Several possible binary complexes among ammonia-borane, aminoborane, and ammonia, via hydrogen and/or dihydrogen bonds, have been investigated to understand the effect of different hybridization. Moller-Plesset second-order perturbation theory with aug-cc-pVDZ basis set was used. The interaction energy is corrected for basis set superposition error, and the Morokuma-Kitaura method was employed to decompose the total interaction energy. Like H3BNH3, the sp(2) hybridized H2BNH2 also participates in H- and dihydrogen bond formation. However, such bonds are weaker than their sp(3) analogs. The contractions of BN bonds are associated with blueshift in vibrational frequency and stretches of BH and NH bonds with redshift. The polarization, charge transfer, correlation, and higher-order energy components are larger in dihydrogen bonded complexes, compared to classical H-bonded ammonia dimers. (C) 2003 American Institute of Physics.