The study of positive homotropic allosterism in supramolecular receptors is important for elucidating design strategies that can lead to increased sensitivity in various molecular recognition applications. In this work, the cooperative relationship between tetrathiafulvalene (TTF)-calix[4]pyrroles and several nitroaromatic guests is examined. The design and synthesis of new annulated TTF-calix[4]pyrrole receptors with the goal of rigidifying the system to accommodate better nitroaromatic guests is outlined. These new derivatives, which display significant improvement in terms of binding constants, also display a positive homotropic allosteric relationship, as borne out from the sigmoidal nature of the binding isotherms and analysis by using the Hill equation, Adair equation, and Scatchard plots. The host-guest complexes themselves have been characterized by single-crystal X-ray diffraction analyses and studied by means of UV-spectroscopic titrations. Investigations into the electronic nature of the receptors were made by using cyclic voltammetry; this revealed that the binding efficiency was not strictly related to the redox potential of the receptor. On the other hand, this work serves to illustrate how cooperative effects may be used to enhance the recognition ability of TTF-calix[4]pyrrole receptors. It has led to new allosteric systems that function as rudimentary colorimetric chemosensors for common nitroaromatic-based explosives, and which are effective even in the presence of potentially interfering anions.

In order to realize significant benefits from the assembly of solid-state materials from molecular cluster superatomic building blocks, several criteria must be met. Reproducible syntheses must reliably produce macroscopic amounts of pure material; the cluster-assembled solids must show properties that are more than simply averages of those of the constituent subunits; and rational changes to the chemical structures of the subunits must result in predictable changes in the collective properties of the solid. In this report we show that we can meet these requirements. Using a combination of magnetometry and muon spin relaxation measurements, we demonstrate that crystallographically defined superatomic solids assembled from molecular nickel telluride clusters and fullerenes undergo a ferromagnetic phase transition at low temperatures. Moreover, we show that when we modify the constituent superatoms, the cooperative magnetic properties change in predictable ways.

We describe a new approach to synthesize two-dimensional (2D) nanosheets from the bottom-up. We functionalize redox-active superatoms with groups that can direct their assembly into multidimensional solids. We synthesized Co6Se8[PEt2(4-C6H4COOH)]6 and found that it forms a crystalline assembly. The solid-state structure is a three-dimensional (3D) network in which the carboxylic acids form intercluster hydrogen bonds. We modify the self-assembly by replacing the reversible hydrogen bonds that hold the superatoms together with zinc carboxylate bonds via the solvothermal reaction of Co6Se8[PEt2(4-C6H4COOH)]6 with Zn(NO3)2. We obtain two types of crystalline materials using this approach: one is a 3D solid and the other consists of stacked layers of 2D sheets. The dimensionality is controlled by subtle changes in reaction conditions. These 2D sheets can be chemically exfoliated, and the exfoliated, ultrathin 2D layers are soluble. After they are deposited on a substrate, they can be imaged. We cast them onto an electrode surface and show that they retain the redox activity of the superatom building blocks due to the porosity in the sheets.

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Hexasubstituted [3]radialenes can be synthetically tuned to function as catholyte materials for neutral pH aqueous organic redox flow batteries.

A new tetrathiafulvalene-salphen uranyl complex has been prepared. The system was designed to study the electronic coupling between actinides and a redox active ligand framework. Theoretical and experimental methods -including DFT calculations, single crystal X-ray analysis, cyclic voltammetry, NMR and IR spectroscopies -were used to characterize this new uranyl complex.A large number of complexes based on organic donor tetrathiafulvalene (TTF) ligands and 3d transition metal centers are known. 1 Complementing studies of these systems are recent efforts to develop TTF-containing complexes of the lanthanide cations. 2 To the best of our knowledge this work has not been extended to the actinide series.Early actinides are typically characterized by more radially extended and accessible f orbitals compared to the lanthanides. Accordingly, substitution of a lanthanide ion for an actinide in a redox active ligand framework offers an opportunity to enhance electronic communication between the ligand and the coordinated metal. 3 Here, we report a uranyl complex (1) based on a TTF-functionalized N,N′-phenylenebis(salicylideneimine) analogue (i.e., TTF salphenH 2 ). Although complex 1 contains a diamagnetic ion, characterizing the interactions between UO 2 2+ and the TTF-ligand represents a crucial first step towards subsequent experiments involving paramagnetic actinyls. Complex 1 was analyzed using a combination of theoretical, electrochemical, and spectroscopic methods. Taken in concert, these studies support the notion that communication between an actinyl cation and a redox active ligand can be achieved. They thus set the stage for more technically challenging studies involving related species such as the PuO 2 2+ cation.The present strategy for obtaining actinide complexes based on TTF-functionalized ligands involves coordinating a uranyl cation to an N,N′-phenylenebis(salicylideneimine) salphentype ligand, specifically the known TTF-salphen dianion ( TTF salphen 2− ). 4 The TTF part of the TTF salphen 2− dianion is redox active and capable of two reversible one-electron oxidations, while the salphen portion of the ligand provides a tetradentate binding site extensively used in actinide science for stabilizing multiple uranium oxidation states (U 4+ , UO 2 1+ , UO 2 2+ ). 3f,5 Complex 1 was thus deemed attractive as a platform for examining electronic coupling effects involving actinide elements and redox active ligands. The synthesis of complex 1 is shown in Scheme 1. Briefly, reacting bis( propylthio)-TTF-benzo-o-diamine 6 with salicylaldehyde and UO 2 (NO 3 ) 2 ·6H 2 O in ethanol provided complex 1 as a red solid in 73% yield. ‡ The 1 H NMR spectrum of this new product was consistent with the uranyl center being complexed by the TTF salphen 2− ligand (see ESI †). 4 Complex 1 (as its methanol complex) was unambiguously characterized in the solid-state via an X-ray crystallographic analysis. Suitable crystals for the analysis were obtained by slow evaporation of a solution of complex 1 in a 1 : 1 mixture of CH 2 C...

Ditopic metalation of a flexible "Pacman"-like tetrathiafulvalene (TTF) modified Schiff-base-calixpyrrole results in the stabilization upon oxidation of an otherwise difficult-to-access mixed-valence TTF radical dimer. EPR and optical spectroscopies were used to characterize the mixed-valence species.

Incorporation of tetrathiafulvalene into the backbone of a known neutral phosphate receptor, diindolylquinoxaline, yields a dual optical-electrochemical chemosensor for dihydrogen phosphate that functions in dichloromethane. This system shows selectivity for dihydrogen phosphate over other small anions and can be used to detect the presence of this analyte via fluorescence quenching or cyclic voltammetry.