Gas-Phase Thermochemistry of MX₃ and M₂X₆ (M = Sc, Y; X = F, Cl, Br, I) from a Composite Reaction-Based Approach: Homolytic versus Heterolytic Cleavage

Abstract

Domain-based local pair natural orbital coupled cluster approach with single, double and improved linear scaling perturbative triples correction via an iterative algorithm, DLPNO−CCSD(T1), was applied within a framework of the Feller-Peterson-Dixon approach to derive gas-phase heats of formation of scandium and yttrium trihalides and their dimers via a set of homolytic and heterolytic dissociation reactions. All predicted heats of formation moderately depend on reaction type with the most and the least negative values obtained for homolytic and heterolytic dissociation, respectively. The basis set size dependence, as well as the influence of static correlation effects not covered by the standard (DLPNO-)CCSD(T) approach, suggest that exploitation of the heterolytic dissociation reactions with formation of M +3 and Xions leads to the most robust heats of formation. The gas-phase formation enthalpies ΔH f °(0 K)/ ΔH f °(298.15 K) and absolute entropies S°(298.15 K) were obtained for the first time for the Sc2F6, Sc2Br6, and Sc2I6 species. For ScBr3, ScI3, Sc2Cl6, Y2Cl6 we suggest a re-examination of available in the literature experimental heats of formation. For other compounds the predicted values were found to be in good agreement with the experimental estimates. Extracted MX3 (M = Sc, Y, and X = F, Cl, Br, and I) 0K atomization enthalpies indicate the weaker bonding when moving from F to I and from Y to Sc. Likewise, the stability of yttrium trihalide dimers degrades when going from F to I. Respective scandium trihalide dimers are less stable, with 0 K dimer dissociation energy decreasing in row F -Cl -Br  I. Correlation of the (n-1)s 2 p 6 electrons on Br and I, inclusion of zero-point energy, relativistic effects, and the effective core-potential correction as well as amelioration of the DLPNO localization inaccuracy was shown to be of similar magnitude and is critical if accurate heats of formation are a goal.

Gas-phase thermochemistry of polycyclic aromatic hydrocarbons: an approach integrating the quantum chemistry composite scheme and reaction generator

“…As expected, 37,47,53,54 the enthalpies of formation turned out to depend on a particular chemical reaction. In this work, we suggest characterizing the enthalpy of formation of each compound with only one most reliable value.…”

“…In this work, we apply the method previously used by us 45–48 as an alternative Feller–Peterson–Dixon DLPNO-CCSD(T1) 49–52 reaction-based approach to derive a set of accurate thermochemical values for some PAHs and related functionalized compounds. Based on earlier reports in the literature on the dependence of predicted enthalpies of formation on a composed chemical reaction, 37,47,53,54 we propose the methodology aimed to reduce the bias. The obtained thermochemical characteristics are relevant for the modeling of processes related to astrochemistry, combustion, petrochemistry, and environmental science.…”

“In Vitro” and “In Vivo” Diagnostic Check for the Thermochemistry of Metal–Organic Compounds

“…The theoretical standard reaction enthalpies (Δ r H 0 ) at 298.15 K were calculated from the following modified Feller–Peterson–Dixon (FPD) method − presented in eq with the difference between the reactants and products for each enthalpy component denoted as Δ symbol where Δ E CBS is the reaction electronic energy change at the complete basis set limit; Δ H CORR is the room temperature enthalpy correction; Δ E CV is the effect from sub-valence electronic correlation; Δ E IT is the effect from utilization of the T1 iterative triples in the DLPNO-CCSD­(T) approach; Δ E PNO is the correction due to using the default NormalPNO instead of more accurate yet computationally demanding TightPNO settings; and Δ E SO is the effect from spin–orbit interactions. This approach was successfully applied by us in the recent studies. − …”