Band 234, Heft 1

A family of Ln 2 CrO 6 ( Ln =Pr, Nd, Sm–Tb) compounds has been re-investigated using powder X-ray diffraction and IR spectroscopy. The structure of β-Nd 2 CrO 6 ≡β-[Nd 2 O 2 ](CrO 4 ) is similar to that of the slag compound [Ba 2 F 2 ](S 6+ O 3 S 2− ) in that it exhibits a disordered arrangement of (CrO 4 ) 2− anions between [Nd 2 O 2 ] 2+ litharge-type blocks. Its structural architecture is also related to other layered α- and γ-[ Ln 2 O 2 ]( A O 4 ) species ( A =S, Cr, Mo), showing various orientations of the tetrahedral anions within the interlayer space. Size relationships between the incorporated tetrahedral anions and formation of different structure types (denoted as M 1-, M 2- and T -type) are reviewed. The possible existence of new compounds which are isostructural with, or structurally related to, β-[Nd 2 O 2 ](CrO 4 ) and bearing other transition metal-centred tetrahedral anions are discussed.

Two annulated triazapentadiene systems, viz. 1,3,5,7,9-pentaazanona-1,3,6,8-tetraenate chloride complexes of Pt II , form CCl 4 solvates, containing the Cl 3 C–Cl···Cl–Pt halogen bonds. These halogen bonds are firstly reported type of Cl 3 C–Cl···Cl–M contacts. In the X-ray structures of two solvates different non-covalent interactions were detected and studied by DFT calculations and topological analysis of the electron density distribution within the framework of QTAIM method at the M06/DZP-DKH level of theory. Estimated energies of these supramolecular contacts vary from 0.6 to 2.4 kcal/mol.

The synthesis, structural characterization, and chemical bonding peculiarities of new intermetallic compounds from Y–Mg–Ni ternary system are reported herein. The crystal structures of these compounds were determined by single-crystal and X-ray powder diffraction analysis. Three ternary compounds were studied: Y 2 Mg 11 Ni 2 [own structure type, monoclinic, Pearson Symbol mS 30, Space Group C 2/ m , a =18.969(4), b =3.6582(7), c =11.845(2) Å, β =125.07(3)°], Y 4 Mg 3 Ni 2 [Ru 4 Al 3 B 2 structure type, tetragonal, P 4/ mmm , tP 18, a =10.8668(2), c =3.59781(12) Å] and YMgNi [MoAlB structure type, orthorhombic, Cmcm , a =3.6713(4), b =17.708(3), c =3.9583(5) Å]. New compositions of Y 1− x Mg x Ni 4 and Y 5− x Mg 24+ x solid solutions were detected: YMg 0.86(1) Ni 4.14(1) [SnMgCu 4 structure type, cubic, F 4̅3 m , cF 24, a =7.0747(6) Å] and Y 4.28(1) Mg 24.72(1) [Ti 5 Re 24 structure type, cubic, I 4̅3 m , cI 58, a =11.2655(11) Å]. The crystal structure peculiarities of these compounds are discussed. A particular attention has been given to Y 2 Mg 11 Ni 2 and its relations with other Mg-containing compounds. Crystallographic analysis together with linear muffin-tin orbital band structure calculations reveals the presence of [Y 2 Ni 4 @Mg 20 ] and [Y 4 Ni 2 @Mg 18 ] clusters in Y 2 Mg 11 Ni 2 phase. For Y 4 Mg 3 Ni 2 the formation of the Ni–Mg nets was observed, while the Y atoms form a monolayer.

A new dysprosium metal–organic framework {[Dy 2 (L) 3 (H 2 O) 4 ]·(acetone) 2 ·(H 2 O) 3 } n (Dy 2 -Acetone) with single-molecule magnet and ferroelectric properties was synthesized through a solvent-induced single-crystal-to-single-crystal (SCSC) transformation. Notably, exchange of the coordinated and guest solvent molecules lead to different magnetic relaxation and ferroelectric properties in the dysprosium MOF system, Dy 2 -DMF and Dy 2 -Acetone. Study reveals that the tunable magnetic relaxation behaviors are most likely a result of different local coordination sphere and lattice solvent molecules within the pores which influenced and tuned the relaxation rates of the magnetization. Moreover, disparate polar solvent molecules confined in the MOFs may be the key factors for their different ferroelectric properties.

Crystallography reveals two polymorphs for the salt [4-(4-acetylphenyl)piperazin-1-ium][2-amino-4-nitrobenzoate], a monoclinic form ( 2 ; modelled as P 2 1 / n with Z′=4) formed directly from the reaction mixture, and a triclinic form ( 1 ; Z′=1) isolated from recrystallisation. Relatively minor differences are noted in the conformations of the anions and of the cations, mainly relating to the twist of, respectively, the carboxylate groups and piperazin-1-ium rings with respect to the phenyl rings they are connected to. The key feature of the packing of both forms is the formation of charge-assisted ammonium-N–H···O (carboxylate) hydrogen bonds which lead to cyclic 12-membered {···HNH ···OCO} 2 synthons in the case of 1 but, supramolecular chains in 2 . The three-dimensional architecture in the crystal of 1 is further stabilised by amine-N–H···O (nitro) and amine-N–H···O (acetyl) hydrogen bonds, leading to double-layers in the bc-plane, which are linked along the a -axis by methylene-C–H···O (carboxylate) and π-stacking interactions. The combination of ammonium-N–H···O (carboxylate) and amine-N–H···O (carboxylate, acetyl) hydrogen bonds consolidate the three-dimensional packing in the crystal of 2 . The greater crystal density, packing efficiency and calculated lattice energy for 1 compared with 2 , suggest the former to be the thermodynamically most stable crystal. An analysis of the Hirshfeld surfaces for 1 and 2 reveal distinctive features that differentiate between the constituents of the two forms and between the ions comprising the asymmetric unit of 2 .

The crystal structures of four azines, namely 1-3-bis(4-methoxyphenyl)-2,3-diaza-1,4-butadiene, 1 , 1,3-bis(2,3-dimethoxyphenyl)-2,3-diaza-1,4-butadiene, 2 , 1,3-bis(2-hydroxy-3-methoxyphenyl)-2,3-diaza-1,4-butadiene, 3 , and 1,3-bis(2-hydroxy-4-methoxyphenyl)-2,3-diaza-1,4-butadiene, 4 , are reported. Molecules of 3 and 4 , and both independent molecules of 2 , Mol A and Mol B, possess inversion centers. The central C=N–N=C units in each molecule is planar with an ( E , E ) conformation. The intermolecular interactions found in the four compounds are C–H···O, C–H–N, C–H---π and π---π interactions. However, there is no consistent set of intermolecular interactions for the four compounds. Compound, 1 , has a two-dimensional undulating sheet structure, generated from C–H···O and C–H···N intermolecular hydrogen bonds. The only recognized intermolecular interaction in 2 is a C–H···O hydrogen bond, which results in a zig-zag chain of alternating molecules, Mol A and Mol B. While 3 forms a puckered sheet of molecules, solely via C–H···π interactions, its isomeric compound, 4, has a more elaborate three-dimensional structure generated from a combination of C–H···O hydrogen bonds, C–H···π and π···π interactions. The findings in this study, based on both PLATON and Hirshfeld approaches, for the four representative compounds match well the reported structural findings in the literature of related compounds, which are based solely on geometric parameters.

Since the contribution of proteins atoms with exceptionally large B-factors, much larger than those of other atoms, to the observed structure factors is negligible, it is therefore recommended to consider with a care the parts of the models where B-factors are inflated to extremely large values. Otherwise, molecular biologists risk to over-interpret structural data, since the positions of these atoms is highly uncertain. In the present communication, maximal B-factor values, over which the atoms can be considered ‘invisible’, are estimated based on the relationships between B-factors and solvent accessible surface areas.