Theoretical study of the stability of species ABH3(ALi…Ne) (original) (raw)
The boranes B3H7 and B6H14. A theoretical investigation
Chemical Physics Letters, 1988
Results of SCF and CPF calculations are reported for B,H, and its dimer BbH,,. They were performed to determine structure and relative energies. As a check for the methods of calculation employed we report large-scale treatments of BH, and B,H,. For BIHl we confirm previous treatments showing the existence of at least three isomers separated by only a few kJ/mol. Dimerization of B,H7 is computed to be exothermic by 74.3 kJ/mol. The most stable isomer of B,H,, is tris-diborane but various other structures are only 10 to 30 kJ/mol higher in energy, indicating non-rigidity on the time scale of NMR measurements, These results allow for a rationalization of experiments.
Stability and bonding in the borane-H 2 complexes
International Journal of Quantum Chemistry, 2012
The ability of substituted boranes, X n BH 3Àn , to form stable complexes with the hydrogen molecule is analyzed by making use of computational chemistry and local reactivity parameters. In these complexes, the hydrogen molecule acts as a Lewis base while the borane moiety is the Lewis acid. Electronegative groups (X ¼ CF 3 , F, OH) are selected to increase the acidity of the borane and it is found that the energetic stability of the complexes is only increased for the trifluoromethyl-substituted Lewis acids, at the MP2/6-311þþg(3df, 3pd) level. It is also found that the BLYP density functional underestimates the adduct stability of these species. On the other hand, fluoroboranes and hydroxyboranes do not form donor-acceptor adducts with the hydrogen molecule; instead, we find weakly bounded van der Waals complexes. Additional features on the intrinsic reactivity of boranes are analyzed with the molecular electrostatic potential and the acceptor Fukui function. The nature of the interaction among the boranes and the hydrogen molecule is explored by using the topological analysis of the electron density through the Bader's Atoms-in-Molecules theory.
A full configuration interaction study of the low-lying states of the BH molecule
Molecular Physics, 1997
A full con® guration interaction study on the BH molecule is presented. The potential energy curves of 20 di erent electronic states have been calculated correlating the four valence electrons. On the two most important states, i.e. the X 1 R + and A 1 P states, a complete study has been performed. This includes the e ect of core electron correlation, estimated via truncated con® guration interaction techniques. The dissociation energy of the molecule in the two states and the height of the predissociative barrier in the A 1 P state have been determined with basis sets of increasing quality.
A full con� guration interaction study of the low-lying states of the BH molecule
1997
A full con® guration interaction study on the BH molecule is presented. The potential energy curves of 20 di erent electronic states have been calculated correlating the four valence electrons. On the two most important states, i.e. the X 1 R + and A 1 P states, a complete study has been performed. This includes the e ect of core electron correlation, estimated via truncated con® guration interaction techniques. The dissociation energy of the molecule in the two states and the height of the predissociative barrier in the A 1 P state have been determined with basis sets of increasing quality.
Comparison of μ2-scaled Hückel theory and Hartree–Fock theory of boranes and carboranes
The Journal of Chemical Physics, 1994
The h-scaled Hiickel method is used to calculate the electronic energy surfaces of the four boranes B,Hz-(12 =8-l 1) and the carborane C,BsH:, . These electronic energy surfaces and their minimum energy geometries are directly compared to both the single crystal x-ray determined structures and to Hartree-Fock optimized geometries. Bond distances differ on the average by 0.04 A between alternate methods. It is shown that h-scaled Hiickel results may be directly interpreted by analysis of the highest occupied and lowest unoccupied molecular orbitals. Also studied by the h-scaled Hiickel and Hartree-Fock methods are the isomerization pathways of BsHi-, B,,H:;, and C,BsHfR . Reaction barriers and transition state geometries found by the two different calculational methods are in fair agreement with each other and known literature values. Using the h-scaled Hiickel method one can readily deduce that the BsHi-and B,,H:; isomerizations are Woodward-Hoffmann allowed reactions. In the case of B,Hi-this allowed mechanism is contrasted to an alternate Woodward-Hoffmann forbidden pathway. Hartree-Fock calculations on the C,BsHT, confirm earlier h-scaled Hiickel based findings, that a second less stable isomer of C,B,H:, exists which, in contradiction to Wade's rules of electron deficient clusters, has a pair of open square faces in the cluster.
Equilibrium Structure and Torsional Barrier of BH 3 NH 3
The Journal of Physical Chemistry A, 2008
Born-Oppenheimer equilibrium structures, r e BO , of the electronic ground state of the borazane (BH 3 NH 3 ) molecule of C 3V point-group symmetry are computed ab initio using the CCSD(T) method with basis sets up to quintuple-quality. Inclusion of the counterpoise correction and extrapolation of the structural parameters to the complete basis set limit yield a best estimate of r e BO of BH 3 NH 3 . The anharmonic force field of BH 3 NH 3 , computed at the CCSD(T) level of theory with a basis set of triple-quality, allows the determination of semi-experimental equilibrium rotational constants, which in turn result in a semi-experimental equilibrium structure, r e SE . The r e BO and r e SE structures are in excellent agreement, indicating the validity of the methods used for their determination. The empirical mass-dependent structure, r m (1) , of BH 3 NH 3 is also determined. Although it is inferior in quality to the previous two structures, it is much more accurate than the standard empirical r 0 and r s structures reported earlier for BH 3 NH 3 . The semi-experimental r e SE as well as the empirical r m
The ab initio limit quartic force field of BH 3
Journal of Computational Chemistry, 2005
The complete quartic force field of BH 3 has been converged to the ab initio limit by extrapolation of core-valence correlation-consistent basis set series (cc-pCVXZ, X ϭ T, Q, 5) of all-electron CCSD(T) (coupled-cluster singles and doubles with perturbative triples) energy points. Additional computations including full coupled-cluster treatments through quadruple excitations (CCSDTQ), scalar relativistic effects, and diagonal Born-Oppenheimer corrections (DBOC) were concurrently executed. Within second-order vibrational perturbation theory (VPT2) our quartic force field yields the fundamental frequencies 1 ϭ 2502.3 cm Ϫ1 , 2 ϭ 1147.2 cm Ϫ1 , 3 ϭ 2602.1 cm Ϫ1 , and 4 ϭ 1196.5 cm Ϫ1 , in excellent agreement with observed gas-phase fundamentals, displaying a mean absolute error of only 0.3 cm Ϫ1. Our converged prediction for the equilibrium bond length of BH 3 is r e ϭ 1.1867 Å.
Journal of Molecular Structure: THEOCHEM, 2008
The conformations of boric acid (1), its conjugate basis (2) and borate anion (3) have been investigated with the B3LYP, HF, MP2 and QCISD methods with a variety of basis sets. Transition-state structures connecting the various minima have been computed. Relative energies are reported at the G3(MP2)//B3LYP level of theory. The lowest-energy conformation of boric acid has C 3h symmetry. The C s conformer lies 4.1 kcal/mol higher in energy and the barrier for inter-conversion is 7.8 kcal/mol. The lowest-energy conformation of (HO) 2 BO À has C 2v symmetry. There are two conformations lying higher in energy by 1.7 and 9.1 kcal/mol, with barriers of 7.8 and 10.3 kcal/mol, respectively. For borate anion two distinct S 4-symmetry minima were located which differ in energy by 1.5 kcal/mol. The computed enthalpies of formation for 1, 2 and 3 are À236.3, À242.9 and À320.8 kcal/mol, respectively.
, and B10H1, are interpreted as resonance hybrids of valence bond structures that only contain two-center two electron bonds. Graph-theoretical techniques are used to count the large number of structures incorporated in the hybrids. Calculated bond orders and charges are compared with the results of LCAO-MO-SCF calculations and with three-center valence bond models. The heats of atomization can be correlated with a 4 term linear equation based on the numbers of neighboring boron atom pairs, terminal BH bonds, bridging BH bonds, and estimates of resonance energies. Resonance energies comprise 1 1 to 29% of the atomization energies for these boron hydrides.
The vibrational spectra of the boron halides and their molecular complexes, part 5 An ab initio stud
Theor Chem Acc, 1997
The optimized structures, interaction energies, Mulliken charges and vibrational spectra of three conformers of a 1:1 complex between boron tri¯uoride and carbon dioxide have been determined by means of ab initio calculations at the second-order level of Mùller-Plesset perturbation theory, using the 6-31G* basis set. All three structures feature a BÁ Á ÁO electron donoracceptor interaction. One of the structures, in which the carbon dioxide axis eclipses one of the BF bonds, was found to be a genuine minimum, one (the corresponding staggered form) a ®rst-order saddle point and the third (a linearly bonded BÁ Á ÁOCO species) a second-order transition state. The computed infrared spectrum of the preferred conformer has been used to predict the appearance of the spectrum of boron tri¯uoride and carbon dioxide co-deposited in cryogenic matrices, which will be reported in a forthcoming publication.