Hydrogen-bonded hexameric cluster of benzyl alcohol in the solid state polymeric organization of <i>p</i>-<i>tert</i>-Butylcalix[5]arene

<p>An uncommon hydrogen-bonded hexameric cluster of benzyl alcohol (<b>2</b>) was formed in hydrophobic space in the layered organisation of the one-dimensional polymeric zigzag array of <b>1</b> in the solid state. The hexameric cluster adopted a distorted cyclohexane-like (12) O–H⋯O hydrogen bond network. The formation of the hexameric cluster was quite sensitive to a tiny structural difference of guests; phenylethylalcohol (<b>3</b>), phenol (<b>4</b>), benzyl amine (<b>5</b>) and aniline (<b>6</b>) did not form any hexameric cluster. The packing coefficient of 0.53 suggested that the hexameric cluster nicely filled the hydrophobic space, which most likely resulted in the effective van der Waals contacts that stabilised the supramolecular organisation composed of the hexameric cluster and the polymeric array of <b>1</b> in the solid state.</p

Anion-Directed Formation and Degradation of an Interlocked Metallohelicate

Although there are many examples of catenanes, those of more complex mechanically interlocked molecular architectures are rare. Additionally, little attention has been paid to the degradation of such interlocked systems into their starting complexes, although formation and degradation are complementary phenomena and are equally important. Interlocked metallohelicate, [(Pd₂L₄)₂]⁸⁺ (<b>2</b>⁸⁺), is a quadruply interlocked molecular architecture consisting of two mechanically interlocked monomers, [Pd₂L₄]⁴⁺ (<b>1</b>⁴⁺). <b>2</b>⁸⁺ has three internal cavities, each of which encapsulates one NO₃^– ion (1:3 host–guest complex, <b>2</b>⊃(NO₃|NO₃|NO₃)⁵⁺) and is characterized by unusual thermodynamic stability. However, both the driving force for the dimerization and the origin of the thermodynamic stability remain unclear. To clarify these issues, BF₄^–, PF₆^–, and OTf^– have been used to demonstrate that the dimerization is driven by the anion template effect. Interestingly, the stability of <b>2</b>⁸⁺ strongly depends on the encapsulated anions (<b>2</b>⊃(NO₃|NO₃|NO₃)⁵⁺ ≫ <b>2</b>⊃(BF₄|BF₄|BF₄)⁵⁺). The origins of this differing thermodynamic stability have been shown through detailed investigations to be due to the differences in the stabilization of the interlocked structure by the host–guest interaction and the size of the anion. We have found that 2-naphthalenesulfonate (ONs^–) induces the monomerization of <b>2</b>⊃(NO₃|NO₃|NO₃)⁵⁺ via intermediate <b>2</b>⊃(ONs|NO₃|ONs)⁵⁺, which is formed by anion exchange. On the basis of this finding, and using <i>p</i>-toluenesulfonate (OTs^–), the physical separation of <b>2</b>⊃(NO₃|NO₃|NO₃)⁵⁺ and <b>1</b>⁴⁺ as OTs^– salt was accomplished

Synthesis and Structure of Feet-to-Feet Connected Bisresorcinarenes

Bisresorcinarenes <b>1a</b>–<b>d</b> were obtained in excellent yields, and <b>1e</b> was finally obtained in 50% yield. X-ray diffraction analysis showed that <b>1a</b> and <b>1b</b> adopted helical conformations, whereas the two resorcinarenes of <b>1c</b>–<b>e</b> were in parallel orientations in which the clefts of the aliphatic chains entrapped one or two solvent molecules. The conformational study revealed that the helix interconversion between the (<i>P</i>)- and (<i>M</i>)-helical conformers depended on the length of the aliphatic chains. <b>1a</b> had the largest energetic barrier to helix interconversion, while in <b>1b</b>, its more flexible aliphatic chains lowered its energetic barriers. The <i>P</i>/<i>M</i> interconversion of <b>1a</b> was coupled with the clockwise/anticlockwise interconversion of the interannular hydrogen bonding of the two resorcinarenes. The large negative entropic contributions indicate that the transition state is most likely more ordered than the ground states, suggesting that the transition state is most likely symmetric and is solvated by water molecules. Calculations at the M06-2<i>X</i>/6-31G­(d,p) level revealed that the more stable (<i>P</i>)-conformation has clockwise interannular hydrogen bonding between the two resorcinarenes

Cooperative Self-Assembly of Carbazole Derivatives Driven by Multiple Dipole–Dipole Interactions

Carbazole possessing phenylisoxazoles self-assembled in a cooperative manner in decalin. X-ray crystal structure analysis revealed that the isoxazole dipoles align in a head-to-tail fashion. DFT calculations suggested that the linear array of dipoles induced the polarization of each dipole, leading to an increase in dipole–dipole interactions. This dipole polarization resulted in cooperative assembly

Synthesis, Characterization, X‑ray Crystal Structure, DFT Calculations, and Catalytic Properties of a Dioxidovanadium(V) Complex Derived from Oxamohydrazide and Pyridoxal: A Model Complex of Vanadate-Dependent Bromoperoxidase

A vanadium­(V) complex with the formula [Et₃NH]­[V^VO₂(sox-pydx)] with a new tridentate ligand 2-[2-[[3-hydroxy-5-(hydroxymethyl)-2-methylpyridin-4-yl]­methylene]­hydrazinyl]-2-oxoacetamide (soxH-pydxH), obtained by condensation of oxamohydrazide and pyridoxal (one of the forms of vitamin B₆), has been synthesized. The compound was characterized by various analytical and spectroscopic methods, and its structure was determined by single-crystal X-ray diffraction technique. Density functional theory (DFT) and time-dependent DFT calculations were used to understand the electronic structure of the complex and nature of the electronic transitions observed in UV–vis spectra. In the complex, vanadium­(V) is found to be pentacoordinated with two oxido ligands and a bianionic tridentate ONO-donor ligand. The vanadium center has square-pyramidal geometry with an axial oxido ligand, and the equatorial positions are occupied by another oxido ligand and a phenolato oxygen, an imine nitrogen, and a deprotonated amide oxygen of the hydrazone ligand. A DFT-optimized structure of the complex shows very similar metrical parameters as determined by X-ray crystallography. The O₄N coordination environment of vanadium and the hydrogen-bonding abilities of the pendant amide moiety have a strong resemblance with the vanadium center in bromoperoxidase enzyme. Bromination experiments using H₂O₂ as the oxidizing agent, with model substrate phenol red, and the vanadium complex as a catalyst show a remarkably high value of <i>k</i>_cat equal to 26340 h^–1. The vanadium compound also efficiently catalyzes bromination of phenol and salicylaldehyde as well as oxidation of benzene to phenol by H₂O₂