Crystal structures and magnetic properties of chiral heterobimetallic chains based on the dicyanoruthenate building block

Abstract

By the reaction of chiral Mn^III Schiff-base complexes with the dicyanoruthenate building block, [Ru(salen)(CN)₂]⁻ (salen²⁻ = N,N′-ethylenebis(salicylideneimine) dianion), two couples of enantiomerically pure chiral cyano-bridged heterobimetallic one-dimensional (1D) chain complexes, [Mn((R,R)-salcy)Ru(salen)(CN)₂]_n (1-(RR)) and [Mn((S,S)-salcy)Ru(salen)(CN)₂]_n (1-(SS)) (Salcy = N,N′-(1,2-cyclohexanediylethylene)bis(salicylideneiminato) dianion), [Mn((R,R)-salphen)Ru(salen)(CN)₂]_n (2-(RR)) and [Mn((S,S)-salphen)Ru(salen)(CN)₂]_n (2-(SS)) (salphen = N,N′-(1,2-diphenylethylene)bis(salicylideneiminato) dianion), were synthesized and structurally characterized. Circular dichroism (CD) and vibrational circular dichroism (VCD) spectra confirm the enantiomeric nature of the optically active complexes. Structural analyses reveal the formation of neutral cyano-bridged zigzag single chains in 1-(RR) and 1-(SS), and double chains in 2-(RR) and 2-(SS). Magnetic studies show that antiferromagnetic coupling is operative between Ru^III and Mn^III centers bridged by cyanide. Compounds 1-(RR) and 1-(SS) show metamagnetic behavior with a critical field of about 7.2 kOe at 1.9 K resulting from the intermolecular π⋯π interactions. Additionally, magnetostructural correlation for some typical cyano-bridged heterobimetallic Ru^III–Mn^III compounds is discussed.