Modulated structures with a harmonic occupational modulation are not suitable for force field methods (including molecular dynamics) or density functional theory (DFT) calculations because fully occupied sites are required. Instead of assuming a random distribution with some constraints, which is a common approach, the harmonic occupational modulation function from a refinement in superspace can be replaced by a block wave function resulting in a model, that represents the hypothetical completely ordered structure with fully occupied sites. If the modulation wave vector corresponds to a commensurate modulation, the corresponding model in physical space can be used for DFT calculations, otherwise a commensurate approximation is needed. As an example, the present approach is applied to the modulated structure of mullite to determine the ideal Al/Si ordering for different compositions and supercell sizes. For the analyzed composition, the calculations yield consistently the same Al/Si ordering pattern. The results are also in qualitative agreement with the refinement of the not fully ordered structure, i.e. the volumes of tetrahedra with Al/Si disorder follow the trend of the Al/Si ordering pattern from the DFT calculations. The example shows that the approach allows to determine structural parameters, that are very difficult or even impossible to access experimentally.

A new Z = 8, Z' = 2 polymoroph of 4-oxo-4-phenylbutanoic (β-benzoylpropionic) acid, C₁₀H₁₀O₃, was obtained. The previously published two polymorphs with CCDC codes VERMAG and VERMAG01 crystallize with Z = 4, Z' = 1 in monoclinic space groups P2₁/c [a = 15.071(10), b = 5.435(9), c = 16.058(10), β = 129.57(10)] and P2₁/n [a = 12.728(6), b = 5.200(3), c = 14.426(6), β = 111.33(3)], respectively. Reported herein polymorph crystallizes in the monoclinic space group P2₁/c and has significant larger cell volume of 1754.51 ų [a = 15.2673(6), b = 5.2028(2), c = 22.3063(8), β = 98.0217(7)]. Structurally, new polymoroph differs from two known other slightly (RMSD of about 0.112-0.183 Å). All polymorphs contain dimers of molecules bounded by intermolecular hydrogen bonds leaving carbonyl groups at position 4 unaffected. 

Compounds containing benzimidazole moiety in solid state often demonstrate the ability to the formation of π-π stacking interactions. In this work, we focused on the investigation of intermolecular hydrogen bonds and parallel displaced (PD) π-π stacking interactions found in the crystals of titled molecules, both crystallize with Z = 2 in the space group P-1. Differences of the π-π stacking interactions parameters depending on the volume of side aromatic substituent in a homologous series, as well as a theoretical estimation of the energy of these interactions using DFT at two different functionals (M06-2X, MPWB95) and three basis sets [6-31G(d), 6-31++G, and 6-31++G(d)] were shown.

The construction of heterocyclic systems including pyrrolone (lactam) and fused imida-/oxa-/thiazolidine fragments is quite relevant due to the broad spectrum of biological activity exhibited by these molecules. In this work, crystal structure and the structural features of 8a-phenylhexahydropyrrolo[1,2-a]pyrimidine-6(2H)-one, C13H16N2O, are reported. Titled compound crystallizes with Z = 4 in the space group P21/n with cell volume of 1109.6(4) Å3 [a = 6.0910(13) Å, b = 17.016(4) Å, c = 10.707(2) Å, β = 90.581(5)°]. Molecules in the solid state are weakly linked by the intermolecular hydrogen bonds C=O···H–N into the chains.

The majority of tunable liquid crystal devices are driven by electric fields. The performance of such devices can be altered by the presence of small amounts of ions in liquid crystals. Therefore, the understanding of possible sources of ions in liquid crystal materials is very critical to a broad range of existing and future applications employing liquid crystals. Recently, nanomaterials in liquid crystals have emerged as a hot research topic promising for its implementation in the design of wearable and tunable liquid crystal devices. An analysis of published results revealed that nanodopants in liquid crystals can act as either ion-capturing agents or ion-generating objects. In this presentation, a recently developed model of contaminated nanomaterials in liquid crystals is analyzed. Nanoparticle-enabled ion capturing and ion generation regimes in liquid crystals are discussed within the framework of the proposed model. This model is in a very good agreement with existing experimental results. Practical implications and future research directions are also discussed.  

This work is devoted to metallomesogenic lanthanide complexes, which have paramagnetic features and effective luminescence, and which can be used as a basis for developing of magneto- and electro - optical devices.  The magnitude and sign of the dielectric anisotropy both play a leading role in this case. However, any direct measurements of the dielectric anisotropy for the most part of metallomesogenic complexes are highly problematic since they only have a smectic phase, and therefore there is no way to produce macroscopic homogeneous samples. This problem can be solved as shown in our investigation due to similarity between the mechanism of the dielectric polarization in liquid crystal phase and that of electrical birefringence in the isotropic phase. We can estimate the dielectric anisotropy in the liquid  crystal phase by studying the electrical birefringence process in the complexes melt at the temperature above the critical point for the phase transition from the isotropic phase to smectic one. We have studied complexes consisting of ions of rare-earth metals such as  Dy, Er, Gd, Tb, and of alkylsulfate counterions and Schiff bases as being ligands.  The number of methylene groups in aliphatic chains of counterions was varied between 0 and 12. It was found that in the series of the substances under investigation the magnitude as well as the sign of electro- optical effect in the isotropic phase depended on length of the counterions, but not depended on the metal ions used. Thus, dielectric anisotropy of smectic lanthanide complexes can be widely changed by variations of chemical structure of the counterions, namely: the dielectric anisotropy can be positive, negative, or close to zero.

A₈Tl₁₁ (A= alkali metal) compounds have been known since the investigations of Corbett et al. in 1995^[1] and still are matter of current discussions as the compound includes one extra electron referred to the charge of the Tl₁₁⁷⁻ cluster. Attempts to substitute the charge by incorporation of a halide succeeded for the lightest homologue of the group, Cs₈Ga₁₁Cl, and powder diffraction experiments for the heavier homologues also suggested the formation of analogous compounds. ^[2] However, X-Ray single crystal studies on A₈Tl₁₁X to prove this substitution and to provide a deeper insight into the influence on the thallide substructure have not yet been performed, probably due to severe absorption combined with air and moisture sensitivity for this class of compounds. In our contribution we present single crystal X-Ray analyses of the new compounds Cs₈Tl₁₁Cl_0.8, Cs₈Tl₁₁Br_0.9 and Cs₅Rb₃Tl₁₁Cl_0.5. It is shown that a (partial) incorporation of halide can also be indirectly determined by examination of the Tl-Tl distances for low resolved data sets, e.g. for Cs_5.7K_2.3Tl₁₁Cl_?. Mixed occupied sites by two different alkali metals indicate a dependence on the cesium content, the systems K/Rb – Tl – Br and K/Rb – Tl – Cl only gave rise to the formation of the higher reduced (K/Rb)₈Tl₁₁ and the less reduced by-product (K/Rb)₁₅Tl₂₇. We have not been able to prove the formation of halide including thallides in the absence of cesium.

[1] Z. C. Dong, J. D. Corbett, J. Cluster Sci. 1995, 6, 187-201.

[2] R. W. Henning, J. D. Corbett, Inorg. Chem. 1997, 36, 6045-6049.

At the request of the authors, the proceedings paper [1] will be retracted. The reason is the ethical conflict of publishing similar paper in this forum and in Crystals. We apologize to our readership for any inconvenience caused.

Reference

1 Cándida Pastor Ramírez; Sylvain Bernès; Rafael Zamorano Ulloa; Daniel Ramírez-Rosales; Samuel Hernández-Anzaldo; Yasmi Reyes-Ortega, Tetramer compound of manganese ions with mixed valence [Mn2IIMn2IV] and its spatial, electronic and magnetic studies. Proceedings of The 1st International Electronic Conference on Crystals, 1 (doi: 10.3390/IECC_2018-05245).

Retraction of the Proceedings Paper: https://sciforum.net/paper/view/conference/5245