Synthesis and characterization of the rare-earth dicyanamides Ln[N(CN)2]3 with Ln=La, Ce, Pr, Nd, Sm, and Eu

The rare-earth dicyanamides Ln[N(CN)₂]₃ (Ln=La, Ce, Pr, Nd, Sm, Eu) were obtained via ion exchange in aqueous medium and subsequent drying: The crystal structures were solved and refined based on X-ray powder diffraction data and they were found to be isotypic: Ln[N(CN)₂]₃; Cmcm (no. 63), Z=4, Ln=La: , , ; Ce: , , ; Pr: , , ; Nd: , , ; Sm: , , ; Eu: , , ). The compounds represent the first dicyanamides with trivalent cations. The Ln³⁺ ions are coordinated by three bridging N atoms and six terminal N atoms of the dicyanamide ions forming a three capped trigonal prism. The structure type is related to that of PuBr₃. The novel compounds Ln[N(CN)₂]₃ have been characterized by IR and Raman spectroscopy (Ln=La) and the thermal behavior has been monitored by differential scanning calorimetry (Ln=Ce, Nd, Eu).     

Tetragonal low-temperature structure of LiAl

The cubic face-centered structure of LiAl (, at ) transforms into a tetragonal body-centered structure (I4₁/amd, , at ). This first-order phase transition at about during heating is probably the reason for the so-called “ anomalies” in some physical properties like specific heat, electrical resistivity and nuclear-spin lattice relaxation. This transition seems to be correlated with the composition Li:Al of the alloy and the amount of Li vacancies.     

Monitoring structural transformations in crystals. Part 4. Monitoring structural changes in crystals of pyridine analogs of chalcone during [2+2]-photodimerization and possibilities of the reaction in hydroxy derivatives

We studied the [2+2]-photodimerization in crystals of pyridine analogs and hydroxy derivatives of chalcone using the X-ray structure analysis. The mutual orientation of adjacent molecules in the crystals was analyzed in a quantitative way and the results were compared with data for known photoactive crystals undergoing the [2+2]-photodimerization. In the case of one pyridine analog, we processed the single-crystal-to-single-crystal photodimerization and determined the structure for the mixed crystal containing both the substrate and the product. We also explained a role of hydrogen bonds in the [2+2]-photodimerization in the case of the hydroxy derivatives of chalcone. C₅H₄N-CO-CHCH-C₆H₅: , , , β=91.318(10)°, monoclinic, . The irradiated crystal of the above analog: , , , β=91.870(10)°, monoclinic, . C₆H₅-CO-CHCH-C₅H₄N: , , , β=110.01(3)°, monoclinic, C2/c,Z=8. C₆H₅-CO-CHCH-C₆H₄(o-OH): , , , β=109.73(5)°, monoclinic, . C₆H₅-CO-CHCH-C₆H₄(p-OH): , , , orthorhombic, .