1,3-Alternate conformer 5,11,17,23-tetra-tert-butyl-25,26,27,28-tetrakis(4-methylsulfanylbenzyloxy)-2,8,14,20-tetrathiacalix[4]arene

The title thia­calix[4]arene derivative, C₇₂H₈₀O₄S₈, adopts a 1,3-alternate conformation, where the four 4-methyl­sul­fan­yl­benzyl groups are located alternately at the two sides of a virtual plane defined by the four bridging S atoms. In the crystal, there are no significant inter­molecular inter­actions present. Some of the peripheral tert-butyl and methyl­sulfanyl groups are disordered over two positions. A region of disordered electron density, occupying voids of ca 700 ų for an electron count of 124, was treated using the SQUEEZE routine in PLATON [Spek (2009 ▶). Acta Cryst. D65, 148–155].

Optical properties of a fabricated self-assembled bottom-up bulk metamaterial

We investigate the optical properties of a true three-dimensional metamaterial that was fabricated using a self-assembly bottom-up technology. The metamaterial consists of closely packed spherical clusters being formed by a large number of non-touching gold nanoparticles. After presenting experimental results, we apply a generalized Mie theory to analyze its spectral response revealing that it is dominated by a magnetic dipole contribution. By using an effective medium theory we show that the fabricated metamaterial exhibits a dispersive effective permeability, i.e. artificial magnetism. Although this metamaterial is not yet left-handed it might serve as a starting point for achieving bulk metamaterials by using bottom-up approaches.

Direct control of the spatial arrangement of gold nanoparticles in organic-inorganic hybrid superstructures

The directed assembly of gold nanoparticles is essential for their use in many kinds of applications, such as electronic devices, biological labels, and sensors. Herein an atomic alteration in the molecular structure of ligand-stabilized gold nanoparticles that can shift the interparticle distance up to 1 nm upon covalent coupling to organic-inorganic superstructures is presented. Gold nanoparticles are stabilized by two octadentate thioether ligands and have a mean diameter of 1.1 nm. The ligands contain a central rigid rod varying in length and terminally functionalized with a protected acetylene. The two peripheral functional groups on each particle enable the directed assembly of nanoparticles to dimers, trimers, and tetramers by oxidative acetylene coupling. This is a wet chemical protocol resulting in covalently bound nanoparticles. These organic-inorganic hybrid superstructures are analyzed by transmission electron microscopy, small angle X-ray scattering, and UV/vis spectroscopy. The focus of the comparison here is the subunit, which is anchoring the bridgehead, either a pyridine or benzene moiety. The pyridine-based ligands reflect the calculated length of the rigid-rod spacer in their interparticle distances in the obtained hybrid structures. This suggests a perpendicular arrangement that results from the coordination of the pyridine's lone pair to the gold surface. An atomic variation in the ligand's center leads to smaller interparticle distances in the case of hybrid structures obtained from benzene ligands. This large difference in the spatial arrangement suggests a tangential arrangement of the interparticle bridging structure in the latter case. Consequently a rather flat arrangement parallel to the particle surface must be assumed for the central benzene unit of the benzene-based ligand.

Cationic recognition by tert-butylcalix[4]arene-functionalized nanoprobes

A nanoparticle-based strategy has been demonstrated using structurally-tailored tert-butylcalixarenes immobilized on gold nanoparticles to tune the guest access to the calixarene cone cavity for cationic recognition. This strategy exploits the interparticle charge-induced aggregation upon selective capture of metal cations into the nanoparticle-immobilized tert-butylcalixarenes, which produces calorimetric changes for the detection. A possible pathway for the binding of M(n+) into the t-BCA structure and the interparticle interaction is proposed for the formation of an electric double layer inducing the interparticle association responsible for the red-shifted surface plasmon resonance band of the nanoparticles. The value of this class of calorimetric nanoprobes will be in the area of designing advanced host-guest probes using a variety of calixarene ligands for ionic recognition in a simplistic detection format.

The role of the ethynyl substituent on the π-π stacking affinity of benzene: a theoretical study

Herein, we report a high-level theoretical study (SCS-RI-MP2(full)/aug-cc-pVTZ) examining the stacking affinity of 1,3,5-triethynylbenzene. The stacking properties of this compound are compared to those of benzene and 1,3,5-trifluorobenzene. The results indicate that the ethynyl substituent improves the stacking affinity of the arene, since the binding energies for the stacked ethynyl-substituted arene dimers are higher than those of both benzene and the fluoro-substituted arene. This interesting behaviour has been studied by examining the energetics, geometries and electron charge density features of the complexes. A query in the Cambridge Structural Database returned several X-ray crystal structures containing π-π stacking interactions of 1,3,5-triethynylaryls that strongly agree with the theoretical results.