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.

Presented here is an anionic nanoporous framework material with mobile guest cations which can perform ion exchanges with different tetraalkylammonium cations, and the resulting tunable pore structures exhibit interesting pore partition effects on gas storage and separation.

The synthesis and characterization of a 4-fold-interpenetrated pseudodiamond metal-organic framework (MOF), Co(II)(pybz)2·2DMF [pybz = 4-(4-pyridyl)benzoate], are reported. N,N-Dimethylformamide (DMF) of the channels can be removed to give the porous framework, and it can also be exchanged for methanol, ethanol, benzene, and cyclohexane. It is a rare example of a stable MOF based on a single octahedral building unit. The single-crystal structures of Co(II)(pybz)2·2DMF, Co(II)(pybz)2, Co(II)(pybz)2·4MeOH, and Co(II)(pybz)2·2.5EtOH have been successfully determined. In all of them, the framework is marginally modified and contains a highly distorted and strained octahedral node of cobalt with two pyridine nitrogen atoms and two chelate carboxylate groups. In air, the crystals of Co(II)(pybz)2·2DMF readily change color from claret red to light pink. Thermogravimetric analysis and Raman spectroscopy indicate a change in coordination, where the carboxylate becomes monodentate and an additional two water molecules are coordinated to each cobalt atom. In a dry solvent, this transformation does not take place. Tests show that Co(II)(pybz)2 may be a more efficient drying agent than silica gel and anhydrous CuSO4. The desolvated Co(II)(pybz)2 can absorb several gases such as CO2, N2, H2, and CH4 and also vapors of methanol, ethanol, benzene, and cyclohexane. If Co(II)(pybz)2 is exposed to air and followed by reactivation, its sorption capacity is considerably reduced, which we associate with a poisoning effect. Because of the long distance between the cobalt atoms in the structure, the magnetic properties are those of a paramagnet.

Two-dimensional (2D) magnetic van der Waals materials provide a powerful platform for studying fundamental physics of low-dimensional magnetism, engineering novel magnetic phases, and enabling ultrathin and highly tunable spintronic devices. To realize high quality and practical devices for such applications, there is a critical need for robust 2D magnets with ordering temperatures above room temperature that can be created via exfoliation. Here the study of exfoliated flakes of cobalt substituted Fe5GeTe2 (CFGT) exhibiting magnetism above room temperature is reported. Via quantum magnetic imaging with nitrogen-vacancy centers in diamond, ferromagnetism at room temperature was observed in CFGT flakes as thin as 16 nm. This corresponds to one of the thinnest room-temperature 2D magnet flakes exfoliated from robust single crystals, reaching a thickness relevant to practical spintronic applications.The Curie temperature Tc of CFGT ranges from 310 K in the thinnest flake studied to 328 K in the bulk. To investigate the prospect of high-temperature monolayer ferromagnetism, Monte Carlo calculations were performed which predicted a high value of Tc ~270 K in CFGT monolayers. Pathways towards further enhancing monolayer Tc are discussed. These results support CFGT as a promising platform to realize high-quality room-temperature 2D magnet devices. IntroductionReceived: ((will be filled in by the editorial staff))Revised: ((will be filled in by the editorial staff))