Scalar and dipolar contributions of rhenium to the relaxation properties of coordinated ligands

The longitudinal relaxation times (T1) of the hydridic ligands and of P-31 in [HRe(CO)4PPh3] (1), [HRe(CO)5] (2), and [Re2-(mu-H)2(CO)8] (3) have been measured as a function of the temperature and of the applied magnetic field. In 1 the relaxation of P-31 is dominated by the scalar interactions with...

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Bibliographic Details
Published in:Inorganic chemistry 1992-03, Vol.31 (5), p.848-852
Main Authors: Beringhelli, T, D'Alfonso, G, Freni, M, Minoja, A. P
Format: Article
Language:English
Subjects:
Chemistry
Chemistry, Inorganic & Nuclear
Condensed matter: electronic structure, electrical, magnetic, and optical properties
Exact sciences and technology
Magnetic resonances and relaxations in condensed matter, mössbauer effect
Nuclear magnetic resonance and relaxation
Physical Sciences
Physics
Relaxation effects
Science & Technology
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Summary:The longitudinal relaxation times (T1) of the hydridic ligands and of P-31 in [HRe(CO)4PPh3] (1), [HRe(CO)5] (2), and [Re2-(mu-H)2(CO)8] (3) have been measured as a function of the temperature and of the applied magnetic field. In 1 the relaxation of P-31 is dominated by the scalar interactions with the quadrupolar isotopes of rhenium up to 7 T. The field dependence of the relaxation rate of phosphorus has allowed the calculation of the coupling constant 1J(Re-P) (1260 +/- 20 Hz) and of the Re relaxation time (22 +/- 1 ns). For the hydridic ligand, dipolar interactions with rhenium account for more than 60% of the observed relaxation rate. 1J(H-Re) for 1 has been estimated as 440 Hz. The relaxation of the classical hydrides in 2 and 3 is completely determined by dipolar interactions with rhenium. 1J(H-Re) for 2 has been determined to be 385 Hz. The length of the Re-H bond (189 +/- 1 pm) in 3 has been calculated from the fitting of the temperature dependence of H-1 relaxation. Anisotropic reorientation was observed for compound 1. The relevance of the H-Re dipolar interaction in classical rhenium polyhydrides is discussed.
ISSN:0020-1669
1520-510X
DOI:10.1021/ic00031a029