Structure and Magnetic Properties of a Giant Cu₄₄^II Aggregate Which Packs with a Zeotypic Superstructure

Reaction of Cu(II) and the aminopolycarboxylate nitrilotripropionic acid (H3ntp) in water leads to the formation of [Cu44(μ8-Br)2(μ3-OH)36(μ-OH)4(ntp)12Br8(OH2)28]Br2·81H2O. The Cu44 aggregates have a central inorganic core corresponding to [Cu24(μ8-Br)2(μ3-OH)24(μ-OH)8]14+ anchored on two bromide anions, and this is encased in a shell of Cu(II)/ligand units. The aggregates pack into a distorted tetragonal array with a very open structure containing large amounts of water of crystallization. The magnetic properties have been studied and, while complicated by the presence of low-lying excited states, indicate that the individual clusters have nonzero spin ground states.