Salts of Sterically Hindered Chalcogen-Varied Herz Cations Including Those with [Te3 Cl14 ]2- and [Te4 Cl18 ]2- Anions

(TeCl)4(TiCl4) with isolated Te4Cl16 and TiCl4 molecules and second-harmonic-generation

(TeCl4)4(TiCl4) is obtained by reaction of TeCl4 and TiCl4 at 50 °C with quantitative yield. The compound is composed of isolated, molecular (TeCl4)4 heterocubane-type units as well as isolated, molecular TiCl4 tetrahedra. The (TeCl4)4 heterocubane is arranged like a body-centred cubic cell with TiCl4 tetrahedra occupying 4 of 6 octahedral sites. (TeCl4)4(TiCl4) crystallizes in the space group I4̄ with an unidirectional alignment of the tetrahedral building units. The structure of the compound is obtained from single crystal X-ray diffraction and confirmed by Rietveld refinement of powder diffraction data. Thermogravimetry, optical spectroscopy, infrared and Raman spectroscopy are employed to further characterize the title compound. Second harmonic generation (SHG) is observed with a strong intensity (1.6-times higher than potassium dihydrogen phosphate/KDP). The SHG effect is observed in the visible spectral regime as the band gap, derived from a Tauc plot, is 2.8 eV.

New 3,1,2,4-benzothiaselenadiazines, related π-heterocycles including Herz cations, radicals and molecular complexes, and Bunte salts

3,1,2,4-Benzothiaselenadiazines, 1,3,2,4-benzodithiadiazines and 1,2,4,3,5-benzotrithiadiazepines are synthesized from Ar–NSN–SiMe3 and chalcogen chlorides, and converted into Herz salts, radicals and molecular complexes, and S- and Se-Bunte salts.

Bis(2,1,3-benzotelluradiazolidyl)2,1,3-benzotelluradiazole: a pair of radical anions coupled by TeN chalcogen bonding

Reduction of 2,1,3-benzotelluradiazole (3) yielded a crystalline solid that features a trimeric dianion formally composed of two [3]˙- and one 3 bridged by unusually asymmetric TeN chalcogen bonds. The solid is diamagnetic due to strong antiferromagnetic coupling, as revealed by CASSCF/CASPT2 and BS-DFT.

Chemistry of Herz radicals: a new way to near-IR dyes with multiple long-lived and differently-coloured redox states

A new synthetic methodology based on the self-condensation of 1,2,3-benzodithiazolyl diradicals (Herz radicals) produces unprecedented 5-6-6-6-5 and 5-6-7-6-5 pentacyclic sulfur-nitrogen near-IR dyes featuring up to five multiple long-lived and differently coloured redox-states.

Donor-Acceptor Complexes between 1,2,5-Chalcogenadiazoles (Te, Se, S) and the Pseudohalides CN- and XCN- (X=O, S, Se, Te)

Donor-acceptor (D-A) complexes between 3,4-dicyano-1,2,5-chalcogenadiazoles [chalcogen=Te (1 a), Se (1 b), S (1 c)] and the pseudohalides CN^- and XCN^- (X=O, S, Se, Te) were studied experimentally and theoretically. For 1 a, they were isolated as [K(18-crown-6)][1 a-CN] (2), [K(18-crown-6)][1 a-NCO] (3), [K(18-crown-6)][1 a-SCN] (4), [K(18-crown-6)][1 a-SeCN] (5), and [K][1 a-NCSe] (6) and characterized by X-ray diffraction (XRD), UV/Vis and NMR spectroscopy, and DFT and QTAIM calculations. For 1 b and 1 c, the complexes were not isolated due to unfavorable thermodynamics. In all isolated complexes, the D-A bonds, stabilized by negative hyperconjugation, were longer than the sum of the covalent radii and shorter than the sum of the van der Waals radii of the bonded atoms. In mixtures of 1 a, F^- , and SeCN^- , the complex [1 a-F]^- was selectively formed in accordance with thermodynamics. The reaction of 1 a with SeCN^- and the cyclic trimeric perfluoro-ortho-phenylene mercury afforded the complex [K(18-crown-6)][SCN]⋅(o-C₆ F₄ Hg)₃ , which was characterized by XRD.

Benzoquinone-Bridged Heterocyclic Zwitterions as Building Blocks for Molecular Semiconductors and Metals

In pursuit of closed-shell building blocks for single-component organic semiconductors and metals, we have prepared benzoquino-bis-1,2,3-thiaselenazole QS, a heterocyclic selenium-based zwitterion with a small gap (λ_max = 729 nm) between its highest occupied and lowest unoccupied molecular orbitals. In the solid state, QS exists in two crystalline phases and one nanocrystalline phase. The structures of the crystalline phases (space groups R3 c and P2₁/ c) have been determined by high-resolution powder X-ray diffraction methods at ambient and elevated pressures (0-15 GPa), and their crystal packing patterns have been compared with that of the related all-sulfur zwitterion benzoquino-bis-1,2,3-dithiazole QT (space group Cmc2₁). Structural differences between the S- and Se-based materials are interpreted in terms of local intermolecular S/Se···N'/O' secondary bonding interactions, the strength of which varies with the nature of the chalcogen (S vs Se). While the perfectly two-dimensional "brick-wall" packing pattern associated with the Cmc2₁ phase of QT is not found for QS, all three phases of QS are nonetheless small band gap semiconductors, with σ_RT ranging from 10^-5 S cm^-1 for the P2₁/ c phase to 10^-3 S cm^-1 for the R3 c phase. The bandwidths of the valence and conduction bands increase with applied pressure, leading to an increase in conductivity and a decrease in thermal activation energy E_act. For the R3 c phase, band gap closure to yield an organic molecular metal with a σ_RT of ∼10² S cm^-1 occurs at 6 GPa. Band gaps estimated from density functional theory band structure calculations on the ambient- and high-pressure crystal structures of QT and QS correlate well with those obtained experimentally.