Formation Constants of the Copper(II) Compounds of Pyridylalpyridylhydrazine

Bivalent copper and the Schiff's base pyridylalpydidylhydrazine form two compounds, composed respectively of one molecule and of two molecules of the organic compound to one atom of copper, and having ultra violet absorption spectra differing only in the value of the molar extinction coefficients at the absorption maxima, 15,100 and 22,450, respectively at 345 mμ. The respective formation constants are 2.4 x 105 and 2.8 x 105 as determined from spectrophotometric data, the method used being unusual in that the ultra violet absorption data provided a direct measure of the free ligand present. Hunt and Diehl ( 1, 2, 3) have shown that pyridylalpridylhydrazine (1,3-bis(2'-pyridyl)-2,3-diaza-l-propene), the Schiffs 0H C H \_N 'N-N Nj base of 2-pyridylcarboxaldehyde and 2-pyridylhydrazine, is a useful reagent for the spectrophotometric determination of small amounts of cobalt in the presence of iron, nickel, copper, and other bivalent transition elements which can be extracted into nonpolar solvents. The cobalt(III)-PDP compound is not extracted. The separation of the other transition elements from cobalt is clean, and the cobalt remains quantitatively in the water layer as one of the most intensely colored of all metal compounds known. In the course of the work, attention was directed toward learning the nature of the iron, nickel and copper compounds. The copper compounds described first by Lions and Martin ( 4) and by Geldard and Lions ( 5) proved of interest because, as shown in the present work, the fonnation constants for the attachment of the second molecule of PDP to the copper atom is greater than that for the first. In this paper we describe the method of measurement used for the determination of these constants. EXPERIMENTAL WORK Apparatus and Materials. Absorption spectra were obtained on a Beckman DU spectrophotometer using 1-cm quartz cells. 1 Department of Chemistry, Iowa State University, Ames, Iowa.