On the Formation and the Structure of the First Bimetallic Borohydride Borate, LiCa3(BH4)(BO3)(2)

We present the first report on the formation and the crystal structure of a bimetallic borohydride borate, LiCa3(BH4)(BO3)(2). It is discovered during decomposition of LiBH4-Ca(BH4)(2)-carbon composite studied for hydrogen storage. A small amount of oxygen impurity in the starting material or introduced during sample preparation gives rise to the formation of [BO3](3-). Its crystal structure was solved from synchrotron powder diffraction data as space group Fd (3) over barm and a = 143911(2) angstrom at 387 degrees C. The experimental structural parameters are closely reproduced and the orientational disorder in [BH4](-) is confirmed by first-principles calculations.