Oxidative Addition of Halogens on Open Metal Sites in a Microporous Spin‐Crossover Coordination Polymer

Abstract

The last decade has witnessed a great activity in the realm of porous coordination polymers (PCPs). Their extreme chemical versatility and porosity has allowed chemists to consider PCPs as a new class of functional materials that are able to mimic, and even improve, the functions of zeolites, for example, storage, separation, and heterogeneous catalysis. [1] Furthermore, implementation of PCPs with solid-state properties (optical, magnetic, charge transport, etc.) would enable the expression of host-guest interactions in sorption and desorption processes in a sensory way as a response of the framework producing drastic physicochemical changes at ordinary temperatures. This almost unexplored strategy could provide a new generation of PCP-based sensors.[2]The chemo-responsive behavior of the Hofmann clathratePd, [3a] Pt [3a] ) based on the spin-crossover properties of the Fe II joints was recently demonstrated. The cooperative response mediated by the components of the framework confers bistable behavior to the solid at room temperature. These PCPs form a 3D pillared-layer-type porous framework consisting of cyano-bridged Fe II M II layers and pz pillar ligands, and adsorb various guest molecules. A bimodal reversible change of spin state at the Fe II sites was observed concomitantly with the uptake of guest molecules switching between the high-spin state (HS, yellow), stabilized by hydroxylic solvents and five-and six-membered aromatic molecules, and the low-spin state (LS, red-brown), stabilized by CS 2 (for M = Pt) [3a] or CH 3 CN (for M = Ni) [3b] at 298 K. In the framework, guest molecules can interact with the pyrazine pillar ligands (site A) and the M II centers (site B). One important feature not yet explored in these PCPs is the coordinative unsaturation of the M II centers. Incorporation of coordinatively unsaturated metal centers, so-called "open metal sites", may enhance the adsorptive selectivity for particular guest substances.[4] Herein we report the chemisorptive uptake of dihalogen molecules involving associative oxidation of Pt II to Pt IV and reduction of the dihalogen to the corresponding halide to give {Fe(pz) [Pt(CN)

Magnetic functionalities in MOFs: from the framework to the pore

“…In previous sections we have already shown some examples that illustrate these possibilities. 67,68,97 (Fig. 1b).…”

Coordination pillared layers using a dinuclear Mn(V) complex as a secondary building unit

“…In particular, three-dimensional (3-D) Hofmann-type compounds {Fe II (pz)[M II (CN) 4 ]} (M = Ni, Pd, Pt), which show cooperative spin transitions have been actively investigated [43][44][45][46][47][48]. These compounds have 3-D porous frameworks consisting of cyanide-bridged Fe II M II bimetallic layers and the pillar ligand pz, and exhibit new functions coupling magnetic and adsorption properties, e.g., magnetic chemoswitching and modulation of the spin-transition temperature by guest molecules [45][46][47][48]. The tetracyanometallate SBUs play an important role in showing strong host-guest interactions as open-metal sites (OMS), however, the metal centres of OMS are limited to Ni II , Pd II and Pt II ions at this stage.…”

Tuning the magneto-structural properties of non-porous coordination polymers by HCl chemisorption

“…Thus, it has been shown that MOFs based on these molecular complexes exhibit magnetic switching at room temperature on physisorption of specific molecules within the porous framework 16,17 . The high sensitivity of these materials is also evidenced by the modification of the transition temperature on oxidative addition reactions following gas sorption at metal sites that are far from the magnetic centres 18,19 . A different approach to tune the magnetic properties of porous solids consists of the modification of the magnetic ground state of the MOF, which can be achieved through gas sorption processes that subtly affect the geometry of either the bridge between metal centres 20 or the ligand substituents 21 .…”