Force constants metal hydride

Fragmentation patterns for these complex hydrides involve loss of H and CO. A more detailed report on HMn(CO)5 (91) shows that pairs of peaks, separated by one mass unit, are seen, corresponding to HMn(CO)+ and Mn(CO)+ (n = 0-5), as well as the doubly charged ions HMn(CO) + and Mn(CO) j+ (w=l-3). The appearance of the peak at m/e 56 (MnH+) is evidence for the existence of a Mn-H bond in the carbonyl hydride. From infrared data, the Mn-H and metal-CO stretching force constants are 1.9 and 2.0-2.7 mdynes/A, respectively, and the relative abundances of ions formed by loss of H and CO from the parent ion are in agreement with these values. 

The rate of proton transfer has been measured for a number of metal hydride/organic amine combinations. The rates appear to follow Marcus behavior see Marcus Treatment), in which the rate goes up with driving force (equation 21, where ab is the rate of proton transfer between AH and B , and Kxr is the equilibrium constant for the proton transfer). Proton transfer appears to be the slow step in the process, rather than slow electron transfer followed by fast H atom transfer, because the rates show an isotope effect. For example, in the self-exchange of [CpM(H,D)(CO)3]/[CpM(CO)3] , kn/ko is 3.6, 3.7, and 3.7 for Cr, Mo, and W. There seems to be a good relation between thermodynamic acidity and kinetic... 

Fig. 6.21 The dispersion curves of PdDo.63 the dashed lines show the dispersion curves of pure palladium. Notice how hydriding the metal has reduced the metal-metal force constants. Reproduced from [58] with permission from the American Physical Society.

Table 6.1. Gaseous heteronuclear diatomic molecules AB(g) hydrogen halides HX interhalogen compounds XK alkali metal hydrides MH, and inter-alkali-metal compounds MM. Electric dipole moments, ionic characters, qjc equilibrium bond distances. Re, vibrational wavenumbers, < dissociation energies at zero K, Dq rednced masses of the predominant isotopomers, /tm and force constants,. ...

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