Squeezing the [Cu−OH···H₂O−Cu]³⁺ Bridge by Cryptate Encapsulation

Treatment of cryptand L1 with Cu(II) generates a H3O2--bridged dicopper(II) cryptate, 2, where the guest anion has responded to steric constraint by a significant shortening of the O−O distance to 2.325(9) Å; computational optimization at the B3LYP/6-31(d) level suggests that the bridging O−H···O H-bond is bent (≈157°) but that the barrier to interchange of the bridging H atom is low (<4 kJ mol-1). This cryptate, rather than the [Cu2L1μCN]3+ species recently claimed to derive from cleavage of the C−C bond of the solvent, is the product of acetonitrile recrystallization of the initially formed reaction product, 1.