Volume 232, Issue 10

The crystal chemistry of nitridoborates with the CO 2 analogous [BN 2 ] 3− ion is reviewed. Such nitridoborates form with the alkali and alkaline earth metals as well as with divalent europium. Also quaternary compounds with mixed cations along with nitridoborate nitrides, oxides, halides and hydrides are discussed. The spectroscopic (IR, Raman, solid state NMR and Mössbauer spectroscopy) and magnetic behavior as well as optical properties are discussed in the light of structure-property relationships.

We report the synthesis and the crystal structure of the new vanadate AgCaVO 4 from laboratory powder X-ray data. Contrary to the previously reported AgBVO 4 (B=Mg, Cd), AgCaVO 4 exhibits the arcanite structure (β-K 2 SO 4 ). Although it exhibits the same structure than arcanite, significant differences are observed. These differences are explained by deriving the atomic displacement field. The change of connectivity within the structure between β-K 2 SO 4 and AgCaVO 4 results from a rotation of the VO 4 tetrahedra giving rise to a change from a face sharing to an edge sharing octahedral chains. Additionally, the thermal expansion of AgCaVO 4 has been investigated up to 800°C.

The five ternary intermetallic compounds M 2 Pt 6 Al 15 ( M =Ca, Sc, Y, La, Lu) were prepared from the elements by arc-melting. The crystal structure was determined via single crystal X-ray diffraction. The title compounds crystallize in a superstructure of the RE 0.67 Pt 2 Al 5 type structure ( P 6 3 / mmc ) in the monoclinic crystal system with space group P 12 1 / m 1 (Sc 2 Pt 6 Al 15 : a =734.19(2), b =1628.96(10), c =734.19(2) pm, β =119.999(3)°; wR =0.0356, 3034 F 2 values, 68 variables). The superstructure can be derived by the superspace formalism using (3+2)D or (3+1)D interpretations of the diffraction data. The structural relation to the subcell structure is discussed on the basis of a group-subgroup scheme. In the crystal structure strongly bonded [Pt 2 Al 4 ] δ − slabs are alternatingly stacked with ordered layers containing M atoms and Al 3 triangles.

A new compound KLi[Sb 2 (C 4 H 2 O 6 ) 2 ]·4H 2 O, 1 , was synthesized in single crystal form by slowly evaporating an aqueous solution of potassium antimony tartrate and lithium nitrate. The structure of 1 consists of homochiral layers of antimony tartrate dimers linked by LiO 4 tetrahedra. The interlayer water molecules can be reversibly driven out by heating or exchanged by small alcohol molecules under ambient conditions, occurring via single-crystal to single-crystal transformations. To accommodate different interlayer molecules, the interlayer space is changed by adjusting the relative lateral shift of neighboring layers. A similar adjustment in the layer stacking also occurs in a structural phase transition caused by order-disorder transformation of the arrangement of interlayer methanol molecules at low temperature.

Crystal structures are reported from data collected at 100 K of ( E )-2-(X-benzylidene)-1-tetralone ( 2 : X=3-O 2 N; 3 : X=4-O 2 N; 5 : X=4-HO; 6 : X=4-Me 2 N; 7 : 4-NC), ( E )-2-(X-benzylidene)-6-MeO-1-tetralone, 8 , and ( E )-2-(X-benzylidene)-5-MeO-1-tetralone 9 . Also reported herein are the Hirshfeld surface calculations for these compounds as well as those of ( E )-2-(X-benzylidene)-1-tetralone ( 1 : X=H; 4: X=4-MeO), whose structures were previously reported. The molecules are not planar as shown by the dihedral angles of 45.66(5)–69.78(5)° between the phenyl groups and by the puckered cyclohexenyl rings. A common feature of the molecular conformations is the C–H···O1(carbonyl) intramolecular hydrogen bond. The carbonyl oxygen atom plays significant roles in the interactions in all compounds baring compound 8 . However, there is no consistent set of intermolecular interaction in this group of compounds. Intermolecular interactions present in each compound are some of the O–H···O, C–H···A (A=O, N or π), A–O···π (A=C or N) and π···π interactions. The only compound exhibiting a classical O–H···O hydrogen bond is compound 5 . C–H···π interactions are found in all compounds, and while π···π interactions are present in compounds 2 , 3 , 7 and 9 , no consistent type of stacking arrangement is shown. The Hirshfeld surface calculations, while generally concurring with the intermolecular interactions indicated by PLATON analyses, also reveal short interactions, which fall below the PLATON cut-off parameters.

7-Hydroxy-3-methoxy-6-oxo-6H-benzo[ c ]- chromene-8-carboxylic acid ( 3a ), 3,7-dihydroxy-6-oxo-6H- benzo[ c ]chromene-8-carboxylic acid ( 3b ), 1,7-dihydroxy-6-oxo-6H-benzo[ c ]chromene-8-carboxylic acid ( 3c ) and 2-bromo-7-hydroxy-6-oxo-6H-benzo[ c ]chromene-8-carboxylic acid ( 3d ) were synthesized and characterized by the method of single crystal X-ray diffraction. Owing to bigger conjugated system and various H-bonds in 7-hydroxy-6-oxo-6H-benzo[ c ]chromene-8-carboxylic skeleton, 3a–3c have excellent fluorescence in ethanol solution and the solid state. The synthons involved in each crystal are identified, and the fluorescence emission differences leading to molecular recognition are determined.

A simple calculation scheme based on the Ahrens ionic radii system is proposed for predicting the lattice parameters of the A I A II B II 2 F 7 disordered cubic fluoride pyrochlores.