Synthesis, structure and supramolecular features of homonuclear iron(III) and heteronuclear iron(III)-cobalt(III) complexes,[FeH_3L][ML](ClO_4)_3 (M = Fe(III) or Co(III). 2D sheet and tetrahedral arrays

摘要

Reaction of [MH_3L~1](ClO_4)_3 (H_3L~1 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 FeL~1 in methanol results in isolation of homonuclear (M = Fe(III)) or heteronuclear(M = Fe(III) and Co(III)) hemideprotonated complexes, [MH_(1.5)L~1](ClO)_(1.5). The complexes are characterized by EA, IR, single crystal structure determination and M?ssbauer spectroscopy. The iron complex,[FeH_(1.5)L~1](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 [FeH_2L~1][CoHL1](ClO_4)_3 ([M_(0.5)M'_(0.5) H_(1.5)L~1]~(1.5+) on average) and gives a homochiral 2D sheet structure, as did the trigonal form of [FeH_(1.5)L~1](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 [FeH_(1.5)L~1](ClO)_(1.5) and [FeH_2L~1][CoHL1](ClO_4)_3, exhibit a room temperature M?ssbauer 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.