Heavy Chalcogenide Research Articles

Optoelectronic properties fine-tuning through chalcogenide-based π-bridge for dye molecules featuring hydantoin anchoring group: first-principle calculations

This study investigates the effect of chalcogenides and electron-withdrawing groups CN and F on the optoelectronic properties using DFT and TD-DFT methods, with a focus on the use of a hydantoin anchoring group as an alternative to carboxylic acid-based groups. The results show that the studied dyes have a planar structure that facilitates intramolecular charge transfer and that propeller-shaped terminal phenyl rings help reduce dye aggregation. The maximum absorption was observed between 485 and 627 nanometres, and bathochromic shifts in UV-Vis spectra were observed in the order NH, S, O, Se, and Te for both F- and CN-containing dyes. Excited-state lifetime was highest for dyes containing heavier chalcogenides. Adsorption energies of the dye onto TiO2 anatase (101) with 3 × 6 supercell were found in the range of 0.13–0.79 eV and 0.61–1.54 eV for CN and F-containing dyes, respectively. Dyes featuring Se and Te exhibit superior properties for dye-sensitized solar cell application, and chalcogenide-based dyes are worthy of experimental synthesis. Overall, the study provides valuable insights into the optoelectronic properties of dyes and their potential use in more efficient solar cell technologies.

Effects of Dispersion and Charge-Transfer Interactions on Structures of Heavy Chalcogenide Compounds: A Quantum Chemical Case Study for (Et2 Bi)2 Te.

The reasons for the unusually small Bi-Te-Bi bond angle of 86.6° observed in the crystal strucure of (Et2 Bi)2 Te are investigated by quantum chemical calculations. With the help of coupled cluster theory at the CCSD(T) level it is demonstrated that the structure of an isolated monomer should have a bond angle larger than 90°, despite a Bi-Bi distance in good agreement with the value of 4.09 Å found in the crystal structure. The discrepancy is resolved by a lengthening of the Bi-Te bond in the crystal, which is shown to be caused by partial electron transfer from neighbouring molecules to the Bi-Te σ* orbital. Through symmetry-adapted perturbation theory at the DFT-SAPT level it is shown that London dispersion interactions are highly important for the packing of molecules in the solid state and, in turn, for the small Bi-Te-Bi bond angle.

Stabilization of intermediate spin states in mixed-valent diiron dichalcogenide complexes

The electronic structure and ground spin states, S, observed for mixed-valent iron–sulfur dimers (FeII-FeIII) are typically determined by the Heisenberg exchange interaction, J, that couples the magnetic interaction of the two metal centres either ferromagnetically (J > 0, S = 9/2) or antiferromagnetically (J < 0, S = 1/2). In the case of antiferromagnetically coupled iron centres, stabilization of the high-spin S = 9/2 ground state is also feasible through a Heisenberg double-exchange interaction, B, which lifts the degeneracy of the Heisenberg spin states. This theorem also predicts intermediate spin states for mixed-valent dimers, but those have so far remained elusive. Herein, we describe the structural, electron paramagnetic resonance and Mössbauer spectroscopic, and magnetic characterization of a series of mixed-valent complexes featuring [Fe2Q2]+ (Q = S2–, Se2–, Te2–), where the Se and Te complexes favour S = 3/2 spin states. The incorporation of heavier chalcogenides in this series reveals a delicate balance of antiferromagnetic coupling, Heisenberg double-exchange and vibronic coupling.

Structural, thermal, vibrational, and optical characterization of Sn–S–Se dichalcogenide system synthesized by high-energy ball milling

Layered tin-based SnS2, Sn(S0.5Se0.5)2, and SnSe2 dichalcogenide semiconductors were synthesized using high-energy ball milling. Structural analyses revealed anisotropic nanostructures with the 2H-polytype. The extended milling time produced nanocrystallites due to the high density of defects and texture indexes. A significant microstrain reduction was achieved by replacing the 1d site with heavier chalcogenides. The presence of microstrained nanocrystallites widens and redshifts the A1g and Eg Raman modes. The redshift effect also occurs when the lattice parameters are increased via doping. The overall exothermic DSC profile exhibited a subtle modification above 450 °C suggestive of SnO2 nucleation. A composition-dependent exciton redshift in UV–Vis was followed by a reduction in the band gap toward lower averaged ionic radii in the 1d site. Multiple straight-line segments in Tauc plots indicate sub-bands as a result of the multilayered structure.

(Invited) Atomic Layer Deposition of MOF from Dissolved Precursors ― ‘Solution ALD’ (sALD)

Metal organic frameworks (MOFs) are crystalline three-dimensional porous solids featuring a high surface area, which have attracted considerable attention in a wide range of applications e.g. in catalysis, hydrogen storage, gas separation, thermoelectric applications or as chemical sensors. Beyond solvothermal synthesis of bulk MOF crystals, growing MOFs thin films has been limited so far to rather conventional solution-based techniques. However, traditional growth methods from solution such as spin-coating, spray-coating or dip-coating generate MOFs thin films with a rather low film quality and an alarming lack of a precise film thickness control under 1 nm. This renders them unsuitable for most industrial applications and severely limits their future application potential.Atomic layer deposition (ALD) provides this capability, but is limited by the necessity to use gaseous precursors in vacuum conditions at temperatures typically above 100°C. This is incompatible with the typically high temperature sensitivity of many hybrid metal-organic compounds such as the MOFs.In this perspective, we have transferred the principles of ALD to precursors dissolved in liquid solvents. The ‘solution ALD’ (sALD) method can be implemented in a variety of microfluidic or slot-die processing devices. We have demonstrated that the principles of classical, gas-based ALD —self-limiting surface reactions— are reproduced in sALD. sALD shares the fundamental properties of standard ‘gas ALD’ (gALD), in particular the self-limiting surface chemistry and the ability to coat deep pores in a conformal manner Furthermore, sALD allows the experimentalist to design new, advantageous, reactions of known semiconductors (oxides, heavier chalcogenides), or to deposit materials otherwise inaccessible to ALD altogether, such as polymers, ionic solids, and metal-organic frameworks. They may be obtained in highly pure, crystalline form at room temperature, either as planar films or as conformal coatings of porous substrates. Based on these advances, we have been able to make the first sALD-derived films of a MOF, Cu-BDC. At any chosen thickness, sALD MOF films feature significantly lower roughness and better adhesion than those generated by the best spray-coating and dip-coating methods available currently.

Heavy chalcogenide-transition metal clusters as coordination polymer nodes.

While metal–oxygen clusters are widely used as secondary building units in the construction of coordination polymers or metal–organic frameworks, multimetallic nodes with heavier chalcogenide atoms (S, Se, and Te) are comparatively untapped. The lower electronegativity of heavy chalcogenides means that transition metal clusters of these elements generally exhibit enhanced coupling, delocalization, and redox-flexibility. Leveraging these features in coordination polymers provides these materials with extraordinary properties in catalysis, conductivity, magnetism, and photoactivity. In this perspective, we summarize common transition metal heavy chalcogenide building blocks including polynuclear metal nodes with organothiolate/selenolate or anionic heavy chalcogenide atoms. Based on recent discoveries, we also outline potential challenges and opportunities for applications in this field.

Magnetoelectric Coupling through the Spin Flop Transition in Ni_{3}TeO_{6}.

We combined high field optical spectroscopy and first principles calculations to analyze the electronic structure of Ni_{3}TeO_{6} across the 53K and 9T magnetic transitions, both of which are accompanied by large changes in electric polarization. The color properties are sensitive to magnetic order due to field-induced changes in the crystal field environment, with those around Ni1 and Ni2 most affected. These findings advance the understanding of magnetoelectric coupling in materials in which magnetic 3d centers coexist with nonmagnetic heavy chalcogenide cations.

Metal-free radical thiolations mediated by very weak bases.

Aromatic thioethers and analogous heavier chalcogenides were prepared by reaction of arene-diazonium salts with disulfides in the presence of the cheap and weak base NaOAc. The mild and practical reaction conditions (equimolar reagents, DMSO, r.t., 8 h) tolerate various functional groups (e.g. Br, Cl, NO2, CO2R, OH, SCF3, furans). Mechanistic studies indicate the operation of a radical aromatic substitution mechanism via aryl, acetyloxyl, thiyl, and dimsyl radicals.

Experimental and Computational Investigations of Tautomerism and Fluxionality in PCP‐ and PNP‐Bridged Heavy Chalcogenides

The monochalcogenides EPiPr2CH2PiPr2 (E = Se, Te) exist as CH2 tautomers in the solid state; the contrast in this finding with that of the preferential formation of PH tautomers by PNP-bridged analogues is addressed through DFT calculations. In solution, the PCP-bridged tellurium derivative undergoes rapid intermolecular tellurium exchange with an activation energy of 21.9 ± 3.2 kJ mol–1.

Silver(I)-(poly)chalcogenide Halides – Ion and Electron High Potentials

Abstract Materials with high dynamics in the solid state are of potential interest in semiconductor science and for a great variety of energy applications. In most of the cases the majority of physical properties of such compounds are directly related to their electronic structure. Optimization of properties is therefore correlated with direct or indirect control of this parameter. Compounds with highly mobile ions like the coinage metal cations and the heavy chalcogenide anions can easily be modified chemically or physically to fine tune their electronic structures. The range of adjustable properties lasts from ion conductivity, magneto resistance, thermoelectricity to a reversible redox-driven switch of semiconductivity. Today, the strong demand on clean energy production, the efficient energy transport and energy storage is a major goal for present and oncoming generations. Stable, mixed-conducting materials will play a major role in this process. The ongoing development of coinage metal chalcogenide halides during the last 50 years reflects the fundamental interest in this field. Many interesting and sometimes unexpected properties have been determined recently which substantiates the great potential of this class of materials. Especially the new class of coinage metal polychalcogenide halides is of potential interest due to their drastic modulations of physical properties driven by a fundamental tuning of its electronic structures. Thermopower and thermal diffusivity, two major properties to tune thermoelectricity can be varied in such a way that drastic changes can be addressed in very small temperature ranges close to room temperature. Herein we report on the recent progress of polychalcogenide and chalcogenide halides with the mobile d 10 ions Ag and Cu putting the main focus on silver compounds.

Self-Assembled Monolayers of Heavy Chalcogenophenes and Dialkyl Heavy Chalcogenides on Au(111)

Self-assembled monolayers (SAMs) of heavy chalcogenophenes and dialkyl heavy chalcogenides on Au(111) were prepared by a vapor adsorption method. The adsorption of heavy chalcogenide analogues was confirmed by X-ray photoelectron spectroscopy. The structures of the films were observed using scanning tunneling microscopy under atmospheric conditions. The SAM of selenophene was stable and showed striped patterns with a row-to-row spacing of 16 ± 1 A. Dibutyl selenide also formed striped patterns but with longer exposure times. Tellurophene and dibutyl telluride were found to adsorb on Au(111) but did not form ordered structures. The interactions of furan and thiophene with Au(111) were not strong enough for the molecule to adsorb on Au(111) at room temperature.

Comments on the molecular structure of B 2O 2(g), Al 2O 2(g) and other chalcogenides of the aluminum family

Thermochemical evidence relating to the structure of the aluminum-family chalcogenides M 2X 2 is reassessed. Contrary to the conclusion of Maloney et al.[1], this evidence suggests that M-X-M-X is not the only plausible structure. We cannot eliminate the X-M-M-X form for B 2O 2 and the cyclic form for Al 2O 2 and heavier chalcogenides. Other evidence is needed to resolve the question. The structural ambiguity contributes potential uncertainty to the published thermodynamic tables[1].