LIGAND SOLVATION AND MACROCYCLIC EFFECT - STUDY OF NICKEL(II)-TETRAMINE COMPLEXES
LIGAND SOLVATION AND MACROCYCLIC EFFECT - STUDY OF NICKEL(II)-TETRAMINE COMPLEXES
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DOI：
10.1021/ic50142a032
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发表时间：
1974-01-01
影响因子：
4.6
通讯作者：
MARGERUM, DW
中科院分区：
文献类型：
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作者：
HINZ, FP;MARGERUM, DW
含5，6，5，6元螯合环的环状毒鼠强-镍络合物的稳定常数比相应的含5，6，5元螯合环的开链毒鼠强络合物的稳定常数大106倍以上。当二至六个甲基取代基被放置在大环配合物六元螯合环的碳原子上时，稳定常数减小2至104倍。环状和开链配体的稳定性增强(大环状效应)几乎完全是由于更有利的氢化作用，但镍-胺键强度没有显著差异。焓的差异是由于大环的配体溶剂化作用减少，在络合物形成中被取代的胺-氢键水较少。构建在大环配体中的更有利的构型熵往往被从溶解的配体释放的较少的水所抵消。这种类型的配体溶剂化效应对于任何可能发生强溶剂化并且施主基团被迫彼此靠近的系统都将是重要的。
The stability constant for the cyclic tetramine-nickel complex with 5, 6, 5, 6-membered chelate rings is more than 106-fold greater than the constant for the corresponding open-chain tetramine complex with 5, 6, 5-membered chelate rings. As two to six methyl substituents are placed on carbon atoms in the six-membered chelate rings of the macrocyclic complexes, the stability constants decrease by factors of 2 to 104. The enhanced stability with the cyclic vs. open-chain ligand (the mac-rocyclic effect) is almost entirely due to more favorable AH, but the nickel-amine bond strengths are not significantly dif-ferent. The enthalpic differences are attributable to the decreased ligandsolvation of the macrocycle which has less amine-hydrogen-bonded water to be displaced in complex formation. The more favorable configurational entropy built into the macrocyclic ligandtends to be offset by less water being released from thesolvated ligand. This typeof ligand solvation effect will be important for any system where strong solvation is possible and the donor groups are forced to be close to one another.