Pyridines with metal ions

Yang NC, Jeong JK, Suh DH (2003) A new conjugated polymer chemosensor functionalised with 2, 6-bis(l, 3,4-oxadiazole-2-yl)pyridine for metal ion recognition. Chem Lett 32 40-41... 

Scrutiny of Chemical Abstracts reveals literally hundreds of structures containing pyridine or its derivatives analyzed by X-ray crystallography, and by far the greater majority are involved in complexes with metallic ions, from which the important piece of information to be gained is the geometry of coordination of the metallic ion. 

Three facts account for the need of cells for both the flavin and pyridine nucleotide coenzymes (1) Flavins are usually stronger oxidizing agents than is NAD+. This property fits them for a role in the electron transport chains of mitochondria where a sequence of increasingly more powerful oxidants is needed and makes them ideal oxidants in a variety of other dehydrogenations. (2) Flavins can be reduced either by one- or two-electron processes. This enables them to participate in oxidation reactions involving free radicals and in reactions with metal ions. (3) Reduced flavins... 

Lewis acids such as BF3, SO3, AICI3, etc., readily react with pyridine to form Lewis salts (Scheme 6.5), and many coordination complexes have been prepared with metallic ions. 

Semiconducting nanorods and nanowires were synthesized by y-irradiation at room temperature and the atmospheric pressure. The experiment was carried out in ethylenediamine and pyridine as solvents. Ethylenediamine (en) and pyridine (py) molecules were coordinated with metal ions and had an effect on the shape like nanorods and nanowires (Jo et al. 2006). Semiconducting nanorod and pearl necklace-like nanowire of CdS and CdSe were successfully synthesized by irradiation with a dose of 90 kGy at room temperature and the atmospheric pressure. When nanorods and nanowires were prepared in en and py, the solvent molecules controlled their morphology. From XRD data, the synthesized CdS and CdSe could be observed on the information of crystallinity of them. In nanorod CdS and CdSe, the intensity of the (0 0 2) diffraction peak was extraordinarily strong. This result indicates that the CdS obtained in py have a preferential [0 0 1] orientation. TEM images displayed rod and pearl necklace like morphology with diameters of several nanometers and lengths of upto several microns. For the shape control, en and py were successfully used to replace the surfactant molecules on the surface of nanoparticles. 

As a bidentate ligand, 2,2 -bipyridine chelates through the two nitrogen centers (1). While this is true for most of the transition metals, stable complexes with C,N -coordination (2) are also formed with metal ions such as Ir(III), Pt(II) and Pd(II). Stable ortho-metalated complexes are also obtained with other ligands such as 2-phenyl pyridine. These ortho-metalated complexes are emissive in fluid solutions and exhibit rich photochemistry. 

Di-(2-pyridyl) pyridine and tetrapyridyl also form complexes with metal ions. Whilst the former functions as a tridentate chelate molecule, it is doubtful if the tetrapyridyl is quadridentate . 

Like the pyridine aldoximes, the ketoximes give metal chelate complexes . The a f-pyridyl oxime of 2-benzoylpyridine gives such complexes whilst the n-pyridyl oxime does not. The stereochemical assignments are based on the Beckmann rearrangement of the oximes , and the behaviour of the two oximes with metal ions is that to be expected from the structures of chelates in this series . The Beckmann rearrangement has been used several times in the pyridine series 8- , The oximes prepared from 2-phenacyl-and 2,6-diphenacyl-pyridine give pyridine-2-acetic acid anilide and pyri-dine-2,6-diacetic acid dianilide, respectively, and must be the n-pyridyl compounds ". ... 

The pyridine-2-carboxylic acids are distinguished by their ability to form chelate complexes with metal ions . The property has been known since Skraup" tested all 19 of the pyridine-carboxylic acids and observed that those with 2-carboxyl groups gave characteristic colours with ferrous ions. The colour is due to an absorption band of low intensity at 4,000 A. 2,6-Dicarboxylic acids absorb at longer wavelengths . 

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