Understanding Cooperativity in Tetrazole-Based Fe(II) Spin-Crossover Coordination Networks: Effects of Alkyl Linkers

Employing first-principles calculations and a model Hamiltonian approach, we study the cooperative spin-crossover properties in Fe-tetrazole coordination polymers upon variation of lengths of alkyl linkers connecting Fe(II) centers. The systematic trend is understood by comparing the properties of a two-C linker Fe-ebtz compound, a computer-generated four-C linker Fe-bbtz compound, and a six-C linker Fe-hbtz compound. Our study reveals that the hysteresis observed in the temperature-driven spin-state transition in this family of compounds is geared by the magnetic superexchange interaction, with the elastic interactions playing an insignificant role in the hysteresis. Upon increasing the lengths of the linkers, by the inclusion of an increasing number of C atoms, the magnetic superexchange interactions between Fe(II) centers, mediated by linkers, weaken, causing a significant drop in hysteresis width between two-C linker and six-C linker compounds. Our predicted hysteresis behavior of the four-C linker compound may be verified in future experiments.