Bis-calix[4]arenes Bridged by an Electroactive Tetrathiafulvalene Unit

Coordination-triggered redox activity of early and late lanthanide calix[4]arene complexes

The methylation of p-tert-butylcalix[4]arene in the distal 1,3-phenolic sites provides H2L = {p-tert-butylcalix[4](OMe)2(OH)2arene}. This unit acts as a rigid coordinating ligand to early and late lanthanide metal ions, enabling the construction of two families of mononuclear compounds featuring (N(nBu)4)[LnIIIL(acac)2]·CH3CN (Ln = Pr (1), Nd (2), Ho (3), and Er (4)) and (N(nBu)4)2[LnIIIL{Mo5O13(OMe)4(NO)}]·CH2Cl2 (Ln = Nd (5) and Er (6)). The metal ions adopt distorted bicapped trigonal prismatic coordination environments, resulting in slow relaxation of the magnetization for 4. These compounds exhibit reversible redox waves at positive potentials, centered within the calix[4]arene ligand, representing a new type of calix[n]arene-based electrochemical activity induced by coordination to the metal centers.

The crystal structure of 25,27-(2,2′-[(2-thioxo-1,3-dithiole-4,5-diyl)disulfanediyl]diethanolate)-26,28-dihydroxycalix[4]arene — dichloromethane (1/1), C36H32Cl2O4S5

C36H32Cl2O4S5, orthorhombic, Pccn (no. 56), a = 15.4426(11) Å, b = 17.4623(13) Å, c = 25.9153(19) Å, V = 6988.4(9) Å3, Z = 8, R gt(F) = 0.0590, wR ref(F 2) = 0.1958, T = 291(2) K.

Functionalised tetrathiafulvalene- (TTF-) macrocycles: recent trends in applied supramolecular chemistry

Tetrathiafulvalene- (TTF-) based macrocyclic systems, cages and supramolecularly self-assembled 3D constructs have been extensively explored as functional materials for sensing and switching applications.

A novel redox-active calix[4]arene-tetrathiafulvalene dyad

A novel redox-active calix[4]arene-TTF 5 was prepared by the reaction of p-tert-butylcalix[4]arene 4 with the tosylated TTF 3 in the presence of cesium fluoride. The structure of the dyad 5 was identified by X-ray diffraction analysis, and the preliminary electrochemical properties of 5 were investigated by cyclic voltammetry (CV), for which two reversible one-electron waves were observed. Moreover, the UV-vis absorption spectra studies show that the dyad 5 undergoes progressive oxidation at the TTF moiety in presence of increasing amounts of Cu2+ or Hg2+.

Calix[4]arenes with electroactive tetrathiafulvalene and quinone units: metal-ion-promoted electron transfer

Metal-ion-promoted electron transfer was observed for compounds 1 and 2 based on the absorption and ESR spectral studies. These results imply that spatially adjacent arrangement of TTF and quinone units in 1 and 2 due to the calix[4]arene platform is favorable for the intramolecular electron transfer.

Methylazacalixpyridines: remarkable bridging nitrogen-tuned conformations and cavities with unique recognition properties

Methylazacalix[n]pyridines (n = 4, 8) and methylazacalix[m]arene[n]pyridines (m = n = 2, 4) have been synthesized by a convenient fragment coupling approach starting from 2,6-dibromopyridine, 2,6-diaminopyridine, and benzene-1,3-diamine. Thanks to the intrinsic electronic nature of nitrogen, which can adopt mainly sp(2) hybridization, allowing it variously to conjugate, partially conjugate, or not conjugate with the adjacent one or two pyridine rings, the resulting nitrogen-bridged calixpyridine derivatives act as a unique class of macrocyclic host molecules with intriguing conformational structures offering fine-tunable cavities and versatile recognition properties. Whilst in solution it is fluxional, in the solid state methylazacalix[4]pyridine adopts a 1,3-alternate conformation with a C(2v) symmetry in which every two bridging nitrogen atoms conjugate with one pyridine ring. After protonation, the methylazacalix[4]pyridinium species has a different conjugation system of its four bridging nitrogen atoms, yielding the similar twisted 1,3-alternate conformations with an approximate S(4) symmetry. The cavity of each protonated methylazacalix[4]pyridine, however, varies finely to accommodate guest species of different size and geometry, such as planar DMF or HO(2)CCO(2) (-) ion, a twisted HO(2)CCO(2) (-) ion, and a tetrahedral ClO(4) (-) ion. As giant macrocyclic hosts, both methylazacalix[8]pyridine and methylazacalix[4]arene[4]pyridine interact efficiently with fullerenes C(60) and C(70) through van der Waals forces. Their ease of preparation, versatile conformational structures, and recognition properties make these multinitrogen-containing calixarenes or cyclophanes unique and powerful macrocyclic hosts in supramolecular chemistry.

Bis(calixcrown)tetrathiafulvalene Receptors

A new class of electroactive receptors has been synthesized, built by covalent association of five subunits: two calixarene platforms for spatial organization, two polyether 3D cavities for cation binding, and one electroactive TTF unit to probe the complexation event. Sodium complexation induces rigidification of the molecular assembly, as shown by 1H NMR titration and single-crystal X-ray crystallographic studies on free receptor 14 and a corresponding complex with two bound sodium atoms per receptor (15-(NaPF6)2). The calixarene units in these receptors change from a pinched cone conformation in the free ligand to a symmetrical cone in the complex. Cyclovoltammetric studies validated the electrochemical recognition concept of these five-member assemblies.

Monitoring the formation of TTF dimers by Na+ complexation

The formation of the two dimeric species [(TTF)2]+* and (TTF+*)2 can be monitored by complexation of Na+ on a calix[4]arene-TTF assembly.