Synthesis, Structure, and Properties of Compounds in the NaHSO_4−CsHSO_4 System. 1. Crystal Structures of Cs_2Na(HSO_4)_3 and CsNa_2(HSO_4_)3

Exploratory synthesis in the NaHSO₄-CsHSO₄ system, aimed at discovering novel proton conducting solids, resulted in the new compounds CsNa₂(HSO₄)₃ and Cs₂Na(HSO₄)₃. Single-crystal X-ray diffraction (performed at room temperature) revealed CsNa₂(HSO₄)₃ to crystallize in the cubic space group P2₁3 with lattice parameters a=10.568(2)Å and Z=4, whereas CS2Na(HSO₄)₃, studied by both single-crystal neutron and X-ray methods, crystallizes in the hexagonal space group P6₃/m. The latter compound has lattice parameters a=8.5712(17) and c=9.980(2)Å, and Z=2. The unit cell volumes are 1180.4(4) and 634.9(2)ų, respectively, giving calculated densities of 2.645 and 3.304 mg m⁻³. Refinement using all observed reflections yielded a weighted residual, R-w(F²), of 0.0515 based on F² X-ray values for CsNa₂(HSO₄)₃. For Cs₂Na(HSO₄)₃ the analogous X-ray and neutron values were 0.0483 and 0.1715, respectively. Both structures contain a single, crystallographically distinct, asymmetric hydrogen bond (as confirmed by NMR investigations) and unique, three-membered (HSO₄)₃ rings. The geometric match between the NaO₆ octahedra and the rings suggests the sodium polyhedra may serve to template the (HSO₄)₃ unit. In CsNa₂(HSO₄)₃ the rings form a distorted cubic close-packed array. The Cs atoms are located within the "octahedral" sites of this array, and the Na atoms, within the "tetrahedral" sites. The rings in CS₂Na(HSO₄)₃ are linked together by NaO6 octahedra to form infinite Na(HSO₄)₃ chains that extend along 001. The hexagonal compound exhibits disorder about the sulfate tetrahedron that suggests a P6₃/m → P6 phase transition may occur upon cooling

The asymmetric aza-silyl-prins reaction: Synthesis of enantiopure piperidines

The design and development of the first asymmetric aza-silyl-Prins reaction is reported, giving rise to valuable and diverse piperidines and pipecolic acid derivatives in both high yields and as single enantiomers. The creation of a novel chiral auxiliary-homoallylic amine for the aza-silyl-Prins reaction is essential to its success

Non-covalent close contacts in fluorinated thiophene-phenylene-thiophene conjugated units: understanding the nature and dominance of O···H versus S···F and O···F interactions towards the control of polymer conformation

Using a simple -conjugated trimer, EDOT-phenylene-EDOT (where EDOT = 3,4-ethylenedioxythiophene), we evaluate the effect that fluorine substituents have upon changes in conformation, conjugation and oxidation potentials in -conjugated structures. These variations are assessed as a function of the fluorine atom’s propensity to feature in hydrogen and/or halogen bonding with other heteroatoms. The molecular motif was chosen because the EDOT unit presents the possibility of competing O···X or S···X non-covalent contacts (where X = H or F). Such non-bonding interactions are acknowledged to be highly influential in dictating molecular and polymer morphology and inducing changes in certain physical properties. We have studied four compounds, beginning with an unsubstituted bridging phenylene ring and then adding one, two or four fluorine units to the parent molecule. Our studies involve single crystal XRD studies, cyclic voltammetry, absorption spectroscopy and density functional theory calculations to identify the dominant non-covalent interactions and elucidate their effects on the molecules described. Experimental studies have also been carried out on the corresponding electrochemically synthesized polymers to confirm that these non-covalent interactions and their effects persist in polymers. Our findings show that hydrogen bonding and halogen bonding feature in these molecules and their corresponding polymers. ABSTRACT: Using a simple -conjugated trimer, EDOT-phenylene-EDOT (where EDOT = 3,4-ethylenedioxythiophene), we evaluate the effect that fluorine substituents have upon changes in conformation, conjugation and oxidation potentials in -conjugated structures. These variations are assessed as a function of the fluorine atom’s propensity to feature in hydrogen and/or halogen bonding with other heteroatoms. The molecular motif was chosen because the EDOT unit presents the possibility of competing O···X or S···X non-covalent contacts (where X = H or F). Such non-bonding interactions are acknowledged to be highly influential in dictating molecular and polymer morphology and inducing changes in certain physical properties. We have studied four compounds, beginning with an unsubstituted bridging phenylene ring and then adding one, two or four fluorine units to the parent molecule. Our studies involve single crystal XRD studies, cyclic voltammetry, absorption spectroscopy and density functional theory calculations to identify the dominant non-covalent interactions and elucidate their effects on the molecules described. Experimental studies have also been carried out on the corresponding electrochemically synthesized polymers to confirm that these non-covalent interactions and their effects persist in polymers. Our findings show that hydrogen bonding and halogen bonding feature in these molecules and their corresponding polymers

Single crystal diffraction images for a room temperature data collection on the LEF-PG co-crystal.

A set of diffraction images collected on a Rigaku FRE+ diffractometer, equipped with HF Varimax confocal mirrors and an AFC12 goniometer and HG Saturn 724+ detector diffractometer. The sample is an organic co-crystal that forms part of a study of the LEF active pharmaceutical ingredient with a range of coformers. The structure with the PG coformer shows strong signs of modulation in the diffraction pattern and structure refinement. The model presented in the paper (submitted to Crystal Growth and Design) does not account for any modulation and serves the purpose of a suitable degree of characterisation precision for this article. The authors wish to make the raw data available so that those with interest and experise in handling modulated structures can perform more detailed modelling studies and/or use the data to test software or for training examples.</span

Structure refinement and chemical analysis of Cs_3Li(DSO_4)_4, formerly ‘Cs_(1.5)Li_(1.5)D(SO_4)_2’

An accurate structure refinement of the deuterated analog of the cesium lithium acid sulfate, formerly identified as ‘Cs₁.₅Li₁.₅D(SO₄)₂’, has been carried out using neutron diffraction methods. Like the protonated material reported earlier (Merinov et al., Solid State Ionics 69 (1994) 53), the compound is cubic, I¯43d; however, the correct stoichiometry is Cs₃Li(DSO₄)₄. There are four formula units per unit cell and six atoms in the asymmetric unit. The lattice constant measured in this work is a=11.743(2)Å, comparable to the earlier results. The structure contains one disordered hydrogen bond, formed between O(2) atoms and located on two of the edges of the single LiO₄ tetrahedron. The Li site occupancy is 1/3; as is that of the deuterium site. This level of site occupancies is consistent with a structure in which hydrogen bonds are formed only when the lithium site is unoccupied, and explains the otherwise close proximity of the Li and D atoms, 1.394(10)Å. This unusual structural feature furthermore leads to a fixed stoichiometry, as confirmed here by chemical analysis of both the deuterated and protonated materials, despite the partial occupancy of the lithium and deuterium (hydrogen) atom sites

A Stereoselective aza-Prins Reaction: Rapid Access to Enantiopure Piperidines and Pipecolic Acids

The aza-Prins reaction is a widely employed and highly efficient method for the preparation of saturated nitrogen-containing heterocycles. Its major drawback has always been a lack of diastereoselectivity and the formation of racemic products. Herein, we address these problems and report, for the first time, the synthesis of both diastereomerically and enantiopure multiply substituted piperidines via the aza-Prins reaction. This method is widely applicable for natural product synthesis and is exemplified here by the synthesis of enantiopure pipecolic acid derivatives. </p

Reassessment of large dipole moment enhancements in crystals: A detailed experimental and theoretical charge density analysis of 2-methyl-4-nitroaniline

The molecular dipole moment of MNA in the crystal has been critically reexamined, to test the conclusion from an earlier experimental charge density analysis that it was substantially enhanced due to a combination of strong intermolecular interactions and crystal field effects. X-ray and neutron diffraction data have been carefully measured at 100 K and supplemented with ab initio crystal Hartree−Fock calculations. Considerable care taken in the measurement and reduction of the experimental data excluded most systematic errors, and sources of error and their effects on the experimental electron density have been carefully investigated. The electron density derived from a fit to theoretical structure factors assisted in the determination of the scale and thermal motion model. The dipole moment enhancement for MNA in the crystal is much less than that reported previously and only on the order of 30−40% (~2.5 D). In addition to the dipole moment, experimental deformation electron density maps, bond critical point data, electric field gradients at hydrogen nuclei, and atomic and group charges all agree well with theoretical results and trends. Anisotropic modeling of the motion of hydrogen atoms, integral use of periodic ab initio calculations, and improved data quality are all aspects of this study that represent a considerable advance over previous work