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Nanostructural Architectures from Molecular Building Blocks. Nanostructural Architectures from Molecular Building Blocks. Molecular building blocks: MBBs are the link between classical synthsis chemistry from in theory the smallest possible unit, and large structures.
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Nanostructural Architectures from Molecular Building Blocks • Molecular building blocks: • MBBs are the link between classical synthsis chemistry from in theory the smallest possible unit, and large structures. • MBBs are molecules that self assemble into larger units. • The limitations of this method are: • Availability of the units, connectivity, and suitable linkers
Nanostructural Architectures from Molecular Building Blocks • Bonding and connectivity • Covalent bonding • Covalent bonds are formed by the sharing of pairs of electrons between atoms. • Best example is the covalent bond between two C atoms. • Sigma bonding along the axis between the two atoms, provides a means of low energy rotation in linear molecules and low energy angle twisting in cyclic molecules. • Sigma bonding defines the general connectivity and framework of the molecule
Nanostructural Architectures from Molecular Building Blocks • Covalent bonding has many advantages: • Covalent bonds lead to extremely stable intermolecular connections, as compared to electrostatic interactions (temperature, ionic strength, pH) • Covalnet bonds are dependable, they do not reorganise, like hydrogen bonds • Protocols exist to form all kinds of covalent bonds for all kinds of building blocks, allowing all possible connectivities
Nanostructural Architectures from Molecular Building Blocks • Coordination complexes • In between the covalent bonds and the other interamolecular interactions are the coordination complexes between organic molecules and metal ions. • The initial description of these metal ligand molecules stems from the ability of metal ions to coordinate ligands electron donating molecules
Nanostructural Architectures from Molecular Building Blocks • Dative bonds: • Interaction of a lone pair with an atom centered molecular orbital. Strength comparable to a sigma bond. • E.g. Bonding between B and N. • Coupling of a molecule to B with a lone pair leads to change in boron from trigonal planar (sp2) to tetrahedral (sp3).
Nanostructural Architectures from Molecular Building Blocks Boroadamantane is a special case, because B is already in sp3 hybridisation and has the final conformation already built in the molecule.
Nanostructural Architectures from Molecular Building Blocks • Interactions • They play a role in base stacking in DNA • Molecular crystals • Polymer chemistry • Foramtion, shape and function of proteins
Nanostructural Architectures from Molecular Building Blocks • Molecular building block approaches • The ultimate goal is the assembly of nanostructures or nanoscale materials through the manipulation of a subunit by chemical modification • The MBB is devisible into one or more chemically/electrostaically active region • Supramolecular Chemistry • Science of electrostatic interaction at the molecular level
Nanostructural Architectures from Molecular Building Blocks • Hydrogen bonding • It is used extensively in Supramolecular Chemistry • Easy means to self assemble large units from smaller subunits, can rearrange • Stability increases with the total amount of Hydrogen bonds
Nanostructural Architectures from Molecular Building Blocks • Crystal Engineering • Hydrogen Bonding has been extensively used in the stabilisation of crystal lattices. • Hydrogen bonding is one of the main bonding in biological molecules • Stabilisation of structures and backbones • Secondary structure stabilisation
Nanostructural Architectures from Molecular Building Blocks • Supramolecular structures • Whole families of Supramolecular structures are known that have been built up only by Hydrogen bonding • Mixing the units in te correct ratios will lead to the self assembly of the desired structures • Cavities, sheets, triangular structures,…..
Nanostructural Architectures from Molecular Building Blocks • Catenanes • Catenanes are a very special class of supramolecular molecules • They come into existence when two macrocycles interpenetrate each other. • The first catenane has been synthesised in very poor yields
Nanostructural Architectures from Molecular Building Blocks • Molecular Zippers • Molecular zippers are formed by amide oliomers • They maximise the amount of Hydrogen bonding and -stacking • Stabiloity increases with oligomer length • Decrease in stability in polar solvents (methanol)
Nanostructural Architectures from Molecular Building Blocks • Covalent Architectures • The Tinkertoy chemist • Idea behind the concept to build all possible structures and shapes from a limited set of molecules where all possible connectivities of each single are known • LEGO block system for organic chemistry
Nanostructural Architectures from Molecular Building Blocks • Stability: • Stability and reactivity are the most important factors • The MBBS should only react during the formation of the structure and result in an inert structure at the end of the reaction • Size • Control over the size is better the smaller the single building blocks are.
Nanostructural Architectures from Molecular Building Blocks • Chemical reactivity • From the box of the 24 molecules the reactivity and reaction chemistry is known and described. • Protocols for all possible linking reactions are known • Engineering all possible shapes is possible
Nanostructural Architectures from Molecular Building Blocks Honeycomb lattices
