Stereoselective formation of dicondensed spiropyran product obtained from the reaction of excess Fischer base with salicylaldehydes: first full characterization by X-ray crystal structure analysis of a DC·acetone crystal

The structure and stereochemistry of the dicondensed spiropyran product (DC-1, X=COOH) obtained from reaction of excess Fischer base with substituted salicylaldehydes has been fully assigned as C with (8R, 10R) configuration on the basis of single crystal X-ray diffraction analysis. The stereoselective formation of DC molecules indicates that the most plausible mechanism for DC formation involves dehydration of the cyclic carbinol intermediate with the aid of intramolecular H-bonding via transition structure TS₁^‡.     

7-trifluoromethylquinoline-functionalized luminescent photochromic spiropyran with the stable merocyanine species both in solution and in the solid state

A new spiropyran (SP2) with the stable merocyanine form (MC2) both in solution and in the solid state at room temperature was designed and synthesized. The stability of MC2 is believed to be due to the electron-withdrawing effect of both the quinoline and the trifluoromethyl groups. (1)H NMR spectra indicate that the ratio of the open form vs the closed form of SP2 is dependent on the polarity of solvents. Single crystals composed of only the open form (MC2) were successfully obtained. X-ray structural analysis indicates that except trifluoromethyl and two methyl groups MC2 is completely planar with an s-trans,s-cis conformation. It should be noted that this is the first report of the X-ray crystal structure of the pure open form of spiropyran. MC2 can be slowly transformed into SP2 at -30 degrees C or lower temperature, and the process is accelerated by visible light irradiation. This special photochromic behavior can be explained by the calculated thermodynamic data. The spectral properties of SP2/MC2 in the presence of different metal ions are also studied, and the results show the potential application of SP2/MC2 in sensing metal ions.     

Photochromism of diarylethene single crystals: crystal structures and photochromic performance

Diarylethenes undergo thermally irreversible and fatigue-resistant photochromic reactions not only in solution but also in the single-crystalline phase. This article describes recent development of the single-crystalline photochromism of diarylethene derivatives. We focused on the relationship between their crystal structures and the photochromic performance. Photocyclization/cycloreversion quantum yields, absorption spectra, the absorption anisotropies, and surface morphology changes are strongly dependent on the conformations and packing structures of the molecules in the crystals.     

A new type of liquid crystal involving hydrogen bonding: single crystal X-ray structure characterization and properties of the liquid crystal

A new liquid crystal involving hydrogen bonding between 4-hexyloxybenzoic acid and 4-octyloxylphenylethynylpyridine has been investigated by DSC, polarizing optical microscopy and X-ray diffraction. The mesogen shows a nematic phase and an unknown liquid crystalline phase. The liquid crystal crystallizes with a triclinic space group P-1 with the parameters: a = 8.879(2)Å, b = 10.137(2)Å, c = 17.629(4)Å; α = 104.16(3)°, β = 95.47(3)°, γ = 101.48(3)°; V = 1490.3(6)ų; Z = 2; F(000) = 572; μ = 0.076 mm^?1; λ(MoK_α) = 0.71073 Å; final R ₁ = 0.0435. The complex is formed by strong intermolecular hydrogen bonding.     

Electronic structure of NaCl crystal in crystal cluster model

Conclusions By the use of the crystal cluster method, it becomes possible (1) to obtain good agreement with band calculations of charge distribution, practically beginning with minimal clusters and, (2) to reproduce well the energy position of the VB; however (3), in order to analyze the detailed structure of density of states of the VB for the NaCl crystal, it is necessary to account for five or six spheres of the environment in order to provide convergence of this most sensitive characteristic. In this case, (4) the calculated model density of states of the atom-representatives of the bases converges with that obtained in the band calculation. In calculations of states of the CB, replacement of the operator of projection on the space of Wannier functions by an external localizing potential leads to a considerable distortion of the spectrum. The states obtained in this region (5) are determined by this external potential; and (6) they should be interpreted as lower states of the CB. (7) The use of a correction for the localizing potential improves the agreement with respect to the width of the optical gap in the series of calculations.Ural Polytechnic Institute. Translated from Zhurnal Strukturnoi Khimii, Vol. 31, No. 2, pp. 17–23, March–April, 1990.     

Cyclooctene epoxidation with H2O2 and single crystal X-ray determined crystal structures of new molybdenum and tungsten catalysts bearing the hydrophilic ligand hydroxymethyldiphenylphosphine oxide

The dioxo molybdenum and tungsten complexes MoO₂Cl₂(OPPh₂CH₂OH)₂ and WO₂Cl₂(OPPh₂CH₂OH)₂ have been synthesized and characterized by FT-IR, ¹H and ³¹P NMR. Their structures, as determined by single crystal X-ray diffraction analysis, reveal distorted octahedral geometries with cis terminal oxygen atoms, trans Cl ligands and that the hydroxymethyldiphenylphosphine oxide ligands coordinate through the oxygen atom bonded to the P atom. Both of the compounds are studied as catalysts for the epoxidation of cis-cyclooctene in the presence of hydrogen peroxide as a source of oxygen. Both complexes showed good activity and very high selectivity for the formation of cyclooctene oxide.     

Electronic structure of the Pt(100) single crystal surface affected by oxygen adsorption

Summary Disappearance Potential Spectroscopy study of the oxygen adsorption on the Pt(100)-(1×1) single crystal surface revealed a regular set of spectral satellites designated as the platinum bulk plasmons.     

Investigation of structure and dynamics in a photochromic molecular crystal by NMR crystallography

A photochromic anil, N-(3,5-di-t-butylsalicylidene)-4-amino-pyridine, has been studied by single-crystal X-ray diffraction, multinuclear magic-angle spinning NMR, and first-principles density functional theory (DFT) calculations. Interpretation of the solid-state NMR data on the basis of calculated chemical shifts confirms the structure is primarily composed of molecules in the ground-state enol tautomer, whereas thermally activated cis-keto and photoisomerised trans-keto states exist as low-level defects with populations that are too low to detect experimentally. Variable temperature ¹³C NMR data reveal evidence for solid-state dynamics, which is found to be associated with fast rotational motion of t-butyl groups and 180° flips of the pyridine ring, contrasting the time-averaged structure obtained by X-ray diffraction. Comparison of calculated chemical shifts for the full crystal structure and an isolated molecule also reveals evidence for an intermolecular hydrogen bond involving the pyridine ring and an adjacent imine carbon, which facilitates the flipping motion. The DFT calculations also reveal that the molecular conformation in the crystal structure is very close to the energetic minimum for an isolated molecule, indicating that the ring dynamics arise as a result of considerable steric freedom of the pyridine ring and which also allows the molecule to adopt a favourable conformation for photochromism.     

Preparation and photochromic properties of oligomeric poly(dimethylsiloxane) with the spiropyran or spirooxazine moiety in the side chain

Spirobenzopyran 1 , with the 3-(diethoxymethylsilyl)-propyl group at the N atom, was synthesized. The condensation reaction of the spiropyran 1 and diethoxydimethylsilane gave oligomeric poly(dimethylsiloxane) with the spiropyran moiety in the side chain. The oligomer was photochromic; its colour changed from colorless to purple-red on uv irradiation and the color faded on visible irradiation or on standing in the dark. The half-decay time of the thermal decoloration was about twice that of monomeric spiropyran dissolved in the dimethylsiloxane oligomer. Photochromic poly(dimethylsiloxane) with the spirooxazine moiety in the side chain was also prepared.     

Dimesitylborane monomer-dimer equilibrium in solution, and the solid-state structure of the dimer by single crystal neutron and X-ray diffraction

Dimesitylborane dimer has been shown to exist in equilibrium with dimesitylborane monomer in solution. This equilibrium has been investigated by variable concentration and variable temperature multinuclear NMR spectroscopy and values for the dissociation constant, enthalpy and entropy of dissociation were found to be K_diss=(3.2±0.4)×10⁻³ M, ΔH=70 kJ mol⁻¹, and ΔS=212 J K⁻¹mol⁻¹, respectively. Ab initio methods have been used to investigate the gas-phase structures and energies of both monomer and dimer, and calculated ¹¹B-NMR shifts are also presented. The solid-state structure of dimesitylborane dimer has been investigated by single crystal X-ray diffraction at 100 K and the position of the bridging hydrogen atoms (B---H=1.340(2), 1.342(2) Å, H---B---H=92.46(14)°) has been determined accurately, for the first time, by single crystal neutron diffraction at 20 K.     

Electronic structure and hydrogen bond in the crystal of paracetamol drugs

We study the density of state (DOS), band structure (BS), and atomic orbit projected density of state (PDOS) of paracetamol crystal adopting the density functional theory (DFT) technique in the local density approximation (LDA). The band structure around the Fermi level and the contributions from p-type orbit of C, N, O, and s-type orbit of H to the total density of state (TDOS) are addressed, and we find that the electronic characteristic is the key to form the hydrogen bond between O and H atoms. We show that the structure of paracetamol crystal consists of the –OH···O=C and –NH···OH hydrogen-bonding cycle by studying a single paracetamol molecule as well as the PDOS graph of O and H atoms in the crystal.     

Diversity of crystal structure with different lanthanide ions involving in situ oxidation-hydrolysis reaction

A series of lanthanide and lanthanide-transition metal compounds with isonicotinic acid (Hina) and oxalate ligands have been synthesized under hydrothermal reactions. X-Ray crystal structure analyses reveal that they have a rich structural chemistry. Three distinct structure types were exhibited with decreasing lanthanide radii: [LnCu(ina)(2)(C(2)O(4))].H(2)O (Ln=La 1, Pr 2, Nd 3) for type I, [Ln(ina)(C(2)O(4))(H(2)O)(2)] (Ln=Sm 4, Eu 5, Gd 6) for type II, and [Ln(ina)(C(2)O(4))(0.5)(OH)] (Ln=Tb 7, Dy 8, Er 9) for type III. The structure of type I has a 3d-4f heterometallic structure and consists of 1D channels along the b axis, which filled with guest water molecules. They exhibit a first 3D uninodal eight-connected framework with a unique 3(6).4(18).5(3).6 topology. Type II has 2D Ln-ina-C(2)O(4) 4(4)-nets, the nitrogen donors of the ina ligand are not coordinated to any of the metal ions, inducing the lower dimensional networks. Type III consists of 2D Ln-C(2)O(4) layers pillared by ina ligands to form a pillared-layer framework. The structure evolution is due to the versatile coordination modes of ina and oxalate ligands as well as the lanthanide contraction effect. Notably, the oxalate ligand was in situ synthesized from orotic acid through an oxidation-hydrolysis reaction. The type III materials show high thermal stability; luminescence properties of Nd 3, Sm 4, Eu 5, Tb 7 are also investigated.     

Synthesis of a new open framework cerium silicate and its structure determination by single crystal X-ray diffraction

Hydrothermal synthesis of a new open framework cerium silicate and its structure determination by single crystal X-ray diffraction are reported.     

Interaction of morpholine and thiomorpholine with molecular diiodine:X-ray crystal structure of morpholinium triiodide

The reactions between the donors morpholine (1) and thiomorpholine (2) with I₂ in low polar solvents (C₆H₆, CHCl₃, CH₂Cl₂) and different donor/I₂ concentration ratios (1:1, 1:2, 1:3) yield solids of stoichiometry 1·I₂, 1H⁺I⁻₃, 1H⁺I⁻₅, 2·I₂, and 2H⁺I⁻₃. Crystals suitable for X-ray structure determination have been obtained only for 1 H⁺I⁻₃. All the solids were characterized by FT-Raman and FT-IR spectroscopies in the region of the v(I-I) frequencies. Studies in solution have been carried out on each of the reactions between 1, 2, and N-methylmorpholine (3) with I₂. The formation constants of their 1:1 adducts determined at 20°C by UV-visible spectroscopy are 1781, 8500, and 8400 dm³ mol⁻¹, respectively. IR spectroscopy shows that I₂ binds the nitrogen of 1 and 2 both in axial and equatorial positions. Further, FT-Raman and ¹³CNMR spectroscopies support the nature of weak adducts between 1 (2) and the molecular diiodine in solution. © 1997 John Wiley & Sons, Inc.