Substitution effects of diborane on the interaction with borazine (inorganic benzene)

The gas phase interaction between borazine (IBz) and diborane (DB) has been investigated using MP2/6-311++G** and M05-2X/6-311++G** methods. The calculations have also been carried out at the same levels on the intermolecular complex formed between benzene (Bz) and DB to compare the modes of interaction. The complexation pattern found in IBz...DB is similar to that of Bz...DB due to their structural similarity. The calculated stabilization energies (SEs) at the MP2/6-311++G** level of theory for IBz...DB and Bz...DB complexes are 1.67 and 3.06 kcal/mol, respectively. The corresponding values obtained from the M05-2X/6-311++G** level of calculation are 2.55 and 3.43 kcal/mol. The variation in the SEs between IBz...DB and Bz...DB is due to the differences in the pi-electron distributions of IBz and Bz rings. Since, DB contains a three center-two electron (3c-2e) electron deficient bond, the substitution of nonbridge hydrogen atoms (H) by different functional groups may influence the nature of interaction between the DB and IBz. Thus, the nonbridge H atom in DB has been substituted by electron withdrawing (CN and Cl) and electron donating (CH(3)) groups. The interaction between substituted DBs and IBz has also been investigated using CCSD(T), MP2, and M05-2X methods. Results reveal that the substitution of the nonbridge H atom of DB by a cyano group significantly influences the calculated stabilization energies (SEs) and geometrical parameters whereas substitution by Cl and CH(3) groups marginally affects the stabilities and geometrical parameters of the substituted complexes. The calculated SEs of various substituted DB and IBz complexes range from 1.87 to 7.91 kcal/mol. Furthermore, evidence shows that SEs vary linearly with the number of substituents present in the complexes. The energy decomposition analysis using the density functional theory-symmetry adopted perturbation theory (DFT-SAPT) method confirms the predominant role played by the dispersion interaction in the stabilization of the various complexes when compared to the electrostatic interaction.