Molecular Structure and Magnetic Properties of µ -Dihydroxo-bis[4-dimethylamino-2,6-pyridine-dicarboxylatoaquoiron(III)] Dihydrate, [(CH3)2NC7H2NO4(H2O)FeOH]2-2H2O

Chia Chih Ou, Roger A. Lalancette, Joseph A. Potenza, Harvey J. Schugar

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Abstract

The crystal and molecular structure of the title complex has been determined from single-crystal three-dimensional x-ray data collected by counter methods. [(CH3)2NC7H2NO4(H2O)FeOH]2 2H2O crystallizes as red-brown prisms in space group C2/m with Z = 2; a = 13.538 (5), b = 10.758 (6), c = 9.331 (3) Å; β = 114.74 (3)°;dcalcd = 1.706, dohsd = 1.72(1)g/ cm3. Least-squares refinement of 907 reflections having I ≥ 3σ(I) gave a conventional R factor of 0.068. The structure consists of discrete centrosymmetric dimeric units in which two crystallographically equivalent Fe(III) ions are bridged by two OH groups. The distorted octahedral NO5 donor set is composed of the bridging OH ions, one H2O molecule, and a tridentate pyridinedicarboxylate ligand. Structural parameters of the planar Fe2(OH)24+ unit include Fe-O bond distances of 1.937 (6) and 1.986 (9) A, an Fe-O-Fe bridging angle of 105.3 (4)°, and an Fe⋯Fe separation of 3.118 (3) A. Comparisons are drawn between the coordination geometry of the title complex and those previously observed for Fe2(OH)24+ complexes of related ligands having either OH or H as the 4-ring substituents. The antiferromagnetism of the title complex is reflected by a gradual decrease of µeff from 4.94 µb (per Fe) at 301 K to 190 µb at 78 K. Magnetic susceptibilities over this temperature range are well described by the spin-spin model for H = -2JS1S2 with S1 = S2 = 5/2 -J = 11-7 (4) cm-1, and g = 2.0. In contrast to the behavior of Cu2(OH)22+ and Cr2(OH)24+ units, spin-spin coupling within Fe2(OH)24+ units is not strongly dependent on the M-OH-M bridging angles.

Original languageEnglish (US)
Pages (from-to)2053-2057
Number of pages5
JournalJournal of the American Chemical Society
Volume100
Issue number7
DOIs
StatePublished - Jan 1 1978

All Science Journal Classification (ASJC) codes

  • Catalysis
  • Chemistry(all)
  • Biochemistry
  • Colloid and Surface Chemistry

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