*3.3. EPR Analysis*

Figure 3 display the EPR spectra of the dendrimer complexes [Cu2(ACR)(NO3)2 and EPR spectrum of ACR ligand is shown for the comparison, The EPR spectrum of the copper complex consists of an anisotropic signal with *g*-components of *g*<sup>1</sup> = 2.238, *g*<sup>2</sup> = 2.075, *g*<sup>3</sup> = 2.065 between 120 and 295 K. The *g*-components are not sensitive towards the recording temperature. In the range of g1-component, a hyperfine structure is hardly resolved, the constant hyperfine being A1 = 16.5 mT. The analysis of EPR parameters of the Cu(II) complex reveals that the *g1*-component adopts a relatively low value, whereas, the magnitude of the hyperfine constant A1 is relatively high. On the basis of Peisach-Blumberg diagram [31], the relation between the values of *g*- and *A*-components can be used as an experimental measure on the composition of the coordination shell around Cu(II) ions: The coordination of nitrogen to Cu(II) provokes a decrease of the g||-value and a corresponding increase in A|| value, while the opposite trend is observed when oxygen is coordinated around Cu(II). The comparison shows that for the complexes of Cu(II) with ACR, the ligand is coordinated to Cu(II) ions mainly through nitrogen atoms (Scheme 1).

The ligand displays a narrow symmetrical signal with a *g*-factor of 2.003, in comparison with the copper complex. The *g*-value and the extremely narrow line width (less than 0.5 mT) implies that the signal comes, most probably, from free radicals. It should be taken into account that the origin of this signal is unclear. It is of importance that the signal, due to the ligand is not observed in the EPR spectrum of the copper complex; hence, all ligand molecules are involved in the complexation.

**Figure 3.** EPR spectra of the complex of [Cu2(ACR)(NO3)2]) and dendrimer ligand ACR (bottom). The recording temperature is indicated.
