Spectroscopic and equilibrium characterization of metal complexes of phenoxy acid herbicides

Chemical Laboratories, P. P. N. College Campus (C. S. J. M. University), Kanpur-208 001,
Uttar Pradesh, India
E-mail : ssskushwaha4l@rediffmail.com Fax : 91-512-2239080
Manuscript received 24 August 2006, revised 2 February 2007, accepted 2 February 2007

The metal complexes of Co^II, Ni^II, Cu^II and Zn^II of phenoxyacetic acid (PAA, inactive) and chloro- ubstituted phenoxyacids (active) of the type ML₂ or ML₂.2H₂O have been isolated and characterized on the basis of elemental analysis, spectral, magnetic and thermal data. The IR data show that the bonding of the carboxylato group to the metal ion is bidentate. Also, potentiometric solution equilibrium study together with calorimetric measurements for evaluation of stability constants and thermodynamic quantities (∆G^o , ∆H^o and ∆S^o) at 25 ^oc (I = 0.10 M, KNO₃) have been made. It is found that in metals, except Cu^II in which phenoxy oxygen and one from carboxylato group is involved, both the oxygen atoms of carboxylato group participate in bonding. The complexation processes are found to be enthalpically and entropically favoured. The mode of complexation, stabilities and thermodynamic parameters of active (chloro-substituted derivatives) and inactive (PAA) are observed to be of comparable magnitudes indicating some other second order factors, other than binary metal complexation, are involved during growth regulation by these herbicides.