Néel Temperature Enhancement by Increasing the In‐plane Magnetic Correlation in Layered Inorganic–Organic Hybrid Materials

Abstract

Magnets with controllable and/or switchable properties are an important topic in modern molecular chemistry.[1] Research in this area led to the discovery of hybrid organic-inorganic multilayer magnets, [2] which have attracted intense interest for several motivations: i) to combine with other important modulatable physical properties, ii) to provide archetype low-dimensional magnets, and iii) to promote cooperation between the inorganic and organic components on magnetic control. [2] Nice examples are provided by the families of metal oxalates, i.e., ferro-, ferri-, or canted antiferromagnetic inorganic layers that are separated by conductive organic radicals, [3] metal phosphonates, [4] and layered metal hydroxides M 2 (OH) 3 X (M --Cu As indicated by theory, dipole-dipole interactions between the layers can lead to the establishment of long-range magnetic order in two dimensions, [5] and the critical temperature, T C , is mainly dependent on the in-plane magnetic correlation, j, which gives rise to the relationship shown in Equation 1:where J is the in-plane ferromagnetic interaction. From this relationship, one can see that j is mainly dependent on J and S.[6] Pioneering studies on this relationship have involved the family of M 2 (OH) 3 X. Investigations mainly focused on exchanging X on the fixed M 2 (OH) 3 plane, and showed that T C is less affected by the interlayer distance.[2] A further question that needs to be answered is the effect of variation of the inorganic layer on T C .However, the in-plane magnetic dimension seems somewhat difficult to control by using only one ligand. Our previous work on the cobalt(II) ion and the trans-cyclohexane-1,2-dicarboxylate (trans-1,2-chdc) ligand demonstrates that the in-plane magnetic correlation can be changed from twodimensional (2D) Co It is worth noting that the solvent-dependent conformations of cyclohexane-1,2-dicarboxylate (1,2-chdc) observed in 1 and 2 are interesting. Density functional theory (DFT) calculations show that the cis and trans conformations are thermally more stable in basic and acidic conditions, respectively (Scheme S1).[8] However, regardless of whether the environment is basic or acidic, the difference in the energy is only 5 kJ Á mol À1 , which suggests that the reaction kinetics would be critical for the conformation of the product. Therefore, different solvents were used to control the conformations, and it was found that no matter what conformer was used initially, i.e., cis-or trans-1,2-chdc, water led to the trans conformation in 1, while ethylene glycol led to the cis conformation in 2, even with a reaction temperature of up to 190 8C. Such a solvent effect on the conformation of 1,2-chdc is unprecedented, and is different to previous studies on the analogous cyclohexane-1,4-dicarboxylate [9] and cyclohex-4-ene-1,2-dicarboxylate, [10] which exhibit cis and trans conformations at low and high reaction temperatures, respectively. Single-crystal X-ray diffraction reveals that all four independent 1,2-chdc ligands in 1 are ...

Tungsten Carbide–Nitride on Graphene Nanoplatelets as a Durable Hydrogen Evolution Electrocatalyst

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The coordination chemistry of cyclohexanepolycarboxylate ligands. Structures, conformation and functions

“…The metal cyclohexanepolycarboxylate frameworks are often similar to benzene polycarboxylate systems and the less investigated cyclohexene polycarboxylate coordination compounds [26]. In this review we show that cyclohexanepolycarboxylate ligands provide a wide range of different geometric isomers, multiple protonated carboxylate groups, a large variety of bonding behavior for the carboxylate groups and specifically, various conformations and geometries of the acid groups in relation to the central cyclohexane ring.…”

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Hydrothermal synthesis and crystal structure of a luminescent 3D lead(II) coordination polymer [Pb(4-cca)]n (4-cca=4-carboxycinnamate)

“…The assembly of metal-organic frameworks (MOFs) from dicarboxylate ligands has been of interest in recent years due to their structural chemistry [1][2][3][4][5][6][7][8][9][10][11] and their physical and chemical properties [1,3,[12][13][14][15][16]. Among these complexes, factors related to the spacer between the two carboxylate ends of the dicarboxylate ligand, e.g.…”