Hydrogen uptake by {H[Mg(HCOO)3]⊃NHMe2}∞ and determination of its H2 adsorption sites through Monte Carlo simulations

A detailed analysis of the solvothermal synthesis in DMF of the polymeric magnesium formate {H[Mg(HCOO)(3)]⊃NHMe(2)}(∞) (1) from Mg(ClO(4))(2)·6H(2)O revealed that the final crystalline product is formed after an acid-catalyzed DMF hydrolysis, producing formic acid and dimethylamine. The former bridges magnesium(II) centers, creating the 3D scaffold, while the latter is trapped inside the cubic cavities of the polymer, engaging in strong hydrogen bonding with the formate ions of the cage. After thermal activation and guest removal, the material was tested for hydrogen uptake at T = 77 K over the 0-80 bar pressure range, and the existence of preferred H(2) adsorption sites was assessed through grand canonical Monte Carlo (GCMC) simulations. No specific low-energy site was found, and the H(2) molecules positions within the framework cavities are mainly dependent on packing effects. Thus, at low H(2) loadings the most populated site is the center of the cubic cavities, even though, at higher pressures, two more "localized" positions have been found by the simulation because of the reduced freedom of movement. The maximum experimental H(2) uptake corresponds to 8.8 mg/g or 13.5 mg/cm(3).

Nickel(II) hydride and fluoride pincer complexes and their reactivity with Lewis acids BX3·L (X = H, L = thf; X = F, L = Et2O)

Reaction of the pincer hydride complex ((tBu)PCP)Ni(H) [(tBu)PCP = 2,6-C(6)H(3)(CH(2)P(t)Bu(2))(2)] with BH(3)·thf in THF at 190 K generates the corresponding borohydride complex ((tBu)PCP)Ni(BH(4)). The kinetically stable (but thermodynamically unstable) species undergoes reversible borane loss. The related fluoride complex ((tBu)PCP)Ni(F) shows the same reactivity towards BF(3)·Et(2)O, producing ((tBu)PCP)Ni(BF(4)) as the main final product. The processes were followed through multinuclear NMR spectroscopy and DFT calculations, at the M06//6-31+G(d,p) level of theory.