LINEAR ENTHALPY RELATIONSHIPS BETWEEN HEATS OF FORMATION OF COMPLEX COMPOUNDS AND HEATS OF LIGANDS III. COPPER(II)-2,2 '-BIPYRIDYL-COPPER(II)-PHENANTHROLINE-N- (meta-SUBSTITUTED PHENYL) GLYCINES TERNARY SYSTEMS

The heats of formation of ternary complex compounds formed of copper(II) with 2,2'-bipyridyl or 1,10-phenanthroline and N-(meta-substituted phenyl)glycines have been determined by calorimatric method at 25 degrees C and I = 0.1 molL(-1) (NaClO4) in 30% (V/V) ethanol solution. By utilizing the data for the protonation of N-(meta-substituted phenyl) glycines determined previously and coupled with the heats of formation of ternary complex compounds, a linear enthalpy relationship: Delta H-M = Q - beta Delta H-L1 (r > 0.99) with a negative slope was obtained. In addition linear entropy relationships were also found to exist between the entropy changes on formation of ternary complex compounds and protonation of the second ligands. The straight lines have approximately the same but negative slopes. The existence of negative slopes for linear enthalpy relationships would imply electrostatic interactions not important in the formation of ternary complex compounds, while back pi bonding formation between metal ion and the first ligand and CFSE as well seem to play a significant role. Whereas negative linear entropy relationships might be accounted for by the change of entropy in configuration while the entropy of chelation and of solvation are almost parallel.