X-ray absorption spectroscopy of transition-metal trichalcogenides

The sulfur K and metal L_III absorption spectra of transition-metal trichalcogenides (TMTC's) were measured. The matrix element effect plays an important role in these spectra. It was considered that the structures up to 5 eV above the absorption edge reflect the chalcogen antibonding band, the metal nonbonding d_z² band, and the metal d bands, and that the higher energy structures are derived from the metal s and p bands. The chalcogen antibonding band arises from chalcogen pairing and the metal d, s, and p bands are the mixture bands with chalcogen p orbitals. Evidence that shows that the lowest conduction band of the group IV TMTC's is the chalcogen antibonding band is presented. The overlap of the metal d and metal s bands is promoted by increasing the atomic number of chalcogen atoms.     

Supramolecular Wiring of Benzo‐1,3‐chalcogenazoles through Programmed Chalcogen Bonding Interactions

The high‐yielding synthesis of 2‐substituted benzo‐1,3‐tellurazoles and benzo‐1,3‐selenazoles through a dehydrative cyclization reaction has been reported, giving access to a large variety of benzo‐1,3‐chalcogenazoles. Exceptionally, these aromatic heterocycles proved to be very stable and thus very handy to form controlled solid‐state organizations in which wire‐like polymeric structures are formed through secondary N???Y bonding interactions (SBIs) engaging the chalcogen (Y=Se or Te) and nitrogen atoms. In particular, it has been shown that the recognition properties of the chalcogen centre at the solid state could be programmed by selectively barring one of its σ‐holes through a combination of electronic and steric effects exerted by the substituent at the 2‐position. As predicted by the electrostatic potential surfaces calculated by quantum chemical modelling, the pyridyl groups revealed to be the stronger chalcogen bonding acceptors, and thus the best ligand candidate for programming the molecular organization at the solid state. In contrast, the thiophenyl group is an unsuitable substituent for establishing SBIs in this molecular system as it gives rise to chalcogen–chalcogen repulsion. The weaker chalcogen donor properties of the Se analogues trigger the formation of feeble N???Se contacts, which are manifested in similar solid‐state polymers featuring longer nitrogen–chalcogen distances.     

Homoleptic pnictogen-chalcogen coordination complexes

The synthesis and structural characterization of dicationic selenium and tellurium analogues of the carbodiphosphorane and triphosphenium families of compounds are reported. These complexes, [Ch(dppe)][OTf](2) [Ch = Se, Te; dppe = 1,2-bis(diphenylphosphino)ethane; OTf = trifluoromethanesulfonate], are formed using [Ch](2+) reagents via a ligand-exchange protocol and represent extremely rare examples of homoleptic pnictogen → chalcogen coordination complexes. The corresponding arsenic compounds were also prepared, [Ch(dpAse)][OTf](2) [Ch = Se, Te; dpAse = 1,2-bis(diphenylarsino)ethane], exhibiting the first instance of an arsenic → chalcogen dative bond. The electronic structures of these unique compounds were determined and compared to previously reported chalcogen dications.     

Chalcogen Bonding: An Overview

In the last few decades, “unusual” noncovalent interactions like anion‐π and halogen bonding have emerged as interesting alternatives to the ubiquitous hydrogen bonding in many research areas. This is also true, to a somewhat lesser extent, for chalcogen bonding, the noncovalent interaction involving Lewis acidic chalcogen centers. Herein, we aim to provide an overview on the use of chalcogen bonding in crystal engineering and in solution, with a focus on the recent developments concerning intermolecular chalcogen bonding in solution‐phase applications. In the solid phase, chalcogen bonding has been used for the construction of nano‐sized structures and the self‐assembly of sophisticated self‐complementary arrays. In solution, until very recently applications mostly focused on intramolecular interactions which stabilized the conformation of intermediates or reagents. In the last few years, intermolecular chalcogen bonding has increasingly also been exploited in solution, most notably in anion recognition and transport as well as in organic synthesis and organocatalysis.     

H2XP…SHY复合物中磷键与硫键的理论研究

用从头算量子化学方法MP2 与CCSD(T)研究了H₂XP和SHY (X, Y=H, F, Cl, Br)分子的P与S之间形成的磷键X―P…S与硫键Y―S…P的本质与规律以及取代基X与Y对成键的影响. 计算结果表明, 硫键比磷键强, 连接在Lewis 酸上的取代基的电负性增大导致形成的磷键或硫键增强, 键能增大, 对单体的结构和性质的影响也增大; 而连接在Lewis 碱上的取代基效应则相反. 硫键键能为8.37-23.45 kJ·mol^-1, 最强的硫键结构是Y 电负性最大而X 电负性最小的HFS…PH₃, CCSD(T)计算的键能是16.04 kJ·mol^-1; 磷键键能为7.54-14.65 kJ·mol^-1, 最强的磷键结构是X 电负性最大而Y 电负性最小的H₂FP…SH₂, CCSD(T)计算的键能是12.52 kJ·mol^-1. 对磷键与硫键能量贡献较大的是交换与静电作用. 分子间超共轭lp(S)-σ^*(PX)与lp(P)-σ^*(SY)对磷键与硫键的形成起着重要作用, 它导致单体的极化, 其中硫键的极化效应较大, 从而有一定的共价特征.     

Activating Chalcogen Bonding (ChB) in Alkylseleno/Alkyltelluroacetylenes toward Chalcogen Bonding Directionality Control

Activation of a deep electron-deficient area on chalcogen atoms (Ch=Se, Te) is demonstrated in alkynyl chalcogen derivatives, in the prolongation of the (C≡)C−Ch bond. The solid-state structures of 1,4-bis(methylselenoethynyl)perfluorobenzene ( 1Se ) show the formation of recurrent chalcogen-bonded (ChB) motifs. Association of 1Se and the tellurium analogue 1Te with 4,4′-bipyridine and with the stronger Lewis base 1,4-di(4-pyridyl)piperazine gives 1:1 co-crystals with 1D extended structures linked by short and directional ChB interactions, comparable to those observed with the corresponding halogen bond (XB) donor, 1,4-bis(iodoethynyl)-perfluorobenzene. This “alkynyl” approach for chalcogen activation provides the crystal-engineering community with efficient, and neutral ChB donors for the elaboration of supramolecular 1D (and potentially 2D or 3D) architectures, with a degree of strength and predictability comparable to that of halogen bonding in iodoacetylene derivatives.     

Chalcogen-Bond-Induced Double Helix Based on Self-Assembly of a Small Planar Building Block

As a rule, helical structures at the molecular level are formed by non-planar units. This makes the design of helices, starting from planar building blocks via self-assembly, even more fascinating. Until now, however, this has only been achieved in rare cases, where hydrogen and halogen bonds were involved. Here, we show that the carbonyl-tellurium interaction motif is suitable to assemble even small planar units into helical structures in solid phase. We found two different types of helices: both single and double helices, depending on the substitution pattern. In the double helix, the strands are connected by additional Te⋅⋅⋅Te chalcogen bonds. In the case of the single helix, a spontaneous enantiomeric resolution occurs in the crystal. This underlines the potential of the carbonyl-tellurium chalcogen bond to generate complex three-dimensional patterns.     

Quantifying the Bonding Strength of Gold‐Chalcogen Bonds in Block Copolymer Systems

Gold‐chalcogen interactions are ubiquitous in gold biological and medicinal systems. Understanding the nature of these interactions can provide the basis for regulating their structures and functionalities, and a reasonable way to interpret the differences in various properties. However, the relative strength of gold‐chalcogen bonds remains controversial, and the conclusions of many related works are inconsistent. Thus, in this work, we successfully quantified the relative strength of Au‐X (X=S, Se, and Te from chalcogenide‐containing A‐B‐A type block copolymers) interactions at the single‐molecule level through single‐molecule force spectroscopy (SMFS) from a kinetic point of view and quantum chemical studies from a thermodynamic point of view. Both sets of results suggested that the strength of the Au‐X bonds decreases as Au‐Te>Au‐Se>Au‐S. Our findings unveiled the relative strength and nature of gold‐chalcogen interactions, which may help expand their application in electronics, catalysis, medicine and many other fields.     

Non-Classical Synthons: Supramolecular Recognition by S⋅⋅⋅O Chalcogen Bonding in Molecular Complexes of Riluzole

Classical examples of supramolecular recognition units or synthons are the ones formed by hydrogen bonds. Here, we report the ubiquity of a S⋅⋅⋅O chalcogen bonded synthon observed in a series of supramolecular complexes of the amyotrophic lateral sclerosis drug riluzole. Although the potential of higher chalcogens such as Se and Te to form robust and directional chalcogen bonded motifs is known, intermolecular sulfur chalcogen bonding is considered to be weak owing to the lower polarizability of S atoms. Here, the robustness and electronic nature of a S⋅⋅⋅O chalcogen bonding non-classical synthon, and the origin of its exceptional directionality have been explored. Bond orders of the drug–coformer chalcogen bonding are found to be as high as one third of a single bond, and they are largely ionic in nature. The contribution of the S⋅⋅⋅O chalcogen bonded motifs to the lattice energies of a series of crystals from the Cambridge Structural Database has been analyzed, showing they can be indeed significant, especially in molecules devoid of strong hydrogen bond donor groups.     

Charge-Assisted Chalcogen Bonds: CSD and DFT Analyses and Biological Implication in Glucosidase Inhibitors

This study reports a combined Cambridge Structural Database and theoretical DFT study of charge assisted chalcogen bonds involving sulfonium, selenonium, and telluronium cations. The chalcogen bond has been recently defined by IUPAC as the net attractive interaction between an electrophilic region associated with a chalcogen atom in a molecular entity and a nucleophilic region in another, or the same, molecular entity. Divalent chalcogen atoms typically have up to two σ-holes and forms up to two ChBs; the same holds for tetravalent chalcogens which adopt a seesaw arrangement. In sulfonium, selenonium, and telluronium salts chalcogen atoms form three covalent bonds, three σ-holes are located opposite to these bonds, and up to three charge assisted ChBs can be formed between these holes and the counterions. The covalent bond arrangement around these chalcogen atoms is similar to trivalent pnictogen atoms and translates into a similar pattern of noncovalent interactions. We have found and studied this type of charge-assisted chalcogen bonds in various sulfonium ion-containing inhibitors of glucosidase, for example, salacinol and kotalanol.     

Methane oxidative carbonylation catalyzed by rhodium chalcogen halides over carbon supports

Gas phase carbonylation of methane is studied in the presence of molecular oxygen over pure carbon carriers and carbon supported rhodium chalcogen halides. Activated carbons and fullerene blacks have been used as carbon supports. XPS and IR-spectroscopy data show the formation of rhodium chalcogen halides in solids prepared by different methods. We have found that the productivity of acetic acid by carbon supported rhodium chalcogen halides depends strongly on the carbon carrier and the method of the catalyst preparation. Namely, the catalyst with highest productivity for the acetic acid is prepared by synthesizing the rhodium chalcogen halide over the carbon support followed by thermal destruction. We have also found that rhodium chalcogen halides over activated carbons are more active compared with fullerene supported catalysts.     

The RhX n (X = S,Se, Te) Coordination Polyhedra in Crystal Structures

The Voronoi–Dirichlet polyhedra (VDP) and the method of intersecting spheres were applied to crystal-chemical analysis of all known compounds whose structures contain rhodium atoms surrounded by chalcogen atoms. The influence of the rhodium valence state and the nature of the chalcogen on the main features of Rh stereochemistry are discussed. Rhodium atoms exhibit coordination numbers of 6, 5, or 4 with respect to S, Se, or Te atoms; in addition to the bonds with chalcogens, rhodium can form 1 to 4 bonds with metal atoms. The VDP volume for Rh(III), Rh(2.67), and Rh(II) atoms in selenides and tellurides very weakly depends on the valence state, whereas in the case of sulfides, the volume increases rather regularly with a decrease in the metal oxidation number from Rh(III) to Rh(I).     

New Forms and Functions of Tellurium: From Polycations to Metal Halide Tellurides

Metal chalcogenides and metal chalcogenide halides are distinguished by their structural diversity and by their very different physical properties. Therefore, the synthesis of novel compounds from this class is always a rewarding goal for the preparatively oriented solid-state chemist. Over the past few years, many syntheses and structural investigations have stimulated the field. The emphasis of the research has been placed on selenium-rich and tellurium-rich compounds, which are characterized by directed covalent bonds between the chalcogen atoms. Compounds with novel chalcogen polycations have also become accessible during the past few years by reacting the chalcogen elements with transition metal halides, or from chemical vapor deposition in the sense of chemical transport reactions. In these compounds, tellurium differs from its lighter homologues by a pronounced tendency towards greater covalence. This article attmepts to provide an overview of new developments in the field of compounds with chalcogen polycations and of metal chalcogenide halides, with an emphasis on compounds containing molybdenum and tungsten as the transition metals and tellurium as the chalcogen.     

Ladder distyrylbenzenes with silicon and chalcogen bridges: synthesis, structures, and properties

[reaction: see text] A cascade-type anionic double cyclization of (o-silylphenyl)(o-halophenyl)acetylenes via lithiation followed by treatment with elemental chalcogen produces silicon and chalcogen-bridged stilbenes. Based on this reaction, a series of silicon and sulfur- or silicon and selenium-bridged ladder distyrylbenzenes have been synthesized. Their chemical modification by oxidation, crystal structures, and photophysical properties are described.     

Synthesis of Dibenzochalcogenaborins and Systematic Comparisons of Their Optical Properties by Changing a Bridging Chalcogen Atom

Novel hetero‐π‐conjugated compounds (dibenzochalcogenaborins) with the same molecular framework, bearing a boron atom as an acceptor and chalcogen atoms as a donor, were synthesized, and systematic comparisons among these molecules were performed. X‐ray crystallographic analysis of these molecules showed similar structures with high planarity. UV/Vis spectroscopy and theoretical calculations revealed that the absorption maxima and the HOMO–LUMO gap changed by systematically changing the bridging chalcogen atom. Dibenzooxaborin and dibenzothiaborin showed fluorescence emission both in solution and in the solid state with a small Stokes shift, indicating the high rigidity of these compounds. On the other hand, dibenzoselenaborin exhibited a very weak fluorescence as a result of the heavy atom effect.     

硫键：从概念形成到实际应用

早期含硫键物质的合成和硫键结构的发现为硫键概念形成奠定了基础。20世纪90年代以来,对硫族原子亲电性和亲核性的探索使人们对硫键的本质有了深刻的认识,促使了硫键概念的形成。此后,化学家分别于2002年和2010年开发了硫键超分子自组装和阴离子识别功能,并开始重视硫键在固体和溶液中的应用。随着对新型分子间作用力关注度的提高,硫键会越来越受到人们的重视,其应用也会有更广阔的前景。     

Synthesis, structure, and spectroelectrochemical investigation of novel ternary Co/S(Se)/Sn clusters derived from binary cobalt stannanediyl complexes

The synthesis and structure of heterobimetallic Co/Sn complexes [(eta5-CpR)Co-Sn[CH(SiMe3)2]2] (CpR = C5Me5 2; C5EtMe4 3) are described. Insertion reactions of sulfur and selenium into the unbridged heteronuclear Co-Sn bonds of 1, 2, and 3 (R= H5 1, Me5 2, EtMe4 3) have been studied. Depending on the stoichiometry of the chalcogen element used, novel ternary Sn-chalcogen-Co clusters (8, 9, 15, and 16) can be synthesized, and their molecular structures, which represent rare examples of crystallographically characterized cases of ternary transition metal/chalcogen/tin complexes, have been determined. Electrochemistry shows that complexes 8 and 9 are able to support reversibly either the removal or addition of one electron. Insertion of a further (Cp)Co-E (E = chalcogen) fragment significantly affects the electron distribution and causes complexes 9 and 16 to undergo two consecutive one-electron oxidations. The EPR spectra of the respective monocations have been recorded. In all cases, the unpaired electron strongly interacts with the cobalt nucleus(i), thus testifying that the main contribution to the relevant HOMO orbitals comes from the cobalt atom(s).     

Walking Down the Chalcogenic Group of the Periodic Table: From Singlet to Triplet Organic Emitters

The synthesis, X‐ray crystal structures, ground‐ and excited‐state UV/Vis absorption spectra, and luminescence properties of chalcogen‐doped organic emitters equipped on both extremities with benzoxa‐, benzothia‐, benzoselena‐ and benzotellurazole ( 1_X and 2_X ) moieties have been reported for the first time. The insertion of the four different chalcogen atoms within the same molecular skeleton enables the investigation of only the chalcogenic effect on the organisation and photophysical properties of the material. Detailed crystal‐structure analyses provide evidence of similar packing for 2_O – 2_Se , in which the benzoazoles are engaged in π–π stacking and, for the heavier atoms, in secondary X???X and X???N bonding interactions. Detailed computational analysis shows that the arrangement is essentially governed by the interplay of van der Waals and secondary bonding interactions. Progressive quenching of the fluorescence and concomitant onset of phosphorescence features with gradually shorter lifetimes are detected as the atomic weight of the chalcogen heteroatom increases, with the tellurium‐doped derivatives exhibiting only emission from the lowest triplet excited state. Notably, the phosphorescence spectra of the selenium and tellurium derivatives can be recorded even at room temperature; this is a very rare finding for fully organic emitters.     

Catalysis with Chalcogen Bonds

Herein, we introduce catalysts that operate with chalcogen bonds. Compared to conventional hydrogen bonds, chalcogen bonds are similar in strength but more directional and hydrophobic, thus ideal for precision catalysis in apolar solvents. For the transfer hydrogenation of quinolines and imines, rate enhancements well beyond a factor of 1000 are obtained with chalcogen bonds. Better activities with deeper σ holes and wider bite angles, chloride inhibition and correlation with computed anion binding energies are consistent with operational chalcogen bonds. Comparable to classics, such as 2,2′‐bipyrroles or 2,2′‐bipyridines, dithieno[3,2‐b;2′,3′‐d]thiophenes (DTTs), particularly their diimides, but also wide‐angle cyclopentadithiazole‐4‐ones are identified as privileged motifs to stabilize transition states in the focal point of the σ holes on their two co‐facial endocyclic sulfur atoms.     

Preparation, structure, and amphoteric redox properties of p-phenylenediamine-type dyes fused with a chalcogenadiazole unit.

4,7-Bis(dialkylamino)benzo[c][1,2,5]chalcogenadiazoles are a novel class of organic dyes that undergo reversible two-stage one-electron oxidation as well as one-electron reduction. They exhibit absorption maxima in the long-wavelength region, which are assigned as intramolecular charge transfer bands from the phenylenediamine moiety to the electron-accepting heterocycle. Their redox properties as well as molecular and crystal structures are affected by the alkyl substituents on the amino nitrogen and/or by the chalcogen atom (O, S, Se) in the heterocycle.