Thermodynamic N-Donor trans Influence in Labile Pseudo-Octahedral Zinc Complexes: A Delusion?

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• 作者：Lilit Aboshyan-Sorgho ; Timoth茅e Lathion ; Laure Gu茅n茅e ; C茅line Besnard ; Claude Piguet
• 刊名：Inorganic Chemistry
• 出版年：2014
• 出版时间：December 15, 2014
• 年：2014
• 卷：53
• 期：24
• 页码：13093-13104
• 全文大小：754K
• ISSN：1520-510X

文摘

While the forces responsible for the chelate effect are well-established in coordination chemistry, the origin and implementation of the related thermodynamic trans influence remains debatable. This work illustrates a simple approach for quantifying this effect in labile pseudo-octahedral [Zn(Lk)₃]²⁺ complexes lacking stereochemical preferences (Lk = L1鈥?b>L4 are unsymmetrical didentate 伪,伪鈥?diimine ligands). In line with statistics, the triply degenerated meridional isomers mer-[Zn(Lk)₃]²⁺ are stabilized by 0.8 鈮?螖G_exch^mer鈫抐ac 鈮?4.2 kJ/mol over their nondegenerated facial analogues fac-[Zn(Lk)₃]²⁺ and therefore display no apparent trans influence at room temperature. However, the dissection of the free energy terms into opposite enthalpic (favoring the facial isomers) and entropic (favoring the meridional isomers) contributions reveals a trans influence assigned to solvation processes occurring in polar solvents. Altogether, the thermodynamic trans influence operating in [Zn(伪,伪鈥?diimine)₃]²⁺ complexes is 1鈥? orders of magnitude smaller than the chelate effect. A weak templating effect provided by a noncovalent lanthanide tripod is thus large enough to produce the wanted facial isomer at room temperature.