Kinetics of complexation of Ni2+ in hydrogen bonded solvents: nickel malonate in water-glycerine solutions

Advances in Molecular Relaxation and Interaction Processes Pub Date : 1982-07-01 DOI:10.1016/0378-4487(82)80028-9

Warren Hirsch , Sergio Petrucci

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Abstract

The kinetics of complexation at 25°C of nickel malonate in water-glycerine mixtures has been studied by the pressure-jump relaxation technique. For the water-glycerine mixtures, the ratio k_f/K_F, (namely the ratio between the forward rate constant k_f and the pre-equilibration constant for the bimolecular diffusion step K_F), shows a decrease within a factor of two from pure water to 49% glycerine in water. This decrease, if significant, is at variance with the apparently random scatter of the same data for water-fructose mixtures. In order to decide whether these changes in k_f/K_F reflect solvation of nickel ion, or modification of the chelation mechanism, the complexation of Ni(NCS)₂ at 10°C in the same solvent of composition 49% glycerine has been studied. It is proposed that the changes in k_f/K_F, may be caused by the changes in the K_F with solvent composition, namely with changes in the ion-pair distance rather than with changes in the reaction mechanism. This is reflected in the constancy of the k_f's with solvent composition.

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氢键溶剂中Ni2+络合动力学:丙二酸镍在水-甘油溶液中

用压力跳变弛豫技术研究了丙二酸镍在水-甘油混合物中25℃时的络合动力学。对于水-甘油混合物，比率kf/ kf(即正向速率常数kf与双分子扩散步骤kf的预平衡常数之间的比率)显示，从纯水到水中甘油含量为49%，减少了两倍。这种减少，如果有意义的话，与水-果糖混合物的相同数据的明显随机分散不同。为了确定这些kf/ kf的变化是反映了镍离子的溶剂化，还是反映了螯合机制的改变，我们研究了Ni(NCS)2在相同溶剂49%甘油中的10°C络合。提出kf/ kf的变化可能是由于kf随溶剂组成的变化引起的，即离子对距离的变化而不是反应机理的变化。这反映在kf随溶剂组成的常数上。

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Advances in Molecular Relaxation and Interaction Processes

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