EPR investigation of the second 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 ≈︁ 7. The tumbling rate of this species was determined by simulation as 1/τc = 1 × 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.