THE CRYSTAL STRUCTURES OF 9,10-DICHALCOGENAANTHRACENES, C12H8XY, (X, Y) = (S, Se), (S, Te), (Se, Te), and (O, Se)

Synthesis and Conformational Dynamics of Selenanthrene (Oxides): Establishing an Energetic Flexibility Index for Scaffolds

The use of new dynamic scaffolds for constructing inorganic and organometallic complexes with enhanced reactivities is an important new research direction. Toward this fundamental aim, an improved synthesis of the dynamic scaffold selenanthrene, along with its monoxide, trans-dioxide and the previously unknown trioxide, is reported. A discussion of the potential reaction mechanism for selenanthrene is provided, and all products were characterized using 1H, 13C, and 77Se nuclear magnetic resonance (NMR) spectroscopy and single-crystal X-ray crystallography. The dynamic ring inversion processes (i.e., "butterfly motion") for selenanthrene and its oxides were investigated using variable-temperature 1H NMR and density functional theory calculations. The findings suggest that selenanthrene possesses a roughly equal barrier to inversion as its sulfur analogue, thianthrene. However, selenanthrene oxides evidently possess larger inversion barriers as compared to their sulfur analogues due to the enhanced electrostatic intramolecular interactions inherent between the highly polar selenium-oxygen bond and adjacent C-H moieties. Finally, we propose a quantitative "flexibility index" in deg/(kcal/mol) for various tricyclic scaffolds to provide researchers with a comparative scale of dynamic motion across many different systems.

[1,4]Ditellurino[2,3-b:5,6-b′]dipyrazine

The title compound, C₈H₄N₄Te₂, is the first reported [1,4]tellura[2,3-b:5,6-b′]di­pyrazine. Three independent unit-cell mol­ecules are folded along their Te⋯Te axes, with an average angle φ = 57.9°. C—Te—C angles range from 91.48 (6) to 93.80 (6)°. Inter­molecular N⋯Te bonding inter­actions between tellurium atoms of the central ring and the pyrazine N atoms of adjacent mol­ecules result in a supra­molecular helix motif.

[1,4]Ditellurino[2,3-b:5,6-b′]di­pyrazine represents the first reported [1,4]chalcogena[2,3-b:5,6-b′]di­pyrazine containing a heavy chalcogens The asymmetric unit consists of three mol­ecules. In contrast to its sulfur analog, which is planar [Lynch et al. (1994 ▸) Cryst. Struct. Commun.50,1470–1472], C₈H₄N₄Te₂ is folded along the Te⋯Te axis to accommodate the larger chalcogenide atoms. The dihedral angle between the two Te₂C₂ rings of the central ring is 57.9° (mean of three). C—Te bond lengths range from 2.1105 (16) Å to 2.1381 (17) Å, in good agreement with those predicted by their covalent radii. All Te atoms are involved in inter­molecular Te⋯N contacts, with distances in the range 2.894 (2) to 2.963 (2) Å. These result in a spiral supra­molecular assembly, forming helical columns.

10H-Pyrazino[2,3-b][1,4]benzotellurazine, a Novel Tellurium-Containing Heterocyclic System

Condensation of 2,3-dichloropyrazine with 2-aminobenzenetellurole and 2-amino-5-methylbenzenetellurole, generated in situ by reduction of the corresponding ditellurides, resulted in the formation of novel 10H-pyrazino[2,3-b][1,4]benzotellurazine and its 7-methyl derivative. The products were purified via their well-crystallized 5,5-dibromo derivatives. X-ray crystallographic analysis of the title compound indicates that it has a pronounced V-shape and forms hydrogen-bonded dimers. Te, N-containing heterocycles have the potential of offering access to supramolecular assemblies.