Donor chalcogen

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. ... 

A common interpretation of the interaction of chalcogens with nucleophiles considers donation of electron density from a lone pair on the donor atom into the o- (E-X) orbital (Figure 15.1). As the degree of covalency increases, a hypervalent three-centre four-electron bond is formed. Real systems fall somewhere between secondary interactions and hypervalent (three centre - four electron) bonds. The two extremes can be distinguished by the correlation of X-E and E D distances.In the hypervalent case both bond distances decrease simultaneously, whereas in the secondary bond the distances are anticorrelated. This concept has been applied in a study of selenoquinones 15.17 (R = Ph, Me) with short Se 0 contacts,for... 

Fig. 15.1 Molecular orbital diagram of inUamolecular donor (D) - chalcogen (E) interactions...

Intramolecular chalcogen interactions may also stabilize reactive functional groups enabling the isolation of otherwise unstable species or their use as transient intermediates, especially in the case of selenium and tellurium. For example, tellurium(II) compounds of the type ArTeCl are unstable with respect to disproportionation in the absence of such interactions. The diazene derivative 15.23 is stabilized by a Te N interaction. Presumably, intramolecular coordination hinders the disproportionation process. Other derivatives of the type RTeX that are stabilized by a Te N interaction include 8-(dimethylamino)-l-(naphthyl)tellurium bromide, 2-(bromotelluro)-A-(p-tolyl)benzylamine, and 2-[(dimethylammo)methyl]phenyltellunum iodide. Intramolecular donation from a nitrogen donor can also be used to stabilize the Se-I functionality in related compounds." ... 

The potential of the cluster units described here to participate in intermolecular chalcogen-chalcogen interactions combined with the easy modification of their outer coordination sphere with ligands of different nature, i.e., redox active, hydrogen donors, bi-functional, etc., make these systems useful blocks for the construction of supramolecular materials with multi-physical properties. 

The simplest possible coordination compounds of Cd and Hg with chalcogen donors are the anions MCh22. Multinuclear NMR studies of these species (Ch = Se, Te) in NH3 or en solutions with [K(2.2.2-cryptand)]+ counterions have been reported.314 Structural studies31, also combined with new multinuclear NMR measurements, have been performed.316... 

Complexes of Chalcogen Donors with Organotellurium Electrophiles 854... 

Diphosphine mono-chalcogenides are able to bind to metal centres from either one of or both the phosphorus(III) and chalcogen donor centres. This has led to their study as hemi-labile ligands in catalyst systems, whereby one of the donor centres binds strongly to the metal centre and the other one is weakly bound and hence can be readily dissociated or reattached to reveal or protect the active site at a metal centre.28... 

The amido and imido derivates of phosphorus-chalcogen ligands have been of much interest to coordination chemists due to the fact that they possess both hard (nitrogen) as well as soft (chalcogen) donor sites and are therefore able to act as heteroleptic ligand systems.56... 

Predicting the outcome of the reactions between LE chalcogen-donor molecules and di- and inter-halogens is still a challenge, and attempts have been made in this direction by judging whether all the different products could be formed from a common intermediate species following a general pattern of reactivity. In particular, S. Husebye proposed that this species was the [LE-X]4... 

In this chapter we will not attempt to give an overview of all of the knowledge on the reactivity of chalcogen-donor molecules towards di- and inter-halogens, since some aspects of this are discussed in other chapters. Instead, this chapter is dedicated exclusively to the analysis of the chemical bond and structural features of C.-T. adducts between LE chalcogen-donor molecules (E = S, Se) and di- and inter-halogens, and their reactivity towards metal powders. 

More complicated structural situations are observed in di-halogen-rich adducts of chalcogen-donor molecules when further soft-soft halogen halogen interactions intervene, thus generating multidimensional networks (see Chapter 13.1). A clear example is represented by the structure of the compound (dithizone)2 7I2 46 Based on structural data the authors have described the repeating unit in this polymeric compound as a... 

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