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1 H NMR T 1 (min) data and structure in a series of rhenium polyhydride complexes and the contribution of M‐H dipole–dipole relaxation
Author(s) -
Luo XiaoLiang,
Howard Judith A. K.,
Crabtree Robert H.
Publication year - 1991
Publication title -
magnetic resonance in chemistry
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.483
H-Index - 72
eISSN - 1097-458X
pISSN - 0749-1581
DOI - 10.1002/mrc.1260291317
Subject(s) - chemistry , dipole , rhenium , neutron diffraction , relaxation (psychology) , proton , crystallography , hydride , spin–lattice relaxation , bond length , diffraction , analytical chemistry (journal) , atomic physics , nuclear magnetic resonance , metal , crystal structure , nuclear physics , inorganic chemistry , physics , social psychology , psychology , organic chemistry , optics , chromatography
The unusual species [ReH 5 (H 2 ){P( p ‐tolyl) 3 } 2 ], for which a neutron diffraction study shows an intermediate HH bond distance of 1.357 Å, is studied by variable‐temperature 1 H NMR spin‐lattice ( T 1 ) relaxation time measurements. The T 1 relaxation rate goes through a maximum at low temperature and the resulting T 1 (min) value is 66 ms. This is within the range of T 1 (min) values found for classical ReH 7 L 2 complexes, so H 2 complexes with such long HH bond distances are undetectable by the T 1 method. The observed T 1 (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 T 1 (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 T 1 (min) values for Re 2 H 8 (PEt 2 Ph) 4 .