Sodium Tris 2,4-pentanedionato cobaltate II

The compound was first obtained in low yield by adding excess aqueous sodium acetylacetonate to a solution of sodium dinitrobis(2,4-pentanedionato)cobaltate(III). The procedure below is similar to that of Dwyer and Sargeson,i omitting the rather tedious recrystallization from methanol-ether. 

A solution of 47.6 g. (0.2 mole) of cobalt(II) chloride 6-hydrate in 270 ml. of methanol is added drop by drop with vigorous stirring over a 25-minute period to a solution of 24 g. (0.6 mole) of sodium hydroxide and 60 g. (0.6 mole) of 2,4-pentanedione in 

400 ml. of methanol. The fine reddish precipitate is filtered with suction and washed thoroughly with methanol until the washings are nearly colorless (about oOO ml.). It is then washed with ether, sucked dry, and dried over sulfuric acid at atmospheric pressure to constant weight. The yield is 74 g., 98%. Anal. Calcd. for CioH2i06NaCo C, 47.49 H, 5.58. Found C, 47.66 H, 5.65. 

The compound shows no melting or decomposition on heating to 260°. It is sparingly soluble in water and methanol. The separation of the bis compound, presumably Co(acac)2(H20)2, from aqueous solution has been reported. The dissociation of the anion has been studied.One 2,4-pentanedionato group is easily replaced by various nitrogeneous bases.  

The visible spectrum of the sodium salt in methanol has the same shape as that of diaquo complex in chloroform a split peak at 511 and 488.5 mu (e 13), with a shoulder at 461 m/a. The charge-transfer band is at 278 m/u.. The infrared spectrum in the range 4000-650 cm. is very similar to that of Co(acac)2, except that all the peaks are much sharper. 

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A series of neutral addition compounds of bis(2,4-pentanedio-nato) cobalt (II), Co(acac)2, can be obtained by adding the desired base to a benzene solution of this compound. The adducts are all less soluble than the starting compound the yields are high, and most are quite pure without recrystallization. An ionic compound, sodium tris(2,4-pentanedionato)cobaltate-(II), is also easily made it is somewhat less satisfactory as a starting material for the adducts. 

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