Triaqua(pyridine-2,6-dipicolinato-O,N,O')iron(III) Bis(pyridine-2,6-dipicolinato-O,N,O')iron(III) Hexahydrate: an Unusual Ion-Pair Compound

The reaction of dipicolinic acid (2,6-pyridinedicarboxylic acid) with FeCl₃ results in the unusual title ion-pair compound, [Fe(C₇H₃NO₄)(H₂O)₃][Fe(C₇H₃NO₄)₂].6H₂O. Each Fe atom has an octahedral geometry. The dipicolinate ligands are nearly planar, with the two in the anion being perpendicular to each other and displaying a dihedral angle of 93.74 (6)°. The Fe—O(carboxylate) bond distances are comparable and range from 2.008 (2) to 2.028 (2) Å, while the Fe—N distances are 2.059 (2), 2.054 (2) and 2.054 (2) Å. The Fe—O(water) distances are 1.971 (2), 1.987 (2) and 2.004 (2) Å. The cation, anion and water molecules are involved in an extensive three-dimensional hydrogen-bonding network, with O...O distances ranging from 2.36 (2) to 2.953 (3) Å and angles ranging from 129 to 177°.

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