Binary association complexes of LiH, BeH/sub 2/, and BH/sub 3/. Relative isomer stabilities and barrier heights for their interconversion: energy barriers in the dimerization reactions

Journal Article · Thu Mar 26 00:00:00 EST 1987 · J. Phys. Chem.; (United States)

DOI:https://doi.org/10.1021/j100291a034· OSTI ID:6541991

DeFrees, D J; Raghavachari, K; Schlegel, H B; Pople, J A; Schleyer, P v.R.

Ab initio molecular orbital theory has been used to study the six compounds Li/sub 2/H/sub 2/, LiBeH/sub 3/, LiBH/sub 4/, Be/sub 2/H/sub 4/, BeBH/sub 5/, and B/sub 2/H/sub 6/. Geometry optimizations and vibrational analysis at the HF/6-31G* level indicate Li--(H)/sub 2/--Li (D/sub 2h/), Li--(H)/sub 2/--BeH (C/sub 2v/), Li--(H)/sub 3/--BH (C/sub 3v/), HBe--(H)/sub 2/--BeH (D/sub 2h/), HBe--(H)/sub 3/--BH (C/sub 3v/), and H/sub 2/B--(H)/sub 2/--BH/sub 2/ (D/sub 2h/) to the most stable forms. Inclusion of electron correlation corrections at the MP4/6-31G** level does not alter these conclusions. Other isomers were also examined in detail, and it was found that the potential energy surfaces for the species are generally flat. Activation energies for isomer interconversion and hydrogen scrambling reactions are generally less than 10 kcal mol/sup -1/. Examination of the HF/3-21 G potential surfaces indicates that there is no activation energy for the dimerization of LiH or BeH/sub 2/. The same is true for the dimerization of BH/sub 3/ at the correlated MP26-31G* level, although a small barrier is found on the HF/6-31G* surface. Enthalpies of complexation at 298 K from separate LiH, BeH/sub 2/, and BH/sub 3/ fragments, ..delta..H/sup 0//sub 298/, computed by using the HF/6-31G* harmonic frequencies and the MP4/6-31G** electronic energies are as follows: Li/sub 2/H/sub 2/, -45.9; LiBeH/sub 3/, -43.6; LiBH/sub 4/, -60.1; Be/sub 2/H/sub 4/, -30.5; BeBH/sub 5/, -45.7; B/sub 2/H/sub 6/, -36.0 kcal mol/sup -1/.

• Research Organization: Carnegie-Mellon Univ., Pittsburgh, PA
• OSTI ID: 6541991
• Journal Information: J. Phys. Chem.; (United States), Vol. 91:7
• Country of Publication: United States
• Language: English

Related Subjects

37 INORGANIC
ORGANIC
PHYSICAL AND ANALYTICAL CHEMISTRY
BERYLLIUM HYDRIDES
DIMERIZATION
BORON HYDRIDES
LITHIUM HYDRIDES
ACTIVATION ENERGY
BOND LENGTHS
MOLECULAR MODELS
MOLECULAR STRUCTURE
THEORETICAL DATA
ALKALI METAL COMPOUNDS
ALKALINE EARTH METAL COMPOUNDS
BERYLLIUM COMPOUNDS
BORON COMPOUNDS
CHEMICAL REACTIONS
DATA
DIMENSIONS
ENERGY
HYDRIDES
HYDROGEN COMPOUNDS
INFORMATION
LENGTH
LITHIUM COMPOUNDS
MATHEMATICAL MODELS
NUMERICAL DATA
POLYMERIZATION
400201* - Chemical & Physicochemical Properties