Intramolecular interactions mercury

Nonconjugated dienes and polyenes have triplet photochemistry which may be considered to arise from intramolecular interaction of one excited double bond with an isolated ground-state double bond. For example, the photocyclization of enrfo-dicyclopentadiene can be effected using acetone as a sensitizer.286 Other more flexible 1,5-dienes, when sensitized to triplet states, cross couple to yield bicyclo[2.1.1]-hexane structures. For instance, triplet mercury atoms convert both 1,5-hexadiene and 1,5-cyclooctadiene to such structures.267 Irradiation of the cyclooctadiene in the presence of cuprous chloride produces the tricyclo derivative in good yield266 but recent evidence again indicates that this latter reaction may proceed via free-radical intermediates.269... 

With simple Hg thiolates the structures of bis(ethanethiolato)mercury Hg(SEt)2321 and of the cysteamine complex [Hg S(CH2)2NH3 2]Cl2322 have reference character, as only weak or no secondary bonds are present, and therefore the central S—Hg—S entities can be considered to be unperturbed. In mercury bis(tri-t-butoxysilanethiolate) Hg[SSi(o-t-Bu)3], with a strictly linear S—Hg—S unit, two weak intramolecular O II g interactions obviously do not affect the bonding in this unit.323... 

In the solid state, the pyridine nitrogen atom of compound 10 forms secondary interactions with the mercury center. Intramolecular coordination of the nitrogen atom is, however, not observed in derivative 11 in which N —> Si 7t-bonding possibly monopolizes the nitrogen lone pair. 

The centrosymmetrical complex 154, formed by interaction of the quinolyl ligand with HgCl2, features intramolecular coordination of one of the cyclopentadiene C=C bonds to the mercury center. The resulting Hg-C(sp2) distances of 2.81 and 2.88 A are longer than typical Hg-C c-bonds but remain much shorter than the sum of the van der Waals radii. This dihapto interaction does not result in a significant lengthening of the coordinated C=C... 

Stacking in all of these complexes is the result of additional intermolecular aurophilic interactions between four of the six Au1 atoms in adjacent units giving rise to stacked linear-chain structures with a -BBABBA- pattern. The intermolecular Au1- -Au1 distances, between 3.0658(7) and 3.3298(5) A, are usually similar or slightly shorter (in the case of the mercury derivative) than the intramolecular ones, with average distances between 3.08 and 3.493 A (see Table XXI). Only in the case of the TCNQ derivative the intermolecular aurophilic contacts (3.152 A) are clearly shorter than the intramolecular ones (3.457, 3.471 and 3.534 A), which could be ascribed to charge-transfer from the electron-rich gold center to the electron acceptor TCNQ. 

SC6H4NH2. Many of these complexes have a polymeric structure and in the cases that the metal is linearly coordinated there are several possibilities of stabilization as M- S, Hg- Hg, M- N (in heterocyclic thiolates), intramolecular NH- -S, or intermolecular CH- N interactions or ti-ti stacking. For mercury other type of neutral complexes of the form [HgR(SC6H4NH2)]... 

Mercury is a soft metal and as such it is expected to form secondary bonds, most readily with sulfur, selenium, and other heavy non-metals. The situation is, however, more complex and secondary interactions with other electronegative atoms have also been observed in the solid state. Interatomic distances longer than the expected van der Waals distances are, moreover, sometimes observed between molecules orientated such that weak interactions lead to particular arrangements in the crystal [69]. The are numerous examples of secondary bonds in organomercury chemistry although most are intramolecular there are several examples of inter-molecular secondary bonds leading to supramolecular self assembly. A review has been published on this subject [70] and many new examples have subsequently been reported. 

The reformation of the reduced disulfide bonds on oxidation at short times is possible presumably because the protein conformation is partially maintained at the electrode surface by the Hg-S interaction, intramolecular hydrogen bonding, and by the internal disulfide bonds not accessible for interaction with the mercury electrode. 

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