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.

Water Structure and Dynamics in Homochiral [Zn(l-L)(X)] Metal–Organic Frameworks

“…The intrinsic chemical diversity and porosity make metal-organic frameworks (MOFs) promising materials for several technological applications, including gas storage (e.g., methane and hydrogen storage), 1-11 carbon capture, [12][13][14][15][16][17] hydrocarbon separation, [18][19][20] catalysis, [21][22][23][24][25][26][27] electrical [28][29] and proton [30][31][32][33][34][35][36][37][38][39][40][41][42] conductivity, magnetism [43][44][45][46][47][48] and luminescence. 49 However, despite their versatility, several frameworks display low stability when exposed to moisture, which has limited the use of MOFs in industrial applications thus far.…”

Cooperative High‐Temperature Spin Crossover Accompanied by a Highly Anisotropic Structural Distortion

“…Iron‐containing cyanoheterometallic frameworks, including analogues of Hofmann clathrates, are another family of intensively studied SCO materials that can possess bi‐stability over a wide range of temperatures up to and above room temperature . They are also known for their sensitivity to the inclusion of guests into large guest‐accessible pores within a coordination framework . The variety of these SCO complexes is related to the number of different cyanometallates (Ni II , Pd II , Pt II , Cu I , Ag I , Au I , Cr III , Nb IV ) and N‐donor aromatic ligands (pyridines, pyrimidines, pyridazine, triazoles) that are suitable for the construction of these rigid polymeric structures …”

Guest Modulated Spin States of Metal Complex Assemblies

“…Hoffman‐type iron(II) SCO‐CPs/MOFs of type [Fe(pz)M(CN) 4 ] ( Fe–M ; M = Ni, Pt, Pd, pz = pyrazine) are representative host materials that exhibit SCO behaviors linked to guest occupancy of the stable pores in these materials (Figure a). The effects of the accommodation of diverse guest species, including solvents, gases, halogens and organic molecules on both the structures and the SCO behaviors of the Fe–M materials have been investigated. For instance, it was demonstrated that Fe–Ni adsorbed toluene, acetone, ethanol, methanol and acetonitrile molecules leading to the resulting host–guest composites showing SCO behaviors with different transition temperatures (Figure b).…”