Chalcogen atoms

Dibismuthines are very sensitive to oxidation. Thus tetramethyldibismuthine fumes ia air, and tetraphenyldibismuthine ia toluene solution rapidly absorbs oxygen. Under controlled conditions, dibismuthines react with chalcogens resulting ia cleavage of the bismuth—bismuth bond and iasertion of a chalcogen atom (105,138,140—142) ... 

These interactions are most commonly observed for divalent chalcogen atoms and the nitrogen atom (the electron donor D) lies within the X-E-Y (E = S, Se, Te) plane, preferably along the extension of one of the covalent bonds as in 15.3. This anisotropy is a clear indication that these short E N contacts have some bonding character, i.e., they are subject to the geometric restrictions of orbital overlap. Eor example, in the diselenide 15.4 the nitrogen lone pairs are clearly oriented towards the Se-Se linkage. ... 

The involvement of a chalcogen atom in an intramolecular interaction may influence the reactivity of the chalcogen centre as a result of steric or electronic effects. This feature may lead to unique reaction patterns. Eor example, the sulfur(II) centre involved in an intramolecular contact... 

Transannular interactions in macroheterocycles including two chalcogen atoms 97YGK1006. 

A bis(chelate) structure was found for the closely related germylene [MeC(NPr )2]2Ge, which was also made from GeCl2(dioxane) and 2 equivalents of the lithium amidinate (colorless crystals, 81%). The same synthetic approach was used to make bis(amidinato) metal dichlorides of silicon and germanium in high yields (83-95%). Rapid oxidative addition of chalcogen atom sources (styrene sulfide and elemental Se) to the germylene derivatives resulted in a series... 

TI4SCI4 and T SeCh melt at 440 and 442°C, respectively. They can be distilled between 650 and 700°C without decomposition. They are insoluble in H2O and organic solvents, but soluble in aqueous alkaline solutions. With cone, acids, decomposition takes place. The electric conductivity has been determined to be 1.4-10 and 2.1-10 fl cm for TI4SCI4 and TUSeCU, respectively. The probable structural formula is Tl3(TlCl4Y). The compounds thus, presumably, consist of Tli,4Cl4,4Y2/8 octahedra that are interconnected by the chalcogen atoms to linear chains (321). 

The effect shown in Fig. 9 is a result of the bond-bond interaction which is a characteristic feature for chains and rings of two-valent chalcogen atoms. It can also be recognized from the relatively large bond interaction force constants fir of such compounds. The stretching force constants /r(SS) of polysulfur compounds depend on the SS bond distances as shown in Fig. 10. The data used in this figure include several excited electronic states of the S2 molecule as well as the disulfide anion and a number of sulfur homocycles [77]. 

Like the three-coordinate aluminum and gallium alkoxides, the corresponding thiolates, selenolates, and tellurolates require very bulky substituents at the chalcogen atom to ensure a low metal coordination number. In addition, the steric requirements associated with the preservation of the low coordination number at the metal are increased by the longer M—S and M—Se bond lengths. The ten examples of low-coordinate,... 

As described previously, the two dimethyl amino methyl groups on the 2,6-position of the phenyl ring of teluride 161 act as internal ligands (Koten s arms) and stabilize the cation generated at the central Te atom (see Equation 44). Furukawa and co-workers subsequently showed that these Koten s arms also activate the molecule to release alkyl substituents which are attached to the central chalcogen atom <1995JA10153> and <1997BCJ2571>. For example,... 

Species with Chalcogen Atoms within the Cage... 

The chalcogen atoms readily insert into Li-C or Mg-C bonds and this method is widely used to prepare in situ these reagents for further reactions. 

Hence, chalcogenoamidophosphinic acids of general formula R2P(E)NHR (27) can be considered as dichalcogenophosphinic acids with one of the chalcogen atoms replaced by an amido group. These amido species are still normally referred to as acids due to their acidic amide protons. They are accessible from reaction of thiophosphinic chlorides and primary amines (Equation 43) or from reaction of aminophosphines with elemental chalcogen... 

A very large number of heterocyclic compounds are known consisting solely of phosphorus and chalcogen atoms, as well as those containing phosphorus, chalcogen and carbon or other hetero atoms. Such heterocycles have been the subject of several reviews2,83,84 and the discussion here will be limited to some representative examples of these compounds. 

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