Author:
Assi Zeina,Schneider Alexander Gareth,Ulpe Anna Christina,Bredow Thomas,Rüscher Claus Henning
Abstract
The B–H bond length of the borohydride anion (BH4−) in alkali metal borohydrides MBH4 with M = Na, K, Rb, Cs, and diluted in different alkali halide matrices, was investigated experimentally by infrared spectroscopy (FTIR) and theoretically using first principles calculations. The peak positions in IR absorption spectra of NaBH4 pressed at 754 MPa in halides NaX and KX with X = Cl, Br, I show significant variations indicating ion exchange effects between the halide and NaBH4. For NaBH4 in NaBr, NaI, KBr and KI pellets, the peak positions indicate that BH4− could be highly diluted in the AX matrix, which renders an isolation of BH4− in AX (i-BH4−). For NaBH4 in NaCl and KCl pellets, a solution of BH4− in AX occurred only after a further thermal treatment up to 450 °C. The observed peak positions are discussed with respect to the lattice parameter (a0), anion to cation ratio (R = rA/rX), standard enthalpy of formation (ΔfH) and ionic character (Ic) of the halides. A linear relation is obtained between ν3(i-BH4−) and the short-range lattice energies of AX. Density functional theory (DFT) calculations at generalized gradient approximation (GGA) level were used to calculate the IR vibrational frequencies ν4, ν3 and ν2 + ν4 for series of compositions Na(BH4)0.25X0.75 with X = Cl, Br, I, and MBH4. The theoretical and experimental results show the same trends, indicating the rigidity of the B–H bond length and the failure of Badger’s rule.
Subject
Inorganic Chemistry,Condensed Matter Physics,General Materials Science,General Chemical Engineering
Cited by
1 articles.
订阅此论文施引文献
订阅此论文施引文献,注册后可以免费订阅5篇论文的施引文献,订阅后可以查看论文全部施引文献