Theoretical study of the triangular bonding complex formed by carbon tetrabromide, a halide, and a solvent molecule in the gas phase.

MP2(full)/aug-cc-pVDZ(-PP) computations predict that new triangular bonding complexes CBr4...X-...H-C (where X- is a halide and H-C refers to a protic solvent molecule) consist of one halogen bond and two hydrogen bonds in the gas phase. Carbon tetrabromide acts as the donor in the halogen bond, while it acts as an acceptor in the hydrogen bond. The halide (which commonly acts as an acceptor) can interact with both carbon tetrabromide and solvent molecule (CH3CN, CH2Cl2, CHCl3) to form a halogen bond and a hydrogen bond, respectively. The strength of the halogen bond obeys the order CBr4...Cl->CBr4...Br->CBr4...I-. For the hydrogen bonds formed between various halides and the same solvent molecule, the strength of the hydrogen bond obeys the order C-H...Cl->C-H...Br->C-H...I-. For the hydrogen bonds formed between the same halide and various solvent molecules, the interaction strength is proportional to the acidity of the hydrogen in the solvent molecule. The diminutive effect is present between the hydrogen bonds and the halogen bond in chlorine and bromine triangular bonding complexes. Complexes containing iodide ion show weak cooperative effects.