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DAVIDFLEISCHER A N D HENRY FREISPR
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THE CALORIMETRIC DETERMINATION OF THE HEATS OF COORDINATION REACTIONS BYDAVID FLEISCHER A N D HENRY FHEISER Department of Chemistry, University of Pittsburgh, Pittsburgh 13, Pennsylvania Received August 66,1958
Two methods for calorimetrically determining the heats of stepwise coordination reactions with metal ions are described. One of these methods enables the calculation of the stability constant from the calorimetric data. The calorimetrically determined heats of reaction of the divalent ions of copper, nickel and cobalt with 8-quinolinol, 2-methyl- and 4-methyl-8quinolinol are compared with the heats of reaction obtained from the temperature dependence of the stability constant. The solvent system employed is 50 volume yo dioxane-water.
In spite of the great value of detailed thermodynamic data for interpreting chelation effects on a molecular basis, very few heat and entropy data have been determined. Almost without exception, these quantities have been found from the temperature dependence of the equilibrium constant (stability method). The data on diamines collected by AtcIntyre' shows that the heats of chelation for the same systems, reported by different investigators, are often in disagreement. A very few investigators have determined the heats of coordination reactions by direct calorimetric measurement. Fyfe2 found the heats of coordination for some metal ions with ammonia calorimetrically. His results are in good agreement with those found from the stability method. The heats of reaction of ethylenediamine and Nmethylethylenediamine with copper(I1) and nickel(TI) have been determined calorimetrically by Basolo and Murmann3 and by Davies, et aL4 While the calorimetric results agree with each other and with the stability method results of some investigntors,1s5 they are in conflict with the stability method heats of Charles* fouiid the heats of reaction of a series of divalent cat,ions with ethylenediaminetetrnacetic acid by calorimetric measurement and compared his results with those derived from the stability method by Cariiii and A.lartell.g The agreement is poor. The inow toward calorimetric deterniiiiations has, despite the inadequacies of the stability method, been very slow. The systems investigated have all been nineliable to experimental simplifications that nre not generally applicable to chelate reactions. None of the examples presented above involves solubility problems, since all of these chelates are charged species, but this is not generally true. Only in the case of the ethylenediamine renctions was more thnn one product formed, iiecessitatiiig the use of the stability constants in analyzing the data. The presence of more than one chelate species, however, is the rule ( 1 ) G. H. MoIntyre, Jr., Ph.D. Thesis, The Pennsylvania State College, 1953. ( 2 ) W. 9. Fyfe, J. Chem. SOC.,2018, 2023 (1952). (3) F. Basolo and R. I
