Volume 240, Issue 5-6

The use of liquid bismuth as reactive or inert flux medium for the growth of intermetallic phases is reviewed. Besides systematic phase analytical studies with respect to discovery of new phases, large, mm-sized single crystals allow direction dependent physical property studies.

The absence of a stereogenic center in N -cycloalkyl-4-methyl-2,2-dioxo-1 H -2λ 6 ,1-benzothiazine-3-carboxamides (cycloalkyl moiety is cyclopropyl, cyclobutyl, cyclopentyl, cyclohexyl, cycloheptyl, cyclooctyl) does not interfere with their ability to be crystallized from the ethanol solution into a centrosymmetric or a non-centrosymmetric space group. The non-centrosymmetric crystals containing opposite conformer of a molecule were obtained using aqueous acetic acid as another solvent. Pairs of enantiomorphic crystals have the same crystal shape and unit cell parameters and can only be recognized by X-ray diffraction study due to anomalous dispersion. The formation of such unusual enantiomers may be caused by the ability of the sulfur atom to become a stereogenic center due to the different participation of the oxygen atoms of the sulfonyl group in hydrogen bonds formation. Similar to classical polymorphic modifications, the enantiomorphic crystals may differ in their biological activity. Analgesic activity does not depend on the type of conformation of 1,2-benzothiazine, while the diuretic effect is much stronger in the case of the crystals containing one type of conformer. This property of 1,2-benzothiazines is to be expected of great importance in future drug developments.

Single crystal specimens of lead phosphate oxyapatite, Pb 10 (PO 4 ) 6 O, were prepared and the structure was refined in P 6 ‾ $P\overline{6}$ space group. The crystal structure was a superstructure of aristotype apatite structure doubled in the c -axis. This superstructure was characterized by change in width of the anion channel, namely change in sizes of regular A 2 triangles as ‘large – middle – small – middle – (large – )’ along <001> in 2 × c of the parent structure. A half of in-channel (guest) O 2− were located at either one of two positions ( X 1 site positions) split from the center of the smallest triangle ( A 2c triangle) along <001> with 50 % probability each. The rest scattered over four positions on the c -axis near two middle-size triangles in the cell with far less probabilities. Attraction between A 2c-site Pb 2+ and X 1-site O 2− made A 2c triangle the smallest, while 6s2 lone electron pairs of Pb 2+ hindered O 2− to locate at the center of A 2c triangle. This commensurately modulated structure was required to balance different sizes of A 2 triangles and least distortion of (PO 4 ) 3− complex anion simultaneously in the host structure.

A new uranyl silicate [(K,Na) 4 Cl 2 ][(UO 2 ) 6 (Si 2 O 7 ) 2 F 2 ] ( 1 ) was obtained from melt in evacuated silica tubes. The crystal structure of 1 is orthorhombic, Pnma , a  = 36.8677(7), b  = 7.7946(2), c  = 19.1931(4) Å, V  = 5,515.5(2) Å 3 . It represents a microporous framework comprised of Ur O 5 and Ur O 4 F pentagonal bipyramids and Si 2 O 7 disilicate groups. The framework contains two types of channels with the size of 8.14 × 8.66 and 6.38 × 4.42 Å 2 ; the smaller ones host the potassium cations while the larger ones contain more complex alkali-chloride species.

The title species has been studied in two crystalline forms resulting from reports describing (1) a centrosymmetric form [ P 2 1 / n , Z ′ = 1.0] and (2) a Sohncke form [ P 2 1 , Z ′ = 2.0; Flack parameter = −0.04(2)]. They are related by the fact that (a) the two have, approximately, the same cell constants, while (b) Z ′ is doubled in the latter in the course of losing the n-glide plane. The existence of species displaying such a remarkable relationship was noted approximately 75 years ago, but, ignored probably because the discoverers (see below) never completed the necessary experimental work to fully document the phenomenon, inasmuch as (1) crystallography was in its infancy then and (2) synthesizing the necessary, pure, chiral species and growing the necessary high-quality crystals was a major challenge which has, not even yet, been accomplished. Moreover, O. Hassel, the major player in this field, was distracted by his work on the chair-boat equilibrium in cyclohexane and related rings systems for which he eventually won the Nobel Prize (1969). Herein, we have attempted to contribute a chapter to this curious crystallographic phenomenon, which has been made even more fascinating by the observation that a ruthenium Grubbs catalyst belongs in the racemic mimic class.

The thermal decomposition of copper(II) hydroxide, malachite, and azurite was studied using X-ray photoelectron spectroscopy in operando within the spectrometer’s working chamber. We found that copper(II) hydroxide breaks down completely at 160 °C, forming copper(II) oxide (tenorite), which has a similar structure. Azurite has a more complex decomposition process, where a water molecule is split first, followed by the release of carbon dioxide to form copper(II) oxide. Malachite is the most resistant to decomposition, as it starts to break down only at 280 °C, with the simultaneous splitting of water and carbon dioxide due to the hydrogen bond between the hydroxide and carbonate groups. Therefore, the crystal structure and the presence of hydrogen bonds determine the conditions and stages of thermal decomposition of these copper compounds.

Single crystals of two new calcium perrhenates, anhydrous Ca(ReO 4 ) 2 ( 1 ) and K 2 Ca 3 (ReO 4 ) 8 ·4H 2 O ( 2 ), were prepared during solid-state and solution attempts to prepare the potassium analog of NaCa(ReO 4 ) 3 . Both structures can be regarded as frameworks comprised of vertex-sharing CaO 8 and ReO 4 polyhedra. 1 is a complete structural analog of Sr(ReO 4 ) 2 while 2 corresponds to its own structure type. It is also the first hydrated binary perrhenate to date. We discuss the similarities and differences in the structures of alkaline earth perrhenates and pertechnetates; existence of more complex and elegant metal-perrhenate architectures is predicted.