Abstract
We report the synthesis and the characterization of six new heterometallic chloranilato-based ferrimagnets formulated as (NBu4)[MnCr(C6O4Cl2)3]·nG with n = 1 for G = C6H5Cl (1), C6H5I (3), and C6H5CH3 (4); n = 1.5 for G = C6H5Br (2) and n = 2 for G = C6H5CN (5) and C6H5NO2 (6); (C6O4Cl2)2− = 1,3-dichloro,2,5-dihydroxy-1,4-benzoquinone dianion. The six compounds are isostructural and show hexagonal honeycomb layers of the type [MnCr(C6O4Cl2)3]− alternating with layers containing the NBu4+ cations. The hexagons are formed by alternating Mn(II) and Cr(III) connected by bridging bis-bidentate chloranilato ligands. The benzene derivative solvent molecules are located in the hexagonal channels (formed by the eclipsed packing of the honeycomb layers) showing π-π interactions with the anilato rings. The six compounds behave as ferrimagnets with ordering temperatures in the range 9.8–11.2 K that can be finely tuned by the donor character of the benzene ring and by the number of solvent molecules inserted in the hexagonal channels. The larger the electron density on the aromatic ring and the larger the number of solvent molecules are, the higher Tc is. The only exception is provided by toluene, where the formation of H-bonds might be at the origin of weaker π-π interactions observed in this compound.
Highlights
One of the main advantages of molecule-based magnets is the possibility to modulate or tune the properties of the magnets by changing or modifying the building blocks used to prepare them [1]
Another family of molecule-based magnets whose properties can be modified by changing the constituent metallic atoms is the series of oxalato-based two-dimensional (2D) magnets formulated as (A)[MIIMIII(C2O4)3] (A+ = monocation; MII = Mn, Fe, Co, Ni, Cu, . . . ; MIII = Fe, Cr, . . . ; C2O42− = oxalate dianion, Figure 1b) that show ferro, ferri, or canted antiferromagnetic ordering with Tc ranging from 6 K to 48 K depending on M(II) and M(III) [13,14,15,16,17,18,19,20,21,22]
A third and recent example is the series of anilato-based heterometallic 2D honeycomb magnets formulated as (A)[MIIMIII(C6O4X2)3]·G, where A+ is a monocation; M(II) and M(III) are transition metal ions as Mn(II), Fe(II), Cr(III), and Fe(III), G may be many different solvent molecules, and C6O4X22− is the 1,3-disubstituted-2,5-dihydroxy- 1,4-benzoquinone dianion, known as anilato-type ligands [23]
Summary
One of the main advantages of molecule-based magnets is the possibility to modulate or tune the properties of the magnets by changing or modifying the building blocks used to prepare them [1]. This change has already allowed a tuning of the ordering temperatures in the series of compounds (NBu4)[MnCr(C6O4X2)3] (X = H, Cl, Br, and I) [23] The third important difference is the size; the hexagonal cavities of the honeycomb structure are twice as large in the anilato-based compounds and, when packed in an eclipsed way, originate hexagonal channels with BET areas of up to 1440 m2/g [26] These hexagonal channels may be filled with solvent molecules (in contrast to the oxalato-based compounds) that can be removed, giving rise, in some cases, to important changes in the magnetic properties.
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