Extended three-dimensional supramolecular architectures derived from trinuclear (bis-β-diketonato)copper(ii) metallocycles

Abstract

Neutral trinuclear (triangular) copper(II) complexes of type [Cu₃L₃] incorporating the 1,4-aryl linked bis-β-diketonato bridging ligands, 1,1-(1,4-phenylene)-bis(butane-1,3-dione) (H₂L²), 1,1-(1,4-phenylene)-bis(pentane-1,3-dione) (H₂L³) and 1,1-(1,4-phenylene)-bis(4,4-dimethylpentane-1,3-dione) (H₂L⁴) have been demonstrated to react with selected heterocyclic nitrogen donor bases to generate extended supramolecular architectures whose structures have been confirmed by X-ray diffraction. Thus on reaction with 4,4′-bipyridine (bipy), [Cu₃(L²)₃] yields polymeric structures of type {[Cu₃(L²)₃(bipy)(THF)]·2.75THF}_n and {[Cu₃(L²)₃(bipy)(THF)]·bipy·0.75THF}_n while with pyrazine (pyz), {[Cu₃(L²)₃(pyz)]·0.5THF}_n was obtained. Each of these extended structures contain alternating triangle/linker units in a one-dimensional polymeric chain arrangement in which two of the three copper sites in each triangular ‘platform’ are formally five-coordinate through binding to a heterocyclic nitrogen atom. Interaction of the multifunctional linker unit hexamethylenetetramine (hmt) with [Cu₃(L³)₃] afforded an unusual, chiral, three-dimensional molecular framework of stoichiometry [Cu₃(L³)₃(hmt)]_n. The latter incorporates the trinuclear units coordinated to three triply bridging hmt units. In marked contrast to the formation of the above structures incorporating bifunctional linker units and five-coordinate metal centres, the trinuclear platform [Cu₃(L²)₃] reacts with the stronger difunctional base 1,4-diazabicyclo[2.2.2]-octane (dabco) to yield a highly symmetric trigonal columnar species of type {[Cu₃(L⁴)₃(dabco)₃]·3H₂O}_n in which each copper centre is octahedrally coordinated.