The mechanochemical reaction of LiBH₄ with MnCl₂ produces the neutral complex Mn(BH₄)₂. Thermal desorption studies show that the mechanochemical reaction of NaBH₄ with MnCl₂produces a different species, apparently Na₂Mn(BH₄)₄, that undergoes dehydrogenation of a much lower weight percent H at a ~20 °C higher temperature than the neutral Mn(BH₄)₂. Vibrational spectroscopy also reveals that a complex manganese borohydride(s) in addition to Mn(BH₄)₂ are formed from the mechanochemical reactions. Analysis of the vibrational spectra in conjunction with DFT calculations on a model Mn(BH₄)₄^2− complex suggest bidentate binding of the [BH₄]^− ligands to the Mn center in the anionic complex. The calculated highest frequencies of the B−H stretching modes (corresponding to the “freeâ€� B−H bonds) agree well with the experimental frequencies and support the presence of this structural feature.

LiSc(BH₄)₄ has been prepared by ball milling of LiBH₄ and ScCl₃. Vibrational spectroscopy indicates the presence of discrete Sc(BH₄)₄^− ions. DFT calculations of this isolated complex ion confirm that it is a stable complex, and the calculated vibrational spectra agree well with the experimental ones. The four BH₄^− groups are oriented with a tilted plane of three hydrogen atoms directed to the central Sc ion, resulting in a global 8 + 4 coordination. The crystal structure obtained by high-resolution synchrotron powder diffraction reveals a tetragonal unit cell with a = 6.076 Ã… and c = 12.034 Ã… (space group P-42c). The local structure of the Sc(BH₄)₄^− complex is refined as a distorted form of the theoretical structure. The Li ions are found to be disordered along the z axis.

Experimental (IR and Raman) and theoretical (Kohn-Sham calculations) methods are used in a combined analysis aimed at refining the available structural data concerning the molecular guests in channels formed by stacked dibenzo-18-crown-6 (DB18C6) crown ether. The calculations are performed for a simplified model comprising isolated DB18C6 unit and its complexes with either H₂O or H₃O⁺ guests, which are the simplest model ingredients of a one-dimensional diluted acid chain, to get structural and energetic data concerning the formation of the complex and to assign the characteristic spectroscopic bands. The oxygen centers in the previously reported crystallographic structure are assigned to either H₂O or protonated species.

By means of ¹H-NOESY- and Raman-spectroscopic analyses, we experimentally demonstrated the presence of the equatorial N — Me conformer of King's sultam 4b in solution, resulting from a rapid equilibrium. As a consequence, the value of the N lone-pair anomeric stabilization should be revised to 1.5-1.6 kcal/mol. Independently from the N tilting, natural bond orbital (NBO)-comparative analyses suggest that the S d* orbitals do not appear as primordial and stereospecific acceptors for the N lone pair. Second, the five-membered-ring sultams do not seem to be particularly well-stabilized by the S — C σ* orbital in the N-substituted pseudo-axial conformation, as opposed to an idealized anti-periplanar situation for the six-membered-ring analogues. In this latter case, the other anti-periplanar C — C σ* and C(1') — H/C(2') σ*orbitals are as important, if not more, when compared to the S — C σ* participation. In the pseudo-equatorial conformation, γ-sultams particularly benefit from the N lone-pair hyperconjugation with the anti-periplanar S — O₁ σ* and C(2) — H/C or C(1') — H/C σ* orbitals. This is also the case for δ-sultams when the steric requirement of the N-substituent exceeds 1.6 kcal/mol. When both axial and equatorial conformations are sterically too exacting, the N-atom is prone to sp² hybridization or/and conformational changes (i.e., 12c). In that case also, the mode of stereoelectronic stabilization differs from γ- to δ-sultams.