Experimental and computational studies on solvent-free rare-earth metal borohydrides R(BH4)3 (R = Y, Dy, and Gd)

Solvent-free trivalent rare-earth metal borohydrides R(BH4)(3) (R= Y, Dy, and Gd) were synthesized from RCl3 and LiBH4 through solid-state metathesis reactions and characterized by powder x-ray or neutron diffraction measurement and Raman spectroscopy combined with first-principles calculations. The crystal structure of R(BH4)(3) was clarified to adopt a primitive cubic structure with Y(BH4)(3): a = 10.852(1) angstrom, Dy(BH4)(3): a=10.885(3) angstrom, and Gd(BH4)(3): a = 10.983(5) angstrom in space group Pa (3) over bar (No. 205), the [BH4](-) complex anions of which locate on the edges of a distorted cube composed of R3+. Based on the crystal structure, the observed Raman scattering positions are theoretically assigned such that the BH4 bending is at 1050-1300 cm(-1) and BH4 stretching is at 2250-2400 cm(-1), respectively. In addition, the computational studies on Y(BH4)(3) suggested it to be an insulator that occupied B 2s, 2p and H 1s orbitals with little contribution from Y, and the heat of formation was Delta H = -113 kJ/mol BH4, which was estimated from (1/3) Y+ B + 2H(2) -> (1/3)Y(BH4)(3).