Lanthanide monohydrides

Lanthanide monohydride complexes, such as bi(cyclopentadienyl) lanthanide hydrides, can be conveniently prepared by the reactions of lanthanide mono-alkyl or -aryl complexes with organosilanes under mild reaction conditions (Figure 8.27) [82]. 

Fig, 7. Linear behavior of the binding energies of the lanthanide monohydrides for fixed 4f occupation number. Data taken from Dolg and Stoll (1989). 

Fig. 8. Binding energies for the two low-lying superconfigurations (SC) (I, 4f o2o II, 4f"+ o2o ) of the lanthanide monohydrides. Extrapolated theoretical values for pseudopotential configuration interaction calculations based on the b, e entries in table 15.

Binding eneigies bond lengths R, vibrational frequencies and dipole moments for the ground states of selected lanthanide monohydrides from relativistically corrected density-functional studies in comparison... 

Magnesium—nickel hydride, 4458 Plutonium(III) hydride, 4504 Poly(germanium dihydride), 4409 Poly(germanium monohydride), 4407 Potassium hydride, 4421 Rubidium hydride, 4444 Sodium hydride, 4438 f Stibine, 4505 Thorium dihydride, 4483 Thorium hydride, 4535 Titanium dihydride, 4484 Titanium—zirconium hydride, 4485 Trigermane, 4415 Uranium(III) hydride, 4506 Uranium(IV) hydride, 4536 Zinc hydride, 4486 Zirconium hydride , 4487 See COMPLEX HYDRIDES, PYROPHORIC MATERIALS See entry LANTHANIDE—TRANSITION METAL ALLOY HYDRIDES... 

Pyykko (1979b) used the Dirac-Hartree-Fock one-centre expansion method for the monohydrides to calculate relativistic values for the lanthanide and actinide contraction, i.e. 0.209 A for LaH to LuH and 0.330A for AcH to LrH. The corresponding nonrelativistic value derived from Hartree-Fock one-center expansions for LaH and LuH is 0.191 A, i.e., for this case 9.4% of the lanthanide contraction is due to relativistic effects. The experimental value of 0.179 A would suggest a correlation contribution of-14.4% to the lanthanide contraction if one assumes that the relativistic theoretical values are close to the Dirac-Hartree-Fock limit, which is certainly not true for the absolute values of the bond lengths themselves. Moreover, it is well known that for heavy elements relativistic and correlation contributions are not exactly additive. Corresponding nonrelativistic calculations for AcH and LrH have not been performed and experimental data are not available to determine relativistic and electron correlation effects for the actinide contraction. Table 8 summarizes values for the lanthanide and actinide contraction derived from theoretical or experimental molecular bond lengths. It is evident from Ihese results... 

Very little experimental information is available for the monohydrides of the lanthanide elements. Their ground state configuration may be assumed to correspond to one of the following two superconfigurations (SC) ... 

The main difficulty here is to clearly separate effects that can hardly be separated, namely relativistic and electron-correlation effects. Nevertheless, pioneering studies of this effect date back to the mid 1970s [1140]. Four-component methods have been employed to determine the contribution which is solely due to relativity [1141]. The four-component approach, for which Dirac-Hartree-Fock and — to also account for correlation effects — relativistic MP2 calculations have been utilized, confirms results first obtained with relativistic effective core potential methods [1142,1143]. It has been found [1141] that between 10% and 30% of the lanthanide contraction and 40% to 50% of the actinide contraction are caused by relativity in monohydrides, trihydrides, and monofluorides of La, Lu and Ac, Lr, respectively. 

A study of the monohydrides, monoxides, and monofluorides of lanthanides and actinides using ab initio all-electron and pseudopotential techniques is also available. The spectroscopic constants of low-lying electronic states of ThO " ... 

---