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

Abstract

In this work, we report a new octanuclear cluster based on Fe ^III and the ligand 1 H-imidazole-4,5-dicarboxylic acid, [Et ₃NH] ₁₂[Fe ₈(IDC) ₁₂]·10DMF·13H ₂O ( 1), with a metal core containing eight Fe ^III 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 {[Fe ₈(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 [Fe ₈(IDC) ₁₂] ^12–. Mössbauer spectra recorded at different temperatures show an isomer shift and quadrupole splitting parameters that confirm the existence of only Fe ^III-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 Fe ^III atoms located at the corners of the cube and connected by μ-1κ ² N, O:2κ ² N′, O‴-IDC ^3– bridges. Additionally, the magnetic measurements reveal a weak antiferromagnetic coupling in the Fe ₈ ^III 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 1 H-imidazole-4,5-dicarboxylic acid and Fe ^III 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.