Syntheses, crystal structures and characterizations of new zinc (II) and lead (II) carboxylate-phosphonates

Journal of Molecular Structure 740 (2005) 181–186 www.elsevier.com/locate/molstruc

Syntheses, crystal structures and characterizations of new zinc (II) and lead (II) carboxylate-phosphonates Jun-Ling Song, Jiang-Gao Mao* State Key Laboratory of Structure Chemistry, Fujian Institute of Research on the Structure of Matter, The Chinese Academy of Sciences, Fuzhou 350002, People’s Republic China Received 9 December 2004; revised 18 January 2005; accepted 19 January 2005

Abstract The syntheses, crystal structures and characterizations of two new divalent metal carboxylate-phosphonates, namely, Zn(H3L)$2H2O (1) and Pb(H3L)(H2O)2 (2) (H5La4-HO2C–C6H4–CH2N(CH2PO3H2)2) have been reported. Compound 1 features a 1D column structure in which the Zn(II) ions are tetrahedrally coordinated by four phosphonate oxygen atoms from four phosphonate ligands, and neighboring such 1D building blocks are further interconnected via hydrogen bonds into a 3D network. The carboxylate group of H3L anion remains noncoordinated. Compound 2 has a 2D layer structure. Pb(II) ion is 7-coordinated by four phosphonate oxygen atoms from four phosphonate ligands and three aqua ligands. The interconnection of Pb(II) ions via bridging H3L anions results in a h001i layer. The carboxylate group of the H3L anion also remains non-coordinated and is oriented toward the interlayer space. Solid state luminescent spectrum of compound 1 exhibits a strong broad blue fluorescent emission band at 455 nm under excitation at 365 nm at room temperature. q 2005 Elsevier B.V. All rights reserved. Keywords: Metal phosphonates; Hydrothermal reaction; Chain compounds; Layered materials; Fluorescence

1. Introduction During the past two decades, the chemistry of metal phosphonates has been extensively studied due to its potential applications in catalysis, molecular recognition, ion exchange, non-linear optics and sensors [1]. Metal phosphonates exhibit various structural types such as 1D chain, 2D layer and 3D open frameworks. Materials with open framework structures are expected to find their use as hybfrid composite materials in electro-optical and sensing applications in the future [2,3]. The strategy of attaching functional groups such as carboxylic acids, crown ethers and amines to the phosphonic acids has been also found to be an effective route for the synthesis of metal phosphonates with open-framework architectures [3–11]. Studies on metal amino-carboxylate-phosphonates are still relatively rare [5c,8,9,12–16]. A new layered zirconium diphosphonate fluoride, ZrHF(O3PCH2)2NHC3H6CO2, was reported * Corresponding author. Tel.: C86 5913704836; fax: C86 5913714946. E-mail address: [email protected] (J.-L. Song). 0022-2860/$ - see front matter q 2005 Elsevier B.V. All rights reserved. doi:10.1016/j.molstruc.2005.01.034

recently by Vivani, et al. [12]. Transition metal and lanthanide compounds of several amino-acid-phosphonic acids have been isolated, and their structures range from1D chain, 2D layer to 3D porous network [5c,9,11,12,17]. To further our studies on divalent metal carboxylate-phosphonates, we have synthesized a carboxylate-diphosphonate ligand, 4-HO2C–C6H4–CH2N(CH2PO3H2)2 (H5L) in which the carboxylate group is well separated from the diphosphonate moiety. Hydrothermal reactions of the above ligand with metal(II) acetates resulted in two new divalent metal carboxylate-phosphonate hybrids, namely Zn(H3L)$2H2O (1) and Pb(H3L)(H2O)2 (2). Herein we report their syntheses and crystal structures.

2. Experimental 2.1. Materials and methods All chemicals were obtained from commercial sources and used without further purification. Elemental analyses

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were performed on a Vario EL III elemental analyzer. Thermogravimetric analyses were carried out on a NETZSCH STA 449C unit at a heating rate of 15 8C/min under a nitrogen atmosphere. IR spectra were recorded on a Magna 750 FT-IR spectrometer photometer as KBr pellets in the 4000–400 cmK1. Photoluminescence analyses were performed on an Edinburgh FLS920 fluorescence spectrometer. 2.2. Preparation of H5L H5L was prepared by a Mannich type reaction of 4-(aminomethyl) benzoic acid (15.1 g, 0.1 mol), 16 ml of hydrochloric acid, 20 ml of deionized water, phosphorous acid (32.8 g, 0.4 mol) and paraformaldehyde (9.0 g, 0.3 mol) according to procedures previously described [18]. 2.2.1. Synthesis of Zn(H3L).2H2O (1) A mixture of 1.0 mmol of zinc(II) acetate, 0.5 mmol of H5L and 10.0 ml of deionized water was sealed into an autoclave equipped with a Teflon liner (25 ml), and then heated at 180 8C for 5 days. The initial and final PH values are 2.5 and 2.0, respectively. Colorless crystals of 1 were recovered in a ca. 48% yield (base on zinc). Elemental analysis for 1 C20H34N2O20P4Zn2: C, 27.33; H, 4.21; N, 3.12%. Calcd: C, 27.39; H, 3.91; N, 3.19. IR data (KBr, cmK1): 3412 s, 3010 w, 2957 w, 1718 m, 1650 m, 1417 w, 1331 m, 1253 m, 1143 vs, 1029 m, 1015 m, 924 w, 761 w, 598 w, 504 w, 466 w. 2.2.2. Synthesis of Pb(H3L)(H2O)2 (2) A mixture of 0.75 mmol of lead(II) acetate, 0.25 mmol of H5L and 10.0 ml of deionized water was sealed into an autoclave equipped with a Teflon liner (25 ml), and then heated at 110 8C for 4 days. The initial and final PH values are 3.0 and 2.5, respectively. Colorless crystals of 2 were recovered in a ca. 51% yield (base on lead). Elemental analysis for 2, C10H17NO10P2Pb: C, 20.61; H, 2.81; N, 2.52%. Calcd: C, 20.69; H, 2.95; N, 2.41. IR (KBr, cmK1): 3435 s, 2348 w, 1700 m, 1639 m, 1498 w, 1422 w, 1319 w, 1276 w, 1127 m, 1097 vs, 1054 m, 974 m, 747 w, 575 w, 468 w. 2.3. X-ray structure determination Single crystals of 1 and 2 were mounted on a Siemens Smart CCD diffractometer equipped with a graphite˚ ). Intensity monochromated MoKa radiation (lZ0.71073 A data were collected by the narrow frame method at 293 K. The data sets were corrected for Lorentz and polarization as well as for absorption by the SADABS program for 1 or j scan technique for 2 [19]. Both structures were solved by direct methods and refined by full-matrix least-squares fitting on F2 by SHELX-97 [19]. All non-hydrogen atoms, in 1 and 2 were refined with anisotropic thermal parameters. All hydrogen atoms except those of the water molecules

were located at geometrically calculated positions. Final cycle of refinements reveals featureless residual peak and ˚ from O2W) and K0.58 eA ˚3 ˚ 3 (0.63 A hole of 0.68 eA 3 ˚ ˚ ˚ (1.57 A from O31) for compound 1; and 2.11 eA (1.01 A 3 ˚ ˚ from Pb1) and K2.86 eA (1.06 A from Pb1) for compound 2, respectively. O(3w) and O(4w) of compound 1 are disordered and each has two orientations (O(3w), O(5w) and O(4w), O(6w)) with an occupancy factor of 50% for each site. Crystallographic data and structural refinements are summarized in Table 1. Important bond distances and angles are listed in Table 2. Crystallographic data (excluding structure factors) for the two structures reported in this paper have been deposited with the Cambridge Crystallographic Data Centre as supplementary publication no. CCDC Nos. 248437 and 248438. Copies of the data can be obtained free of charge on application to CCDC, 12 Union Road, Cambridge CB2 1EZ, UK (fax: C44 1223 336-033; e-mail: [email protected]). 2.4. Results and discussion Compound 1 features a 1D column structure. As shown in Fig. 1, the asymmetric unit of compound 1 contains two unique Zn(II) atoms. Both Zn(II) ions are tetrahedrally coordinated by four phosphonate oxygen atoms from four H3L anions. The Zn–O distances range from 1.900(4) to ˚ , which are comparable to those reported in other 1.960(4) A zinc (II) phosphonates [2b,8a,16a]. The H3L anion is tetradentate, and bridges with four Zn(II) ion unidentately by using its phosphonate oxygen atoms. One phosphonate Table 1 Crystal data and structure refinement for 1, and 2 Compound Formula fw Space group ˚ a/A ˚ b/A ˚ c/A a/8 b/8 g/8 ˚3 V/A Z Dc/g cmK3 m(Mo–Ka)/mmK1 F(000) Reflections collected Independent reflections Observed reflections [IO2s(I)] Goodness-of-fit (GOF) R1/wR2 [IO2s(I)] R1/wR2 (all data) R1Z

P

kFo jKjFc k=

P

1 C10H17NO10P2Zn 438.56 Pba2 11.180(2) 37.010(7) 7.9740(16) 90 90 90 3299.4(11) 8 1.766 1.734 1792 18,018 5951 [R(int)Z 0.0738] 4586

2 C10H17NO10P2Pb 580.38 PK1 6.08900(10) 8.0971(3) 16.6445(5) 94.320(2) 95.0180(10) 102.460(2) 794.48(4) 2 2.426 10.873 552 4048 2746 [R(int)Z 0.0282] 2675

1.002

1.096

0.0501/0.1026 0.0751/0.1130

0.0348/0.0948 0.0359/0.0961

jFo j;wR2 Z

P

w½ðFo Þ2 KðFc Þ2 2 =

P

w½ðFo Þ2 2

1=2

J.-L. Song, J.-G. Mao / Journal of Molecular Structure 740 (2005) 181–186 Table 2 ˚ ] for 1 and 2 Important bond lengths [A

also protonated. The interconnection of the above two types of ZnO4 tetrahedra by bridging H3L anions results in a 1D column along c-axis with the non-coordinated carboxylate group as a pendant group (Fig. 2). Two types of rings are formed: 8-member ring composed of two Zn(II) ions and two bridging phosphonate groups, and 12-member ring formed by two Zn(II) ions, one phosphonate group and one H3L anion. These columns are further interlinked via hydrogen bonds among the carboxylate groups, noncoordinated phosphonate oxygen atoms and lattice aqua molecules into a 3D network (Fig. 3). The O(2)/O(41a) (symmetry operator: KxC1/2, yK1/2, z), O(3)/O(11b) (symmetry operator: KxC1/2, yC1/2, zK1) and O(13)/ O(2wc) (symmetry operator: Kx, Ky, z) separations are ˚ , respectively (Table 2). 2.644(6), 2.607(6) and 2.784(6) A Compound 2 features a 2D layer structure. There is one unique Pb(II) ion in the asymmetric unit (Fig. 4). Pb(II) ion is seven coordinated by four phosphonate oxygen atoms from four ligands and three aqua ligands. The Pb–O ˚ , which are distances range from 2.588(5) to 2.699(5) A comparable to those reported in other lead (II) phosphonates [20]. The coordination geometry of Pb(1) can be described ad a j-PbO7 irregular polyhedron with the lone pair electrons of the Pb(II) ion occupying the eighth coordination site. The coordination mode of the ligand is the same as that in the compound 1. Each pair of Pb atoms are bridged by a pair of bridging phosphonate groups to form a dimeric unit, and these dimeric units are bridged by H3L anions into a h001i 2D layer (Fig. 5). The interlayer distance is about ˚ . The carboxylate moieties of the H3L anions are 16.6 A orientated into the interlayer space. These layers are further interlinked via hydrogen bonds among the carboxylate groups, phosphonate oxygen atoms and lattice water molecules into a 3D network (Fig. 6). The O(1W)/O(22) (symmetry operator: KxC1, KyC2, KzC2), O(2W)/

Compound 1 Zn(2)–O(21)#1 Zn(2)–O(22) Zn(2)–O(33)#2 Zn(2)–O(43) Zn(1)–O(32)#1 Zn(1)–O(23) Zn(1)–O(31) Zn(1)–O(12)#3 C(1)– O(1) C(1)–O(2) C(11)–O(6) C(11)–O(7) O(2)/O(41)#6 O(3)/O(11)#5 Compound 2 Pb(1)–O(12)#1 Pb(1)–O(11)#2 Pb(1)–O(21) Pb(1)–O(13)#3 Pb(1)–O(2W)#4 Pb(1)–O(1W) Pb(1)–O(2W) C(7)–O(2) O(1W)/O(22)#8 O(2W)/O(22)#3

1.900(4) 1.924(4) 1.936(4) 1.960(4) 1.916(4) 1.940(5) 1.941(4) 1.949(4) 1.303(8) 1.217(8) 1.305(8) 1.224(8) 2.644(6) 2.607(6)

P(1)–O(3) P(1)–O(4) P(1)–O(5) P(2)–O(8) P(2)–O(9) P(2)–O(10) P(3)–O(11) P(3)–O(12) P(3)–O(13) P(4)–O(14) P(4)– O(15) P(4)– O(16) O(13)/O(2W)#4

1.497(5) 1.570(5) 1.484(4) 1.517(5) 1.502(5) 1.526(5) 1.506(5) 1.518(5) 1.502(5) 1.494(4) 1.497(4) 1.568(5) 2.784(6)

2.588(5) 2.590(5) 2.597(5) 2.602(5) 2.628(5) 2.668(5) 2.699(5) 1.315(10) 2.740(7) 2.736(7)

P(1)–O(11) P(1)–O(12) P(1)–O(13) P(2)– O(21) P(2)– O(22) P(2)– O(23) C(7)–O(1)

1.529(5) 1.516(5) 1.540(5) 1.518(5) 1.520(5) 1.565(5) 1.207(11)

O(2)/O(13)#5 O(1W)/O(22)#7

2.595(7) 2.740(7)

183

Symmetry transformations used to generate equivalent atoms: for 1 #1; K xC1, Ky, z; #2 x, y, zC1; #3 x, y, zK1; #4 Kx, Ky, z; #5 KxC1/2, yC1/ 2, zK1; #6 KxC1/2, yK1/2, z. For 2: #1 KxC1, KyC1, KzC2; #2 xC1, yC1, z; #3 x, yC1, z; #4 KxC2, KyC2, KzC2; #5 KxC1, Ky, KzC1; #6 xK1, yK1, z; #7 x, yK1, z; #8 KxC1, KyC2, KzC2; #9 xK1, y, z.

group (O(21), O(22), and O(23)) of H3L is tridentate, whereas the other one is singly protonated and is unidentate. The amine group and the carboxylate group of H3L anion are also 1H-protonated and remain non-coordinated. The oxygen atoms (O(1) and O(4)) of benzoic acid moieties are Zn1a O11 O12 O13

O33a

P1

N1

O22 Zn2 P2

O2

O43

Zn2b O21

O21b

O1

O23

O42

O32

O32b O12c

P4

O41

Zn1b

O3 N2

Zn1 O31

O4

P3 O33

Zn2c

Fig. 1. ORTEP representation of the asymmetric unit of compound 1. The thermal ellipsoids are drawn at 50% probability. The lattice water molecules have been omitted for clarity. Symmetry code: a: x, y, 1Cz; b: 1Kx, Ky, z; c: x, y, K1Cz.

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a

b c

Fig. 2. A 1D column of zinc phosphonate along the c-axis in 1. The ZnO4, CPO3 tetrahedra are shaded in dark and light gray, respectively. The –CH2– C6H4–COOH moieties have been omitted for clarity.

b a

Fig. 5. A h001i layer in 2. The CPO3 tetrahedra are shaded in light gray. Pb, N and O atoms are drawn as open, gray and crossed circles, respectively. The –CH2–C6H4–COOH groups have been omitted for clarity.

Fig. 3. View of the structure of 1 down the c-axis. The ZnO4, CPO3 tetrahedra are shaded in dark and light gray, respectively. N, C and O atoms are represented by gray, black and crossed circles, respectively. Hydrogen bonds are drawn as dotted lines.

O(22) (symmetry operator: x, yC1, z), O(1W)/O(22) (symmetry operator: xK1, y, z) and O(2)KO(13) (symmetry operator: 1Kx, Ky, 1Kz), separations are 2.740(7), ˚ , respectively. 2.736(7), 2.740(7), and 2.595(7) A The broad IR bands at 3412 and 3010 cmK1 for compound 1 can be assigned to the O–H stretching vibrations, such band appeared at 3435 for compound 2. The absorption bands at 1720 and 1435 cmK1 for the carboxylate group in the free ligand [18] have been shifted

slightly to 1718 and 1417 cmK1 in compound 1; and 1700 and 1422 cmK1 for compound 2. These shifts are relatively small due to the non-coordination nature of the carboxylate groups in both compounds. The bands from 900 to 1100 cmK1 are due to the stretching vibrations of the tetrahedral CPO3 group in compound 1 and 2. 2.5. Luminescence property and TGA study The solid-state luminescent property of compound 1 was studied at room temperature. The free carboxylate-diphosphonate H5L ligand shows no emission in the visible region. The emission spectrum of zinc (II) phosphonate, compounds 1, exhibits a strong blue fluorescent emission band at lmaxZ455 nm under excitation at 365 nm, as depicted in Fig. 7. The origin of the emission band of 1 is

b c

Fig. 4. ORTEP representation of the selected unit in 2. The thermal ellipsoids are drawn at 50% probability. Symmetry codes: a: 2Kx, 2Ky, 2Kz; b: 1Kx, 1Ky, 2Kz; c: x, K1Cy, z; d: K1Cx, K1Cy, z; e: 1Cx, 1C y, z; f: x, 1Cy, z.

a

Fig. 6. View of the structure of 2. The CPO3 tetrahedra are shaded in light gray. Pb, N, C and O atoms are drawn as open, gray, black and crossed circles, respectively.

Intensity of Fluorescence (ArbitraryUnits)

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15.1%. No theoretical value can be used for comparison since the intermediate products were not characterized. The second step started from 629 8C and continued up to 1000 8C, corresponding to the further combustion of the phosphonate ligand. The final product is mainly Pb(PO3)2 mixed with small amount of other unidentified compounds. The total weight loss of 29.3% is much lower than the calculated value (37.1%) if compound 2 has been completely converted to be Pb(PO3)2. The incompleteness of the decomposition can also be evidenced from the slope of its TGA curve.

455 nm (ex 365 nm)

15000

10000

5000

400

500

600

700

Wavelength (nm )

Acknowledgements

Fig. 7. Solid-state emission spectrum of compound 1 at room temperature.

neither due to metal-to-ligand charge transfer (MLCT) nor ligand-to-metal charge transfer (LMCT) in nature, but can be attributed to an intra-ligand emission state, as reported for other zinc(II) complexes with carboxylate-diphosphonate ligands [21]. The TGA curves of 1 reveal three main steps of weight losses (Fig. 8). The first one began at 83 8C and completed at 176 8C, which corresponds to the release of two lattice water molecules. The weight loss of 7.3% is slightly smaller than the calculated value of 8.2%. The second step covers a temperature range of 280–715 8C, which corresponds to the partial decomposition of the phosphonate ligand. The third step started from 795 8C and continued up to 1000 8C, corresponding to the further combustion of the phosphonate ligand. The final product is Zn(PO3)2. The total weight loss of 50.5% is slightly less than the calculated value (50.9%). There are two main steps of weight losses for compound 2. The first step started from 155 8C and completed at 544 8C, corresponding to the release of two aqua ligands and the partial decomposition of phosphonate ligands. The weight loss is 100 Compound 2

Weight (%)

90 80 70 Compound 1

60 50 200

400

600

185

800

Temperature (°C ) Fig. 8. TGA curves for compounds 1 and 2.

1000

This work was supported by the National Natural Science Foundation of China (20371047) and NSF of Fujian Province (No. E0420003). We thank Prof. Han-Hua Zhao for his great help with the data collection for compound 1.

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