Association Patterns in (HF)_m(H₂O)_n (m + n = 2−8) Clusters

Abstract

In an attempt to understand the phase behavior of aqueous hydrogen fluoride, the clustering in the mixture is investigated at the molecular level. The study is performed at the mPW1B95/6-31+G(d,p) level of theory. Several previous studies attempted to describe the dissociation of HF in water, but in this investigation, the focus is only on the association patterns that are present in this binary mixture. A total of 214 optimized geometries of (HF)n(H2O)m clusters, with m + n as high as 8, were investigated. For each cluster combination, several different conformations are investigated, and the preferred conformations are presented. Using multiple linear regressions, the average strengths of the four possible H-bonding interactions are obtained. The strongest H-bond interaction is reported to be the H2O...H-F interaction. The most probable distributions of mixed clusters as a function of composition are also deduced. It is found that the larger (HF)n(H2O)m clusters are favored both energetically and entropically compared to the ones that are of size m + n < or = 3. Also, the clusters with equimolar contributions of HF and H2O are found to have the strongest interactions.

Assessment of hydrogen bond strengths and cooperativity in self- and cross-associating cyclic (HF)m(H2O)n(m+n= 2 to 8) clusters

“…The HB energies in the dimers also follow this rank ordering, i.e., F-HÁ Á ÁO (8.5 to 9.9 kcal mol À1 ) 4 F-HÁ Á ÁF (3.6 to 4.7 kcal mol À1 ) 4 O-HÁ Á ÁO (3.4 to 5.2 kcal mol À1 ) 4 O-HÁ Á ÁF (0.7 to 3.6 kcal mol À1 ). Interestingly, the present HB energy rank ordering (by the MTA and in dimers) is similar to that reported by Baburao and coworkers, 18 i.e., F-HÁ Á ÁO (À15.0 kcal mol À1 ) 4 F-HÁ Á ÁF (À8.8 kcal mol À1 ) 4 H-OÁ Á ÁH (À6.7 kcal mol À1 ) 4 O-HÁ Á ÁF (À3.9 kcal mol À1 ), who reported the average HB interaction energy (DE HB ) based on the multiple regression analysis (eqn (1)) as discussed above. It is emphasized here that although the HB energy rank ordering of different HBs by the MTA is similar to that reported by Baburao and coworkers, 18 numerically smaller and importantly only average values were reported by the latter approach.…”

“…Interestingly, the present HB energy rank ordering (by the MTA and in dimers) is similar to that reported by Baburao and coworkers, 18 i.e., F-HÁ Á ÁO (À15.0 kcal mol À1 ) 4 F-HÁ Á ÁF (À8.8 kcal mol À1 ) 4 H-OÁ Á ÁH (À6.7 kcal mol À1 ) 4 O-HÁ Á ÁF (À3.9 kcal mol À1 ), who reported the average HB interaction energy (DE HB ) based on the multiple regression analysis (eqn (1)) as discussed above. It is emphasized here that although the HB energy rank ordering of different HBs by the MTA is similar to that reported by Baburao and coworkers, 18 numerically smaller and importantly only average values were reported by the latter approach. Furthermore, the direct estimation of individual HB energy is possible by the MTA along with cooperativity contribution toward individual HBs.…”

“…14,15 The thermodynamic modelling of these systems is also shown to be difficult possibly due to the inaccuracy of the model which fails to incorporate strong HB interactions between HF and water molecules correctly. [16][17][18] The HF and H 2 O both form strong selfassociating F-HÁ Á ÁF and O-HÁ Á ÁO and cross-associating F-HÁ Á ÁO and O-HÁ Á ÁF HB interactions in these HF-water mixtures. 19 Thus, in order to understand the properties of HF-water mixtures, it is indispensable to have quantitative estimates of these different HB interactions.…”

“…They reported the HB interaction energy in FHÁ Á ÁH 2 O and H 2 OÁ Á ÁF À complexes to be 6.26 and 25.24 kcal mol À1 , respectively, at the MP2/aug-cc-pVDZ+(2s2p/2s) level of theory. One of the interesting studies was by Baburao and coworkers, 18 wherein the association patterns in mixed (HF) m (H 2 O) n (m + n = 2 to 8) clusters were explored to understand the phase behaviour of aqueous HF. The average HB interaction energy (DE HB ) corresponding to different types of HBs, viz.…”

Cat-CrNP as new material with catalytic properties for 2-chloro-2-propen-1-ol and ethylene oligomerizations

“…Cat-CrNP was obtained as violet-gold crystals. In the crystal of title compound, molecules of nitrilotriacetate complex compound of chromium(III) with 1,10-phenanthroline are linked via C–H···O hydrogen bonds and π-π interactions to produce blocks along b-axis, whereas water molecules interact via O (water) –H···O (water) interactions to form a centrosymmetric, alternately arranged (H 2 O) 4 (cyclic-planar, tetrameric 0–4-A structure) and (H 2 O) 8 (cyclic-chair, octameric 0–8-I structure) water clusters, which produce tapes extending along a-axis 30 – 32 . In the crystal packing, the adjacent blocks and tapes are connected through C–H···O (water) and O (water) –H···O hydrogen bonds to form a 3D framework structure (Fig.…”