title: Guest modulation of spin-crossover transition temperature in a porous iron(II) metal-organic framework: experimental and periodic DFT studies.
abstract: The synthesis, structure, and magnetic properties of three clathrate derivatives of the spin-crossover porous coordination polymer {Fe(pyrazine)[Pt(CN)4]} (1) with five-membered aromatic molecules furan, pyrrole, and thiophene is reported. The three derivatives have a cooperative spin-crossover transition with hysteresis loops 14-29 K wide and average critical temperatures Tc =201 K (1⋅fur), 167 K (1⋅pyr), and 114.6 K (1⋅thio) well below that of the parent compound 1 (Tc =295 K), confirming stabilization of the HS state. The transition is complete and takes place in two steps for 1⋅fur, while 1⋅pyr and 1⋅thio show 50 % spin transition. For 1⋅fur the transformation between the HS and IS (middle of the plateau) phases occurs concomitantly with a crystallographic phase transition between the tetragonal space groups P4/mmm and I4/mmm, respectively. The latter space group is retained in the subsequent transformation involving the IS and the LS phases. 1⋅pyr and 1⋅thio display the tetragonal P4/mmm and orthorhombic Fmmm space groups, respectively, in both HS and IM phases. Periodic calculations using density functional methods for 1⋅fur, 1⋅pyr, 1⋅thio, and previously reported derivatives 1⋅CS2 , 1⋅I, 1⋅bz(benzene), and 1⋅pz(pyrazine) have been carried out to investigate the electronic structure and nature of the host-guest interactions as well as their relationship with the changes in the LS-HS transition temperatures of 1⋅Guest. Geometry-optimized lattice parameters and bond distances in the empty host 1 and 1⋅Guest clathrates are in general agreement with the X-ray diffraction data. The concordance between the theoretical results and the experimental data also comprises the guest molecule orientation inside the host and intermolecular distances. Furthermore, a general correlation between experimental Tc and calculated LS-HS electronic energy gap was observed. Finally, specific host-guest interactions were studied through interaction energy calculations and crystal orbital displacement (COD) curve analysis.
authors.affiliation: Departament de Química Inorgànica and Institut de Recerca de Química Teòrica i Computacional, Universitat de Barcelona, Barcelona 08028 (Spain).
authors.forename: Daniel
authors.initials: D
authors.lastname: Aravena
authors.forename: Zulema Arcís
authors.initials: ZA
authors.lastname: Castillo
authors.forename: M Carmen
authors.initials: MC
authors.lastname: Muñoz
authors.forename: Ana B
authors.initials: AB
authors.lastname: Gaspar
authors.forename: Ko
authors.initials: K
authors.lastname: Yoneda
authors.forename: Ryo
authors.initials: R
authors.lastname: Ohtani
authors.forename: Akio
authors.initials: A
authors.lastname: Mishima
authors.forename: Susumu
authors.initials: S
authors.lastname: Kitagawa
authors.forename: Masaaki
authors.initials: M
authors.lastname: Ohba
authors.forename: José Antonio
authors.initials: JA
authors.lastname: Real
authors.forename: Eliseo
authors.initials: E
authors.lastname: Ruiz
keywords: Hofmann clathrates; density functional calculations; magnetic properties; metal-organic frameworks; spin-crossover compounds