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 FeIII and the ligand 1H-imidazole-4,5-dicarboxylic acid, [Et3NH](12)[Fe-8(IDC)(12)]center dot 10DMF center dot 13H(2)O (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-). Mossbauer 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 mu-1 kappa N-2,O:2 kappa N-2',O '''-IDC3- 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 1H-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.