Abstract
Complexation of zinc(II) and cadmium(II) ions with 2,2′-bipyridine (bpy) are studied in N,N-dimethylacetamide (DMA) by calorimetry. Formation constants, enthalpies, and entropies of five mononuclear complexes, [Zn(bpy)n]2+ (n=1–3) and [Cd(bpy)n]2+ (n=1,2), are determined, and compared with the corresponding values in an analogous but less bulky solvent, N,N-dimethylformamide (DMF). The zinc complexes are more stable and the formation is more exothermic in DMA than in DMF, whereas the solvent effect on the cadmium complexes are rather small. A largely positive value of the enthalpy of transfer of Zn2+ from DMF to DMA shows that the greater stability of the zinc complexes in DMA is due to the weaker solvation of the metal ion, which is caused by the steric hindrance of DMA molecules. The transfer enthalpies become smaller in the order Zn2+>[Zn(bpy)]2+>[Zn(bpy)2]2+>[Zn(bpy)3]2+ and dictate gradual relaxation of the steric effect in the complexes. On the other hand, the transfer enthalpies of Cd2+ and its complexes are all small, indicating that the hindrance is insignificant in the vicinity of this larger cation.
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Koide, M., Suzuki, H. & Ishiguro, Si. Solution equilibria of zinc(II) and cadmium(II) complexes with 2,2′-bipyridine in N,N-dimethylacetamide at 25°C. J Solution Chem 25, 1261–1270 (1996). https://doi.org/10.1007/BF00972650
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DOI: https://doi.org/10.1007/BF00972650