Three-dimensional honeycomb structure

The lubricity theory explains the resistance of a polymer to deformation. Stiffness and rigidity are explained as the resistance of intermolecular friction. The plasticizer acts as a lubricant to facilitate movement of macromolecules over each other, thus giving the resin an internal lubricity. The gel theory is applied to predominantly amorphous polymers. It proposes that their rigidity and resistance to flex are due to an internal three-dimensional honeycomb structure or gel. The spatial dimensions of the cell in a brittle resin are small because their centers of attraction are closely spaced and deformation cannot be accommodated by internal movement in the cell-locked mass. Thus, the elasticity limit is low. Conversely, a thermoplastic or thermosetting polymer with widely separated points of attachment between its raacroraolecules is flexible without plasticization. 

Keeping the above structures in view, the natural zeolites have a unique three-dimensional honeycomb structure (Fig. 2.6i), which creates an open and negatively charged framework through which liquid and gases can be exchanged or... 

The coordination chemistry of oxalate (ox, C2042-) compounds provides a series of very interesting compounds from the stereochemical and magnetic points of view [197]. Most frequently the compounds form honeycomb layers in the presence of transition metal ions, in which the stereochemistry of the metal ion coordination sphere alternates between A and A. However, a three-dimensional homochiral structure is also possible. On the other hand, the negative charge of the oxalates necessitates the incorporation of cations between them, which provides the opportunity to introduce chirality and additional functionality in materials. The compound formed between homochiral manganese II oxalate and iron II tris bipyridinc (bpy) with formula [Mn oxls]2 " [Fcn(bpy)3]2+ crystallises in the space group fJ4 32. 

Zeolite is a crystalline, porous aluminosilicate mineral with a unique interconnecting lattice structure. This lattice structure is arranged to form a honeycomb framework of consistent diameter interconnecting channels and pores. Negatively charged alumina and neutrally charged silica tetrahedral building blocks are stacked to produce the open three-dimensional honeycomb framework. 

Th0 GgI Theory. This theory extends the lubrication theory by having the plasticizer break the resin-resin attachments of a three-dimensional honeycomb or gel structure and by masking these centers of attachment from each other, preventing their reformation. This gel is formed by loose attachments occinring at intervals along the polymer chain. This facilitates the movement of plasticizer molecules, thus imparting flexibihty. 

Among the inorganic open-framework compounds, the family of phosphates is a large one [3]. A large variety of open-framework metal phosphates of different architectures have been synthesized in the last few years. They include one-dimensional (ID) linear chain and ladder structures, two-dimensional (2D) layer structures and three-dimensional (3D) channel structures [4]. In the linear chain and ladder structures, four-membered metal phosphate units of the type M2P2O4 share comers and edges respectively. Zero-dimensional four-membered zinc phosphates have been synthesised and characterized recently [5]. Several open-framework metal carboxylates have also been reported [6] and the presence of a hierarchy of zinc oxalates covering the monomer, dimer, chain, honeycomb-layer and 3D structures has indeed been established [7]. 

Figure 7. Hierarchy of zinc oxalate structures (a) monomer, (b) dimer, (c) one-dimensional chain (d) two-dimensional honeycomb layer (e) three-dimensional structure.

Figure 2.5.1 Schematic representation of some of the discrete and extended supramolecular architectures that can be prepared by metal-directed self-assembly (a) 1D polymeric chains (b) discrete macrocyclic structures (c) two-dimensional grid- and honeycomb-like networks (d) three-dimensional diamandoid open frameworks...

We mentioned earlier (see Section V,C,1) that for the two-dimensional compounds of formula (catliMnCrCoxlg], with cat+ standing for a monovalent cation, each metal site of a given chirality (A or A) is surrounded by three metal sites of the opposite chirality (A or A), so that within a layer all the Mn(II) sites have the same chirality and all the Cr(III) sites have the other chirality. If the Mn(II) and Cr(III) sites had the same chirality, the hexagons of the honeycomb structure could no longer be closed, and the structure would be three- instead of two-dimensional. This structure as a whole would obviously be chiral 86). 

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