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

Abstract The reaction of 2,2- cis -[Rh 2 (acam) 4 (H 2 O) 2 ]ClO 4 ( 1 ) (Hacam=acetamide) with sodium halides in aqueous solution gave crystals of [Rh 2 (acam) 4 X] n · mn H 2 O (X=Cl, Br, I). The composition of the products depended on the reaction temperature. The anhydrous compounds, [Rh 2 (acam) 4 X] n (X=Cl, 2 ; Br, 3 ; I, 4 ), were obtained at 40 °C, and the hydrated compounds, [Rh 2 (acam) 4 Cl] n ·7 n H 2 O ( 2 ·7 n H 2 O), [Rh 2 (acam) 4 Br] n ·3 n H 2 O ( 3 ·3 n H 2 O) and [Rh 2 (acam) 4 I] n ·2 n H 2 O ( 4 ·2 n H 2 O), 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 Rh 2 5+ units in the crystals can be assigned as the δ RhRh * MO from the RhL bond lengths, when compared with the corresponding Rh 2 4+ 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.