Hydrogen Bonding Effects in Anion Binding Calixarenes

A series of disubstituted urea, thiourea and dansyl amide calix[4]arene based anion receptors have been prepared and characterised by X-ray crystallography. The structures show a fine balance of intramolecular urea α-tape, and ureacalixarene phenolic oxygen atom hydrogen bonding patterns. Both motifs are in competition with the anion binding behaviour of the compounds in solution

Exo-π-bonding to an ortho-carborane hypercarbon atom: systematic icosahedral cage distortions reflected in the structures of the fluoro-, hydroxy- and amino-carboranes, 1-X-2-Ph-1,2-C2B10H10 (X = F, OH or NH2) and related anions

The structures of derivatives of phenyl-ortho-carborane bearing on the second cage hypercarbon atom a pi-donor substituent (F, OH, O-, NH2, NH- and CH2-) were investigated by NMR, X-ray crystallography and computational studies. The molecular structures of these compounds, notably their cage C1-C2 distances and the orientations of their pi-donor substituents (OH, NH2, NH- and CH2-) show remarkable and systematic variations with the degree of exo pi-bonding, which varies as expected with the pi-donor characteristics of the substituent

The crystal structure of alpha-La2Mo2O9 and the structural origin of the oxide ion migration pathway

We describe for the first time the full 3D atomic structure of room-temperature alpha-La2Mo2O9. The material, despite its simple chemical formula, has a remarkable 312 crystallographically unique atoms and is thus one of the most complex oxide structures reported to date. Despite this complexity, the structural results offer significant insight into the O2- migration pathway in the anion conducting high-temperature form, beta-La2Mo2O9. The material contains a mixture of 4, 5, and 6 coordinated Mo sites, suggesting that variable Mo coordination number is a key factor in providing a low-energy O2- conduction pathway. We provide quantitative analysis showing that the positions in the ordered array of 216 oxygen sites of alpha-La2Mo2O9 are directly related to the average sites occupied in beta-La2Mo2O9, providing compelling evidence that the high-temperature conducting form of the material has a time-averaged version of the low-temperature structure

N,N-diethyl-5-nitropyridin-2-amine.

In the title compound, C9H13N3O2, the asymmetric unit contains two almost identical but crystallographically independent mol­ecules. The mol­ecules are linked together by pairs of weak C-H...O inter­actions into zigzag chains, which, in turn, form corrugated layers perpendicular to the a axis

Variable temperature structural study of bismuth lead vanadate, BiPb₂VO₆

At room temperature, monoclinic BiPb2VO6 is a polar, noncentrosymmetric, second harmonic generation active material and its crystal structure is among the more complex to be solved ab initio from powder diffraction data. In its stability range, BiPb2VO6 also exists in a high symmetry, orthorhombic form. Both phases have been structurally characterized by a combination of X-ray and neutron diffraction data. Their mutual relationship, as well as that to the known compounds of the BiM(2)AO(6) (M = Mg, Ca, Mn, Cu, Zn, Pb and A = P, V, As) family, has been established

Synthesis and crystal structure of BiCd2AsO6

A new compound BiCd2AsO6 has been prepared and its crystal structure determined by single crystal X-ray diffraction. The unit cell parameters are: a = 8.618(l) angstrom, b = 11.949(2) angstrom and c = 5.4407(7) angstrom and the space group Cmc2(1)center dot BiCd2AsO6 is therefore noncentrosymmetric and polar. It contains seven coordinate Bi and Cd atoms, and As in AsO4 tetrahedral groups aligned in the same direction along the polar axis of the crystal. (c) 2004 Elsevier SAS. All rights reserved

alpha-Bi2Sn2O7 - a 176 atom crystal structure from powder diffraction data

Pyrochlore-type bismuth tin oxide, Bi2Sn2O7, is a technologically important material used in applications such as catalysis and gas sensing. Its room temperature structure has been solved by a method of simulated annealing of combined X-ray and neutron diffraction data, followed by Rietveld refinement. With 176 crystallographically independent atoms in the asymmetric unit, it is one of the largest structures solved to-date from powder diffraction data. In addition to the number of unique atoms, additional crystallographic difficulty stems from the fact that the true symmetry of this structure is lower than the apparent metric symmetry of the unit cell

Polymorphism of non-linear optical material N-(4-nitrophenyl)-N-methylamino-acetonitrile (NPAN)

Two new crystalline polymorph modifications of the non-linear optical material N-(4-nitrophenyl)-N-methylamino-acetonitrile (NPAN) have been found and their structures have been established by X-ray analysis. The low-temperature structure of previously known polymorph of NPAN has also been determined. The comparative analysis of the packing of the NPAN molecules in these polymorphs provides the hints to the process of crystallization of the NPAN in different conditions