EQUILIBRIUM-CONSTANT FOR COORDINATIVE POLYMERIZATION OF AN O,O'-DIHYDROXYAZOBENZENE DERIVATIVE WITH NI(II) ION IN WATER

Equilibrium constant (K-CP) for coordinative polymerization is measure d for the first time. Constant K-CP is defined as [L](cp)/[M][L], wher e [L](cp) represents the concentration of the ligand present in the co ordination polymer. Plot of absorbance changes measured for 3, a water -soluble derivative of o,o'-dihydroxyazobenzene, against the concentra tion of Ni(II) ion indicates formation of a 1 : 1-type complex in wate r at pH 7.74 and 25 degrees C when Ni(II) is added in excess of 3. The 1 : 1-type complex can be either Ni3, the monomeric complex, or (Ni3) (n), the coordination polymer. The equilibrium constant for formation of the 1 : 1-type complex is estimated as 10(13.10) by using UO22+ ion as the competing metal ion. For the Ni(II) complex of an o,o'-dihydro xyazobenzene derivative attached to poly(ethylenimine), the formation constant is estimated as 10(5.36). Due to the structure of the polymer , possibility of coordinative polymerization is excluded for the polym er-based ligand. The much greater equilibrium constant for formation o f the Ni(II) complex of 3, therefore, indicates formation of(Ni3), ins tead of Ni3. The value of K-CP for (Ni3)(n) shows that only 10(-7)% of the initially added 3 is left unpolymerized when Ni(II) is added in e xcess of 3 by 10(-4)M. (C) 1997 John Wiley & Sons, Inc.