Nanoporous Cobalt(II) MOF Exhibiting Four Magnetic Ground States and Changes in Gas Sorption upon Post-Synthetic Modification

Abstract

We present the syntheses, structural characterization, gas sorption, I2 uptake, and magnetic properties of a double-walled porous metal-organic framework, [Co(II)3(lac)2(pybz)2]·3DMF (1·3DMF, purple, where pybz = 4-pyridyl benzoate, lac = d- and l-lactate) and of its post-synthetic modified (PSM) congeners, [Co(II)3(lac)2(pybz)2]·xGuest (xGuest = 6MeOH, purple; 4.5EtOH, purple; 3PrOH, purple; 2C6H6, purple; 2.7I2, black), [Co(II)3(lac)2(pybz)2] (1, purple), [Co(II)3(pybz)2(lac)2(H2O)2]·7H2O (1a·7H2O, green), and [Co(III)Co(II)2(pybz)2(lac)2(H2O)2]I·2H2O·1.5DMSO (1b·I(-)·2H2O·1.5DMSO, yellow, DMSO = dimethyl sulfoxide). Crystallography shows that the framework is not altered by the replacement of DMF by different solvents or by the removal of the solvent molecules during the single-crystal to single-crystal (SC-SC) transformations, while upon exchange with H2O or partial oxidation by molecular iodine, the crystallinity is affected. 1 absorbs N2, H2, CH4, CH3OH, C2H5OH, PrOH, C6H6, and I2, but once it is in contact with H2O the absorption efficiency is drastically reduced. Upon PSM, the magnetism is transformed from a canted antiferromagnet (1·3DMF and 1·xGuest) to single-chain magnet (1), to a ferrimagnet (1a·7H2O), and to a ferromagnet (1b·I(-)·2H2O·1.5DMSO). Raman spectroscopy suggests the color change (purple to green 1a·7H2O or yellow 1b·I(-)·2H2O·1.5DMSO) is associated with a change of geometry from a strained octahedron due to the very acute chelating angle (∼60°) of the lactate of a cobalt center to a regular octahedron with a monodentate carboxylate and one H2O. The magnetic transformation is explained by the different interchain exchanges (J'), antiferromagnetic for 1·3DMF and 1·xSolvent (J' < 0), SCM for 1 (J' verge to 0), and ferromagnetic for 1a·7H2O (J' > 0), between homometal topological ferrimagnetic chains (two octahedral and one tetrahedral Co(II) ions) connected by the double walls of pybz at 13.3 Å (shortest Co···Co). For 1b·I(-)·2H2O·1.5DMSO the moment of the tetrahedral site is turned off, thus stabilizing a ferromagnetic state (J' > 0). The present stabilization of four magnetic ground states is unique in the field of metal-organic frameworks as well as the electrical conductivity of 1·2.7I2.

Recent Advances on Anilato-Based Molecular Materials with Magnetic and/or Conducting Properties

“…Very recently Harris et al [201] have reported on the synthesis and full characterization of (Me 2 NH 2 ) 2 [Fe 2 L 3 ]·2H 2 O·6DMF (45), the first structurally characterized example of a microporous magnet containing the Cl 2 An 3− ·chloranilate radical species, where solvent-induced switching from Tc = 26 to 80 K has been observed. 45 shows the common 2D honeycomb layered packing where the layers are eclipsed along the crystallographic c axis, with a H 2 O molecule located between Fe centers, leading to the formation of 1D hexagonal channels (Figure 33).…”

“…Anilates are also particularly suitable for the construction of microporous MOFs with strong magnetic coupling and they have been shown to generate extended frameworks with different dimensionality and large estimated void volumes, which could potentially give rise to materials with permanent porosity [112]. Very recently Harris et al [201] have reported on the synthesis and full characterization of (Me2NH2)2[Fe2L3]•2H2O•6DMF (45), the first structurally characterized example of a microporous magnet containing the Cl2An 3− •chloranilate radical species, where solvent-induced switching from Tc = 26 to 80 K has been observed. 45 shows the common 2D honeycomb layered packing where the layers are eclipsed along the crystallographic c axis, with a H2O molecule located between Fe centers, leading to the formation of 1D hexagonal channels (Figure 33).…”

Magnetic functionalities in MOFs: from the framework to the pore

“…11). 41 The structure contains M-O-M connectivity within the wellseparated square chains, which provides a short pathway for magnetic exchange. Interestingly, the solvent molecules that fill the pores can be exchanged with several guests without affecting the integrity of the structure, including gases (N 2 , H 2 and CH 4 ) and volatile guests (methanol, ethanol, propanol, benzene).…”

Crystal structure of poly[diaquabis(μ2-biphenyl-2,4′-dicarboxylato-κ2 O:O′)tris(μ2-1,1′-biphenyl-4,4′-diylbis(1H-imidazole)-κ2 N:N′)dicobalt(II)] monohydrat, C82H64N12O11Co2

“…In the last two decades, Co(II)-based coordination polymers (Co-CPs) have drawn considerable attention because of their huge diversity and versatility structure and potential applications in the areas of magnetism, catalysis, adsorption/separation, nonlinear optics etc [1][2][3][4]. According to a survey of the previous references, bis(imidazole) ligands, as well-known N-donor ligands, have been widely utilized for tunability of structural frameworks [5,6].…”