Synthesis, structure and supramolecular features of homonuclear iron(III) and heteronuclear iron(III)–cobalt(III) complexes, [FeH3L][ML](ClO4)3 (M = Fe(III) or Co(III). 2D sheet and tetrahedral arrays

Abstract

Reaction of [MH3L1](ClO4)3 (H3L1 is the tripodal ligand derived from the condensation of tris(2-aminoethyl)amine (tren) with three equivalents of 4-methyl-5-imidazolecarboxaldehyde and M=Fe(III) or Co(III)) with FeL1 in methanol results in isolation of homonuclear (M=Fe(III)) or heteronuclear (M=Fe(III) and Co(III)) hemideprotonated complexes, [MH1.5L1](ClO)1.5. The complexes are characterized by EA, IR, single crystal structure determination and Mössbauer spectroscopy. The iron complex, [FeH1.5L1](ClO)1.5, exists as three polymorphs, trigonal, cubic and hexagonal. The trigonal and cubic forms exhibit a homochiral 2D sheet and tetrahedral supramolecular structure, respectively. The former crystallized as a racemic conglomerate and the latter crystallized as a racemic compound. The hexagonal polymorph was an impurity in the trigonal form and exhibits a layered supramolecular structure. The heteronuclear cluster is formulated as [FeH2L1][CoHL1](ClO4)3 ([M0.5M′0.5 H1.5L1]1.5+ on average) and gives a homochiral 2D sheet structure, as did the trigonal form of [FeH1.5L1](ClO)1.5. Both the 2D sheet and tetrahedral cluster supramolecular assemblies are held together by intermolecular imidazole–H⋯imidazolate hydrogen bonds as shown by IR spectroscopy and the structures. The iron(III) complex of both 2D sheet supramolecular structures, the trigonal form of [FeH1.5L1](ClO)1.5 and [FeH2L1][CoHL1](ClO4)3, exhibit a room temperature Mössbauer spectrum that has signals attributable to the 2T (low spin) and 6A (high spin) iron(III). At 77K the 2T signal grows in intensity relative to the 6A signal.