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

The sequential interaction of preformed [Cu2(L1)2(THF)2] (where H2L1 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(L4)2]"¢2H2O (where H2L4 is 1,1-(4,4"²-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"²-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(L1)2(mpip)2]"¢2mpip incorporates two 5-coordinate, square pyramidal metal centres as does tetranuclear [{Cu2(L1)2}2(dmpip)2]"¢2dmpip. In contrast, dinuclear [Cu2(L1)2(dmpip)4]"¢dmpip and [{Cu2(L1)2}2(thiomorph)4]"¢3thiomorph each contain two 5-coordinate and two 6-coordinate centres. Each of [Cu2(L4)2(THF)2]"¢2THF and Cu2(L4)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"²-linked phenylene rings of H2L3 results in generation of a dinuclear [Cu2L2] species rather than a trinuclear (triangular) [Cu3L3] 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"² positions.