The structural and vibrational properties of the isostructural compounds Ca₂FeH₆ and Sr₂RuH₆ are determined by periodic DFT calculations and compared with their previously published experimental crystal structures as well as new experimental vibrational data. The analysis of the vibrational data is extended to the whole series of alkaline-earth iron and ruthenium hydrides A₂TH₆ (A = Mg,Ca,Sr; T = Fe, Ru) in order to identify correlations between selected frequencies and the T-H bond length. The bulk moduli of Ca₂FeH₆ and Sr₂RuH₆ have also been determined within DFT. Their calculated values prove to compare well with the experimental values reported for Mg₂FeH₆ and several other compounds of this structure.

The effects of milling and doping NaAlH₄ with TiCl₃, TiF₃ and Ti(OBuⁿ)₄, and of cycling doped NaAlH₄ have been investigated by infrared (IR) and Raman spectroscopy and X-ray powder diffraction. Milling and doping produce similar effects. Both decrease the crystal domain size (~900 Å for milled and ~700 Å for doped, as compared to ~1600 Å for unmilled and undoped NaAlH₄) and increase anisotropic strain (by a factor >2.5, mainly along c). They also influence structure parameters such as the axial ratio c/a, cell volume and atomic displacement amplitudes. They show IR line shifts by ~15 cm^−1 to higher frequencies for the Al–H asymmetric stretching mode ν₃, and by ~20 cm^−1 to lower frequencies for one part of the H–Al–H asymmetric bending mode ν₄, thus suggesting structural changes in the local environment of the [AlH₄]^− units. The broad ν₃ bands become sharpened which suggests a more homogeneous local environment of the [AlH₄]^− units, and there appears a new vibration at 710 cm^−1. The Raman data show no such effects. Cycling leads to an increase in domain size (1200–1600 Å), IR line shifts similar to doped samples (except for TiF₃: downward shift by ~10 cm^−1) and a general broadening of the ν₃ mode that depend on the nature of the dopants. These observations support the idea that some Ti diffusion and substitution into the alanate lattice does occur, in particular during cycling, and that this provides the mechanism through which Ti-doping enhances kinetics during re-crystallisation.

Alkali borohydrides MBH₄ and their deuterides have been investigated by X-ray and neutron powder diffraction (M=K,Rb,Cs) and by infrared and Raman spectroscopy (M=Na,K,Rb,Cs). At room temperature the compounds crystallize with a cubic high temperature (HT) structure having Fm3m  symmetry in which the [BH₄]^− complexes are disordered. At low temperature (LT) the potassium compound transforms into a tetragonal low temperature structure having P4₂/n mc symmetry in which the [BH₄]^− complexes are ordered such as in the isotypic sodium congener. The B---H distances within the complex as measured on the deuteride at 1.5 K are 1.205(3) Å. Indications for a partial ordering in the rubidium and cesium compounds exist but are not sufficient for a full structural characterization. Infrared and Raman spectra at room temperature are fully assigned for both hydrides and deuterides, including the overtones and combination bands, the Fermi resonance type interactions and the ¹⁰B to ¹¹B splitting due to the presence of natural boron in the samples.

Raman spectra of the alkali borohydride series MBH₄ (M=Li, Na, K, Rb, Cs) have been measured as a function of temperature in the range 300–540 K. For the cubic modification of M=Na, K, Rb and Cs, the analysis of the Raman line widths suggests that the energy barrier of reorientation of the [BH₄]^− anions decreases as a function of cation size in the sequence Na: 12.1(5), K: 9.2(4), Rb: 8.8(3) and Cs: 8.2(4) kJ/mol. For the hexagonal high temperature modification of LiBH₄, the data suggest two energy barriers of reorientation at ~5 and ~ 60 kJ/mol, respectively.