Volume 218, Issue 7

The new complex oxide (V 0.5 Re 0.5 )O 2 has been synthesized under high pressure of 60 kbar at 1000°C, and its crystal structure determined by single crystal X-ray diffraction data analysis (S.G.: P 4 2 / mnm , a = 4.6357(4) Å, c = 2.8292(3) Å, V = 60.80(1) Å 3 ). This compound adopts a rutile-type structure with random cat ion distribution on one crystallographic site. The substitution of 50 vanadium by rhenium stabilizes the high temperature form of VO 2 at room temperature. The cation ratio of 1 : 1 was confirmed by EDX analysis performed by electron microscopy on the same crystals used for X-ray diffraction.

The prospect of carrying out quantitative crystal structure analyses by direct methods with electron diffraction intensity data from zeolites is evaluated for two related materials: ZSM-5 and ZSM-11. The stacked plate-like arrays of ZSM-5 induce intensity perturbations from secondary electron scattering; nevertheless, the T-site positions can be found by direct methods. Intensity data from smaller ZSM-11 microcrystals are more favorable for ab initio analysis so that some oxygen positions are found during Fourier refinement. For intergrowths of one zeolite in the other, the nature of the inclusions has been found to depend on the dominant species. If ZSM-5 is dominant, the apparent ZSM-11 inclusions (assuming a preferred platy orientation) could be rather large, whereas if ZSM-11 is dominant, the ZSM-5 inclusions extend over only 3 or 4 unit cells.

The structures of ZrNCl on one hand and TiOCl and AlOCl on the other hand are analysed in comparison with the Zintl phases Ca[Al 2 Si 2 ] and Na[AlSi], respectively. In the former, the [ZrN] + sublattice is isostructural to the [Al 2 Si 2 ] 2- skeleton whereas the latter are orthorhombic distortions of the Na[AlSi] structure. The three structures can be rationalised by means of an inverse Zintl-Klemm concept, in similarity with the Zintl-Klemm concept which accounts for the structures of the Zintl phases. In addition, Ca[Al 2 Si 2 ] presents the same structure than the hexacelsian oxide Ca[Al 2 Si 2 O 8 ] providing a new example of how the cation arrays, in oxides, maintain the structure of their respective alloy.

The crystal structure of NH 4 H 5 (PO 4 ) 2 was investigated at 298 and 80 K by single crystal neutron diffraction. The room temperature modification II crystallizes monoclinic (space group C 2/ c ), a = 10.156(4), b = 7.554(3), c = 9.507(4) Å, β = 100.71(4)°, Z = 4. It is characterized by disorder of the NH 4 + cations and short symmetrical hydrogen bonds (2.422(8) Å) connecting the layers of H 2 PO 4 tetrahedra. The low temperature modification I is monoclinic, (space group P 2 1 / c ), a = 10.040(4), b = 7.628(2), c = 9.558(3) Å, β = 102.51(4)°, Z = 4. Below the phase transition the NH 4 + cations become ordered and the layers of PO 4 tetrahedra are connected by asymmetrical hydrogen bonds (2.427(7) Å) allowing to formulate the phase I as (NH 4 )(H 2 PO 4 )(H 3 PO 4 ). The changes in the thermal ellipsoids and a possible mechanism of the phase transition are discussed.

The crystal structure of orthorhombic Er(HPO 4 )(NO 3 )·3 H 2 O has been determined from X-ray powder diffraction data. The unit cell dimensions are a = 10.1653(4) Å, b = 11.9178(5) Å, c = 6.8533(3) Å, V = 830.26(6), Z = 4. The space group is Pbcm (No. 57) or Pbc 2 1 (No. 29). The structures were solved ab initio using EXPO program and refined by FULLPROF package. Because geometrical features of the two solutions are the same, the crystal structure has been described in the scope of the centrosymmetric Pbcm space group. Positions of the hydrogen atoms were not defined. The erbium atom is eight coordinated. It is surrounded by one nitrate anion, one water molecule and four phosphate groups. [ErO 8 ] polyhedra are linked together through their edges forming infinite chains extended along the c axis. The chains are connected by phosphate groups to form layers palallel to the yz plane. Probable hydrogen bonds are discussed.

The analysis of molecular structures of three derivatives: 5-amino-3-carbomethoxy-1-methyl-1 H -[1,2,4]-triazole ( 1 ), 1-acetyl-5-amino-3-carbomethoxy-1 H -[1,2,4]-triazole ( 2 ) and 5-acetylamino-3-carbomethoxy-1-methyl-1 H -[1,2,4]triazole ( 3 ) indicate the sensitivity of the N2–N1–C5 fragment of the triazole ring to the substitution. Molecular conformations are influenced by several intra- and intermolecular contacts. In all structures very extensive N–H···N/O and C–H (methyl) ···O/N net of secondary interactions is formed. This kind of interactions is common in crystal structures which are proton-deficient and for this reason various types of multi-point interactions are forced. Besides, triazole π ··· π stacking interactions are observed.

The crystal structure of (4-methoxy-phenyl)-[4-(4-methoxy-phenyl)-1-(1-phenylethylideneamino)-2-thioxo-1,2-dihydro-pyrimidin-5-yl]-methanone, has beeen determined by single-crystal X-ray diffraction at 183(2) K. The compound crystallizes in the monoclinic system, space group P 2 1 / c . The O3 and C19 atoms in the methoxy group shows conformational disorder. In the title compound, the pyrimidine ring is slightly nonplanar. The angle between the planes formed by the ring atoms N2–C2–C3 and C1–N1–C4 is 4.0 (1)°. The three phenyl rings form dihedral angles of 147.9 (1), 113.0 (1) and 103.2 (1)° with the pyrimidine ring. The structure is stabilized by weak intermolecular C–H...O interactions.

N -(3-hydroxypyridine-2-yl)salicylidineimine ( 1 ), N -(3-hydroxypyridine-2-yl)-5-bromo salicylideneimine ( 2 ) and their diorganotin(IV) complexes formulated as Me 2 Sn(OC 6 H 4 CH=NC 5 H 3 NO) ( 3 ) and Me 2 Sn(OC 6 H 3 BrCH=NC 5 H 3 NO) ( 4 ) were prepared and characterized by 1 H-NMR, IR, mass spectroscopy and single crystal x-ray diffraction study. The crystal structures of 3 [orthorhombic, Pbna (no 60); a = 10.439(1) Å, b = 13.388(3) Å, c = 19.340(2) Å, Z = 4; V = 2703(1) Å 3 ] and 4 [monoclinic, P 2 1 / a (no 14); a = 7.528(4) Å, b = 16.576(7) Å, c = 12.017(7) Å, β = 97.97(5), Z = 4; V = 1485(1) Å 3 ] have been solved by standard methods and refined by full-matrix least squares (carried out on F 2 ) to R values of 0.066 and 0.046 respectively. The studied tin(IV) complexes ( 3 and 4 ) exhibit the distorted trigonal-bipyramidal geometries around Sn atoms, separately. The tautomeric effects of ligands and the substitution of Br atom to the common molecular structure were discussed beside of the coordination geometries of 3 and 4 .

A mononuclear cobalt(II) complex, [Co(dmpp)(SCN) 2 ], was synthesized using 2,6-bis (3,5-dimethylpyrazolyl)pyridine (dmpp) and thiocyanate anion (SCN), and characterized by IR spectroscopy and single-crystal X-ray diffraction. In addition, cyclic voltammetric studies have been performed. The complex crystalizes in monoclinic space group C 2/ c , with unit cell dimensions a = 15.2469(15), b = 9.1120(9), c = 14.0302(11) Å, β = 95.823(3)°. The cell containes 4 molecules.

Single crystals of L-arginine diphosphate (L-HN:C(NH 2 )NH(CH 2 ) 3 CH(NH 2 )COOH·2 H 3 PO 4 , abbreviated as LADP) with dimensions of ca 15 × 20 × 40 mm and of optical quality were grown by controlled evaporation of aqueous solutions. A structure analysis showed that LADP (space group P 2 1 2 1 2 1 , a 1 = 9.681(2), a 2 = 21.756(4), a 3 = 7.000(14) Å, Z = 4 at 293 K) is isotypic to L-arginine·2 H 3 AsO 4 . The tensors of thermal expansion as well as of dielectric, elastic, thermoelastic, piezoelastic and piezoelectric properties were measured and compared with corresponding properties of L-arginine·H 3 PO 4 ·H 2 O (LAP).

The room temperature structure ( α -form) of the organic compound p -chlorobenzamide, C 7 H 6 ClNO, can be described as a classical three-dimensional periodic superstructure ( α S ) and also as a commensurately modulated structure ( α M ) in (3 + 1)-dimensional superspace. The diffraction pattern is characterized by a clear difference in intensity between main and satellite reflections. All reflections can be indexed with four indices hklm in a triclinic unit cell and one modulation vector in the superspace group P 1̅( αβγ ) with the modulation vector q⃗ = 1/3· a⃗ *. The structure undergoes a phase transition at higher temperature. In this phase transition the modulation vanishes as indicated by the disappearance of the satellite reflections. The resulting high temperature phase ( γ -form) contains one molecule in the asymmetric unit, the space group is P 1̅. The high temperature structure ( γ ) is very close to the reference structure of the modulated model at room temperature. The phase transition can therefore be understood as a loss of the modulation at high temperature.