Binuclear spin-crossover [Fe(bt)(NCS) 2 ] 2 (bpm) complex: A study using first principles calculations.

The spin-crossover [Fe(bt)(NCS) 2 ] 2 (bpm) complex is studied using spin-polarized density functional theory within the generalized gradient approximation, the Hubbard U and the weak van der Waals interactions in conjunction with the projector augmented wave method in its molecular and periodic arrangements. It is shown that the considered complex has three magnetic configurations [high spin state (HS)-HS, HS-low spin state (LS), and LS-LS] corresponding to those observed experimentally after two transition temperatures T c (1) of 163 K and T c (2) of 197 K. For the HS-HS magnetic state, we found that the two Fe centers are antiferromagnetically coupled for both molecular and periodic structures in good agreement with the experimental observations. Our results show that the computed total energy difference between the magnetic state configurations of the considered Fe 2 complex is significantly smaller compared to those reported in the literature for other mono- or binuclear compounds.