Effects of the anion exchange between I⁻ and NCS⁻ coordinated to Co²⁺-centered tetrahedra in the organic–inorganic hybrid halides

Mixed-anion compounds provide a unique playground for local coordination engineering due to their heteroleptic coordination around cations. Here, we successfully synthesized novel thiocyanate-containing organic–inorganic hybrid halides (CH₃NH₃)₂Co(NCS)₄ and (CH₃NH₃)₃CoI₄(NCS) with isolated Co(NCS)₄ tetrahedra and mixed-anion CoI₃(NCS) tetrahedra, respectively. Together with (CH₃NH₃)₂CoI₄ with CoI₄ tetrahedra, they provide different types of anion-coordination around Co²⁺ ions. We compare the magnetic properties of these compounds and discuss the effects of anion exchange between I⁻ and NCS⁻ using density functional theory calculations.