Synthesis and properties of four transition metal complexes of 5-mercapto-1H-tetrazole-1-acetic acid

Polyhedron 33 (2012) 203–208

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Synthesis and properties of four transition metal complexes of 5-mercapto-1H-tetrazole-1-acetic acid Qing Yu, Fu-Ping Huang, Zu-Mei Yang, Jing Jin, He-Dong Bian ⇑, Hong Liang ⇑ Key Laboratory for the Chemistry and Molecular Engineering of Medicinal Resources (Ministry of Education of China), School of Chemistry & Chemical Engineering of Guangxi Normal University, Guilin 541004, PR China

a r t i c l e

i n f o

Article history: Received 17 June 2011 Accepted 16 November 2011 Available online 28 November 2011 Keywords: Transition metal complexes Fascinating structure Photoluminescence Magnetic properties

a b s t r a c t Four transition metal complexes with 5-mercapto-1H-tetrazole-1-acetic acid (H2mtaa), namely [Zn(mtaa)(H2O)]n (1), [Cd(mtaa)(H2O)]n (2), [Mn(Hmtaa)2(H2O)2]n (3) and [Co(Hmtaa)2(H2O)2]n (4), have been synthesized and characterized by X-ray crystallography. In 1, the left and right-handed helices are interconnected to form a double helix, with further linkages via the mtaa ions to form a two-dimensional layer. While in 2, the mtaa ions bridge the interconnected helices to yield a three-dimensional structure. In 3 and 4, the carboxylate groups bridge metal atoms in a syn–anti conformation, leading to a twodimensional sheet. In addition, the photoluminescence of 1 and 2 and the magnetic properties of 3 were investigated. Ó 2011 Elsevier Ltd. All rights reserved.

1. Introduction Metal–organic frameworks (MOFs) have recently attracted intense attention in the field of crystal engineering, due to not only their intriguing supramolecular compositions and versatile framework topologies, but also their potential applications as functional materials in molecular magnetism, catalysis, gas sorption, electrical conductivity, optics, etc. [1–5]. As well as slow evaporation of solvents, gas or liquid diffusion, new synthetic methods used for the preparation of MOFs have been developed, such as solvothermal and microwave approaches [6]. Organic ligands and metal ions are considered the ‘‘primary building units’’, and considerable efforts have been devoted to the design and synthesis of novel ligands comprising multiple coordination sites which can bridge metal atoms into MOFs [7]. Among the various organic ligands, polydentate ligands, such as bifunctional tetrazolyl–carboxylate ligands [8,9], have been extensively investigated and have proved to be a rational choice to synthesize coordination polymers possessing intriguing structural varieties and potential applications. In our previous studies, tetrazole-1-acetic acid was used to construct novel coordination polymers. In those complexes, not only the carboxylate but also the tetrazolyl possessed abundant coordination modes [10]. 1-Organyl-tetrazol-5-thiones are interesting ligands from a structural point of view since they can display a wide range of

⇑ Corresponding authors. E-mail addresses: [email protected] (H.-D. Bian), lianghongby@ya hoo.com.cn (H. Liang). 0277-5387/$ - see front matter Ó 2011 Elsevier Ltd. All rights reserved. doi:10.1016/j.poly.2011.11.036

coordination patterns with metal ions. Due to a variety of potential coordination sites, they can act as monodentate (S or N) or bidentate (N, N or N, S) ligands, forming polymers or interacting with metal ions through their p-electron density [11]. Encouraged by the previous results, we selected 5-mercapto-1H-tetrazole-1-acetic acid (H2mtaa) in order to construct novel transition coordination polymers with fascinating structures. As is well known, the mercapto S atom as well as the carboxylate O atoms and the tetrazolyl ring N atoms can coordinate to metal atoms. So, H2mtaa is a multifunctional ligand. H2mtaa has many coordination modes, (I) in Scheme 1 has previously been reported [12]. Herein, we report four coordination polymers. Two new coordination modes of H2mtaa have been found (Scheme 1).

2. Experiment 2.1. Materials and measurements All the starting reagents were of A.R. grade and were used as purchased. The IR spectra were obtained on a Perkin-Elmer Spectrum One FT-IR spectrometer in the range 4000–400 cm1 using KBr pellets. Elemental analyses for C, H, N and S atoms were carried out on a Model 2400 II Perkin-Elmer elemental analyzer. X-ray powder diffraction (XRD) intensities were measured on a Rigaku D/max diffractometer (Cu Ka, k = 1.54056 Å). The single-crystalline powder samples were prepared by crushing the crystals and they were scanned from 3° to 70° with a step of 5° min1. Calculated patterns of the complexes were generated with PowderCell. Steady state fluorescence measurements were performed using an FL3-P-TCSPC

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M

M

O

S M

O

M

M (I)

M

N

HN

N

N

N

N

N

N

N

N

N

N

S

O

M

M

O

M

S

O

O

M

M (III)

(II) Scheme 1. The coordination modes of H2mtaa.

Steady-State & Time-Resolved Fluorescence spectrofluorometer at ambient temperature in the solid state. The variable temperature susceptibility measurements on microcrystalline samples were carried out with a MPMS XL-7 SQUID magnetometer in the temperature range 2.0–300.0 K at a magnetic field of 1000 Oe. A diamagnetic correction to the observed susceptibilities was applied using Pascal’s constants. 2.2. Syntheses of the complexes 2.2.1. Synthesis of [Zn(mtaa)(H2O)]n (1) H2mtaa (0.1602 g, 1 mmol) was dissolved in distilled water (10 mL). Then ZnO powder (0.08139 g, 1 mmol) was added. The mixture was stirred at 90 °C for 3 h and then cooled. The suspension was filtrated. The filtrate was allowed to slowly concentrate by evaporation at room temperature. Three months later, a colorless block crystal was obtained. Yield: 0.1691 g (70%, based on Zn(II)). Anal. Calc. for C3H4N4O3SZn: C, 14.92; H, 1.67; N, 23.20; S, 13.28. Found: C, 14.85; H, 1.53; N, 23.43; S, 13.49%. IR (cm1): 3165 (ms), 2955 (ms), 1652 (vs), 1404 (ms), 1379 (vs), 1282 (vs), 1208 (ms), 1131 (w), 820 (ms). 2.2.2. Synthesis of [Cd(mtaa)(H2O)]n (2) This was synthesized similarly to 1, except that CdO (0.1284 g, 1 mmol) was used instead of ZnO. The crystals obtained were

beautiful light yellow blocks. Yield: 0.1962 g (68%, based on Cd(II)). Anal. Calc. for C3H4N4O3SCd: C, 12.49; H, 1.40; N, 19.42; S, 11.11. Found: C, 12.55; H, 1.50; N, 19.53; S, 11.29%. IR (cm1): 3518 (ms), 2922 (ms), 1614 (vs), 1508 (ms), 1444 (ms), 1388 (ms), 1354 (ms), 819 (w). 2.2.3. Synthesis of [Mn(Hmtaa)2(H2O)2]n (3) H2mtaa (0.1602 g, 1.0 mmol) was dissolved in distilled water (5 mL), and then a solution of Mn(ClO4)26H2O (0.3620 g, 1 mmol) in H2O (5 mL) was added dropwise. The pH value was adjusted to 4.0 with triethylamine. The mixture was stirred at 80 °C for 2 h and then cooled and filtered. The filtrate was allowed to slowly concentrate by evaporation at room temperature. Two months later, light yellow block crystals were obtained. Yield: 0.2988 g (73%, based on Mn(II)). Anal. Calc. for C6H10MnN8O6S2: C, 17.61; H, 2.46; N, 27.38; S, 15.67. Found: C, 17.85; H, 2.53; N, 27.43; S, 15.79%. IR (cm1): 3524 (ms), 3080 (ms), 2956 (ms), 1621 (vs), 1508 (ms), 1440 (ms), 1417 (w), 1388 (ms), 1355 (ms), 1322 (ms), 1101 (w), 816 (w). 2.2.4. Synthesis of [Co(Hmtaa)2(H2O)2]n (4) A solution of CoCl26H2O (0.2379 g, 1 mmol) in H2O (5 mL) was added dropwise to a solution of H2mtaa (0.1602 g, 1.0 mmol) in THF (5 mL). The pH value was adjusted to 4.0 with triethylamine. The mixture was stirred at 80 °C for 2 h and then cooled and

Table 1 Crystal data and structure refinement summary for complexes 1–4. Complex

(1)

(2)

(3)

(4)

Empirical formula Formula weight Crystal system Space group a (Å) b (Å) c (Å) b (°) V (Å3) Z Calculated density (mg/m3) Absorption coefficient (mm1) F(0 0 0) Crystal size (mm3) h range for data collection (°) Limiting indices

C3H4N4O3SZn 241.53 monoclinic P2(1)/n 6.607(2) 8.627(3) 12.793(4) 103.281(4) 709.6(4) 4 2.261 3.723 480 0.40  0.19  0.15 2.87–25.01 6 6 h 6 7 10 6 k 6 9 15 6 l 6 14 3598 1249 [R(int) = 0.0271] 1249/3/109 1.009 R1 = 0.0212 wR2 = 0.0518 R1 = 0.0257 wR2 = 0.0546

C3H4N4O3SCd 288.56 monoclinic Cc 14.5188(14) 7.0134(5) 7.3808(9) 110.8030(10) 702.56(12) 4 2.728 3.373 552 0.09  0.08  0.05 3.00–25.02 16 6 h 6 17 8 6 k 6 7 8 6 l 6 6 1739 1042 [R(int) = 0.0712] 1042/2/109 1.055 R1 = 0.0371 wR2 = 0.0904 R1 = 0.0381 wR2 = 0.0915

C6H10MnN8O6S2 409.30 monoclinic P21/c 7.6253(2) 7.1141(2) 27.1040(6) 91.206(2) 1469.99(7) 4 1.849 1.228 828 0.40  0.20  0.12 2.96–26.37 9 6 h 6 8 8 6 k 6 8 33 6 l 6 33 7647 2995 [R(int) = 0.022] 2995/2/222 1.087 R1 = 0.0321 wR2 = 0.0776 R1 = 0.0405 wR2 = 0.0848

C6H10CoN8O6S2 413.27 monoclinic C2/c 27.913(3) 7.0475(9) 7.4912(12) 104.656(2) 1425.7(3) 4 1.925 1.543 836 0.27  0.25  0.11 1.51–25.01 23 6 h 6 32; 6 6 k 6 8; 8 6 l 6 8 3411 1249 [R(int) = 0.0340] 1249/0/106 1.095 R1 = 0.0593 wR2 = 0.2132 R1 = 0.0658 wR2 = 0.2196

Reflections collected Independent reflections Data/restraints/parameters Goodness-of-fit (GOF) on F2 Final R indices [I > 2r(I)] R indices (all data)

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Q. Yu et al. / Polyhedron 33 (2012) 203–208 Table 2 Selected bond distances (Å) and angles (°) for 1–4. 1 (symmetry codes: A: x + 1, y  1/2, z + 1/2; B: x + 2, y  1/2, z + 1/2; C: x  1, y, z) Zn1–O3 1.992(2) Zn1–N4 2.023(2) Zn1–O2B 2.046(2) O3–Zn1–N4 118.5(8) O3–Zn1–O2B 87.9(7) N4–Zn1–O2B 99.3(8) O3–Zn1–S1A 116.5(6) N4–Zn1–S1A 116.9(6)

Zn1–S1A Zn1– O1C

2.303(9) 2.459(2)

O2B–Zn1–S1A O3–Zn1–O1C N4–Zn1–O1C O2B–Zn1–O1C S1A–Zn1–O1C

110.8(6) 79.3(7) 82.4(7) 166.1(7) 80.1(5)

2 (symmetry codes: A: x, y + 2, z + 1/2; B: x  1/2, y  1/2, z; C: x  1/2, y + 1/2, z; D: x  1/2, y + 3/2, z + 1/2) Cd1–O2A 2.259(7) Cd1–N3B Cd1–O1 2.295(7) Cd1–S1C Cd1–O3 2.336(8) Cd1–S1D O2A–Cd1–O1 85.3(3) O3–Cd1–S1C O2A–Cd1–O3 79.7(3) N3B–Cd1–S1C O1–Cd1–O3 94.3(3) O2A–Cd1–S1D O2A –Cd1–N3B 157.6(3) O1–Cd1–S1D O1–Cd1–N3B 79.7(3) O3–Cd1–S1D O3–Cd1–N3B 85.0(3) N3B–Cd1–S1D O2A–Cd1–S1C 97.4(2) S1C–Cd1–S1D O1–Cd1–S1C 78.5(2) 3 (symmetry codes: A: x + 1, y  1/2, z + 1/2; B: x, y + 1/2, z + 1/2) Mn1–O2A 2.165(2) Mn1–O3 Mn1–O1 2.167(2) Mn1–O5 Mn1–O4B 2.167(2) Mn1–O6 O2A–Mn1–O1 84.4(6) O4B–Mn1–O5 O2A–Mn1–O4B 179.4(5) O3–Mn1–O5 O1–Mn1–O4B 96.1(6) O2A–Mn1–O6 O2A–Mn1–O3 94. 8(6) O1–Mn1–O6 O1–Mn1–O3 178.1(5) O4B–Mn1–O6 O4B–Mn1–O3 84.7(6) O3–Mn1–O6 O2A–Mn1–O5 89.8(7) O5–Mn1–O6 O1–Mn1–O5 86.8(6) 4 (Symmetry codes: A: x + 1/2, y + 1/2, z + 1; B: x, y, z  1/2; C: x + 1/2, y + 1/2, z + 3/2) Co1–O1 2.089(5) Co1–O2B Co1–O3 2.089(5) O1–Co1–O3A 87.8(2) O3–Co1–O2C O1–Co1–O2B 95.6(2)

2.354(9) 2.604(3) 2.636(3) 172.5(2) 95.7(2) 109.3(2) 164.3(2) 93.9(2) 87.8(2) 93.6(8)

2.172(2) 2.189(2) 2.190(2) 90.7(7) 91.5(6) 90.8(7) 94.4(6) 88.8(7) 87.3(6) 178.8(6)

2.101(5) 90.4(2)

filtered. The filtrate was allowed to slowly concentrate by evaporation at room temperature. Two months later, red prism crystals were obtained. Yield: 0.2728 g (66%, based on Co(II)). Anal. Calc. for C6H10CoN8O6S2: C, 17.44; H, 2.44; N, 27.11; S, 15.52. Found: C, 17.85; H, 2.53; N, 27.23; S, 15.49%. IR (cm1): 3536 (ms), 2925 (w), 1603 (vs), 1423 (ms), 1380 (vs), 1319 (w), 1294 (ms), 1026 (w), 811 (w). 2.3. Crystal structure determination X-ray crystal data collection for the four complexes was performed on a Bruker Smart 1000 CCD diffractometer with monochromated Mo Ka radiation (k = 0.71073 Å) at 298 K (Table 1). Semi-empirical absorption corrections were applied using the SADABS program. All calculations were carried out with SHELXS-97 and SHELXL-97 [13,14]. The structures were solved by direct methods and refined on |F|2 by the full-matrix least squares method. Selected bond lengths and angles are listed in Table 2. 3. Results and discussion 3.1. Description of the crystal structures The molecular structure of complex 1 is shown in Fig. 1. The Zn1(II) ion is five-coordinated by two carboxylate O atoms (O1C and O2B), one S atom (S1A), one N atom (N4) and one O atom (O3) from a water molecule. As for the local coordination polyhedron of the Zn(II) ion, the s value is 0.79 (s = (b  a)/60), indicating

Fig. 1. View of the coordination environment of the Zn(II) ions in 1 (H atoms are omitted for clarity). Symmetry code: A: x + 1, y  1/2, z + 1/2; B: x + 2, y  1/2, z + 1/2; C: x  1, y, z.

a trigonal bipyramidal geometry. One tetrazolyl N, one S and one O atom of water form the equatorial plane around the Zn1 atom. Two carboxyl O atoms from two different mtaa ligands are in axial

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positions around Zn1. The Zn–O bond lengths are in the range 1.9913(17) to 2.4589(18) Å, which is normal for Zn(II) complexes [15]. In complex 1, each mtaa bridges four Zn(II) ions (mode I). On one hand, the S atom and 4-N atom bridge two Zn(II) ions with a Zn  Zn separation of 4.542(2) Å, leading to an infinite onedimensional left-handed helical chain with a 21 screw axis along the b-axis (Fig. 2a). On the other hand, the carboxylate groups bridge the Zn(II) ions forming a one-dimensional right-handed helical chain (Fig. 2a). The left and right-handed helices interconnect to form a double helix with a hitch of 8.627(3) Å. Each mtaa ligand takes part in left and right-handed helices of different double helices, thus the mtaa ligand links the double helices into twodimensional layers (Fig. 2b). The mercapto group of the ligand in complex 1 is deprotonated and coordinates to the metal ion (mode I). The carboxylate group shows the expected trigonal geometry with carbon–oxygen bond distances of [C2–O1] 1.226(3) and [C2–O2] 1.279(3) Å, and an O– C–O intracarboxylate bond angle [O1–C1–O2] of 126.2(2)°. In the ligand, the angle between the carboxylate and the tetrazolyl groups is 72.2(2)°. The single-crystal X-ray diffraction analysis shows that complex 2 exhibits a novel three-dimensional structure involving doublestranded helices. There is one crystallographically independent Cd(II) center in the asymmetric unit. Each octahedral Cd(II) ion completes its six-coordination by two S atoms, two O atoms and one N atom from five different mtaa ligands, and one O atom from a water molecule. The O atom of the water molecule and one S atom occupy the axial positions, with Cd–O and Cd–S bond lengths of 2.336(8) and 2.636(3) Å, respectively. One N atom (Cd–N, 2.354(3) Å) and one S atom (Cd–S, 2.604(2) Å), and two O atoms (average Cd–O bond length: 2.277 Å) are located in the equatorial plane. The bond lengths in 2 are normal to other Cd(II) complexes [16]. Each mtaa ligand links five Cd(II) ions (mode II). The most striking features of 2 are the interesting arrangement of the mtaa molecules and the unusual coordination of the cadmium atom, forming a unique helical structure. As shown in Fig. 3, the Cd[NO3S2] subunits are alternately bridged by l2-SH and syn–anti carboxylate groups, resulting in a left and a right-handed (Fig. 4a) helix. The two helices are interconnected to form a double helix running along a crystallographic 21 axis in the b direction, with a pitch of 7.473(2) Å, which is equal to the corresponding unit cell length b. Each double helix is connected with six other helices by the flexible mtaa ligands to yield a threedimensional structure (Fig. 4b). In 2, the nearest Cd(II) atoms are

Fig. 3. View of the coordination environment of the Cd(II) ions in 2 (H atoms are omitted for clarity). Symmetry code: A: x, y + 2, z + 1/2; B: x  1/2, y  1/2, z; C: x  1/2, y + 1/2, z; D: x  1/2, y + 3/2, z + 1/2.

bridged by a syn–anti carboxylate group, together with an S atom, with a Cd1  Cd1A separation of 4.147(2) Å. In complex 2, the S atom is deprotonated and bridges two Cd(II) ions with an asymmetric Cd–S bond (mode II). The C–O bonds (1.234(12) and 1.245(13) Å) and O–C–O angle (125.2(10)°) in the carboxylate group show that the carboxylate group can be ionized. In the ligand, the angle between the carboxylate and the tetrazolyl groups is 74.4(8)°. The molecular structures of complexes 3 and 4 are similar, therefore, only the structure of 3 is shown in Fig. 5. The central Mn(II) is sixcoordinated by four oxygen atoms from four bridging carboxylate groups of Hmtaa ligands and two water molecules. The Mn(II) center has a distorted octahedral geometry with two O atoms of water molecules in the axial positions and four carboxylate O atoms in the equatorial plane. The carboxylate groups bridge the Mn(II) atoms in

Fig. 2. (a) 1D double-helix composed of left and right-handed helical chains. (Red for carboxylate groups and purple for the S–N–C atoms of the tetrazolyl groups.) (b) View of 2D layers along the ab plane of complex 1 (Color online).

Q. Yu et al. / Polyhedron 33 (2012) 203–208

207

Fig. 4. (a) 1D double-helix constructed from left and right-handed helical chains. (b) The 3D helical supramolecular framework of complex 2 viewed along the b-axis.

Fig. 5. View of the coordination environment of the Mn(II) atoms in 3 (H atoms are omitted for clarity). Symmetry code: A: x, y + 1, z  1/2; B: x + 3/2, y + 1/2, z + 3/2; C: x + 3/2, y + 3/2, z + 1.

a syn–anti conformation, with a Mn  Mn separation of 5.187(1) Å, leading to a two-dimensional sheet in the bc plane (Fig. 6). In complex 3, the mercapto group of the ligand does not coordinate to the metal ions (mode III). The ligands in 3 mainly adopt the –N–C(@S) form with C–S bond lengths of 1.671(3) and 1.672(3) Å, which are similar to the values found in another metal complex with the mercaptotetrazole ligand [17]. Similar to 1 and 2, the carboxylate group in 3 shows the expected trigonal geometry with carbon–oxygen bond distances of 1.253(2) and 1.254(2) Å for C1, and 1.247(2) and 1.259(2) Å for C4. The O–C–O intracarboxylate bond angles are 125.3(2) and 125.9(2)° for C1 and C4, respectively. 3.2. X-ray power diffraction (XRD) results To confirm whether the crystal structures are truly representative of the bulk materials, XRD patterns of complexes 1–3 were recorded at room temperature (Fig. S1–S3). Although minor differences can be seen in the positions, intensities and widths of some peaks, the results still indicate favorably that the bulk synthesized materials and the as-grown crystals are homogeneous for 1–3. 3.3. Luminescent properties In general, the fluorescence properties of inorganic–organic hybrid coordination complexes, especially with d10 metal centers,

have been investigated owing to their potential applications as photoactive materials [18]. In this paper, the photoluminescent properties of the free H2mtaa ligand, 1 and 2 have been investigated in the solid state at room temperature. The solid state luminescent analyses show that the complexes exhibit different properties (Fig. S4). The fluorescence of the free ligand H2mtaa and 2 is very weak, and the emission spectrum of complex 1 under the excitation wavelength 419 nm shows a broad fluorescent emission centered on 501 nm. The excited-state origins for 1 seem to be due to a ligand-to-metal charge-transfer transition (LMCT) [19]. In this way, the emission color and intensity of the free ligand H2mtaa is significantly affected by its incorporation into complexes containing metal ions. Thus the difference in the intensity of emission results from the different d10 transition-metals, which suggests that the change of radius and coordination geometry has an important effect on the fluorescent properties [20].

3.4. Magnetic properties The magnetic susceptibility was measured in the temperature range 2–300 K (Fig. S5). The value of vMT at 300 K for 3 is 4.43 cm3 K mol1. As the temperature is lowered, vMT decreases regularly to 1.68 cm3 K mol1 at 2 K. The data can be fitted by the expansion series of lines for an S = 5/2 antiferromagnetic quadratic

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Appendix A. Supplementary data CCDC 806320, 806321, 806322, and 806323 contain the supplementary crystallographic data for 3, 1, 4 and 2. These data can be obtained free of charge via http://www.ccdc.cam.ac.uk/conts/ retrieving.html, or from the Cambridge Crystallographic Data Centre, 12 Union Road, Cambridge CB2 1EZ, UK; fax: (+44) 1223-336033; or e-mail: [email protected]. Supplementary data associated with this article can be found, in the online version, at doi:10.1016/j.poly.2011.11.036. References

Fig. 6. The 2D layers linked by carboxylate groups of complex 3 viewed in the bc plane.

P layer [21], based on the exchange Hamiltonian H = nn  JSi  Sj which runs over all pairs of nearest-neighbor spins i and j, Eq. (1)

X Cn Ng 2 l2B ¼ 3h þ vjJj hn1

ð1Þ

where h = kT/|J|S(S + 1), C1 = 4, C2 = 1.448, C3 = 0.228, C4 = 0.262, C5 = 0.119, C6 = 0.017, and N, g and lB have their usual meanings. The best fit is given by the super exchange parameter g = 2.021(2), J = 0.288(3) cm1. The J value is small and negative, which indicates weak antiferromagnetic coupling in this complex. In previous literature, polynuclear manganese(II) complexes bridged by carboxylate groups show small and negative J values, which is usually indicative of antiferromagnetic behavior. Generally, the magnitude of |J| increases with the number of carboxylate bridges [22]. In addition, the |J| value is highly dependent on the conformation modes of the bridge between the metal centers. The syn–syn mode causes a larger |J| value than the other triatomic bridges, while the l2, g1-carboxylato bridges are less capable of transmitting magnetic interactions than l2, g2-carboxylato bridges [23]. In our case, the Mn(II) ions are bridged by single carboxylate groups in the syn–anti mode, which indicates that there is a weak exchange coupling between the metal centers. The exchange (J = 0.288 cm1) is comparable to those reported for other singly bridged Mn(II) complexes [23,24].

4. Conclusion In summary, we have successfully synthesized four new hybrids based on a new mercapto-, carboxylate-containing ligand, 5-mercapto-1H-tetrazole-1-acetic acid, with metal salts. The results reveal that it is promising to build up specific structures via the combination of transition metals and mercapto-carboxylate ligands. The varied coordination modes of the ligand found in the present work prove that it is a useful building block in the preparation of novel hybrid frameworks with potential magnetic and luminescent properties. Acknowledgements We gratefully acknowledge the National Natural Science Foundation of China (No. 21061002) and the Guangxi Natural Science Foundation of China (2010GXNSFF013001, 2011GXNSFC018009, 0832098).

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