Five functionalized bis(beta-diketones) and their Cu(II) molecular squares are described. The new bis(beta-diketones), m-pbhxH(2) (3), 5-MeO-m-pbaH(2) (4),.5-BuO-mpbaH2 (5), 2-Me0-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-pbprH(2) (2). Ligand 3 has long alkyl chains in its,6-diketone moieties, while ligands 4-7 have alkoxy substituents on their aromatic rings. When treated with Cu-2, the new bis(fidiketones) 3, 4, 5, and 7 afford molecular squares, Cu-4(mpbhx)(4) (10), Cu-4(5-MeO-m-pba)(4) (11), Cu-4(5-BuO-m-pba)(4) (12), and Cu-4(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 the three of the molecular squares withour guest molecules, and for five adducts fo the squares with (fullerene) guests. The Cu center dot center dot center dot Cu distances in the "empty" squares wider range depending on the guest molecule involved. cs-(polypyridine) and pi-bonded (fullerene) Guests. The Cu center dot center dot center dot Cu distances in the empty squares range from 14.0904 ; those in the adducts vary over a wider range depending on the guest molecule involved.