Two different dicationic N-donors, based on the DABCO diamine, have been studied as templates for polyiodides. The results present a new strategy for polyiodide stabilization, which involves both N⋯I halogen bonding and cation–anion interactions. This is highlighted by the self-assembly of an unprecedented discrete pseudo-linear dodecaiodide species.

Tripodal cationic N-donor ligands exhibit sterically controlled self-assembly of tetrahedral M6L4 coordination cages that promote selective anion encapsulation (PF6− > OTf−) in the solid state. The described method is a potential template for stepwise assembly of hetero-ligand coordination cages and polymers.

Understanding the self-assembly of small structural units into large supramolecular assemblies remains one of the great challenges in structural chemistry. We have discovered that tetrahedral supramolecular cages, exhibiting the shapes of Archimedean solids, can be self-assembled by hydrogen bonding interactions using tricationic N-donors (1 or 2) in cooperation with water (W). Single crystal X-ray analysis shows that cage (2)4(W)6, assembled in an aqueous solution of cation 2 and KPF6, consists of four tripodal trications linked by six water monomers and resembles the shape of a truncated tetrahedron. Similarly, cage (1)4(W6)4 spontaneously self-assembles in an aqueous solution of cation 1 and NH4PF6 and consists of four tripodal cations and four water hexamers. Here, each of the four (H2O)6 units act as tritopic nodes between three distinct tripodal cations forming a polyhedron similar to the cantellated tetrahedron. These two well-defined cages are assembled via total of 12 and 36 hydrogen bonds, respectively. Both cages possess interior solvent-accessible volumes exceeding 1000 Å3. Furthermore, each one of the (H2O)6 clusters in face-centered cubic structure 1b acts as a node between two distinct (1)4(W6)4 units, and thus a solvent-filled tubular three-dimensional network (tube diameter of ∼6.5 Å) is generated that mimics the structure of diamond at the nanometer scale. To our knowledge, this is the first example of such species being formed entirely via hydrogen bonding interactions.

Exact knowledge of the crystal structure of drugs and lead compounds plays a significant role in the fields of crystal engineering, docking, computational modeling (drug–receptor interactions), and rational design of potent drugs in pharmaceutical chemistry. The succinic acid cocrystal of the systemic antifungal drug, itraconazole, reported by Remenar et al. (J. Am. Chem. Soc.2003, 125, 8456–8457) (CSD: IKEQEU), represents one of the classical examples displaying a molecular fitting mechanism in the solid state. In this work, we disclose the X-ray single-crystal structure of the cis-itraconazole–succinic acid (2:1) cocrystal and found that it differs slightly from the previously reported structure by the location of the elements (C, H, and N) in the 1,2,4-triazol-5-one ring. By making use of the new solid-state structure, we have also applied an enhanced disorder model, which, in turn, uncovered the intriguing halogen bond (XB) interactions (0.86 × van der Waals distance of C–Cl···N), which were previously unnoticed. Furthermore, the crystal structure of cis-itraconazole reported by Peeters et al. (Acta Crystallogr.1996, C52, 2225–2229) (CSD: TEHZIP) is also revisited. For the structure of neat cis-itraconazole, new low-temperature as well as a revised ambient temperature (0 °C) X-ray single crystal structures with new disorder models are described. More importantly, a weak halogen bonding interaction (0.9 × van der Waals distance of C–Cl···O) has now been perceived in this structure. The XB contacts remained without consideration in the original report primarily due to the lack of its recognition, at that time. In addition to these new findings, solid-state NMR and the thermoanalytical properties were examined by thermogravimetric analysis and differential scanning calorimetry.

Eleven asymmetrically quaternized dicationic ammonium-based room-temperature ionic liquids (DRTILs) with bis(trifluoromethanesulfonyl)imide (TFSI) were synthesized and characterized, along with 11 analogous dibromide precursors. Two-step synthesis was used to diquaternize tetramethyl-1,3-propanediamine and 2-(dimethylamino)-ethyl ether amines with a variety of alkyl and ether functionalized side chain groups (R1 ≠ R2). Each salt contain 1 to 3 ether groups located either in a linkage or in a side chain moieties. Structural and thermoanalytical properties, water content, and viscosity have been characterized using, for example, NMR, mass spectrometry (MS), X-ray diffraction, and thermal analysis (TG/DTA, DSC). DRTILs have extensive fluid ranges [(∼330 to 370) °C], which are the consequence of low glass transition [(−60 to −40) °C] and high thermal degradation temperatures of the salts [(279 to 325) °C; heating rate 1.25 °C·min–1]. Thermal stabilities of DRTILs were examined as a function of a heating rate [(1.25, 2.5, 5, 10, and 20) °C·min–1], and degradation onset temperature overshoots of about (45 to 55) °C were observed between the slowest and the fastest heating rates. Thereby it is suggested that ILs should preferably be analyzed by TG using heating rates of ≤ 5 °C·min–1 in order to reduce the possibility of an erroneous interpretation of the thermal stability. The ether group count and its location affected the viscosities significantly, which varied between (1150 and 6670) mPa·s at RT and lowered significantly when heated at 60 °C, being typically ≤ 200 mPa·s. The ether-functionalized DILs are potentially applicable in various IL applications, such as lubricants, heat transfer fluids, high temperature synthesis solvents, or as stationary phase in applications such as gas chromatography, MS, and capillary electrophoresis.

The halogen bonding (XB) between elemental iodine (I2) and neutral 1,4-diazabicyclo[2.2.2]octane (DABCO) and its monoalkylated PF6– salts was studied by X-ray crystallographic, thermoanalytical, and computational methods. DABCO was found to form both 1:1 and 1:2 complexes with I2 showing an exceptionally strong halogen bond (ΔEcp = −73.0 kJ/mol) with extremely short N···I distance (2.37 Å) in the 1:1 complex (1a). In the more favored 1:2 complex (1b), the XB interaction was found to be slightly weaker [ΔEcp = −64.4 kJ/mol and d(N···I) = 2.42 Å] as compared to 1a. The monoalkylated DABCO salts (2PF6–7PF6) form corresponding 1:1 XB complexes with I2 {[2···I2]PF6–([7···I2]PF6} similarly to the parent free base DABCO, but both X-ray diffraction and calculated (M05-2X/def2-TZVPP) geometrical parameters indicate that the XB interactions are somewhat weaker than with DABCO itself but can nonetheless be considered as moderately strong halogen bonds. The solid -state packing of the monoalkyl DABCO complexes is greatly affected by the length of the lipophilic hydrocarbon chain as the long-tail cations show increasing amphiphilic character. However, partly as a consequence of the amphiphilic nature of parent monoalkyl DABCO PF6– salts, their I2 complexes exhibit a reversible binding of I2 into their originally nonporous crystal lattices. This was verified by thermal analysis and X-ray powder diffraction studies of 2PF6–7PF6 and their corresponding I2 complexes. By varying the length of the alkyl chain, the release temperature of I2 can be tuned from 75 °C ([4···I2]PF6) to 100 °C ([7···I2]PF6). Furthermore, these highly stable (preservable for months in normal laboratory conditions) I2 complexes can be prepared with three different routes: by mixing in solution, by mechanochemical grinding of the components, and via gas-to-solid reaction (i.e., I2 vapor to solid PF6– salts).

“The best catalyst is no catalyst.” With growing public concern over global warming and the amount of greenhouse gases, it is important to reduce the amount of chemicals and eliminate waste, to obtain better results in a simple, selective, safe, and environmentally benign fashion compared to conventional tedious chemical synthesis. Herein, we disclose an environmentally benign, rapid, catalyst/promoter/coupling reagent-free cyclization procedure of free amino acids to furnish exclusively cyclic dipeptides (2,5-diketopiperazines, DKPs) in excellent or even quantitative yield, along with their solid state self-assembling properties. This process is extremely simple and highly efficient with little or no traditional synthetic skills and without any chromatographic purification. Synthesis of structurally diverse DKPs has been achieved with a dramatic decrease in the reaction time, the amount/number of solvents used, a significant increase in the yield and nearly complete elimination of waste. As a result, this is an excellent example for the environmentally benign, clean and green chemistry concept. The most exciting outcome of our investigation is an unusual case of chiral self-recognition encountered upon the cyclization of rac-pipecolic acid, which resulted in the formation of the meso-product exclusively.

A detailed understanding of the mode of packing patterns that leads to the gelation of low molecular mass gelators derived from bile acid esters was carried out using solid state NMR along with complementary techniques such as powder X-ray diffraction (PXRD), differential scanning calorimetry (DSC), thermogravimetric analysis (TGA) and polarizing optical microscopy (POM). Solid state 13C{1H} cross polarization (CP) magic angle spinning (MAS) NMR of the low molecular mass gel in its native state was recorded for the first time. A close resemblance in the packing patterns of the gel, xerogel and bulk solid states was revealed upon comparing their 13C{1H}CPMAS NMR spectral pattern. A doublet resonance pattern of 13C signals in 13C{1H}CPMAS NMR spectra were observed for the gelator molecules, whereas the non-gelators showed simple singlet resonance or resulted in the formation of inclusion complexes/solvates. PXRD patterns revealed a close isomorphous nature of the gelators indicating the similarity in the mode of the packing pattern in their solid state. Direct imaging of the evolution of nanofibers (sol–gel transition) was carried out using POM, which proved the presence of self-assembled fibrillar networks (SAFINs) in the gel. Finally powder X-ray structure determination revealed the presence of two non-equivalent molecules in an asymmetric unit which is responsible for the doublet resonance pattern in the solid state NMR spectra.

Eight new monocationic quaternary ammonium (QA) salts with the bis(trifluoromethanesulfonyl)imide (TFSI) anion were prepared by metathesis using our previously reported QA halides as precursors. New salts were characterized both in liquid and solid state using 1H and 13C NMR techniques, mass spectroscopy and elemental analysis together with X-ray diffraction and thermoanalytical methods. In addition, residual water content, viscosity and conductivity measurements were made for three of the room-temperature ionic liquids (RTILs). The crystal structures of three compounds were determined by X-ray single crystal diffraction. Powder diffraction was used to study the crystallinity of the solid salts and to compare structural similarities between the single crystals and the microcrystalline bulk powders. Three of the salts are liquid below room temperature, having broad liquid ranges (∼300 °C), and in total five out of eight salts melt below 100 °C. Moreover, powder diffraction data of the two RTILs were able to be measured at sub-ambient temperatures using in situ low-temperature powder X-ray diffraction revealing high crystallinity on both RTILs below their freezing point. The RTILs presented relatively high conductivities (∼0.1–0.2 S m−1) and moderate to relatively low viscosities. The determined physicochemical properties of the reported ILs suggest their applicability on various applications such as heat transfer fluids, high temperature synthesis and lubricants.

Tripodal cationic N-donor ligands exhibit sterically controlled self-assembly of tetrahedral M6L4 coordination cages that promote selective anion encapsulation (PF6− > OTf−) in the solid state. The described method is a potential template for stepwise assembly of hetero-ligand coordination cages and polymers.