N‐Butylpyridinium undecachlorocarbadodecaborate and comparison with similar compounds

The title compound, C₉H₁₄N⁺·CHB₁₁Cl₁₁⁻, was obtained in the course of our continuing studies of the low‐melting salts of closo‐ and nido‐carborane cage anions with alkylpyridinium and dialkylimidazolium cations. The title compound is the first example of a pyridinium salt of a perchlorinated carborane anion. The structure consists of one N‐butylpyridinium cation counterbalanced by one perchlorinated carborane cage anion per asymmetric unit. By changing the counter‐ion, different packings are observed, and to try to understand this the new structure is compared with five similar compounds.     

Rapid and scalable synthesis of chiral porphyrin cage compounds

An improved and scalable synthetic route to chiral porphyrin cage compounds, which will be used as catalytic machines for the encoding of information into polymers, has been developed. The porphyrin cage was made chiral by introducing one or two nitro groups on its xylylene sidewalls. This nitration was performed with fuming nitric acid at low temperature and occurred in a highly regioselective fashion. The latter was thought to be the result of the binding of a nitronium cation inside the cavity of the cage compound, directing the reaction to the sidewalls. However, ¹H NMR titrations of the porphyrin cage compound with either nitric acid or the nitronium salt [NO₂][BF₄] revealed that the effect of the host-guest binding of the nitronium ion on the selectivity of the reaction is negligible. Instead, protonation of the porphyrin plays an essential role as it prevents the ring from being oxidized, allowing the nitration to be directed to the sidewalls.     

High Thermal Resistance of Epoxy/Cyanate Ester Hybrids Incorporating an Inorganic Double-Decker-Shaped Polyhedral Silsesquioxane Nanomaterial

In this study, we prepared a difunctionalized cyanate ester double-decker silsesquioxane (DDSQ-OCN) cage with a char yield and thermal decomposition temperature (T_d) which were both much higher than those of a typical bisphenol A dicyanate ester (BADCy, without the DDSQ cage) after thermal polymerization. Here, the inorganic DDSQ nanomaterial improved the thermal behavior through a nano-reinforcement effect. Blending the inorganic DDSQ-OCN cage into the epoxy resin improved its thermal and mechanical stabilities after the ring-opening polymerization of the epoxy units during thermal polymerization. The enhancement in the physical properties arose from the copolymerization of the epoxy and OCN units to form the organic/inorganic covalently bonded network structure, as well as the hydrogen bonding of the OH groups of the epoxy with the SiOSi moieties of the DDSQ units. For example, the epoxy/DDSQ-OCN = 1/1 hybrid, prepared without Cu(II)-acac as a catalyst, exhibited a glass transition temperature, thermal decomposition temperature (T_d), and char yield (166 °C, 427 °C, and 51.0 wt%, respectively) that were significantly higher than those obtained when applying typical organic curing agents in the epoxy resin. The addition of Cu(II)-acac into the epoxy/BADCy and epoxy/DDSQ-OCN hybrids decreased the thermal stability (as characterized by the values of T_d and the char yields) because the crosslinking density and post-hardening also decreased during thermal polymerization; nevertheless, it accelerated the thermal polymerization to a lower curing peak temperature, which is potentially useful for real applications as epoxy molding compounds.     

Chemical Derivatization and Characterization of Novel Antitrypanosomals for African Trypanosomiasis

The search for novel antitrypanosomals and the investigation into their mode of action remain crucial due to the toxicity and resistance of commercially available antitrypanosomal drugs. In this study, two novel antitrypanosomals, tortodofuordioxamide (compound 2) and tortodofuorpyramide (compound 3), were chemically derived from the natural N-alkylamide tortozanthoxylamide (compound 1) through structural modification. The chemical structures of these compounds were confirmed through spectrometric and spectroscopic analysis, and their in vitro efficacy and possible mechanisms of action were, subsequently, investigated in Trypanosoma brucei (T. brucei), one of the causative species of African trypanosomiasis (AT). The novel compounds 2 and 3 displayed significant antitrypanosomal potencies in terms of half-maximal effective concentrations (EC₅₀) and selectivity indices (SI) (compound 1, EC₅₀ = 7.3 μM, SI = 29.5; compound 2, EC₅₀ = 3.2 μM, SI = 91.3; compound 3, EC₅₀ = 4.5 μM, SI = 69.9). Microscopic analysis indicated that at the EC₅₀ values, the compounds resulted in the coiling and clumping of parasite subpopulations without significantly affecting the normal ratio of nuclei to kinetoplasts. In contrast to the animal antitrypanosomal drug diminazene, compounds 1, 2 and 3 exhibited antioxidant absorbance properties comparable to the standard antioxidant Trolox (Trolox, 0.11 A; diminazene, 0.50 A; compound 1, 0.10 A; compound 2, 0.09 A; compound 3, 0.11 A). The analysis of growth kinetics suggested that the compounds exhibited a relatively gradual but consistent growth inhibition of T. brucei at different concentrations. The results suggest that further pharmacological optimization of compounds 2 and 3 may facilitate their development into novel AT chemotherapy.     

A fluoresceinophane: 19,4,16‐trioxa‐1(2,10)‐anthracena‐2(1,2)‐benzenacyclohexadecaphane‐17,3(19H)‐dione

A novel macrocycle containing fluorescein, the highly fluorescent title compound, C₃₁H₃₂O₅, has a xanthene core and a benzyl unit that are planar. The latter is rotated by 72.99 (3)° from the xanthene mean plane. The C₁₁ alkyl tether and the xanthene group adopt a cage‐like structure and the xanthene adopts a quinoid‐type configuration. The compound crystallizes as a racemic mixture with one molecule of each isomer per unit cell. Even though the planes described by the xanthene and the benzene rings of different molecules are separated by 3.341 (4) and 3.73 (1) Å, respectively, there is insufficient overlap between the aryl units to promote π‐stacking.     

Anion Control in the Self-Assembly of a Cage Coordination Complex

An anion is encapsulated in the center of the new cage compound [Ni₆(atu)₈X]X₃ (X=Cl—for the structure see picture—or Br; Hatu=amidinothiourea). A combination of Lewis acid–base and hydrogen-bonding interactions cause the square-planar [Ni(Hatu)₂]²⁺ units, after deprotonation, to assemble to form this compound. A remarkable feature is the anion dependence of the cage formation; nitrate, acetate, and perchlorate are unsuitable as templates.     

A covalent organic cage compound acting as a supramolecular shadow mask for the regioselective functionalization of C60

A trigonal-bipyramidal covalent organic cage compound serves as an efficient host to form stable 1 : 1-complexes with C₆₀ and C₇₀. Fullerene encapsulation has been comprehensively studied by NMR and UV/Vis spectroscopy, mass spectrometry as well as single-crystal X-ray diffraction. Exohedral functionalization of encapsulated C₆₀via threefold Prato reaction revealed high selectivity for the symmetry-matched all-trans-3 addition pattern.

The taming of the Prato reaction: a covalent organic cage compound serves as a supramolecular template for the regioselective functionalization of C₆₀.     

A thallium(I) tetranuclear cubic cage unit in an interpenetrated supramolecular polymer: A new precursor for the preparation of Tl2O3 nanostructures

A new thallium(I) supramolecular polymer, [Tl₄(μ₃-4-BN)₄]_n (1) [9-HBN = 4-hydroxy benzonitrile], with a disordered cubic cage structural unit has been synthesized and characterized. The single-crystal X-ray data of compound 1 shows one type of Tl^I ion in the tetranuclear cubic cage structure with a coordination number of three. In addition to two intra cage thallophilic interactions in 1, each thallium(I) atom has a weak Tl?N secondary interaction with the nitrile group of the 4-BN⁻ ligand. Finally the Tl-ions attain the O₃Tl?NTl₂ coordination sphere with a stereo-chemically ‘active’ electron lone pair on the metal. The self assembly between the benzonitrile groups of one cubic cage structure with an adjacent one with a Tl?N short contact, by π-π stacking and weak hydrogen bonding interactions, results in the formation of a new interpenetrating thallium(I) supramolecular polymer. The thermal stability of 1 was studied by thermo gravimetric (TG) and differential thermal analyses (DTA). Nanostructures of thallium(III) oxide were prepared from a calcination process of compound 1 fine powder at 743 K. These nanostructures were characterized by X-ray powder diffraction (XRD) and scanning electron microscopy (SEM).     

Synthesis,structure, and optical properties of CsU2(PO4)3

CsU₂(PO₄)₃ was synthesized in highest yield by the reaction in a fused-silica tube of U, P, and Se in a CsCl flux at 1273 K. It crystallizes with four formula units in space group P2₁/n of the monoclinic system in a new structure type. The structure of CsU₂(PO₄)₃ is composed of U and Cs atoms coordinated by PO₄^3? units in distorted octahedral arrangements. Each U atom corner shares with six PO₄^3? units. Each Cs atom face shares with one, edge shares with two, and corner shares with three PO₄^3? units. The structure shares some features with the sodium zirconium phosphate structure type. X-ray powder diffraction results demonstrate that the present CsU₂(PO₄)₃ compound crystallizes in a structure different from the previously reported β′- and γ-CsU₂(PO₄)₃ compounds. CsU₂(PO₄)₃ is highly pleochroic, as demonstrated by single-crystal optical absorption measurements.     

Photobehaviour of phenyl-containing methacrylate polymers

The emisssion spectra and photobehaviour were investigated for compounds of general formula COO(CH₂)_nC₆H₅ (n = 1?3) located either in small compounds. diluted in methacrylate copolymers, or incorporated as pendant units in methacrylate homopolymers. All the polymers considered show only monomeric emission. In spite of this, the singlet lifetimes of the polymers were shorter than those of small model compounds. This result shows that, even in the absence of excimer formation. the photobehaviour of a polymer can be different from that of the corresponding monomeric model compounds. The quenching rate constants when n = 2 were measured in solvents.of different thermodynamic character employing several quenchers. The results show that preferential absorption is not significant in determining the quenching rate constant but that the polymer is more sensitive to steric hindrance than the model compound.     

Trinuclear Cage‐Like ZnII Macrocyclic Complexes: Enantiomeric Recognition and Gas Adsorption Properties

Three zinc(II) ions in combination with two units of enantiopure [3+3] triphenolic Schiff‐base macrocycles 1 , 2 , 3 , or 4 form cage‐like chiral complexes. The formation of these complexes is accompanied by the enantioselective self‐recognition of chiral macrocyclic units. The X‐ray crystal structures of these trinuclear complexes show hollow metal–organic molecules. In some crystal forms, these barrel‐shaped complexes are arranged in a window‐to‐window fashion, which results in the formation of 1D channels and a combination of both intrinsic and extrinsic porosity. The microporous nature of the [Zn₃ 1 ₂] complex is reflected in its N₂, Ar, H₂, and CO₂ adsorption properties. The N₂ and Ar adsorption isotherms show pressure‐gating behavior, which is without precedent for any noncovalent porous material. A comparison of the structures of the [Zn₃ 1 ₂] and [Zn₃ 3 ₂] complexes with that of the free macrocycle H₃ 1 reveals a striking structural similarity. In H₃ 1 , two macrocyclic units are stitched together by hydrogen bonds to form a cage very similar to that formed by two macrocyclic units stitched together by Zn^II ions. This structural similarity is manifested also by the gas adsorption properties of the free H₃ 1 macrocycle. Recrystallization of [Zn₃ 1 ₂] in the presence of racemic 2‐butanol resulted in the enantioselective binding of (S)‐2‐butanol inside the cage through the coordination to one of the Zn^II ions.     

New Molecular Cage Clusters of Pb by Encapsulation of Mg

Endohedral clusters formed from the Zintl ions Pb₁₀^2? and Pb₁₂^2? are particularly stable and therefore suitable for the assembly of larger aggregates. We therefore investigate the formation of Mg‐doped lead clusters in the gas phase, and demonstrate that a whole series of new molecular cage clusters of lead can be generated by encapsulation of magnesium. Mass spectrometry reveals that some of the cluster compounds, with one and two Mg atoms attached to the lead clusters, display large intensities compared to the pure lead clusters, which indicates that the compound clusters are particularly stable. The magnesium‐doped lead‐cluster assemblies were further analyzed within a molecular‐beam electric deflection experiment. Almost vanishing permanent dipole moments for MgPb_10–16 support the idea that a single Mg atom could be encapsulated within a highly symmetric lead cage, which results in structures with not only enhanced stability but also increased symmetry compared to the pure lead clusters Pb_N.     

Luminescence Properties of C‐Diazaborolyl‐ortho‐Carboranes as Donor–Acceptor Systems

Seven derivatives of 1,2‐dicarbadodecaborane (ortho‐carborane, 1,2‐C₂B₁₀H₁₂) with a 1,3‐diethyl‐ or 1,3‐diphenyl‐1,3,2‐benzodiazaborolyl group on one cage carbon atom were synthesized and structurally characterized. Six of these compounds showed remarkable low‐energy fluorescence emissions with large Stokes shifts of 15100–20260 cm^?1 and quantum yields (Φ_F) of up to 65 % in the solid state. The low‐energy fluorescence emission, which was assigned to a charge‐transfer (CT) transition between the cage and the heterocyclic unit, depended on the orientation (torsion angle, ψ) of the diazaborolyl group with respect to the cage C? C bond. In cyclohexane, two compounds exhibited very weak dual fluorescence emissions with Stokes shifts of 15660–18090 cm^?1 for the CT bands and 1960–5540 cm^?1 for the high‐energy bands, which were assigned to local transitions within the benzodiazaborole units (local excitation, LE), whereas four compounds showed only CT bands with Φ_F values between 8–32 %. Two distinct excited singlet‐state (S₁) geometries, denoted S₁(LE) and S₁(CT), were observed computationally for the benzodiazaborolyl‐ortho‐carboranes, the population of which depended on their orientation (ψ). TD‐DFT calculations on these excited state geometries were in accord with their CT and LE emissions. These C‐diazaborolyl‐ortho‐carboranes were viewed as donor–acceptor systems with the diazaborolyl group as the donor and the ortho‐carboranyl group as the acceptor.     

Synthesis and characterization of meso-ferrocenylethynyl 5,15-diphenylporphyrins

A series of four meso-ferrocenylethynyl (5,15-diphenylporphyrinato)nickel(II) derivatives have been synthesized by Sonogashira coupling reactions. Three of these compounds contain the electron-withdrawing groups including -CHO, -CHC(CN)₂, and -CCC₆H₄NO₂ at the remaining meso position, with a view to preparing push-pull chromophores, in which ferrocene serves as the electron donor. All the new compounds have been characterized spectroscopically and the molecular structure of one of these porphyrins (compound 11) has also been determined. The studies show that although the ferrocenylethynyl group can extend the π system of the central porphyrin core, the cyclopentadienyl rings of ferrocene are almost orthogonal to the porphyrin ring. This hinders ferrocene serving as a good electron donor in these systems.     

Periphery-substituted [4+6] salicylbisimine cage compounds with exceptionally high surface areas: influence of the molecular structure on nitrogen sorption properties

The synthesis of various periphery‐substituted shape‐persistent cage compounds by twelve‐fold condensation reactions of four triptycene triamines and six salicyldialdehydes is described, where the substituents systematically vary in bulkiness. The resulting cage compounds were studied as permanent porous material by nitrogen sorption measurements. When the material is amorphous, the steric demand of the cages exterior does not strongly influence the gas uptake, resulting in BET surface areas of approximately 700 m² g^?1 for all cage compounds 3 c – e , independently of the substituents bulkiness. In the crystalline state, materials of the same compounds show a strong interconnection between steric demand of the peripheral substituent and the resulting BET surface area. With increasing bulkiness, the overall BET surface area decreases, for example 1291 m² g^?1 (for cage compound 3 c with methyl substituents), 309 m² g^?1 (for cage compound 3 d with 2‐(2‐ethyl‐pentyl) substituents) and 22 m² g^?1 (for cage compound 3 e with trityl substituents). Furthermore, we found that two different crystalline polymorphs of the cage compound 3 a (with tert‐butyl substituents) differ also in nitrogen sorption, resulting in a BET surface area of 1377 m²g^?1, when synthesized from THF and 2071 m²g^?1, when recrystallized from DMSO.     

Synthesis and crystal structure of 1D polyoxometalate-based composite compound, [{Gd(NMP)6}(PMo12O40)]n (NMP=N-methyl-2-pyrrolidone)

A novel compound, [{Gd(NMP)₆}(PMo₁₂O₄₀)]_n, has been synthesized and characterized by IR, and UV spectroscopy, and single crystal X-ray structural analysis. It forms an unprecedented one-dimensional zigzag chain built from alternating polyanions and cationic units through Mo-O_t-Gd-O_t-Mo links in the crystal. In the compound, Gd³⁺ is eight-coordinated with a bicapped trigonal prism geometry environment of oxygen atoms. The results of the single crystal X-ray diffraction analyses and IR are agreement and both show the metal cation units are coordinately bonded to the Keggin cluster. The UV spectrum of the title compound suggests that the compound is entirely dissociated in dilute solution.     

Electronic structures of the boron cage molecules B4H4, B4Cl4 and B4F4

Ab initio calculations have been performed on B₄H₄, B₄Cl₄ and B₄F₄ in order to aid our understanding of the bonding in these compounds, which is presumably based on a tetrahedral boron cage. This cage has only 8 electrons and so is less than that expected on the basis of the usual framework electron counting rules. Basis sets with polarisation functions were used at the SCF, CI and CPF levels of theory to confirm that the T _d structures are indeed more stable than the D _4h ones. Davidson-Roby population analyses were able to show that many factors, including 3-centre 2-electron bonding and backbonding from the ligand to the boron cage, are of importance in determining the relative stability of the three compounds, of which B₄Cl₄ is the only one that has yet been observed experimentally.     

FeGa3 and RuGa3: Semiconducting Intermetallic Compounds

The intermetallic compounds FeGa₃ and RuGa₃ were prepared from the elements using a Ga flux and their structures were refined from single-crystal X-ray data. Both compounds crystallize with the FeGa₃ structure type (tetragonal, space group P4₂/mnm, Z=4). Electrical resistivity measurements revealed a semiconducting behavior for FeGa₃ and RuGa₃, which is in contrast to the good metallic conductivity observed for the isotypic compound CoGa₃. The origin of the different electronic properties of these materials was investigated by first-principle calculations. It was found that in compounds adopting the FeGa₃ structure type the transition metal atoms and Ga atoms interact strongly. This opens a d-p hybridization bandgap with a size of about 0.31 eV in the density of states at the Fermi level for 17-electron compounds (i.e., FeGa₃ and RuGa₃). The electronic structure of CoGa₃ (an 18-electron compound) displays rigid band behavior with respect to FeGa₃. As a consequence, the Fermi level in CoGa₃ becomes located above the d-p hybridization gap which explains its metallic conductivity.     

Synthesis,Characterization, and Thermal Behavior of Carboranyl–Styrene Decorated Octasilsesquioxanes: Influence of the Carborane Clusters on Photoluminescence

Novel polyhedral oligomeric silsesquioxanes (POSS) or octasilsesquioxanes with carboranyl–styrene fragments attached to each corner are described. These compounds have been synthesized by olefin‐metathesis reactions between octavinylsilsesquioxane and carboranyl–styrene compounds that possess different substituents (Ph, Me, or H). In all cases, these reactions, which were catalyzed by the Grubbs catalyst, are highly regioselective and yield exclusively the E isomers. The existence of the carborane cage in the POSS structure induces a remarkable thermal stability in these compounds. After combustion at 1000 °C, these carboranyl–POSS compounds exhibit a mass loss lower than 10 %. The UV/Vis absorption data of these carboranyl–POSS compounds shows a slight bathochromic shift with respect to the carboranyl–styrene monomers, with an absorption maximum around 262 nm. Nevertheless, important differences in the emission spectra of the carboranyl–POSS compounds with regard to their carboranyl–styrene precursors are observed; the phenyl‐o‐carborane‐containing POSS compound exhibits the highest fluorescence intensity (Φ_F=44 %), whereas for the POSS compound bearing the methyl substituent, and for the unsubstituted o‐carborane clusters, the fluorescence intensity is much lower (Φ_F=9 and 2 %, respectively). This is precisely the reverse of what occurs with the monomers, in which the unsubstituted o‐carboranyl–styrene compound exhibits the highest Φ_F, and a quenching of the fluorescence is observed in the phenyl‐o‐carboranyl–styrene compound. In addition, a large red shift of around 100 nm is observed for the POSS compounds with respect to their precursors. These experimental results can only be accounted for by the spatial ordering induced by the POSS core that eases interactions, which otherwise would not occur. These results have been confirmed by time‐dependent density functional theory (TDDFT) calculations that exclude a photoinduced electron transfer (PET) process in the POSS compounds.     

Variety of mesophases in compounds with an increasing number of lactate units in the chiral chain

Liquid-crystalline compounds with different numbers of lactate units, n, in the chiral part were synthesised and mesomorphic properties studied. Physical properties were compared with respect to n. In the compound with one lactate unit in the chiral part the TGBA–TGBC–SmC* phase sequence was detected. For two lactate units the antiferroelectric SmC*_A phase occurs. Finally, three-lactate material exhibits the tilted hexatic SmI*(F*) phase below the ferroelectric SmC* phase. Dielectric spectroscopy and spontaneous tilt and polarisation were measured. For the three-lactate compound the temperature dependences were analysed in the vicinity of the SmC*–hexatic phase transition, and these properties compared with the theoretically predicted behaviour.