Electron spin resonance spectra of a ferromagnetic alternating spin chain (S 1=�, S 2=�)

Single-crystal e.s.r., spectra of the 1:1 adduct of copper(II) hexafluoro-acetylacetonate and the free radical 2,4,4,5,5-pentamethyl-3-oxido-4,5-dihydroimidazol-1-oxyl (NITMe), Cu(hfac)2(NITMe), have been recorded at room temperature at both X- and Q-band frequencies. At X-band frequency the liquid-helium-temperature spectra have also been collected. Linewidth analysis has been performed by considering the dipolar and anisotropic spin–spin interactions together, indicating that in the present compound the D tensor relative to the nearest-neighbour radical copper(II) interaction must be axial, with the unique axis approximately parallel to the Cu—O (nitroxide) bond. The low-temperature spectra show a g shift due to effects of short-range order effects.