Computer Aided Electron Parmagnetic Resonance Spectroscopy in the Speciation of pH-Dependent equilibria for CuKTSM2 Complex

An extensive reinvestigation of EPR spectra of [{2,2′-[1-(1-ethoxyethyl)-1,2-ethanediylidene]bis[N,N-dimethyl- hydrazinecarbothioamidato]}(2-)N2,N 2′,S,S′]copper(II) (CuKTSM2) was performed over a large pH range at room temperature. A thorough speciation was possible only by massive use of computer simulation of spectra at room temperature and careful exploration of linewidth details. EPR data vs. pH for CuKTSM2 clearly establishes the existence in solution of two distinguishable forms, at pH = 1.7 and at pH = 6.4. Spin Hamiltonian parameters and the correlation time were precisely discriminated by a new strategy based on computer-aided EPR spectroscopy and the choice of a suitable microwave frequency.