SYNTHESIS, STRUCTURES, AND MAGNETIC-PROPERTIES OF FE-2, FE-17, AND FE-19 OXO-BRIDGED IRON CLUSTERS - THE STABILIZATION OF HIGH GROUND-STATE SPINS BY CLUSTER AGGREGATES

The compound[Fe(heidi)(H2O)]2, where H(3)heidi = N(CH2COOH)(2)(CH2CH2OH), crystallizes in a triclinic space group P (1) over bar, with a = 6.838(1) Angstrom, b = 7.058(1) Angstrom, c = 9.676(2) Angstrom, alpha = 103.29(1)degrees, beta = 93.58(1)degrees, gamma = 97.83(1)degrees and is a dinuclear iron(III) compound with the two iron atoms linked by the alkoxide function of the ligand. The dinucleating ability of this ligand is also present in the two polyiron(III) oxyhydroxide cluster compounds [Fe-19(mu(3)-O)(6)(mu(3)-OH)(6)(mu(2)-OH)(8)(heidi)(10)(H2O)(12)](1+) and [Fe-17(mu 3-O)(4)(mu 3-OH)(6)(mu 2-OH)(10)(heidi)(8)(H2O)12](3+) which crystalize in the same unit cell together with 60 lattice waters and four nitrate anions in the triclinic space group P (1) over bar, with a = 12.693(13) Angstrom, b = 18.060(17) Angstrom, c = 28.784(15) Angstrom, alpha = 93.66(6)degrees, beta = 94.95(6)degrees, gamma = 89.88(8)degrees. These clusters contain trapped iron hydroxide mineral portions produced by a modified hydrolysis of iron(III) in the presence of the ligand. They are the largest polyiron(III) oxyhydroxide clusters synthesized to date. A detailed investigation of their magnetic properties using ac and dc susceptibility measurements and EPR and Mossbauer spectroscopies reveals that in at least one of the clusters the ground state spin cannot be smaller than S = 33/2, the largest spin ground state so far observed in a molecular cluster.