Abstract
The lattice energies of [H2GaNH2]3, [H2BNH2]3 and [H2GeCH2]3 in their experimentally determined space groups, P21/m, Pmn21 and Pbcm, respectively, were calculated using density functional methods for periodic structures with the ab initio periodic code CRYSTAL17. Using the basis set pob-TZVP for all calculations, B3LYP including Grimme's D3 dispersion correction was found to reproduce experimental bond distances and angles most accurately. CRYSTAL17 was also used to optimize geometries and calculate energies of the molecular structures in the gas phase. While the chair conformation of the six-membered rings is found in all of the crystals, only [H2GeCH2]3 retains this as the preferred conformation in the gas phase. By contrast, a twist-boat conformation is preferred for both [H2GaNH2]3 and [H2BNH2]3 in the gas phase, and thus a correction for this change in conformation must be included in corresponding sublimation enthalpy calculations. In addition to the D3 dispersion correction, all lattice energies included a correction for basis set superposition error. The lattice energies for [H2GaNH2]3, [H2BNH2]3 and [H2GeCH2]3 were 153.5, 120.8 and 84.9 kJ mol−1, respectively. These values were used to calculate the sublimation enthalpies, which exhibited good agreement for the single case where an experimental measurement is available, namely [H2BNH2]3 (exp ΔHsub(298), 119 ± 12 kJ mol−1; calcd, 119.4 kJ mol−1). The energetic impact of the crystal structure was assessed by minimizing the structures of each molecule in each of the three space groups spanned by them experimentally and calculating their respective lattice energies. In every case, the experimentally observed space group was the one computed to be the most stable.
Highlights
Volatility is a necessary property for molecules to function as precursors in chemical vapor deposition and related processes
All intermolecular H/H contacts occur between hydridic and protic hydrogens, and the majority of the H/H distances occur at or slightly above the expected van der Waals distance (2.2 A). Both [H2BNH2]3 and [H2GaNH2]3 exhibit several contacts that are $0.2 Ashorter than the van der Waals contact distance, which places them in the range of typical dihydrogen bonds
Comparison of the crystal energies to the energy of the gas phase molecules having the same chair conformation found in the solid state yielded lattice energies of 120.77, 153.49 and 84.87 kJ molÀ1, respectively
Summary
Volatility is a necessary property for molecules to function as precursors in chemical vapor deposition and related processes. In the case involving solid precursors, the heat of sublimation ðDHsubÞ is useful for predicting the equilibrium gas-phase concentration of a precursor. Lattice energy depends on the strength of intermolecular bonds present in the crystalline phase and there has been great interest in structures exhibiting dihydrogen bonds. Ammonia– borane and related compounds, including [H2BNH2]3, exhibit intermolecular dihydrogen bonds and have been the focus of. While the previous study modeled the dihydrogen bond strength computationally based on the difference in energy between gas phase monomers and dimers, the current study includes all intermolecular interactions and reports heats of sublimation that in one case, [H2BNH2]3, can be compared to an experimental value.[23] The current study expands on earlier work by calculating the lattice energy of crystalline [H2BNH2]3, [H2GaNH2]3 and [H2GeCH2]3. The atomic labelling scheme was uni ed for all 29448 | RSC Adv., 2019, 9, 29448–29455
Sign-in/Register to view highlights & summary Sign-in/Register to access full text options 
Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have
Schedule a call
