Antiferromagnetic to Ferromagnetic Coupling Crossover in Hybrid Nickel Chain Perovskites

We synthesize and characterize the magnetic and thermodynamic properties of the quasi one-dimensional organic-inorganic hybrid ANiCl₃ compounds [A = N(CH₃)₄⁺, CH₃NH₃⁺, (CH₃)₂NH₂⁺, C(NH₂)₃⁺, and CH(NH₂)₂⁺]. Additionally, the crystal structure of (CH₃)₂NH₂NiCl₃ is reported. These materials possess chains of face-sharing NiCl₆ octahedra in a triangular array. The chains run in one direction and are separated from one another by organic cations of different sizes and geometries. In accordance with the 90° superexchange model, we find that the nature of the magnetic coupling within chains can be predicted by the value of the Ni-Cl-Ni angle. As the Ni-Cl-Ni angle decreases from 90°, the magnetic interactions become increasingly antiferromagnetic. These findings provide a foundation for predicting the magnetic properties of quasi one-dimensional organic-inorganic hybrid ANiCl₃ compounds.