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 LPX→BD*B‑O for B3O3H3…C2HX (X=Cl, Br, NH2), and BDC‑C→BD*B‑O for B3O3H3…C2HX (X=H, CH3) complexes. Complexes of B3O3H3 with acetylene and its substituted derivatives.