Influence of Host-Guest and Host-Host Interactions on the Spin-Crossover 3D Hofmann-type Clathrates {FeII(pina)[MI(CN)2]2}•xMeOH (MI = Ag, Au)

The synthesis, structural characterization and magnetic properties of two new isostructural porous 3D compounds with the general formula {Fe-II(pina)[(MCN)-C-I)(2)](2)}center dot xMeOH (x = 0-5; pina = N-(pyridin-4-yl)-isonicotinamide; M-I = Ag-I and x similar to 5 (1 center dot xMeOH); M-I = Au-I and x similar to 5 (2 center dot xMeOH)) are presented. The single-crystal X-ray diffraction analyses have revealed that the structure of 1 center dot xMeOH (or 2 center dot xMeOH) presents two equivalent doubly interpenetrated 3D frameworks stabilized by both argentophilic (or aurophilic) interactions and interligand C=O center dot center dot center dot HC H-bonds. Despite the interpenetration of the networks, these compounds display accessible void volume capable of hosting up to five molecules of methanol which interact with the host pina ligand and establish an infinite lattice of hydrogen bonds along the structural channels. Interestingly, the magnetic studies have shown that solvated complexes 1 center dot xMeOH and 2 center dot xMeOH display two- and four-step hysteretic thermally driven spin transitions, respectively. However, when these compounds lose the methanol molecules, the magnetic behavior changes drastically giving place to gradual spin conversions evidencing the relevant influence of the guest molecules on the spin-crossover properties. Importantly, since the solvent desorption takes place following a single-crystal-to-single-crystal transformation, empty structures 1 and 2 (x = 0) could be also determined allowing us to evaluate the correlation between the structural changes and the modification of the magnetic properties triggered by the loss of methanol molecules.