Externally and Internally Functionalized Copper(II) β-Diketonate Molecular Squares

Five functionalized bis(β-diketones) and their Cu(II) molecular squares are described. The new bis(β-diketones), m-pbhxH2 (3), 5-MeO-m-pbaH2 (4), 5-BuO-m-pbaH2 (5), 2-MeO-m-pbaH2 (6), and 2-MeO-m-pbprH2 (7), were prepared by reaction of the corresponding aldehydes with phospholenes, as we previously reported for m-pbaH2 (1) and m-pbprH2 (2). Ligand 3 has long alkyl chains in its β-diketone moieties, while ligands 4-7 have alkoxy substituents on their aromatic rings. When treated with Cu2+, the new bis(β-diketones) 3, 4, 5, and 7 afford molecular squares, Cu4(m-pbhx)4 (10), Cu4(5-MeO-m-pba)4 (11), Cu4(5-BuO-m-pba)4 (12), and Cu4(2-MeO-m-pbpr)4 (13), respectively. Two of the new molecular squares, 10 and 12, contain longer-chain substituents and are soluble in a wider range of organic solvents. The other squares, 11 and 13, contain external and internal methoxy groups, respectively, and they show smaller changes in solubility. Single-crystal X-ray analyses are reported for three of the molecular squares without guest molecules, and for five adducts of the squares with σ- (polypyridine) and π-bonded (fullerene) guests. The Cu⋯Cu distances in the "empty" squares range from 14.047 to 14.904 Å; those in the adducts vary over a wider range depending on the guest molecule involved. (Chemical Equation Presented).