The molecular structure of growth units building crystals is a fundamental issue in the crystallization processes from aqueous solutions. In this work, a systematic investigation of pre-nucleation clusters and their hydration characteristics in aqueous CaSO4 solutions was performed using ab initio calculations and molecular dynamics (MD) simulations. The results of ab initio calculations and MD simulations indicate that the dominant species in aqueous CaSO4 solutions are monodentate ion-associated structures. Compared with charged ion clusters, neutral clusters are more likely to be present in an aqueous CaSO4 solution. Neutral (CaSO4)m clusters are probably the growth units involved in the pre-nucleation or crystallization processes. Meanwhile, hydration behavior around ion associated species in aqueous CaSO4 solutions plays an important role in related phase/polymorphism selections. Upon ion clustering, the residence of some water molecules around Ca2+ in ion-associated species is weakened while that of some bridging waters is enhanced due to dual interaction by Ca2+ and SO42−. Some phase/polymorphism selections can be achieved in aqueous CaSO4 solutions by controlling the hydration around pre-nucleation clusters. Moreover, the association trend between calcium and sulfate is found to be relatively strong, which hints at the low solubility of calcium sulfate in water.

In this study, the structural characteristics of high-coordinated Ca–Cl complexes present in mixed CaCl2–LiCl aqueous solution were investigated using density functional theory (DFT) and molecular dynamics (MD) simulations. The DFT results show that [CaClx]2–x (x = 4–6) clusters are quite unstable in the gas phase, but these clusters become metastable when hydration is considered. The MD simulations show that high-coordinated Ca–chloro complexes are possible transient species that exist for up to nanoseconds in concentrated (11.10 mol·kg–1) Cl– solution at 273 and 298 K. As the temperature increases to 423 K, these high-coordinated structures tend to disassociate and convert into smaller clusters and single free ions. The presence of high-order Ca–Cl species in concentrated LiCl solution can be attributed to their enhanced hydration shell and the inadequate hydration of ions. The probability of the [CaClx]2–xaq (x = 4–6) species being present in concentrated LiCl solution decreases greatly with increasing temperature, which also indicates that the formation of the high-coordinated Ca–Cl structure is related to its hydration characteristics.

A highly chemo-, regio-, and stereoselective method for the synthesis of (Z)-vinylic selenosulfides and (Z)-vinylic tellurosulfides in a one-pot reaction of terminal alkynes, diaryl disulfides, and diaryl diselenides (ditellurides) catalyzed by simple base cesium hydroxide monohydrate is described. Due to the different activities of the carbon–chalcogen bonds, the target products cleave selectively and act as a kind of readily available platform molecule for the synthesis of tetrasubstituted alkenes. The mechanism of thioselenation was studied by experimental and theoretical methods.

In this work, a systematic investigation of the competition coordination of H2O and Cl– with Ni2+ in saturated NiCl2 aqueous solution at room temperature was conducted using density functional theory (DFT), Car–Parrinello molecular dynamics (CPMD) simulations, and extended X-ray absorption fine structure (EXAFS) spectra. The calculated results reveal that the six-coordinated structure is favorable for [NiClx(H2O)n]2–x (x = 0–2; n = 1–12) clusters in the aqueous phase. The hydration energy calculation shows that the six-coordinated solvent-shared ion pair (SSIP) ([Ni(H2O)6(H2O)n−6Cl]+) is more stable than its contact ion pair (CIP) ([NiCl(H2O)5(H2O)n−5]+) isomer as n ≥ 9 in the aqueous phase, and the six-coordinated solvent-shared ion pair with a dissociated double Cl– (SSIP/d) ([Ni(H2O)6(H2O)n−6Cl2]0) is more preferable than its CIP ([NiCl2(H2O)4(H2O)n−4]0) and solvent-shared ion pair with single dissociated Cl– (SSIP/s) ([NiCl(H2O)5(H2O)n−5Cl]0) isomers as n ≥ 11. The six-coordinated SSIP/d ([Ni(H2O)6(H2O)n−6Cl2]0) conformers are the dominant structures in a saturated NiCl2(aq) solution (NiCl2 concentration: ∼5.05 mol·kg–1, corresponding to n ≈ 11). The CPMD simulations exhibited that there are six water molecules with Ni–O distance at ∼205.0 pm on average around each Ni2+ in the first hydration sphere, even in the saturated NiCl2 aqueous solution (∼5.05 mol·kg–1) at room temperature, and no obvious Ni–Cl interaction was found. The EXAFS spectra revealed that the first solvation shell of Ni2+ is an octahedral structure with six water molecules tightly bound in the NiCl2(aq) solution with a concentration ranging from 1.00 to 5.05 mol·kg–1, and there is no obvious evidence of Ni–Cl contact ion pairs. A comprehensive conclusion from the DFT, CPMD, and EXAFS studies is that there is no obvious direct contact between Ni2+ and Cl–, even in saturated NiCl2 aqueous solution at room temperature.

The molecular structure of growth units building crystals is a fundamental issue in the crystallization processes from aqueous solutions. In this work, a systematic investigation of pre-nucleation clusters and their hydration characteristics in aqueous CaSO4 solutions was performed using ab initio calculations and molecular dynamics (MD) simulations. The results of ab initio calculations and MD simulations indicate that the dominant species in aqueous CaSO4 solutions are monodentate ion-associated structures. Compared with charged ion clusters, neutral clusters are more likely to be present in an aqueous CaSO4 solution. Neutral (CaSO4)m clusters are probably the growth units involved in the pre-nucleation or crystallization processes. Meanwhile, hydration behavior around ion associated species in aqueous CaSO4 solutions plays an important role in related phase/polymorphism selections. Upon ion clustering, the residence of some water molecules around Ca2+ in ion-associated species is weakened while that of some bridging waters is enhanced due to dual interaction by Ca2+ and SO42−. Some phase/polymorphism selections can be achieved in aqueous CaSO4 solutions by controlling the hydration around pre-nucleation clusters. Moreover, the association trend between calcium and sulfate is found to be relatively strong, which hints at the low solubility of calcium sulfate in water.