Synthesis and Characterization of a Heterometallic Extended Architecture Based on a Manganese(II)-Substituted Sandwich-Type Polyoxotungstate

The reaction of [α-P2W15O56]12− with MnII and DyIII in an aqueous basic solution led to the isolation of an all inorganic heterometallic aggregate Na10(OH2)42[{Dy(H2O)6}2Mn4P4W30O112(H2O)2]·17H2O (Dy2Mn4-P2W15). Single-crystal X-ray diffraction revealed that Dy2Mn4-P2W15 crystallizes in the triclinic system with space group P1¯, and consists of a tetranuclear manganese(II)-substituted sandwich-type phosphotungstate [Mn4(H2O)2(P2W15O56)2]16− (Mn4-P2W15), Na, and DyIII cations. Compound Dy2Mn4-P2W15 exhibits a 1D ladder-like chain structure based on sandwich-type segments and dysprosium cations as linkers, which are further connected into a three-dimensional open framework by sodium cations. The title compound was structurally and compositionally characterized in solid state by single-crystal XRD, powder X-ray diffraction (PXRD), Fourier-transform infrared spectroscopy (FTIR), thermogravimetric (TGA), and elemental analyses. Further, the absorption and emission electronic spectra in aqueous solutions of Dy2Mn4-P2W15 and Mn4-P2W15 were studied. Also, magnetic properties were studied and compared with the magnetic behavior of [Mn4(H2O)2(P2W15O56)2]16−.


Introduction
Polyoxometalates (POMs) are discrete early transition metal-oxide cluster anions whose physicochemical properties can be tuned by the incorporation of additional transition metal centers [1,2]. A large number of transition metal containing POMs have been synthesized and characterized with enhanced properties, for instance, robustness and stability emerging from the POM moiety and the predictable functional properties, depending on their electronic nature, originating from the redox metal centers. To date, transition metal (3d), lanthanide (4f), and mixed 3d-4f containing POM hybrids have been studied, which can be broadly classified as follows [3][4][5][6][7][8][9].
(a) Three-dimensional (3d)-POMs [10][11][12][13][14] (b) 4f-POMs [4,15] chemical stability of the MOFs depend on the nature of the organic constituents/linkers, which might be destroyed during the activation of the porous material through elimination of solvent molecules in frameworks [33]. These difficulties could be overcome by the introduction of rigid metal clusters anions, such as POMs and lanthanide cations to the system. Moreover extensive-and additive properties of such materials can be finely tuned through variation of POM precursors and transition metal centers, respectively.
Following this idea, we selected the trilacunary Wells-Dawson type POM ligand, Na 12 [α-P 2 W 15 O 56 ]·24H 2 O (P 2 W 15 ) [34], as a building block unit and introduced Dy III ions and Mn II ions cations to build up POM-based heterometallic extended frameworks.
Herein, we report a facile and convenient "one-pot" procedure for the synthesis of a heterometallic all inorganic system Na 10 (OH 2 ) 42 15 ), which forms a framework structure, and so we designate as a Polyoxometalate Inorganic Framework, or POMIF. The title compound was structurally and compositionally characterized in solid state by single-crystal XRD, powder X-ray diffraction, Fourier-transform infrared spectroscopy, and thermal and elemental analyses. In solution state, UV-vis absorption spectroscopy and luminescence spectroscopy were performed. Furthermore, in order to check the bulk purity and to probe the solution state stability of the Dy 2 Mn 4 -P 2 W 15

Experimental
The POM ligand, Na 12 [35], were synthesized according to the literature methods, and were characterized by IR spectroscopy. All reactions were carried out under aerobic conditions. All of the other reagents were purchased commercially and were used without further purification.

Synthesis
Synthesis procedure for Dy 2 Mn 4 -P 2 W 15 : MnCl 2 ·4H 2 O (0.12 g, 0.6 mmol) was dissolved in 20 mL of water. Then Na 12 [α-P 2 W 15 O 56 ]·24H 2 O (0.88 g, 0.1 mmol) was added to the above solution. Then, 0.30 mL of 1 M Dy(NO 3 ) 3 ·5H 2 O (0.13 g, 0.3 mmol) was added to this solution in small portions. The pH value of the mixture was adjusted to 7.6 by adding CH 3 COONa (0.50 g, 6 mmol) in small portions under stirring. The resultant turbid orange solution was stirred at room temperature for 10 min, and then heated for 1 h at 80 • C. The resulting solution was filtered and left to slowly evaporate at room temperature, and orange crystals were obtained after approximately three weeks. Yield 229. 8

Methods
Elemental analyses were performed at the Institute for Applied Materials, Karlsruhe Institute of Technology. Fourier transform IR spectra were measured on a Perkin-Elmer Spectrum One Spectrometer with samples prepared as KBr discs at the Institute of Nanotechnology, Karlsruhe Institute of Technology. X-ray powder diffraction patterns were measured at room temperature using a Stoe STADI-P diffractometer with a Cu-Kα radiation at the Institute of Nanotechnology, Karlsruhe Institute of Technology. UV-vis spectra and fluorescent spectra were recorded on Cary 500 UV-vis-NIR spectrophotometer and Cary Eclipse fluorescence spectrophotometer, respectively, at the Institute of Nanotechnology, Karlsruhe Institute of Technology.

Crystallography
Data were measured at 180(2) K on a Rigaku Oxford Diffraction SuperNova E diffractometer (Rigaku Europe, Kemsing, UK) with Mo-Kα radiation from a microfocus source, and corrected semi-empirically for absorption. Structure solution was by dual-space direct-methods (SHELXT) [36], followed by full-matrix least-squares refinement (SHELX-2016) [37], with anisotropic thermal parameters for all the ordered non-H atoms. In a few cases, rigid-bond restraints (RIGU) were applied to the thermal parameters of mutually-bonded sodium cations and aquo oxygen atoms. Some of the lattice waters and aquo ligands coordinated to sodium cations were disordered; these were was modelled using pairs of isotropic partial-occupancy (0.60 and 0.40) oxygen atoms, with similarity restraints (SADI) applied to Na-O bond lengths where necessary. No attempt was made to locate any water H-atoms. Further details of the X-ray structural analysis are given in Table 1. Further details of the crystal structure investigation may be obtained from FIZ Karlsruhe, 76344 Eggenstein-Leopoldshafen, Germany (Fax: (+49)7247-808-666; e-mail: crysdata@fiz-karlsruhe.de, on quoting the deposition number CSD-433863).

Magnetic Measurements
Magnetic susceptibility measurements were collected using a Quantum Design MPMS3 and MPMS-XL SQUID magnetometer (Quantum Design, San Diego, CA, USA). DC susceptibility measurements for all of the compounds were performed at temperatures ranging from 2 to 300 K, using an applied field of 1 kOe. Magnetization versus field data was collected between 2 and 5 K with applied field between 0 and 7 T. The AC data were collected using an oscillating magnetic field of 3.5 Oe. All data were corrected for diamagnetic contributions from the eicosane and core diamagnetism, estimated using Pascal's constants [38].

Synthesis
The heterometallic compound Na 10 (OH 2 ) 42 [35]. In order to avoid one of the major difficulties, which is the formation of precipitate, due to the reaction of highly oxophilic lanthanides ions with highly negative and oxygen rich system like POMs, sodium acetate, and Dy III ions were added slowly in portions. This illustrates the challenges of rationalizing the mechanistic pathways of heterometallic POM isolation in the form of crystals. To the best of our knowledge, Dy 2 Mn 4 -P 2 W 15 not only represents the first all inorganic heterometallic 3D POMIF compound based on Wells-Dawson type [α-P 2 W 15 O 56 ] 12− , but also provides a feasible route to the formation of highly robust multifunctional extended structures base on POMs.

Structure
Single-crystal X-ray diffraction revealed that Dy 2 Mn 4 -P 2 W 15 crystallizes in the triclinic system with space group P1, and consists of tetranuclear manganese-substituted sandwich-type [Mn 4 (H 2 O) 2 (α-P 2 W 15 O 56 ) 2 ] 16− (Mn 4 -P 2 W 15 ), Na and Dy III cations ( Figure 1). The crystal structure can be viewed as a one-dimensional (1D) ladder-like chain, built up of the sandwich anions Mn 4 -P 2 W 15 and the Dy III ions ( Figure 2). Each Dy III center connects two Mn 4 -P 2 W 15 subunits via two W=O···Dy bonds and the bond lengths are in the range 2.31-2.42 Å. The Dy III ions are octacoordinate and possess square antiprism geometry ( Figure 1). The coordination environment is completed by six terminal water molecules and two bridged oxygen atoms from two sandwich-type polyoxoanion. Furthermore, the Dy III ions can be viewed as µ 2 -bridges which link two Mn 4 -P 2 W 15 into a 1D network structure which are further extended into a three-dimensional open framework by the sodium cations (Na 1 , Na 4 , and Na 5 ), while Na 2 and Na 3 are just charge-balancing segments on the surface of the POM. The adjacent ladder-like chains are connected by the sodium cations to form a two-dimensional framework ( Figure 3

Characterizations
Infrared is spectroscopy is one of the most frequently employed techniques for the characterization of polyoxometalates, due to its characteristic peaks in the in the region (1200-450 cm −1 ), which is called the fingerprint region for the POM backbone [39]. The similarity in the IR spectra of Na 10 (OH 2 ) 42 (Figure 4) suggests that the attachment of the Dy III cations on the Mn 4 -P 2 W 15 surface has not changed the vibration modes in Dy 2 Mn 4 -P 2 W 15 , except for some minor shifts that are observed due to the influence of the dysprosium linkers ( Figure 4).

Characterizations
Infrared is spectroscopy is one of the most frequently employed techniques for the characterization of polyoxometalates, due to its characteristic peaks in the in the region (1200-450 cm −1 ), which is called the fingerprint region for the POM backbone [39]. The similarity in the IR spectra of and Na16[Mn4(H2O)2(α-P2W15O56)2]·53H2O ( Figure 4) suggests that the attachment of the Dy III cations on the Mn4-P2W15 surface has not changed the vibration modes in Dy2Mn4-P2W15, except for some minor shifts that are observed due to the influence of the dysprosium linkers ( Figure 4). Since the FTIR studies were not a helpful tool to check the bulk purity of the product in this case, we decided to carry out the powder X-ray diffraction (PXRD) analysis for the compounds Dy2Mn4-P2W15, Mn4-P2W15 and P2W15, in order to examine the bulk purity of the title product ( Figure 5). The experimental PXRD pattern of Dy2Mn4-P2W15 corresponds well to the simulated PXRD pattern, indicating that the bulk phase materials are isomorphous. The very minor differences in peak intensity and 2 theta values are likely due to the loss of some lattice water molecules, bearing in mind that the simulated patterns are generated from the single crystal X-ray diffraction data set, which was collected at 100 K.  Since the FTIR studies were not a helpful tool to check the bulk purity of the product in this case, we decided to carry out the powder X-ray diffraction (PXRD) analysis for the compounds Dy 2 Mn 4 -P 2 W 15 , Mn 4 -P 2 W 15 and P 2 W 15 , in order to examine the bulk purity of the title product ( Figure 5). The experimental PXRD pattern of Dy 2 Mn 4 -P 2 W 15 corresponds well to the simulated PXRD pattern, indicating that the bulk phase materials are isomorphous. The very minor differences in peak intensity and 2 theta values are likely due to the loss of some lattice water molecules, bearing in mind that the simulated patterns are generated from the single crystal X-ray diffraction data set, which was collected at 100 K.

Characterizations
Infrared is spectroscopy is one of the most frequently employed techniques for the characterization of polyoxometalates, due to its characteristic peaks in the in the region (1200-450 cm −1 ), which is called the fingerprint region for the POM backbone [39]. The similarity in the IR spectra of Na10(OH2) 42 Figure 4) suggests that the attachment of the Dy III cations on the Mn4-P2W15 surface has not changed the vibration modes in Dy2Mn4-P2W15, except for some minor shifts that are observed due to the influence of the dysprosium linkers ( Figure 4). Since the FTIR studies were not a helpful tool to check the bulk purity of the product in this case, we decided to carry out the powder X-ray diffraction (PXRD) analysis for the compounds Dy2Mn4-P2W15, Mn4-P2W15 and P2W15, in order to examine the bulk purity of the title product ( Figure 5). The experimental PXRD pattern of Dy2Mn4-P2W15 corresponds well to the simulated PXRD pattern, indicating that the bulk phase materials are isomorphous. The very minor differences in peak intensity and 2 theta values are likely due to the loss of some lattice water molecules, bearing in mind that the simulated patterns are generated from the single crystal X-ray diffraction data set, which was collected at 100 K.  Thermogravimetric analysis of Dy2Mn4-P2W15 was performed between 20 and 900 °C under a nitrogen atmosphere to determine the number of crystal waters ( Figure 6). The continuous weight loss of about 10% between 25 and 330 °C can be attributed to the loss of all lattice and coordinated water molecules present in Dy2Mn4-P2W15.   Elemental analysis on Mn, Dy, O, W, P, and Na was also carried out by means of inductively coupled plasma optical emission spectrometry, and the results are presented in Section 2.1.
Solution state UV−vis measurements were performed on Mn 4 -P 2 W 15 , Dy 2 Mn 4 -P 2 W 15 and P 2 W 15 in order to investigate the incorporation of metal centers in the polytungstate framework and to check the structural integrity in solution. The UV-Vis absorption spectra show that the Dy 2 Mn 4 -P 2 W 15 is like that of Mn 4 -P 2 W 15 in solution, which is one of the most stable POMs in solution. However the absorption spectra of Dy 2 Mn 4 -P 2 W 15 and Mn 4 -P 2 W 15 are significantly different from that of the P 2 W 15 precursor, which gives a clear indication that the incorporation of metal centers in the polytungstate framework has an extensive effect on the physicochemical properties of the resulting clusters. However, information about the possibility that there are coordinated Dy III cations on the POM surface in solution phase cannot be achieved from these studies. The UV-Vis spectra (Figure 7) show absorbance bands between 200 and 400 nm, which can be associated with the characteristic charge-transfer bands of terminal oxygen and bridging oxygen atoms to tungsten centers, respectively (oxygen-to-metal charge transfer (O → M LMCT). Thermogravimetric analysis of Dy2Mn4-P2W15 was performed between 20 and 900 °C under a nitrogen atmosphere to determine the number of crystal waters ( Figure 6). The continuous weight loss of about 10% between 25 and 330 °C can be attributed to the loss of all lattice and coordinated water molecules present in Dy2Mn4-P2W15.   When compared to absorption studies, emission spectroscopy is an advantageous tool, particularly in any heterometallic system, to investigate the origin of the emission bands, since in comparison with the non-Ln containing materials, the Ln-containing systems often have higher luminescence efficiency, better photochemical stability, and prolonged fluorescence life times. The lanthanide's emission is substantially induced by the photoexcitation of the oxygen-to-metal charge transfer (O → M LMCT) bands of 4f-POM systems [31,40]. Consequently, in order to gain insight on the solution behavior of the title compound, the luminescent properties of Dy 2 Mn 4 -P 2 W 15 and Mn 4 -P 2 W 15 were measured at room temperature under the same excitation of 275 nm. As shown in Figure 8, Dy 2 Mn 4 -P 2 W 15 displays an intense characteristic photoluminescence emission band (450-650 nm wide) centered at 545 nm, which can be assigned to the 4 F 9/2 → 6 H 13/2 and 4 F 9/2 → 6 H 11/2 transitions in Dy III ions, while the weak emission of Dy III ions at 379 can be attributed to the 4 F 9/2 → 6 H 15/2 transition [41]. It should also be noted that the Dy III emission bands (450-650 nm) overlap with the characteristic broad Mn II emission band (Figure 9) (ca. 500-600 nm) [42], and therefore are not distinguishable. The presence of the emission band of Dy III ions at 379 nm (only observed in the photoluminescence spectrum of Dy 2 Mn 4 -P 2 W 15 ) (Figure 8), indicating the existence of [{Dy(OH 2 ) 6 } 2 Mn 4 P 4 W 30 O 112 (H 2 O) 2 ] 10− in solution. However, whether the extended framework is preserve in solution cannot be determined from these data. Further, it can also be observed that the emission profile slightly changes and emission intensity increases drastically in the case of Dy 2 Mn 4 -P 2 W 15 . Although the solutions were only weakly luminescent, distinct differences could be observed not only in the emission intensity, but also in the number of emissions bands. When compared to absorption studies, emission spectroscopy is an advantageous tool, particularly in any heterometallic system, to investigate the origin of the emission bands, since in comparison with the non-Ln containing materials, the Ln-containing systems often have higher luminescence efficiency, better photochemical stability, and prolonged fluorescence life times. The lanthanide's emission is substantially induced by the photoexcitation of the oxygen-to-metal charge transfer (O → M LMCT) bands of 4f-POM systems [31,40]. Consequently, in order to gain insight on the solution behavior of the title compound, the luminescent properties of Dy2Mn4-P2W15 and Mn4-P2W15 were measured at room temperature under the same excitation of 275 nm. As shown in Figure 8, Dy2Mn4-P2W15 displays an intense characteristic photoluminescence emission band (450-650 nm wide) centered at 545 nm, which can be assigned to the 4 F9/2 → 6 H13/2 and 4 F9/2 → 6 H11/2 transitions in Dy III ions, while the weak emission of Dy III ions at 379 can be attributed to the 4 F9/2 → 6 H15/2 transition [41]. It should also be noted that the Dy III emission bands (450-650 nm) overlap with the characteristic broad Mn II emission band (Figure 9) (ca. 500-600 nm) [42], and therefore are not distinguishable. The presence of the emission band of Dy III ions at 379 nm (only observed in the photoluminescence spectrum of Dy2Mn4-P2W15) (Figure 8), indicating the existence of [{Dy(OH2)6}2Mn4P4W30O112(H2O)2] 10− in solution. However, whether the extended framework is preserve in solution cannot be determined from these data. Further, it can also be observed that the emission profile slightly changes and emission intensity increases drastically in the case of Dy2Mn4-P2W15. Although the solutions were only weakly luminescent, distinct differences could be observed not only in the emission intensity, but also in the number of emissions bands.   When compared to absorption studies, emission spectroscopy is an advantageous tool, particularly in any heterometallic system, to investigate the origin of the emission bands, since in comparison with the non-Ln containing materials, the Ln-containing systems often have higher luminescence efficiency, better photochemical stability, and prolonged fluorescence life times. The lanthanide's emission is substantially induced by the photoexcitation of the oxygen-to-metal charge transfer (O → M LMCT) bands of 4f-POM systems [31,40]. Consequently, in order to gain insight on the solution behavior of the title compound, the luminescent properties of Dy2Mn4-P2W15 and Mn4-P2W15 were measured at room temperature under the same excitation of 275 nm. As shown in Figure 8, Dy2Mn4-P2W15 displays an intense characteristic photoluminescence emission band (450-650 nm wide) centered at 545 nm, which can be assigned to the 4 F9/2 → 6 H13/2 and 4 F9/2 → 6 H11/2 transitions in Dy III ions, while the weak emission of Dy III ions at 379 can be attributed to the 4 F9/2 → 6 H15/2 transition [41]. It should also be noted that the Dy III emission bands (450-650 nm) overlap with the characteristic broad Mn II emission band (Figure 9) (ca. 500-600 nm) [42], and therefore are not distinguishable. The presence of the emission band of Dy III ions at 379 nm (only observed in the photoluminescence spectrum of Dy2Mn4-P2W15) (Figure 8), indicating the existence of [{Dy(OH2)6}2Mn4P4W30O112(H2O)2] 10− in solution. However, whether the extended framework is preserve in solution cannot be determined from these data. Further, it can also be observed that the emission profile slightly changes and emission intensity increases drastically in the case of Dy2Mn4-P2W15. Although the solutions were only weakly luminescent, distinct differences could be observed not only in the emission intensity, but also in the number of emissions bands.

Magnetic Properties
To further characterize the physical properties of both POM complexes, SQUID measurements were conducted on polycrystalline materials. Firstly, we studied the static magnetic behavior of the building block POM unit using neat polycrystalline powders under an applied dc field of 1 kOe in the temperature range 2 to 300 K (Figure 10a). The room temperature χ M T product (where χ M is molar magnetic susceptibility) for the building block is close to the expected value for four isolated Mn II ions for Mn 4 -P 2 W 15 , i.e., 16.8 cm 3 K mol −1 (cf. 17.5 cm 3 K mol −1 for four Mn II , s = 5/2, g = 2.00). Upon cooling, the χ M T product stays constant down to ca. 50 K, after which it smoothly decreases reaching 3.2 cm 3 K mol −1 at 1.8 K, indicating that antiferromagnetic interactions are be operative within the cluster. Furthermore, we studied the molar magnetization (M β ) as function of applied magnetic field at 2 and 5 K in the field range 0-7 T. The M β versus applied field, H, for the compound Mn 4 -P 2 W 15 , indicates a strong antiferromagnetic interaction, as observed in the almost linear behavior of the magnetization curves. The M β (H) data at the maximum field (7 T) and the lowest temperature (2 K) yield a value of 14.8 µ β (Figure 10b). The isotropic nature of the compound Mn 4 -P 2 W 15 allows for us to simultaneously fit the χ M T(T) and M β (H) using the simple Heisenberg Hamiltonian, taking into account two exchange interactions, i.e., .025 for all Mn II ions and two small interactions of similar magnitude reproduce the small down turn in χ M T(T) and M β (H) (solid lines in Figure 10), i.e., J 1 = −0.463(1) cm −1 between nearest Mn II ions, while J 2 = −0.342(1) cm −1 for the Mn II at longer distances. These values are in line with those found in previous work [35].

Magnetic Properties
To further characterize the physical properties of both POM complexes, SQUID measurements were conducted on polycrystalline materials. Firstly, we studied the static magnetic behavior of the building block POM unit using neat polycrystalline powders under an applied dc field of 1 kOe in the temperature range 2 to 300 K (Figure 10a). The room temperature χMT product (where χM is molar magnetic susceptibility) for the building block is close to the expected value for four isolated Mn II ions for Mn4-P2W15, i.e., 16.8 cm 3 K mol −1 (cf. 17.5 cm 3 K mol −1 for four Mn II , s = 5/2, g = 2.00). Upon cooling, the χMT product stays constant down to ca. 50 K, after which it smoothly decreases reaching 3.2 cm 3 K mol −1 at 1.8 K, indicating that antiferromagnetic interactions are be operative within the cluster. Furthermore, we studied the molar magnetization (Mβ) as function of applied magnetic field at 2 and 5 K in the field range 0-7 T. The Mβ versus applied field, H, for the compound Mn4-P2W15, indicates a strong antiferromagnetic interaction, as observed in the almost linear behavior of the magnetization curves. The Mβ(H) data at the maximum field (7 T) and the lowest temperature (2 K) yield a value of 14.8 μβ (Figure 10b). The isotropic nature of the compound Mn4-P2W15 allows for us to simultaneously fit the χMT(T) and Mβ(H) using the simple Heisenberg Hamiltonian, taking into account two exchange interactions, i.e.,  After magnetically characterizing the building block POM, we proceed with the study of the magnetic properties of the POMIF, i.e., Dy2Mn4-P2W15. As can be observed in Figure 10a, the χMT(T) shows a room temperature χMT value of 45.3 cm 3 K mol −1 close to the value that is expected for the building block and two non-interacting dysprosium ions, i.e., 45.8 cm 3 K mol −1 for four Mn(II), s = 5/2, g = 2.00 and two Dy III , J = 15/2; gJ = 4/3). Likewise, the χMT product starts decreasing below 100 K, reaching a minimum value of 24.5 cm 3 K mol −1 . In this case, the drop observed in the χMT product could arise from a combined effect of the antiferromagnetic exchange operating in the Dy2Mn4-P2W15 unit along with the anisotropic magnetic properties of Dy III ions, that is, depopulation of the ligand field levels. The Mβ(H) for compound Dy2Mn4-P2W15 similarly shows very anisotropic behavior and no saturation of the Mβ(H) (see Figure 11), with a Mβ value of 25.3 μβ at the maximum field (7 T) and the lowest temperature (2 K). Additionally, we have tested the dynamic behavior of this complex at 2 K in the frequency range 1-1500 Hz without and with applied dc fields (ranging from 0 to 5 kOe), and an oscillating magnetic field of 3.5 Oe. No out of phase component in could be observed within the measurement parameters of our equipment and there is SMM behavior under these conditions. After magnetically characterizing the building block POM, we proceed with the study of the magnetic properties of the POMIF, i.e., Dy 2 Mn 4 -P 2 W 15 . As can be observed in Figure 10a, the χ M T(T) shows a room temperature χ M T value of 45.3 cm 3 K mol −1 close to the value that is expected for the building block and two non-interacting dysprosium ions, i.e., 45.8 cm 3 K mol −1 for four Mn(II), s = 5/2, g = 2.00 and two Dy III , J = 15/2; g J = 4/3). Likewise, the χ M T product starts decreasing below 100 K, reaching a minimum value of 24.5 cm 3 K mol −1 . In this case, the drop observed in the χ M T product could arise from a combined effect of the antiferromagnetic exchange operating in the Dy 2 Mn 4 -P 2 W 15 unit along with the anisotropic magnetic properties of Dy III ions, that is, depopulation of the ligand field levels. The M β (H) for compound Dy 2 Mn 4 -P 2 W 15 similarly shows very anisotropic behavior and no saturation of the M β (H) (see Figure 11), with a M β value of 25.3 µ β at the maximum field (7 T) and the lowest temperature (2 K). Additionally, we have tested the dynamic behavior of this complex at 2 K in the frequency range 1-1500 Hz without and with applied dc fields (ranging from 0 to 5 kOe), and an oscillating magnetic field of 3.5 Oe. No out of phase component in could be observed within the measurement parameters of our equipment and there is SMM behavior under these conditions.

Conclusions
In conclusion, an all inorganic heterometallic extended framework incorporating POM units has been synthesized in aqueous media under "one-pot" conditions. This Polyoxometalate Inorganic Framework, or POMIF, [{Dy(HO2)6}2Mn4P4W30O112(H2O)2] 10− (Dy2Mn4-P2W15), was prepared by reaction of Mn II ions and Dy III ions with the trilacunary Dawson ion [α-P2W15O56] 12− . The hydrated salt of Dy2Mn4-P2W15 was structurally characterized in the solid state by single-crystal X-ray diffraction, X-ray powder diffraction (XRD), Fourier transform infrared (FTIR) spectroscopy, and thermal and elemental analyses and in solution by UV-Visible absorption spectroscopy and luminescence emission spectroscopy. Furthermore, magnetic properties were also studied and compared with Na16[Mn4(H2O)2(α-P2W1SO56)2]·53H2O. We are presently attempting to synthesize analogs containing various combinations of 3d and 4f elements in order to do systematic and comparative studies of the resultant frameworks.

Conclusions
In conclusion, an all inorganic heterometallic extended framework incorporating POM units has been synthesized in aqueous media under "one-pot" conditions. This Polyoxometalate Inorganic Framework, or POMIF, [{Dy(HO 2 ) 6 } 2 Mn 4 P 4 W 30 O 112 (H 2 O) 2 ] 10− (Dy 2 Mn 4 -P 2 W 15 ), was prepared by reaction of Mn II ions and Dy III ions with the trilacunary Dawson ion [α-P 2 W 15 O 56 ] 12− . The hydrated salt of Dy 2 Mn 4 -P 2 W 15 was structurally characterized in the solid state by single-crystal X-ray diffraction, X-ray powder diffraction (XRD), Fourier transform infrared (FTIR) spectroscopy, and thermal and elemental analyses and in solution by UV-Visible absorption spectroscopy and luminescence emission spectroscopy. Furthermore, magnetic properties were also studied and compared with Na 16 [Mn 4 (H 2 O) 2 (α-P 2 W 1S O 56 ) 2 ]·53H 2 O. We are presently attempting to synthesize analogs containing various combinations of 3d and 4f elements in order to do systematic and comparative studies of the resultant frameworks.