Details
| Original language | English |
|---|---|
| Article number | 510 |
| Journal | CRYSTALS |
| Volume | 12 |
| Issue number | 4 |
| Publication status | Published - 6 Apr 2022 |
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 (∆fH) 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.
Keywords
- alkali metal borohydride, BH in halide, first principle calculations, infrared spectroscopy
ASJC Scopus subject areas
- Chemical Engineering(all)
- General Chemical Engineering
- Materials Science(all)
- General Materials Science
- Physics and Astronomy(all)
- Condensed Matter Physics
- Chemistry(all)
- Inorganic Chemistry
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In: CRYSTALS, Vol. 12, No. 4, 510, 06.04.2022.
Research output: Contribution to journal › Article › Research › peer review
}
TY - JOUR
T1 - The Rigidity of the (BH4)-Anion Dispersed in Halides AX, A = Na, K; X = Cl, Br, I, and in MBH4 with M = Na, K, Rb, Cs
AU - Assi, Zeina
AU - Schneider, Alexander Gareth
AU - Ulpe, Anna Christina
AU - Bredow, Thomas
AU - Rüscher, Claus Henning
N1 - Funding Information: Funding: ZA was funded by DAAD Ref 441: A/10/97515. CHR used LUH-internal support and RU764/6-1, AGS and ACU were funded within the DFG project of BR1768/8-1.
PY - 2022/4/6
Y1 - 2022/4/6
N2 - 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 (∆fH) 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.
AB - 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 (∆fH) 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.
KW - alkali metal borohydride
KW - BH in halide
KW - first principle calculations
KW - infrared spectroscopy
UR - http://www.scopus.com/inward/record.url?scp=85128638387&partnerID=8YFLogxK
U2 - 10.3390/cryst12040510
DO - 10.3390/cryst12040510
M3 - Article
AN - SCOPUS:85128638387
VL - 12
JO - CRYSTALS
JF - CRYSTALS
SN - 2073-4352
IS - 4
M1 - 510
ER -