All the chemicals and solvents were reagent grade and purchased from commercial sources and used without further purification. Pyridine-2,4-dicarboxylate acid and metalloligand L^Cu were synthesized according to procedures already reported outlined in the literature [21] . Element analyses for C, H and N were performed with a PerkineElmer 240C elemental analyzer. Infrared spectra were obtained from a sample powder pelletized with KBr disks on a Nicolet Nexus 470 spectrometer (Germany) over a range of 400 - 4000 cm⁻¹. Thermogravimetric analysis (TGA) measurements were carried out in the temperature range of 25˚C - 800˚C on a PerkineElmer Pyis 1 system in a nitrogenpurge with a heating rate of 10˚C/min. The temperature dependence of molar magnetic susceptibility was measured under an applied field of 1000 G in the form of χ_mT versus T in the range of 1.8 - 300 K by Quantum Design MPMS XL-5. The influence of sample holder background was subtracted by the automatic subtraction feature of the software.

The methanol solution of Sm(NO₃)₃・6H₂O (44 mg, 0.1 mmol) was slowly diffused into a dimethyl sulfoxide solution (DMSO) of L^Cu (62 mg, 0.1 mmol) through 1 mL DMSO blank solvent as the buffer solution. After several days, the obtained blue crystals were collected by filtration, washed with methanol. Yield: 50 mg, 60.6% (based on Cu). Anal. Calcd for C₆₈H₈₈Cu₃N₆O₄₂S₁₁Sm₂(2453.57): C, 33.29; H, 4.11; N, 3.41. Practical found: C, 33.32; H, 4.12; N, 3.40. IR (KBr, cm⁻¹): 3419(s), 2980(m), 2924(m), 2354(m), 1660(s), 1617(s), 1555(s), 1476(m), 1390(s), 1341(s), 1261(m), 1181(w), 1083(w), 1009(s), 942(m), 899(w), 825(w), 783(m), 739(m), 684(s), 530(w), 463(w).

CP-2 was obtained as light blue block crystals with the same synthetic method as that of 1 except that Sm(NO₃)₃・6H₂O was replaced by Dy(NO₃)₃・6H₂O (46 mg, 0.1 mmol). Yield: 6 mg, 18% (base on Cu). Anal. Calcd for C₆₀H₆₀Cu₃N₆O₃₆S₈Dy₂(2195.38): C, 32.83; H, 3.37; N, 3.83. Found: C, 32.56; H, 3.36; N, 3.88. IR (KBr, cm⁻¹): 3434(s), 2992(w), 2912(w), 2372(s), 1654(s), 1611(s), 1537(m), 1476(w), 1402(s), 1329(s), 1248(w), 1089(w), 1022(m), 954(w), 832(w), 783(w), 733(m), 684(m), 524(w).

Sizeable and high-quality single crystals of two compounds were selected carefully from little glass tubes, and mounted on a glass fiber with epoxy resin covered. All measurements were obtained by a Rigaku Saturn 724⁺ CCD imaging plate diffractometer with graphite-monochromated Mo-Ka radiation (λ = 0.71073 Å) at room temperature. The two crystals structures were solved by direct methods, while the non-hydrogen atoms were subjected to anisotropic refinement on F² through full-matrix least-squares with SHELX-97 package [40] [41] [42] . All the non-hydrogen atoms were determined with anisotropic thermal displacement coefficients. Hydrogen atoms were treated isotropically according to a riding model, beyond that the hydrogen atoms were located in idealized positions. The contribution of missing solvent molecules (DMSO, CH₃OH) to the diffraction pattern was subtracted from the reflection data by the “SQUEEZE” method as implemented in PLATON [43] . Details of the crystal parameters, data collection and refinement of CPs 1 and 2 are listed in Table 1, while the selected bond lengths are listed in Table 2.

CPs 1 and 2 were crystallized from the reactions between metalloligand [Cu(2,4-pydca)₂] and Sm(NO₃)₃・6H₂O/Dy(NO₃)₃・6H₂O, respectively. According to the literature, the reported pydca-based 3d-4f structures were obtained from rare earth hydrates, copper oxide/copper acetate hydrate and pyridine-2,4-dicarboxylic acid through the hydro-thermal synthetic approach [28] - [33] . Compared to the hydro-thermal syntheses of above pydca-based 3d-4f structures, the inter-diffusion method was applied as a mild way for the crystallization of 1 and 2. In this work, our synthetic strategy uses DMSO as the buffer solution, which can slow the interactions between L^Cu and lanthanide ions. As a result, well shaped crystals of 1 and 2 can be obtained from the cushion breaker. It is obviously that the use of blank solvent as buffer solution provides a stable condition for the reaction between two different reactive components [21] . Compared with the conventional hydro-thermal/solvent-thermal synthetic

approach, the inter-diffusion method here plays an important role in the crystallization process of CPs 1 and 2.

The result of single crystal X-ray structural analysis reveals that CP-1 crystallizes in the triclinic crystal system with P-1 space group and exhibits a 3D framework structure. The asymmetric unit consists of one [Sm(DMSO)₂(CH₃OH)]³⁺ cation, one and half [L^Cu]²⁻ ions.

The coordination mode of Sm atom and the connecting modes of L^Cu metalloligands in CP-1 are shown in Figure 1. As in Figure 1(a), each Sm atom is coordinated by eight O atoms from five L^Cu metalloligands, two DMSO molecules and one CH₃OH molecule forming a square antiprism spatial configuration and exhibiting D_4d symmetry. In accordance with Figures 1(b)-(d), CP-1 have three different L^Cu metalloligands: both L^Cu1 and L^Cu5 units connect with four Sm atoms through the carboxylic oxygen atoms showing a four-connecting mode, while the L^Cu4 unit connect with two Sm atoms exhibiting a single-bridged mode. Attributable to the bidentate coordination mode of carboxylic acid in L^Cu1 and

Symmetry transformations used to generate equivalent atoms for 1: #1 −x, −y, −z − 1; #2 −x + 2, −y + 1, −z + 1; #3 −x + 2, −y + 1, −z; #4 −x + 1, −y, −z; for 2: #1 x − 1, y, z; #2 x, y − 1,z; #3 x, y, z − 1; #4 x, y, z + 1; #5 x, y + 1, z; #6 x + 1, y, z.

L^Cu5 units, a {Sm₂} cluster is constituted by four μ₂-bridged carboxyl groups (Figure 2(a)). These {Sm₂} clusters can be linked by four L^Cu metalloligands to build a quadrangular ring (Figure 2(b)). Extension of such rings through six-connected {Sm₂} clusters leads to the whole 2D layer structure (Figure 2(c)) showing a classic sql network (Figure 2(d)). These 2D layers are further extended to the 3D framework (Figure 2(e)) via the L^Cu4 metalloligands (Figure 2(f)), which can be regarded as the pillars of the 3D structure. The packing diagram showing the 3D extending structure of CP-1 from a axis is displayed in Figure 3. As in Figure 3, CP-1 exhibits a porous structure with various channels traversing the framework. Due to the small steric hindrance of DMSO molecules and long lengths of L^Cu units, 3D framework of 1 possesses big cavities in these channels. The solvent accessible volume of CP-1 calculated by PLATON is 855.1 ų (38.3%), which is large enough for hosting the solvent molecules (seven DMSO and two CH₃OH). The network analysis based on TOPOS program reveals that CP-1 can be simplified to a (6,6)-connected network with {4⁹ × 6⁶} topology, which is depicted in Figure 4. As in Figure 4, the {Sm₂} clusters act as

the vertexes of the geometry, while the sides are formed by L^Cu metalloligands.

The selected bond lengths of CPs 1 and 2 are listed in Table 2. As shown in Table 2, the lengths of Cu-N bond range from 1.981(3) to 1.984(3) Å, while the value of Cu-O fall into the range of 1.971(3)-2.238(4) Å. Among the Cu-O bond, the lengths between Cu atoms and O atoms from water molecules are larger than the distances between Cu atoms and O atoms from carboxylates. Bond lengths of Sm-O vary from 2.316(4) to 2.531(8) Å. In the {Sm₂} cluster, the shortest distance between two Sm atoms is 4.491(1) Å.

The X-ray crystallography study identifies that CP-2 also crystallizes in the triclinic crystal system with P-1 space group and consists of the porous 3D framework structure. The asymmetric unit of CP-2 contains one [Dy(DMSO)₂]³⁺ cation, one [Dy(DMSO)(CH₃OH)]³⁺ cation, two [L^Cu]²⁻ ions and one [L^Cu(DMSO)]²⁻ ion. Interestingly, one of the terminal coordinated O atom from L^Cu has been replaced by a DMSO molecule during the synthetic process of CP-2.

In accordance with Figure 5(a), Dy atoms in CP-2 have two different coordination environments: Dy1 is coordinated by eight O atoms from four L^Cu metalloligands, one L^Cu (DMSO) metalloligand and two DMSO molecules, while Dy2 is coordinated by eight O atoms from four L^Cu metalloligands, one L^Cu (DMSO) metalloligand, one DMSO molecule and one CH₃OH molecule. According to the concrete crystal structure, there are three kinds of L^Cu metalloligands in CP-2. As shown in Figure 5(b) and Figure 5(c), both L^Cu1 (DMSO) and L^Cu2 units in a four-connected mode are linked with two Dy1 and two Dy2 atoms through the carboxylic oxygen atoms. The L^Cu3 unit in CP-2 connects with one Dy1 and one

Dy2 atom via four carboxylic oxygen atoms with the chelate mode (Figure 5(d)). Similarly to CP-1, Dy1 and Dy2 atom in CP-2 can be built to a {Dy₂} cluster with the help of L^Cu1 (DMSO) and L^Cu2 units (Figure 6(a)). The connection of such {Dy₂} clusters and L^Cu metalloligands (Cu2 and Cu3) through the carboxyl groups also forms a quadrangular configuration (Figure 6(b)). As depicted in Figure 6(c), these quadrangular configurations link with each other to construct the 2D network structure with (4,4) topology. With the assist of L^Cu1 (DMSO) (Figure 6(d)), these 2D networks can also be extended to a 3D framework structure (Figure 6(e)). The overall structure of CP-2 can be viewed as a grid-like frame with square channels traversing the framework (Figure 7). The solvent accessible volume of CP-2 is 2945.2 ų (49.6%), which is large enough for hosting the solvent molecules (four DMSO and one CH₃OH). The regular 6-connected mode of {Dy₂} cluster lead to a {4¹² × 6³} topological network (Figure 8). The topology structural difference between CP-1 and CP-2 is mainly due to the distinct connection modes of L^Cu metalloligands in CPs 1 and 2.

The averagelength (1.971(4) Å) of Cu−N bond in CP-2 is little larger than the value that in CP-1 (1.952(5) Å). As for the Cu-O bond in CP-2, the bond lengths range from 1.933(4) Å to 2.388(5) Å. The distance (2.388(5) Å) between Cu

atom and O atom from DMSO molecule is little larger than the value between Cu atoms and O atoms from water molecules (2.238(9) Å for Cu2, 2.306(8) Å for Cu3). Bond lengths of Dy-O range from 2.260(3) Å to 2.808(5) Å. The shortest distance of Dy・・・Dy in {Dy₂} cluster is 5.020(1) Å in the CP-2.

Thermal properties of CPs 1 and 2 were examined by thermogravimetric analysis (TGA) from 25˚C to 800˚C in a nitrogen atmosphere with a heating rate of 10˚C/min. Thethermogravimetric curve of CPs 1 and 2 are shown in Figure 9. As shown in the Figure 9, the first weight loss of CP 1 (5.21%) occurs from 50˚C to 118˚C, corresponding to the loss of four methanol molecules (calcd: 5.22%). Further weight loss (19.05%) appears from 142˚C to 236˚C, corresponding to the loss of six free DMSO molecules (calcd: 19.10%). In the temperature range of 273˚C - 341˚C, four coordinated and one free DMSO molecules (15.84%) lose with the rise of temperature (calcd: 15.92%). After 350˚C, the organic groups of CP-1 start to lose and the skeleton structure starts to crumble. As for CP-2, the first weight loss of 2.86% (calcd: 2.92%) is observed from 50˚C to 110˚C for two MeOH molecules, which is similar to that of CP-1. The following weight loss (14.07%) occurs from 158˚C to 229˚C, which is corresponding to four solvent DMSO molecules (calcd: 14.23%). The third stage of weight loss (14.96%) starts at 280˚C, after that, four coordinated DMSO molecules escape until 342˚C (calcd: 14.23%). With the increase in temperature, the 3D framework of CP-2 begins to collapse.

The temperature dependence of magnetic susceptibility is recorded for crystalline samples of CPs 1 and 2 at an applied magnetic field of 1000 Oe in the temperature range of 1.8 - 300 K. The measurement results are shown in Figure 10 and Figure 11, respectively, in which χ_m is the molar magnetic susceptibility. As in Figure 10, The χ_mT values of CP-1 at room temperature is 1.62 cm³ K mol⁻¹, which is a little smaller than the theoretical value (1.69 cm³ K mol⁻¹) for a two isolated Sm³⁺ ions (S = 5/2, g = 2/7) and three Cu²⁺ ions (S = 1/2, g = 2) without magnetic interaction. Upon decreasing the temperature, the χ_mT product drops slowly to a minimum of 0.47 cm³ K mol⁻¹ at 1.8 K. This decrease in χ_mT may originate in the antiferromagnetic interaction between metal centers. The magnetic data in the range of 50 - 300 K followed the Curiee-Weiss fitting with a Curie constant of C = 1.8 cm³ K mol⁻¹ and negative Weiss constant of θ = −57.7 K.

As shown in Figure 11, the room temperature χ_mT value of CP-2 is 29.36 cm³ K mol⁻¹, which is a little smaller than the theoretical value of 29.48 cm³ K mol⁻¹ for three Cu²⁺ ion (S = 1/2, g = 2) and two Dy³⁺ ions (S = 5/2, g = 4/3) due to the thermally populated excited states of Dy³⁺ [44] . Upon sample cooling, the χ_mT

value decreases continuously to a minimum value of 17.55 cm³ K mol⁻¹ at 7 K. After that, the χ_mT value increases sharply to18.49 cm³ K mol⁻¹at 1.8 K. The transformation trend of χ_mT curve below 7 K suggests the presence of weak intramolecular ferromagnetic correlation. And this magnetic difference is due to the different electron spin of the two center metals. The data in the range 100 - 300 K were fitted to the Curie-Weiss law, yielding C = 29.50 cm³ K mol⁻¹ and θ = −16.59 K, which indicates the weak ferromagnetic interactions between the spincenters at 100 - 300 K.