Does borazine-water behave like benzene-water? A matrix isolation infrared and ab initio study

A theoretical investigation on the complexes of B3O3H3 with acetylene and its substituted derivatives

The complexes of B₃O₃H₃ with acetylene and its substituted derivatives C₂HX (X=H, F, Cl, Br, CH₃, NH₂) are explored by theoretical calculations using MP2 and M06-2X methods with aug-cc-pVDZ as the basis set. The different molecular electrostatic potential features of B₃O₃H₃ with benzene (C₆H₆) and borazine (B₃N₃H₆) result in different stable structures of the complexes with C₂HX. The geometric analysis indicates that the global minimum is the parallel stacked (PS) structure with the linear C-C triple bond lies on the top of B₃O₃H₃, and this is much different from that of the B₃N₃H₆...C₂HX complex, in which the C-H bond directs towards the B₃N₃H₆ ring (T-shaped). The H-bonded structure where the C-H interacts with the O atom of B₃O₃H₃ is found to be a local minimum. Besides, there is an additional X…O halogen-bonded structures for the B₃O₃H₃…C₂HX (X=Cl, Br) complexes. As for the PS geometry, when one H atom in C₂H₂ is replaced by different X groups, the binding energies of the complexes increases in the order of F<H<Cl<Br<CH₃<NH₂, which is mainly determined by the strength of the π-hole bond. The nature of interaction in these complexes is further studied by the atoms-in-molecules (AIM) and noncovalent interaction (NCI) analysis. The natural bond orbital (NBO) analysis indicates that the main orbital interaction arises from LP_X→BD*_B‑O for B₃O₃H₃…C₂HX (X=Cl, Br, NH₂), and BD_C‑C→BD*_B‑O for B₃O₃H₃…C₂HX (X=H, CH₃) complexes. Complexes of B₃O₃H₃ with acetylene and its substituted derivatives.

From the propargyl alcohol–water complex to the propargyl alcohol dimer: where does the propargyl alcohol–methanol complex fit in?

A correlation was recognized between the structures of PA–H₂O, PA–MeOH and PA dimer complexes that could help predict the structures of larger systems in a systematic way.

Combined TDDFT and AIM Insights into Photoinduced Excited State Intramolecular Proton Transfer (ESIPT) Mechanism in Hydroxyl- and Amino-Anthraquinone Solution

Time-dependent density functional theory (TDDFT) and atoms in molecules (AIM) theory are combined to study the photoinduced excited state intramolecular proton transfer (ESIPT) dynamics for eight anthraquinones (AQs) derivatives in solution. The calculated absorption and emission spectra are consistent with the available experimental data, verifying the suitability of the theory selected. The systems with the excited-state exothermic proton transfer, such as 1-HAQ, 1,5-DHAQ and TFAQ, emit completely from transfer structure (T), while the reactions for those without ESIPT including 1,4-DHAQ and AAAQ appear to be endothermic. Three reaction properties of three systems (1,8-DHAQ, DCAQ and CAAQ) are between the exothermic and endothermic, sensitive to the solvent. Energy scanning shows that 1,4-DHAQ and AAAQ exhibit the higher ESIPT energy barriers compared to 1-HAQ, 1,5-DHAQ and TFAQ with the "barrierless" ESIPT process. The ESIPT process is facilitated by the strengthening of hydrogen bonds in excited state. With AIM theory, it is observed that the change in electrons density ρ(r) and potential energy density V(r) at BCP position between ground state and excited state are crucial factors to quantitatively elucidate the ESIPT.

The borazine dimer: the case of a dihydrogen bond competing with a classical hydrogen bond

Dimers of borazine were studied using matrix isolation infrared spectroscopy and ab initio quantum chemical calculations. Computations were performed at the MP2 and M06-2X levels of theory using the 6-311++G(d,p) and aug-cc-pVDZ basis sets for the various homodimers. At both levels of theory, an aligned stacked structure was found to be the global minimum, which was nearly isoenergetic to a parallel displaced structure. A T-shaped structure, where the N-H of one borazine pointed towards the N of the second borazine, was found to be a local minimum. In addition to these structures, a dihydrogen bonded structure, where the hydrogen attached to the nitrogen of borazine interacted with the hydrogen attached to the boron atom of another borazine, was also indicated. Experimentally, we observed the T-shaped dimer and the dihydrogen bonded dimer. This is one of the rare examples of experimental evidence for a dihydrogen bond, in a system other than in a metal hydride. These results for the borazine dimer were clearly different from the benzene dimer where the parallel displaced structure was found to be the global minimum followed by the T-shaped structure at the MP2/aug-cc-pVDZ level of theory. AIM, EDA and NBO analyses were carried out for all the structures to explore the nature of interactions.