Switching of magnetic properties by topotactic reaction in a 1D CN-bridged Ni(II)-Nb(IV) system.

Two 1D CN-bridged assemblies: the nearly straight Li[Ni(cyclam)][Nb(CN)]·7.5HO (1) chains and the zigzag-shaped Li[Ni(cyclam)][Nb(CN)]·2HO (2) chains, are obtained in the reaction between [Ni(cyclam)] and [Nb(CN)] 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.