In this paper we have determined the thermodynamic parameters for the isomerization between the ${alpha}$-cis and the ${eta}$-cis isomers in vanadium(V)-propylenediaminetetraacetate complex in water by $^{51}V$ NMR spectroscopy. In addition, the effects of organic solvents (methanol, formamide and dimethylsulfoxide) and inorganic salts (NaCl, $NaClO_4;and;NH_4Cl$) on the isomerization in solution have been investigated.