STRUCTURE AND FERROMAGNETIC INTERACTIONS IN OPEN-SHELL SUPRAMOLECULARASSEMBLIES CONSTRUCTED FROM RADICAL CATIONS AND HEXACYANOMETALLATE ANIONS

The goal of our work was to design in a controlled manner open-shell s upramolecular assemblies with dominant intermolecular ferromagnetic in teractions. Along this line, the compounds of formula rad(6)M(CN)(6)I- 3 . 2H(2)O with M = Cr, Fe, and Co have been synthesized; rad(+) stand s for the -4,4,5,5-tetramethyl-4,5-dihydro-1H-imidazo-1-oxyl 3-N-oxide radical cation. The crystal structures have been solved. The three co mpounds are isomorphous. They crystallize in the trigonal space group P3 (a = 13.178(3) Angstrom, c = 10.763(6) Angstrom for M = Fe). The st ructure may be viewed as a two-dimensional honeycomb lattice, with thr ee kinds of hexagons and three kinds of rad---rad magnetic interaction s. In addition, for M = Cr and Fe, there is a fourth kind of magnetic interaction, occurring between the M(CN)(6)(3-) anion and the radical core. The magnetic properties of the three compounds have been investi gated. They are characteristic of dominant ferromagnetic interactions to which weak antiferromagnetic interactions are superimposed. A quant itative interpretation of the magnetic data has been developed. In par ticular, for the chromium derivative, three out of four interactions h ave been found to be ferromagnetic, including the rad---Cr(CN)(6) inte raction. The spin topologies of our supramolecular assemblies have bee n discussed in the context of the spin frustration phenomenon. The pot entialities of the supramolecular chemistry of open-shell units have b een emphasized.