Rhodamine Salicylaldehyde Hydrazone Dy(III) Complexes

Jan 30, 2018 - ABSTRACT: Three new dysprosium(III) complexes [Dy2(HL1-o)2(L1)-. (NO3)3][Dy(NO3)5]·1.5ACE·0.5Et2O (1), [Dy(L1)3]·2.5MeOH·MeCN. (2),...
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Cite This: Inorg. Chem. XXXX, XXX, XXX−XXX

Rhodamine Salicylaldehyde Hydrazone Dy(III) Complexes: Fluorescence and Magnetism Mei-Jiao Liu,† Juan Yuan,† Jin Tao,‡ Yi-Quan Zhang,*,‡ Cai-Ming Liu,§ and Hui-Zhong Kou*,† †

Department of Chemistry, Tsinghua University, Beijing 100084, P. R. China Jiangsu Key Laboratory for NSLSCS, School of Physical Science and Technology, Nanjing Normal University, Nanjing 210023, P. R. China § Beijing National Laboratory for Molecular Sciences, Center for Molecular Science, Institute of Chemistry, Chinese Academy of Sciences, Beijing 100190, P. R. China ‡

S Supporting Information *

ABSTRACT: Three new dysprosium(III) complexes [Dy2(HL1-o)2(L1)(NO3)3][Dy(NO3)5]·1.5ACE·0.5Et2O (1), [Dy(L1)3]·2.5MeOH·MeCN (2), and [Dy(L 2 ) 3 ]·MeOH·MeCN (3) (HL 1 = rhodamine B salicylaldehyde hydrazine, HL2 = rhodamine B 3-methylsalicylaldehyde hydrazine) were synthesized and characterized. Purple complex 1 contains two ring-open ligands HL1-o and shows fluorescence of the rhodamine amide moiety, whereas yellow complexes 2 and 3 are comprised of ring-close ligands (L1/2)− and display fluorescence of the salicylaldehyde Schiff base part. For 2 and 3, Dy(III) ions are nine coordinated by the six oxygen and three nitrogen atoms of three chelate (L1/2)− ligands, but the arrangements of the three ligands are different owing to the methyl substituent on HL2. There are three short predominant Dy−Ophenoxy bonds in 2 and 3. The largest Ophenoxy−Dy− Ophenoxy angle is 148.64(17)° for 2 and 89.63(13)° for 3. Magnetic studies reveal that complex 2 is a field-induced single-molecule magnet (Ueff = 104.2 K under a dc magnetic field of 2000 Oe), and 3 exhibits only a magnetic relaxation behavior owing to the quantum tunneling of magnetization (QTM). Furthermore, ab initio calculations illustrate that the disposition of predominant Dy−Ophenoxy bonds affects the magnetic anisotropy of the Dy(III) ions and relaxation processes of complexes 2 and 3.

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sensors, photochromic systems, or near-infrared fluorescence.11 To the best of our knowledge, the rhodamine B-based lanthanide SMMs are very scarce.12 Under the circumstances, we envisage modifying rhodamine B-based ligands, synthesizing lanthanide SMMs with ring-open/-close forms, and further studying their fluorescence and magnetism.13 Here, the reactions of ligand HL1 or HL2 with dysprosium nitrate hydrates are studied (Scheme 1). Purple complex [Dy2(HL1-o)2(L1)(NO3)3][Dy(NO3)5]·1.5ACE·0.5Et2O (1) and yellow complex [Dy(L1)3]·2.5MeOH·MeCN (2) are obtained in the absence or presence of trimethylamine. Yellow complex [Dy(L2)3]·MeOH·MeCN (3) was obtained in a manner similar to that of complex 2. Moreover, complexes 1 and 2 show interesting fluorescence. Complexes 2 and 3 exhibit similar coordination modes but have distinct dynamic magnetic properties.

INTRODUCTION Recently, studies on single-molecule magnets (SMMs) have made great strides in enhancing energy barrier (Ueff) and blocking temperature (TB) properties,1 as shown, for example, in the dysprosium(III) complex [Dy(Cpttt)2][B(C6F5)4], which possesses the largest Ueff of 1837 K and the highest TB of 60 K.2 Although it has been accepted that the ideal models for Dy(III) SMMs should have strong axial and weak equatorial ligand fields,3,4 the implementation of these models is usually not easy. Nevertheless, it can be possibly realized via the optimization of the coordination environment by changing coordinated small molecules5 or subtle modification of ligands.6 What’s more, ligand modification might lead to different molecular structures and coordinated modes. It is well-known that the ratio of reactants,7 temperature,8 and solvents9 of the reaction system play an important role in obtaining SMMs with diverse structures and magnetism. The rhodamine-based ligands can respond to metallic ions and display a color change and fluorescence.10 This behavior is related to the ring-open or ringclose form of the rhodamine amide moiety. Thus, the introduction of rhodamine-based derivatives to SMMs could yield multifunctional complexes. However, current investigations on rhodamine-based ligands focus mainly on chemo© XXXX American Chemical Society

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RESULTS AND DISCUSSION Synthesis. The reaction of HL1/2 with Dy(NO3)3·6H2O in acetone gave a purple solution, indicative of the formation of a Received: January 30, 2018

A

DOI: 10.1021/acs.inorgchem.8b00219 Inorg. Chem. XXXX, XXX, XXX−XXX

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ligands are ring-close. The powder X-ray diffraction (PXRD) patterns and microelemental analyses of CHN for complexes 1 and 3 indicate that the solid is pure (Figure S4). Crystal Structures. Crystal data and structural details for complexes 1−3 are listed in Table 1, and important bond distances and angles are collected in Tables 2 and 3.

Scheme 1. Synthesis of Complexes 1−3

Table 2. Selected Bond Distances (Å) and Bond Angles (deg) for Complex 1 Dy1−O1 Dy1−O2 Dy1−O3 Dy1−O4 Dy1−O7 Dy1−O8 Dy1−O9 Dy1−O10 Dy1−N1 Dy1−O1−Dy2 Dy1−O3−Dy2

ring-open RhB ligand owing to the acidic condition of the reactant solution. Single crystals of complex 1 suitable for structural determination were obtained by slow diffusion of ether into the acetone reaction solution at room temperature. Interestingly, when triethylamine was added to the above purple solution, a light yellow solution formed, from which complex 2 or 3 could be isolated. The color change could be observed visually when Et3N was added in small portions four times (Figure S2 in the Supporting Information). The UV−vis absorption spectra of the solution clearly show that the intensity of the absorption at 560 nm due to the ring-open rhodamine dramatically decreases and that of the shoulder peak at 410 nm increases. The latter is responsible for the yellow color of the solution. A comparison of the spectra for HL1 for complexes 1−3 in ethanol (Figure S3) indicates that the new peak around 400 nm might be due to ligand to metal charge transfer. Single crystals of complexes 2 and 3 were grown by heating the reaction solution of methanol and acetonitrile in an oven at 60 °C. The presence of ring-open ligands in the purple complex 1 is proven by the crystal structure data. Complexes 2 and 3 are yellow, and their crystal structures show that all the

2.356(6) 2.366(6) 2.317(6) 2.389(6) 2.478(8) 2.409(7) 2.423(7) 2.471(7) 2.571(7) 96.5(2) 97.1(2)

Dy2−O1 Dy2−O2 Dy2−O3 Dy2−O5 Dy2−O6 Dy2−O11 Dy2−O12 Dy2−N2 Dy2−N3 Dy1−O2−Dy2

2.292(6) 2.377(6) 2.308(6) 2.419(6) 2.371(6) 2.456(6) 2.473(7) 2.602(7) 2.536(7) 93.9(2)

Complex 1 crystallizes in the triclinic space group, P1.̅ The main structure of 1 consists of two parts, [Dy2(HL1o)2(L1)(NO3)3]2+ and [Dy(NO3)5]2− (Figure 1a). Two moieties are connected by two hydrogen bonds with N6··· O19 and N4···O23 distances of 2.922 and 2.876 Å, respectively. The [Dy2(HL1-o)2(L1)(NO3)3]2+ cation contains two ringopen ligands HL1 and one ring-close (L1)−, chelating two Dy(III) ions. The Dy1 ion is nine coordinated by four oxygen atoms from two nitrate ions, two oxygen atoms and one nitrogen atom from one HL1-o ligand, and two phenoxyl oxygen atoms from two bridging HL1-o/(L1)− ligands. The Dy2 ion is also nine coordinated by two oxygen atoms from one nitrate ion, four oxygen and two nitrogen atoms from two chelating HL1-o/(L1)− ligands, and one bridging phenoxyl oxygen atom. Dy1 and Dy2 ions are bridged by three phenoxyl

Table 1. Crystal Data for Complexes 1−3

formula formula weight T (K) crystal system space group a (Å) b (Å) c (Å) α (deg) β (deg) γ (deg) V (Å3) Z ρcalc (g cm−3) μ (mm−1) F(000) data/restraints/parameters GOF on F2 Rint R1, wR2 [I > 2σ(I)] R1, wR2 (all data) CCDC

1

2

3

C111.5H121Dy3N20O35 2788.77 173 triclinic P1̅ 17.1579(5) 19.1288(5) 19.9183(5) 74.850(2) 83.176(2) 86.962(2) 6263.8(3) 1 1.479 10.131 2816 23763/1096/1589 1.108 0.0717 0.0720, 0.1966 0.1061, 0.2147 1816184

C109.5H118DyN13O11.5 1962.66 173 monoclinic P21/c 15.9478(4) 20.4636(9) 31.9377(7) 90 92.527(2) 90 10412.7(6) 2 1.252 4.355 4096 21304/52/1255 1.020 0.0475 0.0836, 0.2327 0.1277, 0.2714 1816185

C111H118DyN13O10 1956.68 173 monoclinic P21/c 13.5190(4) 24.6020(5) 30.6886(13) 90 101.933(3) 90 9986.3(6) 2 1.301 4.528 4084 14358/92/1271 1.041 0.0395 0.0525, 0.1319 0.0663, 0.1471 1816186

B

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influence the magnetic anisotropy and ac magnetic properties.16 From this perspective, we speculate that complex 2 shows magnetic properties better than those of 3.5a,17 The neutral molecules are far apart with the shortest Dy···Dy separations of 13.647 and 13.519 Å for complexes 2 and 3, respectively, and are connected by the weak interactions of C−H···π (Figure S6). UV−Vis and Fluorescence. The ring-open ligand HL1 contains a rhodamine amide moiety and a photosensitive salicylaldehyde Schiff base part. The absorption curves (Figure S3) indicate that different from HL1, complexes 1−3 display an absorption band around 400 nm. No absorption peak above 500 nm is observed for HL1, 2, or 3. However, 1 shows a broad band between 500 and 600 nm due to the ring-open rhodamine B, which is responsible for the purple color of the complex. In addition, the rhodamine moiety can make metallic complexes exhibit fluorescence under different pH values in solution.18 Complexes 1 and 2 show weak fluorescence in the solid state (Figure S7). Relatively obvious fluorescence of HL1, 1, and 2 can be observed upon dilution in poloxamer 407 (Figure S8). When the acetone solutions of HL1, 1, and 2 are irradiated at 365 nm, HL1 and 2 emit green fluorescence, while 1 shows orange (Figure S9). Given that the free HL1 and (L1)− ligands in 2 are ring-close, the green fluorescence should originate from the Schiff base part. The fluorescence spectra for HL1 and complexes 1−3 in acetone solution and as solids are depicted in Figure 2. The free ligand HL1 and complexes 1−3 in acetone (Figure 2a) exhibit a broad emission between 400 and 550 nm due to the Schiff base part. The fluorescence of complex 3 resembles that of 2, consistent with the fact that the ligand (L2)− in complex 3 is ring-close. Complex 1 presents an additional emission band around 570 nm, typical of the ring-open rhodamine amide moiety in solution.10,11 In contrast, their solid fluorescence displays some differences (Figure 2b) upon excitation at an optimal wavelength of 470 nm (Figure S10). Complex 1 has an obvious emission band at 660 nm and emits red fluorescence due to the ring-open RhB amide moiety, where it is 23 nm blue-shifted compared with that of the solid RhB (683 nm).19 For HL1, the solid fluorescence exhibits multiple emission bands (around 525, 600, and 660 nm), while complex 2 displays a strong emission peak at 523 nm and a weak one around 660 nm, as well as a shoulder peak around 600 nm. Thus, the strong emission bands at 523 or 525 and 600 nm in HL1 and 2 should be attributed to the Schiff base part, and the

Table 3. Selected Bond Distances (Å) and Bond Angles (deg) for Complexes 2 and 3 Dy1−O1 Dy1−O2 Dy1−O3 Dy1−O4 Dy1−O5 Dy1−O6 Dy1−N1 Dy1−N2 Dy1−N3 O1−Dy1−O2 O1−Dy1−O3 O2−Dy1−O3

2

3

2.224(5) 2.263(5) 2.244(5) 2.400(4) 2.460(4) 2.413(4) 2.615(5) 2.707(5) 2.617(5) 82.7(2) 89.45(19) 148.64(17)

2.248(3) 2.223(3) 2.222(4) 2.464(3) 2.478(3) 2.450(3) 2.630(4) 2.648(4) 2.639(4) 87.69(12) 89.63(13) 88.12(13)

oxygen atoms with the Dy1···Dy2 distance of 3.466 Å. The Dy−O−Dy bridging angles are in the range of 93.9(2)− 97.1(2)°. The Dy3 ion of [Dy(NO3)5]2− is coordinated by five nitrate ions with Dy−O bond distances in the range of 2.378(7)−2.577(8) Å, not as close as those of complexes (nBu4N)2[Dy(NO3)5] (2.426(4)−2.453(5) Å) and (BDTTTP)5[Ln(NO3)5] (2.42(2)−2.52(2) Å).14 Both complexes 2 and 3 crystallize in the monoclinic space group, P21/c, and consist of neutral [Dy(L1/2)3] molecules, as shown in Figures 1b and 1c. The central Dy(III) ions are nine coordinated by six oxygen atoms and three nitrogen atoms from three chelating ring-close ligands. The Dy(III) ion is close to a spherical tricapped trigonal prism (D3h), evaluated by using the SHAPE software15 (Table S1). The three Dy−Ophenoxy bond lengths are in the range of 2.224(5)−2.263(5) Å for 2 and 2.222(4)−2.248(3) Å for 3, obviously shorter than other coordination bonds. Despite their similar formulas, the disposition of three L1/2 ligands is, however, different for 2 and 3 (Figure S5). The three (L1)− ligands coordinate to Dy in a meridional mode in complex 2, while the three (L2)− ligands arrange in a facial manner around Dy in complex 3, owing to the steric hindrance of the methyl in (L2)−. As a result, the largest Ophenoxy−Dy−Ophenoxy bond angle is 148.64(17)° in 2, while that of 3 is only 89.63(13)°. This indicates that the subtle ligand modification makes a difference in the coordination environment of Dy(III). It has been found that the arrangement of short coordination bonds (predominant bonds) could

Figure 1. Crystal structures of complexes 1 (a), 2 (b), and 3 (c). Hydrogen atoms and solvents have been omitted for clarity. Only two hydrogen atoms attached to N4 and N6 are shown for 1. C

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Figure 2. Fluorescence spectra for HL1 and complexes 1−3 in acetone (a) (λex = 365 nm, [HL1] = [1] = [2] = [3] = 5 × 10−6 M) and as solids (b) (λex = 470 nm).

relatively weak emission peak at 660 nm in HL1 and 2 is due to a tiny amount of ring-open rhodamine B. Compared with the fluorescence in acetone, the change of emission peaks has been a common phenomenon owing to the aggregation-caused quenching (ACQ) effect of the solid.20 Magnetic Properties. The variable-temperature magnetic susceptibilities of complexes 1−3 were measured under an external magnetic field of 1000 Oe in the temperature range of 2−300 K. As shown in Figure 3, the χmT value of 1 at 300 K is

deviation from coplanarity for the Dy2O2 cores and the large dihedral angle between the DyO2 plane and the benzene plane should be responsible for the ferromagnetic exchange in 1.21e At room temperature, the χmT values are 13.84 and 14.06 cm3 K mol−1 for 2 and 3, respectively, comparable to the theoretical value of 14.17 cm3 K mol−1 for an isolated Dy(III) ion. As the temperature is lowered, the χmT values of 2 and 3 remain essentially constant with only a little decrease until 100 K. With further cooling, the χmT value for 2 decreases regularly to a minimum of 11.25 cm3 K mol−1 at 2 K. In contrast to 2, the χmT value of 3 decreases more rapidly with decreasing temperature to 9.35 cm3 K mol−1 at 6 K and then increases to a maximum of 9.52 cm3 K mol−1 at 4 K, before decreasing again to 9.27 cm3 K mol−1 at 2 K. Considering that complexes 2 and 3 are mononuclear, the high temperature decrease of χmT should be due to the thermal depopulation of Stark sublevels for the Dy(III) ion and/or intermolecular antiferromagnetic interactions. The field dependence of the magnetization with the applied magnetic field in the range of 0−50 kOe was investigated at 2 K. As shown in Figure 3 (inset), the magnetization values for 1−3 increase rapidly at a low field (0−10 kOe) and then grow slowly reaching the maximum of 18.0 Nβ (1), 5.3 Nβ (2), and 6.6 Nβ (3) at 50 kOe, still less than the theoretical saturated values of 30 Nβ (1) and 10 Nβ (2 and 3) expected for isolated Dy(III) ions. This can be attributed to crystal field effects leading to significant magnetic anisotropy of the Dy(III) ions. To investigate magnetic dynamics for complexes 1−3, the temperature-dependent ac magnetic susceptibilities were collected under zero and 2000 Oe dc fields. Complexes 1 and 3 show non-zero out-of-phase (χ″) values under a dc field of 2000 Oe, but no peaks are observed (Figure S11). This suggests that the quantum tunneling of magnetization (QTM) process is still very strong under a 2000 Oe dc field. For complex 2, under a zero dc field, χ″ signals show no peaks until 2 K due to QTM. When an external dc field of 2000 Oe is applied, χ″ displays strong frequency dependence and peaks, typical of a field-induced single-molecule magnet. Below 5 K, the increase of χ″ indicates that the QTM has not been completely suppressed at low temperature, which is a common phenomenon in lanthanide SMMs.22 In the high temperature region, the Arrhenius law (τ = τ0 exp(Ueff/kT)) is employed to extract parameters τ0 (4.84 × 10−9 s) and energy barrier Ueff (93.8 K) (red line in Figure 4c). The ln τ vs 1/T plot is not linear, indicating that magnetic dynamics cannot be simply

Figure 3. Variable-temperature magnetic susceptibilities under a 1000 Oe dc field for complexes 1−3. The solid lines represent simulations from ab initio calculations for 2 and 3. Inset: Magnetization curve for complexes 1−3 at 2 K.

41.84 cm3 K mol−1, close to the theoretical value of 42.51 cm3 K mol−1 of three non-interacting Dy(III) ions (6H15/2, g = 4/3). When the complex is cooled, the χmT value of 1 decreases slightly from 300 to 100 K and then decreases rapidly reaching the minimum of 30.91 cm3 K mol−1 at 4 K. The high temperature decrease of χmT is probably due to the thermal depopulation of Stark sublevels for Dy(III) ions. The slight increase of χmT to 31.64 cm3 K mol−1 from 4 to 2 K suggests the presence of a weak intramolecular ferromagnetic interaction between two triply Ophenoxy-bridged Dy(III) ions.21a−d The magnetic exchange is related to the Dy−O−Dy bond angle and the dihedral angle of the Dy2O2 core, and a low Dy−O−Dy angle less than 105° and good coplanarity of the Dy2O2 core will lead to Dy···Dy antiferromagnetic exchange.21e The Dy− O−Dy angles are very low (93.9(2)−97.1(2)°) in complex 1; however, the Dy2O2 cores are far from a plane, with the Dy− O−Dy−O torsion angles in the range of 27.6−45.1°. The D

DOI: 10.1021/acs.inorgchem.8b00219 Inorg. Chem. XXXX, XXX, XXX−XXX

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Figure 4. Plots of the temperature-dependent in-phase (a) and out-of-phase (b) ac susceptibility, fitting of temperature dependence of relaxation time (c), and Cole−Cole plots under a 2000 Oe dc field with solid lines as Debye fits (d) for 2.

Figure 5. Magnetization blocking barriers of complexes 2 (a) and 3 (b). The thick black lines represent the Kramers doublets as a function of their magnetic moment along the magnetic axis. The green lines correspond to diagonal QTM; the blue line represents the off-diagonal relaxation process. The numbers at each arrow stand for the mean absolute value of the corresponding matrix element of the transition magnetic moment.

and k is Boltzmann’s constant. C and τ0 are the fitting parameters of the different relaxation mechanisms. The reliable fitting results were found to be as follows: C = 2.69 × 10−2, n = 3.89, τ0 = 3.28 × 10−7, and Ueff = 104.2 K. The dark green curve (shown in Figure 4c) represents the isolated Raman process, which is described by the equation τ−1 = CTn. This result indicates that the Raman process plays a major role in the low temperature region. Semicircular Cole−Cole plots for 2 were fitted using a generalized Debye model for a single relaxation

modeled assuming the thermally activated Orbach process. Considering the fact that the plot shows no obvious linear region at low temperatures, the data are fitted by using Orbach and Raman processes as in eq 1: ⎛ −U ⎞ τ −1 = CT n + τ0−1 exp⎜ eff ⎟ ⎝ kT ⎠

(1)

where τ is the inverse of the ac frequency, T is the temperature of the corresponding peak, Ueff is the effective energy barrier, E

DOI: 10.1021/acs.inorgchem.8b00219 Inorg. Chem. XXXX, XXX, XXX−XXX

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Figure 6. Calculated orientations of the local main magnetic axes of the ground (green) and first excited (purple) Kramers doublets on the Dy(III) ions of complexes 2 (a) and 3 (b).

process at 9, 12, and 15 K. The fitting parameters are listed in Table S2, and α is in the range of 0.30−0.35. Complexes 2 and 3 have a coordination configuration similar to that of the Dy(III) ion, with a difference only in the spatial arrangement of Dy−Ophenoxy bonds. However, their magnetic properties are completely different: 2 is a SMM while 3 is not. In order to understand the magnetism of complexes 2 and 3 from a theoretical perspective, ab initio calculations were performed. Theoretical Calculations. CASSCF calculations based on X-ray determined geometry (Figure S12) were carried out with the MOLCAS 8.2 program package. The calculated dc magnetic susceptibilities are consistent with experimental values in the range of 20−300 K and show slight differences below 20 K. The differences might be due to the intrinsic errors caused by the calculation method, magnetic measurements, or the presence of intermolecular magnetic coupling, which was not considered in the calculations. The calculated energy levels (cm−1) of the Kramers doublets (KDs), g (gx, gy, gz) tensors, and mJ values of the lowest KD of complexes 2 and 3 are listed in Table S3. The calculated ground gz values are 19.748 (gx,y = 0.006, 0.007) and 13.033 (gx,y = 0.974, 4.963) for 2 and 3, respectively, which suggests that complex 2 has a significant axial anisotropy and that 3 shows no apparent axial anisotropy. The calculated tunneling gap (Δtun) between the ground KDs (±15/2 as the major component) is as high as 0.99 μB (Figure 5b), which confirms the extremely large QTM in the ground KD for 3.1n In contrast, complex 2 shows a small transverse magnetic moment (0.22 × 10−2 μB) in the ground KD (±15/ 2), indicating probable Orbach and Raman processes besides the QTM pathway (Figure 5a). This result explains why the experimental energy barrier (104.2 K) is much lower than the calculated energy gap of 284.3 K between the ground and first excited states and implies that the QTM effect between the ground KDs still works as a shortcut to reduce U eff significantly.5a The angles (θ) between the local main magnetic axes of the ground and first excited Kramers doublets for complexes 2 and 3 are 2.9° and 19.6° (Figure 6), respectively, which also confirms the larger tunneling gap in the ground state of complex 3. Furthermore, the main magnetic axes in 2 are nearly parallel to the O2···O3 line (dashed line in Figure 6a) and are close to the two short Dy−Ophenoxy (O2 and O3)

bonds. This result is similar to that of reported complex Dy(LH)3 (LH− is the anion of 2-hydroxy-N′-[(E)-(2-hydroxy3-methoxyphenyl)methylidene]benzhydrazide).23 In contrast, the magnetic axis of 3 deviates far from all three short Dy− Ophenoxy bonds. This illustrates the fact that the arrangement of short Dy−O bonds affects the magnetic anisotropy of the Dy(III) ion and the SMM properties. Moreover, Table S4 collects wave functions with definite projection of the total moment |mJ⟩, and it can be seen that the mJ components for the lowest two doublets of 2 are much purer than those of 3. Thus, the theoretical calculations support the above experimental predictions that the disposition of the predominant Dy−O bonds plays a key role in the magnetic anisotropy.24

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CONCLUSIONS We have demonstrated that Dy(III) complexes of ring-open/close rhodamine B derivatives can be obtained by adjusting the acidity and basicity of the reaction solution. Complexes 1−3 display fluorescence relevant to the conjugated xanthene moiety and planar Schiff base parts. As far as we are aware, for the first time both ring-open HL1 and ring-close (L1)− are present in a molecule of complex 1. Furthermore, we have shown that the arrangement of three predominant Dy−Ophenoxy bonds played an important role in the magnetic anisotropy of Dy(III) for complexes 2 and 3, which has been verified by ab initio calculations. The present result reemphasizes the importance of ligand modification in adjusting magnetic properties. Future work will focus on the fluorescent ring-open/-close rhodamine 6G18-based lanthanide SMMs to further improve SMM properties.25

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EXPERIMENTAL SECTION

Syntheses. All reagents were commercially available and used without further purification. The ligands HL1 and HL2 were synthesized by the literature method.26 [Dy2(HL1-o)2(L1)(NO3)3][Dy(NO3)5]·1.5ACE·0.5Et2O (1). The ligand HL1 (0.5 mmol) was dissolved in acetone (5 mL), and solid Dy(NO3)3·6H2O (0.3 mmol) was added to the mixture while being stirred at room temperature. The colorless solution turned into a deep purple solution immediately. After it was stirred for a few minutes, the resulting solution was filtered, and slow diffusion of ether into the filtrate in a test tube afforded purple, irregular-shaped single crystals. Yield: about 40% (based on the Dy(III) salt). Anal. Calcd for F

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Inorganic Chemistry C111.5H121Dy3N20O35 (2788.77): C, 48.02; H, 4.37; N, 10.05. Found: C, 47.9; H, 4.3; N, 10.0. [Dy(L1)3]·2.5MeOH·MeCN (2). The ligand HL1 (0.3 mmol) was suspended in methanol (18 mL) and acetonitrile (9 mL), and solid Dy(NO3)3·6H2O (0.1 mmol) was added to the mixture while being stirred at room temperature to afford a deep purple solution. Triethylamine (0.6 mmol, 84 μL) was added to the above reaction solution, and the color of the solution became yellow. After it was stirred for a few minutes, the solution was filtered, and the filtrate was placed in an oven at 60 °C for 24 h. Small yellow block-shaped crystals suitable for X-ray single-crystal diffraction were obtained. The crystals were efflorescent in the air. Yield: about 60% (based on the Dy(III) salt). [Dy(L2)3]·MeOH·MeCN (3). Yellow block-shaped crystals of complex 3 suitable for X-ray single-crystal diffraction were obtained in a manner similar to that for complex 2 except that HL2 was used instead of HL1. The obtained crystals were stable in the air. Yield: about 46% (based on the Dy(III) salt). Anal. Calcd for C111H118DyN13O10 (1956.68): C, 68.13; H, 6.08; N, 9.31. Found: C, 67.6; H, 6.1; N, 9.0. Physical Measurements. PXRD measurements were recorded on a Bruker D8 ADVANCE X-ray diffractometer. The IR spectra with a KBr tablet were obtained on WQF-510A FTIR equipment. Elemental analyses (C, H, and N) were performed on an Elementar Vario Cario Erballo analyzer. The UV−vis absorption spectra were measured with a TU-1901 spectrophotometer. Single-crystal X-ray data were collected on a Rigaku SuperNova, Dual, Cu at zero, AtlasS2. The structure was solved by direct methods (SHELXS-2013) and refined by a full matrix least-squares method based on F2 using the SHELXL-2013 or SHELXL-2014/7 program. Hydrogen atoms were added geometrically and refined using a riding model. The fluorescence spectra were recorded on an F98 fluorospectrophotometer. Temperature- and fielddependent magnetic susceptibility measurements were carried out on a Quantum Design MPMS-XL5 SQUID magnetometer. The experimental susceptibilities were corrected for diamagnetism of Pascal’s constants. Ab Initio Computations. Complete active space self-consistent field (CASSCF) calculations on complexes 2 and 3 (see Figure S6 for the calculated model structures of complexes 2 and 3) based on singlecrystal X-ray determined geometry have been carried out with the MOLCAS 8.2 program package.27 The basis sets for all atoms use atomic natural orbitals from the MOLCAS ANO-RCC library: ANORCC-VTZP for the Dy(III) ion, VTZ for close O and N, and VDZ for distant atoms. The calculations employed the second-order Douglas− Kroll−Hess Hamiltonian, where scalar relativistic contractions were taken into account in the basis set and the spin−orbit couplings were handled separately in the restricted active space state interaction (RASSI-SO) procedure. For the fragment of an individual Dy(III) ion, active electrons in the 7 active spaces include all f electrons (CAS(9 in 7)) in the CASSCF calculation. To exclude all doubts, we calculated all the roots in the active space. We have mixed the maximum number of spin-free states that was possible with our hardware (all from 21 sextets, 128 from 224 quadruplets, and 130 from 490 doublets).

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charge via www.ccdc.cam.ac.uk/data_request/cif, or by emailing [email protected], or by contacting The Cambridge Crystallographic Data Centre, 12 Union Road, Cambridge CB2 1EZ, UK; fax: +44 1223 336033.

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AUTHOR INFORMATION

Corresponding Authors

*E-mail: [email protected]. *E-mail: [email protected]. ORCID

Yi-Quan Zhang: 0000-0003-1818-0612 Cai-Ming Liu: 0000-0001-7184-6693 Hui-Zhong Kou: 0000-0002-7510-052X Notes

The authors declare no competing financial interest.

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ACKNOWLEDGMENTS This work was supported by the 973 program (2013CB933403), the National Natural Science Foundation of China (21571113, 21771115, and 11774178), and the Natural Science Foundation of the Jiangsu Higher Education Institutions of China (16KJB430020).

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S Supporting Information *

The Supporting Information is available free of charge on the ACS Publications website at DOI: 10.1021/acs.inorgchem.8b00219. Additional crystal structures and data, FT-IR spectroscopy and powder X-ray diffraction analyses, dc and ac magnetic susceptibility data, spin density distributions, photoluminescence spectra and lifetimes, and TD-DFT computational results (PDF) Accession Codes

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DOI: 10.1021/acs.inorgchem.8b00219 Inorg. Chem. XXXX, XXX, XXX−XXX

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Inorganic Chemistry

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