New Highly Charged Iron(III) Metal–Organic Cube Stabilized by a Bulky Amine

In
this work, we report a new octanuclear cluster based on FeIII and the ligand 1H-imidazole-4,5-dicarboxylic
acid, [Et3NH]12[Fe8(IDC)12]·10DMF·13H2O (1), with a metal
core containing eight FeIII connected by only one type
of organic ligand. A peak at 573 m/z in the mass spectra of the compound suggests the adduct species
{[Fe8(IDC)12]+8H}4–. By X-ray
photoelectron spectroscopy, the oxidation state of the iron cation
was confirmed to be 3+, also identifying the presence of a quaternary
nitrogen species, which act as a countercation of the anionic metal
core [Fe8(IDC)12]12–. Mössbauer
spectra recorded at different temperatures show an isomer shift and
quadrupole splitting parameters that confirm the existence of only
FeIII-HS in the structure of 1. X-ray analysis
reveals that compound 1 crystallizes in the orthorhombic
system space group Ibam, confirming a molecular cluster
structure with an almost regular cube as geometry, with the FeIII atoms located at the corners of the cube and connected
by μ-1κ2N,O:2κ2N′,O‴-IDC3– bridges. Additionally, the magnetic
measurements reveal a weak antiferromagnetic coupling in the Fe8III coordination cluster (J =
−3.8 cm–1). To the best of our knowledge, 1 is the first member of the family of cubes assembled with
1H-imidazole-4,5-dicarboxylic acid and FeIII cation, exhibiting high pH stability over a broad pH range, making
it an ideal candidate for the design of supramolecular structures
and metal–organic frameworks.