Remarkable Energy Barrier for Magnetization Reversal in 3D and 2D Dysprosium‐Chloranilate‐Based Coordination Polymers

Abstract

Herein, two coordination polymers (CPs) [{Dy(Cl2An)1.5(CH3OH)}⋅4.5 H2O]n (1) and [Dy(Cl2An)1.5(DMF)2]n (2), in which Cl2An is chloranilate (2,5‐dihydroxy‐1,4‐benzoquinone dianion), exhibiting field‐induced single‐molecule magnet behavior with moderate barrier of magnetization reversal are reported. Detailed structural and topological analysis disclosed that 1 has a 3D network, whereas 2 has a 2D layered‐type structure. In both CPs, magnetic measurements showed weak antiferromagnetic exchange interaction between the dysprosium centers and field‐induced slow magnetic relaxation with barriers of 175(9)K and 145(7)K for 1 and 2, respectively. Notably, the energy barriers of magnetization reversal of 1 and 2 are remarkable for metal–chloranilate‐based 3D (1) and 2D (2) CPs. The temperature and field dependence of relaxation time indicate the presence of multiple relaxation pathways, such as direct, quantum tunneling of magnetization, Raman, and Orbach processes, in both CPs. Ab initio theoretical calculations reinforced the experimentally observed higher energy barrier in 1 as compared with 2 due to the presence of large transverse anisotropy in the ground state in the latter. The average transition magnetic moment between the computed low‐lying spin–orbit states also rationalized the relaxation as Orbach and Raman processes through the first excited state. BS‐DFT calculations were carried out for both CPs to provide more insight into the exchange interaction.

The Complete Series of Lanthanoid-Chloranilato Lattices with Dimethylsulfoxide: Role of the Lanthanoid Size on the Coordination Number and Crystal Structure

“…The use of anilato-type ligands (3,6-disubstituted-2,5-dihydroxy-1,4-benzoquinone dianion = C 6 O 4 X 2 2− , Scheme 1a) to prepare MOFs constitutes a very appealing strategy since these ligands may present several different coordination modes, including monodentate (1kO, Scheme 1b), bidentate (1k 2 O,O , Scheme 1c), monodentate-bidentate (1kO;2k 2 O ,O , Scheme 1d), bis-bidentate (1k 2 O,O ;2k 2 O ,O , Scheme 1e) and more complex modes From the magnetic point of view, anilato ligands mediate weak antiferromagnetic couplings, modulated by X, when connecting transition metals [26,27], but they show a negligible coupling when connecting lanthanoids, due to the poor overlap of Ln(4f) and O(2d) orbitals [28][29][30][31][32][33]. This isolation has resulted in the observation of single-ion magnet behaviour in a few examples of Ln-anilato lattices [34][35][36][37].…”

“…We also present the magnetic properties of all the members of the series and show that the Er derivative (11) displays a field-induced single-ion magnet behaviour with an activation energy of 23(2) K. Note that the magnetic properties of the Er and Dy From the magnetic point of view, anilato ligands mediate weak antiferromagnetic couplings, modulated by X, when connecting transition metals [26,27], but they show a negligible coupling when connecting lanthanoids, due to the poor overlap of Ln(4f) and O(2d) orbitals [28][29][30][31][32][33]. This isolation has resulted in the observation of single-ion magnet behaviour in a few examples of Ln-anilato lattices [34][35][36][37].…”

Reversible tuning of luminescence and magnetism in a structurally flexible erbium–anilato MOF

“…S17 †). 16,20,35,36 Photoluminescence properties Photoluminescence (PL) was excited using short laser pulses at a wavelength of 355 nm and analysed both spectrally and temporally. Near UV laser irradiation photoexcites the trz 2 An linker dianion in all compounds.…”

“…11,12 Among the organic linkers which can either act as a powerful antenna or isolate magnetically the Ln III metal ions, 3,6-disubstituted (X)-2,5-dihydroxybenzoquinone derivatives with X ¼ H, F, Cl, Br, I or CN (i.e. anilates) have recently been studied as building blocks for Ln III -based frameworks, [13][14][15][16] leading to several bi-dimensional (2D) and a few three-dimensional (3D) lattices [17][18][19][20] with interesting properties such as luminescence, SIM behaviour, gas/solvent adsorption/desorption and solvent exchange. 21 These bridging ligands couple (antiferro)magnetically the transition metal centers but they provide a good magnetic isolation with Ln III metal ions as a result of the negligible overlap with the 4f orbitals.…”

Hexanuclear NiII4LnIII2 Complexes with SMM Behavior at Zero Field for Ln = Tb, Dy, Ho

“…The discovery of the first single-molecule magnet, a [Mn 12 ] cluster, attracted enormous interest to the synthesis of various homo-/heterometallic complexes having the potential to behave as molecular magnets. − In the case of transition-metal complexes, the ground spin state ( S ) and anisotropy parameter ( D ), which are inversely related to each other, and the presence of spin–orbit coupling, responsible for quenching of the orbital angular momentum, are the three decisive parameters that hinder the obtainment of single-molecule magnets with the potential for practical applications. − This problem has been somewhat resolved by combining lanthanoid ions with transition-metal ions. − The high-spin ground state and unquenched orbital angular momentum leading to significant single-ion anisotropy increase the energy barrier of magnetization ( U eff ) and consequently make the Ln­(III) metal ions (e.g., Tb­(III), Dy­(III) and Ho­(III)) highly promising for single-molecule magnetism. − On the other hand, a combination of 3d–4f metal ions is even more promising, as the 3d metal ions (e.g., Cu II , Ni II , Fe II , Co II , Cr III ) are usually involved in ferromagnetic exchange coupling with the lanthanoid ions and these exchange interactions lead to an increment in the ground-state spin multiplicity. − Moreover, the quantum tunneling of the magnetization (QTM), which decreases the anisotropy barrier and consequently hampers the SMM behavior of the complexes, can be restricted by such a combination and thus relatively large effective energy barriers, hysteresis, and relaxation times are observed for many 3d–4f complexes. − Thus, the main challenge for synthetic chemists is to synthesize complexes which can retain their magnetic state even after the removal of an external magnetic field. In recent years, on consideration of these factors, the design and synthesis of various heterometallic 3d–4f ions such as Fe II –Ln III , Ni II –Ln III , Co II –Ln III , Cr III –Ln III , and Zn II –Ln III have been reported. − Among these, Ni II –Ln III complexes have attracted enormous attention, as the Ni­(II) ion also possesses significant single ion anisotropy and the combination of Ni­(II) ions with the highly anisotropic lanthanoid ions increases the anisotropy barrier ( U eff ) and blocking temperature ( T B ). − …”