Volume 231, Issue 4

Single-crystal growth experiments in the system CsF-Er 2 O 3 -SiO 2 resulted in the simultaneous crystallization of two chemically related compounds within the same run: Cs 2 Er[Si 6 O 14 ]F (phase I) and Cs 2 Er[Si 4 O 10 ]F (phase II). They represent the first examples for cesium erbium silicates containing fluorine. Basic crystallographic data are – phase I: space group Cmca , a =17.2556(6) Å, b =24.6565(7) Å, c =14.4735(5) Å, V =6157.9(3) Å 3 , Z =16; phase II: space group Pnma , a =22.3748(7) Å, b =8.8390(2) Å, c =11.9710(4) Å, V =2367.5(1) Å 3 , Z =8. The structures were determined by direct methods and refined to residuals of R (| F |)=0.0229 for 2920 (phase I) and 0.0231 for 2314 (phase II) independent observed reflections with I >2σ( I ). The structure of phase I represents a previously unknown structure type with a three dimensional tetrahedral framework consisting of Q 3 and Q 4 groups in the ratio 2:1. Basic building units of the network are unbranched sechser single-chains running parallel to [001]. The network can be conveniently built up from the condensation of tetrahedral layers parallel to (010) or (100), respectively. The crystal structure of phase II can be classified as a tubular or columnar chain silicate indicating that the backbones of the structure are multiple chains of silicate tetrahedra. This structure is isotypic to a Cs 2 Y[Si 4 O 10 ]F, a compound that has been characterized previously. Alternatively, both compounds can be described as mixed octahedral-tetrahedral frameworks, which can be classified according to their polyhedral microensembles . A topological analysis of both nets is presented.

The crystal structure of Rb 2 Ca 2 Si 3 O 9 has been characterized by X-ray diffraction techniques and Raman spectroscopy. Crystal growth was performed by the flux method in closed platinum capsules using a polycrystalline ceramic precursor as well as RbCl as a mineralizer. The crystal structure was solved from a single-crystal diffraction data set acquired at 23 °C and refined to a final residual of R(|F|)=0.022 for 1871 independent reflections. Basic crystallographic data are as follows: monoclinic symmetry, space group type P 1 n 1, a =6.5902(3) Å, b =7.3911(3) Å, c =10.5904(4) Å, β=93.782(3)°, V =514.72(3) Å 3 , Z =2. With respect to the silicate anions the compound can be classified as a sechser single-chain silicate. The undulated chains run parallel to [-101] and are connected by Rb and Ca cations, which are distributed among four crystallographically independent sites. In a first approximation the coordination polyhedra of the two different calcium ions in the asymmetric unit can be described by distorted trigonal prisms and tetragonal pyramids, respectively. The two rubidium sites exhibit more irregular coordination spheres with eight to nine next neighbors. Structural investigations on the new phase are completed by solid state micro-Raman spectroscopy. DFT-calculations were employed for the interpretation of the spectroscopic data including the allocation of the bands to certain vibrational species.

Eight crystal structures are reported here: substituted ( E ) benzaldehyde 7-chloro-1-methyl-4H-quinolinyl-4-ylidene-hydrazones, 1 , [substituted benzaldehyde: XYC 6 H 4 CHO: X,Y=H,H; 2-F,H; 3-F,H; 4-F,H; 3-Cl,H; 4-Cl,H; 2-Br,H and 2,3-Cl 2 ]. None of the molecules, 1 , are overall planar: angles between the phenyl and and quinolinyl rings vary from <5°, for ( 1 :X,Y=3-F,H; 4-F,H; 3-Cl,H and 2,3-Cl 2 ) to 15–16° for ( 1 : X,Y=H,H and 4-Cl,H). The supramolecular arrangements in the parent compound ( 1 : X=Y=H) are generated solely from C–Z···π (Z=H and Cl) interactions, while the supramolecular arrangements for each of the halo derivatives arise from combinations of π···π and some of C–Z···π (Z=H, F, Cl) and C–H···Z (Z=N, F, Cl) intermolecular interactions: in each case different assemblies result. While there are possibilities for π(quin)···π(quin), π(quin)···π(phen) and π(phen)···π(phen) interactions [quin and phen refer to the quinolinyl and phenyl moieties], only compounds ( 1 : X,Y=2,3-Cl 2 ) and ( 1 : X,Y=4-Cl,H) exhibit all three, ( 1 : X,Y=2-Br,H) just π(quin)···π(quin) of the three, and in the others two of the three. All the halo derivatives exhibit π(quin)···π(quin) interactions. It is argued that steric hindrance between molecules, generated by the halo substituents, prevents the halo derivatives from adopting the packing arrangements of the parent compound, ( 1 : X,Y=H,H). As there appears to be no reason, steric or otherwise, why compound ( 1 : X,Y=H,H) cannot utiilize π···π interactions, it is apparent that the packing of molecules via the C–Y···π interactions is the most stable.

The crystal structures of two isomeric 3-(2H-1,3-benzodioxol-5-ylmethyl)-2-(aryl)-1,3-thiazolidin-4-one compounds ( 1 : aryl=4-O 2 NC 6 H 4 ; 2 : aryl=3-O 2 NC 6 H 4 ) are reported. In both these nonplanar, compounds, the carbonyl oxygen is involved in intramolecular C–H···O hydrogen bonds. However, there are significant differences in the sets of intermolecular interactions, in particular the roles of the oxygen atoms, exhibited by the two compounds. Thus in 1 , a dioxolyl oxygen and the two nitro group oxygen atoms are each involved in different chain forming C–H···O intermolecular hydrogen bonds, while the carbonyl oxygen atom is not involved in any intermolecular interaction. In 2 , the dioxolyl oxygen atom is involved in the formation of centrosymmetric dimers, the carbonyl oxygen in three different C–H···O hydrogen bonds and the nitro group oxygens in two N–O···π(aryl) interactions. Compound 2 exhibits also C–H···π(phenyl), π(phenyl)···π(phenyl) and π(benzodioxolyl)···π(benzodioxolyl) interactions, while in 1 only the latter interaction is present. Compound 1 crystallizes in the monoclinic space group, P 2 1 /a with Z=4, while compound 2 crystallizes in the triclinic space group, P 1̅, with Z=2.

The crystal structure analysis of the bis(mefloquinium) chloride p-fluorobenzenesulphonate salt reveals a rare example of a kryptoracemate given that the cations exhibit a non-crystallographic enantiomeric relationship. The conformations of the cations are based on a skewed letter L with the (piperidinium-2-yl)methanol group sitting almost normal to and directed away from the quinolinyl residue. The most prominent feature of the molecular packing is the formation of supramolecular helical chains along the a -axis, being sustained by pairs of hydroxyl-O–H···O (sulphonate), piperidinium-N–H···O (sulphonate) and piperidinium-N–H···Cl hydrogen bonds. Geometric and Hirshfeld surface analyses of the crystal structure shows significant differences in supramolecular aggregation between the cations due to the presence of different anions and this is the likely reason for the observed kryptoracemic behaviour.