Switching magnetic interactions in the NiFe Prussian Blue Analogue: an ab initio inspection

The magnetic interaction in the Ni(II)–Fe(III) Prussian Blue Analogue is investigated by means of Difference Dedicated Configuration Interaction (DDCI) calculations. Embedded cluster calculations are performed to extract the exchange coupling constant J with respect to an opening of the Ni–NC–Fe bridge while maintaining a rigid Fe(CN)6 unit. It is shown that such active distortion significantly modifies the magnetic interaction scheme in the material. Not only a ferromagnetic to antiferromagnetic transition is observed, but the J value is varied from +11.4 cm−1 to −12.5 cm−1 when the Ni–Fe cyanide bridge is opened by 20°. The enhancement of the intersite hopping electron transfer integral by a factor of 1.5 can be correlated with the observed Na+-ion mobility in a unified “cation-coupled electron transfer” (CCET) process. These results stress the complexity and originality of this class of compounds evidenced by the versatility of their magnetic network.