Organic Bridging Ligands

In the field of porous supramolecular metal complexes, both molecular and extended-solid materials have been extensively studied in recent years. A particularly well-studied class of compounds is the metal-containing molecular squares, that is, square-shaped porous tetrameric structures (30,108). These have been prepared by several approaches, the most common being the reaction of an organic bridging ligand with a metal complex that has available cis-coordination sites (109-113) (Fig. 13). However, the resulting metal centers are usually coordinatively saturated, which makes it difficult for guest molecules to interact directly with the metal atoms. 

Cu-hedp compounds involving second organic bridging ligands... 

Each of the complexes described in this section have been synthesised, at least initially, by the serendipitous assembly of manganese salts or pre-formed clusters of Mn with a combination of one or more flexible organic bridging ligands. These species represent the vast majority of SMMs reported to date. Mn cluster chemistry involves complicated processes in which the crystallographically characterised products are almost certainly not the only complexes present in solution at any one time and where the synthesis also involves the protonation/deprotonation, redox chemistry and structural rearrangement of many species simultaneously. Thus, mechanistic, kinetic and any other detailed studies of the reaction processes are almost impossible. 

One of the most successful routes for SMM synthesis is the reaction between a pre-formed Mn cluster and (a) solvent, (b) reductant/oxidant, and/or (c) flexible organic bridging ligand. Commonly the metal complexes used are the triangular species [64] [Mn30(02CR)6(py)3] , but all Mn x > 2) clus-... 

Simple procedures to prepare multifunctional ligands. Organic bridging ligands having multifunctionalities require many intricate synthetic steps while metalloligands with multifunctionalities can be obtained from combination of simple connectors and linkers. 

Self-assembled coordination poiymers containing transition metal ions and organic bridging ligands have attracted intensive interest because of their potentiai abiiities for selective inclusion and transformation of ions and molecules [I-4]. Construction of a variety of assembled structures plays an important role in designing the size and shape of vacancy. Both the variety of assembled structures and sorption of guest molecules can affect the properties of assembled complexes. 

Organic Bridging Ligands.—Experiments with a pyrazine-2-carboxylate complex have given kinetic evidence of free-radical intermediates, exemplifying the chemical mechanism of electron transfer. In equation (56) and (57), HL = pyrazine-2-carboxylic... 

The first known instance of the synthesis of MOFs through an electrochemical route was performed by Mueller and coworkers, who pioneered a technique of anodic dissolution of the cation of a MOF metal centre within a solution of an organic bridging ligand and conducting salt, resulting in formation of, in this case, Cu-MOF (also known as HKUST-1 [Cu3(btc)2], btc = 1,3,5-benzenetricarboxylate, see Fig. 2) without side... 

---