Chloride substitution induced by mechano-chemical reactions between NaBH4 and transition metal chlorides

Cl- to BH4- ion substitution was induced in NaBH4 through mechano-chemical reactions with all the first period transition metal chlorides and CdCl2. The products were identified by Rietveld refinement of powder X-ray and neutron diffraction data to be mainly Na(BH4)(1-x)Cl-x. These possess cubic NaCl-type structures, with unit cell parameters between 5.7801(3) and 5.6576(2) angstrom, and compositions ranging from x = 0.69 (with Cu) to 0.92 (with Zn). Infrared spectroscopy of selected samples confirms the substitution through a shift of the vibrational modes of the BH4- group towards higher wavenumbers. An observed shape change of the vibrational features from Lorentzian to Gaussian is related to the presence of the transition metal. There is no correlation between x and the thermal behavior of the samples. The lowest decomposition temperature is found for the Zn containing sample (103 degrees C), while Cd leads to the highest value (521 degrees C). Their behavior is related to the presence of NaZn(BH4)(3) and metallic Cd in the samples, respectively. (C) 2011 Elsevier B. V. All rights reserved.