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Lone Electron Pair (lone + electron_pair)
Selected AbstractsPersistence of the stereochemical activity of the Bi3+ lone electron pair in Bi2Ga4O9 up to 50,GPa and crystal structure of the high-pressure phaseACTA CRYSTALLOGRAPHICA SECTION B, Issue 3 2010Alexandra Friedrich The crystal structure of the high-pressure phase of bismuth gallium oxide, Bi2Ga4O9, was determined up to 30.5,(5),GPa from in situ single-crystal in-house and synchrotron X-ray diffraction. Structures were refined at ambient conditions and at pressures of 3.3,(2), 6.2,(3), 8.9,(1) and 14.9,(3),GPa for the low-pressure phase, and at 21.4,(5) and 30.5,(5),GPa for the high-pressure phase. The mode-Grüneisen parameters for the Raman modes of the low-pressure structure and the changes of the modes induced by the phase transition were obtained from Raman spectroscopic measurements. Complementary quantum-mechanical calculations based on density-functional theory were performed between 0 and 50,GPa. The phase transition is driven by a large spontaneous displacement of one O atom from a fully constrained position. The density-functional theory (DFT) model confirmed the persistence of the stereochemical activity of the lone electron pair up to at least 50,GPa in accordance with the crystal structure of the high-pressure phase. While the stereochemcial activity of the lone electron pair of Bi is reduced at increasing pressure, a symmetrization of the bismuth coordination was not observed in this pressure range. This shows an unexpected stability of the localization of the lone electron pair and of its stereochemical activity at high pressure. [source] On the correlations between the polyhedron eccentricity parameters and the bond-valence sums for the cations with one lone electron pair.ACTA CRYSTALLOGRAPHICA SECTION B, Issue 3 2009Addendum Systematic variations of the bond-valence sums calculated from the poorly determined bond-valence parameters [Sidey (2008), Acta Cryst. B64, 515518] have been illustrated using a simple graphical scheme. [source] High-pressure crystal structure of the non-linear optical compound BiB3O6 from two-dimensional powder diffraction dataACTA CRYSTALLOGRAPHICA SECTION B, Issue 1 2009R. E. Dinnebier Our recently proposed method for automatic detection, calibration and evaluation of Debye,Scherrer ellipses using pattern-recognition techniques and advanced signal filtering was applied to the two-dimensional powder diffraction data of the non-ferroelectric, non-centrosymmetric non-linear optical (NLO) compound ,-BiB3O6 as a function of pressure. At ambient conditions, ,-BiB3O6 crystallizes in the space group C2 (phase I). In the pressure range between P = 6.09 and 6.86,GPa, it exhibits a first-order phase transition into a structure with the space group C1 (P1) [phase II at P = 8.34,GPa: a = 7.4781,(6), b = 3.9340,(4), c = 6.2321,(6),Å, , = 93.73,(1), , = 102.93,(1), , = 90.76,(1)°, and V = 178.24,(3),Å3]. Non-linear compression behaviour over the entire pressure range is observed, which can be described by two Vinet relations in the ranges from P = 0.0 to 6.09,GPa, and from P = 6.86 to 11.6,GPa. The extrapolated bulk moduli of the high-pressure phases were determined to be K0 = 38,(1),GPa for phase I, and K0 = 114,(10),GPa for phase II. The crystal structures of both phases were refined against X-ray powder diffraction data measured at several pressures between 0.0 and 11.6,GPa. The structural phase transition of ,-BiB3O6 is mainly characterized by a reorientation of the [BO3]3, triangles, the [BO4]5, tetrahedra and the lone electron pair which is localized at Bi3+, in order to optimize crystal packing. [source] On the correlations between the polyhedron eccentricity parameters and the bond-valence sums for the cations with one lone electron pairACTA CRYSTALLOGRAPHICA SECTION B, Issue 4 2008Vasyl Sidey Applicability of the Wang,Liebau polyhedron eccentricity parameter in the bond-valence model [Wang & Liebau (2007). Acta Cryst. B63, 216,228] has been found to be doubtful: the correlations between the values of the polyhedron eccentricity parameters and the bond-valence sums calculated for the cations with one lone electron pair are probably an artifact of the poorly determined bond-valence parameters. [source] Nickel vanadium tellurium oxide, NiV2Te2O10ACTA CRYSTALLOGRAPHICA SECTION C, Issue 4 2009Dong Zhang Single crystals of nickel(II) divanadium(V) ditellurium(IV) decaoxide, NiV2Te2O10, were synthesized via a transport reaction in sealed evacuated silica tubes. The compound crystallizes in the triclinic system (space group P). The Ni atoms are positioned in the 1c position on the inversion centre, while the V and Te atoms are in general positions 2i. The crystal structure is layered, the building units within a (010) layer being distorted VO6 octahedra and NiO6 octahedra. The metal,oxide layers are connected by distorted TeO4E square pyramids (E being the 5s2 lone electron pair of TeIV) to form the framework. The structure contains corner-sharing NiO6 octahedra, corner- and edge-sharing TeO4E square pyramids, and corner- and edge-sharing VO6 octahedra. NiV2Te2O10 is the first oxide containing all of the cations NiII, VV and TeIV. [source] Sodium iodine(V) oxyfluoride, NaIO2F2ACTA CRYSTALLOGRAPHICA SECTION C, Issue 7 2008Jean-Paul Laval As an extension of a general structural study concerning fluorides and oxyfluorides of cations presenting a stereochemically active electronic lone pair, until now limited to tellurium(IV) phases, the previously unknown structure of NaIO2F2 corresponds to a new structure type based on isolated IO2F2, polyhedra forming sheets separated by Na+ layers. The sodium ion is octahedrally coordinated with 2/m site symmetry, while the IV atom has m2m symmetry with a stereochemically active lone electron pair. The O and F atoms (both with m symmetry) are bonded to the IV atoms in a fully ordered manner. A comparison with the structure of ferroelastic KIO2F2 and with structures based on hexagonal close packing of anions, mainly rutile-type and FeTeO3F-type, reveals differences that are attributed to the smaller ionic radius of Na+ and the ordering of the Na and I cations. [source] 2-(N,N -Diphenylamino)benzoic acidACTA CRYSTALLOGRAPHICA SECTION C, Issue 8 2001Anna Bou Shaped like a distorted propeller, molecules of the title compound, C19H15NO2, form centrosymmetric dimers in the crystalline phase in which the carboxy groups are linked through two hydrogen bonds. These dimers are arranged in columns held together via dispersive interactions between the phenyl moieties. The N atom and the three surrounding C atoms lie almost in the same plane, which implies that the lone electron pair of the N atom is involved in conjugation with the , systems of the phenyl fragments. [source] Multiferroicity in In-Containing PerovskitesCHEMPHYSCHEM, Issue 1 2010A new class of perovskite materials containing Indium at the A positions is Highlighted herein. New oxides of composition (In1,xMx)MO3 (x=0.112,0.176, M=Fe0.5Mn0.5), prepared at high pressures, exhibit the same structure as BiFeO3 (see picture) with TN close to RT and show multiferroic properties. This work shows that a polar distortion can be realized without the presence of a lone electron pair. [source] | ||||||||||