Hierarchical assembly of discrete copper(ii) metallo-structures from pre-assembled dinuclear (bis-β-diketonato)metallocycles and flexible difunctional co-ligands

Abstract

The sequential interaction of preformed [Cu₂(L¹11)₂(THF)₂] (where H₂L¹11 is 1,1-(1,3-phenylene)-bis(4,4-dimethylpentane-1,3-dione incorporating a 1,3-phenylene linker between its two β-diketone domains) and [Cu₂(L⁴44)₂]·2H₂O (where H₂L⁴44 is 1,1-(4,4′-oxybiphenylene)-bis(4,4-dimethylpentane-1,3-dione) incorporating a flexible oxybiphenylene linkage between the two β-diketone groups) with the potentially difunctional aliphatic non-planar co-ligands, N-methylpiperazine (mpip), N,N′-dimethylpiperazine (dmpip) and 1,4-thiomorpholine (thiomorph) is reported. A series of extended molecular assemblies exhibiting a range of di- and tetranuclear assemblies were obtained and their X-ray structures determined. Dinuclear [Cu₂(L¹11)₂(mpip)₂]·2mpip incorporates two 5-coordinate, square pyramidal metal centres as does tetranuclear [{Cu₂(L¹11)₂}₂(dmpip)₂]·2dmpip. In contrast, dinuclear [Cu₂(L¹11)₂(dmpip)₄]·dmpip and [{Cu₂(L¹11)₂}₂(thiomorph)₄]·3thiomorph each contain two 5-coordinate and two 6-coordinate centres. Each of [Cu₂(L⁴44)₂(THF)₂]·2THF and Cu₂(L⁴44)₂(mpip)₂]·H₂O incorporate only 5-coordinate metal centres, with the latter complex forming a one-dimensional hydrogen bonded ribbon-like structure directed along the crystallographic a-axis. In keeping with the documented tendency for the smallest, least strained assembly to form in supramolecular self-assembly processes, the incorporation of the flexible “oxy” linkage between the 4,4′-linked phenylene rings of H₂L³33 results in generation of a dinuclear [Cu₂L₂2] species rather than a trinuclear (triangular) [Cu₃L₃33] species of the type formed by the more rigid bis-β-diketonato ligand analogue in which the biphenylene rings separating the β-diketone domains are directly coupled in their 4,4′ positions.