Solvation and halogeno complexation of the manganese(II) ion in N-methyl-2-pyrolidone
Solvation and halogeno complexation of the manganese(II) ion in N-methyl-2-pyrolidone
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DOI：
10.1016/j.molliq.2004.10.028
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发表时间：
2005-05
影响因子：
6
通讯作者：
Yue Zhang;Natsumi Watanabe;Y. Umebayashi;S. Ishiguro
中科院分区：
文献类型：
--
作者：
Yue Zhang;Natsumi Watanabe;Y. Umebayashi;S. Ishiguro
在298K下，用滴定量热法研究了N-甲基-2-吡咯烷酮(N-甲基-2-吡咯烷酮)中锰(II)离子与氯离子和溴离子的络合作用。结果表明，在N-甲基-2-吡咯烷酮(N-甲基-2-吡咯烷酮)中，锰(II)离子形成一系列单核MnCln(2−n)+(n=1-4)和MnBrn(2−n)+(n=1-3)络合物，并求出它们的生成常数、生成热和络合熵。NMP与金属离子的络合作用明显弱于N，N-二甲基丙酰胺(DMPA)，而与N，N-二甲基乙酰胺(DMA)的络合程度几乎相同，但它们与金属离子的配位能力基本相同。这表明与金属离子配位的溶剂分子之间的空间相互作用在NMP中明显弱于DMPA，而在NMP和DMA中几乎相同。锰(II)离子在DMPA中为5-溶剂化，在DMA中为6-溶剂化。在NMP中的络合行为表明，与在DMA中一样，锰(II)离子在NMP中是六元溶剂化的。由于NMP是相对于丙酰基CH3CH2(CO)-的DMPA的平面反式类似物，平面反式DMPA的金属离子周围的溶剂化空间效应的大小可能与DMA的相似。因此，金属离子在非质子酰胺溶剂中的局部构象，特别是配位的羰基氧原子附近的构象对金属离子的溶剂化空间效应起着决定性的作用。
Chloro and bromo complexation of the manganese(II) ion has been studied in N-methyl-2-pyrolidone (NMP) by titration calorimetry at 298 K. It is found that the manganese(II) ion forms a series of mononuclear MnCln(2−n)+(n=1–4) and MnBrn(2−n)+(n=1–3) complexes in NMP, and their formation constants, enthalpies and entropies have been obtained. The complexation in NMP is significantly weaker than that in N,N-dimethylpropionamide (DMPA), while it is almost to the same extent as that in N,N-dimethylacetamide (DMA), despite that these solvents coordinate to the metal ion through the carbonyl oxygen atom, and their electron-pair donating abilities are similar. This indicates that steric interaction among solvent molecules coordinated to the metal ion is significantly weaker in NMP than that in DMPA, while it is almost to the same extent in NMP and DMA. The manganese(II) ion is five-solvated in DMPA, and six-solvated in DMA. The complexation behavior in NMP implies that the manganese(II) ion is six-solvated in NMP, like in DMA. As NMP is a planar trans analogue of DMPA with respect to the propionyl group CH3CH2(CO)–, the magnitude of solvation steric effect around the metal ion for the planar trans DMPA may be similar to that for DMA. It is thus concluded that the local conformation, particularly around the coordinating carbonyl oxygen atom, plays a decisive role in the solvation steric effect of the metal ion in aprotic amide solvents.