Field-Induced Single-Molecule Magnets of Dysprosium Involving Quinone Derivatives

Abstract

The coordination reaction of the [Dy(hfac)₃(H₂O)₂] units (hfac⁻ = 1,1,1,5,5,5-hexafluoroacetylacetonate) with the two quinone-based derivatives 4,7-di-tert-butyl-2-(3,5-di-tert-butyl-4-oxocyclohexa-2,5-dien-1-ylidene)benzo[d][1,3]dithiole-5,6-dione (L¹) and 7,8-dithiabicyclo[4.2.0]octa-1,5-diene-3,4-dione,2,5bis(1,1-dimethylethyl) (L²) led respectively to the complexes [Dy(hfac)₃(H₂O)(L¹)] (1) and [Dy(hfac)₃(H₂O) (L²)]⋅(C₆H₁₄)(CH₂Cl₂) (2)⋅(C₆H₁₄)(CH₂Cl₂). X-ray structures on single crystal of 1 and 2⋅(C₆H₁₄)(CH₂Cl₂) revealed the coordination of the Dy^III on the bischelating oxygenated quinone site and the formation of dimeric species through hydrogen bonds. Ac magnetic measurements highlighted field-induced single-molecule magnet behavior with magnetic relaxation through a Raman process.

1. Introduction

The design of the coordination surrounding of magneto-active ions is a challenging task; a choice of o-quinone-like dioxolenes for this purpose seems to be promising for several reasons: (i) o-dioxolenes possess a redox activity, their oxidation state may be changed directly in the coordination sphere of the metal ion [1,2,3]. Organic radical semiquinone form is often associated to transition metal to design complexes displaying chemical and physical properties, such as valence tautomerism [4], photo-and thermo-mechanical effects [5]. o-Quinone-like dioxolenes in quinone, semiquinone [6,7,8,9] or catecholate [10,11,12] oxidation states have been associated with lanthanide ions to generate luminescence [13] and single-molecule magnet (SMM) behavior [14,15,16], as well as magnetic or optical switching [17,18,19,20]. It is worth mentioning that SMM behavior is associated to the observation of slow magnetic relaxation at the molecular scale, leading to the opening of a hysteresis loop at low temperature. The recent discovery of organometallic complexes of dysprosium with high blocking temperature [21,22,23,24] make them potential candidates for high density data storage; (ii) due to chelating ability, o-dioxolenes form stable complexes with almost all metals; (iii) o-quinone may be modified with various additional redox-active, free radical bearing or coordination-capable functional fragments to provide possibilities for the switching of the redox and/or magnetic state of the molecule [25].

The interest for metal dithiolenes emerged due to their potential applications in molecular conductors and superconductors [26]. Moreover, they have been recently employed to study electronic spin decoherence for quantum computation [27,28,29].

The two following o-quinone derivatives, 4,7-di-tert-butyl-2-(3,5-di-tert-butyl-4-oxocyclohexa-2,5-dien-1-ylidene)benzo[d][1,3]dithiole-5,6-dione (L¹) [30] and 7,8-dithiabicyclo[4.2.0]octa-1,5-diene-3,4-dione,2,5bis(1,1-dimethylethyl) (L²) [31] (Chart 1), have been selected to be involved in coordination reaction with the [Dy(hfac)₃(H₂O)₂] precursor (hfac = 1,1,1,5,5,5-hexafluoroacetylacetone) (Scheme S1). L² is a multi-chelating ligand which presents both 1,2-dithiolene and 1,2-dioxolene coordination sites. Some of us previously demonstrated that single- and two-electrons reduction led to the respective formation of semiquinonate species and catecholate or dithiolate species depending on the nature of the metallo-fragments. Moreover, a regioselectivity of the coordination reaction was observed depending on the hard or soft acidity of the metal ion [31,32,33,34].

In the present paper, the reaction between L¹ or L² in presence of [Dy(hfac)₃(H₂O)₂] led to the coordination on the 1,2-quinone site (regioselectively in case of L²) without reduction of it. Magnetic properties of the resulting [Dy(hfac)₃(H₂O)(L¹)] (1) and [Dy(hfac)₃(H₂O)(L²)]⋅(C₆H₁₄)(CH₂Cl₂) (2)⋅(C₆H₁₄)(CH₂Cl₂) complexes are investigated.

2. Results and Discussion

2.1. X-ray Structures

4,7-di-tert-butyl-2-(3,5-di-tert-butyl-4-oxocyclohexa-2,5-dien-1-ylidene)benzo[d][1,3]dithiole-5,6-dione (L¹). This ligand was recently reported by some of us [30]. The IR and NMR data are given in SI. In order to have an optimal structural comparison between the free L¹ quinone and the corresponding coordination complex (1), its X-ray structure was determined at 150 K on dark purple single crystals obtained from n-hexane-ether solution on cooling. A quick description is given in the following lines. L¹ crystallized in the tetragonal space group P-4 (N°81) (Figure S1 and Table S1). The asymmetric unit is composed of one almost planar organic molecule of L¹. The three C=O distances range from 1.197(3) to 1.233(4) Å, which is consistent with a double bond character. Alternated bond lengths distribution in the dioxolene ring of L¹ is also typical of sterically hindered o-quinones. Thus, the single crystal X-ray structure confirmed the quinone form of L¹ at 150 K. The crystal packing of L¹ revealed a stacking of the molecules along the c axis; nevertheless, the bulky tert-butyl groups prevented any strong π-π interaction. Thus, the cohesion of the crystal is mainly guaranteed through short S1⋅⋅⋅O1 (3.246 Å) and S2⋅⋅⋅O2 (3.300 Å) contacts. One could remark that to optimize the overlap between the π orbitals of the oxygen and sulfur atoms, the quinone fragment is not planar (Figure 1).

[Dy(hfac)₃(H₂O)(L¹)] (1). The coordination reaction of the tris(1,1,1,5,5,5-hexafluoroacetylacetonate)bis(aqueous)Dy^III ([Dy(hfac)₃(H₂O)₂]) with 4,7-di-tert-butyl-2-(3,5-di-tert-butyl-4-oxocyclohexa-2,5-dien-1-ylidene)benzo[d][1,3]dithiole-5,6-dione (L¹) [30] (Chart 1) in CH₂Cl₂ led to the formation of the complexes [Dy(hfac)₃(H₂O)(L¹)] (1). Moreover, 1 crystallized in the monoclinic space group C2/c (Table S1) and an ORTEP view of the asymmetric unit is depicted in Figure S1. The latter is composed of one complex of formula [Dy(hfac)₃(H₂O)(L¹)] (Figure 1a). The mononuclear species is formed by coordination of the bischelating quinone fragment to the Dy^III metal center. The quinone character is confirmed by the two C16 = O7 (1.240(5) Å) and C21 = O8 (1.236(5) Å) bond lengths. The dioxolene ring of the ligand in 1 also retains an alternated (non-aromatic) distribution of bond lengths. The coordination sphere of the Dy^III is filled by three bischelating hfac⁻ anions and one water molecule. The arrangement of the L¹, the three hfac⁻ anions and the coordinated water molecule formed a polyhedron, having a C_4v spherical capped square antiprism as the closest ideal symmetry (Table S2). The deviations from the ideal symmetries are calculated using the SHAPE software [35].

The coordination to the [Dy(hfac)₃(H₂O)] unit makes similar short S⋅⋅⋅O contacts like those observed for the X-ray structure of the free L¹ ligand impossible. Consequently, the arrangement of the quinone changed with carbonyl groups on either side of the plane formed by the six-membered ring of the quinone. The crystal packing revealed the formation of a dimeric structure through hydrogen bonds thanks to the coordinated water molecule. Five short O⋅⋅⋅O contacts ranging from 2.873 Å to 2.965 Å have been identified, leading to a Dy⋅⋅⋅Dy intermolecular distance of 5.981 Å (Figure 1b). The shortest intermolecular Dy⋅⋅⋅Dy distance not involved in a dimer was measured at 10.579 Å.

Finally, the dimers of 1 were organized in a parallel way along the b axis, while the quinone derivatives L¹ were organized in an orthogonal way with the neighboring L¹ (Figure 1c). Such arrangement allowed the carbonyl group involving the O10 atom to point towards the two sulfur atoms of the neighboring molecule leading to O10⋅⋅⋅S1 and O10⋅⋅⋅S2 distances of 3.934 Å and 3.536 Å (Figure S2).

[Dy(hfac)₃(H₂O)(L²)]⋅(C₆H₁₄)(CH₂Cl₂) (2)⋅(C₆H₁₄)(CH₂Cl₂). The coordination reaction of the tris(1,1,1,5,5,5-hexafluoroacetylacetonate)bis(aqueous)Dy^III ([Dy(hfac)₃(H₂O)₂]) with 7,8-dithiabicyclo[4.2.0]octa-1,5-diene-3,4-dione,2,5bis(1,1-dimethylethyl) (L²) [26] (Chart 1) in CH₂Cl₂ led to the formation of the complexes [Dy(hfac)₃(H₂O)(L²)]⋅(C₆H₁₄)(CH₂Cl₂) ((2)⋅(C₆H₁₄)(CH₂Cl₂)). 2⋅(C₆H₁₄)(CH₂Cl₂) crystallized in the monoclinic space group P2₁ (Table S1). The asymmetric unit is composed of eight molecules [Dy(hfac)₃(H₂O)(L²)] (Figure 2a) and its ORTEP view is shown in Figures S3 and S4. The bischelating dioxolene site in a quinone form is coordinated to the [Dy(hfac)₃(H₂O)] unit, in agreement with the oxophilic character of the lanthanide ion, in contrast with what was observed for the bischelating dithiolene coordination site, which is coordinated to the soft Pd^II [34]. The quinone form of L² was confirmed by the C=O bond lengths, ranging from 1.064 Å to 1.417 Å (average distance of 1.230 Å). The coordination sphere of the Dy^III is filled with three bischelating hfac⁻ anions and one water molecule. The deviations from the ideal symmetries for each Dy^III surrounding are calculated using the SHAPE software (Table S3) [35]. The eight coordination polyhedron symmetries corresponding to the eight crystallographically independent dysprosium can be classified into two groups, with Dy1, Dy2 and Dy5 adopting a D_3h spherical tricapped trigonal prism, while the five others adopted a C_4v spherical capped square antiprism. Since one water molecule coordinated to the Dy^III is present, the formation of dimers through hydrogen bonds is observed (Figure 2b). For each dimer, three short O⋅⋅⋅O contacts ranging from 2.653 Å to 3.039 Å have been identified, leading to an average Dy⋅⋅⋅Dy intermolecular distance of 5.868 Å. The shortest intermolecular Dy⋅⋅⋅Dy distance not involved in a dimer was measured at 9.657 Å. H⋅⋅⋅F and F⋅⋅⋅F contacts ensured the cohesion between the different dimers (Figure S5).

One could remark that even if both X-ray structures of 1 and 2⋅(C₆H₁₄)(CH₂Cl₂) involved similar dimerization of the complexes through hydrogen bond due to the remaining coordinated water molecules, a slight structural difference could be noticed. Indeed, the dimer of 1 involved both O_w⋅⋅⋅O_w (2.954 Å) and O_w⋅⋅⋅O_hfac (average distance of 2.919 Å) short contacts, while in 2⋅(C₆H₁₄)(CH₂Cl₂), only O_w⋅⋅⋅O_hfac (average distance of 2.835 Å) are involved. Previous systems, published by some of us, already showed that the coordination of the quinone-tetrathiafulvalene-quinone triad [14] or quinone-(extended-TTF)-quinone triad [17] to the [Dy(hfac)₃] unit led to the observation of a remaining coordinated water molecule and such dimerization through O_w⋅⋅⋅O_hfac short contacts only. In others words, 1 is the only system showing O_w⋅⋅⋅O_w short contact susceptible to induce difference in the magnetic behavior.

2.2. Magnetic Properties

2.2.1. Static Magnetic Measurements

The magnetic susceptibility (χ_M) was measured for both 1 and 2 compounds in the temperature range of 2–300 K and their thermal dependence of the χ_MT products is depicted in Figure 3. The experimental room temperature values for 1 and 2 are respectively 13.62 cm³·K·mol⁻¹ and 13.77 cm³·K·mol⁻¹, in agreement with the expected value considering one isolated Dy^III ion (⁶H_15/2 ground state multiplet) (14.17 cm³·K·mol⁻¹) [32]. When decreasing the temperature, χ_MT products decrease monotonically down to 8.61 cm³·K·mol⁻¹ for 1 and 10.28 cm³·K·mol⁻¹ for 2. Such magnetic behavior is attributed to the thermal depopulation of the M_J states and antiferromagnetic dipolar interactions. Indeed, some of us demonstrated that the formation of dimer through hydrogen bonds led to antiferromagnetic interactions up to -0.65 cm⁻¹ between the two Dy^III ions [17]. In such a situation, the observed χ_MT value at 2 K is close to 10 cm³·K·mol⁻¹, which is in agreement with the observed value for 2, while a lower value is observed for 1. Such a low value might be attributed to stronger antiferromagnetic interaction in 1 than in 2 and previously reported examples [14,17], because the O_w⋅⋅⋅O_w contact is the shortest one. Considering that the dipolar interaction is proportional to 1/r³ (where r³ is the distance between the two spin carriers), it is reasonable to consider that the inter-dimer dipolar interaction would be negligible compared to the intra-dimer dipolar interaction.

The measured magnetizations at 50 kOe are 5.46 μ_B for 1 and 5.24 μ_B for 2 far from the expected saturated value of 10 μ_B, due to the magnetic anisotropy of the systems (inset of Figure 3) [36]. The two magnetizations at 2 K showed significant differences, i.e., slower increase at low field for 1 than for 2, in agreement with possible stronger antiferromagnetic interaction in 1 than in 2. Moreover, the slope of the magnetization at higher fields might also suggest a different composition of the ground state. Thus, the nature of the M_J ground doublet state could also play a role in the χ_MT low value for 1.

2.2.2. Dynamic Magnetic Measurements

The high magnetic moment and the strong magnetic anisotropy of the Dy^III ion in an O9 surrounding could be suitable parameters to observe a slow relaxation of its magnetization [14,17]. The molar ac magnetic susceptibility (χ_M) was measured for both compounds 1 and 2 in order to study the dynamic magnetic properties. No out-of-phase signal (χ_M″) was detected in zero magnetic field in the frequency range 1–1000 Hz for 1 (Figure S6) and the reason is usually imputed to a fast magnetic relaxation through a quantum tunneling of the magnetization (QTM). The latter can be cancelled, applying a dc magnetic field, as shown in Figure S6. The field dependence of the magnetic susceptibility revealed that a good compromise for the applied magnetic field value is 1600 Oe. Under such an applied field, 1 highlighted a frequency dependence of the magnetic susceptibility (Figure S7). An extended Debye model [37,38] was used to extract the temperature dependence of the relaxation time, fitting simultaneously both χ_M′ and χ_M″ (Figure S8 and Table S4), which are depicted in Figure 4.

The full formula for the relaxation rate of the magnetization as a sum of the different possible contributing processes is given in the following Equation (1):

$${\tau }^{-1}=\underset{Orbach}{\underbrace{{\tau }_0^{-1}\exp \left(\frac{\Delta }{T}\right)}}+\underset{Raman}{\underbrace{C{T}^n}}+\underset{{\tau }_{TI}^{-1},QTM}{\underbrace{\frac{B_1}{1+B_2{H}^2}}}+\underset{Direct}{\underbrace{AT{H}^m}}$$

(1)

with the different relaxation rates standing for the Orbach, the Raman, the QTM (quantum tunneling of the magnetization), and the direct processes, respectively; and the different parameters (τ₀, Δ, τ_TI, n, C and A) are found by fitting the experimental data, whereas m exponent is supposed to be tabulated and known values.

Since no high-frequency shift for the maxima of the out-of phase contribution was observed under an applied magnetic field, direct spin-phonon relaxation process was discarded. The relaxation time of the magnetization (τ) can be fitted using the thermally dependent Raman process only (τ⁻¹ = CTⁿ). The best fit was obtained with the following parameters: C = 175(19) s⁻¹ K⁻ⁿ and n = 1.95(11) (Figure 4 and Figure S9). The presence of both acoustic and optical phonons could induce the observation of n values between 2 and 7 [39,40,41], instead of the expected n value of 9 for Kramers ions [42]. It is worth noticing that the slow relaxation fraction is low (about 25% of the sample susceptibility) at 2 K. The non-relaxing fraction was extracted from the extrapolation of the normalized Argand plot to the x-axis at a given temperature (Figure S10). Thus, the field dependence of the magnetic susceptibility was checked at higher frequency (Figure S6), showing that a non-zero contribution is present at a higher frequency than 10,000 Hz.

In case of 2, an out-of phase component of the magnetic susceptibility was observed without applied magnetic field (Figure 5 and Figure S11) at 2 K. Two contributions can be observed at 100 Hz and higher than 10,000 Hz. Application of a dc field induced a shift of the two χ_M’’ contributions at lower frequency. The value of 1200 Oe was selected as the optimal field. Under the 1200 Oe applied field, a frequency dependence of the magnetic susceptibility was observed (Figure 5 and Figure S12).

At 2 K, a single signal was observed centered at 80 Hz, while when increasing the temperature, a second contribution localized at a lower frequency appeared in the experimental frequency windows. The temperature dependence of the relaxation time for the two contributions of the magnetic susceptibility was extracted, fitting simultaneously χ_M′ and χ_M″ with a modified extended Debye model (Figure S14 and Table S5). The relaxation time of the magnetization (τ) for the two high frequency (HF) and low frequency (LF) contributions can be fitted using the thermally dependent Raman process only (τ⁻¹ = CTⁿ).

The best fits were obtained with C = 3.93(69) s⁻¹K⁻ⁿ and n = 6.81(16) and C = 1.44(27) s⁻¹K⁻ⁿ and n = 7.78(11) (Figure 6 and Figure S9) for the HF and LF contributions, respectively. The slow magnetic relaxation fraction represents the main part of the sample (about 90% of the sample) (Figure S14). One could be tempted to attribute the HF and LF contributions to the magnetic relaxation of the Dy^III in C_4v and D_3h coordination environment regarding the intensity ratio.

The compounds 1 and 2 displayed a magnetic relaxation mainly through a pure Raman process (Figure 4, Figure 6 and Figure S9), which could be justified by the applied magnetic field (cancelling of the QTM), the moderate value of the field (the direct process is not the fastest magnetic relaxation process) and the low temperature range at which the relaxation times are extracted (below 10 K), leading to a negligible Orbach contribution. Recently, several Dy^III-based SMMs displaying pure Raman magnetic relaxation under moderate applied field in the low temperature range have been reported [43,44,45,46,47,48,49]. For some of the reported example in

Table 1. Examples of dysprosium SMMs relaxing through Raman process.

Compounds	Local Geometries Around LnIII Centers	Magnetic Properties (Field Induced SMM)	Ref.
[Dy2(tta)6(Q)]∙2CH2Cl2 (tta = 2-thenoyltrifluoroacetylacetonate, Q = 2,2′-cyclohexa-2,5-diene-1,4-diylidenebis(4,7-di-tert-butyl-1,3-benzodithiole-5,6-dione)	Square antiprism geometry	H = 1200 Oe Ueff = 26.5(2) K τ0 = 1.9(7) × 10−7 s C = 289(93) s−1 K−n n = 1.88(39)	[17]
[(Dy(HB(pz)3)2)2(μ-tetraoxolene)]·2CH2Cl2 (HB(pz)3 = hydrotris(pyrazolyl)borate (μ-tetraoxolene = chloranilate)	Triangular dodecahedral geometry	H = 1600 Oe Ueff = 24 K τ0 = 3 × 10−5 s C = 2.7 × 10−3 s−1 K−n n = 7 (fixed)	[15]
[Dy(acac)2(CH3OH)]2(μ-Mq) (acac = acetylacetone) (μ-Mq = 2-methyl-8-hydroxyquinoline)	Hexagonal bipyramid geometry	H = 2000 Oe Ueff = 75.6 K τ0 = 2.1 × 10−8 s C = 0.76 s−1 K−n n = 3.4	[45]
[Dy(tta)3(mbpymNO)] (mbpymNO = 4-methylbipyrimidine-2-N-oxide)	Square antiprism geometry	H = 1000 Oe Ueff = 99.6 K τ0 = 2.1 × 10−9 s C = 0.24 s−1 K−n n = 4.9	[46]
[Dy(tta)3(phenNO)] (phenNO = 1,10-phenantroline-1-oxide)	Square antiprism geometry	H = 1000 Oe Ueff = 159.1 K τ0 = 1.9 × 10−10 s C = 5 × 10−3 s−1 K−n n = 5.2	[46]
[Dy(tmhd)3(dppz)] (tmhd = 2,2,6,6-tetramethyl-3,5-heptanedione) (dppz = dipyrido[3,2-a:2′,3′-c]phenazine)	Distorted square-antiprism	H = 1000 Oe Ueff = 247.8 K τ0 = 2.22 × 10−11 s C = 4.28 × 10−4 s−1 K−n n = 5.43	[48]
[Dy2Cp *4(μ-BPh4)][Al(OC(CF3)3)4] (Cp * = 1,2,3,4,5-pentamethylcyclopentadiene) (BPh4 = tetraphenylborate)	/	H = 1000 Oe Ueff = 490 K τ0 = 1.785 × 10−8 s C = 1.50 × 10−4 s−1 K−n n = 3.86	[49]
[Dy(hfac)3(L1)]n	Square-antiprism geometry	H = 1000 Oe C = 0.12(9) s−1 K−n n = 6.10(48)	[43]
{[Dy(hfac)3(L2)]⋅0.5(CH2Cl2)⋅2(C6H14)	Square-antiprism geometry	H = 1000 Oe C = 0.71(6) s−1 K−n n = 3.75(25)	[44]
[Dy(hfac)3(L3)]n	Square-antiprism geometry	H = 1000 Oe C = 125(36) s−1 K−n n = 2.82(13)	[44]
[Dy(hfac)3(L4)]n	Square-antiprism geometry	H = 1000 Oe C = 48.8(41) s−1 K−n n = 2.73(6)	[44]
(1)	spherical tricapped trigonal prism geometry	H = 1000 Oe C = 175(19) s−1 K−n n = 1.95(11)	this work
(2)	spherical tricapped trigonal prism geometry and spherical capped square antiprism	H = 1000 Oe C = 3.93(69) and 1.44(27) s−1 K−n n = 6.81(16) and 7.78(11)	this work

, an Orbach process can be involved in the magnetic relaxation in the high temperature range, in which an out-of-phase contribution of the magnetic susceptibility was measured.

The variation of the dynamic parameters could be attributed to the nature of the surrounding, symmetry of the coordination sphere, as well as the nature of the matrix (crystal packing) and they cannot be easily compared.

3. Conclusions

In this article, the two 4,7-di-tert-butyl-2-(3,5-di-tert-butyl-4-oxocyclohexa-2,5-dien-1-ylidene)benzo[d][1,3]dithiole-5,6-dione (L¹) and 7,8-dithiabicyclo[4.2.0]octa-1,5-diene-3,4-dione,2,5bis(1,1-dimethylethyl) (L²) ligands coordinated the Dy(hfac)₃ unit. The X-ray structures of the two mononuclear complexes revealed that the quinone form of the ligands is kept and dimers are identified due to the presence of remaining coordinated water molecules which allowed the formation of hydrogen bonds. Both compounds [Dy(hfac)₃(H₂O) (L¹)] and [Dy(hfac)₃(H₂O) (L²)] displayed a field-induced single-molecule magnet behavior, with magnetic relaxation occurring through a Raman process. Even if the general structure around the metal is similar for both compounds, slight modification of the arrangement of the dysprosium in the dimeric structures can lead to magnetic changes.

4. Materials and Methods

4.1. Synthesis. General Procedures and Materials

The precursor [Dy(hfac)₃(H₂O)₂] (hfac⁻ = 1,1,1,5,5,5-hexafluoroacetylacetonate anion) [50], 4,7-di-tert-butyl-2-(3,5-di-tert-butyl-4-oxocyclohexa-2,5-dien-1-ylidene)benzo[d][1,3]dithiole-5,6-dione (L¹) [30] and the 7,8-dithiabicyclo[4.2.0]octa-1,5-diene-3,4-dione,2,5bis(1,1-dimethylethyl) (L²) [31] were synthesized following previously reported methods. All other reagents were commercially available and used without further purification.

4.2. Synthesis of Complexes [Dy(hfac)₃(L¹)] (1) and [Dy(hfac)₃(L²)]⋅(C₆H₁₄)(CH₂Cl₂) (2)

[Dy(hfac)₃(H₂O) (L¹)] (1). Notably, 16.4 mg of [Dy(hfac)₃(H₂O)₂] (0.02 mmol) were dissolved in 10 mL of CH₂Cl₂ and then added to a pink-purple solution of 10 mL of CH₂Cl₂ containing 10.0 mg of L¹ (0.02 mmol). The resulting solution changed color from purple to green when adding the Dy^III salt. After 20 min of stirring, 20 mL of n-hexane were layered at room temperature. Suitable deep green single crystals of 1 suitable for X-ray diffraction study were obtained by slow diffusion, followed by a slow evaporation in the dark. Yield (determined from isolated single crystals) 21.8 mg (84%). Anal. Calcd (%) for C₄₄H₄₃DyF₁₈O₁₀S₂: C 40.65, H 3.31; found: C 40.29, H 3.43.

[Dy(hfac)₃(H₂O)(L²)]⋅(C₆H₁₄)(CH₂Cl₂) (2)⋅(C₆H₁₄)(CH₂Cl₂). Notably, 16.4 mg of [Dy(hfac)₃(H₂O)₂] (0.02 mmol) were dissolved in 10 mL of CH₂Cl₂ and then added to a violet solution of 10 mL of CH₂Cl₂ containing 5.6 mg of L² (0.02 mmol). The resulting solution changed color from violet to green when adding the Dy^III salt. After 15 min of stirring, 20 mL of n-hexane were layered at room temperature. Suitable deep green single crystals of (2)⋅(C₆H₁₄)(CH₂Cl₂) for X-ray diffraction study were obtained by slow diffusion followed by a slow evaporation in the dark. Yield (determined from isolated single crystals) 12.8 mg (59%). Anal. Calcd (%) for C₂₉H₂₃DyF₁₈O₉S₂: C 32.12, H 2.12; found: C 31.89, H 2.13.

4.3. Crystallography

Single crystals of L¹, 1 and 2⋅(C₆H₁₄)(CH₂Cl₂) were mounted on a D8 VENTURE Bruker-AXS diffractometer for data collection (MoK_α radiation source, λ = 0.71073 Å), from the diffractometric center X (CDIFX), University of Rennes 1, France (Table S1). SHELXT program [51] was used to solve the structures with a direct method and refinements were done with the SHELXL-14/7 program [52] using a full matrix least-squares method on F². It is worth to notice that the bad quality of the obtained single crystal does not allowed a high level of refinement. Moreover, 2 contains large solvent accessible voids in which residual peak of diffraction were observed and SQUEEZE procedure of PLATON [53] was performed. Residual electronic density and the volume of voids are in agreement with 8 n-hexane and 8 dichloromethane molecules per asymetric unit. CCDC number is 2,039,846–2,039,848 for compounds L¹, 1 and 2⋅(C₆H₁₄)(CH₂Cl₂), respectively.

4.4. Physical Measurements

The elemental analyses of the compounds were performed at the Centre Régional de Mesures Physiques de l’Ouest, Rennes. The static susceptibility measurements were performed on solid polycrystalline samples with a Quantum Design MPMS-XL SQUID magnetometer. The following values of magnetic field were used 0.2 kOe, 2 kOe and 10 kOe respectively for the temperature range of 2–20 K, 20–80 K and 80–300 K in order to prevent any saturation effect. The ac magnetic susceptibility measurements were performed on both Quantum Design MPMS-XL SQUID magnetometer (1–1000 Hz frequency range) and Quantum Design PPMS (10–10000 Hz frequency range) system equipped with an AC/DC probe. Immobilized selected and crunched single crystals were employed to realize the magnetic measurements and the latter were all corrected for the diamagnetic contribution as calculated with Pascal’s constants.