Fundamental Thermochemical Properties of Ammonia Borane and Dehydrogenated Derivatives (BNHn, n = 0−6)

The heats of formation for BN, HBNH, H 2 BNH 2, and H 3 BNH 3 and their radicals, anions, cations, and protonated species were predicted using the CCSD(T) method with correlation consistent basis sets extrapolated to the complete basis set and core−valence, scalar relativistic, spin−orbit, and zero-point energy corrections. Chemical accuracy (±1 kcal/mol) is obtained for these heats of formation, allowing reliable results for electron and hydride affinities, ionization energies, basicities (neutral proton affinities), acidities (anion proton affinities), and bond dissociation energies of the BNH n ( n = 0−6) molecules. The closed shell BNH n molecules, except for H 3 BNH 3 (double diffuse functions on B and N required), do not bind an electron and behave as nitrogen acids and bases. Protonation of H 3 BNH 3 leads to nearly spontaneous H 2 release. The closed shell BNH n species exhibit ionization energies similar or smaller than those of hydrocarbons, and for the H 2 BNH radical, its ionization energy (∼5.9 eV) is close to that of the alkali elements. Except for H 3 BNH 3, the NH bonds are systematically stronger than the BH bonds, and the BDE(NH) values tend to increase with increasing multiple character of the BN bonds. Trends and comparisons between properties obtained through reactions on the N and B atoms are given. Comparisons with properties of hydrocarbons show similarities and differences between the two isoelectronic series.