Volume 231, Issue 5

Two missing compounds within the binary K-Se system have been synthesized and structurally characterized by means of single-crystal diffraction. β -K 2 Se 2 comprises cell parameters that are in line with predictions made from the series α / β -A 2 Ch x . K 2 Se 4 , in contrast, incorporates “Se 5 2– ” chains with 50% occupation of the terminal selenium atoms, and has been synthesized on a rather unconventional solvothermal pathway employing successively mercury and ethylene dithiol as solvents.

The metastable nanocrystalline γ-Ga 2 O 3 with the particles’ dimensions about 2 nm was prepared by coprecipitation method and its structure was studied using X-ray powder diffraction. The corresponding diffraction pattern is characterized by a strong broadening of diffraction peaks. The Debye function analysis method (DFA) was applied to calculate the full profile of the XRD pattern for the first time. Earlier reported structural models of the γ-Ga 2 O 3 were examined with respect to experimental diffraction data. The influence of crystallite sizes on the diffraction pattern was considered. The obtained structure of the disordered γ-Ga 2 O 3 has vacancies in 8a and 16d spinel positions and additional atoms in 8b, 16c and 48f non-spinel positions. The proposed structure differs from those reported by the ratio between occupancies of the tetrahedral and octahedral gallium positions.

The new compound Ag 2 Mn 3 (VO 4 ) 3 was synthesized by hydrothermal and solid state reaction routes, and its crystal structure was determined from single-crystal X-ray diffraction data. Ag 2 Mn 3 (VO 4 ) 3 crystallizes with a monoclinic symmetry, space group C 2/ c , with a =11.8968(11) Å, b =13.2057(13) Å, c =6.8132(7) Å, β =111.3166(15) (°) and V =997.16(17) Å 3 ( Z =4). Its crystal refinement yielded the residual factors R ( F )=0.0249 and wR ( F 2 )=0.0704 for 95 parameters and 1029 independent reflections at a 3 σ ( I ) level. Ag 2 Mn 3 (VO 4 ) 3 can be considered as a new member of the AA ′ MM ′ 2 ( X O 4 ) 3 alluaudite family. The specific arrangement of M and M ′ octahedral sites and of X tetrahedral sites gives rise to two different channels aligned along the crystallographic c -axis and containing the A and A ′ sites. The A , A ′, M , and X sites are fully occupied by Ag + , Mn 2+ , and V 5+ , respectively; whereas a Mn 2+ /Mn 3+ mixture is observed in the M ′ site.

Structures are reported of ( E )-((2-((pyridin-2-yl)hydrazonyl)methyl)arene compounds, 2-aryl-CH=N–CH)-pyridine, 8 , namely (aryl=2,4-(HO) 2 C 6 H 3 , 8a ; 2,5-(HO) 2 C 6 H 3 , 8b , 2–HOC 6 H 4 , 8c , as the hemihydrate, [ (8c) 2· (H 2 O ) ], 2–HO–5–O 2 NC 6 H 3 , 8d ; and 2,6-(MeO) 2 C 6 H 3 , 8e . Intramolecular O1–H1··· N2 (hydrazonyl) hydrogen bonds are consistantly found in each of the hydroxy compounds, 8a–8d . However, a diverse array of classical intermolecular hydrogen bonds, X–H···Y (X or Y = O or N) are found in 8a–8e . Classical intermolecular hydrogen bonds in 8a are chain forming N3–HN3···O1 and O2–H2···N1 (pyridinyl) intermolecular hydrogen bonds, while in the isomer, 8b, dimer forming N3–HN3···N1 (pyridinyl) and chain forming O2–H2···O1 (pyridinyl) hydrogen bonds are present. The hydrate molecule in [ (8c) 2 · (H 2 O) ] is involved in Ow–Hw···N1 intermolecular hydrogen bonding: also present in [ (8c) 2 ·(H 2 O) ] are chain forming N3–HN3···O2 bonds. The only intermolecular classical hydrogen bonds present in 8d and 8e , are the dimer forming N3–HN3···N1 (pyridinyl) bonds. Thus only compounds, 8b , 8d and 8e , exhibit dimer forming N3–HN3···N1 (pyridinyl) hydrogen bonds, previously reported fora range of (aryl-CH=N–CH)-pyridine derivatives. The occurence of N3–HN3···N1(pyridinyl) hydrogen bonds in many (aryl-CH=N–CH)-pyridine derivatives demonstrates the importance of such hydrogen bonds. However, as found in 8a and [ (8c) 2 · ( H 2 O ) ], suitable sited donor substituents or the presence of solvate molecules can result in other classical hydrogen bonds being preferred.

Two new isostructural octahedral complexes [CoX(H 2 O)( salophen )]·H 2 O·EtOH (X=Cl ( 1 ), Br ( 2 ); salophen = N,N ′-bis(salicylidene)-1,2-diaminobenzene) have been prepared by reaction of CoX 2 and H 2 salophen in a mixture of ethanol and dichloromethane (1:1) and characterized by IR spectroscopy and elemental analysis. Crystal structures of both 1 and 2 are molecular and built up of [CoX(H 2 O)( salophen )] complex molecules and solvate water and ethanol molecules. The salophen ligand occupies the equatorial plane of the hexacoordinated Co(III) atom while halogenido and aqua ligands are placed in the axial positions. The crystal packings are formed by O–H···O hydrogen bonds and additional π–π stacking interactions. The results of thermogravimetric studies of 1 and 2 revealed that the loss of solvating molecules takes place first.

The title structures of biuret-cyanuric acid (2/2) monohydrate, C 10 H 18 N 12 O 11 , 1 [ P 1̅, Z =2, a =8.2598(4) Å, b =10.8795(5) Å, c =11.9138(6) Å, α =67.036(1)°, β = 79.842(2)°, γ =69.859(2)°, V =924.38(8) Å 3 ], and of biuret-glutaric acid (1/1), C 7 H 13 N 3 O 6 , 2 [ P 1̅, Z =2, a =5.0044(3) Å, b =7.0832(3) Å, c =14.9803(10) Å, α =102.860(4)°, β = 91.899(3)°, γ =102.202(4)°, V =504.20(5) Å 3 ], show usual features both in constitution and intermolecular contacts except for a slightly longer C=O bond length in one of the carbonyl groups in 2 . The biuret molecules have conformations with anti-parallel arrangement of the carbonyl groups. In each structure O–H…O and N–H…O hydrogen bonds of the moderate strength are present. The new results are compared with other structures which contain biuret molecules. The influence of the hydrogen bonding on the bond length of the carbonyl group C=O in the fragment NH 2 -(C=O)-NH with amine and hydroxyl donors has also been investigated. It transpires that the C=O…H angle of about 120° favors a slight elongation of the C=O bond length. The elongation of the C=O bond is more susceptible to the relative orientation of the C=O group with regard to amine over hydroxyl groups. This is the likely explanation why one of the C=O bonds in 2 is slightly longer than usual because this carbonyl group is simultaneously involved in two hydrogen bonds where C=O…H–O and C=O…H–N satisfy the 120° condition. Vibrational spectra of the title structures were also recorded and assigned.

Discontinuous modulation functions called crenel and saw-tooth have been developed for description and refinement of strongly modulated crystal structures with abrupt changes of modulation parameters. Although used for refinement of many modulated structures and mentioned in books on aperiodic crystals, technical details of such refinements have never been published and remained hidden in the source code of the refinement program Jana2006. In this article we explain how to recognize discontinuous modulations in a Fourier map and how to refine structures where crenel or saw-tooth functions are combined with additional secondary modulation. Three sets of functions suitable for such combination are presented: the traditional ortho-harmonics, and newly developed sets of Legendre polynomials and x-harmonics. Tiny differences between refinements based on particular function sets are demonstrated using simulated as well as existing modulated structures.