Effects of Empirical Dispersion Energy on the Geometrical Parameters and Relative Energy of a Salicylideneaniline Molecular Switch in the Solid State

Jean Quertinmont,Tom Leyssens,Johan Wouters,Benoît Champagne

doi:10.3390/cryst8030125

Abstract

The geometries of the enol (E) and keto (K) forms of a crystalline salicylideneaniline molecular switch, (E)-2-methoxy-6-(pyridine-3-yliminomethyl)phenol (PYV3), have been determined using periodic density functional theory (DFT) calculations with a variety of exchange-correlation functionals (XCFs). They are compared to X-ray diffraction (XRD) data as well as to geometries obtained using empirical dispersion energy in the form of the second iteration of Grimme’s scheme, either with its original parameters (DFT-D2) or with parameters revised for the solid state (DFT-D*). Using DFT, a good agreement with experiment on the unit cell parameters is obtained with the PBEsol, PBEsol0, and ωB97X XCFs. DFT-D2 contracts the unit cell too much with all considered XCFs, whereas DFT-D* lessens this effect thus allowing B3LYP, PBE, and PBE0 to achieve reasonable agreement with respect to XRD data. When considering molecular geometries, both DFT and DFT-D* have a similar effect on the bond lengths, both systematically underestimating (overestimating) the length of the single (double) bonds (within 0.003 Å), as well as on valence angles attaining differences of 2° with respect to XRD data. The errors on the torsion angles are less spread out with DFT-D* (averaging 1°) than DFT for which only PBEsol, PBEsol0, and ωB97X perform well. Finally, the relative keto–enol energies, ΔEKE, have been calculated, showing that the inclusion of dispersion energy stabilizes the keto form more than it does the enol form. This results in the PBE and PBEsol XCFs wrongly predicting the keto form as the most stable form.

Highlights

Thermochromic and photochromic compounds have been extensively studied and still attract a lot of attention as they have many potential applications [1,2,3,4,5,6,7,8]
By performing comparisons with X-ray diffraction (XRD) data, a recent contribution [10] has demonstrated that HSEsol [12], PBEsol0, and ωB97X [11] can already be effective but, in this work, we investigated whether the addition of empirical dispersion energy, as proposed by Grimme [13], could further improve these results
We have shown that the use of the original dispersion parameters (DFT-D2) over-contracts the unit cell for the selected XCFs (B3LYP [16], PBE [17], PBE0 [18], PBEsol [19], PBEsol0, and ωB97X)

Summary

Introduction

Thermochromic and photochromic compounds have been extensively studied and still attract a lot of attention as they have many potential applications [1,2,3,4,5,6,7,8]. In [10], so far, a more precise description of the solid state can be obtained by modifications to the DFT energy we showed the effectiveness of three XCFs (HSEsol [12], PBEsol0, and ωB97X [11]) in optimizing the by adding London dispersion interactions (Equation (1)) in the form of empirical terms as proposed by molecular and crystal structures of three salicylideneanilines. Grimme in atoms order ito better steepness of the function Since this scheme was parameterized for modifications clusters, Ugliengo andacoworkers dispersion energy in molecular crystals, leading to DFT-D*

Structure

Computational Aspects

Crystal Structures and Molecular Geometries

Method

The The

Conclusions