
authors.forename: Ying-Ji
authors.initials: YJ
authors.lastname: Sun
authors.forename: Lei Z
authors.initials: LZ
authors.lastname: Zhang
authors.forename: Peng
authors.initials: P
authors.lastname: Cheng
authors.forename: Hua-Kuan
authors.initials: HK
authors.lastname: Lin
authors.forename: Shi-Ping
authors.initials: SP
authors.lastname: Yan
authors.forename: Dai-Zheng
authors.initials: DZ
authors.lastname: Liao
authors.forename: Zong-Hui
authors.initials: ZH
authors.lastname: Jiang
authors.forename: Pan-Wen
authors.initials: PW
authors.lastname: Shen
mesh_terms: D001386:Azides / Q000737:chemistry; D001639:Bicarbonates / Q000737:chemistry*; D001665:Binding Sites; D001881:Borates / Q000737:chemistry; D002245:Carbon Dioxide / Q000737:chemistry*; D002257:Carbonic Anhydrase Inhibitors; D002256:Carbonic Anhydrases; D002384:Catalysis; D003035:Cobalt / Q000737:chemistry; D018360:Crystallography, X-Ray; D007700:Kinetics; D008968:Molecular Conformation; D009942:Organometallic Compounds / Q000138:chemical synthesis / Q000737:chemistry*; D013055:Spectrophotometry, Infrared; D013056:Spectrophotometry, Ultraviolet; D013861:Thiocyanates / Q000737:chemistry; D014867:Water / Q000737:chemistry*
chemical_list: D001386:Azides; D001639:Bicarbonates; D001881:Borates; D002257:Carbonic Anhydrase Inhibitors; D009942:Organometallic Compounds; D013861:Thiocyanates; D014867:Water; D002245:Carbon Dioxide; D003035:Cobalt; D002256:Carbonic Anhydrases; C031760:thiocyanate