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.