Synthesis, Structures, and Magnetic Properties of Fe2, Fe17, and Fe19 Oxo-Bridged Iron Clusters: The Stabilization of High Ground State Spins by Cluster Aggregates

[Fe(heidi)(H2O)]2, where H3heidi = N(CH2COOH)2(CH2CH2OH), crystallizes in a triclinic space group P̅1, with a 6.838(1), b 7.058(1), c 9.676(2) Å, α 103.29(1), β 93.58(1), γ 97.83(1)° and is a dinuclear Fe(III) compd. with the two Fe 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 compds. [Fe19(μ3-O)6(μ3-OH)6(μ2-OH)8(heidi)10(H2O)12]1+ and [Fe17(μ3-O)4(μ3-OH)6(μ2-OH)10(heidi)8(H2O)12]3+ which crystallize in the same unit cell together with 60 lattice waters and four nitrate anions in the triclinic space group P̅1, with a 12.693(13), b 18.060(17), c 28.784(15) Å, α 93.66(6), β 94.95(6), γ 89.88(8)°. These clusters contain trapped Fe hydroxide mineral portions produced by a modified hydrolysis of Fe(III) in the presence of the ligand. They are the largest polyiron(III) oxyhydroxide clusters synthesized to date. A detailed study of their magnetic properties using a.c. and d.c. susceptibility measurements and EPR and Moessbauer 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 obsd. in a mol. cluster. [on SciFinder(R)]