Bis(<i>o</i>-phenylenebis(acetylacetonato))dicopper(II): A Strained Copper(II) Dimer Exhibiting a Wide Range of Colors in the Solid State

The bis(β-diketone) o-pbaH2 (o-phenylenebis(acetylacetone), 1) reacts readily with Cu2+. Although this reaction was expected to yield a trimeric product (2) on geometric grounds, the binuclear complex Cu2(o-pba)2 (3) is obtained instead. Materials containing Cu2(o-pba)2 adopt a variety of colors, depending on the solvents used in preparation: dark green (microcrystalline, 3a), golden-brown (ansolvous, 3b), green-brown (CHCl3−C6H6 solvate, 4), dark blue (nitrobenzene solvate, 5), or violet (toluene solvate, 6). Complexes 5 and 6 contain 1D chains of Cu2(o-pba)2 molecules joined by weak Cu···O interactions. Crystalline adducts [Cu2(o-pba)2L]n (7 and 8) containing 1D polymeric chains are also obtained upon reaction of 3 with bridging ligands (L = 1,2-bis(4-pyridyl)ethane or 4,4′-bipyridine, respectively). All of the new metal complexes except for 3a have been characterized by X-ray analysis.