Supramolecular Architecture by Secondary Bonds

Modem Supramolecular Gold Chemistry Gold-Metal Interactions and Applications. Edited by Antonio Laguna 

Copyright 2008 WILEY-VCH Verlag GmbH Co. KGaA, Weinheim ISBN 978-3-527-32029-5 

Finally, although much less frequent, there are also supramolecular gold materials formed as a result of the presence of different types of interactions in which n electron density is responsible for the formation of a supermolecule or a supramolecular array. Thus, Au- %, —H- % or % n interactions will also be considered in this chapter. 

Supramolecular Cold Entities Built with Cold-Non-Metal Secondary Bonds 

This section will examine selected examples of supramolecular entities built by means of contacts in which gold is the acceptor of electron density, and which can have different classes of donors non-metals different from hydrogen, which may be some of the atoms in Groups 17,16,15 or 14 a hydrogen atom of a covalent NM—H bond, where the non-metal is in most cases a carbon or a cloud of electron density. 

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This is the most comprehensive family of supramolecular architectures involving self-assembly and self-organization promoted by secondary bonds. Selected examples are collected in Schemes 6 and Scheme 7. Scheme 6 comprises organometallic halides. 

Mesitylselenium iodide, 2,4,6-Me3C6H2SeI, has a supramolecular self-organized architecture, 203, based on secondary bonds between iodine and iodine, and between iodine and selenium pairs. Similar self-organization by secondary bonding... 

A secondary bond , as defined by Alcock [6-8], is an interaction between two atoms characterized by a distance longer than the sum of the covalent radii but shorter than the sum of the van der Waals radii of the corresponding atoms. Such secondary interactions are weaker than normal covalent or dative bonds, but strong enough to connect individual molecules and to modify the coordination geometry of the atoms involved. They are often present in a crystal, thus resulting in self-assembled supermolecules or supramolecular architectures. For gold complexes,... 

Although the cyclic dimers are connected by additional H-bonds, the authors did not observe a super-tetrahedral network. Notably, a 2 1 alcohol-amine complex 14 15, was also observed [41] between 4-methoxyphenol (15) and methylhydrazine (14) (Scheme 5). Thus, a dimer formed by a primary amine and a secondary amine in such cases does not have the general requisites to generate a supramolecular architecture. 

Organothalhum(III) thiosemicarbazone derivatives are usually self-organized in solid state supramolecular architectures. An example is (/>-anisaldehyde thiosemi-carbazonato) dimethylthallium(III), which contains four-membered chelate rings (with Tl-N 2.56 A and Tl-S 2.991 A) interconnected in chains by Tl- -S secondary bonds (T1---S 3.304 A) [159],... 

The coordination geometry around antimony is pentagonal bipyramidal, with a benzene molecule occupying one axial site another axial site is occupied by a chlorine atom bonded to antimony by a primary Sb-Cl bond. In the equatorial plane there are two primary (normal covalent) Sb-Cl bonds (in the range 2.340-2.378 A) whereas three other secondary Sb- -Q interactions (range 3.401-4.04 A) distort the geometry and contribute to the formation of the supramolecular architecture. The supramolecular assembly exists only in the solid state in solution or melt disassembly occurs. 

A relatively new field called supramolecular chemistry has been developed over the last three decades. Supramolecular assemblies and supramolecular polymers differ from macromolecules, where the monomeric units are covalently linked. In a supramolecular polymer, the monomeric units self-assemble via reversible, highly directional, noncova-lent interactions. These types of bonding forces are sometimes called secondary interactions. Hydrogen bonding is the secondary force most utilized in supramolecular chemistry, but metal coordination and aromatic tt-tt electronic interactions have also been used. From a materials standpoint, supramolecular assemblies are promising because of the reversibility stemming from the secondary interactions. The goal is to build materials whose architectural and dynamical properties can respond reversibly to external stimuli. Solid phases are prepared by self-assembly from solution. In the solid-state, supramolecular polymers can be either crystalline or amorphous. 

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