Synthesis and Characterization of Two Intensely Colored Tris(benzoylcyanoxime)iron(II) Anionic Complexes

Abstract

Two intensely blue-colored complexes, P(C6H5)4[Fe(BCO)3] (1) and Na[Fe(BCO)3] (2), where BCO− is the benzoylcyanoxime anion, have been prepared and characterized in solution and in the solid state. The crystal structure of 1 has been determined at several temperatures (100, 155, 225, and 293 K) and consists of layers of P(C6H5)4+ cations and [Fe(BCO)3]− anions. The latter exist as a pair of fac-Δ and Λ enantiomers in a monoclinic unit cell in the P2(1)/n space group. Iron(II) has a trigonal-prismatic N3O3 coordination environment with average Fe−N and Fe−O bond distances of 1.866 and 1.956 Å, respectively, bonds that are unusually short and indicate a 1A1g low-spin ground state for iron(II). A sample of 1 prepared with iron-57 has been studied by Mössbauer spectroscopy between 4.2 and 430 K and found to be low-spin iron(II) in studied temperature range. The stepwise formation constants for 1 in aqueous solution at 296 K and pH of 7 are log β1 = 0.85 ± 0.1, log β2 = 3.55 ± 0.15, and log β3 = 6.36 ± 0.15. Both 1 and 2 exhibit irreversible oxidation of iron(II) at ∼1.0 V, indicating a significant degree of the ligand-to-iron charge transfer. Thus, 1 and 2 are rare examples of highly colored iron(II) anionic complexes that do not contain aromatic heterocyclic amine ligands, such as bipyridine or phenanthroline.

Department(s)

Chemistry and Biochemistry

Document Type

Article

DOI

https://doi.org/10.1021/ic8004322

Keywords

anions, absorption, lLigands, molecular structure, temperature dependence

Publication Date

2008

Journal Title

Inorganic chemistry

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