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Synthesis, Crystal Structure, and Magnetic Properties of a Bis-Dinuclear Oxo-Bridged Iron(III) Complex with p-Sulfonatocalix[4]arene



Reaction of sodium p-sulfonatocalix[4]arene (Na4C4AS) with iron(III) nitrate and 1,10-phenanthroline in water affords a compound in which a coordinated p-sulfonatocalix[4]arene anion (C4AS4–) bridges two oxo-bridged iron(III) dinuclear units, {FeIII2(μ-O)(H2O)5(phen)2}. The crystal structure of the compound also reveals noncoordinated C4AS4– anions and crystallization water molecules. The coordinated p-sulfonatocalix[4]arene links the {FeIII2(μ-O)(H2O)5(phen)2} dinuclear units through two of the four sulfonate groups in the 1,2 (syn) and 1,3 (anti) modes. The complete structure may be viewed as Fe-hinged calixarene bicapsules. The study of the magnetic susceptibility reveals strong antiferromagnetic interactions between the iron(III) ions within the dinuclear units. Because the structural features of the two Fe–O–Fe oxo bridges are very similar, the magnetic data can be fitted well by considering one exchange coupling constant, J = –127(1) cm–1, which is in agreement with previously found values for oxo-bridged diiron(III) complexes with similar structural features. This opens up the possibility of polynuclear complexes stabilized in water and of control of their magnetic properties.