An atom in molecules study of infrared intensity enhancements in fundamental donor stretching bands in hydrogen bond formation

Abstract

Vibrational modes ascribed to the stretching of X-H bonds from donor monomers (HXdonor) in complexes presenting hydrogen bonds (HF···HF, HCl···HCl, HCN···HCN, HNC···HNC, HCN···HF, HF···HCl and H2O···HF) exhibit large (4 to 7 times) infrared intensity increments during complexation according to CCSD/cc-pVQZ-mod calculations. These intensity increases are explained by the charge-charge flux-dipole flux (CCFDF) model based on multipoles from the Quantum Theory of Atoms in Molecules (QTAIM) as resulting from a reinforcing interaction between two contributions to the dipole moment derivatives with respect to the vibrational displacements: charge and charge flux. As such, variations that occur in their intensity cross terms in hydrogen bond formation correlate nicely with the intensity enhancements. These stretching modes of HXdonor bonds can be approximately modeled by sole displacement of the positively charged hydrogens towards the acceptor terminal atom with concomitant electronic charge transfers in the opposite direction that are larger than those occurring for the H atom displacements of their isolated donor molecules. This analysis indicates that the charge-charge flux interaction reinforcement on H-bond complexation is associated with variations of atomic charge fluxes in both parent molecules and small electronic charge transfers between them. The QTAIM/CCFDF model also indicates that atomic dipole flux contributions do not play a significant role in these intensity enhancements.

Infrared intensity analysis of hydroxyl stretching modes in carboxylic acid dimers by means of the charge–charge flux–dipole flux model

“…However, according to Table , the cross‐contribution between charge and charge flux, A C × CF , is preponderant for all dimers, being able to explain alone a significant amount of the infrared intensity increment. As mentioned before, this same contribution was also able to explain most of the infrared intensity increments seen for HX modes in simpler dimers . The linear regression coefficient ( R 2 ) between Δ A and Δ A C × CF is 0.74, as shown in Supporting Information Figure S1, but increases to 0.90 as we remove the point corresponding to the formic acid homodimer.…”

“…Supporting Information Table S5 shows the variations in atomic charge values during dimerization as obtained in B2PLYP/aug‐cc‐pVTZ calculations by using the QTAIM and NPA formalisms. As observed for simpler dimers, the hydrogen atom of the proton donor group (hydroxyl) loses more electronic charge during dimerization according to both these charge models (around 0.06 and 0.02 e , respectively, for QTAIM and NPA). Finally, QTAIM and NPA also agree that the oxygen atom from the carbonyl group becomes more negatively charged during hydrogen bond formation (around −0.03 and −0.07 e , respectively, for QTAIM and NPA).…”

“…However, the cross‐term charge‑charge flux predominates in all dimers. The infrared intensity increments of XH stretching bands of donor monomers in mono‐dentate complexes, such as HF…HF, HCl…HCl, HCN…HCN, HNC…HNC, HCN…HF, HF…HCl and H 2 O…HF, were also explained as resulting from a reinforcing interaction between the quantities mentioned here due to the dimerization process, that is, electronic charge transfers that reinforce dipole moment derivatives caused by the displacement of charged atoms. This was pointed out as a possible general feature of HB complexes …”

“…Thus, although there are some theoretical studies regarding the variations of infrared intensities for the XH stretching modes of simple dimers, along with investigations dealing with the perturbation caused by hydrogen bonds in molecular polarizabilities of amino acids and the cooperative effects of these interactions on water clusters, the study of charge redistributions during the formation of more complicated dimers is still scarce. For example, bidentate dimers (HCOOH…HCOOH, FCOOH…FCOOH, among others), which can be bonded by two HBs between hydroxyl and carbonyl groups (O…H), have not yet been subjected to infrared intensity variation investigations via the CCFDF/QTAIM model, although they were analyzed by the equilibrium charges charge flux (ECCF) model, which does not include terms to deal explicitly with the variations in atomic polarizabilities …”

Transparent sunlight conversion film based on carboxymethyl cellulose and carbon dots

“…) is 7%, 43%, 42%, 52% higher than that of CMC film, respectively. According to the literature (Terrabuio, Richter, Silva, Brunsb, & Haiduke, 2014), it is noted that the intensity of infrared vibration band is determined by two factors, dipole moment and energy transition, respectively. However, the probability of energy transition is dependent on the properties of functional groups.…”