Arseniy A. Otlyotov

The results of the exhaustive conformational sampling are contrasted with metadynamics‐based CREST simulations for a set of 13 gas‐phase forms of clinical drug molecules retrieved from the CD25 dataset. [ Chem. Sci . 2021 , 12 (19), 6551] The GFN1‐ and GFN2‐xTB methods complement each other in the identification of the most stable conformer. The GFN‐FF performs worse due to fundamental differences between the force field and the density functional theory (DFT) potential energy surfaces. Conformational entropies (S _conf ) from the systematic search as well as from the standard CREST entropy mode calculations with the single‐point Hessian (SPH) deactivated are in reasonable agreement with their molecular dynamics counterparts that account for torsional correlation [ J. Chem. Theory Comput . 2022 , 18 , 7166–7178]. The CREST entropy mode evaluations on the DFT‐refined geometries using the activated SPH routine yield too large S _conf values for some species due to the overestimation of the Boltzmann entropy averaging () contribution.

Mixing a few contemporary semiempirical methods with a number of conformational sampling techniques can identify the most stable gas-phase conformers of vitamins. The conformational entropies obtained in this way are only estimations.

Gas-phase enthalpies of formation (Δ_fH°(g, 298 K)) of Sc, Ti, V, Cr, Mn, Fe, and Co tris(acetylacetonates) were predicted using the reaction-based approach implemented in the recently developed program. Energies of working reactions were computed by employing the Feller-Peterson-Dixon composite scheme in conjunction with the DLPNO-CCSD(T)/CBS and also using several DFT model chemistries. A careful analysis of the literature data on the experimental and theoretical Δ_fH° (g, 298 K) of the relevant transition metal oxides, fluorides, and chlorides revealed the most reliable values to be used as references in the reaction-based approach. The predicted enthalpies of formation of M(acac)₃ complexes were utilized for the rationalization of the literature-available experimental data. The difference between theoretical and experimental Δ_fH° (g, 298 K) falls within the error margins in the case of V(acac)₃, Fe(acac)₃, and Co(acac)₃. For Mn(acac)₃, the theoretical Δ_fH° (g, 298 K) agrees better with the value obtained from an older study. In the case of Sc(acac)₃ and Cr(acac)₃, the discrepancies between experiment and theory reach 13.1 and 6.1 kcal mol^-1, respectively. For Ti(acac)₃, the predicted Δ_fH° (g,298 K) = -374.8 ± 4.5 kcal mol^-1 is probably the only currently available value.

We present a benchmark set LIMIXCARB_RE12 comprising 12 reference DLPNO‐CCSD(T₁)/CPS(6,7)/CBS(cc‐pwCVTZ/cc‐pwCVQZ)//PBE0‐D3(BJ)/def2‐TZVP binding energies for the sizeable (up to 69 atoms) clusters of Li⁺ ion with mixed cyclic and linear organic carbonates. A number of computationally cheaper DLPNO‐CCSD(T)‐based Feller‐Peterson‐Dixon protocols including contributions due to core‐valence electron correlation, using more accurate iterative triples correction (T₁) and tighter‐than‐default PNO settings are examined with respect to their accuracy and efficiency. Particular splittings of the total binding energy into components allow maintaining high accuracy (deviations less than 0.2 kcal mol⁻¹) at significantly reduced computational cost. Much faster convergence of the DLPNO‐CCSD(T) binding energies to the reference values is reached if Ahlrichs' def2 basis sets are used instead of their correlation‐consistent Dunning counterparts. Evaluation of the DFT approximations against the LIMIXCARB_RE12 reveals double hybrid PWPB95‐D4 in conjunction with CBS(def2‐TZVPP/def2‐QZVPP) extrapolation to be the best performer with mean signed deviation (MSD) of only −0.1 kcal mol⁻¹ followed by r²SCAN‐D4/D3(BJ) and r²SCAN‐3c (MSD < 1 kcal mol⁻¹), while hybrid B3LYP and PBE0 functionals complemented with D3(BJ) or D4 dispersion corrections are clearly inferior. The obtained results provide a guide for the accurate calculations of the binding energies of the microsolvated clusters and can be used for the development and validation of the emerging computational methods.

A new database of conformational energies (semi-empirical, DFT and reference RI-SCS-MP2/CBS) of Li⁺ clusters with organic carbonates, LICARB806, is introduced. Representative low-energy conformers of these systems are determined.

An impact of an electronic structure or force field method, gas‐phase thermodynamic correction, and continuum solvation model on organic carbonate clusters (S)_n conformational and binding energies is explored. None of the tested force field (GFN‐FF, GAFF, MMFF94) and standard semiempirical methods (PM3, AM1, RM1, PM6, PM6‐D3, PM6‐D3H4, PM7) can reproduce reference RI‐SCS‐MP2 conformational energies. Tight‐binding GFNn‐xTB methods provide more realistic conformational energies which are accurate enough to discard the least stable conformers. The effect of thermodynamic correction is moderate and can be ignored if the gas phase conformational stability ranking is a goal. The influence of continuum solvation is stronger, especially if reinforced with the Gibbs free energy thermodynamic correction, and results in the reduced spread of conformational energies. The cluster formation binding energies strongly depend on a particular approach to vibrational thermochemistry with the difference between traditional harmonic and modified scaled rigid – harmonic oscillator approximations reaching 10 kcal mol⁻¹.

Groups 10-12 metalloporphyrins have been recognized for their numerous properties essential for the development of new sensing materials. In this work, accurate gas-phase enthalpies of formation, Δ_fH_m⁰(g,298.15), are predicted for the series of Ni, Cu, Zn, Pd, Ag, and Cd tetraphenylporphyrins (MTPPs) on the basis of the reaction-based Feller-Peterson-Dixon approach and high-level ab initio DLPNO-CCSD(T) calculations. Our recently developed automatic generator of the balanced chemical reactions was employed to reduce the bias of the theoretical Δ_fH_m⁰(g,298.15) toward a particular reaction. Theoretical Δ_fH_m⁰(g,298.15) for ZnTPP (227.0 ± 3.4 kcal mol^-1) does not support the previously reported experimental value of 132 ± 2 kcal mol^-1. The origin of the discrepancy probably lies in the experimental solid-state Δ_fH_m⁰(ZnTPP, cr,298.15) as it stems from our theoretical evaluations of the Δ_fH_m⁰(cr,298.15) values for the entire set of transition metal TPP complexes. The large discrepancy between experiment and theory also holds when different DFT functionals (ωB97M-V, PBE0-D4, and B3LYP-D4) paired with quadruple-ζ quality basis sets are used for the theoretical calculations. Experimental revisiting of the solid-state enthalpy of formation of ZnTPP and analogue measurements for other transition metal TPPs are needed to resolve the observed discrepancy. Based on the predicted enthalpies of formation of MTPPs, the relative energies of the metal-ligand bonding are evaluated and the trends are compared to those for the complexes of the unsubstituted porphyrin with the same set of metals derived in [Can. J. Chem., 2009, 87, 1063]. According to both studies, Pd complexes exhibit the strongest bonding, while the Cd species are the least stable metallocomplexes within the considered series.

The experimental gas‐phase thermochemistry of reactions: M⁺(S)_n–1 + S → M⁺(S)_n and M⁺ + nS→ M⁺(S)_n, where M is an alkali metal and S is acetonitrile/ammonia, is reproduced. Three approximations are tested: (1) scaled rigid‐rotor‐harmonic‐oscillator (sRRHO); (2) the sRRHO(100) identical to (1), but with all vibrational frequencies smaller than 100 cm⁻¹ replaced with 100 cm⁻¹; (3) Grimme's modified scaled RRHO (msRRHO) (Grimme, Chem. Eur. J., 2012, 18, 9955–9964). The msRRHO approach provides the most accurate reaction entropies with the mean unsigned error (MUE) below 5.5 cal mol⁻¹ K⁻¹ followed by sRRHO(100) and sRRHO with MUEs of 7.2 and 16.9 cal mol⁻¹ K⁻¹. For the first time, we propose using the msRRHO scheme to calculate the enthalpy contribution that is further utilized to arrive at reaction Gibbs free energies (∆G_r) ensuring the internal consistency. The final ∆G_r MUEs for msRRHO, sRRHO(100) and sRRHO schemes are 1.2, 3.6 and 3.1 kcal mol⁻¹.

The geometry and electronic structures of iron(II) complexes with porphyrin (FeP) and tetrabenzoporphyrin (FeTBP) in ground and low-lying excited electronic states are determined by DFT (PBE0/def2-TZVP) calculations and the complete active space self-consistent field (CASSCF) method, followed by the multiconfigurational quasi-degenerate second-order perturbation theory (MCQDPT2) approach to determine the dynamic electron correlation. The minima on the potential energy surfaces (PESs) of the ground (³A_2g) and low-lying, high-spin (⁵A_1g) electronic states correspond to the planar structures of FeP and FeTBP with D_4h symmetry. According to the results of the MCQDPT2 calculations, the wave functions of the ³A_2g and ⁵A_1g electronic states are single determinant. The electronic absorption (UV–Vis) spectra of FeP and FeTBP are simulated within the framework of the simplified time-dependent density functional theory (sTDDFT) approach with the use of the long-range corrected CAM-B3LYP function. The most intensive bands of the UV–Vis spectra of FeP and FeTBP occur in the Soret near-UV region of 370–390 nm.