Structure of the mixed-metal carbonate KAgCO₃ revisited: order-disorder (OD) polytypism and allotwinning.

Crystals of KAgCO3 belong to an order-disorder (OD) family of structures composed of layers of two kinds. There are two polytypes with a maximum degree of order [MDO1: Pccb; MDO2: Ibca, doubled a-axis compared with MDO1], which are both realised to a different extent in two crystals under investigation [volume fraction MDO1:MDO2 in crystal (I): 0.0216:0.

Solvatomorphism of 9,9'-[1,3,4-thiadiazole-2,5-diylbis(2,3-thiophendiyl-4,1-phenylene)]bis[9H-carbazole]: isostructurality, modularity and order-disorder theory.

During a systematic investigation of the crystallization behaviour of 9,9'-[1,3,4-thiadiazole-2,5-diylbis(2,3-thiophendiyl-4,1-phenylene)]bis[9H-carbazole] (I), six single crystalline solvates were obtained and characterized by X-ray diffraction at 100 K. The structure of the hemi-2-butanone (MEK) solvate contains two crystallographically independent molecules of (I) related by pseudo-inversion symmetry. The structure is polytypic and composed of non-polar (I) layers and polar solvent layers.

Polymorphism of CaTeO3 and solid solutions Ca(x)Sr(1-x)TeO3.

Single crystals and microcrystalline samples of the calcium tellurate(IV) phases alpha-, beta-, beta'- and gamma-CaTeO3 as well as of two solid solutions Ca(x)Sr(1-x)TeO3 (x = 0.55 and 0.77) have been synthesized and characterized by X-ray diffraction and thermal analysis.