TRANSMISSION OF MAGNETIC-INTERACTIONS THROUGH AN ORGANOMETALLIC COUPLER - A NOVEL FAMILY OF METALLOCENE-SUBSTITUTED ALPHA-NITRONYL AMINOXYLRADICALS

The capability of metallocene bridges as new organometallic magnetic c ouplers is evaluated by studying the family of diradicals 2 (M = Fe, R u) consisting of two purely organic alpha-nitronyl aminoxyl radicals c onnected by a 1,1'-metallocenylene bridge. Preliminary studies perform ed with 2-metallocenyl-alpha-nitronyl aminoxyl monoradicals 1 (M = Fe, Ru, Os), as reference compounds, show the presence of a small spin de nsity on the central metal of the metallocenes. This fact makes the me tallocene units effective bridges to transmit magnetic interactions by a spin polarization mechanism. The study of the magnetic properties o f diradicals 2 in the solid state and in diluted frozen solutions reve als the existence of an intramolecular antiferromagnetic exchange inte raction between the radical subunits whose strength is highly dependen t on the molecular conformation adopted by the diradical. As shown by crystal data and by ESR measurements, an intramolecular hydrogen bond between the two radical units forces the molecule to adopt a cisoid mo lecular conformation, which determines that the magnetic interaction o ccurs by a direct through-space interaction between the two SOMOs of t he two radical units along with the classical spin polarization mechan ism through the sigma-bonds of the metallocene unit. Lattice constants for both structures are as follows: 1 (M = Fe), C17H21FeN2O2, a = 7.1 70(1) Angstrom, b = 10.135(2) Angstrom, c = 10.683(2) Angstrom, alpha = 88.88(3)degrees, beta = 83.42(3)degrees, gamma = 79.75(3)degrees, tr iclinic, P (1) over bar, Z = 2; 2 (M = Fe), C24H32FeN4O4, a = 11.848(3 ) Angstrom: b = 11.785(2) Angstrom, c = 17.728(4) Angstrom, beta = 106 .25(2)degrees, monoclinic, P2(1)/n, Z = 4.