The influence of the anion nature and layer composition on the anion-layer interaction in Mg-Al layered double hydroxides (LDHs) is investigated using density functional theory. Changes in the strength of the anion-layer interaction are assessed calculating the potential energy surface (PES) associated to the interlayer anion (OH(-)/Cl(-)) in Mg-Al-OH and Mg-Al-Cl LDHs. The layer composition is varied changing the divalent to trivalent cation proportion (R). Mg-Al-OH is thus investigated with R = 2, 3, 3.5 and Mg-Al-Cl with R = 3. It is found that the PES for OH(-) in Mg-Al-OH/R = 3 presents wider energy basins and lower energy barriers than any other of the investigated compositions. It is shown that the latter is connected to the number of hydrogen bonds formed by the anions. These results have interesting implications for understanding the enhancement of the physicochemical properties of LDHs upon changing composition.

The origin of non-additivity in hydrogen bonds (H-bonds), usually termed as H-bond cooperativity, is investigated in H-bonded linear chains. It is shown that H-bond cooperativity originates solely from classical electrostatics. The latter is corroborated by comparing the H-bond cooperativity in infinitely-long H-bonded hydrogen cyanide, 4-pyridone and formamide chains, assessed using density functional theory (DFT), against the strengthening of the dipole-dipole interaction upon the formation of an infinite chain of effective point-dipoles. It is found that the magnitude of these effective point-dipoles is a consequence of mutual polarization and additional effects beyond a polarizable point-dipole model. Nevertheless, the effective point-dipoles are fully determined once a single H-bond is formed, indicating that quantum effects involved in H-bonding are circumscribed to nearest-neighbor interactions only; i.e. in a linear chain of H-bonds, quantum effects do not contribute to the H-bond non-additivity. This finding is verified by estimating cooperativity along the dissociation path of H-bonds in the infinite chains, using two empirical parameters that account for polarizability, together with DFT association energies and molecular dipoles of solely monomers and dimers.

Layered double hydroxides (LDHs) are materials with capacity of conducting anions. To get insight into the mechanisms controlling LDH intrinsic anionic transport properties, it is investigated the effect of composition on the anion diffusion coefficients in LDHs containing Mg or Zn as divalent cation, Al or Ga as trivalent cation, and OH − or Cl − as interlaminar anion. Diffusion coefficients are estimated simulating diffusion with a kinetic Monte Carlo algorithm on a potential energy surface (PES) associated with the dry interlayer anion. The PES is calculated using density functional theory. We find that at room temperature, diffusion coefficients increase as the difference in electronegativity between metal atoms composing the layers grows. However, at higher temperatures, systems with narrower PES basins become the ones with larger diffusion coefficients, owing to shorter residence times prior to hopping to a neighbor basin. We also find that Cl − has smaller diffusion coefficient than OH − owing to the less capacity of the former to form hydrogen bonds than the latter. These results illustrate the connection between the LDH atomic composition and its properties, knowledge that is desirable for rationally design LDHs with improved properties.

The layered double hydroxides (LDHs) containing Mg2+, Al3+, and OH– (MgAl-OH), commonly known as meixnerite, meixnerite-like, or activated LDH, act as catalyst in the cyanoethylation of alcohols, for which the catalytic activity depends on the LDH composition, particularly on the ratio R between the amount of Mg2+ and Al3+. It is known that MgAl-OH with R = 3 presents the largest catalytic activity when the reactants are methanol and acrylonitrile. To determine the molecular basis of such behavior, the adsorption of OH–, CH3O–, and H2O on the (001) surfaces of MgAl-OH with compositions R = 2, 3, and 3.5 is investigated using density functional theory. It is found that the peculiar catalytic activity of MgAl-OH in the methanol cyanoethylation reaction correlates with the capability of the MgAl-OH surface to stabilize CH3O–a process in which hydrogen bonding plays a crucial roleand the reactivity of the adsorbed CH3O– lone pairs.

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