Band 233, Heft 8

The alkaline-earth tri-mercurides A Hg 3 ( A =Ca, Sr, Ba) were yielded from stoichiometric melts of the elements in pure phase (in the case of Sr with Sr 11 Hg 54 as a by-product) and their structures were determined by means of single crystal X-ray data. As reported long ago from powder data, CaHg 3 and SrHg 3 crystallize in the Ni 3 Sn-type ( P 6 3 / mmc , a =662.26(2)/689.39(3), c =501.64(2)/510.38(3) pm, Z =2, R 1=0.0233/0.0306 for A =Ca/Sr). The structure consists of a hexagonal close packing of ordered layers A Hg 3 or a dense packing of anti-cuboctahedra [ A Hg 12 ] (as cation coordination polyhedra, CCP) and [Hg 6 ] octahedra fused via opposite faces to form columns along c . BaHg 3 crystallizes in a unique structure type ( P 4/ ncc , a =1193.04(3), c =958.02(5) pm, Z =12, R 1=0.0461). It contains three crystallographically different Hg atoms, which form layers of distorted flat square pyramids. In contrast to the layers of the BaAl 4 -type, 15${1 \over 5}$ of the pyramids are missing. Due to the 45 degree rotation of adjacent layers, the connection between the layers is not a ‘apical-to-apical’ one like in BaAl 4 , but is established by ‘apical-to-basal’ bonds. Compared to the Ca and Sr compound, the CCPs of the two different Ba atoms, which are embedded between the pyramid layers, are increased to 12+4 and 14+2 (for Hg+Ba). For all title compounds and the Li phase LiHg 3 , which is isotypic to CaHg 3 , the electronic band structures were calculated within the framework of the FP-LAPW DFT method. Even though the compounds are metals and exhibit only very slight minima of the tDOS at the Fermi level, the electron transfer from the alkali/alkaline-earth element towards mercury is almost complete. Thus, Coulomb interactions and the optimized size and arrangement of the A CCPs, besides the flexible Hg–Hg bonding within the polyanion, determine the structure formation.

The interactions of π-systems with lone-pairs of electrons are known and have been described in biological systems, involving lone-pairs derived from metals, metalloids, sulfur, oxygen and nitrogen. This study describes a bibliographic survey of the disulfide-bound sulfur(lone-pair) interactions with π-systems residing in the flavin adenine dinucleotide (FAD) cofactor of oxidoreductase enzymes (flavoenzymes). Thus, of the 172 oxidoreductase enzymes evaluated for gamma-S(lone-pair)…π(FAD) interactions, 96 proteins (56%) exhibited these interactions corresponding; 61% of 350 the constituent monomers featured at least one gamma-S(lone-pair)…π(FAD) interaction. Two main points of association between the S(lone-pair) and the isoalloxazine moiety of FAD were identified, namely at the centroid of the bond linking the uracil and pyrazine rings (60%), and the centroid of the uracil ring (37%). Reflecting the nature of the secondary structure in three prominent classes of oxidoreductase enzymes: glutathione disulfide reductases (GR; 21 proteins), trypanothione disulfide reductases (TR, 14) and sulfhydryl oxidases (SOX, 22), the approach of the gamma-S(lone-pair) to the FAD residue was to the si-face of the isoalloxazine ring system, i.e. to the opposite side as the carbonyl residue, for all GR and TR examples, and to the re-face for all SOX examples. Finally, the attractive nature of the gamma-S(lone-pair)…π(FAD) interactions was confirmed qualitatively by an examination of the non-covalent interaction plots.

The isonicotinamide-malonic acid (2/1) co-crystal salt ( 2IN·C3 ) exhibits a first-order displacive structural phase transition from low-temperature triclinic P 1̅ crystal structure to high-temperature monoclinic C 2/ c crystal structure and vice versa at the transition temperatures of 298 (1) and 295 (1) K, respectively, as determined by variable-temperature SCXRD analysis and DSC measurements. The asymmetric unit of 2IN·C3 comprises three malonic acid molecules and six isonicotinamide molecules at the low-temperature phase, and this is reduced to a half-molecule of malonic acid and an isonicotinamide molecule in the high-temperature phase. The carboxyl and pyridinium H atoms are disordered at both phases. The observed phase transition near room temperature is triggered by the molecular displacement of the isonicotinamide molecule and the syn - anti conformational transformation of the malonic acid molecule with deviation angles of 10.4 and 11.7°, respectively, which induced an energy change of 19.1 kJ mol −1 in the molecular cluster comprising a central isonicotinamide molecule and eight neighboring molecules. However, the total interaction energy of the molecular cluster of a central malonic acid molecule and eight neighboring molecules does not change significantly upon the phase transition. The molecules of isonicotinamide structures except IN·IN + ·triazole ‒ form zero-dimensional finite arrays or one-dimensional chains as the primary supramolecular construct by carboxyl···pyridyl (−35.9 to −56.7 kJ mol −1 ) and carboxamide···carboxamide (−53.6 to −68.7 kJ mol −1 ) or carboxyl···carboxamide (−52.6 to −67.1 kJ mol −1 ) synthons.

Single crystals of [C(NH 2 ) 3 ][HC(NH 2 ) 2 ]PbI 4 (GuFAPbI 4 ) and [HSC(NH 2 ) 2 ][HC(NH 2 ) 2 ]PbI 4 (TuFAPbI 4 ) were obtained from solutions of the binary halides in HI or DMF. Large crystals grown from HI are dark-brown while single phase powders synthesized from DMF are orange. The crystal structure of GuFAPbI 4 ( I 2/ m , Z =12, a =14.3147(2), b =12.7591(2), c =25.7377(4)Å), β=101.459(1), 4256 refl., 196 param., R 1 =0.024, wR 2 =0.061) represents a 2D perovskite with a new motif similar to Ruddlesden-Popper phases (AX) m (A′BX 3 ) n and m = n =1. The layers are formed by corner-sharing PbI 6 octahedra. According to the cut-out of the 3-D perovskite the structure of GuFAPbI 4 can be assigned as a (210)-oriented representative. So one octahedron is linked in trans-position and two in cis-orientation. The structure of TuFAPbI 4 ( P 2 1 / n , Z =12, a =14.4208(6), b =12.7545(7), c =26.3982(11) Å), β=100.609(3)°, 6808 refl., 275 param., R 1 =0.048, wR 2 =0.096) represents a simple distortion variant of GuFAPbI 4 . GuFAPbI 4 and TuFAPbI 4 were further characterized by vibrational spectroscopy and optical spectroscopy. The optical band gap was determined as 2.34 eV in agreement to the observed color. So both compounds are not suitable as a dye in the PSC perovskite solar cell. Similar to other Pb-containing 2D perovskites there is a significant excitonic peak (2.31 eV). TuFAPbI 4 represents the first example with protonated thiourea as an organic cation. Therefore, we characterized protonated thiourea iodide and introduce protonated thiourea [HSC(NH 2 ) 2 ] + as a new cation for hybrid halogeno perovskites.

Unusual conformations have been found in a new calix[8]arene and in new solvates of two known calix[6]arenes. The chair-like conformation with 2/ m point group symmetry was found for the first time in the dimethylformamide (DMF) disolvate of the basic calix[6]arene ( 1 ) without substituents in the lower and upper rims. Such symmetry is driven by the guest geometry allowing for two equivalent hydrogen bonding patterns in the chair seat. This avoids cone distortion found in the other chair-like conformers, although they have energies lower than that of new symmetrical conformer. The molecular conformation of hexa(carboxymethoxy)calix[6]arene ( 2 ) is also described as a dimethylsulfoxide (DMSO) pentasolvate. Its conformation can be described as a 1,3,5-closed cone with three alternate phenyl rings inclined inwards to the cone, thereby closing the cone entrance. Such a conformation also suggests five acid groups are pointed towards the same side of the calyx base and are able to bind metal ions or basic compounds in the lower rim, while inclusion of guests into the cone cavity is hindered. Both inclusion and cooperative acid binding/coordination abilities are still more hindered in the lowest energy 1,2,3-alternate cone conformer of 2 . The role of the solvent in avoiding cone distortion was highlighted by inspecting the conformations of 5,11,17,23,29,35,41,47-octanitro-49,50,51,52,53,54,55,56-octa-n-butoxycalix[8]arene ( 3 ) and the known nitro analogues having methyl instead of n-butyl groups. Cone distortion is found in the non-solvated crystal form of 3 , while non-classical hydrogen bonds with tetrahydrofuran preclude this in the literature analogue.

The structure of hydrated calcium uranyl carbonate, mineral sharpite, has been solved for the first time. The structure is orthorhombic, space group Cmcm , with the unit-cell parameters a =4.9032 (4), b =15.6489 (11), c =22.0414 (18) Å, V =1691.2 (2) Å 3 , Z =4. The structure was refined from 858 unique observed reflections to a final R =5.48% (GOF=1.48). The structure is based upon infinite Ca 2+ -uranyl-carbonate sheets, which are unique among uranyl minerals and inorganic compounds. They result from edge-sharing of triangles, occupied by CO 3 , and hexagons that are occupied both by UO 8 and Ca 2+ (H 2 O) 3 O 5 . Thus, topology of the sheets is identical to rutherfordine, (UO 2 )(CO 3 ). Nevertheless Ca 2+ is occupying one of the hexagons of the topology in sharpite. Sheets are extremely corrugated, stacked perpendicular to b and linked by H-bonds and Van Der Waals interactions, only. The ideal chemical formula of sharpite is {Ca(H 2 [3] O) 3 [(UO 2 ) 3 (CO 3 ) 3.6 O 0.2 ]} 0 , Z =4; however, one of the C sites was found to be only partially occupied. The character of sharpite structure is probably a key to understand its scarcity of occurrences in Nature.

M. von Laue discovered diffraction of X-rays in the crystal in 1912 and W. H. Bragg and W. L. Bragg determined the first crystal structures in 1913. Soon after that (1916–1918), Bernardo Eduard Brixy, a Croatian Franciscan, published papers (in Croatian language) on generation and properties of X-rays and on the theory of interference of X-rays in a general, triclinic, case. The main points of the Brixy papers are outlined.