Ignacio Vargas-Baca

Supramolecular macrocycles reversibly assembled by Te … O chalcogen bonding

Organic molecules with heavy main-group elements frequently form supramolecular links to electron-rich centres. One particular case of such interactions is halogen bonding. Most studies of this phenomenon have been concerned with either dimers or infinitely extended structures (polymers and lattices) but well-defined cyclic structures remain elusive. Here we present oligomeric aggregates of heterocycles that are linked by chalcogen-centered interactions and behave as genuine macrocyclic species. The molecules of 3-methyl-5-phenyl-1,2-tellurazole 2-oxide assemble a variety of supramolecular aggregates that includes cyclic tetramers and hexamers, as well as a helical polymer. In all these aggregates, the building blocks are connected by Te…O–N bridges. Nuclear magnetic resonance spectroscopic experiments demonstrate that the two types of annular aggregates are persistent in solution. These self-assembled structures form coordination complexes with transition-metal ions, act as fullerene receptors and host small molecules in a crystal.

Supramolecular chromotropism of the crystalline phases of 4,5,6,7-tetrafluorobenzo-2,1,3-telluradiazole.

The remarkable effect that secondary bonding interactions can have on the macroscopic properties of a material is illustrated by two polymorphs of the title compound. The phase which is most stable under ambient pressure and temperature consists of puckered supramolecular ribbon polymers assembled by Te--N secondary bonding interactions and displays a characteristic red-orange color. A second yellow phase consists of ribbons with alternating short and long intermolecular Te--N secondary bonding distances and is metastable; at 127 °C the material undergoes an exothermic irreversible transition to the red polymorph. A third phase consists of pyridine-solvated supramolecular dimers; it is also yellow and transforms into the red phase after the crystals effloresce. Computational DFT studies indicate that the observed changes in optical properties are related to intermolecular mixing of π orbitals enabled by the supramolecular interactions and the symmetry of the supramolecular synthon.

WEAKLY BONDING INTERACTIONS IN ORGANOCHALCOGEN CHEMISTRY

Abstract Weakly bonding interactions are a subject of interest for many areas of chemistry. For example, these interatomic forces are central in the association processes that lead to molecular recognition, self-assembly of supramolecular structures, crystal packing and crystal growth. The activity of biological macromolecules is determined by the structures they adopt as a result of such forces and the interaction with their substrates. The useful macroscopic properties (electric, optical or magnetic) of some materials depend on organization at a molecular level and electronic communication between neighboring molecules.

Tetrakis(imino)pyracene Complexes Exhibiting Multielectron Redox Processes

The differences in redox behavior of the monofunctional bis(imino)acenaphthene (BIAN) and bifunctional tetrakis(imino)pyracene (TIP) ligands have been explored by treatment of the latter with PI(3), TeI(4), or BI(3). These reactions result in the formation of products involving the transfer of three or four electrons. Accompanying DFT calculations reveal that in each case the extent of electron transfer from each p-block element into the TIP ligand is dependent upon the element-TIP bonding interactions.

Sterically Directed Functionalization of the Redox-Active Bis(imino)acenaphthene Ligand Class: An Experimental and Theoretical Investigation

The synthesis, characterization, and theoretical study of the sterically directed functionalization of the redox-active bis(imino)acenaphthene (BIAN) ligand class has been explored. With dependence on the steric congestion encompassing the N-C-C-N fragment of the Ar-BIAN ligand, functionalization can be directed to proceed either via a radical backbone dearomatization or a nucleophilic imine C-alkylation pathway. The structures of the Ar-BIAN derivatives 14-19 were determined by means of single-crystal X-ray diffraction. The reaction pathways involved in Ar-BIAN functionalization were monitored by means of EPR spectroscopy. The experimental results and observations were examined in conjunction with DFT-D calculations in order to explain the driving forces that direct the pathways leading to Ar-BIAN functionalization.

Reversibly Trapping Visible Laser Light through the Catalytic Photo-oxidation of I– by Ru(bpy)32+

A Gaussian, visible laser beam traveling in a hydrogel doped with NaI and Ru(bpy)3Cl2 spontaneously transforms into a localized, self-trapped beam, which propagates without diverging through the medium. The catalytic, laser-light-induced oxidation of I(-) by [Ru(bpy)3](2+) generates I3(-) species, which create a refractive index increase along the beam path. The result is a cylindrical waveguide, which traps the optical field as bound modes and suppresses natural diffraction. When the beam is switched off, diffusion of I3(-) erases the waveguide within minutes and the system reverts to its original composition, enabling regeneration of the self-trapped beam. Our findings demonstrate reversible self-trapping for the first time in a precisely controllable, molecular-level photoreaction and could open routes to circuitry-free photonics devices powered by the interactions of switchable self-trapped beams.

Experimental and Theoretical Investigations of 1,4,5,7 Dithiadiazepines

Abstract A 1,4,5,7-dithiadiazepinyl radical has been prepared and characterized by ESR. Properties of this novel family of 9 π-electron systems are discussed on the basis of DFT calculations.

Reagents that Contain Se-H or Te-H Bonds

Abstract Species that contain bonds between hydrogen and selenium or tellurium have a characteristic high reactivity, which can be harnessed in the synthesis of valuable organic compounds. This overview includes the synthesis of dihydrides, alkali metal hydrochalcogenides, chalcogenols, chalcogenocarboxylic and chalcogenocarbamic acids, and their application in reactions of reduction, addition to unsaturated compounds, and nucleophilic substitution.

Photochemical isomerization of a C2N4S2 ring into a diazene

The eight-membered rings (ArC)2N4(SPh)2[Ar = 4-XC6H4(X = Br, CF3)] undergo photoisomerization to the purple diazenes PhSNC(Ar)NNC(Ar)NSPh by a first-order process that is thermally smmetry-forbidden, but photochemically allowed.

Preparation and Structure of a Sixteen-Membered Ring with Alternating CN and SN Groups

Abstract The reaction of trisilylated benzamidines ArCN2(SiMe3)3 with PhSCl in a 1:3 molar ratio produces cyclic compounds of the type (ArCNS(Ph)N)n (n=2, 4) in addition the diazenes trans-PhSNC(Ar)N=NC(Ar)NSPh. The X-ray structure of the sixteen-membered ring (4-BrC6H4)4C4N8S4Ph4 has been determined.