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Cite this: Dalton Trans., 2013, 42, 13397

Received 10th May 2013,Accepted 6th June 2013

DOI: 10.1039/c3dt51227d

www.rsc.org/dalton

Series of dinuclear and tetranuclear lanthanide clustersencapsulated by salen-type and β-diketionate ligands:single-molecule magnet and fluorescence properties†

Wen-Bin Sun,*a Bing-Lu Han,a Po-Heng Lin,b Hong-Feng Li,a Peng Chen,a

Yong-Mei Tian,a Muralee Murugesu*b and Peng-Fei Yan*a

Three dinuclear [Ln2H2OL12(acac)2]·solvent (1, Ln = Gd, solvent = 2CH2Cl2; 2, Ln = Tb, no solvent; 3, Ln =

Er, solvent = (C2H5)2O), and two tetranuclear lanthanide clusters [Ln4(μ3-OH)2L22(acac)6]·2(solvent) (4,

Ln = Tb, solvent = CH3OH; 5, Ln = Dy, solvent = CH3CN) were characterized in terms of structure, fluore-

scence and magnetism. The dinuclear lanthanide complexes were constructed by a rigid salen-type

ligand H2L1 = N,N’-bis(salicylidene)-o-phenylenediamine and β-diketonate (acac = acetylacetonate)

ligands, while the tetranuclear clusters were formed from the flexible ligand H2L2 = N,N’-bis(salicylidene)-

1,2-ethanediamine. Crystal structure analysis indicates that the rigid ligand favors the double-decker

sandwich structure (Ln2L12), in which the two lanthanide ions have different coordination numbers and

geometry, while the more flexible ligand (H2L2) leads to planar tetranuclear clusters. The relationship

between their respective magnetic anisotropy and ligand-field geometries and their fluorescence pro-

perties was investigated. The Dy and Tb-containing clusters exhibit typical visible fluorescence properties,

and single-molecule magnet behavior is seen in complex 5.

Introduction

Single-molecule magnets (SMMs) exhibiting slow magneticrelaxation have recently attracted much attention due to theirpotential for use in high-density information storage, mole-cular spintronics, quantum computing devices and magneticrefrigeration.1–4 Among them, lanthanide SMMs continue toflourish in these fields due to the presence of the large spinground state (ST) and Ising-type magnetoanisotropy (D) inthese systems.1,5 Lanthanide(III) ions such as Tb(III), Dy(III), orHo(III) with a large amount of spin and spin–orbit coupling arewidely investigated and used in the field of SMMs.6–9 However,the pure 4f-based SMMs are relatively scarce due to thedifficulty in promoting magnetic interactions between thebridging ligand orbital and the 4f orbital of the lanthanide

ions. Ligands with orbitals able to overlap the 4f orbitals ofthe lanthanide ions are preferred for constructing pure lantha-nide-based SMMs.10,11 On the other hand, the orbital energyof these ligands could match well with the lowest excited statelevel of lanthanide(III) ions and absorb light in the UV regionand transfer the energy via an “antenna effect”, finally result-ing in an enhancement of fluorescence emission. Besides theenergy matching, a multidentate ligand that can encapsulatethe lanthanide(III) ions, protecting them from vibration coup-ling which may quench fluorescence and keeping them as dis-crete molecules avoiding intermolecular interaction, is crucialthe in construction of these fluorescent and magnetic mole-cule materials.11–13 Thus, a well-selected ligand is one of thekey factors in building multifunctional lanthanide-basedmaterials.

Among these ligands, polyalcohols, carboxylic acid deriva-tives, oximate derivatives and Schiff-base ligands were success-fully used in the isolation of high-energy barrier SMMs.14

Especially, Schiff-base and β-diketonate ligands have been suc-cessfully used in the construction of magnetic and fluorescentmaterials,8b,15,16 while research into bifunctional materialsboth with SMM and luminescent properties is scarce.17 It isworth noting that the emission spectrum with fine splittingcould serve as a means of accessing the magnetism of thelanthanide-based SMMs and these pioneering works attemptto correlate the magnetic and emission properties.

†Electronic supplementary information (ESI) available: Additional magneticmeasurements, selected bond lengths and angles and IR data for 1–5 wereincluded. CCDC 830602, 830603, 830605, 839728 and 837060 . For ESI and crys-tallographic data in CIF or other electronic format see DOI: 10.1039/c3dt51227d

aKey Laboratory of Functional Inorganic Material Chemistry Ministry of Education,

Heilongjiang University, No. 74, Xuefu Road, Nangang District, Harbin 150080,

P. R. China. E-mail: wenbinsun@126.com, yanpf@vip.sina.com;

Tel: +86 10-8660-8042bDepartment of Chemistry and Centre for Catalysis Research and Innovation,

University of Ottawa, 10 Marie-Curie, Ottawa, ON, Canada K1N 6N5.

E-mail: m.murugesu@uottawa.ca

This journal is © The Royal Society of Chemistry 2013 Dalton Trans., 2013, 42, 13397–13403 | 13397

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Recently, we successfully developed a useful synthetic strat-egy involving both salen-type and β-diketonate ligands toisolate tetranuclear planar lanthanide cluster complexes.18,19

In these clusters, the salen-type ligand plays a critical role indetermining the coordination geometry of lanthanide ionsand the β-diketonate ligand mainly plays the role of pushingthe lanthanide ions into the N2O2 coordination pocket of thesalen-type ligands, and obviously the steric hindrance ofthe ligand dominates the formation of this type of lanthanideclusters. In our more recent work, when the rigid salen-typeligands are used, a dinuclear dysprosium complex could beobtained and magnetic analysis demonstrated that it behavesas a Dy2 SMM with a distinct coordination environment andleads to two unique relaxation modes due to the single-iontype relaxation mechanism. Even the Yb2 analogue displays afield-induced SMM behavior and as well near-infrared emis-sion was observed.18 In order to confirm this synthetic strategyand tune the magnetic properties of these SMMs, by changingthe coordination ligands, two new salen-type ligands withrigid and flexible backbones are used (Scheme 1). In thepresent work, three dinuclear lanthanide analogues Gd(III) (1),Tb(III) (2) and Er(III) (3) from the rigid salen-type ligand (H2L

1)and two planar tetranuclear Tb(III) (4) and Dy(III) (5) from aflexible salen-type ligand (H2L

2) were successfully isolated toillustrate this synthetic strategy. Complex 5 displays SMM be-havior and metal-centered emissions. Herein, we report theirpreparation, structural characterization, and magnetic andfluorescence properties.

Results and discussion

Complexes 1–3 were prepared by refluxing H2L1 (N,N′-bis(sali-

cylidene)-o-phenylenediamine) with solid Ln(acac)3·H2O as themetal precursor in dichloromethane (CH2Cl2) solution. Inorder to obtain crystals of clusters 4 and 5 constructed withH2L

2, which is similar to our recently reported ligand (H2L),19

the same experimental conditions were used i.e. refluxing theligand and Ln(acac)3·H2O precursor in a mixed solvent ofmethanol and acetonitrile. It is also noteworthy that these twosalen-type ligands act not only as the ligands in this reactionbut also as the base, thus promoting the formation of hydrox-ide ligands from water molecules introduced by the startingmaterials. Similar bifunctional ligands have been reported inthe literature.19,23 Moreover, changes to the molar ratiobetween the ligand and Ln(acac)3·H2O as well as using adifferent reaction solvent result in noncrystalline materials.

Structural analysis

Single-crystal X-ray diffraction, IR analysis (Fig. S1, 2)† andcharge-balance considerations indicate that complexes 1–3 areessentially isomorphous, taking complex 2 as an example todescribe the structure, the partially labelled crystal structure isshown in Fig. 1. Complexes are crystallized in a monocliniccrystal system in the space group P21/n (Table 1). Due to boththe radii of the Tb(III) ions being large relative to the transitionmetal ions, and the two imine N atoms and two phenolic Oatoms of the rigid ligand H2L

1 lying nearly in a plane giving asmall pocket, Tb(III) ions could not locate in the center of theinner N2O2 set. The Tb(III) ions have to coordinate above orbelow the planar ligands. As shown in Fig. 1, the Tb2 ionbetween the two decks of ligands, is placed above one ligandand is ligated by two N atoms and two O atoms from thisligand with Tb2–N3, Tb2–N4, Tb2–O3, and Tb2–O4 distancesequal to 2.475(3), 2.475(4), 2.238(2) and 2.182(3) Å, respect-ively. The Tb2 ion is also located under another ligand and isligated through two phenolic O atoms of this ligand withTb2–O1 and Tb2–O2 distances of 2.377(3) and 2.345(3) Å,respectively. There is one water (O9) atom completing theseven-coordination geometry of the Tb2 ions, with a Tb2–O9distance of 2.372(3) Å. This leads to a distorted capped trigonalprism, in which O2, O4 and N4, and O1, O3 and N3 form thetwo triangle planes of the trigonal prism and one water mole-cule, O9, is located above the distorted square plane formed byO1, O2, O3 and O4 (Fig. 1 bottom). The Tb2 ion is near to thisplane with a 0.2877 Å distance. The Tb1 ion is located abovethe top ligand and coordinated by two N and two O atomsfrom this ligand with Tb1–N1, Tb1–N2, Tb1–O1, and Tb1–O2distances of 2.551(3), 2.563(4), 2.347(2) and 2.352(3) Å, respecti-vely. There are two bidentate acac ligands finishing the

Fig. 1 Molecular structure of 2 [Tb2H2OL12(acac)2] (top) and the polyhedralrepresentation of the dinuclear core emphasising the distorted square antiprism(dark yellow) and capped trigonal prism (green). Colour code: green (Tb), blue(N), red (O), gray (C). H atoms were omitted for clarity.

Scheme 1 Schematic of the salen-type and acac ligands.

Paper Dalton Transactions

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8-coordination geometry through four O atoms, the distancesof Tb1–O5, Tb1–O6, Tb1–O7 and Tb1–O8 are equal to 2.326(3),2.394(3), 2.325(3), and 2.303(3) Å. This forms a distortedsquare-antiprismatic geometry (Fig. 1 bottom). The two squarebases of the square antiprism for Tb1 consist of the O5, O6,O7 and O8, and O1, O2, N1 and N2 atoms. The Tb1 and Tb2ions are bridged by the two μ2-phenolic O1 and O2 atoms, witha Tb1–Tb2 distance of 3.8754(3) Å, and Tb1–O1–Tb2 and Tb1–O2–Tb2 angles of 110.23(9) and 111.22(10)°. It is interestingthat the two Tb(III) ions show distinct coordination numbersand environments.

Complexes 4 and 5 are constructed with H2L2 and acac

ligands. They are crystallographically isostructural and therepresentative crystal structure of 5 is depicted in Fig. 2. Asexpected, they give tetranuclear planar lanthanide clusters, all8-coordinate Dy(III) ions are coplanar and linked by a combi-nation of μ3-hydroxo (O3 and O3′), ketonate (O8 and O8′) andphenoxo (O1, O2, O1′, and O2′) oxygen atoms. The two Dy2and Dy2′ ions are located in the inner N2O2 coordinationpocket of the two salen-type ligands (Fig. S2)† with Dy2–O1,Dy2–O2, Dy2–N1 and Dy2–N2 distances equal to 2.372(2),2.328(2), 2.499(3) and 2.556(3) Å, respectively. Two triply brid-ging hydroxide (O3 and O3′) atoms lie approximately 0.87 Åabove and below the Dy4 plane. The μ3-OH groups form nearsymmetrical bridges to the metal centers, with Dy2–O3, Dy1–O3 and Dy1′–O3 distances of 2.313(2), 2.370(2) and 2.372(2) Å,respectively, as well as Dy2–O3–Dy1, Dy2–O3–Dy1′ and Dy1′–O3–Dy1 angles of 100.49(8), 111.52(8), and 109.12(8)°, respect-ively. There are six bidentate anionic acac− groups above andbelow the planar core chelating to the four Dy(III) ions. In thisDy4 cluster, the 8-coordinate Dy1 and Dy2 ions exhibit a dis-torted square-antiprismatic geometry. The two square bases ofthe square antiprism for Dy1 consist of O1′, O3′, O3 and O6,and O2, O7, O9 and O8, whereas for Dy2, the two square basesare defined by the atoms N1, N2, O1 and O3, and O2, O5, O4

and O8 (Fig. S3 in the ESI).† The two square antiprisms sharethree oxygen atoms, O2, O3 and O8, which form a triangularface (Fig. 2 and Fig. S3)† with distances of 2.62, 2.78 and2.85 Å for O2⋯O8, O3⋯O8 and O2⋯O3, respectively. The fourDy(III) ions are located at the corners of a parallelogram withdistances and angles between the metal centers described inFig. S4 in the ESI.†

As expected, these tetranuclear planar Dy4 structures aresimilar to our recently reported series of Ln4 clusters encapsu-lated by salen-type H2L and acac ligands (Scheme 1),19 which

Table 1 Crystallographic data and structure refinement for complexes 1–5

1 2 3 4 5

Empirical formula C52H47Cl4Gd2N4O9 C50H44N4O9Tb2 C54H53Er2N4O10 C63H76N4O19Tb4 C66H78Dy4N6O18FW (g mol−1) 1328.24 1162.73 1252.52 1828.96 1893.34Crystal system Monoclinic Monoclinic Monoclinic Monoclinic TriclinicSpace group P21/n P21/n P21/n C2/c P1̄Temperature (K) 296(2) 296(2) 296(2) 296(2) 296(2)a (Å) 15.4707(6) 12.9763(5) 16.0195(15) 25.4209(13) 11.9873(5)b (Å) 19.5166(8) 19.4129(7) 19.6394(18) 14.9879(8) 12.6398(5)c (Å) 17.8732(8) 19.3280(7) 16.2270(15) 21.0093(11) 14.0357(9)α (°) 90 90 90 90 112.4560(10)β (°) 91.0720(10) 106.2460(10) 90.722(2) 115.9440(10) 101.5560(10)γ (°) 90 90 90 90 105.7770(10)V (Å3) 5395.6(4) 4674.5(3) 5104.8(8) 7198.0(7) 1777.28(15)ρcacd (Mg m−3) 1.635 1.652 1.630 1.688 1.769M (mm−1) 2.692 3.061 3.327 3.949 4.226F (000) 2620 2296 2484 3576 924Collected reflections 39 320 34 033 37 184 25 792 13 167Independent reflections 13 360 11 585 12 704 8903 8774Rint 0.0410 0.0491 0.0693 0.0398 0.0171R1 [I > 2σ(I)] 0.0352 0.0344 0.0514 0.0486 0.0253wR2 (all data) 0.0746 0.0659 0.1482 0.1274 0.0601Goodness of fit on F2 1.004 0.969 0.966 1.042 1.037

Fig. 2 Molecular structure of 5 (top) and side view of the planar Dy4 core witha green plane across four Dy(III) ions (bottom). The coordination polyhedra ofthe Dy1 and Dy2 ions are depicted. All hydrogen atoms and dissociative mole-cules have been omitted for clarity. Color code: green (Dy), blue (N), red (O),gray (C).

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results from the similar ortho-diamine backbone of ligandH2L

1 and H2L2. The torsion angles of NCCN (ortho-diamine)

are 53.34° in cyclohexane-1,2-diamine and 53.91° in theethane-1,2-diamine backbone, respectively. Thus, this is anefficient synthetic strategy for tetranuclear planer lanthanideclusters incorporating diverse flexible salen-type and β-diketo-nate analogues. However, for complexes 1–3, the torsion angleof NCCN in the benzene-1,2-diamine (H2L

1) backbone is 0.07°,it is nearly a plane consisting of NCCN. The direct influence ison the inner coordination N2O2 pocket, a more flexible ligandfavours the encapsulation of large lanthanide ions, whereasfor the rigid ligand (e.g. H2L

1) the narrow pocket consisting ofthe planar N2O2 could not encompass the large lanthanideions, thus a double-decker sandwich structure formed. Thesedouble-decker sandwich structures are popular for the lantha-nide complexes constructed from aromatic ortho-diamine-based Schiff base analogues.20

Fluorescence properties

The visible photoluminescence (PL) spectra of 2 (Tb2), 4 (Tb4)and 5 (Dy4) in the solid-state were measured at room tempera-ture (Fig. 3 and Fig. S6).† They exhibit characteristic metal-centered emission in the visible field.24 The emission spectraof 2 and 5 consist of four main bands centered around 489,545, 583 and 620 nm that are assigned to the characteristictransitions of 5D4 → 7FJ (J = 6, 5, 4 and 3) for Tb(III) ions(Fig. S6).† In which, the 5D4 → 7F5 transition (545 nm) isclearly the strongest and results in a green emission. It is inter-esting to note that the lowest excited energy level (4F9/2) of theDy(III) ion (20 830 cm−1) is similar to that (5D4) of the Tb(III)ion (20 430 cm−1). Thus the ligands suitable for Tb photolumi-nescent compounds would be efficient for Dy complexes. Likemost Dy-containing compounds, the photoluminescencespectrum of 5 shows two sharp emission bands at 480 and574 nm attributed to the 4F9/2 →

6H15/2 and4F9/2 →

6H13/2 tran-sitions, respectively (Fig. 3). Generally, the later transition isdominant in most Dy(III)-centered emissions. In this case,interestingly, the main emission center changed from 574 nm

to 480 nm with the yellow varying to blue emission after for-mation of the tetranuclear complex, which is likely to be dueto the different coordination environment around the lantha-nide(III) ions.

The ligand field plays a crucial role both in the fluorescentand the SMM properties, it is challenging to design a ligandfield which possesses both the suitable triplet state to matchthe first exited state of lanthanide(III) ions and the suitablesymmetry to stimulate the magnetic anisotropy of the para-magnetic centers displaying SMM behavior. Recently, thefluorescence emission of the 4f-based SMM systems (Dy(III) orYb(III)) has been proven to be an efficient method of correlatingthe energy gaps between the ground-state multiplets with thethermal relaxation energy barriers, and further to support thetheoretical results of the crystal-field components. Fortunatelywe found this system possessed both fluorescent and SMMproperties, while the emission line involving the ground-state6H15/2 is not sufficiently well resolved to evaluate the fine sepa-ration between the two states at highest energy. Nevertheless,according to the present synthetic strategy, the alterationof rigid and flexible backbone ligands is promising to geta bifunctional fluorescent and SMM system for studying thecorrelation between the fluorescent and SMM properties.

Magnetic properties

The dc magnetic measurements were performed on polycrys-talline samples of 1000 Oe (Fig. 4) and the field dependence ofthe magnetization for 1 to 5 in the temperature range of 2.5 to8 K were also obtained and are shown in Fig. S7–11.† Thevalues of χT at room temperature are 16.05, 21.25, 19.47, 56.08and 58.81 cm3 K mol−1 for complexes 1 to 5 respectively.According to the free-ion approximation of each lanthanideion, Gd(III) (8S7/2, S = 7/2; L = 0, g = 2, χT = 7.88 cm3 K mol−1),Tb(III) (7F6, S = 3, L = 3, g = 3/2, χT = 11.82 cm3 K mol−1), Dy(III)(6H15/2, S = 5/2, L = 5, g = 4/3, χT = 14.17 cm3 K mol−1), Er(III)(4I15/2, S = 3/2, L = 6, g = 6/5, χT = 11.48 cm3 K mol−1). Thetheoretical values for two non-interacting lanthanide ions arecalculated to be 15.76, 23.64 and 22.96 cm3 K mol−1 for 1, 2and 3, respectively. The theoretical value for four non-interact-ing lanthanide ions are calculated to be 47.52 and 56.68 cm3 Kmol−1 for 4 and 5, respectively. The experimental χT values at

Fig. 3 Emission spectra of 5 and Dy(acac)3·H2O in the solid-state.Fig. 4 Temperature dependence of the χT product for complexes 1–5 under anapplied field of 1000 Oe.

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room temperature are close to the theoretical values. On lower-ing the temperature the χT product remains fairly constantdown to ∼50 K for 1 before dropping rapidly down to12.29 cm3 K mol−1 at 2.5 K. Due to the isotropic nature ofGd(III) ions it is reasonable to assume that the latter behavioris indicative of intramolecular antiferromagnetic interactions.As for complexes 2, 3, 4 and 5, the χMT product decreasesgradually and more rapidly until a slightly higher temperatureof ∼70 K, which is likely to be due to crystal-field effects (i.e.thermal depopulation of the Ln(III) Stark sublevels) and thepossible antiferromagnetic dipole–dipole interaction betweenthe molecules is not ruled out.

The M versus H and H/T data at high fields for all complexesare given in Fig. S7–11.† For complex 1, the magnetizationreaches near saturation at 14.17Nβ with an applied field of7 T. This value is close to the expected theoretical value of14.00Nβ (g = 2). The magnetization measurements for com-plexes 2, 3, 4 and 5 show a relatively rapid increase below ∼1 Tand a slow linear increase without complete saturation up to7 T. Their magnetization values (10.86, 9.06, 23.61 and19.23Nβ) are lower than their theoretically derived values(18.00, 18.00, 36.00 and 40.00Nβ for 2, 3, 4 and 5, respectively).As aforementioned, the complexes may have low-lying excitedstates or significant magnetic anisotropy resulting in largedifferences between experimental and theoretical values.Further confirmation was obtained from the M vs. H/T plots(Fig. S7–11),† the non-superposition of the M vs. H/T plots athigher field indicates the presence of low-lying excited statesor significant magnetic anisotropy.

In order to study the magnetic dynamic behavior of thesesystems, the alternating-current (ac) susceptibility at variousfrequencies and temperatures in the absence of dc fields ismeasured and depicted in Fig. 5 and S12.† For 5, both in-phase (χ′) and out-of-phase (χ′′) susceptibilities show a fre-quency dependence, this clearly indicates the slow relaxationof magnetization arising from single-ion magnet (SIM) behav-ior. However, no full peak was observed, in the lanthanidesystems the tail of a peak generally indicates the presence ofquantum tunneling of magnetization (QTM) which is usuallyseen in 4f-based SMMs. For the frequency dependence of theout-of-phase ac susceptibility (χ′′) measurement, the peaks areclearly detected, and the data was fitted to the Arrhenius law(τ = τ0 exp(Ueff/kT), Fig. S13)† providing an effective relaxationenergy barrier of Ueff 13.95 K and pre-exponential factor τ05.01 × 10−6 which lies in the normal range of 10−6–10−10, therelatively large value is indicative of the existence of QTM.

The Cole–Cole plots (Fig. S13 right)† in the form of χ′′ vs. χ′show an asymmetrical shape and can be fitted to the general-ized Debye model25 with an α value range of 0.168–0.270 (α = 0for a Debye model). The relatively large α values are in agree-ment with a wide distribution of relaxation times, and theasymmetric Cole–Cole plots at low temperatures might suggestthe occurrence of multiple relaxations most likely associatedwith distinct anisotropic centres. All these magnetic para-meters clearly indicate that the remarkable complex 5possesses a SMM nature.

ExperimentalGeneral information

All chemicals and solvents were obtained from commercialsources and were used as received, without further purifi-cation. Elemental (C, H and N) analyses were performed on aPerkin-Elmer 2400 analyzer. Fourier transform IR spectra weremeasured on a Perkin-Elmer Spectrum One spectrometer withsamples prepared as KBr pellets. Visible and NIR emissionand excitation were recorded on an Edinburgh FPLS 920 fluo-rescence spectrophotometer. The salen-type ligands H2L

1 andH2L

2 were prepared according to the literature report andlanthanide precursors, Ln(acac)3·H2O, where Ln = Gd(III),Tb(III), Dy(III), Er(III) and Yb(III) were prepared according to aliterature procedure previously described.20a,21

Synthesis of dinuclear complexes (1–3)

The same procedure was employed in preparing the four com-plexes; hence, only compound 2 [Tb2H2OL

12(acac)2] will be

described in detail. To 20 mL of dichloromethane solution ofH2L

1 (0.159 g, 0.5 mmol), solid Tb(acac)3·H2O (0.241 g,0.5 mmol) was slowly added under stirring. The solution wasrefluxed for 4 h and the mixture was then cooled to roomtemperature and filtered. Diethyl ether was layered on top ofthe filtrate to give yellow single crystals of 2 in one week.

Fig. 5 Temperature and frequency dependence of the out-of-phase ac suscep-tibility (χ’’) under a zero dc field for complex 5.

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Elemental analyses, infra-red and yields for complexes 1–3

Yields: 0.466 g (70%) for (1), 0.378 g (65%) for (2) and 0.407 g(69%) for (3). Elemental analysis (%) calcd forC52H47Cl4Gd2N4O9 (1): C, 47.02; H, 3.57; N, 4.22; found C,46.79, H, 3.68, N, 4.05; C50H44N4O9Tb2 (2): C, 51.65; H, 3.81;N, 4.82; found C, 51.31, H, 3.78, N, 4.45; C54H53Er2N4O10 (3):C, 51.78; H, 4.27; N, 4.47; found C, 50.94, H, 3.98, N, 4.58; IR(KBr) for (1): ν = 1621, 1607, 1583, 1539, 1515, 1474, 1387,1287, 1260, 1183, 1151, 1016, 916, 750, 656, 529 cm−1; (2): ν =1619, 1607, 1582, 1539, 1516, 1474, 1386, 1286, 1261, 1184,1149, 1016, 916, 749, 656, 529 cm−1; (3): ν = 1621, 1609, 1583,1540, 1523, 1475, 1386, 1287, 1264, 1186, 1149, 1018, 917, 748,657, 531 cm−1.

Synthesis of tetranuclear complexes 4 and 5

The same procedure was employed in preparing the two com-plexes, compound 5 [Dy4(μ3-OH)2L

22(acac)6]·2MeCN will be

described in detail. To 10 mL of an acetonitrile solution ofH2L

2 (0.270 g, 1.0 mmol) 10 mL of a methanol solution ofDy(acac)3·H2O (0.485 g, 1.0 mmol) was slowly added understirring. The solution was refluxed for 3 h, and the filtrate wasallowed to crystallize at room temperature by slow evaporation.Yellow crystals, suitable for single-crystal X-ray diffractionanalysis, were obtained after 2 weeks.

Elemental analyses, infra-red and yields for complexes 4, 5

Yield: 0.947 g (50%) for 4 and 0.967 g (52%) for 5. Elementalanalysis (%) calcd for C63H76N4O19Tb4 (4): C, 41.37; H, 4.19; N,3.06; found C, 41.19, H, 4.21, N, 2.89; C66H78Dy4N6O18 (5): C,41.87; H, 4.15; N, 4.44; found C, 41.68, H, 4.04, N, 4.29. IR(KBr) for (4): ν = 3573, 1633, 1603, 1516, 1393, 1289, 1016, 922,756, 644 cm−1; (5): ν = 3577, 1635, 1602, 1517, 1388, 1289,1018, 921, 759, 644 cm−1.

X-ray crystallographic analysis and data collection

Single-crystal X-ray data of the four clusters were collected at293 K on a Bruker SMART CCD diffractometer equipped withgraphite monochromatized Mo-Kα radiation (λ = 0.71073 Å).The structure was solved by direct and Patterson methods andrefined by the full-matrix least-squares methods on F 2, whichwere performed using the SHELXTL-97 software package.22b,c

The location of lanthanide atoms was easily determined, andO, N, C and H atoms were subsequently determined from thedifference Fourier maps. The non-hydrogen atoms wererefined anisotropically. The H atoms were introduced in calcu-lated positions and refined with fixed geometry with respect totheir carrier atoms. All of the crystal data and structure refine-ment details for these four compounds are summarized inTable 1. Selected bond lengths and angles for 1–5 are listed inTable S1.† Crystallographic data for all structures can beobtained from Cambridge Crystallographic Data Centre as sup-plementary publication no. CCDC 830602 (1), 830603 (2),830605 (3), 839728 (4) and 837060 (5).

Magnetic measurements

The magnetic susceptibility measurements were obtainedusing a Quantum Design SQUID magnetometer MPMS-XL 7operating between 2.5 and 300 K for dc-applied fields rangingfrom −7 to 7 T, ac susceptibility measurements were carriedout under an oscillating ac field of 3 Oe and ac frequenciesranging from 1 to 1500 Hz. Magnetization data were collectedat 100 K to check for ferromagnetic impurities which werefound to be absent in all samples. A diamagnetic correctionwas applied for the sample holder.

Conclusions

Three dinuclear and two tetranuclear lanthanide complexeswere prepared and characterized in terms of structure, fluore-scence and magnetism. It is proved that the use of salen-typeand β-diketonate ligands is ideal for isolation of low nuclearlanthanide multifunctional materials. The structural analysesdemonstrated that the rigid ligand favors the dinuclear half-decker sandwich structure with different coordinationnumbers and geometries for the two lanthanide(III) ions, whilethe more flexible ligand leads to planar tetranuclear clusters.This provides an efficient method by which to tune thesedouble-decker sandwich lanthanide complexes and constructsingle metal ion complexes and/or multinuclear clusters. Themixed ligands could simultaneously induce the luminescenceand single-molecule magnetism of lanthanide(III) ion centers.This gives a facile method with which to investigate therelationship between the structure of lanthanide compoundsand their magnetic or luminescent properties. We are cur-rently trying to tune the environments of the lanthanide(III)ions to keep their coordination geometry and vary the ligandfield around the lanthanide(III) ion, thus potentially promotingtheir magnetic or fluorescent properties. This may be the wayto elucidate accurately the influence of the ligand field aroundthe lanthanide(III) ions.

Acknowledgements

This work was financially supported by the NSFC of China(21272061, 21102039 and 51102081), Heilongjiang University(QL201021, 13k067 and 13k068), NSERC-DG, CFI, ORF andERA.

Notes and references

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