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

摘要

The reaction of 2,2-cis-[Rh_2(acam)_4(H_2O)_2]ClO_4(1)(Hacam=acetamide)with sodium halides in aqueous solution gave crystals of [Rh_2(acam)_4X]_n·mnH_2O(X=Cl,Br,I).The composition of the products depended on the reaction temperature.The anhydrous compounds,[Rh_2(acam)_4X]_n(X=Cl,2;Br,3;I,4),were obtained at 40 deg C,and the hydrated compounds,[Rh_2(acam)_4Cl]_n·7nH_2O(2·7nH_2O),[Rh_2(acam)_4Br]_n·3nH_2O(3·3nH_2O) and [Rh_2(acam)_4I]_n·2nH_2O)(4·2nH_2O),were obtained at room temperature (15-25 deg 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 #delta#_(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 -1.2K,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 exchang interaction.