Synthesis, Structure, And Magnetic Properties Of Cu2l2cl2 (Lh = N-Salicylidene-1,2-Ethanediamine) - A New S=1/2 Spin-Liquid Candidatele

The synthesis, room temperature crystal and molecular structure, and magnetic properties are reported for the new compound Cu2L2Cl2, where L- is the tridentate anion of N-salicylidene-1,2-ethanediamine. The compound crystallizes in the monoclinic space group P2(1/c) with a = 6.213(5) angstrom, b = 11.622(5) angstrom, c = 14.260(5) angstrom, beta = 100.240(5)degrees, and Z = 2. The crystal consists of dichloro-bridged binuclear molecules. The four-membered Cu2Cl2 bridging unit is strictly planar owing to crystallographic inversion symmetry. The geometry at the copper(II) centers is approximately square pyramidal, with the base plane formed by the cis-nitrogen atoms and the phenolic oxygen atom of the tridentate L- ligand and one chloride ion; the fifth, apical site is occupied by the basal chloride ligand of the neighboring copper center. The intradimer copper-copper separation is 3.271(1) angstrom. The out-of-plane Cu-Cl distance is 2.824(1) angstrom and the bridging Cu-Cl-Cu angle is 78.58(2)degrees. Unit a translations of the binuclear molecules generate ladder-like chains of copper atoms parallel to [100]. Each dimer is connected to each of its two nearest neighbors by Cu-Cl center dot center dot center dot H-N-Cu and Cu-O center dot center dot center dot H-N-Cu H bonding interactions. Interladder Cu-N-C-H center dot center dot center dot Cl-Cu and Cu-N-C- H center dot center dot center dot O-Cu interactions give rise to a 3D, coupled two-chain lattice. The dependence of the magnetization (M) on the applied magnetic field (H) up to 7.5 T at 1.7 K, and the temperature dependence of the inverse magnetic susceptibility (chi(-1)) between 1.7 K and 250 K show that the compound behaves as an ideal S = 1/2 paramagnet. This persisting spin disorder is tentatively attributed to the formation of an unusual spin-liquid state where ferromagnetic and antiferromagnetic exchange interactions between the Cu-II centers cancel.