Syntheses, Characterization, and Magnetic Properties of Four New

Aug 17, 2005 - Carboxylate and hydroxyl groups interlace the chain to form an organic−inorganic hybrid layered structure. The results of magnetic ...
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Syntheses, Characterization, and Magnetic Properties of Four New Layered Transition-Metal Hydroxyl-Carboxylate-Phosphonates: [M(CH(OH)(CO2)(PO3H))(H2O)2] (M ) Mn, Fe, Co, Zn)

CRYSTAL GROWTH & DESIGN 2005 VOL. 5, NO. 5 1795-1799

Ruibiao Fu, Shengchang Xiang, Huishuang Zhang, Jianjun Zhang, and Xintao Wu* State Key Laboratory of Structural Chemistry, Fujian Institute of Research on the Structure of Matter, Chinese Academy of Science, Fuzhou, Fujian 350002, People’s Republic of China Received February 22, 2005

ABSTRACT: Four new layered transition-metal hydroxyl-carboxylate-phosphonates, [M(CH(OH)(CO2)(PO3H))(H2O)2] (M ) Mn (1), Fe (2), Co (3), Zn (4)), have been successfully hydrothermally synthesized and characterized by single-crystal X-ray diffraction as well as with elemental analysis, infrared spectroscopy, thermogravimetric analysis, and magnetic measurement. These isomorphous compounds crystalline in the monoclinic space group P21/c with a ) 5.678(2)-5.800(2) Å, b ) 15.469(6)-15.664(5) Å, c ) 7.846(3)-7.911(2) Å, β ) 109.287(4)-110.332(3)°, V ) 649.5(4)-676.5(4) Å3, and Z ) 4. In these compounds, transition-metal [MO6] (M ) Mn, Fe, Co, Zn) octahedra and [PCO3] tetrahedra are connected to each other through corners into an infinite wriggled chain. Carboxylate and hydroxyl groups interlace the chain to form an organic-inorganic hybrid layered structure. The results of magnetic measurements revealed the presence of antiferromagnetic interactions of M(II) ions (M ) Mn, Fe, Co) in compounds 1-3, respectively. Introduction During the past three decades, metal phosphonates as a new class of inorganic-organic materials have attracted a great deal of research interest due to their structural diversities and many potential and practical applications, including Langmuir-Blodgett film (LB),1,2 meso-/microporous materials,3-5 ion exchangers,6 small molecular sensors,3,7-8 adsorption/desorption,9,10 catalysts,11,12 and nonlinear optics.2,13 Usually, metal monophosphonates (M/R-PO3) have a layered structure and are very useful in the area of intercalation chemistry.14-22 Metal diphosphonates (M/O3P-R-PO3) are important in preparing meso-/microporous materials because of their three-dimensional pillarlike structure with an open framework, which could be adjusted through modifying lengths and shapes of the organic units.3,4,23,24 Some metal phosphonates contain interesting structures, such as zeolite-like,25-27 an inorganic channel with an organic shell,28,29 cagelike,30-38 a homochiral framework,39-41 and ring/sphere clusters.42-44 Furthermore, many microporous compounds have been prepared lately through designing and synthesizing phosphonic acids with additional functional groups such as amino, hydroxyl, and carboxyl, which could increase the solubility of metal phosphonates.45-49 Phosphonic acids with hydroxyl and carboxyl groups as ligands could provide many coordination modes, resulting in various interesting structures. Therefore, 2-hydroxylphosphonoacetic acid (H4L) with a chiral carbon atom and three functional groups (-OH, -COOH, and -PO3H2) was used as a ligand to synthesize four new layered transition-metal hydroxyl-carboxylate-phosphonates: [M(CH(OH)(CO2)(PO3H))(H2O)2] (M ) Mn (1), Fe (2), Co (3), * To whom correspondence should be addressed. E-mail: wxt@ fjirsm.ac.cn. Fax: +86-591-83714946. Tel: +86-591-83792837.

Zn (4)). In this paper, we report the syntheses, characterizations, and magnetic properties of these compounds. Experimental Section Materials and Methods. 2-Hydroxylphosphonoacetric acid solution was obtained from Changzhou City Jianghai Chemical Factory as a water treatment agent (48.0 wt %). Other chemicals of reagent grade quality were obtained from commercial sources without further purification. Compounds 1-4 were synthesized in 25 mL Teflon-lined stainless steel vessels under autogenous pressure. The reactants were stirred homogeneously before heating. Elemental analyses were carried out with a Vario EL III element analyzer. Infrared spectra were obtained on a Nicolet Magna 750 FT-IR spectrometer. Thermogravimetric analysis (TGA) was performed on a NETZSCH STA449C instrument under nitrogen gas at a heating rate of 15 °C min-1 from room temperature to 800 °C. Magnetic measurements were acquired on a PPMS-9 instrument. Powder X-ray diffraction (XRD) patterns were acquired on a DMAX-2500 diffractometer using Cu KR radiation under ambient conditions. Synthesis of [Mn(CH(OH)(CO2)(PO3H))(H2O)2] (1). A mixture of Mn(CH3COO)2‚4H2O (0.2474 g, 1.009 mmol), LiOH‚ H2O (0.1682 g, 4.009 mmol), CH(OH)(CO2H)(PO3H2) solution (0.5 mL, 2 mmol), 2.0 mL of acetic acid, and 8.0 mL of H2O was heated to 120 °C for 48 h. Colorless crystals were obtained in 42.7% yield (0.1031 g) based on Mn(CH3COOH)2‚4H2O. The final pH value of this reaction mixture was 3.22. The purity of the product was checked by powder X-ray diffraction. Anal. Calcd for C2H7MnO8P (1): C, 9.81; H, 2.88. Found: C, 9.80; H, 2.61. IR (KBr pellet, cm-1): 3450 vs, 3261 vs, 2935 w, 2301 m, 1668 w, 1585 vs, 1429 m, 1373 m, 1238 s, 1200 s, 1165 m, 1068 s, 1039 m, 953 s, 852 m, 800 m, 768 m, 665 w, 634 m, 569 m, 496 s, 453 m. Synthesis of [Fe(CH(OH)(CO2)(PO3H))(H2O)2] (2). A mixture of FeCl2‚4H2O (0.2220 g, 1.117 mmol), NaF (0.1702 g, 4.053 mmol), CH(OH)(CO2H)(PO3H2) solution (0.5 mL, 2 mmol), 2.0 mL of acetic acid, and 8.0 mL of H2O was heated

10.1021/cg050065j CCC: $30.25 © 2005 American Chemical Society Published on Web 08/17/2005

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to 120 °C for 24 h. Yellow crystals were obtained in 31.1% yield (0.0854 g) based on FeCl2‚4H2O. The final pH value of this reaction mixture was 2.0. The pattern of powder XRD is agreement with that simulated from single-crystal X-ray data, which indicates a homogeneous phase. Anal. Calcd for C2H7FeO8P (2): C, 9.77; H, 2.87. Found: C, 9.73; H, 2.91. IR (KBr pellet, cm-1): 3450 vs, 3265 vs, 2939 w, 2725 w, 2293 m, 1585 vs, 1425 s, 1365 s, 1236 s, 1196 s, 1165 s, 1070 s, 1037 s, 951 s, 850 m, 808 m, 771 m, 667 w, 613 m, 577 m, 511 s, 455 m. Synthesis of [Co(CH(OH)(CO2)(PO3H))(H2O)2] (3). A mixture of Co(CH3COO)2‚4H2O (0.2496 g, 0.9968 mmol), NaF (0.1675 g, 3.989 mmol), (NH2CH2CH2)3N‚4HCl (0.6339 g, 2.170 mmol), CH(OH)(CO2H)(PO3H2) solution (0.5 mL, 2 mmol), 2.0 mL of acetic acid, and 8.0 mL of H2O was heated to 120 °C for 120 h. Red crystals were obtained in 76.8% yield (0.1887 g) based on Co(CH3COOH)2‚4H2O. The final pH value of this reaction mixture was 3.42. The purity of the product was also checked by powder X-ray diffraction. Anal. Calcd for C2H7CoO8P (3): C, 9.65; H, 2.83. Found: C, 9.56; H, 2.93. IR (KBr pellet, cm-1): 3438 s, 3361 s, 3246 s, 2943 m, 2301 m, 1657 w, 1585 vs, 1425 s, 1365 s, 1240 s, 1200 s, 1165 s, 1066 s, 1036 s, 951 s, 852 m, 822 m, 777 m, 669 w, 579 s, 501 s, 459 w. Synthesis of [Zn(CH(OH)(CO2)(PO3H))(H2O)2] (4). A mixture of Zn(CH3COO)2‚2H2O (0.2211 g, 1.007 mmol), NaF (0.0611 g, 1.454 mmol), CH(OH)(CO2H)(PO3H2) solution (0.5 mL, 2 mmol), and 10.0 mL of H2O was heated at 120 °C for 48 h. Colorless crystals were obtained in 63.3% yield (0.1627 g) based on Zn(CH3COO)2‚2H2O. The final pH value of this reaction mixture was 2.30. Through altering the quantity of NaF to adjust the pH value, compound 4 can be prepared in a pH range of 1.13-3.39. The pattern of powder XRD is in agreement with that simulated from single-crystal X-ray data, which indicates a homogeneous phase. Anal. Calcd for C2H7ZnO8P (4): C, 9.40; H, 2.76. Found: C, 9.29; H, 2.46. IR (KBr pellet, cm-1): 3450 vs, 3277 vs, 2941 m, 2305 m, 1659 w, 1585 vs, 1429 s, 1371 s, 1240 s, 1200 s, 1165 s, 1072 vs, 1041 s, 957 s, 852 m, 822 m, 773 m, 640 m, 577 w, 513 s, 459 w. Single-Crystal X-ray Diffraction. X-ray data were collected at a temperature of 130.15 K on a Rigaku Mercury CCD/ AFC diffractometer (for compounds 1-3) and at a temperature of 293(2) K on a Siemens SMART-CCD diffractometer (for compound 4) using graphite-monochromated Mo KR radiation (λ(Mo KR) ) 0.710 73 Å). Data for compounds 1-3 were reduced with CrystalClear v1.3, and data for compound 4 were reduced and absorption corrected with SMART and SADABS software, respectively. The structures of compounds 1-4 were solved by direct methods and refined by full-matrix leastsquares techniques on F2 using SHELXTL-97.50 All nonhydrogen atoms were treated anisotropically. The positions of H7 atoms in compounds 1 and 2 were generated geometrically, while the positions of all other hydrogen atoms were determined from difference Fourier maps with fixed isotropic thermal parameters. Crystallographic data for compounds 1-4 are summarized in Table 1. Selected bond distances and angles are presented in Table 2.

Results and Discussion Infrared Spectroscopy. The bands at about 3450, 3260, and 2300 cm-1 correspond to the O-H stretching vibrations of water molecules and hydroxyl and phosphonate groups, respectively. The carboxylate group appears at around 1585 cm-1 (very strong) and 1238 cm-1 (medium). A strong absorption band around 1200 cm-1, three medium to strong absorption bands in the range of 951-1072 cm-1, and a medium absorption band in the range of 768-777 cm-1 can be attributed to the stretching vibrations of PdO, P-O, and P-C of the phosphonate group, respectively. Single-Crystal Structures. Compounds 1-4 are isomorphous with the space group P21/c. Compound 1

Fu et al. Table 1. Crystallographic Data for Compounds 1-4

formula formula wt temp (K) space group a (Å) b (Å) c (Å) β (deg) V (Å3) Z Dcalcd (g cm3) µ (mm-1) GOF on F2 R1/wR2 (I >2σ(I))a

1

2

3

4

C2H7MnO8P 244.99 130.15 P21/c 5.800(2) 15.664(5) 7.911(2) 109.729(2) 676.5(4) 4 2.405 2.198 1.117 0.0188/ 0.0486

C2H7FeO8P 245.98 130.15 P21/c 5.731(2) 15.504(6) 7.861(3) 109.287(4) 659.2(5) 4 2.478 2.541 1.145 0.0245/ 0.0601

C2H7CoO8P 248.98 130.15 P21/c 5.678(2) 15.469(6) 7.846(3) 109.522(3) 649.5(4) 4 2.546 2.899 1.082 0.0201/ 0.0478

C2H7ZnO8P 255.42 293 P21/c 5.7200(7) 15.533(2) 7.8528(9) 110.332(3) 654.2(1) 4 2.593 4.009 1.078 0.0794/ 0.1980

a R1 ) ∑(||F | - |F ||)/∑|F |; wR2 ) {∑w[(F 2 - F 2)]/∑w[(F 2 o c o o c o )2]}0.5.

Table 2. Selected Bond Distances (Å) and Angles (deg) for Compounds 1-4a Mn (1)

Fe (2)

Co (3)

Zn (4)

M(1)-O(1) M(1)-O(2) M(1)-O(3) M(1)-O(4) M(1)-O(5)#1 M(1)-O(6)

2.265(1) 2.177(1) 2.123(1) 2.220(1) 2.210(1) 2.064(1)

2.180(2) 2.119(2) 2.098(2) 2.168(2) 2.138(2) 2.043(2)

2.144(1) 2.075(1) 2.077(1) 2.137(1) 2.122(1) 2.011(1)

2.184(7) 2.081(7) 2.052(7) 2.149(10) 2.147(7) 1.981(7)

O(2)-M(1)-O(1) O(2)-M(1)-O(4) O(2)-M(1)-O(5)#1 O(3)-M(1)-O(1) O(3)-M(1)-O(2) O(3)-M(1)-O(4) O(3)-M(1)-O(5)#1 O(4)-M(1)-O(1) O(5)#1-M(1)-O(1) O(5)#1-M(1)-O(4) O(6)-M(1)-O(1) O(6)-M(1)-O(2) O(6)-M(1)-O(3) O(6)-M(1)-O(4) O(6)-M(1)-O(5)#1

87.83(4) 73.86(4) 87.54(4) 91.34(5) 96.45(5) 169.47(4) 87.86(4) 84.32(4) 175.19(4) 95.66(4) 91.45(4) 175.49(4) 88.02(5) 101.64(4) 93.26(4)

87.90(6) 76.16(6) 88.48(6) 90.65(7) 97.24(7) 172.18(6) 88.02(6) 84.97(6) 175.95(6) 95.91(6) 90.71(6) 177.39(6) 84.99(7) 101.51(7) 92.98(6)

89.32(6) 77.68(5) 88.29(5) 90.53(6) 96.33(6) 172.87(5) 87.54(6) 85.58(6) 176.75(5) 96.07(5) 89.59(6) 177.92(5) 85.46(6) 100.46(6) 92.86(5)

88.8(3) 77.0(3) 87.8(3) 90.2(3) 95.2(3) 170.3(4) 88.8(3) 83.9(4) 176.4(3) 96.6(3) 89.8(3) 176.1(3) 88.4(3) 99.3(3) 93.6(3)

a Symmetry transformations used to generate equivalent atoms: (#1) x, -y + 1/2, z + 1/2.

is taken as an example to describe their structures in detail. The asymmetric unit of compound 1 includes one Mn(II) ion, one H2L2- (L ) CH(O)(CO2)(PO3)) anion, and two coordinated water molecules (Figure 1). The H2L2anion is chelated to the Mn(II) ion through one carboxylate oxygen atom (Mn1-O2 ) 2.177(1) Å) and one hydroxyl oxygen atom (Mn1-O4 ) 2.220(1) Å) with a very small bond angle (O2-Mn1-O4 ) 73.86(4)°). As a result, the Mn(II) ion is in a distorted-octahedral coordination geometry, which is completed by two phosphonate oxygen atoms from the other two equivalent H2L2- anions (Mn1-O6 ) 2.064(1) and Mn1-O5d ) 2.210(1) Å) and two coordinated water molecules (Mn1-O1 ) 2.265(1) Å and Mn1-O6 ) 2.127(1) Å). That is to say, each Mn(II) ion links three H2L2- anions and two water molecules through Mn-O covalent bonds. On the other hand, the H2L2- anion is tridentate, the carboxylate together with hydroxyl groups chelating one Mn(II) ion (Mn1a) and the phosphonate group linking the other two Mn(II) centers (Mn1 and Mn1b). [MnO6] octahedra and [CPO3] tetrahedra connect each other via corners (O5) into a wriggled chain along the c axis (Figure 2a). Carboxylate and hydroxyl groups interlace

Transition-Metal Hydroxyl-Carboxylate-Phosphonates

Figure 1. ORTEP view of the coordination geometries of manganese and phosphorus of 1, showing the asymmetric unit (ellipsoids at 50% probability). Dashed lines represent hydrogen bonds. Symmetry code for the generated atoms: (a) x 1, -y + 1/2, z - 1/2; (b) x, -y + 1/2, z - 1/2; (c) -x, y + 1/2, -z + 1 /2; (d) x, -y + 1/2, z + 1/2: (e) -x + 1, -y + 1, -z + 1; (f) -x, -y, -z + 1.

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Figure 3. Polyhedral view of the two neighboring layers of compounds 1 showing the hydrogen bonds (pink lines). [MnO6], [CPO3], O, C, and H are represented by yellow octahedra, blue tetrahedra, red dots, green dots, and white dots, respectively. Unrelated atoms are omitted for clarity.

Figure 4. TGA curves of compounds 1-4.

Figure 2. Polyhedral views of the (a) wavelike chain, (b) twodimensional framework structure, and (c) wavelike layer of compound 1. [MnO6], [CPO3], O, and C are indicated by yellow octahedra, blue tetrahedra, red dots and green dots, respectively. The hydrogen atoms are omitted for clarity.

the wriggled chains to form a wavelike manganese hydroxyl-carboxylate-phosphonate hybrid layer (Figure 2b,c). In addition, between two neighboring layers there are three different hydrogen bonds, which play an important role in packing the 2D layers into a threedimensional structure (Figures 1 and 3). First, the protonated phosphonate oxygen (O7) forms a strong

hydrogen bond with the uncoordinated carboxylate oxygen atom (O8f) (O7‚‚‚O8f ) 2.580(2) Å). Second, one coordinated water molecule (O1) interacts with the coordinated corboxylate oxygen atom (O2e) through a hydrogen bond with a 2.838(2) Å separated distance. Finally, the other coordinated water molecule (O3) forms a hydrogen bond with one phosphonate oxygen atom (O5c) (O3‚‚‚O5e ) 2.769(2) Å). Thermogravimetric Analysis. As shown in Figure 4, the initial weight loss temperature of compounds 1 and 4 is about 215 °C, which is different from that for compound 3 (about 275 °C). A small amount of water molecules of compound 2 start to be lost at about 165 °C, and most water molecules are lost near 240 °C. Except for the initial weight loss temperature, thermogravimetric analysis (TGA) curves of these compounds are nearly similar, with three main continuous weight losses. Herein, we also use compound 1 as an example to illuminate the three weight loss curves in detail. The first step is from 215 to 255 °C with 14.2% weight loss, corresponding to the loss of two coordinated water molecules (calculated 14.7%). Following that, the second step ends at 430 °C with 17.4% observed weight loss. During the final step within a temperature range from

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µB) of compound 1 is consistent with the expected spinonly value of 5.92 µB (g ) 2, s ) 5/2), according with the reported magnetic moments of Mn(II) in rang of 5.25.9 µB.51,52 Upon cooling, the χmT product is almost constant from 305 to 89 K. Thereupon, χmT decreases more quickly to 3.38 emu K mol-1 at 4 K. In the temperature range of 4-305 K, the magnetic susceptibility follows the Curie-Weiss law (χm-1 ) 0.16(3) + [0.2360(2)]T) (r ) 0.999 96), with C ) 4.24 emu K mol-1 and Θ ) -0.66 K. The decrease of the χmT value with decreasing temperature and negative Θ value suggest an antiferromagnetic interaction of Mn(II) ions.51,52 The effective magnetic moment per iron(II) ion (5.54 µB) at 305 K is higher than the expected spin-only value of 4.90 µB (g ) 2, s ) 2).52-55 During the temperature decrease, the effective magnetic stays constant down to 100 K (5.51 µB) and then decreases more rapidly to 3.90 µB at 4 K. Between 4 and 305 K, the magnetic susceptibility for compound 2 fits well to the Curie-Weiss law (χm-1 ) 1.15(6) + [0.2576(4)]T) (r ) 0.9999), with C ) 3.88 emu K mol-1 and Θ ) -4.46 K. The decrease of χmT value with decreasing temperature and negative Θ value suggest an antiferromagnetic interaction of Fe(II) ions.51,52 During the process of temperature decrease, the χmT product of compound 3 decreases gradually from 3.04 emu K mol-1 at 305 K to 1.65 emu K mol-1 at 4 K. From the equation mentioned above, at 305 K the effective magnetic moment per cobalt atom (µeff ) 4.93 µB) is obviously higher than the reported spin-only value of 3.87 µB and is in the range of 4.4-5.2 µB due to orbital contribution at room temperature.51,52 In temperature range 20-305 K, the magnetic susceptibility for compound 3 is consistent with the Curie-Weiss law (χm-1 ) 5.5(1) + [0.3154(6)]T) (r ) 0.9999), with C ) 3.17 emu K mol-1 and Θ ) -17.3 K. The decrease of χmT value with decreasing temperature and negative Θ value suggest an antiferromagnetic interaction of the Co(II) ion.51,52 Conclusion

Figure 5. Thermal dependence of the χmT (solid squares) product and for compounds (a) 1, (b) 2, and (c) 3. The inset shows the magnetic susceptibility (χm, solid squares) and inverse magnetic susceptibility (χm-1, open squares) plotted as a function of temperature for compounds (a) 1, (b) 2, and (c) 3.

430 to 580 °C, the phosphonate group breaks down, and the final product may be mainly composed of MnHPO4. Magnetic Properties. The temperature dependence of the χmT product, magnetic susceptibility (χm), and inverse magnetic susceptibility (1/χm) for compounds 1-3 at 10 kOe in the temperature range 4-305 K are shown in Figure 5. By using the equation µeff ) (8χmT)1/2, at 305 K the effective magnetic moment per manganese atom (5.84

Four new layered transition-metal hydroxyl-carboxylate-phosphonates have been prepared under lowtemperature hydrothermal conditions. These compounds are structural isomorphism, containing cornershared [MO6] (M ) Mn, Fe, Co, Zn) octahedra and [CPO3] tetrahedra wriggled chains, which are interlaced by carboxylate and hydroxyl groups into a layered structure. Magnetic measurements revealed the presence of antiferromagnetic interactions of M(II) ions (M ) Mn, Fe, Co) in compounds 1-3. These compounds all crystallize in achiral space groups, because a racemic mixture of 2-hydroxylphosphonoacetic acid would decrease the probability of coordination polymers crystallizing in acentric or achiral space groups. The use of the ligand to prepare acentric or achiral coordination polymers is underway. Acknowledgment. This research was supported by grants from the State Key Laboratory of Structure Chemistry, Fujian Institute of Research on the Structure of Matter, the National Ministry of Science and Technology of China (No. 001CB1089), the Chinese Academy of Sciences (CAS), the National

Transition-Metal Hydroxyl-Carboxylate-Phosphonates

Science Foundation of China (Nos. 20273073, 20333070, and 90206040), and the Science Foundation of CAS and Fujian Province for research funding support (Nos. 2004HZ01-1, 2003J042, 2004J041, and Z0513022). Supporting Information Available: X-ray crystallographic information files (CIF) for compounds 1-4 and figures giving XRD patterns of experiments compared to those simulated from X-ray single-crystal data (black line) for compounds 1-4. This material is available free of charge via the Internet at http://pubs.acs.org.

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