General methods
All reagents and solvents of reagent grade were purchased from
commercial sources and used as received except specified.
Methanol was dried by heating over iodine activated magnesium
with a magnesium loading of 5 gm/lit. Then the dried methanol
was kept over 20% m/v 3 Å molecular sieves for 4–5 days before
using. Acetonitrile was dried over calcium hydride. Deoxygenation
of the solvent and solutions was effected either by repeated
vacuum/purge cycles or bubbling with argon for 30 min or using
freeze-pump-thaw cycles. UV–Vis spectra were recorded on a
Perkin Elmer Lambda 25 UV–Vis spectrophotometer. FT-IR spectra
of the solid samples were taken on a Perkin Elmer spectrophotometer
with samples prepared as KBr pellets. Solution electrical
conductivity was measured using a Systronic 305 conductivity
bridge. 1H NMR spectra were recorded in a 400 MHz Varian FT
spectrometer. Chemical shifts (ppm) were referenced either with
an internal standard (Me4Si) or to the residual solvent peaks. The
X-band Electron Paramagnetic Resonance (EPR) spectra were