3.5. EPR Spectroscopy
Electron paramagnetic resonance (EPR) spectroscopy of the dinuclear
Cu(II) nitrate complex was recorded using powdered sample
at ambient temperature (300 K) [40]. The X-band spectrum was
not well-resolved because of a rather large linewidth, and quasiisotropic
signals were observed in Fig. 5. The spectrum in the solid
sample only displayed fairly broad signals centered at g = 2.102
without hyperfine structure. A broad spectrum for dinuclear copper
complex with g = 2.10–2.11 indicated that the existence of an
antiferromagnetic spin-spin interaction between the magnetically
nonequivalent two Cu(II) ions [41,42]. The significant deviation
of the lowest g value from the free electron value (2.0023) demonstrated
that the unpaired electrons of Cu(II) lie in a dx2y2 ground
state, and such broad signals are consistent with square-pyramidal
geometry [40]. For a dinuclear copper(II) system (S = 1/2 ion pair),
the spin-spin coupling is determined by the isotropic exchange
constant J and by anisotropic interactions such as dipolar and anisotropic
and antisymmetric exchange [43].