Hydrated Sulfate Clusters SO42–(H2O)n (n = 1–40): Charge Distribution Through Solvation Shells and Stabilization

Investigations of inorganic anion SO42– interactions with water are crucial for understanding the chemistry of its aqueous solutions. It is known that the isolated SO42– dianion is unstable, and three H2O molecules are required for its stabilization. In the current work, we report our computational study of hydrated sulfate clusters SO42–(H2O)n (n = 1–40) in order to understand the nature of stabilization of this important anion by water molecules. We showed that the most significant charge transfer from dianion SO42– to H2O takes place at a number of H2O molecules n ≤ 7. The SO42– directly donates its charge only to the first solvation shell and surprisingly, a small amount of electron density of 0.15|e| is enough to be transferred in order to stabilize the dianion. Upon further addition of H2O molecules, we found that the cage effect played an essential role at n ≤ 12, where the first solvation shell closes. During this process, SO42– continues to lose density up to 0.25|e| at n = 12. From this point, additional water molecules do not take any significant amount of electron density from the dianion. These results can help in development of understanding how other solvent molecules could stabilize the SO42– anion as well as other multicharged unstable anions

Peculiar Transformations in the C_<i>x</i>H_<i>x</i>P_4–<i>x</i> (<i>x</i> = 0–4) Series

In the current work, we performed a systematic study of the C_<i>x</i>H_<i>x</i>P_4–<i>x</i> (<i>x</i> = 0–4) series using an unbiased CK global minimum and low-lying isomers search for the singlet and triplet P₄–C₄H₄ species at the B3LYP/6-31G** level of theory. The selected lowest isomers were recalculated at the CCSD(T)/CBS//B3LYP/6-311++G** level of theory. We found that the transition from a three-dimensional tetrahedron-like structure to a planar structure occurs at <i>x</i> = 3, where planar isomers become much more stable than the tetrahedral structures due to significantly stronger π bonds between carbon atoms in addition to increasing strain energy at the carbon atom in the tetrahedral environment

Al and Ti location in the MFI orthorhombic HZSM-5 framework. DFT calculation and neutron diffraction experiment

Abstract For the first time the neutron diffraction study of HZSM-5 zeolites with the general composition of (H1+x)[Al3+xSi4+12-xO24] × wH2O in the orthorhombic approximation (sp. gr. Pnma, z = 8) and initial silicate modules Si/Al = 12, 25, 40 was carried out. As a result, the composition was refined, the distribution of Al3+ ions over the tetrahedral sites (T sites) of the structure was found, and their content in each of them was estimated. It was found that T sites occupation in HZSM-5 structure differ depending on Si/Al, while samples with the same silicate module (Si/Al = 40) obtained under different synthesis conditions differ in the distribution of Al3+ ions over T sites of the structure. It was shown that the calculation of HZSM-5 zeolites crystal structure with substitutions in T sites performed using the VASP 5.2 program with different optimizations (atomic coordinates and unit cell parameters) can only reveal the most thermodynamically energetically favorable sites for Si4+ atoms substitution with other atoms (aluminum and titanium) without predicting their content in each site and regardless zeolite synthesis conditions and type of substituent atom. The relationship between HZSM-5 zeolites catalytic properties and silicate module (Si/Al, Si/Ti) was found and it cannot be ruled out that HZSM-5 catalytic activity is related to Ti4+ ions distribution over the tetrahedral sites of the structure. Graphical Abstrac