Solid-state DFT Calculations Research Articles

Structure of Carbon-Coated C12A7 Electride via Solid-State NMR and DFT Calculations

C12A7 calcium aluminate electride (C12A7:e–) is a novel inorganic functional material with mayenite crystal structure. Because of its physical and chemical properties, C12A7:e– can find application as a catalyst carrier in various reactions, including ammonia synthesis. However, the low specific area of this material imposes limitations on its use in catalysis. This limitation can be circumvented by synthesis within carbon nanoreactors as the carbon-coated particles resist sintering. We investigate by solid-state 27Al nuclear magnetic resonance (NMR) spectroscopy the structure of C12A7 electride prepared by the carbon nanoreactor process. An accurate determination of NMR parameters via simultaneous application of both DFT calculations and solid-state NMR proved the structure of carbon-coated C12A7 electride to be identical to the one of materials synthesized by more conventional routes. It was shown that the conducting electrons of C12A7:e– do not alter the cage structure, thus leading to similar NMR para...

Phosphorescent C∧C* Cyclometalated Thiazol-2-ylidene Iridium(III) Complexes: Synthesis, Structure, and Photophysics

The synthesis and characterization of the first cyclometalated arylthiazole-based iridium(III) phosphorescent emitters of the general structure IrL2(acac) with L = 3-(4-bromophenyl)-4,5-dimethyl-1,3-thiazol-2-ylidene and 3-(4-methylphenyl)-4,5-dimethyl-1,3-thiazol-2-ylidene and acac = acetylacetonato is presented. All complexes were isolated isomerically pure and were unambiguously assigned by a solid-state structure, DFT calculations, and 2D NMR studies. Investigation of their emission behavior revealed emission maxima at 495 ± 5 nm. Quantum chemical calculations were used to calculate the energy differences between the possible isomers and to understand the emission behavior.

Insights into the Correlation of Aluminum Distribution and Brönsted Acidity in H-Beta Zeolites from Solid-State NMR Spectroscopy and DFT Calculations.

Here we utilized 27Al MAS/MQMAS and 31P MAS NMR of quantitative adsorption of trimethylphosphine oxide (TMPO) and DFT calculations to elucidate the relationship between Al distribution and Brönsted acidity of series H-Beta zeolites derived from dealumination of Al-rich H-Beta zeolite. Three types of Brönsted acid strengths corresponding to different specific Al T-sites were demonstrated. The removal of one framework Al in 5MR2--2Al and 6MR-2Al sites led to increasing the Brönsted acid strength of dealuminated H-Beta. Our findings on such exact correlation between specific Al distributions and corresponding Brönsted acid sites may guide the controlling Al distribution to get desired acid properties through zeolite synthesis or finely tuned dealumination, which has a great impact on the catalytic activity and selectivity of zeolite catalysts.

Structure determination from X-ray powder diffraction, DFT calculation, and Hirshfeld surface analysis of two fused bicyclic and tricyclic compounds

Crystal structures of two fused cyclic systems have been determined from X-ray powder diffraction data and their molecular geometries and intermolecular interactions have been analyzed by solid state DFT calculation and Hirshfeld surface evaluation, respectively.

Effect of pressure on two polymorphs of tolazamide: why no interconversion?

Two polymorphs of tolazamide, N-[(azepan-1-ylamino)carbonyl]-4-methylbenzenesulfonamide, a sulfonylurea anti-diabetic drug, have different densities and molecular packings. Polymorph II converts into polymorph I in the solid state on heating or via recrystallization if solvent-assisted. The effect of pressure on the two forms and the possibility of a transformation to a denser form on compression have been studied. No phase transitions have been observed in either of the forms in a pentane–isopentane mixture (when no recrystallization is possible). Polymorph II recrystallized partly into a denser polymorph I in methanol at 0.1 GPa, but the transformation stopped at an early stage. Solid state DFT calculations of the two forms as well as conformational landscape investigation in the gas phase were used to rationalize this result. The anisotropic pressure-induced strain of the two polymorphs has been compared in relation to changes in the hydrogen bond geometry and the behavior of stacking interactions.

Anion-π recognition between [M(CN)6]3- complexes and HAT(CN)6: structural matching and electronic charge density modification.

Hexacyanidometalates (M = FeIII, CoIII) and multisite anion receptor HAT(CN)6 (1,4,5,8,9,11-hexaazatriphenylenehexacarbonitrile) recognize each other in acetonitrile solution and self-assemble into the novel molecular networks (PPh4)3[M(CN)6][HAT(CN)6] (M = Fe, 1; Co, 2) and (AsPh4)3[M(CN)6][HAT(CN)6]·2MeCN·H2O (M = Fe, 3; Co, 4). 1-4 contain the stacked columns {[M(CN)6]3-;[HAT(CN)6]}∞ separated by the organic cations. All of the M-C[triple bond, length as m-dash]N vectors point collectively towards the centroids of pyrazine rings on neighboring HAT(CN)6 molecules, with Ncyanidecentroidpyrazine distances that are under 3 Å. The directional character and structural parameters of the new supramolecular synthons correspond to collective triple anion-π interactions between the CN- ligands of the metal complexes and the π-deficient areas of HAT(CN)6. Physicochemical characterisation (IR spectroscopy, UV-Vis spectroscopy, cyclic voltammetry) and dispersion-corrected DFT studies reveal the dominating charge-transfer (CT) and polarisation characters of the interactions. The electronic density flow occurs from the CN- ligands of [M(CN)6]3- to the HAT(CN)6 orbital systems and further, toward the peripheral -CN groups of HAT(CN)6. Solid-state DFT calculations determined the total interaction energy of HAT(CN)6 to be ca. -125 kcal mol-1, which gives ca. -15 kcal mol-1 per one CN-HAT(CN)6 contact after subtraction of the interaction with organic cations. The UV-Vis electronic absorption measurements prove that the intermolecular interactions persist in solution and suggest a 1 : 1 composition of the anion-π {[M(CN)6]3-;[HAT(CN)6]} chromophore, with the formation constant Kadd = (5.8 ± 6) × 102 dm3 mol-1 and the molar absorption coefficient εadd = 180 ± 9 cm-1 dm3 mol-1 at 600 nm, as estimated from concentration-dependent studies.

Insight into the formation of the tert-butyl cation confined inside H-ZSM-5 zeolite from NMR spectroscopy and DFT calculations.

Solid-state NMR experiments and DFT calculations have been carried out to determine the complex structures of coadsorbed (13)C-labeled tert-butanol and NH3 in acidic H-ZSM-5 zeolite. It is found, besides the physically adsorbed tert-butanol/NH4(+) complex on Brønsted acid sites, the tert-butylamine cation is formed as well, confirming the presence of the tert-butyl cation confined in zeolite channels. Furthermore, (13)C-(27)Al double-resonance solid-state NMR spectroscopy is adopted to determine the host/guest interaction between the carbocation and the zeolite framework.

Exploiting polymorphism in second sphere coordination: thermal transformation, NLO properties and selective mechanochemical synthesis

The racemic organic building block L acting as a first sphere ligand yields a new second sphere adduct [LH]+·[FeCl4]− crystallizing as racemic polymorphs α and β. Solid-state DFT calculations show that polymorph β is the kinetic adduct as observed experimentally. The β-phase crystallizes in the polar space group Pna21 and displays NLO properties. Mechanochemical synthesis yields only the β-phase.

Tripeptides on Gold Nanoparticles: Structural Differences between Two Reverse Sequences as Determined by Solid-State NMR and DFT Calculations.

The reverse-sequence peptides CysAlaAla and AlaAlaCys may attach to gold nanoparticles through the thiol group, and they differ primarily by whether the charged amino or the carboxylate group is proximal to the sulfur. Alanine residues in these peptides are not expected to interact significantly with the gold surface and serve to place a large separation between the amino and carboxylate groups. Solid-state NMR experiments and DFT calculations were performed to explore the structural differences between CysAlaAla on gold nanoparticles and AlaAlaCys on gold nanoparticles. It is found that the relative positions between the thiol, amino, and carboxylate groups strongly influences the structures of the peptide-gold systems. CysAlaAla orients parallel to the gold surface in a monolayer fashion, whereas AlaAlaCys forms an interdigitating bilayer-like structure that is oriented upright relative to the gold surface.

Far infrared spectra of solid state l-serine, l-threonine, l-cysteine, and l-methionine in different protonation states

In this study, experimental far infrared measurements of l-serine, l-threonine, l-cysteine, and l-methionine are presented showing the spectra for the 1.0–13.0 pH range. In parallel, solid state DFT calculations were performed on the amino acid zwitterions in the crystalline form. We focused on the lowest frequency far infrared normal modes, which required the most precision and convergence of the calculations. Analysis of the computational results, which included the potential energy distribution of the vibrational modes, permitted a detailed and almost complete assignment of the experimental spectrum. In addition to characteristic signals of the two main acid-base couples, CO2H/CO2− and NH3+/NH2, specific side chain contributions for these amino acids, including CCO and CCS vibrational modes were analyzed. This study is in line with the growing application of FIR measurements to biomolecules.

Superstructure of a substituted zeolitic imidazolate metal-organic framework determined by combining proton solid-state NMR spectroscopy and DFT calculations.

We report the supercell crystal structure of a ZIF-8 analog substituted imidazolate metal-organic framework (SIM-1) obtained by combining solid-state nuclear magnetic resonance and powder X-ray diffraction experiments with density functional theory calculations.

On the relaxation dynamics in active pharmaceutical ingredients: solid-state1H NMR, quasi-elastic neutron scattering and periodic DFT study of acebutolol hydrochloride

Molecular dynamics of acebutolol hydrochloride was thoroughly explored by combining QENS and NMR experiments with solid-state DFT calculations.

Asymmetric boron-complexes containing keto-isoindolinyl and pyridyl groups: solvatochromic fluorescence, efficient solid-state emission and DFT calculations

A small series of keto-isoindolinyl and pyridyl-containing boron complexes with significant large Stokes shifts and solvatochromic fluorescence are reported.

Identifying the Structure of the Intermediate, Li2/3CoPO4, Formed during Electrochemical Cycling of LiCoPO4.

In situ synchrotron diffraction measurements and subsequent Rietveld refinements are used to show that the high energy density cathode material LiCoPO4 (space group Pnma) undergoes two distinct two-phase reactions upon charge and discharge, both occurring via an intermediate Li2/3(Co2+)2/3(Co3+)1/3PO4 phase. Two resonances are observed for Li2/3CoPO4 with intensity ratios of 2:1 and 1:1 in the 31P and 7Li NMR spectra, respectively. An ordering of Co2+/Co3+ oxidation states is proposed within a (a × 3b × c) supercell, and Li+/vacancy ordering is investigated using experimental NMR data in combination with first-principles solid-state DFT calculations. In the lowest energy configuration, both the Co3+ ions and Li vacancies are found to order along the b-axis. Two other low energy Li+/vacancy ordering schemes are found only 5 meV per formula unit higher in energy. All three configurations lie below the LiCoPO4–CoPO4 convex hull and they may be readily interconverted by Li+ hops along the b-direction.

New insight into the hydrocarbon-pool chemistry of the methanol-to-olefins conversion over zeolite H-ZSM-5 from GC-MS, solid-state NMR spectroscopy, and DFT calculations.

Over zeolite H-ZSM-5, the aromatics-based hydrocarbon-pool mechanism of methanol-to-olefins (MTO) reaction was studied by GC-MS, solid-state NMR spectroscopy, and theoretical calculations. Isotopic-labeling experimental results demonstrated that polymethylbenzenes (MBs) are intimately correlated with the formation of olefin products in the initial stage. More importantly, three types of cyclopentenyl cations (1,3-dimethylcyclopentenyl, 1,2,3-trimethylcyclopentenyl, and 1,3,4-trimethylcyclopentenyl cations) and a pentamethylbenzenium ion were for the first time identified by solid-state NMR spectroscopy and DFT calculations under both co-feeding ([(13) C6 ]benzene and methanol) conditions and typical MTO working (feeding [(13) C]methanol alone) conditions. The comparable reactivity of the MBs (from xylene to tetramethylbenzene) and the carbocations (trimethylcyclopentenyl and pentamethylbenzium ions) in the MTO reaction was revealed by (13) C-labeling experiments, evidencing that they work together through a paring mechanism to produce propene. The paring route in a full aromatics-based catalytic cycle was also supported by theoretical DFT calculations.

Electron Localization of Polyoxomolybdates with ε-Keggin Structure Studied by Solid-State 95Mo NMR and DFT Calculation

We report electron localization of polyoxomolybdates with ε-Keggin structure investigated by solid-state (95)Mo NMR and DFT calculation. The polyoxomolybdates studied are the basic ε-Keggin crystals of [Me3NH]6[H2Mo12O28(OH)12{MoO3}4] · 2H2O (1), the crystals suggested to have a disordered {ε-Mo12} core of [PMo12O36(OH)4{La(H2O)2.75Cl1.25}4]·27H2O (2), and the paramagnetic Keggin crystals of [H2Mo12O30(OH)10{Ni(H2O)3}4] · 14H2O (3). The spectra of (95)Mo static NMR of these samples were measured under moderate (9.4 and 11.7 T) and ultrahigh magnetic fields (21.8 T). From spectral simulation and quantum chemical calculation, the NMR parameters of the chemical shift and quadrupole interactions for (95)Mo were estimated. By the analysis based on the result for 1, it was found for 2 that although the {ε-Mo12} core is disordered, the eight d(1) electrons in it are not completely localized on four Mo-Mo bonds. Furthermore, it was shown for 3 that the d(1) electrons are localized to make the Mo-Mo bonds, while the unpaired electrons are also almost localized on the paramagnetic Ni(II) ions.

Borohydrides: from sheet to framework topologies

The five novel compounds ALiM(BH4)4 (A = K or Rb; M = Mg or Mn) and K3Li2Mg2(BH4)9 crystallizing in the space groups Aba2 and P2/c, respectively, represent the first two-dimensional topologies amongst homoleptic borohydrides. The crystal structures have been solved, refined and characterized by synchrotron X-ray powder diffraction, neutron powder diffraction and solid-state DFT calculations. Minimal energies of ordered models corroborate crystal symmetries retrieved from diffraction data. The layered Li-Mg substructure forms negatively charged uninodal 4-connected networks. It is shown that this connectivity cannot generate the long sought-after, bimetallic Li-Mg borohydrides without countercations when assuming preferred coordination polyhedra as found in Mg(BH4)2 and LiBH4. The general properties of the trimetallic compound series are analogous with the anhydrous aluminosilicates. Additionally, a relationship with zeolites is suggested, which are built from three-dimensional Al-Si-O networks with a negative charge on them. The ternary metal borohydride systems are of interest due to their potential as novel hydridic frameworks and will allow exploration of the structural chemistry of light-metal systems otherwise subject to eutectic melting.

Solid-state NMR measurements and DFT calculations of the magnetic shielding tensors of protons of water trapped in barium chlorate monohydrate

The magnetic shielding tensors of protons of water in barium chlorate monohydrate are investigated by means of solid-state NMR spectroscopy, both for static powders and under magic-angle spinning conditions.

Dynamics of water molecules and sodium ions in solid hydrates of nucleotides

The dynamics of the co-ordinating water and metal cations in solid hydrates of nucleotide salts is explored with solid-state NMR spectroscopy and DFT calculations.

Identification of mixed bromidochloridotellurate anions in disordered crystal structures of (bdmim)2[TeX2Y4] (X, Y = Br, Cl; bdmim = 1-butyl-2,3-dimethylimidazolium) by combined application of Raman spectroscopy and solid-state DFT calculations

The discrete mixed [TeBrxCl6−x]2− anions in their disordered crystal structures have been identified by using the phases prepared by the reaction of 1-butyl-2,3-dimethylimidazolium halogenides (bdmim)X with tellurium tetrahalogenides TeX4 (X=Cl, Br) as examples. Homoleptic (bdmim)2[TeX6] [X=Cl (1), Br (2)] and mixed (bdmim)2[TeBr2Cl4] (3), and (bdmim)2[TeBr4Cl2] (4) are formed depending on the choice of the reagents, and their crystal structures have been determined by single-crystal X-ray diffraction. The coordination environments of tellurium in all hexahalogenidotellurates are almost octahedral. Because of the crystallographic disorder, the mixed [TeBr2Cl4]2− and [TeBr4Cl2]2− anions in 3 and 4 cannot be identified in their crystal structures. Pawley refinement of the X-ray powder diffraction patterns of 1–4 indicates the presence of single phases in all four products. The solid state Raman spectra of 1–4 were assigned with help of DFT calculations that were performed both for the discrete anions in vacuum and for the complete crystal structures employing periodic boundary conditions. The fundamental vibrations of the homoleptic [TeX6]2− (X=Cl, Br) anions could be well reproduced by the solid-state DFT computations and enabled a complete assignment of the Raman spectra. While the presence of cis-isomers in both [TeBr2Cl4]2− and [TeBr4Cl2]2− could be inferred by the computed fundamental vibrations, that of trans-isomers among the reaction products is, however, also possible. The pathway of the formation of [TeX4Y2]2− isomers from TeX4 and Y− (X, Y=Cl, Br) was also explored by DFT calculations both in vacuum and in solution and indicated that both reactions afforded 80mol% of cis-isomers and 20mol% of trans-isomers.