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At least 19 recordsLinked to original sources
PubMed2003

Resonance-assisted intramolecular chalcogen-chalcogen interactions?

High-level B3LYP/6-311+G(3df,2p) density functional calculations have been carried out for a series of saturated chalcogenoaldehydes: CH(X)-CH(2)-CH(2)YH (X, Y=O, S, Se, Te). Our results indicate that in CH(X)-CH(2)-CH(2)YH (X=Y=O, S, Se) the X-H...X intramolecular hydrogen bond (IHB) competes in strength with the X...XH chalcogen-chalcogen interaction, while the opposite is found for the corresponding tellurium-containing analogues. For those derivatives in which X does not equal Y, X being the more electronegative atom, the situation is more complicated due to the existence of two non-equivalent X-H and Y-H tautomers. The Y-H tautomer is found to be lower in energy than the X-H tautomer, independently of the nature of X and Y. For X=O, S, Se and Y=S, Se the most stable conformer b is the one exhibiting a Y-H...X IHB. Conversely when Y=Te, the chelated conformer d, stabilized through a X...YH chalcogen-chalcogen interaction is the global minimum of the potential energy surface. Systematically the IHB and the chalcogen-chalcogen interactions observed for saturated compounds are much weaker than those found for their unsaturated analogues. This result implies that the nonbonding interactions involving chalcogen atoms, mainly Se and Te, are not always strongly stabilizing. This conclusion is in agreement with the fact that intermolecular interactions between Se and Te containing systems with bases bearing dative groups are very weak. We have also shown that these interactions are enhanced for unsaturated compounds, through an increase of the charge delocalization within the system, in a mechanism rather similar to the so call Resonance Assisted Hydrogen Bonds (RAHB). The chalcogen-chalcogen interactions will be also large, due to the enhancement of the X-->Y dative bond, if the molecular environment forces the interacting atoms X and Y to be close each other.

Chalcogens↗
PubMed2002

The role of chalcogen-chalcogen interactions in the intrinsic basicity acidity of beta-chalcogenovinyl(thio)aldehydes HC([double bond]X)[bond]CH[double bond]CH[bond]CYH.

The intrinsic acidity and basicity of a series of beta-chalcogenovinyl(thio)aldehydes HC([double bond]X)[bond]CH[double bond]CH[bond]CYH (X=O, S; Y=Se, Te) were investigated by B3LYP/6-311+G(3df,2p) density functional and G2(MP2) calculations on geometries optimized at the B3LYP/6-31G(d) level for neutral molecules and at the B3LYP/6-31+G(d) level for anions. The results showed that selenovinylaldehyde and selenovinylthioaldehyde should behave as Se bases in the gas phase, because the most stable neutral conformer is stabilized by an X[bond]H...Se (X=O, S) intramolecular hydrogen bond (IHB). In contrast the Te-containing analogues behave as oxygen or sulfur bases, because the most stable conformer is stabilized by typical X...Y[bond]H chalcogen-chalcogen interactions. These compounds have a lower basicity than expected because either chalcogen-chalcogen interactions or IHBs become weaker upon protonation. Similarly, they are also weaker acids than expected because deprotonation results in a significantly destabilized anion. Loss of the proton from the X[bond]H or Y[bond]H groups is a much more favorable than from the C[bond]H groups. Therefore, for Se compounds the deprotonation process results in loss of the X[bond]H...Se (X=O, S) IHBs present in the most stable neutral conformer, while for Te-containing compounds the stabilizing X...Y[bond]H chalcogen-chalcogen interaction present in the most stable neutral conformer becomes repulsive in the corresponding anion.

Journal Article↗
PubMed2006

Theoretical investigations on chalcogen-chalcogen interactions: what makes these nonbonded interactions bonding?

To understand the intermolecular interactions between chalcogen centers (O, S, Se, Te), quantum chemical calculations on pairs of model systems were carried out. For the oxygen derivatives, one of the components of the supermolecules consists of dimethyl ether, while the second component is either dimethyl ether (1) or ethynyl methyl ether (2) or methyl cyanate (3). The model calculations were also extended to the sulfur (4-6), selenium (7-9), and tellurium congeners (10-12). The MP2/SDB-cc-pVTZ, 6-311G level of theory was used to derive the geometrical parameters and the global energies of the model systems. A detailed analysis based on symmetry adapted perturbation theory (SAPT) reveals that induction and dispersion forces contribute to the bonding in each case. For 1-3 the electrostatic energy also contributes to the intermolecular bonding, but not for 4-12. The NBO analysis reveals that the interaction in the dimers 1-3 is mainly due to weak hydrogen bonding between methyl groups and chalcogen centers. Similar hydrogen bonding is also found in the case of 4 and to a lesser extent in 5 and 7. For the aggregates with heavier centers the chalcogen-chalcogen interaction dominates, and hydrogen bonding only plays a minor role. Electron-withdrawing groups on the chalcogen centers increase the interaction energy and reduce the intermolecular distance dramatically. The one-electron picture of an interaction between the lone pair of the donor and the chalcogen carbon sigma orbital allows a qualitatively correct reproduction of the observed trend.

Journal Article↗
PubMed2003

A world beyond hydrogen bonds? -Chalcogen-chalcogen interactions yielding tubular structures.

It is shown that tubular structures arise in the solid state through close chalcogen-chalcogen (X...X) contacts. As examples a variety of cyclic systems containing sulfur and selenium centers is presented. Common to all of them are close contacts between the chalcogen centers of neighboring stacks giving rise to a zigzag or ladder-type arrangement. In the case of cyclic systems of ring size 24-33 the resulting tubes are able to include hydrocarbons as guest molecules. For 2,7-ditelluraocta-3,5-diyne (17) the close contacts between the tellurium centers of the acyclic C(2) symmetric building blocks generate a helical arrangement in which n-hexane was included. The favored X...X contacts can be traced back to np(X)-sigma*(X[bond]C) interactions.

Biomimetic Materials↗
PubMed2007

Activation of the disulfide bond and chalcogen-chalcogen interactions: an experimental (FTICR) and computational study.

Dimethyldisulfide (I) is the simplest model of the biologically relevant family of disubstituted disulfides. The experimental study of its gas-phase protonation has provided, we believe for the first time, a precise value of its gas-phase basicity. This value agrees within 1 kJ mol-1 with the results of G3 calculations. Also obtained for the first time was the reaction rate constant for the bimolecular reaction between I and its protonated form, IH+, to yield methanethiol and a dimethyldithiosulfonium ion. This constant is of the order of magnitude of the collision limit. A computational mechanistic study based on the energetic profile of the reaction, completed with Fukui's and Bader's treatments of the reactants and transition states fully rationalizes the regioselectivity of the reaction as well as the existence of a shallow, flat Gibbs energy surface for the reaction. The mechanistic relevance of the chalcogen-chalcogen interaction and the C--H...S bonds has been demonstrated.

Algorithms↗
PubMed2004

Chalcogen-chalcogen bonds in edge-sharing square-planar d8 complexes. Are they possible?

A theoretical study of the formation of X-X bonds in complexes with the general formula [M(2)(mu-X)(2)L(4)] (M = group 10 and X = group 16 elements) having d(8) transition-metal atoms is presented. The existence of two energy minima for some complexes, with short and long X-X distances, is shown by density functional theory calculations, and the factors responsible for it are analyzed, including a strong influence of the nature of the metals and ligands on the relative stability of the two isomers. The influence of the bite angle of chelating terminal ligands and the nature of the donor atom on the relative stabilities of the two isomers are also discussed.

Journal Article↗
PubMed2003

Cyclization triggered by deprotonation: the gas-phase acidity of 1,8-chalcogen-bridged naphthalenes.

High-level density functional theory computations have been used to estimate the gas-phase (intrinsic) acidities of the complete series of 1,8-chalcogen-bridged naphthalene derivatives. The existence of a chalcogen-chalcogen bond in chalcogen-bridged naphthalene derivatives plays a crucial role in the intrinsic acidity of the system. For 1,8-naphthalenedilylbis(oxy), where this bond does not exist, the para C-H group is the most acidic site, whereas for the remaining compounds, deprotonation of the ortho CH groups is the most favorable process. Deprotonation of the aromatic rings has a large effect on the strength of the bonds of the five-membered ring. These effects depend on the nature of the heteroatoms forming the X-Y bridge, and modulate the acidity of the molecule. Also importantly, when one of the heteroatoms is oxygen, ortho and para deprotonation lead to cleavage of the X-Y bridge. This bond fission favors the formation of a CYC (Y = S, Se, Te) three-membered ring that enhances the stability of the anion and, therefore, increases the acidity of these compounds. We have shown that, whereas this cyclization process is energetically favorable for oxygen-containing compounds, it is not favorable for the remaining derivatives.

Journal Article↗
PubMed1997

Mononuclear Molybdenum(IV) Complexes with Two Multiply Bonded Chalcogen Ligands in Trans Configuration and Chelating Biphosphine Ligands.

A series of molybdenum(IV) complexes of the type trans-Mo(Q)(Q')(P&arcraise;P)(2) has been prepared where Q and Q' are chalcogen ligands (O, S, Se, Te) and P&arcraise;P is either cis-1,2-bis(diphenylphosphino)ethylene (dppee) or 1,2-bis(diphenylphosphino)ethane (dppe). X-ray crystallographic studies were carried out to investigate how the Mo-Q distance is influenced by the mutually competitive d(pi)-p(pi) interactions between the p(x)() and p(y)() orbitals of the chalcogen ligands and the d(xz)() and d(yz)() orbitals of the molybdenum center. trans-Mo(O)(2)(dppee)(2) (1) has been prepared by the hydrolysis and deprotonation reaction of [Mo(O)(Cl)(dppee)(2)]Cl with NaOH in methanol. The compounds where Q represents the heavier chalcogens (S, Se, Te) have been prepared by the reaction between trans-Mo(N(2))(2)(P&arcraise;P)(2) and a chalcogen source: trans-Mo(S)(2)(dppee)(2) (2), BzS(3)Bz (dibenzyl trisulfide); trans-Mo(Se)(2)(dppee)(2) (3), elemental Se; trans-Mo(Te)(2)(dppee)(2) (4), TePEt(3) (Et = ethyl); trans-Mo(S)(2)(dppe)(2) (5), BzS(3)Bz; trans-Mo(Se)(2)(dppe)(2) (6), Se. trans-Mo(O)(S)(dppee)(2) (7) was obtained from the reaction of MoCl(3)(THF)(3) (THF = tetrahydrofuran), dppee, and NaHS in a mixture of THF and methanol. The attempted preparation of 7 by the reaction of SO(2) and trans-Mo(N(2))(2)(dppee)(2) yielded Mo(SO(2))(2)(dppee)(2) (8). 1 crystallizes in the monoclinic space group P2(1)/c (No. 14, Z = 2) with a = 11.1340(15) Å, b = 18.435(2) Å, c = 12.515(2) Å, and beta = 110.999(9) degrees; 2 crystallizes in the triclinic space group P&onemacr; (No. 2, Z = 1) with a = 10.102(4) Å, b = 10.722(4) Å, c = 12.195(3) Å, alpha = 100.95(3) degrees, beta = 95.04(4) degrees, and gamma = 117.81(2) degrees; 3 crystallizes in the monoclinic space group P2(1)/c (No. 14, Z = 2) with a = 11.186(5) Å, b = 18.005(8) Å, c = 12.761(9) Å, and beta = 110.35(4) degrees; 4 crystallizes in the triclinic space group P&onemacr; (No. 2, Z = 2) with a = 12.681(4) Å, b = 19.280(5) Å, c = 10.454(3) Å, alpha = 104.60(2) degrees, beta = 111.61(2) degrees, and gamma = 75.12(2) degrees; 5 crystallizes in the monoclinic space group C2/c (No. 15, Z = 8) with a = 49.515(7) Å, b = 10.9286(12) Å, c = 18.203(3) Å, and beta = 98.306(12) degrees; 6 crystallizes in the monoclinic space group C2/c (No. 15, Z = 8) with a = 49.566(9) Å, b = 10.9765(15) Å, c = 18.282(3) Å, and beta = 98.541(13) degrees; 7 crystallizes in the triclinic space group P&onemacr; (No. 2, Z = 1) with a = 10.040(1) Å, b = 10.563(1) Å, c = 12.162(2) Å, alpha = 75.30(1) degrees, beta = 85.93(1) degrees, and gamma = 63.21(1) degrees; 8 crystallizes in the monoclinic space group C2/c (No. 15, Z = 4) with a = 21.534(6) Å, b = 12.4271(13) Å, c = 19.550(5) Å, and beta = 118.480(14) degrees. The UV/vis and the (31)P{(1)H} NMR data for compounds 1-7 are also reported and discussed.

Journal Article↗
PubMed2002

CdS nanoparticles modified to chalcogen sites: new supramolecular complexes, butterfly bridging, and related optical effects.

All present approaches to surface modification of nanoparticles (NPs) with organic ligands exploit metal (cadmium) sites as anchor points. To obtain efficient interaction of NP surface with p-orbitals of organic chromophores, we utilize the chalcogen (sulfur) sites on the NP surface. These sites present several advantages stemming from a stronger interaction of their atomic orbitals with both modifier and NP core. The chalcogen modification of CdS was achieved by using a mixed ligand (2,2'-bipyridyl-N,N')(malonato-O,O')-copper(II) monohydrate complex. The weak monodentate ligands (water) are replaced by a copper-sulfur bond during the modification reaction. The structure of the product was investigated by optical spectroscopy, electron spin resonance, and nuclear magnetic resonance. The modified NP can be described as a few tens (<40) of (2,2'-bipyridyl-N,N')(malonato-O,O')-copper units attached to the CdS core. Steady-state and time-resolved luminescence measurements, molecular orbital calculations, and UPS data indicate that delocalized surface states enveloping the surface chalcogen atoms of NP, transition metal, and p-orbitals of the bipyridine ligand are present in the synthesized species. The delocalized states are made possible due to the bridging of p-levels of sulfur and pi-orbitals of bipyridine by butterfly d-orbitals of the transition metal atom placed between them. Chalcogen-modified NP can be considered as a new member of the family of supramolecular compounds based on transition metal complexes. Both NP and metal complex parts of the prepared supramolecules are very versatile structural units, and new molecular constructs of similar design, in which quantum effects of NPs are combined with optical properties of transition metal complexes, can be obtained with different NPs and metal complexes.

Journal Article↗
PubMed2006

Screening of potentially toxic chalcogens in erythrocytes.

Previous literature reports have demonstrated that a number of human diseases, including inflammation and cancer, can be caused by environmental and occupational exposure to toxic compounds, via DNA damage, protein modifications, or lipid peroxidation. The present study was undertaken to screen the toxicity of a variety of chalcogens using erythrocytes as a model of cell injury. The toxicity of these compounds was evaluated via quantification of hemolysis and lipid peroxidation. The present investigation shows that diphenyl ditelluride and phenyl tellurides are toxic to erythrocytes. The organoselenium compounds were not toxic to erythrocytes even when tested at high concentrations and with a hematocrit of 45%. The hemolytic effect of tellurides was not positively correlated with thiobarbituric acid-reactive substance (TBARS) production suggesting that lipid peroxidation is not involved in the hemolysis provoked by organotellurium compounds. The results suggest that chalcogen compounds may be toxic to human erythrocytes, depending on their structure.

Chalcogens↗
PubMed2006

Synthesis, properties, and reactions of a series of stable dialkyl-substituted silicon-chalcogen doubly bonded compounds.

The first dialkyl-substituted silicon-chalcogen doubly bonded compounds [R2Si=X; R2=1,1,4,4-tetrakis(trimethylsilyl)butane-1,4-diyl, X = S (4), Se (5), and Te (6)]were synthesized by the reactions of an isolable dialkylsilylene R2Si: (3) with phosphine sulfide, elemental selenium, and elemental tellurium, respectively. Systematic changes of characteristics of silicon-chalcogen double bonds are elucidated by X-ray analysis, UV-vis spectroscopy, and DFT calculations. In the solid state, the unsaturated silicon atom in 4-6 adopts planar geometry and the extent of the shortening of Si=X double bonds from the corresponding Si-X single bonds decreases in the order 4 > 5 > 6. In the absorption spectra of 4-6, pi -->pi* transition bands are observed distinctly in addition to n -->pi* transition bands. Both the n -->pi* and pi -->pi* transitions are red-shifted in the order 4 < 5 < 6, and the difference between the energies of the two transitions is kept almost constant among 4-6. The tendency is explained using the qualitative perturbation theory and is reproduced by the DFT calculations for model silanechalcogenones. Addition reactions of water, methanol, and isoprene to 4-6 are reported.

Journal Article↗
PubMed2007

Highly selective double chalcogenation of isocyanides with disulfide-diselenide mixed systems.

A highly selective method for introducing thio and seleno groups into a variety of isocyanides has been developed based on the elucidation of the relative reactivities of organic dichalcogenides and chalcogen-centered free radicals. When the reactions of aromatic isocyanides (ArNC) with organic disulfides (R'SSR') and diselenides (R''SeSeR'') are conducted upon irradiation with a tungsten lamp through Pyrex (hnu>300 nm), simultaneous introduction of both thio and seleno groups into the isocyanides takes place to provide the corresponding thioselenation products (R'S-C(=NAr)-SeR'') in good yields with excellent selectivity. In the cases of aliphatic isocyanides (RCN), a novel diselenide-assisted bisthiolation of RNC with diaryl disulfides (Ar'SSAr') proceeds successfully to give the corresponding bisthiolation products (Ar'S-C(=NR)-SAr'), although the same photoirradiated reaction of RNC with diaryl disulfides does not occur in the absence of diselenide. These double chalcogenation reactions are assumed to proceed via the formation of imidoyl radical intermediates by the reaction of isocyanides with relatively reactive thio radicals (compared with seleno radicals). The obtained thioselenation products can be employed as useful precursors for the construction of beta-lactam framework by the formal [2+2] cyclization with ketene equivalents.

Journal Article↗
PubMed2005

On the temperature percolation in a w/o microemulsion in the presence of organic derivatives of chalcogens.

The course of temperature percolation in a w/o microemulsion system comprising water/bis(2-ethylhexyl) sulfosuccinate sodium, AOT/isooctane affected by the presence of additives has been investigated. Additives, viz., organic derivatives of chalcogens including dipyridyl diselenide (Py2Se2), diphenyl diselenide (Ph2Se2), and dipyridyl ditelluride (Py2Te2), have been assimilated in the reverse micellar system. Formulations have been studied in terms of (i) the concentration variation of additives, (ii) the change in omega (= [H2O]/[AOT]), and (iii) the change in the nonpolar continuum, S (= [oil]/[AOT]). Phenyl derivatives hinder the percolation, whereas the pyridyl derivative in moderate amounts favors the phenomenon. The estimated values of the critical exponents are lower than those predicted by the dynamic percolation theory. The association model has been implemented to access the thermodynamic parameters of droplet clustering. Pyridyl compounds are expected to alter the rigidity of the surfactant monolayer, which could help to promote the attractive interdroplet interaction. FT-IR spectroscopy has been used to elucidate the changes occurring in the core water in the presence of organic derivatives of chalcogens as the droplet size is increased. Results have been rationalized in terms of the alteration in the physicochemical behavior of the water/AOT/isooctane microemulsion in the presence of additives.

Journal Article↗
PubMed2004

[N]Chalcogena[N]pericyclynes: DFT studies on binaric carbon-chalcogen compounds.

[structure: see text] DFT studies on [N]chalcogena[N]pericyclynes (n = 3-6, 8) demonstrate their relative stability and hence their possible existence as stable species. By minimizing repulsive interactions between the chalcogens' lone pairs, the molecules adopt structures that resemble, in shape, cycloalkanes or elemental chalcogens. [3]Chalcogena[3]pericyclynes may be interconverted with their valence tautomers, benzene derivatives with three fused three-membered rings.

Journal Article↗
PubMed2007

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.

Journal Article↗