EPR INVESTIGATION OF THE 2ND SPHERE COORDINATION OF (CR(CN)5(NO))3- WITH PROTONATED POLYETHYLENEIMINE

The second sphere coordination of protonated, branched polyethleneimine (PEI) with [Cr(CN)5(NO)]3-(CPN) was studied by EPR spectroscopy. The interaction between the CPN complex ion and protonated PEI is reported as a function of pH. Simulation of the spectra indicated that ca. 98% of the CPN is bound to the polymer at pH almost-equal-to 7. The tumbling rate of this species was determined by simulation as 1/tau-c = 1 x 10(-8) s-1. The binding of CPN by PEI was influenced by the addition of other salts. Exchange interaction between Cu2+ and CPN was observed on the simultaneous binding of these two paramagnetic species to PEI. The pH dependence of the exchange was measured. At an intermediate pH range (7-9), CPN binds in the second and Cu2+ in the first sphere. The exchange interaction increases with the 'loading' of the polymer with the two paramagnetic species. Based on these results, a model is proposed for the species in solution.