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P21/n Space Group (p21/n + space_group)
Selected AbstractsCrystal Structures and Magnetic Properties of Nitronyl Nitroxide RadicalsHELVETICA CHIMICA ACTA, Issue 4 2003Alexander Zakrassov The crystal structures and magnetic properties of the nitronyl nitroxide radicals 4,5-dihydro-4,4,5,5-tetramethyl-3-oxido(1H -imidazol-1-yloxyl) (1), 4,5-dihydro-2,4,4,5,5-pentamethyl-3-oxido(1H -imidazol-1-yloxyl) (2), 2-(4-chlorophenyl)-4,5-dihydro-4,4,5,5-tetramethyl-3-oxido(1H -imidazol-1-yloxyl) (3), and 4,5-dihydro-2-(2-hydroxy-5-nitrophenyl)-4,4,5,5-tetramethyl-3-oxido(1H -imidazol-1-yloxyl) (4) are reported. Compound 1 has two polymorphic forms: the , phase is monoclinic (P21/n space group), with a single molecule in the asymmetric unit, and the , phase is monoclinic (P21/c space group), with four molecules in the asymmetric unit. In the two polymorphs, the molecules are arranged in dimers formed by hydrogen bonds of the type CH,,,ON. The crystal structure of 3 contains layers of antiparallel ribbons of molecules. Compound 4 crystallizes with solvent molecules, and an intramolecular hydrogen bond is formed between the 2-OH group of the phenyl ring and the nitroxide O-atom. Compound 4 also loses the two O-atoms of the nitroxide moiety upon heating to 90°. Magnetic measurements showed that both , and , polymorphs of 1 exhibit antiferromagnetic coupling. The best fit to the experimental data was obtained using BleanyBower's singlet-triplet model (H=,2JSaSb): J=,11.2,K for the , phase and J=,15.0,K for the , phase. Compounds 3 and 4 show no evidence for spin coupling. [source] Microstructure and Microwave Dielectric Properties of xCa(Al0.5Nb0.5)O3+(1,x)SrTiO3 Solid SolutionsJOURNAL OF THE AMERICAN CERAMIC SOCIETY, Issue 10 2010Mingzhe Hu The crystal structure evolution and microwave (MW) dielectric properties of xCa(Al0.5Nb0.5)O3+(1,x)SrTiO3 (xCAN+(1,x)ST, 0,x,1.0, ) dielectric ceramics were investigated. X-ray diffraction patterns illustrated that a single perovskite solid solution could be formed between the two end members; however, minor amount of pyrochlore phase was also detected in the composition range of 0.5,x,0.9. With the increase of x value, the crystal structure gradually evolved from a simple Pm3m cubic to a monoclinic P21/n space group with the octahedral tilting and the B-site ordering structure transition subsequently developed. The MW dielectric properties of xCAN+(1,x)ST solid solutions were elaborately investigated and correlated to their crystal structures. The microscopic structure-related thermal parameters in the xCAN+(1,x)ST solid solution were analyzed in terms of the Claussius,Mossotti equation to reveal the original contributors in temperature coefficients. Temperature coefficient-compensated ceramic could be obtained in the xCAN+(1,x)ST system in the range of 0.5 GeTe2O6, a germanium tellurate(IV) with an open frameworkACTA CRYSTALLOGRAPHICA SECTION C, Issue 5 2009Nefla Jennene Boukharrata The structure of an already evidenced but still uncharacterized GeTe2O6 phase consists of isolated GeO6 octahedra connected via isolated TeO3 units. The germanium cations occupy a site with symmetry. The Te and O atoms are in general positions of the P21/n space group. This structure corresponds to a new type of tetravalent tellurate and is different from other AB2X6 structures in which the B cation presents a stereochemically active electronic lone pair. It derives from the pseudo-hexagonal MI2O6 (M = Mg, Mn, Co and Fe) type by a strong monoclinic distortion caused by the much smaller size of Ge4+ compared with the divalent M cations. [source] Assembly of a two-dimensional layer structure with 1,4-bis(1H -benzimidazol-1-ylmethyl)benzene dihydrate via hydrogen bonds and ,,, interactionsACTA CRYSTALLOGRAPHICA SECTION C, Issue 3 2008Chuan-Mei Wu In the title compound, C22H18N4·2H2O, the organic fragment lies across a centre of inversion in the P21/n space group. The water molecules form C(2)-type hydrogen-bonded chains which are linked to the 1,4-bis(1H -benzimidazol-1-ylmethyl)benzene molecules through O,H...N hydrogen bonds, forming sheets reinforced by ,,, stacking interactions between the aromatic rings within the layers. [source]
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