E 41 fc frequency counter

Using a Varian Cary 50 Bio spectrophotometer (Varian Inc., Paolo Alto, CA, USA), visible spectra in the 300–800 nm range were captured at 25 °C. For all systems under investigation, magnetic circular dichroism (MCD) spectra were captured at 25 °C using a Jasco J-1500 spectrometer (Jasco Corporation, Ishikawa-machi, Hachioji-shi, Tokyo Japan). The MCD spectra were captured using a Permanent Magnet PM-491 accessory and collected in a magnetic field of +1.6 T in the N/S field direction. All spectroscopic measurements were collected in the pH range of 2.5 to 11. The reactions were carried out in a 0.3 mol L1 KCl solution with a ligand concentration of 6 × 10⁻⁴ mol L⁻¹. 2.0 mL was used for each sample. With the aid of a Mettler Toledo pH meter and modest additions of concentrated KOH and HCl solutions, the pH values were determined. The electron paramagnetic resonance (EPR) spectra were recorded on a Bruker ELEXSYS E500 CW-EPR X-Band spectrometer equipped with an ER 036TM NMR Teslameter and an E 41 FC frequency counter (Bruker AXS GmbH, Karlsruhe, Germany). A microwave power of 10 mW, a modulation frequency of 100 kHz, a modulation amplitude of 10 G, a time constant of 82 ms, and a conversion time of 164 ms were adopted. The samples were sealed in quartz tubes and placed inside a standard EPR quartz tube for measurements.

Visible spectra of complexes were recorded at 25 °C on Varian Carry 50 Bio spectrophotometer. The electron paramagnetic resonance (EPR) spectra were recorded on Bruker ELEXSYS E500 CW-EPR, X-Band spectrometer, equipped with ER 036TM NMR Teslameter and E 41 FC frequency counter. The EPR simulated spectra and all EPR parameters were obtained by the Biomolecular EPR Spectroscopy Software of Wilfred R. Hagen (Hagen 2009 ). Circular dichroism (CD) spectra were recorded on Jasco J-1500 magnetic circular dichroism spectrometer in 230–800 nm range. The same concentrations were used for both spectroscopic and potentiometric studies.