Spin-Orbit-Induced Anomalous pH-Dependence in 1H NMR Spectra of CoIII Amine Complexes: A Diagnostic Tool for Structure Elucidation
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- 作者：Kaspar Hegetschweiler ; Dirk Kuppert ; Jochen Huppert ; Michal Straka ; and Martin Kaupp
- 刊名：Journal of the American Chemical Society
- 出版年：2004
- 出版时间：June 2, 2004
- 年：2004
- 卷：126
- 期：21
- 页码：6728 - 6738
- 全文大小：325K
- 年卷期：v.126,no.21(June 2, 2004)
- ISSN：1520-5126
文摘
The pH-dependent 1H NMR characteristics of a series of CoIII-(polyamin)-aqua andCoIII-(polyamin)-(polyalcohol) complexes, [Co(tach)(ino-
3-O1,3,5)]3+ (13+), [Co(tach)(ino-3-
1,2,6)]3+ (23+),[Co(tach)(taci--
1-2-O2,6)]3+ (33+), [Co(ditame)(H2O)]3+ (43+), and [Co(tren)(H2O)2]3+ (53+), were studiedin D2O by means of titration experiments (tach = all-cis-cyclohexane-1,3,5-triamine, ino = cis-inositol, taci= 1,3,5-triamino-1,3,5-trideoxy-cis-inositol, tren = tris(2-aminoethyl)amine, ditame = 2,2,6,6-tetrakis-(aminomethyl)-4-aza-heptane). A characteristic shift was observed for H(-C) hydrogen atoms in the
-position of a coordinated amino group upon deprotonation of a coordinated oxygen donor. For a cis-H-C-N-Co-O-H arrangement, deprotonation of the oxygen donor resulted in an additional shielding(shift to lower frequency) of the H(-C) proton, whereas for a trans-H-C-N-Co-O-H arrangement,deprotonation resulted in a deshielding (shift to higher frequency). The effect appears to be of rather generalnature: it is observed for primary (13+-53+), secondary (43+), and tertiary (53+) amino groups, and for thedeprotonation of an alcohol (13+-33+) or a water (43+, 53+) ligand. Spin-orbit-corrected density functionalcalculations show that the high-frequency deprotonation shift for the trans-position is largely caused by adifferential cobalt-centered spin-orbit effect on the hydrogen nuclear shielding. This effect is conformationdependent due to a Karplus-type behavior of the spin-orbit-induced Fermi-contact shift and thus onlysignificant for an approximately antiperiplanar H-C-N-Co arrangement. The differential spin-orbitcontribution to the deprotonation shift in the trans-position arises from the much larger spin-orbit shift forthe protonated than for the deprotonated state. This is in turn due to a trans-effect of the deprotonated(hydroxo or alkoxo) ligand, which weakens the trans Co-N bond and thereby interrupts the Fermi-contactmechanism for transfer of the spin-orbit-induced spin polarization to the hydrogen nucleus in question.The unexpectedly large long-range spin-orbit effects found here for 3d metal complexes are traced backto small energy denominators in the perturbation theoretical expressions of the spin-orbit shifts.
3-O1,3,5)]3+ (13+), [Co(tach)(ino-3-1,2,6)]3+ (23+),[Co(tach)(taci--1-2-O2,6)]3+ (33+), [Co(ditame)(H2O)]3+ (43+), and [Co(tren)(H2O)2]3+ (53+), were studiedin D2O by means of titration experiments (tach = all-cis-cyclohexane-1,3,5-triamine, ino = cis-inositol, taci= 1,3,5-triamino-1,3,5-trideoxy-cis-inositol, tren = tris(2-aminoethyl)amine, ditame = 2,2,6,6-tetrakis-(aminomethyl)-4-aza-heptane). A characteristic shift was observed for H(-C) hydrogen atoms in the-position of a coordinated amino group upon deprotonation of a coordinated oxygen donor. For a cis-H-C-N-Co-O-H arrangement, deprotonation of the oxygen donor resulted in an additional shielding(shift to lower frequency) of the H(-C) proton, whereas for a trans-H-C-N-Co-O-H arrangement,deprotonation resulted in a deshielding (shift to higher frequency). The effect appears to be of rather generalnature: it is observed for primary (13+-53+), secondary (43+), and tertiary (53+) amino groups, and for thedeprotonation of an alcohol (13+-33+) or a water (43+, 53+) ligand. Spin-orbit-corrected density functionalcalculations show that the high-frequency deprotonation shift for the trans-position is largely caused by adifferential cobalt-centered spin-orbit effect on the hydrogen nuclear shielding. This effect is conformationdependent due to a Karplus-type behavior of the spin-orbit-induced Fermi-contact shift and thus onlysignificant for an approximately antiperiplanar H-C-N-Co arrangement. The differential spin-orbitcontribution to the deprotonation shift in the trans-position arises from the much larger spin-orbit shift forthe protonated than for the deprotonated state. This is in turn due to a trans-effect of the deprotonated(hydroxo or alkoxo) ligand, which weakens the trans Co-N bond and thereby interrupts the Fermi-contactmechanism for transfer of the spin-orbit-induced spin polarization to the hydrogen nucleus in question.The unexpectedly large long-range spin-orbit effects found here for 3d metal complexes are traced backto small energy denominators in the perturbation theoretical expressions of the spin-orbit shifts.