Charge Transfer via the Dative N−B Bond and Dihydrogen Contacts. Experimental and Theoretical Electron Density Studies of Small Lewis Acid−Base Adducts

Abstract

The electronic characteristics of the dative N−B bond in three Lewis acid−base adducts, hydrazine borane, hydrazine bisborane, and ammonia trifluoroborane, are analyzed by an approach combining experimental electron density determination with a broad variety of theoretical calculations. Special focus is directed to the weak dihydrogen contacts in hydrazine borane. The Atoms In Molecules partitioning scheme is complemented by additional methods like the Source Function, and the Electron Localizability Indicator. For the multipole-free theoretical models of hydrazine borane and hydrazine bisborane, a weak charge donation from Lewis base to acid of about 0.05 e is found, whereas multipole refinement of theoretical and experimental structure factors resulted in opposite signs for the Lewis acid and base fragments. For ammonia trifluoroborane, the donation from Lewis base to acid is slightly larger (about 0.13 e) in the multipole-free models, and the charges obtained by multipole refinement retain the direction of the charge donation but show quite large variations. The natural population analysis charges predict larger charge donations (0.35 e) from the Lewis bases to the acids for the three title complexes. Although the three compounds exhibit intermolecular interactions of different types and strengths, including classical hydrogen bonds, F···H contacts and the already mentioned dihydrogen bonds, almost no charge transfer is detected between different molecules within the crystal environment. The main electronic effect of the formation of the Lewis acid-base adducts and of the crystallization is an increase in the charge separation within the ammonia/hydrazine fragments, which is supported by all investigated bond and atomic properties. The nature of the dative N-B bond is found to be mainly electrostatic, but with a substantial contribution of covalency. The F-B bonds show similarities and differences from the N-B bonds, which makes a distinction of coordinative (or dative) bonds from polar covalent interactions possible.

Hydrazine Borane and Hydrazinidoboranes as Chemical Hydrogen Storage Materials

“…By XRD of a single crystal, Goubeau and Ricker reported an orthorhombic Pccn (56) space group [10]. More recently, the structure was solved using an orthorhombic Pbcn (60) space group with all of the B, N and H atoms belonging to the 8 d sites; Further, the cell parameters were refined [24,31,32]. As shown in Table 1, the cell parameters a, b and c are in good agreement.…”

“…As shown in Table 1, the cell parameters a, b and c are in good agreement. Neutron diffraction experiment permitted to obtain correct coordinates of the H atoms [31]. The N-B, N-N, N-H and B-H bonds as well as the N-H···H-B and N-H···N interactions were described.…”

“…The nature of the N-B coordinative (or dative) bond (1.596 Å) exhibits an electrostatic feature mainly, but with substantial contribution of covalence with a large electron population of ~2.1 electrons and a small donation of ~0.05 electron from the Lewis base (N) to the Lewis acid (B). With respect to the N-H···H-B intermolecular weak interaction (2.01(1)-2.41(1) Å) [31], it allows a head-to-tail network of the hydrazine borane molecules (Figure 2), which rationalizes the solid state of the material [24]. The N-H···N intermolecular interactions (2.114 Å) occur with the head-to-tail network, according to planes parallel to the a-axis.…”

Molecular Structure and Real‐Space Bonding Descriptors (AIM, ELI‐D) of Phenyl(triphenylstannyl)telluride

“…Dative bonds are represented by an RJI of at least 95 %. [13] The ELI-D is displayed for two different iso values in Figure 4. At Y = 1.4 the Te-Sn basin is not visible as the ELI-D value at the attractor position is 1.34.…”

The Search for Hydrogen Stores on a Large Scale; A Straightforward and Automated Open Database Analysis as a First Sweep for Candidate Materials

“…One approach to increase the hydrogen content still further would be to replace the relatively hydrogen-poor anion by one with a higher hydrogen:boron ratio. Many strong hydrogen storage candidates exist among covalent boron-hydrogen compounds such as NH3BH3 [62], NH3B3H7 [63] and H4N2BH3 [64]. The B-N-H combination is not an arbitrary one but defines a distinctive family of complex molecular species that are stabilised by the dative bond between the strong electron-donating Lewis base, nitrogen and the strong electron-accepting Lewis acid, boron [65,66].…”