Volume 231, Issue 2

The crystal structure of Cs 2 CuP 2 O 7 [monoclinic, Cc , a =7.460(6), b =12.973(10), c =9.980(8) Å, β=111.95(2)°, V =895.8(12) Å 3 ] prepared by solid-state reactions is based upon open framework formed by corner sharing between CuO 4 distorted squares and P 2 O 7 groups. The framework is porous and has a very low framework density of 13.4 Cu+P atoms per 1 nm 3 . Cs + cations reside in large framework cavities. The heteropolyhedral network in the title compound is based upon three-dimensional (3;4)-connected net that has a three-membered CuP 2 ring as its elementary unit. In terms of reticular chemistry, this net should be considered as an augmented diamond ( dia ) net. The Cu–P net can be obtained from the latter by the replacement of its nodes by the CuP 2 triangles. This replacement is strongly non-centrosymmetric, since all CuP 2 triangles are oriented along the same direction, which provides a crystal chemical explanation for the absence of a symmetry centre in the structure. Cs 2 CuP 2 O 7 is the first compound in the A 2 CuP 2 O 7 family (A=alkaline metal), which is based upon three-dimensional copper pyrophosphate framework.

The crystal structure of the new Er 6 Zn 23 Ge intermetallic compound was established by X-ray diffraction analysis on a twinned crystal (space group Fm3̅m , Wyckoff sequence: f 2 edba , cF 120–Zr 6 Zn 23 Si, a = 12.7726(6) Å). The crystal is composed of two nearly equal size domains, whose mutual orientation is described by a 180° rotation around the cubic [111] axis, i.e. a spinel-type twinning law, not common for intermetallics. Applying the nanocluster approach, Er 6 Ge octahedra and centered two-shell Zn 45 clusters were found as structural building blocks, filling the crystal space in a NaCl-like arrangement. This description was adopted to interpret the twinning in terms of stacking faults in the fcc cubic close packed arrangement. Moreover, the assembly of the nanocluster units is proposed as a possible mechanism for crystal growth and twin formation, in agreement with the principle of the interface energy minimization. Experimental conditions such as supersaturation and co-formation of other phases are also considered as favorable factors for Er 6 Zn 23 Ge twin formation.

The Li-rich ternary intermetallic compounds with the idealized end-member compositions Li 3 CuSn (CSD-427099) and Li 6 Cu 2 Sn 3 (CSD-427100) were synthesized from the pure elements by induction melting in Ta crucibles and annealing at 400°C. Both powder and single-crystal XRD investigations were performed. Li 3 CuSn crystallizes in space group P 6/ mmm [ a =4.5769(2), c =8.461(2) Å; wR 2 =0.073 for 180 unique F 2 -values and 25 free variables]. All atoms are located along [00 z ], [1/3 2/3 z ] and [2/3 1/3 z ]; individual sites are arranged in layers parallel to (00.1). One site is fully, one partially occupied by Sn atoms. Fully but mixed occupation with Cu and Li atoms was found for one site. The remaining electron-density distribution resulting from the strong anisotropic displacement parallel to the c axis is considered in four further sites, which are mixed occupied with (Li, Cu, □), but modelled solely by Li atoms. The crystal structure exhibits analogies with that of Li 2 CuSn ( F 4̅3 m ); comparable layers occur parallel to {111} but the stacking sequence and packing density differs adopting cubic symmetry. In Li 6 Cu 2 Sn 3 [space group R 3̅2 /m , a =4.5900(2), c =30.910(6) Å; wR 2 =0.039 for 253 unique F 2 -values for 25 free variables] all atoms are arranged again at (00 z ), (1/3 2/3 z ) and (2/3 1/3 z ). Three sites are fully occupied (two by Sn atoms, a further one by Li atoms). Three additional positions are mixed occupied by Cu and Li atoms. The crystal structure is closely related to that of the binary phases Li 13 Sn 5 and Li 5 Sn 2 ; the substitution of Li by Cu atoms and vice versa is evident. The structural relationship to Li 13 Ag 5 Si 6 , which is permeable for Li ions, makes the title compound interesting as anode material in Li-ion batteries.

The solid solutions La 2– x Pr x O 2 MnSe 2 (0≤ x ≤1) and La 2– x Nd x O 2 MnSe 2 (0≤ x ≤0.6) were synthesized in a NaI/KI flux between 800 and 900°C. The selenide oxides adopt a ZrCuSiAs-related structure with modulated [MnSe 2 ] 2– -layers which consist of a mixture of edge- and corner-sharing MnSe 4/2 -tetrahedra. The crystal structures are described with a (3+1)D model in superspace group Cmme ( α 0½)0s0. The modulation vector q can be controlled by partial substitution of La 3+ for Pr 3+ and Nd 3+ via the unit cell volume leading to, amongst others, (La 0.55 Pr 0.45 ) 2 O 2 MnSe 2 with α =1/6, which allows the projection onto 3D space by using a simple sixfold a axis.

Quantitative phase composition and morphological characterization of 12 human gallbladder stones (GS1–GS12) retrieved from patients of eastern India have been carried out using IR-spectroscopy, powder X-ray diffraction (PXRD) and scanning electron microscopy (SEM). The FTIR spectra indicated that the primary composition of gallstones studied was cholesterol. X-ray powder diffraction study revealed cholesterol monohydrate (CHM) as the major crystalline phase in GS1–GS12. The Rietveld analysis showed that nine of the gallstones were composed exclusively of CHM, while the remaining three stones contained in addition to CHM, small amounts (4.2–10.6 wt%) of calcium carbonate as aragonite and vaterite. The crystallite size of CHM in GS1–GS12 varied between 82(6) and 249(3) nm. The SEM images of gallstones showed different crystal habits of CHM such as plates, thin rods, rectangular and hexagonal blocks, which resulted into different levels of agglomeration at the mesoscopic scale. Presence of numerous parasitic eggs with a typical muskmelon surface in three gallstones (GS2, GS7 and GS9) suggests possible association between the liver fluke infection and biliary stone formation in these patients. To the best of our knowledge, the study constitutes the first report of X-ray quantitative phase analysis of gallstones using the Rietveld methodology.

The atomic distribution in crystal structures becomes very complex if atoms are disordered and randomly distributed over positions not being fully occupied. Interatomic distances between neighboring atoms might be too close for simultaneous occupancies and thus are mutually exclusive. The distribution of atoms over crystallographic positions avoiding close contacts with neighboring atoms represents an NP-complete problem that is believed to have no efficient solution. Here, we use Boolean satisfiability (SAT) techniques to find a valid atomic distribution pattern in the crystal structure. Distance constraints are encoded as conjunctions of logical disjunctions over Boolean variables and handed to a SAT solver. If a solution exists, the solver supplies a satisfying assignment to the Boolean variables yielding a valid distribution after decoding. That way the hitherto unsolved problem of distributing k atoms over n positions has an elegant solution related to one of the most central problems in computer science.

Crystallization of Cd[S 2 CN(iPr)CH 2 CH 2 OH] 2 from ethanol yields the coordination polymer [{Cd[S 2 CN(iPr)CH 2 CH 2 OH] 2 }·EtOH] ∞ ( 1 ) within 3 h. When the solution is allowed to stand for another hour, the needles begin to dissolve and prisms emerge of the supramolecular isomer (SI), binuclear {Cd[S 2 CN(iPr)CH 2 CH 2 OH] 2 } 2 ·2EtOH ( 2 ). These have been fully characterized spectroscopically and by X-ray crystallography. Polymeric 1 has 2-fold symmetry and features dithiocarbamate ligands coordinating two octahedral Cd atoms in a μ 2 κ 2 -tridentate mode. Binuclear 2 is centrosymmetric with two ligands being μ 2 κ 2 -tridentate as for 1 but the other two being κ 2 -chelating leading to square pyramidal geometries. The conversion of the kinetic crystallization product, 1 , to thermodynamic 2 is irreversible but transformations mediated by recrystallization (ethanol and acetonitrile) to related literature SI species, namely coordination polymer [{Cd[S 2 CN(iPr)CH 2 CH 2 OH] 2 } 3 ·MeCN] ∞ and binuclear {Cd[S 2 CN(iPr)CH 2 CH 2 OH] 2 } 2 ·2H 2 O·2MeCN, are demonstrated, some of which are reversible. Three other crystallization outcomes are described whereby crystal structures were obtained for the 1:2 co-crystal {Cd[S 2 CN(iPr)CH 2 CH 2 OH] 2 } 2 :2[3-(propan-2-yl)-1,3-oxazolidine-2-thione] ( 3 ), the salt co-crystal [iPrNH 2 (CH 2 CH 2 OH)] 4 [SO 4 ] 2 {Cd[S 2 CN(iPr)CH 2 CH 2 OH] 2 } 2 ( 4 ) and the salt [iPrNH 2 (CH 2 CH 2 OH)]{Cd[S 2 CN(iPr)CH 2 CH 2 OH] 3 } ( 5 ). These arise as a result of decomposition/oxidation of the dithiocarbamate ligands. In each of 3 and 4 the binuclear {Cd[S 2 CN(iPr)CH 2 CH 2 OH] 2 } 2 SI, as in 2 , is observed strongly suggesting a thermodynamic preference for this form.