Syntheses, Crystal Structures, and Magnetic Properties of Two Mn(II

Jul 15, 2010 - Nanjing University, Nanjing 210093, P. R. China, ‡State Key Laboratory ... of Chemistry & Chemical Engineering, Jinggangshan Universi...
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DOI: 10.1021/cg100127w

Syntheses, Crystal Structures, and Magnetic Properties of Two Mn(II) Coordination Polymers Based on the 5-Aminotetrazole Ligand: Effect of Sources of Ligand on Construction of Topological Networks

2010, Vol. 10 3429–3435

Tian-Wei Wang,† Dong-Sheng Liu,*,†,‡,§ Chang-Cang Huang,‡ Yan Sui,†,§ Xi-He Huang,‡ Jian-Zhong Chen,*,‡ and Xiao-Zeng You*,† †

State Key Laboratory of Coordination Chemistry, School of Chemistry and Chemical Engineering, Nanjing University, Nanjing 210093, P. R. China, ‡State Key Laboratory Breeding Base of Photocatalysis, College of Chemistry & Chemical Engineering, Fuzhou University, Fuzhou, Fujian 350108, P. R. China, and §College of Chemistry & Chemical Engineering, Jinggangshan University, Ji’an, Jiangxi 343009, P. R. China Received January 27, 2010; Revised Manuscript Received June 23, 2010

ABSTRACT: Two new Mn(II) coordination polymers, [Mn15(atz)18(μ3-OH)4(μ3-SO4)4]n 3 9nH2O (1) and [Mn8(atz)4(μ-OH)4(μ4-SO4)4(H2O)4]n 3 nH2O (2) (atz = 5-aminotetrazolate), have been prepared under similar hydrothermal conditions except the difference of the source of the atz ligand. They were characterized by single-crystal X-ray diffraction studies, variable temperature (1.8-300 K) magnetic measurements, and thermal gravity analysis. The results of X-ray crystallographic analysis reveal that compound 1 is a 3D coordination polymer with a (3,4)-connected (83)4(86)3 topology, which is built from trinuclear [Mn3(μ3-SO4)(μ3-OH)] clusters and bridging mononuclear Mn centers. In compound 2, it contains a 3D inorganic cationic afli symbol of which is [Mn8(μ3-OH)4(μ4-SO4)4]n4þ network with an unprecedented (4,6)-connected topological net, the Schl€ (33 3 82 3 9)2(36 3 84 3 95). The inorganic cationic net is templated by the atz ligands to form a microporous framework with hydrophilic channels. The variable temperature magnetic data indicate that 1 exhibits antiferromagnetic behavior, whereas 2 shows ferrimagnetic behavior.

Introduction Construction of metal-organic coordination polymers continues to attract intense attention due to their fascinating architectures and topologies1-10 as well as their potential application as functional materials in many areas.11-27 Synthesizing compounds with controllable structures and properties is a very important topic and also a great challenge, and the crystal-engineering design plays a very important role in this system.27 Recently, in situ ligand synthesis, as a new approach in crystal engineering of coordination polymers first proposed by Champness and Schr€ oder in 1997,28 has been 29-31 Various coordination compounds developed extensively. with an intriguing variety of architectures, topologies, and novel properties have been well prepared by using in situ synthesized ligands. It is particularly interesting to notice that tetrazoles and their derivatives have shown the capability of yielding various coordination compounds. Xiong et al. borrowed Sharpless’ idea32 and prepared a series of tetrazolebased coordination polymers by the in situ synthesis of tetrazoles from various nitriles with azide.33-41 Most of the coordination compounds were prepared by hydro(solvo)thermal methods. The combination of hydrothermal reactions with in situ synthesis under relatively high temperature and pressure is always accompanied by many unexpected reactions, such as dehydrogenative carbon-carbon coupling, hydroxylation of aromatic rings, cycloaddition of organic nitriles with azide and ammonia, redox reaction, etc.28-30,42 This method provides an effective pathway to crystalline

compounds with in situ synthesized ligands which are inaccessible or difficult to obtain by routine synthetic methods.43,44 In comparison with preparing compounds with in situ synthesized ligands, the desired compounds produced from hydrothermal reaction of a metal salt with the available ligand can be controlled by adjusting the reaction conditions. However, to the best of our knowledge, investigation of using the same ligand but from different sources in the construction of coordination nets has never been documented to date. Therefore, the development of a new approach in designing new metal-organic frameworks via altering the source of the same ligand will be another challenge. 5-Aminotetrazolate, as a multifunctional small molecular ligand, is isosteric with the carboxylate group and has five binding sites (one amino group and four amino-nitrogen atoms). It has been used to construct some interesting MOFs from the in situ generated or available atz ligand.36,45-49 As a part of our ongoing study using the in situ generated Hatz ligand to construct coordination polymers,45,46 a new coordination polymer of [Mn15(atz)18(μ3-OH)4(μ3-SO4)4]n 3 9nH2O (1) was obtained from the in situ generated ligand. Interestingly, when the in situ generated atz ligand was replaced by the available Hatz ligand under similar reaction conditions, a different 3D microporous coordination polymer of [Mn8(atz)4(μ3-OH)4(μ4-SO4)4(H2O)4]n 3 nH2O (2) was prepared. In this paper, we will report the synthesis, structures, and magnetic properties of compounds 1 and 2. Experimental Section

*To whom correspondence should be addressed. E-mail: D.-S.L., [email protected]; J.-Z.C., [email protected]; X.-Z.Y., youxz@ nju.edu.cn.

Reagents and Physical Measurements. All reagents and solvents employed are commercially available and used without further purification. Infrared spectra were recorded in the range 4000400 cm-1 on a Perkin-Elmer FT-IR spectrum 2000 spectrometer

r 2010 American Chemical Society

Published on Web 07/15/2010

pubs.acs.org/crystal

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Scheme 1. Hydrothermal Synthesis of Compounds 1 and 2

Wang et al. Table 1. Crystal Data and Structure Refinement for Compounds 1 and 2 1

using KBr pellets. Elemental analyses were determined with a Perkin-Elmer model 240C instrument. Thermal analyses were performed on a Delta Series TGA7 instrument in N2 atmosphere with a heating rate of 10 °C/min from 30 to 750 °C. Powder X-ray diffraction (PXRD) data were obtained by using a Rigaku D/MAX 2500 V/PC diffractometer with Cu Ka (λ = 1.54056 A˚) radiation. A step size of 0.05° and counting time of 1.2 s/step were applied in a 2θ range of 8.0-60.0°. Magnetic susceptibility measurements of the crystalline samples were carried out on a Quantum Design MPMS-XL7 SQUID magnetometer. Caution! Sodium azide is potentially explosive. Only a small amount of material should be prepared, and it should be handled with care. Synthesis of [Mn15(atz)18(μ3-OH)4(μ3-SO4)4]n 3 9nH2O (1). A mixture of MnSO4 3 H2O (0.085 g, 0.5 mmol), NaN3 (0.065 g, 1.0 mmol), DCDA (DCDA = dicyandiamide, 0.168 g, 2.0 mmol), and water (5 mL) was stirred for 30 min in air and then sealed in a 23 mL Teflon autoclave and heated to 130 °C for 3 days (Scheme 1). After the sample was cooled to room temperature at a rate of 10 °C/h, colorless prism-shaped crystals were obtained in ca. 32% yield based on Mn(II). Anal. Calcd for C18H58Mn15N90O29S4: C, 7.32; H, 1.98; N, 42.71. Found: C, 7.27; H, 1.83; N, 42.68. Synthesis of [Mn8(atz)4(μ3-OH)4(μ4-SO4)4(H2O)4]n 3 nH2O (2). The hydrothermal procedure of the preparation of compound 2 is similar to that for 1 except that NaN3 was replaced by Hatz. Colorless needle-shaped crystals were obtained in ca. 45% yield based on Mn(II). Anal. Calcd for C4H22Mn8N20O25S4: C, 3.64; H, 1.68; N, 21.25. Found: C, 3.59; H, 1.72; N, 21.73. Compounds 1 and 2 are air-stable and insoluble in water and common organic solvents. X-ray Crystallographic Determination. Suitable single crystals of two compounds were mounted on glass fibers for X-ray measurement. Reflection data were collected at room temperature on a Rigaku Saturn 724 CCD diffractometer for compounds 1 and 2 with graphite monochromatized Mo KR radiation (λ = 0.71073 A˚), respectively. Crystal structures were solved by the direct method and different Fourier syntheses. All calculations were performed by using the SHELX-97 program.50 All non-hydrogen atoms were refined by full-matrix least-squares techniques on F2 with anisotropic thermal parameters. Hydrogen atoms associated with disordered atoms were not included in the structural refinements. The hydrogen atoms for the amino groups of 1 and 2 were fixed at calculated positions and refined by using a riding mode. The hydroxyl hydrogen atoms and H atoms of water molecules for 1 were found from difference map and refined with O-H distance restraint (0.82(1) A˚) and U(H)=1.2Ueq(O), and the hydroxyl hydrogen atoms and H atoms of coordination water molecules for 2 were found and refined from difference map. For 1, one μ3-atz ligand locates at the 2-fold axis, causing a 2-fold disorder of this ligand and thus two possible orientations of the amino group and the associated C atom of the amino group. The disorder was treated by performing half-occupancies with C and N atoms of the tetrazole ring and the amino groups of the tetrazole ligands. Crystal data and details of the data collection and the structure refinement are given in Table 1. Selected bond lengths and bond angles of the compounds are listed in Table S1 (Supporting Information). The CCDC reference numbers are 722566 and 748324 for 1 and 2.

Results and Discussion It is well-known that the structure of the final product can be influenced by various factors,46,49,51-57 such as the ratio

2

empirical formula C18H58Mn15N90O29S4 C4H22Mn8N20O25S4 formula weight 2951.88 1318.08 crystal system cubic orthorhombic Pnma space group I43d a (A˚) 21.015(2) 9.240(2) b (A˚) 21.015(2) 6.913(1) c (A˚) 21.015(2) 16.095(3) R (deg) 90 90 β (deg) 90 90 γ (deg) 90 90 9281.4(18) 1028.1(4) V (A˚3) Z 4 1 2.112 2.129 Fcal (g/cm3) -1 2.171 2.680 μ (mm ) GOF 1.063 1.048 0.0419 0.0375 R1 (I >2δ(I))a 0.1307 0.1279 wR2 (all data)b 0.922, -0.569 max. peak, hole/(e A˚-3) 0.502, -0.365 P P P P 2 a b R1 = ||Fo| - |Fc||/ |Fo|. wR2 = [ w(Fo - Fc2)2/ w(Fo2)2]1/2.

between metal salts and ligands, pH value,51 temperature,57 reaction time, counterions,54 and even the sources of metal and the ligand. In this study, it is noticeable that there is one critical factor to govern the formation of the final products: the same ligand from different sources, in situ generated ligand for 1 and commercially available ligand for 2. The excess of the dicyandiamide reagent is another critical factor in these experiments. In the synthesis of compound 1, the organic base dicyandiamide not only reacts with the NaN3 to in situ generate the atz ligand but also offers the hydroxyl group when it is hydrolyzed under the hydrothermal condition. It is suggested that the Sharpless32,58 [2 þ 3] tetrazole synthesis method works effectively in the in situ formation of Mn tetrazolate from the reaction of dicyandiamide and NaN3. But in the synthesis of compound 2, it is an optimum choice to prepare the pure product by hydrolyzing the organic base dicyandiamide slowly to generate the hydroxyl group. When introducing the hydroxyl from the strong base, we cannot get the pure product, which is always accompanied with some unidentifiable powders. Crystal Structure of Compound 1. Compound 1 is isostructural with the Cd compound which has been reported by us recently.46 It is a 3D coordination polymer built from trinuclear [Mn3(μ3-OH)(μ3-SO4)]3þ clusters and mononuclear Mn(II) centers (Figure 1). As illustrated in Figure 1, Mn2 adopts a pseudo-octahedral coordination geometry that is formed by four nitrogen atoms from four atz ligands [Mn1-N 2.240(4) ∼ 2.275(4) A˚], one oxygen atom from sulfate anion [Mn1-O2 2.142(4) A˚], and one OH- group [Mn1-O3 2.209(3) A˚]. The hydroxyl acts as a μ3-bridge linking three equivalent Mn2 atoms, generating an equilateral triangle with Mn 3 3 3 Mn distances equal to 3.639(1) A˚. The Mn2-O3-Mn2(A) angle is 110.9(1)° and the OHgroup is displaced out of the Mn2- Mn2(A)-Mn2(B) plane, which results in the formation of a noncoplanar [Mn3(μ3OH)] trimetric unit. The sulfate anion resides on a 3-fold axis, acting as an architectural truss to support the trimetric unit to form a stable [Mn3(μ3-OH)(μ3-SO4)] cluster. The cluster is surrounded by three identical μ4-atz ligands, each of which sets up an N-N bridge between two Mn2 ions via two neighboring nitrogen atoms (N2 and N3) from one tetrazole ring. The ligand is also bonded to Mn1 and Mn2 ion via N4 and N5 atoms, respectively. Simultaneously, the neighboring Mn1 and Mn2 are linked through two

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Figure 1. View of the coordination environment of Mn2þ and the ligand in compound 1 at 30%. Hydrogen atoms and disordered water molecules are omitted for clarity. Symmetry codes: (A) 0.5 þ y, 0.5 - z, -x; (B) -z, 0.5 þ x, 0.5 - y; (C) -0.25 þ y, -0.25 þ x, 0.25 - z; (D) 0.25 - x, 0.75 - z, -0.25 þ y; (E) 0.25 þ y, 0.75 - x, -0.25 þ z; (F) 0.5 þ y, 0.5 þ z, -0.5 þ x; (G) 0.25 - z, 0.75 - y; -0.25 þ x; (H) 0.25 þ z, 0.75 - y, 0.25 - x; (I) 0.5 - x, y, -z. (a) View of the coordination environment of Mn1; each Mn1 links to four [Mn3(μ3-OH)(μ3-SO4)] clusters. (atz ligands are partly drawn for clarity; Mn1 and Mn2 atoms are colored in pink and cyan, respectively.) (b) Packing diagram of 1 through atz connected. (Amino groups of atz ligands and water molecules are omitted for clarity.) (c) View of the 3D (3,4)-connected topological network with the Schl€afli symbol of the (83)4(86)3 network for 1. The Mn1 node and the center of the trinuclear Mn2 cluster are represented by the pink ball and the cyan ball, respectively.

neighboring nitrogen atoms of the other μ3-atz (mode II) and μ4-atz ligands and hence constitute a paddle wheel. The shortest distance of the Mn1 3 3 3 Mn2 distance is 3.981(1) A˚. Each Mn1 ion locates at the special position and adopts the octahedral coordination geometry with six N atoms from six atz ligands. The equatorial positions are occupied by four different but symmetry-related N4 atoms [Mn1-N4 2.259(4) A˚] from four atz ligands, and the axial positions are occupied by two symmetry-related N8 atoms [Mn1-N8 2.232(6) A˚] of the other two atz ligands. Thus, each Mn1 is linked to four [Mn3(μ3OH)(μ3-SO4)]3þ clusters (Figure 1a), and each cluster is connected to three Mn1 centers, giving rise to a complicated 3D network (Figure 1b). Taking the clusters as 3-connected nodes and the Mn1 centers as 4-connected nodes, the 3D network represents a (3,4)-connected topological 3D network with the Schl€afli symbol59 of (83)4(86)3 (Figure 1c). Compared with the known (3,4)-connected nets in coordination polymers,60-65 the structure of 1 provides another valuable prototype of (3,4)connected nets which may be important for the design of MOFs, since three- and four-connected centers are readily available in coordination chemistry. Crystal Structure of Compound 2. The structure of compound 2 is a 3D framework network with strip-shaped

chains and trinuclear triangular [Mn3(μ3-OH)]5þ clusters. As illustrated in Figure 2, Mn1 adopts a distorted-octahedral coordination geometry that is formed by two nitrogen atoms from two symmetry-related atz ligands [Mn1-N 2.344(3) A˚], four oxygen atoms from two sulfate anions, one OH- group, and one coordinated water molecule [Mn1-O 2.160(4)2.198(3) A˚]. The Mn2 ion locates at the special position and adopts the octahedral coordination geometry with two N atoms and four oxygen atoms. The equatorial positions are occupied by two different but symmetry-related pairs of oxygen atoms [Mn2-O 2.159(2)-2.209(3) A˚] from two sulfate anions and two hydroxyl groups, and the axial positions are occupied by two symmetry-related N1 atoms [Mn1-N1 2.231(3) A˚] from two atz ligands. In this compound, the hydroxyl acts as a μ3-bridge linking one Mn1 atom and two equivalent Mn2 atoms, generating an isosceles triangle with a Mn 3 3 3 Mn separation of 3.660(1) and 3.456(1) A˚ (Figure 2). The Mn-O4-Mn angle is about 106-114°, so the OH- group is displaced out of the Mn1Mn2-Mn2(i) plane, which results in the formation of a noncoplanar [Mn3(μ3-OH)] triangular cluster. The triangular clusters [Mn3(μ3-OH)]5þ are linked together by sharing the Mn2 ions and templated by μ4-atz ligands to form a

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Figure 2. View of the coordination environment of Mn2þ and atz ligand in 2 at 50%, Hydrogen atoms and disordered water molecules are omitted for clarity. Symmetry codes: (i) 1 - x, 0.5 þ y, 1 - z; (ii) x, 0.5 - y, z; (iii) 1 - x, -y, 1 - z; (iv) x, -0.5 - y, z; (v) -0.5 þ x, 0.5 - y, 1.5 - z; (vi) 1 - x, -0.5 þ y. (a) View of the 3D packing diagram of 2 with the free water residing in the voids (left), and the subunit of 2: the metal hydroxide strip-shaped chain (right). (The magnetic Δ-chain is highlighted with the dashed green line.) (b) View of the unprecedented (4,6)-connected topological network with the Schl€ afli symbol of the (33 3 82 3 9)2(36 3 84 3 95) network for 2. The Mn node and the center of sulfate groups are represented by the pink ball and blue ball, respectively.

strip-shaped metal Δ-chain along the b axis direction (Figure 2a, right). The μ4-SO4 anion resides on a 2-fold axis and acts as a bridging-ligand. On one end, three O atoms of the sulfate anion act as a cap to cover the trimetric unit of the [Mn3(μ3-OH)]5þ cluster, and on the other end, one O atom of the sulfate anion links to the Mn atom of the other stripshaped metal Δ-chain. Each strip-shaped metal Δ-chain is connected with four identical chains via the μ4-SO4 bridge to generate a 3D metal-organic framework with 1D rhombus channels (Figure 2a, left). The sizes of the channels are about 9.28  9.28 A˚2. Notably, the inner surface of the rhombus channel is decorated with amino groups of the atz ligands, coordination water molecules, and hydroxyl groups toward the cavity interiors, resulting in a hydrophilic channel. The lattice water molecules reside in the hydrophilic channels and further stabilize the 3D framework structure through extensive hydrogen bonds, which are formed between the coordinated water molecules and the lattice water molecules. After the removal of the free water molecules of compound 2, it is exceptionally microporous, with a total potential solvent accessible volume of 19.3% calculated using PLATON.66 Alternatively, the structure of 2 can be described in terms of strip-shaped chains of oxo-centered trinuclear manganese clusters, [Mn3(μ3-OH)]5þ, connected by the μ4-atz bridges; then the chains are interconnected by the μ4-SO4 bridges to

form a 3D porous framework with the intercalated water molecules in the rhombus channels. Further simple description of the structure of 2 can be like this: it is constructed by an inorganic cationic [Mn8(μ3-OH)4(μ4-SO4)4]n4þ network (Figure S1) and templated by atz anions, and the free water molecules reside in the rhombus hydrophilic channels. Topologically, when we take the μ3-OH and the μ4-atz as linkers between three Mn atoms, the μ4-SO4 and the Mn1 atoms as 4-connected nodes, and the Mn2 as 6-connected nodes, respectively, compound 2 can be regarded as a (4,6)-connected topological net (Figure 2b), with the Schl€ afli symbol59 of 3 2 6 4 5 (3 3 8 3 9)2(3 3 8 3 9 ) and the vertex symbol or long symbol67 of (3.8.3.8.3.92)(3.3.3.3.3.3.8.8.8.8.92.92.94). Although a few (4,6)-connected networks with three types of vertexes have been identified and categorized by O’Keeffe et al., such as alw, bix, fsi, fsk, spl, urk, and url, to the best of our knowledge, compound 2 with such a (4,6)-connected topology is unprecedented, which has never been reported to date.68 Magnetic Properties. The magnetic susceptibilities of 1 and 2 were measured in the 1.8-300 K temperature range at 2 kOe, and they are shown as χmT and χm versus T plots (Figures 3 and 5). The experimental χmT value of 1 at room temperature is 59.60 emu K mol-1, which is somewhat lower than the spin-only value (65.63 emu 3 K/mol) expected for fifteen magnetically isolated high-spin MnII ions, considering

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Figure 3. Temperature dependence of χm and χmT for 1 at 2 kOe.

Figure 4. Field-dependent magnetization for 1 at 1.8 K.

g = 2.00 and S = 5/2. The 1/χm vs T plot above 30 K is exactly linear following the Curie-Weiss law with C = 66.51 emu 3 K/mol and θ = -55.78 K (Figure S2 of the Supporting Information). The C value corresponds to g = 2.01, being normal for the spin only coupling of octahedral Mn(II) ions. Upon cooling from room temperature, the χmT value of 1 steadily decreases until it reaches a minimum at 1.8 K, suggesting an antiferromagnetic behavior. A round peak is observed in the χm versus T curve, indicating antimagnetic ordering. The antiferromagnetic ordering is further confirmed by the field-cooled (FC) and zero field-cooled (ZFC) magnetizations measurement: In the low-temperature region of 1.8-10 K in the low external field of 10 Oe, the curves of FC and ZFC magnetizations (Figure S3, Supporting Information) are identical. Furthermore, at 1.8 K in the applied field of up to 70 kOe, the field dependence of magnetization increases almost linearly, reaching 17.22 Nβ at 70 kOe (Figure 4), which is far from the saturation value of 75.38 Nβ for fifteen MnII ions (S = 5/2 and g = 2.01). This behavior is consistent with the antiferromagnetic nature of the Mn(II) 3 3 3 Mn(II) exchange interaction through the tetrazolato and the μ3-OH bridges. ututhor The plot of χmT vs T for compound 2 indicates that it looks like ferrimagnetism (Figure 5). The χmT value at room temperature is 23.65 emu K mol-1, much smaller than the spin-only value (35.0 emu K mol-1) expected for eight magnetically isolated high-spin MnII ions, considering g = 2.00 and S = 5/2. Upon lowering the temperature, the value

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of χmT gradually decreases, and it attains a minimum of 18.0 emu K mol-1 at 10 K and then exhibits an abrupt increase to a maximum of 26.0 emu at 1.8 K before decreasing at very low temperature. The 1/χm vs T plot in the range 60-300 K obeys the Curie-Weiss law with C = 28.87 emu K mol-1 and θ = -66.54 K (Figure S4, Supporting Information). At 1.8 K, the field dependence of the magnetization first increases abruptly below 200 Oe and then increases slowly (Figure 5a); the magnetization value is 11.56 Nβ at 70 kOe, which is far from the saturation value of 40.0 Nβ for eight MnII ions (S = 5/2) (Figure 5a inset a). In addition, a hysteresis loop is observed at 1.8 K with a remnant magnetization (Mr) of 0.43 Nβ and a coercive field (Hc) of 13.0 Oe (Figure 5a, inset b), which is consistent with spin-canted behavior. In the low-temperature region 1.8-10 K in the low external field of 10 Oe, the curves of FC (Hdc = 10 Oe) and ZFC magnetizations (Figure S5, Supporting Information) diverge at approximately 3 K. The ac susceptibility measurements (Figure 5b) show a signal in the imaginary (χ00 ) below 3 K. These features prove that magnetic ordering occurs at about 3 K, indicating a critical temperature at about 3 K. According to the structure of compound 2, the trinuclear triangular [Mn3(μ3-OH)]5þ clusters in the strip-shaped chains are bridged μ4-atz ligands (Figure 2a, left). The intrachain interactions through these μ3-OH and N-N bridge exchange pathways are principally antiferromagnetic, which causes compound 2 to exhibit antiferromagnetic behavior above 10 K. Such behavior can be attributed to spin frustration, well accorded with the triangular frustrated lattice linked by vertex-sharing in the Δ-chain (Figure 2a, right).69 The relatively large value of f = |θ|/TN = 22.2 (from the above θ = -66.54 and TN = 3 K, defined by dc and ac susceptibility, see below) is consistent with the presence of spin frustration. Below10 K, the magnetic susceptibility increases to a maximum at 1.8 K before decreasing at very low temperature, which happens probably because the number of the metal centers is odd, preventing the total spin value of the spin-carries to arrive at zero, and/or because a spin-canting behavior is induced by DzyaloshinskyMoriya interactions,70,71 which lead to the presence of weak ferromagnetism. From the divergence of FC and ZFC magnetization curves and the existence of a hysteresis loop, the observed magnetic susceptibility increase below about 3 K unambiguously indicates the presence of both canted antiferromagnetism and long-range magnetic order below 3 K. It should be noted that spin frustration is also observed in Co and Fe compounds, which contain not only canted antiferromagnetism but long-range magnetic order at low temperature.72,73 Powder X-ray Diffraction. PXRD experiments were carried out on 1 and 2 in order to establish their crystalline phase purity. As shown in the PXRD patterns (Figure S6, Supporting Information), the PXRD patterns of bulk samples 1 and 2 are consistent with the simulated patterns based on the singlecrystal data, indicating the presence of mainly one crystalline phase in the corresponding coordination polymers 1 and 2. IR Spectroscopy. The IR spectra of compounds 1 and 2 (Figure S7, Supporting Information) show a medium strong intensity band in the range 3300-3490 cm-1, which can be assigned to the ν(NH) characteristic stretching frequency of the amino groups (for 1, 3468 and 3369 cm-1; 2, 3400 and 3234 cm-1). All of them show the blue shift from the bands observed at 3485 and 3382 cm-1 for the free ligand. Besides these, the strong bands around 1630 cm-1 and 1440 cm-1 are also observed, which associate with ν(CdN)/ring stretching vibrations plus δ(N-H)NH, NH2 of the atz ligand.74

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Figure 5. Temperature dependence of χm and χmT for 2 at 2 kOe. (a) Isothermal magnetization of 2 at 1.8 K: (inset a) field-dependent magnetization curve; (inset b) hysteresis loop. (b) ac magnetic susceptibility of real and imaginary components for 2 measured under Hdc = 0 Oe and Hac = 1 Oe applied fields.

In 1, the SO42- adopts a μ3 coordination mode and leads to a low site symmetry C3v. The bands show medium strong intensity at 985 and 448 cm-1; these may be attributable to the symmetric S-O stretching mode (ν1) and the symmetric SO42- bending mode (ν2). The band at 627 cm-1 can be attributable to a ν4 mode. The strong band around 1160 cm-1 splitting into two bands, 1162 and 1075 cm-1, may be assigned to the ν3 mode.75 In 2, both the bands at 987 and 457 cm-1 associated with the symmetric S-O stretching (ν1) and the symmetric SO42- bending vibrations (ν2) appear with medium intensity, and the ν3 and ν4 splitting into three bands at 922, 1017, 1085 and 567, 593, 610 cm-1 corresponds to the ν3 and ν4 modes, respectively. This result suggests that the symmetry of the sulfate ion is again lowered and reduced to C2v.75,76 It is consistent with the crystallographic structure of 2, in which the SO42- adopts a μ4 coordination mode and leads to a low site symmetry C2v. Thermal Stability Analyses. The thermal stability of the two compounds in N2 was examined by the TG techniques in the temperature range 30-800 °C. The TG curves (Figure S8 and 9, Supporting Information) for 1 and 2 are at a heating rate of 10 °C/min under N2 atmosphere. As shown in Figure S8, weight loss of 5.72% between 30 and 160 °C consists of the corresponding calculated values of 5.59% for 1, due to the loss of nine free water molecules. And after that, the continuous weight loss above 350 °C corresponds to the decomposition of hydroxyl groups, atz ligands, and sulfate anions. A weight loss of 7.1% (calcd, 6.82%) for 2 occurs in the range of 30-190 °C (Figure S9), corresponding to the loss of five water molecules. Then there is continuous weight

loss above 300 °C, owing to the collapse of the framework of 2 due to the decomposition of anions. Conclusion In summary, two Mn(II) compounds have been successfully prepared under similar conditions except the difference of the atz ligand sources. The strong antiferromagnetic compound 1 has been obtained from the in situ generated atz ligand, whereas the ferrimagnetic compound 2 has been prepared from using commercially available atz ligand. Topological analysis of the two compounds indicates that distinct topological networks are presented before us. The structure of 1 provides another valuable prototype of the (3,4)-connected topological net with the Schl€ afli symbol of (83)4(86)3. Noticeably, the 3D microporous framework compound 2 possesses an unprecedented (4,6)-connected topological net with the Schl€ afli symbol of (33 3 82 3 9)2(36 3 84 3 95). This work demonstrates that the variation of synthesis conditions is critical to successful isolation of 3D metal polymer zeotypes with distinct properties in some particular systems. Further investigations on such an interesting system will be applied to other metal-ion cases in our future work. Acknowledgment. This work is supported by the NSFC (20721002 and 50772023), the Natural Science Foundation of Fujian Province (2007J0148) and JiangXi Province (2007GZH1667), and the open funds of the State Key Laboratory of Coordination Chemistry of Nanjing University and Department of Education of Jiangxi Province (GJJ10536).

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Crystal Growth & Design, Vol. 10, No. 8, 2010

Supporting Information Available: X-ray crystallographic data in CIF format, PXRD, IR spectra, TGA, and partly magnetic plots for compounds 1 and 2. This material is available free of charge via the Internet at http://pubs.acs.org.

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