Magnetic nuclei hydrides

Boron s electron deficiency does not permit conventional two-electron bonds. Boron can form multicenter bonds. Thus the boron hydrides have stmctures quite unlike hydrocarbons. The B nucleus, which has a spin of 3/2, which has been employed in boron nuclear magnetic resonance spectroscopy. 

Boron compounds contain two isotopes B10 and B11 of natural abundances 19% and 81%, respectively. Although both these isotopes possess magnetic moments, the Bn nucleus is better suited to the high resolution experiment because of its (1) greater natural abundance, (2) smaller quadrupole moment, and (3) larger nuclear moment. Because of the broad range of structures possible in boron compounds, particularly the hydrides, there has been considerable NMR work done in this field to confirm previously proposed structures and in a few cases to first establish geometry of a compound. The B11 spectra of tetraborane and a tetraborane derivative arc considered below. 

Bulky H should not diffuse or show marked oscillational movement as indicated by magnetic resonance studies. The hydridic model actually provides a reasonable explanation for the mean amplitude of H vibrations (ca. 0.2 A.) and is noncommittal about diffusion. Conceivably, the barrier to diffusion comprising an Is2- configuration about the proton is in effect lowered by the distance of the barrier from the mean position of the nucleus. If the movement of hydrogen is quasitautomeric—for example, in keto-enol tautomerism—one may consider that it moves from one potential well to another as a proton. 

Proton magnetic resonance studies have also shown the presence of metal-hydrogen species in cyanide solutions of rhodium, platinum, and iridium (Table IX). In particular, the addition of CN- to a boiled aqueous solution of rhodium trichloride, followed by reduction with sodium boro-hydride, yields a solution that contains an Rh—H complex in moderately high concentrations and is stable in the absence of oxygen for several years (108). The observed coupling of the proton with the Rh10 nucleus (spin ) confirms the presence of an Rh—H bond (108). 

The spectroscopy of multinuclear magnetic resonance in solution is one of the most important analytical methods in structural studies of transition metal hydride complexes. Among different nuclei, the proton plays the main role because H NMR provides a direct information about spectral properties of the hydride ligands. In addition the proton, being a non-quadrupolar and long-relaxing nucleus, gives rise to well-resolved NMR spectra which are very... 

The exact relativistic theory of magnetic shielding in one-electron atoms has been extended by Pyper and Pyper and Zhang to deal with a point charge dipole model of the nucleus. Relativistic calculations of the rotational g-factor of the hydrogen halides and noble gas hydride cations have been carried out by Enevoldsen et al. ... 

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