Coordination Chains and Ln(III) Coordination Layers - ACS Publications

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Series of Novel 3D Heterometallic Frameworks Based on the Co(II) Coordination Chains and Ln(III) Coordination Layers Sheng-Yun Liao,† Wen Gu,†,‡ Lin-Yan Yang,† Tian-Hao Li,† Jin-Lei Tian,† Li Wang,† Ming Zhang,† and Xin Liu*,†,‡ †

Department of Chemistry, Nankai University, Tianjin, China 300071 Tianjin Key Laboratory of Metal and Molecule Based Material Chemistry, Tianjin, China 300071

‡

S Supporting Information *

ABSTRACT: A family of novel Co(II)−Ln(III) heterometallic coordination polymers [Ln2Co(tia)4(H2O)4]∞ (tia2− = 5(1H-1,2,3-triazol-1-yl) isophthalate, Ln = La 1, Ce 2, Pr 3, Nd 4, Sm 5, Eu 6, Gd 7, Tb 8, Dy 9) have been synthesized through in situ ligand transformation reactions, in which 5-(4carboxy-1H-1,2,3-triazol-1-yl) isophthalic acid (H3ctia) undergoes decarboxylation and double deprotonation to tia2−. X-ray structural analysis reveals that compounds 1−9 are isomorphous. The heterometallic Ln3+ and Co2+ ions are connected by the dianionic linker (tia2−) to form unique 3D heterometallic frameworks. Moreover, we have systematically investigated the magnetic behaviors and fluorescent properties of these compounds. The out-of-phase ac signals observed for 9 suggest slow magnetization relaxation, which is unusual in 3D coordination polymers, especially in 3D heterometallic frameworks. In NIR regions, complexes 3, 4, 5, and 9 show the characteristic luminescence of the corresponding Ln(III ions.

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INTRODUCTION The search for new compounds with exciting magnetic and photomagnetic properties promoted chemists to combine 3d and 4f spin carriers within the same molecule or framework. A large number of heterometallic complexes1 have been reported, and many of them are focused on Cu−Ln, Mn−Ln, and Ni−Ln systems,2 while the Co−Ln system,3 especially for 3D Co−Ln heterometallic complexes, and their magnetic and luminescent properties are rare.4 Thus, to study the synthesis and magnetic and luminescent properties of the high dimensional Co(II)− Ln(III) coordination polymers is of timely interest. On the other hand, the general routines for constructing 3d− 4f heterometallic complexes are as follows: (i) using classic bridging ligands5 such as CN−, SCN−1, RCOO−1, etc. to link the complex building blocking; (ii) application of mixed organic ligands;6 (iii) application of metalloligands;7 (iv) application of multiple N- and O-donor ligands.8 Among these strategies, multidentate ligands containing N- and O-donors, particularly for heterocyclic polycarboxylic ligands such as pyridine-2,4dicarboxylic acid and pyrazine-2,3-dicarboxylic acid, are verified to be good candidates in the construction of heterometallic complexes. That is because lanthanide and transition metal ions possess different affinities for N and O atoms, owing to the hard−soft acid/base classification. However, to the best of our knowledge, the lack of flexibility and the relatively few donor atoms makes it difficult to construct 3D heterometallic coordination polymers. Herein, we synthesized phenyl heterocyclic polycarboxyl acid H3ctia (H3ctia = 5-(4-carboxy-1H-1,2,3triazol-1-yl) isophthalic acid; see Scheme 1) as the starting © 2012 American Chemical Society

Scheme 1. Conversion of Ligand H3ctia in Construction of 1−9

material to construct 3D Co(II)−Ln(III) hetermetallic complexes in consideration of the following points. (i) It contains more O donors and N donors. (ii) The big size and the semirigidity may be beneficial to the formation of high dimensional polymers. In addition, the traditional one-pot method usually does not lead to the desirable 3d−4f assemblies but mostly to pure 3d or 4f compounds. In the present case, the stepwise experimental procedure has been successfully used to isolate genuine heterometallic complexes.9 Herein, we reported nine novel 3D Co−Ln heterometallic coordination polymers [Ln2Co(tia)4(H2O)4]∞, Received: March 8, 2012 Revised: June 12, 2012 Published: June 15, 2012 3927

dx.doi.org/10.1021/cg300326e | Cryst. Growth Des. 2012, 12, 3927−3936

Crystal Growth & Design

Article

11.95% (12.60%). 3211, 1617, 1558, 1440, 1380, 1223, 923, 854, 782, 730, 598 cm−1. Anal. Found (Calcd) and IR (KBr pellets, cm−1) for (3) C40H28Pr2CoN12O20 (1337.46): 35.40% (35.92%); H, 2.08% (2.11%); N, 12.46% (12.57%). 3361, 1618, 1563, 1440, 1382, 1254, 1223, 1122, 928, 855, 730, 597 cm−1. Anal. Found (Calcd) and IR (KBr pellets, cm−1) for (4) C40H28Nd2CoN12O20 (1344.13): C, 35.40% (35.74%); H, 2.08% (2.10%); N, 12.46% (12.50%). 3355, 1619, 1564, 1440, 1381, 1254, 1221, 1121, 922, 856, 730, 592 cm−1. Anal. Found (Calcd) and IR (KBr pellets, cm−1) for (5) C40H28Sm2CoN12O20 (1356.37): C, 35.42% (35.42%); H, 2.20% (2.08%); N, 12.30% (12.39%). 3359, 1620, 1564, 1255, 1223, 1121, 1063, 781, 590 cm−1. Anal. Found (Calcd) and IR (KBr pellets, cm−1) for (6) C40H28Eu2CoN12O20 (1359.58): C, 35.29% (35.34%); H, 2.08% (2.07%); N, 12.01% (12.36%). 3361, 1568, 1441, 1386, 1257, 1223, 1121, 1064, 924, 781, 590 cm−1. Anal. Found (Calcd) and IR (KBr pellets, cm−1) for (7) C40H28Gd2CoN12O20 (1370.15): C, 35.33% (35.06%); H, 2.05% (2.06%); N, 12.33% (12.27%). 3359, 1619, 1567, 1441, 1385, 1221, 1122, 1064, 928, 781, 589 cm−1. Anal. Found (Calcd) and IR (KBr pellets, cm−1) for (8) C40H28Tb2CoN12O20 (1373.50): C, 34.70% (34.98%); H, 2.05% (2.05%); N, 12.36% (12.24%). 3359, 1620, 1568, 1442, 1224, 1123, 1061, 929, 781, 588 cm−1. Anal. Found (Calcd) and IR (KBr pellets, cm−1) for (9) C40H28Dy2CoN12O20 (1380.65): C, 34.80% (34.79%); H, 2.09% (2.04%); N, 12.26% (12.17%). 3416, 1566, 1443, 1226, 1125, 1061, 928, 780, 571 cm−1.

which were synthesized by a new stepwise methodthe hydrothermal synthetic method, in combination with an ultrasonic method.

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EXPERIMENTAL SECTION

Materials and General Methods. All reagents and solvents for synthesis and analysis were commercially available and used as received. IR spectra were recorded in the range of 4000−400 cm−1 on a Perkin-Elmer spectrometer with KBr pellets. Elemental analyses for C, H, and N were carried out on a Model 2400 II, Perkin-Elmer elemental analyzer. X-ray powder diffraction (XRPD) intensities were measured on a Rigaku D/max-IIIA diffractometer (Cu Kα, λ =1.54056 Å). The single crystalline powder samples were prepared by crushing the crystals and scanned from 3° to 60° with a step of 0.1°/s. TG experiments were performed in flowing air on a NETZSCH TG 209 instrument with a heating rate of 10 °C/min. Near infrared spectra were recorded on an Edinburgh FLS-920P spectrophotometer. Magnetic Study. The magnetic susceptibility measurements of the polycrystalline samples were measured over the temperature range of 2−300 K with a Quantum Design MPMS-XL 7 SQUID magnetometer using an applied magnetic field of 1000 Oe. Diamagnetic corrections to the observed susceptibilities were made with Pascal’s constants. X-ray Structure Determination. Diffraction data for complexes 1−9 were collected with a Bruker SMART APEX CCD instrument with graphite monochromatic Mo Ka radiation (λ = 0.71073 Å). The data were collected at 293(2) K. The absorption corrections were made by multiscan methods. The structure was solved by charge flipping methods with the program Olex2 and refined by full-matrix leastsquares methods on all F2 data with Olex2. The non-hydrogen atoms were refined anisotropically. Hydrogen atoms of water molecules were located in a different Fourier map and refined isotropically in the final refinement cycles. Other hydrogen atoms were placed in calculated positions and refined by using a riding model. The final cycle of fullmatrix least-squares refinement was based on observed reflections and variable parameters. Crystallographic data for 1−9 are given in Table1. Selected bond lengths and angles are given in Tables S1−S9 (Supporting Information). Synthesis of H3ctia. 5-Azidoisophthalic acid (2.08 g, 10 mmol) (prepared according to the literature method10) was dissolved in a 1:2 mixture of water and dimethylsulfoxide (90 mL), and then propiolic acid (0.62 mL, 10 mmol) was added. After being stirred for about 30 min, sodium ascorbate (0.20 g, 1 mmol) and copper(II) sulfatepentahydrate (0.025 g, 0.1 mmol) were added into the mixture in turn. The reaction mixture was stirred vigorously at room temperature for two days, and then ice water was added for dilution and the white precipitate was collected by filtration. The precipitate was washed with cold water six times and dried in air (yield: 70% based on 5-azidoisophthalic acid). 1HNMR (100 Hz, DMSO-d6: δ = 8.02 (s, 1H), 8.65 (s, 2H), 9.65 (s, 2H). IR (KBr): 3129.6 cm−1, 1723.9 cm−1, 1545.2 cm−1, 1475.0 cm−1, 1414.0 cm−1, 1331.0 cm−1, 1255.4 cm−1, 1188.2 cm−1, 757.9 cm−1, 712.1 cm−1, 669.7 cm−1. Synthesis of [Ln2Co(tia)4(H2O)4]∞ (1−9). The nine compounds were synthesized following a procedure similar to that exemplified for 2 hereafter. Co(NO3)2 (0.0582 g, 0.02 mmol) and an aqueous solution of H3ctia (16 mL, 0.02 mmol of H3ctia) whose pH was adjusted to 3.5 by sodium hydroxide was mixed in a Teflon-linear autoclave to react for 30 min under 100 W of ultrasound, and then Ce(NO3)3·6H2O (0.0868 g, 0.02 mmol) was added. The reaction mixture was heated in an oven for 3 days and then cooled down to room temperature at a rate of 3 °C/min. Red block crystals suitable for X-ray structural analysis were obtained with a yield of 0.0040 g (14.98% yield based on Ce(NO3)3·6H2O). Elem. Anal. Calcd for C40H28Ce2CoN12O20 (1335.91): C, 35.95%; H, 2.11%; N, 12.58%. Found: C, 35.90%; H, 2.09%; N, 12.51%. IR (KBr pellets, cm−1): 3361, 1618, 1563, 1440, 1381, 1223, 1122, 921, 854, 731, 601 cm−1. Anal. Found (Calcd) and IR (KBr pellets, cm−1) for (1) C40H28La2CoN12O20 (1333.46): C, 35.97% (36.03%); H, 2.23% (2.12%); N,

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RESULT AND DISCUSSION Synthesis Consideration and Coordination Modes of Ligands. The in situ hydrothermal decarboxylation of the aromatic ring in coordination chemistry is very common.11 In 2011, Li12 investigated the in situ decarboxylation of H3ctia when reacting with Mn(NO3)2·6H2O and Co(NO3)2·6H2O under hydrothermal conditions. Similarly, H3ctia underwent decarboxylation and double deprotonation to the dianionic tia2− during the course of construction of complexes {[Ln2Co(tia)4(H2O)4]}∞, as there is no other source of tia2− (Scheme 1). Namely, the carboxylic group is also cleaved from the triazole ring of H3ctia. In complexes 1−9, ligand tia2− presents two coordination modes (see Scheme 2: (a) μ3-bridging; (b) μ5bridging), which are referred to as LM and LN, respectively. Besides, it ́ is worth mentioning that the traditional one-pot synthesis method is not suitable for using H3ctia as the starting materials to prepare the 3d−4f heterometallic complexes, because we only got the 4f homonuclear complexes ({[Ln2(tia)2(H2O)4](NO3)2}∞) when Co(NO3)2·6H2O, Ln(NO3)3·6H2O, and H3ctia were added together into a Teflon-linear autoclave under the hydrothermal condition. Later, we adjusted the experimental methods. Co(NO3)2·6H2O, which has a lower tendency to coordinate with the ligand in comparison with Ln(NO3)3·6H2O and the aqueous solution of H3ctia, was first mixed in a Teflonlinear autoclave to react for 30 min under the 100 W of ultrasound; then Ln(NO3)3·6H2O was added, and the reaction mixture was sealed in the reactor, kept under autogenous pressure at 180 ◦C for 3 days, and then cooled down to room temperature. A series of {[Ln2Co(tia)4(H2O)4]}∞ were obtained. The hydrothermal synthetic method in combination with ultrasonic expands the methods of preparation of heterometallic coordination polymers. Description of Crystal Structure. Single-crystal X-ray analysis of 1−9 indicates that they are isomorphous and crystallize in space group P1̅ (see Table1). Accordingly, the structure of 2 is described representatively here in detail. Complex 2 exhibits a unique 3D coordination framework with micropores based on the Ce(III) layers and the parallel arrangement of 1D Co(II) chains. The asymmetric unit of 2 contains one Ce(III) ion, half a Co(II) ion, two crystallographically independent 3928


compd 2

C40H28CoCe2N12O20 1335.9 293(2) triclinic P1̅ 9.1359(7) 10.7085(8) 12.7553(9) 86.260 84.661 64.421 1 1.980 2.461 655 3.05−27.48 0.0304 11353

5102 352 0.0311, 0.0761

0.0324, 0.0767

1.227

compd 1

C40H28CoLa2N12O20 1333.5 293(2) triclinic P1̅ 9.1705(8) 10.7258(10) 12.7688(12) 86.261(3) 84.515(3) 64.288(3) 1 1.967 2.324 653 3.05−25.01 0.0249 7360

3960 342 0.0340, 0.0859

0.0367, 0.0868

1.313

identification

formula Mr (g/mol) T (K) crystal system space group a (Å) b (Å) c (Å) α (deg) β (deg) γ (deg) Z ρ (g·cm−3) μ (mm−1) F(000) 2θ scan range Rint reflns collected indep reflns parameters R1, ωR2 [I > 2σ(I)] R1, ωR2 [all data] gof on F2

3929

1.176

0.0439, 0.1078

3818 346 0.0409, 0.1064

C40H28CoPr2N12O20 1337.5 293(2) triclinic P1̅ 9.1438(10) 10.6529(12) 12.6229(14) 84.768(3) 84.951(3) 63.115(2) 1 2.036 2.675 657 3.05−25.01 0.0338 7094

compd 3

1.245

0.0398, 0.0904

4983 352 0.0360, 0.0878

C40H28CoNd2N12O20 1344.1 293(2) triclinic P1̅ 9.1392(7) 10.6874(9) 12.6728(10) 85.709(2) 84.911(2) 63.992(2) 1 2.016 2.779 659 3.05−27.48 0.0246 8813

compd 4

compd 5

1.175

0.0345, 0.0656

3866 352 0.0316, 0.0645

C40H28CoSm2N12O20 1356.4 293(2) triclinic P1̅ 9.1722(7) 10.6883(8) 12.6395(10 84.691(2) 84.866(2) 63.115(2) 1 2.050 3.110 663 3.05−25.00 0.0268 7184

Table 1. Crystallographic Data and Structure Refinement Summary for Complexes 1−9

1.008

0.0387, 0.01231

4940 342 0.0344, 0.01139

C40H28CoEu2N12O20 1359.6 293(2) triclinic P1̅ 9.1905(10) 10.6766(12) 12.6087(14 84.331(2) 84.987(2) 62.936(2) 1 2.062 3.303 665 3.04−25.14 0.0248 8694

compd 6

1.295

0.0349, 0.0989

4938 352 0.0312,0.0907

C40H28CoGd2N12O20 1370.2 293(2) triclinic P1̅ 9.2001(16) 10.6759(18) 12.631(2) 83.966(4) 84.790(4) 62.573(3) 1 2.080 3.472 667 3.04−27.49 0.0230 8755

compd 7

1.152

0.0471, 0.1040

3829 352 0.0400, 0.0929

C40H28CoTb2N12O20 1373.5 293(2) triclinic P1̅ 9.1880(9) 10.6721(10) 12.6208(12 84.041(2) 84.911(2) 62.580(2) 1 2.090 3.681 669 3.04−25.00 0.0376 7109

compd 8

1.147

0.0406, 0.1011

3847 352 0.0336, 0.0786

C40H28CoDy2N12O20 1380.7 293(2) triclinic P1̅ 9.237(3) 10.667(3) 12.665(4) 83.704(6) 84.801 62.206(5) 1 2.091 3.847 671 3.04−25.01 0.0380 6675

compd 9

Crystal Growth & Design Article



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Between two Ce(III) coordination layers, the ligands LM use the symmetry-related N3 and O3 to bridge Co(II) ions to form a 1D parallel arrangement coordination chain along the b axis with the separation of Co···Co, 10.7085(8) Ǻ (see Figures 3 and 1). As can be seen clearly from Figures 4 and 5, two kinds of ligands (LM and LN) connect the 1D Co(II) chains and the 2D Ce(III) layers to produce the 3D microporous network along the c-axis (see Figure 6). The 1D channel is spindle shaped and opened along the b axis, with the porous size of 9.2 × 17.58 Å (measured by the Co···Co and Ce···Ce distances), which is filled by coordination water and the benzene and triazole ring of LN. The parallel arrangement of 1D Co(II) chains is sandwiched in the 2D Ce(III) layers. Up to now, this 3D framework based on the Co(II) coordination chains and Ln(III) coordination layers was not reported publicly. To understand the complicated crystal structure, analysis of network topology is used. In 2, the binuclear Ce(III) can be viewed as 8-connected nodes which are connected to four L N and four LM ligands. With the Co(II) center, the ligands L N and L M can be seen as 6-connected, 4-connected, and 3-connected nodes (see Figure 7), respectively. Therefore, this structure can be simplified as an unordinary 4-nodal (3,4,6,8)-connected topological network with the Schläfl i symbol of (4 2·6) 2(4 4·6 2) 2(4 4·6 8·8 3)(4 8·6 14·8 6) (representing the ligand L M, L N, Co(II) and binuclear Ce(III) nodes). It is worth mentioning that complexes 1−8 possess the intriguing 3D network structure with nCo(II)/nLn(III) = 1:2. These AB2 type metal coordination layer accumulation structures are very rare in the literature.13 These compounds have the potential to become the precursors for preparation of the definite constitution mixed metal oxide.14 This will expand a new research field in crystal engineering. XPRD Results. To ascertain the homogeneity of complexes 1−9, the XRPD patterns of 1−9 were analyzed in detail and the

Scheme 2. Coordination Modes of tia2− in 1−9: (a) LM:μ3Bridging; (b) LN:μ5-Bridging

tia2− ligands (one is μ3-bridging and the other is μ5-bridging, as designated infra with LM and LN, respectively), and two coordination water molecules. The Ce(III) atom is eight-coordinated in a bicapped trigonal prismatic coordination geometry with two oxygen atoms (O1 and O2) from LM, four oxygen atoms (O5, O6, O7, and O8) from four LN, and two oxygen atoms (O9 and O10) from two coordinated water molecules, respectively (Figure 1). The Ce−O bond lengths range from 2.421(3) to 2.964(3) Å. The bond angles of O−Ce−O are in the range of 47.21(8)° to 143.60(9)°. The Co(II) center is sixcoordinated with two nitrogen atoms (N3) from two related symmetry LM, two nitrogen atoms (N6) from two related symmetry LN, and two monodentate carboxylate atoms (O3) from another two symmetry related LM to form a slightly distorted octahedral geometry. The bond lengths of Co−O3, Co−N6, and Co−N3 are 2.047(3) Å, 2.208(3) Å, and 2.120(3) Å, respectively. The angles around Co(II) centers vary from 85.28(11)° to 180°. In the ab plane, the ligands LN use O5 and O6, O8 and O7 to bridge Ce(III) ions with the separation of Ce···Ce, 4.9493(5) Å and 4.3913(4) Å along the a axis, while along the b axis, LN use O5 and O7, O8 and O6 to bridge Ce(III) ions with the separation of Ce···Ce, 8.7462(7) and 10.5900(8) Å. Obviously, Ce(III) ions are bridged by the carboxyl oxygen atom of ligands LN to afford 2D sheets in the ab plane (see Figures 2 and 1).

Figure 1. Local coordination environments of CeIII and CoII in compound 2 (some hydrogen atoms are omitted for clarity). 3930



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Figure 2. In the ab plane, the ligand LN using the carboxyl groups to bridge the Ce(III) to form the Ln(III) coordination layers (hydrogen atoms and coordination water molecules are omitted for clarity).

Figure 3. Parallel arrangement Co(II) coordination chains bridged by the ligand LM in the ab plane (hydrogen atoms are omitted for clarity).

for one isolated Co (S = 3/2) and two free Dy (S = 5/2 and gj = 4/3) ions). With decreasing of the temperature, the χMT of complex 9 remains nearly constant until below 50 K and then drops to a value of 28.54 cm3 K mol−1. To roughly simulate experimental magnetic behavior,15 the magnetic susceptibility of 9 can be viewed as the sum of the contributions of one Co(II) and two Dy(III) ions (eq 3). χM(Co) can be expressed as an equation for a mononuclear Co(II) in an octahedral environment as shown in eq 1, where

results were correlated with the respective simulated powder pattern obtained from the single data. As depicted in Figure S1 (Supporting Information), the main peaks of the XRPD patterns overlapping with the computer-simulated patterns may prove the bulk synthesized material and as-grown crystals are homogeneous for 1−9. Magnetic Properties of 4, 7, 8, and 9. Complex 9 has a χMT value of 33.29 cm3 K mol−1 at room temperature, which is slightly larger than the theoretical value (32.21 cm3 K mol−1 3931



Article

Figure 4. Two kinds of ligands (a) LM and (b) LN (hydrogen atoms are omitted for clarity).

x = λ/kT, λ is the spin−orbit coupling parameter, and A is a measurement of the crystal-field strength due to the interelectronic repulsions. χM(Dy) can be described as eq 2 on the assumption that the Dy(III) ion exhibits a splitting of the mj energy levels (Ĥ = ΔJẑ 2) in the axial crystal field, where Δ is the zero-field-splitting parameter. In eq 4, the Weiss θ parameter is introduced to roughly simulate the magnetic interactions between the paramagnetic species. The leastsquares fit to the data (2−300 K) leads to gDy = 1.357, Δ = −0.0523 cm−1, A = 1.3, λ = −130 cm−1, θ = −0.1338 K, and R = ∑(χobsd − χ′cacld)2/∑(χobsd)2 = 1.32 × 10−3. The negative θ suggests probably antiferromagnetic interaction between the paramagnetic species. At temperature < 3 K, the ac-out-phase (χM″) susceptibility (Figure 8, inset) displays frequency-dependent signals whose maxima lie below the operating minimum temperature (1.8 K) of our SQUID instrument. The behavior is indicative of slow magnetization, which is rather close to what Sanjit Nayak16 and George Christou1a

Figure 5. Ligands connecting the Co(II) chains and the Ce(III) layers to afford 3D frameworks (hydrogen atoms and coordination water molecules are omitted for clarity).

Figure 6. Perspective view of the 3D microscope structure of 2 (all of the H atoms are omitted for clarity). 3932



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Figure 8. Plot of χMT (■) vs T for 9 from 2 to 300 K (the solid line denotes the theoretical fit) and temperature dependence of the out-ofphase (χM″) ac susceptibility component (inset) for 9 at different frequencies and zero applied.

Figure 7. Topological representation for the 3D structure of 2: blue, LM; pink, binuclear Ce(III); purple, Co(II); green, LN.

χM =

reported about Dy compounds. This magnetic behavior is not common in 3D coordination polymers,17 especially in 3D heterometallic complexes. χM(Co) =

T χ T − θ M(total)

(4)

Figure 9 shows the temperature dependence of χMT for 4, 7, and 8. These data were collected on the polycrystalline samples

12(A + 2)2 Nβ 2 ⎧ 7(3 − A)2 x ⎨ + 3kT ⎩ 5 25A ⎪

⎪

⎡ 2(11 − 2A)2 x 176(A + 2)2 ⎤ +⎢ + ⎥ 45 675A ⎦ ⎣ ⎛ −5Ax ⎞ ⎡ (A + 5)2 x 20(A + 2)2 ⎤ ⎟ + ⎢ exp⎜ − ⎥ ⎝ 2 ⎠ ⎣ 9 27A ⎦ ⎫ exp( −4Ax)⎬ ⎭

⎪

⎪

⎛ 5Ax ⎞ 7⎧ ⎟ ⎨3 + 2 exp⎜ − ⎝ 2 ⎠ 3⎩

⎫ + exp( −4Ax)⎬ ⎭ χM(Dy) =

(1)

⎛ − 225Δ ⎞ Ng 2β 2 ⎧⎡ ⎟ ⎨⎢225 exp⎜ ⎝ 4kT ⎠ 4kT ⎩⎣ ⎛ −169Δ ⎞ ⎛ −121Δ ⎞ ⎟ + 121 exp⎜ ⎟ + 169 exp⎜ ⎝ 4kT ⎠ ⎝ 4kT ⎠

Figure 9. χMT vs T plots for 4 (pentagon), 7 (circles), and 8 (triangles).

of 4, 7, and 8, respectively, under the magnetic field intensity of 1000 Oe (from 2 to 300 K). The magnetic behaviors of 4 and 7 are very similar. At room temperature, the value of 6.25 cm3 K mol−1 for 4 (the theoretical value 7.15 cm3 K mol−1 for one isolated Co (S = 3/2) and two free Nd(III) (S = 5/2 and gj = 4/5) ions) and 19.25 cm3 K mol−1 for 7 (the theoretical value of 19.63 cm3 K mol−1 for one isolated Co (S = 3/2) and two free Gd (S = 7/2 and gj = 2) ions) is slightly smaller than the theoretical value. With decreasing of the temperature, their χMT value almost remains constant. The χMT value of 8 is 29.89 cm3 K mol−1 at room temperature, which is slightly larger than the theoretical value (27.51 cm3 K mol−1 for one isolated Co (S = 3/2) and two free Tb (S = 3 and gj = 3/2) ions) at room temperature. With decreasing of the temperature, the χMT of 8 remains nearly constant until below 50 K, and then it drops to a value of 17.70 cm3 K mol−1 . The observed χM−1 data of

⎛ −89Δ ⎞ ⎛ −49Δ ⎞ ⎟ + 49 exp⎜ ⎟ + 89 exp⎜ ⎝ 4kT ⎠ ⎝ 4kT ⎠ ⎛ −25Δ ⎞ ⎛ −9Δ ⎞ ⎟ + 9 exp⎜ ⎟ + 25 exp⎜ ⎝ 4kT ⎠ ⎝ 4kT ⎠ ⎛ −169Δ ⎞ ⎛ −Δ ⎞⎤ ⎡ ⎛ −225Δ ⎞ ⎟ ⎟ ⎟ + exp⎜ exp⎜ + exp⎜ ⎝ 4kT ⎠ ⎝ 4kT ⎠⎥⎦ ⎢⎣ ⎝ 4kT ⎠ ⎛ −121Δ ⎞ ⎛ −89Δ ⎞ ⎛ −49Δ ⎞ ⎟ + exp⎜ ⎟ + exp⎜ ⎟ + exp⎜ ⎝ 4kT ⎠ ⎝ 4kT ⎠ ⎝ 4kT ⎠ ⎛ −25Δ ⎞ ⎛ −9Δ ⎞ ⎛ −Δ ⎞⎤⎫ ⎟ + exp⎜ ⎟ + exp⎜ ⎟ ⎬ + exp⎜ ⎝ 4kT ⎠ ⎝ 4kT ⎠ ⎝ 4kT ⎠⎥⎦⎭ (2)

χM(total) = χM(Co) + 2χM(Dy)

(3) 3933



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Figure 10. NIR emission spectra of complexes 3 (a) (λEx = 391 nm), 4 (b) (λEx = 355 nm), 5 (c) (λEx = 401 nm), and 9 (d) (λEx = 302 nm).

Figure 11. (a) TG curves and (b) DTA curves of complexes 3, 6, and 9.

complexes 4, 7, and 8 can be roughly fitted to the Curie−Weiss law with C = 6.31 cm3 K mol−1, θ = −9.90 K for 4, C = 19.31 cm3 K mol−1, θ = −1.15 K for 7, and C = 3.031 cm3 K mol−1, θ = −1.33 K for 8 (see Figure S2 in the Supporting Information). In addition, the zero-field alternating-current (ac) magnetic susceptibility was performed under a frequency of 10−1000 Hz. Because no out-of-phase (χM″) signals are observed in the ac magnetic susceptibility, there is no evidence of slow-relaxation for 4, 7, and 8 (see Figure S3 in the Supporting Information). Photoluminescent Properties of 2−9. Because of the excellent luminescent properties of lanthanide compounds, the solid near-infrared fluorescence of 2−9 was investigated at room temperature. In the NIR region, complexes 3, 4, 5, and 9

show characteristic emissions of Ln(III) ions (Figure 10), which are in agreement with the literature. Excited at 391 nm, complex 3 shows a broad emission band (Figure 10a). The reason for this broad emission band in the 1200−1600 nm range with a fwhm of about 250 nm is that the portion of the energy can reach the 1G4 state and then return to the 3H5 state by irradiation.18 Irritation of complex 4 at 355 nm leads to the characteristic emission bands of Nd(III) ions at 899, 1061, and 1332 nm, which correspond to the 4F3/2−4IJ (J = 9/2, 11/2, and 13/2) f−f transitions of Nd(III)19 (Figure 10b). Complex 5 exhibits the NIR luminescence of Sm(III) ion at 1399 nm, 1285 nm, 1193 nm, 1023 nm, 940 nm, and 895 nm, which correspond to 4G5/2−6Fj (j = 11/2, 9/2, 7/2, 5/2, 3/2, 1/2) (Figure 10c). 3934



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The possible reason for these emission bands is that the excited energy of the Co-tia2− moiety is first transferred to the states of (4I11/2 and 4I13/2) of the Sm(III) ion and then reaches the 4G5/2 state and then returns to the 6FJ states.20 Upon excitation of complex 9 at 370 nm, the characteristic NIR luminescence of Dy(III) ions consists of several bands at λ = 829, 999, 1149, 1305, and 1539 nm, which are attributed to the f−f transitions 4 F9/2 − 6H7/2 + 6F9/2, 6F7/2, 6F5/2, 6F11/2 + 6H9/2 − 6H15/2, and 6 F5/2 − 6H11/2, respectively21 (Figure 10d). Thermal Stability of 1−9. TGA was carried out using polycrystalline samples of complex 3, 6, and 9 in the temperature range of 20−700 °C. Figure 11 shows that all of these complexes show the same thermal behavior. They have one endothermic peak at 260 °C and one exothermic peak at 430 °C on the DTA curves, corresponding to the loss of coordination water and the removal of organic moieties, respectively. The temperatures of losing coordination water, beginning at about 240 °C, and the skeleton collapse, starting at ca. 340 °C, are higher than those of some coordination polymers reported publicly.22 Above 520 °C, there is almost no mass modification. The remnants of complexes 6 and 9 are 33.35 and 34.40%, respectively, which are close to the calculated values (6: 31.98% base on the Eu2O3 and Co2O3; 9: 33.02% base on the Dy2O3 and Co2O3). To confirm the thermal degradation remnant of complex 3, complex 3 was heated to 700 °C in an electric resistance furnace for 5 h. The weight percentage of the residue is 30.91%, which is consistent with the result of the TGA measurement, 31.30%. The result of its XRPD shows the residue is composed of two phases. One is Pr6O11, and the other is PrCoO3 (see Figure S4 in the Supporting Information). The mass ratios of these two phases are 41.2% and 58.8%, respectively. So the decomposition product of complex 3 consists of Pr6O11, Co2O3, and Pr2O3.

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CONCLUSION

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ASSOCIATED CONTENT

Article

AUTHOR INFORMATION

Corresponding Author

*Fax: +86-22-23502779. Tel: +86-22-23505020. E-mail: liuxin64@ nankai.edu.cn. Notes

The authors declare no competing financial interest.

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ACKNOWLEDGMENTS This work was supported by the National Natural Science Foundation of China (No. 21071083 and No. 20771062) and the Tianjin Natural Science Foundation (No. 08JCZDJC21100).

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REFERENCES

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Nine novel Co(II)−Ln(III) (Ln = La, Ce, Pr, Nd, Sm, Eu, Gd, Tb, Dy) coordination polymers of 1−9 have been synthesized through the hydrothermal synthetic method in combination with an ultrasonic method, and their structures have been determined by single-crystal X-ray diffraction. These nine complexes are isomorphous and display novel 3D frameworks based on the parallel arrangement Co(II) coordination chains and Ln(III) coordination layers. The study of the magnetic properties of 4, 7, 8, and 9 shows weak magnetic interaction among the paramagnetic ions. The out-of-phase ac signals observed for 9 suggest the slow-relaxation process, which is not common in 3D coordination polymers, especially in 3D heterometallic coordination polymers. The observed characteristic emission bands of compounds 3, 4, 5, and 9 in NIR regions are due to the sensitization from the ligands (directly coordinated to Ln(III) or coordinated to the d-block). So our present work will not only enrich the crystal engineering strategy but also expand the field of finding the new magnetic and luminescent materials for chemists.

S Supporting Information *

XRPD patterns, additional figures and tables, and X-ray crystallographic files in CIF format of 1−9. This material is available free of charge via the Internet at http://pubs.acs.org. 3935



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Coordination Chains and Ln(III) Coordination Layers - ACS Publications

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