Vibrational spectra of icosabedral closoborate anions B12X2−12 (X = H, D, Cl, Br, I)

doi:10.1016/0584-8539(82)80032-9

Spectrochimica Acta Part A: Molecular Spectroscopy

Volume 38, Issue 10, 1982, Pages 1047-1056

Spectrochimica Acta ...

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Abstract

Vibrational spectra of the salts M₂B₁₂X₁₂ where X = H, D, Cl, Br, I; M = K, Cs are obtained in solid state and in aqueous solution. The vibrational assignment for the undistorted icosahedral anion B₁₂X²⁻₁₂ in the series X = H, D, Cl, Br, I is discussed. The spectral pattern observed is consistent with the selection rules for the I_h point symmetry group. The changes in the spectra of the solid salts due to the crystal field are revealed.

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Citation Excerpt :
The broad features contain contributions from several more narrow bands. A band at ∼2480 cm−1, clearly observed in S3 and possibly present as a shoulder in S1 and S2, could stem from CaB12H12 which is reported to have its strongest band at this position [26]. The origin of the remaining bands observed below 2600 cm−1 is not known.
Ca(BH₄)₂ with 11.6 mass% hydrogen is considered a promising material for hydrogen storage applications due to its high gravimetric and volumetric capacity as well as predicted thermodynamic properties suitable for hydrogen storage purposes. However, the material displays poor reversibility, and a deeper understanding of decomposition pathway and rehydrogenation mechanisms are needed to solve this issue. In this work the rehydrogenation properties of phases present in different samples of decomposed Ca(BH₄)₂ were investigated. The dehydrogenated and rehydrogenated samples were characterized by Powder X-ray Diffraction (PXD) and infrared spectroscopy (IR). The results show that at least one amorphous phase is hydrogenated to form Ca(BH₄)₂ at relatively moderate conditions (100 bar, 305 °C) without addition of a catalyst. Bragg peaks from the earlier reported intermediate phase, CaB₂H_x, disappear during rehydrogenation. However, it cannot be confirmed from the results presented here if this is due to rehydrogenation or if CaB₂H_x is consumed in a reaction with phases formed during rehydrogenation of the amorphous phase(s). Infrared spectra show presence of amorphous decomposition products different from the earlier identified decomposition products CaH₂, CaB₆ and CaB₁₂H₁₂. These phases cannot be identified due to lack of matching literature spectra, but quantitative analysis indicates presence of amorphous products less rich in boron than CaB₆ and CaB₁₂H₁₂.
Alkali and alkaline-earth metal dodecahydro-closo-dodecaborates: Probing structural variations via neutron vibrational spectroscopy
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Citation Excerpt :
To aid in understanding the role of this intermediate, a more detailed knowledge of its vibrational spectroscopic signature is highly desirable. The vibrational spectra of dodecahydro-closo-dodecaborates in the solid state differ considerably from that of the isolated dianion, even in solution [11]. Allis and Hudson [12] reported that the solid-state vibrational spectrum of Cs2B12H12 could not be reproduced with an isolated-ion calculation, but found good agreement using a solid-state calculation.
The hydrogen-weighted phonon densities of states for the series of alkali (A = Li, Na, K, Rb, and Cs) and alkaline-earth (Ae = Mg, Ca, Sr, and Ba) metal dodecahydro-closo-dodecaborates, A₂B₁₂H₁₂ and AeB₁₂H₁₂, were measured via neutron vibrational spectroscopy (NVS). Using the known crystal structures, density functional theory (DFT) phonon calculations were able to closely replicate the observed vibrational spectra. The spectral details were found to differ considerably with structure, indicating that the internal vibrations of the B₁₂H₁₂²⁻ icosahedral anions are sensitive to symmetry-dependent interactions with their crystal surroundings. In contrast, these internal vibrations were relatively unchanged among isomorphic A₂B₁₂H₁₂ and AeB₁₂H₁₂ compounds possessing different metal cations. These results confirm that the combination of NVS and DFT phonon calculations can be used to help validate postulated local crystal symmetries in these types of materials, even in instances where the ordering is only short-range, rendering the materials amorphous with respect to diffraction probes.
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2010, Coordination Chemistry Reviews
Of the challenges that are still to be met to enable the widespread use of H₂ as a fuel for automotive applications, a safe, reliable and cheap method for its storage and transportation is paramount. This need has prompted a massive effort in the synthesis and characterisation of novel hydrides and a better understanding of existing materials. In this review the vibrational spectroscopy and the bonding of a wide range of ternary metal hydride complexes are discussed. The spectroscopic techniques used include transmission and photoacoustic infrared spectroscopy, Raman spectroscopy with excitation wavelengths ranging from 1064 to 515 nm, inelastic neutron scattering spectroscopy and nuclear resonant inelastic X-ray scattering spectroscopy. The systems studied are: the octahedral transition metal hydrides, other geometry's of transition metal hydrides, alkali metal, alkaline earth and aluminium compounds with the borohydride ion, the alkali metal and alkaline earth alanates and the alkali metal gallates. In all cases, while the central atom is the most important determinant of the properties, it has become increasingly clear that the counter-ion is much more than just a spectator; it often plays a key role in determining the stability of the material. As such, varying the counter-ion provides an important mechanism for optimising the desired properties and these are reflected in the spectra. In addition to its use in characterising materials, vibrational spectroscopy is used to investigate reactions and processes. The advantages of vibrational spectroscopy lie in its flexibility: it is not restricted to crystalline systems, amorphous or nanocrystalline materials are readily observable, it is amenable to in situ studies, it is democratic; infrared and Raman spectroscopy are not element specific and uniquely among probes they are able to follow a reaction across a change of state. Vibrational spectroscopy and ab initio calculations are a synergistic pairing. Comparison of computed and experimental spectra provides a stringent test of the calculation, while the calculation provides unambiguous assignments of the spectra. Generation of the inelastic neutron scattering spectrum provides the most reliable test since only the amplitude of motion of the atoms in each mode is required.
Resonance Raman and infrared spectra of [CH<inf>3</inf>C<inf>5</inf>H<inf>4</inf>NiPh<inf>2</inf>PC<inf>3</inf>H<inf>6</inf>PPh<inf>2</inf>]·B<inf>11</inf>H<inf>14</inf>
1992, Spectrochimica Acta Part A: Molecular Spectroscopy
Resonance Raman and infrared spectra of (C₂H₅)₄NB₁₁H₁₄ are reported. Based on the appearance of several bands on going from (C₂H₅)₄NCl to (C₂H₅)₄NB₁₁H₁₄, a vibrational assignment is proposed for the B₁₁H⁻₁₄. These results are compared with corresponding results for several other amine boranes. Resonance Raman and infrared spectra of [CH₃C₅H₄NiPh₂PC₃H₆PPh₂]·B₁₁H₁₄ were obtained. An assignment of frequencies to the fundamental modes of vibration has been made for this compound. The Ni-P vibration frequencies are located at about 202 and 177 cm⁻¹. The Ni-MeCp vibration has also been assigned at about 359 and 230 cm⁻¹.
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1992, Inorganica Chimica Acta
Normal coordinate analysis of icosahedral closoborate anions B<inf>12</inf>Y<sup>2-</sup><inf>12</inf> (Y = H, D, F, Cl, Br, I)
1986, Spectrochimica Acta Part A: Molecular Spectroscopy
A normal coordinate analysis is performed for the dodecaborane anion and its halogen substitutes. This is one of the few existing works in which the challenging problems of molecular vibrations of icosahedral molecules have been attacked. Calculated vibrational frequencies of the spectroscopically active species are in good agreement with observed values. Inactive frequencies, potential energy distributions and calculated mean amplitudes of vibration are also reported.

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Vibrational spectra of icosabedral closoborate anions B12X2−12 (X = H, D, Cl, Br, I)

Abstract

J. Phys. Chem. Solids

Izv. AN SSSR, ser. khim.

Izv. AN SSSR, ser. khim.

J. Am. Chem. Soc.

Can. J. Spectroscopy

Mol. Phys.

Vibrational spectra of icosabedral closoborate anions B₁₂X²⁻₁₂ (X = H, D, Cl, Br, I)