Structure and magnetic properties of ferrimagnetic chains formed by manganese(II) and nitronyl nitroxides

Four ferrimagnetic chains formed by manganese hexafluoroacetylacetonate and different nitronyl nitroxide radicals 2-R- 4,4,5,5-tetramethy1-4,5-dihydro1-H -imidazolyl-1 - oxy 3-oxide (with R = isopropyl, ethyl, methyl, and phenyl) were synthesized. The magnetic susceptibility measurements in the range 6300 K show a divergence at low temperature that is compatible with an infinite array structure. The intrachain interaction is antiferromagnetic and estimated by a numerical fit to be in the range 200-330 cm-'. The monodimensionality is confirmed by the X-ray structure of Mn(hfac)*NIT-i-Pr, which crystallizes in the monoclinic P2Jc space group with a = 20.135 (1) A, b = 9.43 (1) A, c = 15.475 (1) A, @=11 0.74 (2)O, and Z = 4. EPR spectra are consistent with the magnetic data and show a behavior typical of low-dimensional materials. The line width in single-crystal spectra of Mn(hfac)zNIT-i-Pr has an angular dependence of the type (3 cos2 0 - 1)4'3, while the line shape is intermediate between Lorentzian and Gaussian, showing that the exchange narrowing regime is not attained