An infinite zigzag chain of the halide-bridged tetrakis(acetamidato)dirhodium cation radical

The reaction of 2,2-cis-[Rh2(acam)4(H2O)2]ClO4 (1) (Hacam=acetamide) with sodium halides in aqueous solution gave crystals of [Rh2(acam)4X]n·mnH2O (X=Cl, Br, I). The composition of the products depended on the reaction temperature. The anhydrous compounds, [Rh2(acam)4X]n (X=Cl, 2; Br, 3; I, 4), were obtained at 40 °C, and the hydrated compounds, [Rh2(acam)4Cl]n·7nH2O (2·7nH2O), [Rh2(acam)4Br]n·3nH2O (3·3nH2O) and [Rh2(acam)4I]n·2nH2O (4·2nH2O), were obtained at room temperature (15–25 °C). All of the compounds consist of infinite zigzag chains of (RhRhX) units, which are supported by hydrogen bonds involving the NH(acam) and O(acam) atoms. The SOMO of the Rh25+ units in the crystals can be assigned as the δRhRh* MO from the RhL bond lengths, when compared with the corresponding Rh24+ complex. The magnetic susceptibilities of 2, 3 and 4 are described by a 1-D Heisenberg antiferromagnet with g=2.003, 2.012, and 2.065, and J=−8.6, −7.9, and −1.2 K, respectively. The ESR spectra of powdered crystals of 2, 3, and 4 were characteristic of rapid in-chain spin flip-flop exchange, most probably induced by the Heisenberg exchange interaction.