Diversity of the coordination modes of Croconate Violet. Crystal structures, spectroscopic characterization and redox studies of mono-, di- and poly-nuclear iron(ii) complexes

Abstract

The crystal structures of three iron(II) complexes with Croconate Violet [3,5-bis(dicyanomethylene)cyclopentane-1,2,4-trionate dianion = L²⁻] have been determined: K₂[FeL₂(H₂O)₄] 1, {[Fe(2,2′-bipy)L(H₂O)₂]·H₂O}₂2 and {[FeL(H₂O)₂]·2H₂O}_n3. Complex 1 consists of dianionic pseudo-octahedral mononuclear entities containing two N-mono-coordinated ligands in trans positions. Complex 2 consists of dimeric entities with metal atoms bridged by two N-coordinated Croconate Violet ligands. Complex 3 has a polymeric structure with both N- and O-coordinated Croconate Violet ligands: each iron(II) atom is bonded to three different Croconate Violet dianions and each ligand bonds three metal atoms. The magnetic properties have been investigated in the 2–300 K temperature range for complexes 2 and 3. Magnetic susceptibility measurements for these two complexes show the presence of a long distance magnetic coupling (ferromagnetic coupling in 2 with J = +0.18 cm⁻¹ and antiferromagnetic coupling in 3 with J = −0.19 cm⁻¹). The redox properties of the three complexes in dmf solution are compared to those of the free ligand.