2.2 -Dipyridyl: 2,2 -Bipyridine

A A -coordi nation was found in the zinc complex of 2,2 -dipyridyl diselenide, [ZnLCl2].214 The tridentate ligand 6-(2-aminophenyl)-2,2 -bipyridine contains two pyridyl and one aniline donor ligand to form a complex of the form [ZnL2]2+. The X-ray structure shows a distorted octahedral metal center with each ligand twisting from planar to accommodate the meridional binding.215... 

There are six bipyridines whose structures are 2,2 -l, 2,3 -2, 2,4 -3, 3,3 -4, 3,4 -5, and 4,4 -6. The term bipyridine is in accord with current Chemical Abstracts nomenclature, although the compounds have also been named as bipyridyls and dipyridyls. 

There has been considerable interest in the chemistry and electronic structures of cobalt and iron complexes of a s-l,2-disub-stituted ethene-1,2-dithiol1 2 and their Lewis base adducts.3-5 The complexes, and their Lewis base adducts which may contain pyridine, phosphines, NO, dipyridyl (2,2/-bipyridine), etc., are capable of undergoing reversible one-electron transfer reactions, thereby generating a series of complex ions differing from each other by only one unit of electric charge. 

The optical antipodes of tris(l,10-phenanthroline)nickel-(II) perchlorate are more stable than those of the corresponding tris(2,2 -bipyridine)[tris(2,2 -dipyridyl)] compound. In 18 hours, solutions of the 1,10-phenanthroline complexes lose only 50% of their activity. When examined at 589.0 and 546.1 m/x, the antipodes show a large abnormal rotatory dispersion. The precipitation of [Ni(o-phen)s]-[Co(CO)4]2 is the basis for a method of determining cobalt tetracarbonyl hydride. ... 

A 1.04-g. (0.004-mole) sample of Co(acac)2 is dissolved in 25 ml. benzene, and the solution is boiled briefly. On adding a 5-ml. benzene or chloroform solution of 0.005 mole of ligand [1,10-phenanthroline or 2,2 -bipyridine(dipyridyl)], the solution turns from purple to dark red. The reaction mixture is then boiled to a volume of 5-10 ml., whereupon tiny orange needles appear. The slurry is cooled in ice, the precipitate is filtered off, washed with two 3-ml. portions of cold benzene, and air-dried. 

This mixed ligand coordination where carboxylate and pyridyl groups are bound to the same cation is not common. In fact, one could argue that this is in contrast to Pearson s hard/soft acid-base distinction in that the uranyl cation is a hard acid and the dipyridyl linkers are softer in nature. Indeed, U02 -pyridyl coordination (2,2 -bipyridine, terpyridines, etc) is quite rare, even in molecular materials, yet in these extended topologies, it is likely that sterics play a considerable role and that the 4,4 -dipyridyl is uniquely suited to displace H2O groups and serve as a bridging moiety. This is mentioned in this context as... 

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