New discrete and polymeric supramolecular architectures derived from dinuclear (bis-β-diketonato)copper(ii) metallocycles

Abstract

New examples of adducts between di- (and, in one instance, tetra-) functional nitrogen ligands and planar ‘platform-like’ dinuclear copper(II) complexes, [Cu₂L₂], incorporating the 1,3-aryl linked bis-β-diketonato bridging ligand 1,1′-(1,3-phenylene)-bis(4,4-dimethylpentane-1,3-dione) (H₂L) have been synthesised. The X-ray structures of six adduct species are reported. The interaction of [Cu₂(L)₂] with the ditopic ligand aminopyrazine (apyz) yielded the sandwich-like tetranuclear species [(Cu₂L₂(apyz))₂]. A variable-temperature magnetochemical investigation of this product indicated weak antiferromagnetic coupling between the (five-coordinate) copper centres, mediated by the 2-aminopyrazine linkers. An analogous structure, [(Cu₂L₂(dabco))₂] (dabco = 1,4-diazabicyclo[2.2.2]octane), was generated when dabco was substituted for aminopyrazine while use of 4,4′-dipyridyl sulfide (dps) and 4,4′-(1,3-xylylene)-bis(3,5-dimethylpyrazole) (xbp) as the ditopic ‘spacer’ ligands resulted in polymeric species of type [Cu₂L₂(dps)]_n and [Cu₂L₂(xbp)]_n, respectively. These latter species exist as one-dimensional chain structures in which copper(II) centres on different dinuclear platforms are linked in a ‘zigzag’ fashion. In contrast, with 2,2′-dipyridylamine (dpa) a discrete complex of type [Cu₂L₂(dpa)₂] formed in which one potential pyridyl donor from each 2,2′-dipyridylamine ligand remains uncoordinated. The use of the potentially quadruply-bridging hexamethylenetetramine (hmt) ligand as the linker unit was found to give rise to an unusual two-dimensional polymeric motif of type [(Cu₂(L²)₂)₃(hmt)₂]_n. The product takes the form of a (6,3) network, incorporating triply bridging hexamethylenetetramine units.