One-dimensional antiferromagnetism in a linear chain containing zinc(II) and a nitronyl nitroxide

A compound of formula Zn(hfac)2(NIT-i-Pr)(H2O), where hfac = hexafluoroacetylacetonate and NIT-i-Pr = 2-isopropyl-4,4,5,5-tetramethylimidazoline-1-oxyl 3-oxide, was synthesized. The X-ray analysis shows that it crystallizes in the P2(1)/n space group with a = 13.917 (4), angstrom, b = 13.475 (3), angstrom, c = 15.885 (9) angstrom, beta = 99.10 (3)-degrees, and Z = 4. The structure consists of discrete molecules in which the zinc ions are octahedrally coordinated by the oxygens of the hfac molecules, an oxygen of the radical, and that of the water molecule. The hydrogen bond between the water molecule and the uncoordinated oxygen of the radical of an adjacent unit generates a chain structure along the b axis. The magnetic susceptibility and the EPR spectra support the description of the system as a typical one-dimensional Heisenberg antiferromagnet. The exchange-coupling constant, J = 12.2 cm-1, has been evaluated from the magnetic data and is attributed to the short contact (3.45 angstrom) between the NO groups of adjacent radicals. The single-crystal EPR spectra show the angular behavior of the line width and line shape typical of one-dimensional antiferromagnets. Moreover, EPR spectra at high frequency (248 GHz) show the anisotropy effects generated by short-range order, characteristic of one-dimensional systems, which cannot be detected in standard EPR experiments.