Control of channel shapes in a microporous manganese(II)-borophosphate framework by variation of size and shape of organic template cations

The templated microporous compounds [H2(Templ.)][MnII{B2P3O12(OH)}], [templates: 1,3-diaminopropane, C3H10N2 (DAP); piperazine, C4H10N2 (PIP); 1,4-diazacyclo[2.2.2]octane, C6H12N2 (DABCO)] were prepared under mild hydrothermal conditions. The crystal structures (H2DAP-Mn: Pmc2(1) (no. 26), a=1259.43(5), b=949.86(5), c=1135.92(5) pm, Z=4; H2PIP-Mn: Ima2 (no. 46), a=1257.9(1), b=948.69(8), c=1158.19(8) pm, Z=4; H2DABCO-H2PIP-Mn: Ima2 (no. 46), a=1262.90(7), b=961.05(5), c=1151.42(7) pm, Z=4) are characterized by identical framework connectivities [MnII{B2P3O12(OH)}]2-, but vary in shapes (diameters) of the structural channels depending on the shapes of the templating molecule ions. The situation clearly reflects the directing effect of true templates during endotemplating reactions. The experimental results (preparation, chemical analyses, and X-ray refinements) are supported by detailed ab initio calculations (structure optimizations).     

Towards nanotubular structures with large voids: dynamic heteroleptic oligophenanthroline metallonanoscaffolds and their solution-state properties

The assembly of a rigid macrocycle with two exotopic phenanthroline binding sites in combination with linear bis- or trisphenanthrolines and copper(I) ions is used to generate nanoscale double and triple deckers, the latter showing a tubular structure. With supramolecular chemistry expanding to dynamic, large cavity, nanoscale structures, it becomes increasingly important to use robust assembly protocols as well as reliable characterization techniques. To fully elucidate and to describe the dynamic nature of metallonanoscaffolds with large voids, we applied a battery of both direct and indirect solution-state characterization methods. These methods along with the conventional direct methods provide a very useful tool for characterizing tubular nanoscaffold aggregates.     

Theoretical investigations on heteronuclear chalcogen-chalcogen interactions: on the nature of weak bonds between chalcogen centers

To understand the intermolecular interactions between chalcogen centers (O, S, Se, Te), quantum chemical calculations on model systems were carried out. These model systems were pairs of monomers of the composition (CH3)2X1 (X1 = O, S, Se, Te) as the donors and CH3X2Z (with X2 = O, S, Se, Te and Z = Me, CN) as the acceptors. The variation of X1, X2, and Z leads to 32 pairs with 8 homonuclear cases (X1 = X2 = O, S, Se, Te) and 24 heteronuclear cases (X1 not equal X2). The MP2/SDB-cc-pVTZ, 6-311G* level of theory was used to derive the geometrical parameters and the interaction energies of the model systems. The pairs with Z = CN (17-32) show a considerably higher interaction energy than the pairs with CH3 groups only (1-16). Natural bond orbital (NBO) analysis revealed that the interaction of the dimers 1, 2, 5, 6, 9, 10, 13, 14, 17, 21, 25, and 29 is mainly due to weak hydrogen bonding between methyl groups and chalcogen centers. These systems all contain hard chalcogen atoms as acceptors. For all other systems, the chalcogen-chalcogen interaction dominates. The one-electron picture of an interaction between the lone pair of the donor chalcogen atom and the chalcogen-carbon antibonding sigma* orbital serves as a model to qualitatively rationalize trends found in many of these systems. However, it has to be applied with some amount of skepticism. A detailed analysis based on symmetry-adapted perturbation theory (SAPT) reveals that induction and dispersion forces dominate and contribute to the bonding in each case. Hydrogen-bonded compounds involve bonding electrostatic contributions. Compounds dominated by chalcogen-chalcogen interactions exhibit bonding due to electrostatic interactions only if one of the chalcogen atoms involved is sulfur or oxygen.     

Crystal Structures of AlCr2 and MoSi2: Same Structure Type vs. Different Bonding Pattern

In a joint effort utilizing modified sample preparation, microscopy, X-ray diffraction and micro-fabrication, it became possible to prepare single crystals of the “hidden” phase AlCr₂. High-resolution X-ray diffraction analysis is described in detail for two crystals with the similar overall composition, but different degree of disorder, which seems to be the main cause for the differing unit cell parameters. Chemical bonding analysis of AlCr₂ in comparison to prototypical MoSi₂ shows pronounced differences reflecting the interchange of main group element vs. transition metal as majority component.     

Synthesis and Physical Properties of Tunable Aryl Alkyl Ionic Liquids (TAAILs)

Tunable aryl alkyl ionic liquids (TAAILs) based on the imidazolium cation were first reported in 2009. Since then, a series of TAAILs with different properties due to the electron-donating or -withdrawing effect of the substituents at the aryl ring has been developed. Herein, a wide variety of those ionic liquids (ILs) is presented in terms of their cation structure. The authors synthesized ILs containing the bromide or bis(trifluoromethane)sulfonimide anion and 1-aryl-3-alkyl imidazolium cations with various substituents in the ortho and/ or para position of the phenyl ring and alkyl chains of different lengths varying from butyl to dodecyl. The differences of their physical properties (melting point, thermal decomposition, viscosity, electro-chemical window) of these ILs are reported according to their structure.