Nitrogen-14 NMR Study on Solvent Exchange of the Octahedral Cobalt(II) Ion in Neat 1,3-Propanediamine and n-Propylamine at Various Temperatures and Pressures. Tetrahedral-Octahedral Equilibrium
详细信息 查看全文
- 作者：Sen-ichi Aizawa ; Shigeo Iida ; Kayoko Matsuda ; and Shigenobu Funahashi
- 刊名：Inorganic Chemistry
- 出版年：1996
- 出版时间：February 28, 1996
- 年：1996
- 卷：35
- 期：5
- 页码：1338 - 1342
- 全文大小：277K
- 年卷期：v.35,no.5(February 28, 1996)
- ISSN：1520-510X
文摘
Solvated cobalt(II) ions in neat 1,3-propanediamine (tn) andn-propylamine (pa) have been characterized byelectronic absorption spectroscopy and extended X-ray absorption finestructure (EXAFS) spectroscopy. Theequilibrium between tetrahedral and octahedral geometry forcobalt(II) ion has been observed in a neat pasolution,but not in neat diamine solutions such as tn and ethylenediamine (en).The thermodynamic parameters andequilibrium constant at 298 K for the geometrical equilibrium in pawere determined to be 
H
= -36.1 ±2.3kJ mol-1, S = -163 ± 8 Jmol-1 K-1, and K298= 6.0 × 10-3 M-2, where K=[Co(pa)62+]/{[Co(pa)42+][pa]2}.The equilibrium is caused by the large entropy gain in formationof the tetrahedral cobalt(II) species. Thesolventexchange of cobalt(II) ion with octahedral geometry in tn and pasolutions has been studied by the 14N NMRline-broadening method. The activation parameters and rateconstants at 298 K for the solvent exchange reactionsare as follows: H
= 49.3 ± 0.9 kJmol-1, S = 25 ± 3 Jmol-1 K-1, V= 6.6 ± 0.3 cm3 mol-1 at302.1K, and k298 = 2.9 × 105s-1 for the tn exchange, andH = 36.2 ± 1.2 kJ mol-1,S = 35 ± 6 J mol-1K-1,and k298 = 2.0 × 108s-1 for the pa exchange. By comparison of theactivation parameters with those for the enexchange of cobalt(II) ion, it has been confirmed that the kineticchelate strain effect is attributed to the largeactivation enthalpy for the bidentate chelate opening and that theenthalpic effect is smaller in the case of thesix-membered tn chelate compared with the five-membered enchelate.
H = -36.1 ±2.3kJ mol-1, S = -163 ± 8 Jmol-1 K-1, and K298= 6.0 × 10-3 M-2, where K=[Co(pa)62+]/{[Co(pa)42+][pa]2}.The equilibrium is caused by the large entropy gain in formationof the tetrahedral cobalt(II) species. Thesolventexchange of cobalt(II) ion with octahedral geometry in tn and pasolutions has been studied by the 14N NMRline-broadening method. The activation parameters and rateconstants at 298 K for the solvent exchange reactionsare as follows: H = 49.3 ± 0.9 kJmol-1, S = 25 ± 3 Jmol-1 K-1, V= 6.6 ± 0.3 cm3 mol-1 at302.1K, and k298 = 2.9 × 105s-1 for the tn exchange, andH = 36.2 ± 1.2 kJ mol-1,S = 35 ± 6 J mol-1K-1,and k298 = 2.0 × 108s-1 for the pa exchange. By comparison of theactivation parameters with those for the enexchange of cobalt(II) ion, it has been confirmed that the kineticchelate strain effect is attributed to the largeactivation enthalpy for the bidentate chelate opening and that theenthalpic effect is smaller in the case of thesix-membered tn chelate compared with the five-membered enchelate.