Theoretical estimates of the IR spectrum of formamide intercalated into kaolinite

Abstract

Calculations at PM3 and PBE/6-31G levels of part of the IR spectrum of the formamide-kaolinite intercalatation compound based on a 110-atom cluster of kaolinite with one formamide molecule are reported. Frequencies and intensities for the formamide vibrations and stretchings of four cluster hydroxyls were calculated through partial hessian matrices and polar tensors obtained by numerical differentiation of energy gradients and dipole moment. The formamide molecule attaches to the kaolinite inner surfaces in multiple conformations with its CN bond vector parallel to the surfaces. Hydrogen bonds are formed between the formamide hydrogen atoms (both from NH 2 or CH groups) and the siloxane surface and between the formamide oxygen and nitrogen atoms and the aluminol hydroxyls. The general features of the experimental assignment of the spectrum are confirmed, but the observed splitting of formamide bands is attributed to vibrations from differently attached molecules.

Molecular Dynamics Simulation of Basal Spacing, Energetics, and Structure Evolution of a Kaolinite–Formamide Intercalation Complex and Their Interfacial Interaction

“…A similar position and orientation of formamide in the kaolinite interlayer was revealed in the quantum chemistry calculation at the PBE/6-31G level. 31…”

“…This H-bonds scheme agrees well with the quantum chemistry studies on the intermolecular interactions of formamide with the kaolinite tetrahedral surface. 30,31 Other theoretical and experimental studies, 17–20,27–29 however, did not mention the formation of H-bonds involved in the hydrogen atom in the HC═O group. Moreover, the H-bond statistics shows that a certain number of NH groups of formamide are also hydrogen bonded weakly with the oxygen atoms of hydroxyl groups on the octahedral surface.…”

“…21–26 A theoretical method of quantum chemistry has been used to study the interactions of formamide with kaolinite and dickite surfaces. 27–31 It is generally considered that the octahedral surface hydroxyl groups form relatively strong H-bonds with formamide, and the basal oxygens of the tetrahedral surface are able to form relatively weak H-bonds with formamide. The Monte Carlo (MC) simulation of the stable basal spacing and structure of the kaolinite–formamide complex showed that the molecular plane of formamide was basically parallel to the kaolinite surface.…”

Mineral–organic interfacial processes: potential roles in the origins of life

“…335 On the other hand, the intercalation energy of FA-kaolinite obtained at the PM3/6-31G(d) level is less than À12 kcal mol À1 for five different configurations. 338 The difference in the binding energies for different geometries amount to 5.6 and 2.9 kcal mol À1 , respectively.…”

“…335,338 Two of these H-bond contacts are formed between surface hydrogen atom and FA carbonyl oxygen atom, in which the FA oxygen atom behaves as a proton-acceptor. In both intercalated and adsorbed systems, FA forms additional H-bonds with the octahedral surface between the FA carbonyl oxygen atom, the -NH 2 group [335][336][337] and/or nitrogen atom 336,338 and the surface hydroxyl groups. The NH 2 group of FA acts as a proton-donor and the surface oxygen atom behaves as a proton-acceptor.…”