Triangles and tetrahedra: metal directed self-assembly of metallo-supramolecular structures incorporating bis-β-diketonato ligands

Abstract

The interaction of six aryl-linked bis-β-diketones, including a new naphthylene linked species, with copper(II), iron(III) and, in one instance gallium(III), has been investigated with the aim of obtaining metallo-supramolecular assemblies exhibiting different geometries. New examples of two assembly types incorporating the above bis-β-diketones (L) were generated. The first type is represented by a range of molecular triangles of formula [Cu₃(L–H₂)₃](solvent)_n while the second is given by a corresponding selection of less-common neutral molecular tetrahedra of formula [Fe₄(L–H₂)₆](solvent)_n as well as [Ga₄(L–H₂)₆]·8.5THF·0.5H₂O; an example of each type has been characterised by X-ray crystallography. A magnetochemical investigation of [Fe₄(3–H₂)₆]·6THF is reported. The susceptibility is Curie like and consistent with very weak coupling occurring between the iron(III) d⁵ (high spin) centres. The X-ray structures of two trinuclear copper(II) as well as a tetranuclear iron(III) and a tetranuclear gallium(III) assembly confirm their discrete triangular and tetrahedral geometries, respectively. The structure of the gallium(III) species is closely related to that of the corresponding iron(III) species. The tetrahedral structures provide rare examples of such assemblies encapsulating guest solvent molecules – in each case tetrahydrofuran is incorporated in the central cavity.