Heterobimetallic MOFs containing tetrathiocyanometallate building blocks: Pressure-induced spin crossover in the porous {Fe II(pz)[Pd II(SCN) 4]} 3D coordination polymer

Here we describe the synthesis, structure, and magnetic properties of two related coordination polymers made up of self-assembling Fe(II) ions, pyrazine (pz), and the tetrathiocyanopalladate anion. Compound {Fe(MeOH) 2[Pd(SCN) 4]}·pz (1a) is a two-dimensional coordination polymer where the Fe(II) ions are equatorially coordinated by the nitrogen atoms of four [Pd(SCN) 4] 2- anions, each of which connects four Fe(II) ions, forming corrugated layers {Fe[Pd(SCN) 4]} ∞. The coordination sphere of Fe(II) is completed by the oxygen atoms of two CH 3OH molecules. The layers stack one on top of each other in such a way that the included pz molecule establishes strong hydrogen bonds with the coordinated methanol molecules of adjacent layers. Compound {Fe(pz)[Pd(SCN) 4]} (2) is a three-dimensional porous coordination polymer formed by flat {Fe[Pd(SCN) 4]} ∞ layers pillared by the pz ligand. Thermal analysis of 1a shows a clear desorption of the two coordinated CH 3OH molecules giving a rather stable phase (1b), which presumably is a polymorphic form of 2. The magnetic properties of the three derivatives are typical of the high-spin Fe(II) compounds. However, compounds 1b and 2, with coordination sphere [FeN 6], show thermal spin crossover behavior at pressures higher than ambient pressure (10 5 MPa). © 2012 American Chemical Society.This work was supported by the Spanish Ministerio de Ciencia e Innovación (MICINN) (presently Ministerio de Economía y Competitividad) and FEDER funds (CTQ2010-18414, CSD2007-00010, and MAT2011-27233-C02-02) and the Generalitat Valenciana through PROMETEO/2012/049 and ACOMP2012/233 projects.Peer Reviewe