ISSN:
0749-1581
Schlagwort(e):
T1 method
;
Dihydrogen complexes
;
Dipole-dipole relaxation
;
Chemistry
;
Analytical Chemistry and Spectroscopy
Quelle:
Wiley InterScience Backfile Collection 1832-2000
Thema:
Chemie und Pharmazie
Notizen:
The unusual species [ReH5(H2){P(p-tolyl)3}2], for which a neutron diffraction study shows an intermediate H—H bond distance of 1.357 Å, is studied by variable-temperature 1H NMR spin-lattice (T1) relaxation time measurements. The T1 relaxation rate goes through a maximum at low temperature and the resulting T1 (min) value is 66 ms. This is within the range of T1(min) values found for classical ReH7L2 complexes, so H2 complexes with such long H—H bond distances are undetectable by the T1 method. The observed T1(min) value is compared with that calculated from the neutron diffraction data. We consider not only the usual proton-proton dipole-dipole (HHDD) contributions to the relaxation but also the metal-hydride dipole-dipole (MHDD) contributions. The latter are shown to be negligible for most transition metals, but not for Nb, V, Re, Mn, Co and Ta. Inclusion of the MHDD contributions leads to better agreement between the calculated and observed T1(min) values for a series of rhenium polyhydride complexes. The MHDD relaxation also accounts for most of the disparity previously noted between the calculated and observed T1(min) values for Re2H8(PEt2Ph)4.
Zusätzliches Material:
1 Ill.
Materialart:
Digitale Medien
URL:
http://dx.doi.org/10.1002/mrc.1260291317
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