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) 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(3)OH 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(3)OH 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).