Intermolecular HH Vibrations of Dihydrogen Bonded Complexes H₃EH⁻···HOR in the Low-Frequency Region: Theory and IR Spectra

Abstract

The results of DFT calculations of harmonic and anharmonic frequencies of the dihydrogen bonded (DHB) complexes H 3EH (-)...HOR (E = B, Al, Ga and HOR = CH 3OH, CF 3CH 2OH) in gas phase and in low polar medium (by CPCM model) in comparison with the partners are presented. Normal coordinate analysis of the low-frequency modes was carried out to assign the new vibrations induced by DHB formation by the potential energy distribution values. Among them, the intermolecular H...H stretching vibrations only have individual modes. The influence of central atom mass and isotope and the strength of the proton donor effects were determined. The systems convenient for IR studies were chosen from the calculation predictions. The spectral investigation was made on the BH 4 (-)/ROH complexes (ROH = CH 2FCH 2OH (MFE), CF 3CH 2OH (TFE), (CF 3) 2CHOH (HFIP)). The results of temperature dependence, isotope substitution, and influence of the proton-donor strength studies agree with the theoretical conclusions. Combination of experimental and theoretical approaches allowed determining for the first time the intermolecular stretching mode characterizing intrinsic DHB vibrations.

Hydrogen and Dihydrogen Bonds in the Reactions of Metal Hydrides

“…The assignment of the intermolecular H···H stretching mode (ν σ ) having a high characteristic potential energy distribution (PED) of 81–100% was made. Experimental measurements on the DHB complexes of BH 4 – with three alcohols [ROH = FCH 2 CH 2 OH, CF 3 CH 2 OH, (CF 3 ) 2 CHOH] in CH 2 Cl 2 solution revealed a broad ν σ band, confirming the predicted assignment of ν σ and the influence of the acid strength . They showed the correlation of the DHB enthalpy values, Δ H DHB , obtained from experiment, and with the calculated H···H distances (Table ).…”

“…Detailed normal-coordinate analysis of IR spectra in the low-frequency range was performed for dihydrogen-bonded complexes MH 4 – ·HOR (M = B, Al, Ga; ROH = CH 3 OH, CF 3 CH 2 OH) . The assignment of the intermolecular H···H stretching mode (ν σ ) having a high characteristic potential energy distribution (PED) of 81–100% was made.…”

Electronic structure of aqueous borohydride: a potential hydrogen storage medium

“…More recently, borohydride hydration has been studied as part of a large group of molecules that form dihydrogen bonds. [20][21][22][23][24][25] These more recent studies that dealt specifically with borohydride confirmed the existence of a bond between a proton donor and a borohydride hydrogen, but they did not specifically examine borohydride in water. 24,25 With regards to solvation, these experiments were interpreted as yielding ''indirect evidence for [a] linear structure'', 20 referring to…”

The Reaction of Hydrogen Halides with Tetrahydroborate Anion and Hexahydro-closo-hexaborate Dianion

“…The first reaction intermediate was the hydrogen-bonded complex ( INTn HB 3 ) with HCl coordination on π-density of the B 3 triangle facet of the [B 6 H (6−x) Cl x ] 2− (x = 0–5) polyhedron [ 63 ]. It should be noted that the electron density of hydride atoms in [B 6 H 6 ] 2− is much lower than the electron density of B 3 triangle facets; therefore, in contrast to BH 4 − [ 34 , 35 , 64 ], [B 10 H 10 ] 2− [ 49 , 65 ], and [B 12 H 12 ] 2− [ 65 ], the complexation of proton donors occurred exclusively on B 3 triangle facets [ 66 , 67 ]. Upon the successive replacement of H − with Cl − in the closo -borane structure, gradual increases in the electron deficiency of the skeleton of closo -borane and the electrophilicity of boron atoms were observed.…”