Kharkiv University Bulletin. Chemical Series

Energy spectrum and magnetic properties of the decorated spin ladder models of nanomagnets on the base of polymeric transition metal compounds

2024-02-21T22:50:57+00:00

The work is devoted to the theoretical study of the energy spectrum and low-temperature magnetic properties of the decorated spin-ladder model with the polyacene topology and the three types of the site spins. On the base of cluster expansion technique an approximate analytical treatment of lowest part of the energy spectra of two isomeric ladder structures was given. It is shown that the ladder model with singlet ground state is more stable than its isomeric analog with the macroscopic ground state spin. In addition, the numerical study of field dependence of low-temperature magnetization of 8- spin clusters of both ladder models was performed by means of exact diagonalization method. On the base of these results, it was shown the presence of an intermediate plateau in low-temperature magnetization profile of the above spin ladder models.

Internal validation parameters of linear regression equations in QSAR problem

2024-02-21T22:51:00+00:00

The article discusses a set of internal validation parameters that are (or can be) used to describe the quality of regression models in quantitative structure-activity relationship problems. Among these parameters there are well known determination coefficient, root mean square deviation, mean absolute error, etc. Also the indices based at Kullback-Leibler divergence as a measure of distance between two sets have been investigated. All the parameters (indices) were calculated for several regression models which describe boiling point of saturated hydrocarbons (alkanes). Regression models include a four-component additive scheme and equations describing the property as a function of topological indices. The two types of regressions based on these indices are linear dependencies on only one topological index and linear dependencies on topological index and the number of carbon atoms in the hydrocarbon. Various linear regression equations have been described with internal validation parameters that evaluate the quality of the equations from different perspectives. It is shown that a wide set of test parameters is not only an additional yet alternative description of regression models, but also provides the most complete description of the predictive characteristics and quality of the obtained regression model.

Proton solvation: competition between acetone and dimethyl sulfoxide

2024-02-21T22:51:03+00:00

This paper presents results of quantum-chemical study of proton exchange equilibrium between acetone (AC) and dimethyl sulfoxide (DMSO). Basing on the previous study of acid-base equilibria in AC with small additives of DMSO, the most probable composition of the lyonium ion is taken as H(DMSO)₂⁺. The equilibrium geometries and energies of solvents molecules and all possible combinations of proton complexes with one or two solvent molecules were calculated in DFT level of theory using B3LYP functional and 6-31G++(d,p) basis set. The energies of solvated proton complexes were then calculated using PCM method. The energy change corresponding to the equilibrium H(AС)₂⁺ + 2 DMSO ⇄ H(DMSO)₂⁺ + 2 AС is –63.1 kJ mol^–1 in the gas phase, which is in qualitative agreement with the standard Gibbs energy data, obtained experimentally in the gas phase by Kebarle’s group, –77.6 kJ mol^–1, and with ΔG^o₂₉₈ = –49.3 kJ mol^–1for AC solution with small additions of DMSO, determined by the Guss and Kolthoff method.