Switching of magnetic properties by topotactic reaction in a 1D CN-bridged Ni(ii)–Nb(iv) system

Abstract

Two 1D CN-bridged assemblies: the nearly straight Li₂[Ni(cyclam)][Nb(CN)₈]·7.5H₂O (1) chains and the zigzag-shaped Li₂[Ni(cyclam)][Nb(CN)₈]·2H₂O (2) chains, are obtained in the reaction between [Ni(cyclam)]²⁺ and [Nb(CN)₈]⁴⁻ in warm concentrated LiCl water solution. Both compounds are composed of alternating bimetallic Ni(II)–Nb(IV) chains and contain incorporated lithium cations, which compensate the negative charge of the coordination skeleton. The straight chain 1 (Ni–Nb–Ni angle = 153.2°) can be reversibly dehydrated under dry nitrogen flow at room temperature to an intermediate dihydrate phase 1d and further transformed to the zigzag-shaped chain 2 (Ni–Nb–Ni angle = 86.6°) by annealing at 150 °C. The process can be reversed by exposure to high humidity at room temperature, upon which 2 is converted back to 1. This water sorption-induced breathing effect is accompanied by changes in magnetic properties, most notably reflected in different values of saturation magnetization and critical field of metamagnetic transition, which indicate that both intra- and inter-chain interactions are affected by the structure reorganization.