Chiral Templating Activity of Tris(bipyridine)ruthenium(II) Cation in the Design of Three-Dimensional (3D) Optically Active Oxalate-Bridged {[Ru(bpy)₃][Cu_2xNi_2(1-x)(C₂O₄)₃]}_n(0 ≤x≤ 1; bpy = 2,2‘-bipyridine): Structural, Optical, and Magnetic Studies

Three-dimensional oxalate-based {[Ru(bpy) 3 ][Cu 2 x Ni 2(1 - x ) (ox) 3 ]} n (0≤ x ≤ 1, ox = C 2 O 4 2 -, bpy = 2,2‘bipyridine) were synthesized. The structure was determined for x = 1 by X-ray diffraction on single crystal. The compound crystallizes in the cubic space group P 4 1 32. It shows a three-dimensional 10-gon 3-connected (10,3) anionic network where copper(II) has an unusual tris(bischelated) environment. X-ray powder diffraction patterns and their Rietveld refinement show that all the compounds along the series are isostructural and single-phased. According to X-ray absorption spectroscopy, copper(II) and nickel(II) have an octahedral environment, respectively elongated and trigonally distorted. As shown by natural circular dichroism, the optically active forms of {[Ru(bpy) 3 ][Cu x Ni 2(1 - x ) (ox) 3 ]} n are obtained starting from resolved Δ- or Λ-[Ru(bpy) 3 ] 2+ . The Curie−Weiss temperatures range between −55 ( x = 1) and −150 K ( x = 0). The antiferromagnetic exchange interaction thus decreases when the copper contents increases in agreement with the crystallographic structure of the compounds and the electronic structure of the metal ions. At low temperature, the compounds exhibit complex long-range ordered magnetic behavior.