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 degrees. 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.