Tetrakis isothiocyanato bis 2,2-bipyridine niobium IV

Numerous complexes of niobium(IV) and niobium(V) halides with various nitrogen-donor ligands have been reported in the literature. The products obtained from these reactions are critically dependent upon the reaction conditions. Tetrakis(isothiocyanato)bis(2,2 -bipyridine)niobium(IV) can be prepared directly from the hexakis(isothiocyanato)niobate(IV) complex or by the reduction of the hexakis(isothiocyanato)niobate(V) ion according to the published method. This method can also be extended to the preparation of other analogous complexes. 

Since niobium pentachloride and tetrachloride decompose readily in the presence of oxygen or moisture, all solvents and vessels used in the reactions must be dried by accepted methods. The niobium chlorides should also be free of any oxy species. The potassium thiocyanate and 2,2 -bipyridine should be purified by recrystallization from water and ether, respectively, and then dried at a pressure of ca. 10 torr for 72 hrs. 

In an inert-atmosphere dry-box, 2.36 g (0.01 mole) of niobium tetrachloride is suspended in 25 ml of acetonitrile in a 100-ml round-bottomed flask equipped with a magnetic stirring bar. Niobium(IV) chloride is conveniently prepared by reduction of niobium(V) chloride with aluminum metal. This mixture is stirred for ca. 1 hr and then 5.84 g (0.06 mole) of potassium thiocyanate dissolved in 25 ml of acetonitrile is added. Stirring is continued for 4 hr to allow for complete reaction. The red solution is filtered through a medium-porosity sintered-glass frit, separating the insoluble potassium chloride from the soluble K2[Nb(NCS)e]. The KCl precipitate is washed with three 5-ml portions pf 

Inorganic Syntheses, Volume XVI Edited by Fred Basolo Copyright 1976 by McGraw-Hill, Inc. 

Tetrakis(isothiocyanato)bis(2,2 -bipyridine)niobium(IV) is a medium-brown crystalline solid. It is only very slightly soluble in 1,2-dichloroethane, dichlo-romethane, and acetonitrile. These extremely dilute solutions of the complex readily decompose in the presence of oxygen or moisture however, in the solid state the complex appears to be air-stable. It does not melt or decompose below ca. 275°. The infrared spectrum, ultraviolet spectrum, magnetic moment, and x-ray powder diffraction pattern of the product obtained by this procedure are essentially identical to those obtained for the product prepared by the reduction of the hexakis(isothiocyanate)niobate(V) complex.  

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