Synthesis, Structure, and Magnetic Properties of Cu 2 L 2 Cl 2 (LH = N ‐Salicylidene‐1,2‐ethanediamine) – A New S = 1/2 Spin–Liquid Candidate

The synthesis, room temperature crystal and molecular structure, and magnetic properties are reported for the new compound Cu 2 L 2 Cl 2 , where L – is the tridentate anion of N ‐salicylidene‐1,2‐ethanediamine. The compound crystallizes in the monoclinic space group P 2 1/ c with a = 6.213(5) Å, b = 11.622(5) Å, c = 14.260(5) Å, β = 100.240(5)°, and Z = 2. The crystal consists of dichloro‐bridged binuclear molecules. The four‐membered Cu 2 Cl 2 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) Å. The out‐of‐plane Cu–Cl distance is 2.824(1) Å and the bridging Cu–Cl–Cu angle is 78.58(2)°. Unit a translations of the binuclear molecules generate ladder‐like chains of copper atoms parallel to [1 0 0]. Each dimer is connected to each of its two nearest neighbors by Cu–Cl ··· H–N–Cu and Cu–O ··· H–N–Cu H bonding interactions. Interladder Cu–N–C–H ··· Cl–Cu and Cu–N–C–H ··· 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 ( χ –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.