title: Spin crossover transition of Fe(phen)2(NCS)2: periodic dispersion-corrected density-functional study.
abstract: Periodic dispersion corrected DFT calculations have been performed to study the spin-crossover transition of Fe(phen)(2)(NCS)(2) in the molecular and in the crystalline state. We show that London dispersion interactions play a crucial role in the cohesion of the crystals. Based on calculations of vibrational eigenstates of the isolated molecule and of the crystalline phase in both the low- and high-spin states, the transition entropies and enthalpies have been calculated. We demonstrate that, due to the stabilization of the low-spin state by intermolecular dispersion forces, the transition enthalpy at the transition temperature is larger for the crystalline phase in comparison with an isolated molecule. The effective coordination number of the nitrogen atoms of the ligands around the iron atom has been identified as the order parameter driving the quasi-reversible low-spin to high-spin transition in the crystal. Finally, using constrained geometry relaxations at fixed values of the coordination number, we computed the energy barrier of the LS to HS transition and found it to be in a reasonable agreement with the experimental value.
authors.affiliation: Department of Physical and Theoretical Chemistry, Faculty of Natural Sciences, Comenius University, Mlynská Dolina, SK-84215 Bratislava, Slovakia. tomas.bucko@univie.ac.at
authors.forename: Tomáš
authors.initials: T
authors.lastname: Bučko
authors.forename: Jürgen
authors.initials: J
authors.lastname: Hafner
authors.forename: Sébastien
authors.initials: S
authors.lastname: Lebègue
authors.forename: János G
authors.initials: JG
authors.lastname: Ángyán
mesh_terms: D005296:Ferrous Compounds / Q000737:chemistry*; D010618:Phenanthrolines / Q000737:chemistry*; D011789:Quantum Theory; D013861:Thiocyanates / Q000737:chemistry*
chemical_list: D005296:Ferrous Compounds; D010618:Phenanthrolines; D013861:Thiocyanates; C031760:thiocyanate; C025205:1,10-phenanthroline