Spontaneous H2 Loss through the Interaction of Squaric Acid Derivatives and BeH2

The most stable complexes between squaric acid and its sulfur‐ and selenium‐containing analogues (C₄X₄H₂; X=O, S, Se) with BeY₂ (Y=H, F) were studied by means of the Gaussian 04 (G4) composite ab initio theory. Squaric acid derivatives are predicted to be very strong acids in the gas phase; their acidity increases with the size of the chalcogen, with C₄Se₄H₂ being the strongest acid of the series and stronger than sulfuric acid. The relative stability of the C₄X₄H₂ ? BeY₂ (X=O, S, Se; Y=H, F) complexes changes with the nature of the chalcogen atom; but more importantly, the formation of the C₄X₄H₂ ? BeF₂ complexes results in a substantial acidity enhancement of the squaric moiety owing to the dramatic electron‐density redistribution undergone by the system when the beryllium bond is formed. The most significant consequence of this acidity enhancement is that when BeF₂ is replaced by BeH₂, a spontaneous exergonic loss of H₂ is observed regardless of the nature of the chalcogen atom. This is another clear piece of evidence of the important role that closed‐shell interactions play in the modulation of physicochemical properties of the Lewis acid and/or the Lewis base.     

Preparation and characterization of symmetrical bis[4-chloro-2-pyrimidyl] dichalcogenide (S, Se, Te) and unsymmetrical 4-chloro-2-(arylchalcogenyl) pyrimidine: X-ray crystal structure of 4-chloro-2-(phenylselanyl) pyrimidine and 2-(p-tolylselanyl)-4-chloropyrimidine

Synthesis of a novel class of multinucleate pyrimidine chalcogen (S/Se/Te) derivatives has been successfully attempted for the first time by the selective substitution of chlorine at the C-2 position of 2,4-dichloropyrimidine with nucleophilic dichalcogenide anion E₂²⁻ (E = S, Se, Te) to afford bis[4-chloro-2-pyrimidyl] dichalcogenide. The highly electrophilic nature of 2,4-dichloropyrimidine compared to aryl chlorides has been further exploited to prepare a variety of 4-chloro-2-(arylchalcogenyl) pyrimidine compounds by substituting the chlorine exclusively at the C-2 position of 2,4-dichloropyrimidine with a variety of chalcogen bearing aryl anions ArE⁻ (Ar = phenyl, 1-naphthyl, p-tolyl, 4,6-dimethyl-2-pyrimidyl, 2-pyridyl, 4-methyl-2-pyridyl). All the newly prepared symmetrical and unsymmetrical pyrimidyl chalcogen compounds have been thoroughly characterized with the help of various spectroscopic techniques viz., NMR (¹H, ¹³C, ⁷⁷Se), FT-IR and mass spectrometry (in representative cases). The crystal structures of 4-chloro-2-(phenylselanyl) pyrimidine and 2-(p-tolylselanyl)-4-chloropyrimidine have been determined by X-ray crystallography.     

Single‐Step Sulfo‐Selenization Method to Synthesize Cu2ZnSn(SySe1−y)4 Absorbers from Metallic Stack Precursors

Pentenary Cu₂ZnSn(S_ySe_1?y)₄ (kesterite) photovoltaic absorbers are synthesized by a one‐step annealing process from copper‐poor and zinc‐rich precursor metallic stacks prepared by direct‐current magnetron sputtering deposition. Depending on the chalcogen source—mixtures of sulfur and selenium powders, or selenium disulfide—as well as the annealing temperature and pressure, this simple methodology permits the tuning of the absorber composition from sulfur‐rich to selenium‐rich in one single annealing process. The impact of the thermal treatment variables on chalcogenide incorporation is investigated. The effect of the S/(S+Se) compositional ratio on the structural and morphological properties of the as‐grown films, and the optoelectronic parameters of solar cells fabricated using these absorber films is studied. Using this single‐step sulfo‐selenization method, pentenary kesterite‐based devices with conversion efficiencies up to 4.4 % are obtained.     

Die Bildung von Gallium-Chalkogen-Heterokubanstrukturen durch Umsetzung der Alkylgallium(I)-Verbindung Ga4[C(SiMe3)3]4 mit Schwefel,Selen und Tellur

The Formation of Gallium Chalcogen Heterocubanes by the Reaction of the Alkylgallium(I) Compound Ga₄[C(SiMe₃)₃]₄ with Sulfur, Selenium, and Tellurium The alkylgallium(I) compound Ga₄[C(SiMe₃)₃]₄ 1 , which monomerizes in dilute solutions, reacts with elemental sulfur, selenium, and tellurium in boiling n-hexane to yield the corresponding Ga₄X₄R₄ cage compounds in a high yield. As shown by crystal structure determinations, the products have distorted Ga₄X₄ heterocubanes in their molecular centers with a slightly increasing distortion for the heavier chalcogen atoms. While the selenium and tellurium derivatives show a very low solubility in benzene, the sulfur compound dissolves readily accompanied by the dissociation into the (RGaS)₂ dimer.     

Effect of excess electron on structure,bonding, and spectral properties of sulfur/selenium based dichalcogen systems

First principle based quantum chemical methods are employed to characterize structure, bonding, and spectral properties of sulfur and selenium based dichalcogen systems in presence of an excess electron. Inter molecular two-center three-electron (2c-3e) bonding between two chalcogen (X) atoms is described in the systems of the type (R-X)₂^•- (R = Ph, PhCH₂ X = S, Se). In addition, effect of electron withdrawing (-NO₂) and electron donating (-CH₃) groups in phenyl ring on the stability of these 2c-3e bonded systems is also studied in water medium applying a macroscopic hydration model. Molecular parameters and binding energy of the neutral, (R-X)₂ and reduced, (R-X)₂^•- dichalcogen systems are compared. Search for minimum energy structures of these open shell doublet systems are carried out applying various density functionals with dispersion corrections and MP2 method considering 6-311++G (d,p) set of basis functions for all atoms. Effect of water medium is introduced through a macroscopic solvation model based on density (SMD). Frontier molecular orbitals based analysis is carried out for showing the definite presence of 2c-3e bond between two chalcogen atoms in these radical anions of sulfur and selenium based aromatic dichalcogen systems. Excited state calculations are performed on all these systems using Time Dependent Density Functional Theory (TDDFT). UV-Vis spectra are simulated and effect of solvent water on the absorption maximum of these radical anions is discussed. This study illustrates that the combination of electronic effect and geometrical flexibility decides the strength of two-center three-electron bond in these systems.     

Resolidified Chalcogen Precursors for High-Quality 2D Semiconductor Growth

Two-dimensional (2D) semiconductors including transition metal dichalcogenides (TMDCs) have gained attention in optoelectronics for their extraordinary properties. However, the large amount and locally distributed lattice defects affect the optical properties of 2D TMDCs, and the defects originate from unstable factors in the synthesis process. In this work, we develop a method of pre-melting and resolidification of chalcogen precursors (sulfur and selenium), namely resolidified chalcogen, as precursor for the chemical vapor deposition growth of TMDCs with ultrahigh quality and uniformity. Taking WS₂ as an example, the monolayer WS₂ shows uniform fluorescence intensity and a small full-width at half-maximum of photoluminescence peak at low temperatures with an average value of 13.6±1.9 meV. The defect densities at the interior and edge region are both low and comparable, i.e., (9±3)×10¹² cm⁻² and (10±4)×10¹² cm⁻², indicating its high structural quality and uniformity. This method is universal in growing high quality monolayer MoS₂, WSe₂, MoSe₂, and will benefit their applications.     

Theoretical Density Functional Theory insights into the nature of chalcogen bonding between CX2 (X = S,Se, Te) and diazine from monomer to supramolecular complexes

Chalcogen bonding is a noncovalent interaction, highly similar to halogen and hydrogen bonding, occurring between a chalcogen atom and a nucleophilic region. Two density functional theory (DFT) approaches B3LY-D3 and B97-D3 were performed on a series of complexes formed between CX₂ (X = S, Se, Te) and diazine (pyridazine, pyrimidine and pyrazine). Chalcogen atoms prefer interacting with the lone pair of a nitrogen atom rather than with the π-cloud of an aromatic ring. CTe₂ and CSe₂ form a stronger chalcogen bond than CS₂. The electrostatic potential of CX₂ (X = S, Se and Te) reveals the presence of two equivalent σ-holes, one on each chalcogen atom. These CX₂ molecules interact with diazine giving rise to supramolecular interactions. Wiberg bond index and second-order perturbation theory analysis in NBO were performed to better understand the nature of the chalcogen bond interaction.     

Carbonyl Activation by Selenium- and Tellurium-Based Chalcogen Bonding in a Michael Addition Reaction

In the last years the use of chalcogen bonding—the noncovalent interaction involving electrophilic chalcogen centers—in noncovalent organocatalysis has received increased interest, particularly regarding the use of intermolecular Lewis acids. Herein, we present the first use of tellurium-based catalysts for the activation of a carbonyl compound (and only the second such activation by chalcogen bonding in general). As benchmark reaction, the Michael-type addition between trans-crotonophenone and 1-methylindole (and its derivatives) was investigated in the presence of various catalyst candidates. Whereas non-chalcogen-bonding reference compounds were inactive, strong rate accelerations of up to 1000 could be achieved by bidentate triazolium-based chalcogen bond donors, with product yields of >90 % within 2 h of reaction time. Organotellurium derivatives were markedly more active than their selenium and sulphur analogues and non-coordinating counterions like BAr^F₄ provide the strongest dicationic catalysts.     

Electron impact induced fragmentation of 4-alkyl derivatives of 2,6,7-trioxa-1-phosphabicyclo[2.2.2]octane and the corresponding 1-oxides, 1-sulfides and 1-selenides

The electron impact fragmentations of several derivatives of 2,6,7-trioxa-1-phosphabicyclo[2.2.2]octane have been examined by means of high resolution and metastable ion analysis. The principal fragmentation route for bicyclophosphites, phosphates and phosphorothionates involves a loss of formaldehyde, followed by a loss of the PO₂X and HPO₂X groups (X = -, O, S). The behaviour of phosphoroselenates is quite different, due partly to the favoured loss of selenium from the molecular ion before further fragmentation. Fragmentation through C? O bond breaking and a rearranged molecular ion is dependent on the exocyclic chalcogen atom (-, O, S, Se) on phosphorus. The reactions have been rationalized in terms of 1- and 4-substitutions.     

Corannulene Chalcogenides

The introduction of chalcogen atoms into a polycyclic aromatic hydrocarbon structure is an established method to tune material properties. In the context of corannulene (C₂₀H₁₀), a fragment of fullerene C₆₀, such structural adjustments have given rise to an emerging class of functional and responsive molecular materials. In this minireview, our aim is to discuss the synthesis and properties of such chalcogen (sulfur, selenium, and tellurium) derivatives of corannulene.     

Darstellung von [(C2H5)2NH2]3[PS3F]F und [(C2H5)2NH2]3[PS2SeF]F und Kristallstruktur der selenhaltigen Phase

Preparation of [(C₂H₅)₂NH₂]₃[PS₃F]F and [(C₂H₅)₂NH₂]₃ [PS₂SeF]F and Crystal structure of the Phase with Selenium The title compounds were prepared by reaction of diethylammon ium-trithiophosphite with fluoride ions (as diethylammonium fluoride) and sulfur and selenium, respectively. The crystal structure of the selenium containing phase was determined. It does not represent a phosphoranate with a [PS₂SeF₂]^3? anion, but a double salt of [PS₂SeF]^2? with F^?.     

Syntheses,Crystal Structures,and Properties of New Ternary Chalcogenides of Group 4 Metals: Rb4Ti3S14, Cs4Zr3S14, K4Hf3Se14, and K4ZrHf2Se14

The new ternary compounds Rb₄Ti₃S₁₄, Cs₄Zr₃S₁₄, K₄Hf₃Se₁₄, and K₄ZrHf₂Se₁₄ were prepared by reacting the respective transition metals in alkali metal polychalcogenide melts. Two crystallographically independent transition metal cations are present that are coordinated by eight chalcogen atoms (Q) in an irregular fashion or by seven chalcogen atoms yielding a distorted pentagonal bipyramid. The M(1)Q₈ and M(2)Q₇ polyhedra are connected by sharing common edges or trigonal faces leading to the formation of infinite linear one‐dimensional anionic chains running parallel to the [101] direction. The chains are separated by alkali metal cations. The optical band gaps determined are 1.59 eV for Rb₄Ti₃S₁₄, 2.35 eV for Cs₄Zr₃S₁₄, and 2.02 eV for K₄Hf₃Se₁₄. In‐situ X‐ray powder diffractometry demonstrates that Rb₄Ti₃S₁₄ decomposes at 430 °C into Rb₂S₅ and TiS. During the cooling cycle the re‐formation of the polysulfide is observed. According to this result the polysulfide could be prepared using TiS instead of metallic Ti as well.     

Mass spectrometric fragmentation of saturated six membered heterocyclic systems containing two chalcogen family atoms

The mass spectra of six-membered saturated heterocycles containing oxygen, sulphur, selenium and tellurium in the 1,4-positions have been measured. The differing fragmentation modes have been characterized using high resolution, low voltage and metastable ion scan techniques. The important decomposition reactions of the molecular ions involve elimination of C₂H₄ and CH₂X (X is a chalcogen atom) and formation of [C₂H₄X]⁺ and C₂H₅⁺. The propensities of these reactions vary systematically as a function of the ability of the chalcogen to stabilize a positive charge.     

Synthesis and characterization of chalcogen (S and Se) derivatives of 4-chloro- and 4-methoxy-N,N-diisopropylpyridine-2-carboxamide: X-ray structure of 4-methoxy-3-(sulfanylmethyl)- and 4-chloro-3-(selenenylbenzyl)-N,N-diisopropylpyridine-2-carboxamide

Synthesis of chalcogen (S and Se) derivatives of 4-chloro- and 4-methoxy-N,N-diisopropylpyridine-2-carboxamide (1a and 1b respectively) has been reported. 1a and 1b were lithiated with 2 equiv. of n-BuLi or LDA at ?78 °C. Addition of elemental sulfur or selenium to the carbanion led to the formation of corresponding thiolate or selenolate anions respectively. The selenolate anions were aerial oxidized to afford the corresponding diselenides. The thiolate/selenolate anions were quenched with a variety of electrophiles to give unsymmetrical thio/selenoalkanes in moderate to good yields. Reductive cleavage of Se–Se bond has also been studied. The synthesized compounds were characterized by elemental analysis, NMR (¹H, ¹³C and ⁷⁷Se), FT-IR and mass spectral techniques. Crystal structures of two compounds, 6b and 7a, were determined by single crystal X-ray crystallography. Their crystal structure exhibits 1,4-type S?OCH₃ and Se?Cl intramolecular secondary interactions respectively. The relative thermal stability of 3a, 3b and 4a has also been established by thermogravimetric analysis.     

Crystal chemistry,magnetic, and electrical properties of hexagonal plutonium oxide chalcogenides: Pu2O2X, X = O,S, Se

A study was made of the influence of the chalcogen X on the magnetic and electrical properties of Pu₂O₂X (X = O, S, Se) compounds and on bonding in these hexagonal compounds, isostructural with the corresponding rare-earth compounds. The comparison of the cell volumes of Nd₂O₂X and Pu₂O₂X compounds showed that the Pu³⁺ crystal radius decreased from β-Pu₂O₃ to Pu₂O₂Se as “5f delocalization” and 5f-p overlap increased. These plutonium compounds were all found to be antiferromagnetic. This was caused by superexchange coupling interactions via p orbitals of the oxygen and chalcogen ions. The Néel temperature increased from β-Pu₂O₃ (26 K) to Pu₂O₂S (28 K) then to Pu₂O₂Se (34 K) showing that 5f-p covalency was enhanced as the chalcogen electronegativity decreased and the p radial extent increased. The hexagonal β-Pu₂O₃ was found to be an insulator while both other compounds were semiconductors with gaps around 0.5 eV. These gaps were interpreted as the energy separation between the 6d-7s conduction band and the np band of the chalcogen X with some overlap of the occupied 5f states and the np band. A simple electron band scheme of these compounds is proposed on such assumptions.     

Reactions of chloromethyloxirane and dihalopropanols with chalcogens in basic reducing systems

Chloromethyloxirane and 2,3-dibromopropan-1-ol reacted with a solution of selenium or tellurium in the system hydrazin hydrate-potassium hydroxide (K₂Se₂, K₂Te₂) to give allyl alcohol; the reaction was accompanied by regeneration of the initial free chalcogen. 1,3-Dichloropropan-2-ol reacted with selenium in the same system to give oligomeric product having a 2-hydroxypropane-1,3-diyldiseleno monomeric unit, while the reaction with tellurium led to the formation of allyl alcohol and almost complete regeneration of initial tellurium. Probable reaction mechanisms are discussed. Polyselenide oligomers containing a hydroxy group in a monomeric unit were formed in reactions of chloromethyloxirane and 1,3-dichloropropan-2-ol with selenium in the system hydrazine hydrate-2-aminoethanol. Under analogous conditions 2,3-dibromopropan-1-ol was converted into allyl alcohol with regeneration of elemental selenium. Reductive cleavage of polyselenide oligomers gave Se-methyl derivatives of 2-hydroxypropane-1,3-diselenol.     

Cobalt Chalcogenide Clusters. Synthesis,Characterization and DFT Calculations of [Co4Se2(CO)10] and [Co4Te2(CO)11]. Crystal Structure of [Co8Se4(CO)16(μ‐dppa)2]

The reactions of [Co₂(CO)₈] with E(SiMe₃)₂ (E = Se, Te) in CH₂Cl₂ result in the formation of the compounds [Co₄Se₂(CO)₁₀]> ( 1 ) and [Co₄Te₂(CO)₁₁] ( 2 ), respectively. Both cluster complexes have similar molecular structures in which the cobalt atoms form four‐membered rings with μ₄‐bridging chalcogen atoms (Se and Te) above and below the plane of the metal atoms and the carbonyl ligands as either terminal or μ₂‐bridging ligands. DFT‐calculations for both compounds have been carried out in order to obtain some more information about their electronic distribution. In the presence of the phosphine Ph₂PC≡CPPh₂ (dppa), the reaction of [Co₂(CO)₈] with Se(SiMe₃)₂ leads to the formation of [Co₈Se₄(CO)₁₆(μ‐dppa)₂] ( 3 ). During the reaction two molecules of [Co₂(CO)₈] have been added to the acetylene groups of the dppa ligands, whilst the remaining cobalt atoms coordinate to the phosphorus atoms of the phosphine. In this compounds the selenium atoms act as μ₃‐ligands, bridging the metal atoms bonded to the phosphorus with those bonded to the acetylene groups.     

CuClSe1.53Te0.47 and CuClSe0.56Te1.44: Structural and Vibrational Spectroscopic Investigations on Copper(I) Chalcogen Chlorides

CuClSe_1.53Te_0.47 and CuClSe_0.56Te_1.44 are obtained from the reaction of CuCl, Se, and Te in stoichiometric amounts. Both copper(I) selenium tellurium chlorides are monoclinic, space group P2₁/n (no. 14) with lattice constants of a = 7.837(1) Å, b = 4.699(1) Å, c = 10.762(2) Å, β = 104.37(2)°, V = 383.9(1) ų (CuClSe_1.53Te_0.47), and a = 8.074(1) Å, b = 4.830(1) Å, c = 10.973(1) Å, β = 103.87(2)°, V = 415.5(1) ų (CuClSe_0.56Te_1.44), and Z = 4. A common feature of these isostructural compounds are heteroatomic strands [YY'] (Y, Y' = chalcogen). These strands are running along [010] and are connected to layers by chains [CuCl]. Vibrational spectra of CuClSe_1.53Te_0.47, CuClSe_0.56Te_1.44, CuXTe₂ and CuX'Se₂ (X = Cl, Br, I; X' = Cl, Br) are analysed with respect to the bonding relations of the chalcogen chains. Modes derived from IR and Raman spectra are assigned by correlation with tri gonal Se and related copper(I) chalcogen halides. Both, X‐ray structural data and an analysis of the chalcogen vibrational modes in IR and Raman spectra, lead to a detailed insight into the ordering phenomena of the chalcogen chains in this type of copper(I) chalcogen halides.     

Alkalimanganselenide und -telluride A2Mn3X4 – Synthese,Kristall- und Spinstruktur

Alkali Metal Manganese Selenides and Tellurides – Synthesis, Crystal and Spin Structures The compounds Rb₂Mn₃Se₄, Cs₂Mn₃Se₄, Rb₂Mn₃Te₄ and Cs₂Mn₃Te₄ were synthesized by the reaction of alkali metal carbonates with chalcogen and Mn or MnCO₃ in a stream of hydrogen charged with chalcogen. Structural investigations show that all compounds crystallize in isotypic atomic arrangements (Cs₂Mn₃S₄-type, space group Ibam, Z = 4). Additionally neutron diffraction experiments were carried out and yielded the spin structures of Rb₂Mn₃Se₄ and Cs₂Mn₃Se₄ (Shubnikov space group Ibam'). The structural related selenides ALiMnSe₂ and ALiZnSe₂ (A = K, Rb or Cs) were synthesized by analogous reactions. All these compounds are isotypic and crystallize in the BaZn₂P₂-structure type.     

Syntheses,Structures, and Reactivities of Two Chalcogen‐Stabilized Carbones

Electronic effects on the central carbon atom of carbone, generated by the replacement of the S^IV ligand of carbodisulfane (CDS) with other chalcogen ligands (Ph₂E, E=S or Se), were investigated. The carbones Ph₂E→C←SPh₂(NMe) [E=S( 1 ) or Se( 2 )] were synthesized from the corresponding salts, and their molecular structures and electronic properties were characterized. The carbone 2 is the first carbone containing selenium as the coordinated atom. DFT calculations revealed the electronic structures of 1 and 2 , which have two lone pairs of electrons at the carbon center. The trend in HOMO energy levels, estimated by cyclic voltammetry measurements, for the carbones and CDS follows the order of 2 > 1 >CDS. Analysis of a doubly protonated dication and trication complex revealed that the central carbon atom of 2 behaves as a four‐electron donor.