Eva Scholtzová

INFLUENCE OF SYNTHESIS CONDITIONS ON THE FORMATION OF A KAOLINITE-METHANOL COMPLEX AND SIMULATION OF ITS VIBRATIONAL SPECTRA

Kaolinite is often used as a base for the synthesis of new organo-mineral nanomaterials designed for applications in industry and in environmental protection. To make the mineral structure more likely to interact with organic molecules, a kaolinite-methanol complex (KM) can be used. In the present study, different experimental procedures were tested to investigate the formation of the KM. The kaolinitedimethyl sulfoxide intercalation compound (KDS), either wet or dried, was used as a pre-intercalate. The samples obtained were characterized using X-ray diffraction, Fourier-transform infrared spectroscopy, CHNS elemental analysis, 13C CP-magic angle spinning nuclear magnetic resonance (MAS NMR), and 27Al and 29Si MAS NMR techniques. The method of density functional theory with dispersion corrections (DFT-D2) was used to explain the structure and to simulate the vibrational spectra of KM. Theoretical results were compared with experimental data. The most effective formation of the KM (d001 = 11.1 Å — wet; d001 = 8.7 Å — dried) was observed when the dried KDS precursor was used. In such conditions the degree of intercalation reached ~98% after 24 h of reaction time. As indicated by the CHNS elemental analysis, ~1/6 of the inner-surface OH groups were grafted by OCH3 groups. The esterification reaction was less efficient at higher temperatures or when wet KDS was used. In the latter case, the excess of very polar dimethyl sulfoxide molecules prevented intercalation of methanol and further grafting. Detailed analysis of the results of theoretical simulations revealed that the reaction of the KDS with methanol led to the formation of kaolinite with both grafted methoxy groups and intercalated methanol, and water molecules in the interlayer space. The spectra calculated revealed the contribution of individual vibrational modes into the complex bands, i.e. the energy of C-H vibrations was in the order: νasCHmet > νasCHmtx > νsCHmet > νsCHmtx.

Theoretical study of cation substitution in trioctahedral sheet of phyllosilicates. An effect on inner OH group

The effect of substitutions of central cations in the octahedral sheet of trioctahedral phyllosilicates on the inner hydroxyl group was studied applying quantum-mechanical B3LYP/DZP method on cluster models of the solid. Changes of the geometry and of the stretching vibration of the inner hydroxyl group were observed. Calculated vibrational frequencies correlate with experimental spectra of 2:1 trioctahedral minerals of the talc type. The simulation of infrared spectra in the region of the stretching vibration of the inner OH groups was performed for several concentrations of the Ni 2þ cation in the trioctahedral sheet. Simulated spectra are in good agreement with experimental ones of synthetic talc minerals containing different concentrations of the Ni 2þ cation. q 2002 Published by Elsevier Science B.V.

HYDROGEN BONDING AND VIBRATIONAL SPECTRA IN KAOLINITE-DIMETHYLSULFOXIDE AND -DIMETHYLSELENOXIDE INTERCALATES –A SOLID-STATE COMPUTATIONAL STUDY

The aims of this study were to obtain accurate structural information on the dimethyl sulfoxide (DMSO) and dimethylselenoxide (DMSeO) kaolinite intercalates, paying close attention to the hydrogen-bond geometries, and to provide a detailed interpretation of the individual vibrational modes of intercalates under study and relate their energies to the formation of the hydrogen bonds. Accurate positions of all the atoms in the structures of kaolinite:dimethylsulfoxide (K:DMSO) and kaolinite:dimethylselenoxide (K:DMSeO) intercalates have been obtained by the total energy minimization in solid state at density functional theory (DFT) level of the theory. The bond distances and angles in the kaolinite 1:1 layer are in good agreement with those reported in the most recent single-crystal refinement of kaolinite. Computed geometries of DMSO and DMSeO agree well with the high-quality diffraction data and independent theoretical ab initio calculations. The organic molecules are fixed in the interlayer space mainly by three moderately strong O-H⋯O hydrogen bonds, of different strengths, with the O⋯O contact distances being within 2.739–2.932 Å (K:DMSO) and 2.681–2.849 Å (K:DMSeO). Substantially weaker C-H⋯O and O-H⋯S(Se) contacts play only a supporting role. The optimized atomic coordinates were used to calculate the individual vibrational modes between 0 and 4000 cm−1. The maximum red shifts of the OH-stretching modes caused by the formation of the O-H⋯O hydrogen bonds were 407 cm− (K-DMSO) and 537 cm−1 (K-DMeSO), respectively. The Al-O-H bending modes are spread over the large interval of 100–1200 cm−1, but the dominant contributions are concentrated between 800 and 1200 cm−1. Theoretically calculated energies of the OH- and CH-stretching modes show good agreement with the previously published figures obtained from the infrared and Raman spectra of these intercalates.

Crystal and electronic structure of aqua(N-salicylidene-methylester-L-glutamato)Cu(II) monohydrate

Abstract The absolute structure of the title compound, CuNC13H17O7, has been determined. The crystal structure consists of the molecular units Cu(N-sal-5-met-L-glu)(H2O) connected by a three-dimensional network of hydrogen bonds. The coordination polyhedron in the complex is approximately square-pyramidal with a pentacoordinated Cu(II) atom. The base of the pyramid is formed by nitrogen and oxygen atoms belonging to the molecule, while the apex of the pyramid contains a weakly bonded oxygen atom of the carboxylic group of another molecule. The B3LYP/SVP method and basis set in Gaussian98 was used for quantum chemical calculation of the nature of Cu–X (X = O, N) bonds. While the calculated dissociation energy of the weakly bonded crystalline water is only 17.2 kJ/mol, the bonding energy of the water molecule coordinating to the Cu atom is 62.3 kJ/mol.

Ab initio structure determination of 5-anilinomethylene-2,2-dimethyl-1,3-dioxane-4,6-dione from laboratory powder data--a combined use of X-ray, molecular and solid-state DFT study.

The crystal structure of the title compound was solved from laboratory powder diffraction data in the triclinic group P\bar 1 by simulated annealing using the program DASH. Since Rietveld refinements yielded inaccurate geometries the structure was finally refined by geometry optimization using energy minimization in the solid state with the DFT/plane-waves approach. The molecule is essentially planar and its Meldrums acid moiety (2,2-dimethyl-1,3-dioxane-4,6-dione) has a flattened boat conformation. The bond orders in the molecule estimated using a natural bond-orbitals formalism correlate with the optimized bond lengths. The structure in the solid state is based on dimer units in which the molecules are held by N-H...O and C-H...O hydrogen bonds in addition to electrostatic interactions. These units interact through weak C-H...O hydrogen bonds. It is suggested that structure refinement by energy minimization at the DFT level of theory may in many cases successfully replace Rietveld refinement.

(N-salicylidene-D,L-glutamato) (2-methylimidazole)copper(II).

The title racemic compound, [Cu(C12H11NO5)(C4H6N2)], adopts a square-pyramidal Cu(II) coordination with the tridentate N-salicylideneglutamate Schiff base dianion and the 2-methylimidazole ligand in the basal plane. The apex of the pyramid is occupied by a carboxylic acid O atom from the neighbouring chelate at a distance of 2.479(4)A, leading to infinite one-dimensional chains along the crystallographic a axis. Strong N-H...O and O-H...O hydrogen bonds form a helix parallel to the c axis. The electronic structure of the title compound has also been investigated by the B3LYP method.

Combined powder diffraction and solid-state DFT study of [Cu (2,6-dimethoxynicotinate)2(μ-ronicol)2]n complex

Abstract Crystal structure of the title compound was solved from the laboratory powder diffraction data in the P21/c space group. Because Rietveld refinement yielded inaccurate geometry of the structural moieties the structure was finally refined by means of geometry optimization using DFT/plane waves approach in the solid state. The asymmetric unit of [Cu{2,6-(MeO)2nic}2(μ-ron)2]n consists of the copper(II) atom located on an inversion centre, one 2,6-dimethoxynicotinate anion and one ronicol molecule which acts as a bridging ligand coordinated via oxygen atom of the hydroxymethyl group as well as the nitrogen atom of the pyridine ring – μ-ron = bridging 3-pyridylmethanol. Each copper (II) complex unit is connected to the other four units through the ronicol ligands forming 2D sheets running parallel to the bc plane. The structure is stabilized by a strong intramolecular hydrogen bond O—H…O and supported by weak C—H…O hydrogen bonds.

STRUCTURAL AND SPECTROSCOPIC CHARACTERIZATION OF MONTMORILLONITE INTERCALATED WITH N-BUTYLAMMONIUM CATIONS (N = 1–4) – MODELING AND EXPERIMENTAL STUDY

A detailed structural characterization of organo-clays is a key in understanding their properties. In this work, mono-, di-, tri-, and tetra-butylammonium (nBA; n = 1–4) cations intercalated in the layered clay mineral montmorillonite (Mnt) have been studied for the first time by combining a theoretical approach based on density functional theory (DFT) and infrared spectroscopy. The DFT calculations revealed the detailed structure and position of nBA cations in the interlayer space. A relation between the basal spacing (d001 parameter) and the cation size and structure was found, and explained with respect to the structure, composition, and size of the organic cations. Hydrogen bonds between -NHx/-CH3/-CH2 groups of the nBA cations and oxygen atoms of the basal planes of the Mnt layers were found to be an important factor for the arrangement and energetic stabilization of cations in the interlayer space. The N–H…O hydrogen bonds are stronger than C–H…O hydrogen bonds and the stabilization decreases with decreased number of bands. Analysis of DFT-calculated vibrational modes helped in understanding a problematic region of the experimental infrared spectra (4000–3000 cm-1), in which assignment of all vibrational modes unambiguously was not possible because of a significant overlap of broad bands.

Structure of Sulfated Monosaccharides Studied by Quantum Chemical Methods.

Ab initio and DFT analysis have been used to study of geometry of sulfated monosaccharides GlcN,6-SO3- and IdoA 2-SO3- in solvent. The computed low conformational barrier between the interconverting conformers of the IdoA 2-SO3- residue is in agreement with experimental data.

(1-Methylimidazole)(N-salicylidene-rac-glutamato)copper(II)

The title racemic compound, [Cu(C12H11NO5)(C4H6N2)], adopts a square-planar copper(II) coordination mode with the tridentate N-salicylidenglutamato Schiff base dianion and the 1-methylimidazole ligand. Dimers of centrosymmetrically related molecules are formed. The theoretical investigation of the electronic structure of the title compound by the B3LYP method is presented.