Outer-sphere redox reactions of [CoIII(NH3)5(H x P y O z )](m? 3)? complexes. A temperature- and pressure-dependence kinetic study on the influence of the phosphorus oxoanions
作者:Manuel Martinez、Mari-Angel Pitarque、Rudi van Eldik
DOI:10.1039/dt9960002665
日期:——
Outer-sphere redox reactions between [CoIII(NH3)5(HxPyOz)](mâ 3)â(HxPyOzmâ= H2PO2â, H2PO3â, HPO32â, HP2O73â, P2O74â, γ-H2P3O103â, -HP3O104â, -P3O105â, β-H3P3O102â, -H2P3O103â, -HP3O104â or -P3O105â) and [Fe(CN)6]4â have been studied as a function of pH, HxPyOzmâ oxoanion, temperature and pressure. The effect of the oxidation state, size, geometry and extent of protonation of the HxPyOzmâ oxoanions on the precursor-complex formation constant, electron-transfer rate constant, and thermal and pressure activation parameters has been investigated. The values obtained indicate that all the precursor-complex formation equilibrium constants, KOS, are the same except for the non-linear β-H3P3O102â, -H2P3O103â, -HP3O104â and -P3O105â oxoanions, where the values are consistently larger, indicating that hydrogen bonding plays a very important role. The electron-transfer rate constant for a series of [Co(NH3)5(HxPyOz)](mâ 3)â, with linear oxoanions, increases on decreasing the negative charge on the complex k308= 0.73 à 10â3 and (8.5â11)à 10â3 sâ1 for the γ-[Co(NH3)5(P3O10)]2â and γ-[Co(NH3)5(H2P3O10)], respectively}. For the non-linear β-P3O105â oxoanions a threshold is observed when the external oxo groups are protonated k308= 20 à 10â3 for β-[Co(NH3)5(H3P3O10)]+ species and 0.84 à 10â3 sâ1 for β-[Co(NH3)5(H2P3O10)], -[Co(NH3)5(HP3O10)]â or -[Co(NH3)5(P3O10)]2â}. The ÎHâ¡ values are within the range expected, while those of ÎSâ¡ and ÎVâ¡ vary considerably with the extent of protonation of the phosphorus oxoanionic ligands, being 13 J Kâ1 molâ1 and + 36 cm3 molâ1 and 69 J Kâ1 molâ1 and + 13 cm3 molâ1, respectively for the [Co(NH3)5(HP2O7)]â[Co(NH3)5(P2O7)]â couple. The ÎVâ¡ values depend strongly on the oxo group distribution of the oxophosphorus ligand + 13 and + 32 cm3 molâ1 for β- and γ-[Co(NH3)5(P3O10)]2â, respectively}. Hydrogen bonding and solvent reorganization play a key role in the interpretation of the activation parameters.
外球红氧还原反应在 [CoIII(NH3)5(HxPyOz)](m−3)−(HxPyOzm−= H2PO2−, H2PO3−, HPO32−, HP2O73−, P2O74−, γ-H2P3O103−, −HP3O104−, −P3O105−, β-H3P3O102−, −H2P3O103−, −HP3O104− 或 −P3O105−)与 [Fe(CN)6]4− 之间已作为 pH,HxPyOzm− 氧阴离子,温度和压力的函数进行研究。研究了氧化态、大小、几何形状以及 HxPyOzm− 氧阴离子的质子化程度对前驱体-复合物形成常数、电子转移速率常数以及热和压力激活参数的影响。获得的数值表明,所有的前驱体-复合物形成平衡常数 KOS 除了非线性 β-H3P3O102−,−H2P3O103−,−HP3O104− 和 −P3O105− 氧阴离子外,其他都相同,其中的数值始终较大,表明氢键起到了非常重要的作用。对于一系列具有线性氧阴离子的 [Co(NH3)5(HxPyOz)](m−3)− 复合物,电子转移速率常数随着复合物负电荷的减少而增加 k308= 0.73 × 10−3 和 (8.5−11)× 10−3 s−1,分别对应 γ-[Co(NH3)5(P3O10)]2− 和 γ-[Co(NH3)5(H2P3O10)]}。对于非线性 β-P3O105− 氧阴离子,当外部氧基质子化时观察到一个阈值 k308= 20 × 10−3 对于 β-[Co(NH3)5(H3P3O10)]+ 物种,0.84 × 10−3 s−1 对于 β-[Co(NH3)5(H2P3O10)],−[Co(NH3)5(HP3O10)]− 或 −[Co(NH3)5(P3O10)]2−}。ΔH‡ 的数值在预期范围内,而 ΔS‡ 和 ΔV‡ 的数值随着磷氧阴离子配体的质子化程度变化显著,对于 [Co(NH3)5(HP2O7)]−[Co(NH3)5(P2O7)]− 伴侣分别为 13 J K−1 mol−1 和 + 36 cm3 mol−1,以及 69 J K−1 mol−1 和 + 13 cm3 mol−1。ΔV‡ 的值强烈依赖于氧基团在氧磷配体中的分布 β- 和 γ-[Co(NH3)5(P3O10)]2− 的值分别为 + 13 和 + 32 cm3 mol−1}。氢键和溶剂重排在激活参数的解释中起着关键作用。