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 ANiCl 3 compounds [A = N(CH 3 ) 4 + , CH 3 NH 3 + , (CH 3 ) 2 NH 2 + , C(NH 2 ) 3 + , and CH(NH 2 ) 2 + ]. Additionally, the crystal structure of (CH 3 ) 2 NH 2 NiCl 3 is reported. These materials possess chains of face-sharing NiCl 6 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 ANiCl 3 compounds.