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

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 77 K the 2T signal grows in intensity relative to the 6A signal.