FULL PAPER
Dalton
Miao Du,* Xiao-Jun Zhao and Ying Wang College of Chemistry and Life Science, Tianjin Normal University, Tianjin 300074, P. R. China. E-mail:
[email protected]; Fax: +86-22-23540315; Tel: +86-22-23540315
www.rsc.org/dalton
Crystal engineering of a versatile building block toward the design of novel inorganic–organic coordination architectures†
Received 8th March 2004, Accepted 19th May 2004 First published as an Advance Article on the web 14th June 2004
Six novel inorganic–organic coordination supramolecular networks based on a versatile linking unit 4-pyridylthioacetate (pyta) and inorganic CoII, CuII, AgI, ZnII, MnII and PbII salts have been prepared in water medium and structurally characterized by single-crystal X-ray diffraction analysis. Reaction of CoCl2·6H2O with Hpyta afforded a neutral mononuclear complex [Co(pyta)2(H2O)4] (1), which exhibits a two-dimensional (2-D) layered architecture through intermolecular O–HO interactions. Reaction of CuCl2·2H2O with Hpyta yielded a neutral one-dimensional (1-D) coordination polymer {[Cu(pyta)2(H2O)]·0.5H2O}n (2) consisting of rectangle molecular square units, which show a three-dimensional (3-D) supramolecular network through SS and O–HO weak interactions. However, when AgNO3, Zn(OAc)2·2H2O or MnCl2·4H2O salts were used in the above self-assembled processes, the neutral 2-D coordination polymers [Ag(pyta)]n (3), {[Zn(pyta)2]·4H2O}n (4) or {[Mn(pyta)2(H2O)]}n (5) with different topologies were obtained, respectively. While substituting the transition metal ions used in 1–5 with Pb(OAc)2·3H2O, a one-dimensional coordination polymer [Pb(pyta)2]n (6), which shows a novel 2-fold interpenetrating 2-D supramolecular architecture through weak SS interactions, was isolated. It is interesting to note that the building block pyta anion exhibits different configurations and coordination modes in the solid structures of complexes 1–6. These results indicate that the versatile nature of this flexible ligand, together with the coordination preferences of the metal centers, play a critical role in construction of these novel coordination polymers or supramolecules. The spectral and thermal properties of these new materials have also been investigated.
Introduction
DOI: 10.1039/b403498h
Self-assembly processes involving metal ions and well-designed organic ligands have attracted considerable attention currently in the field of supramolecular chemistry and crystal engineering from the viewpoints of the development of new materials with unique electronic, magnetic, catalytic and optical properties.1–4 So far, a variety of discrete and a wide range of one- or multi-dimensional infinite solid-state coordination architectures have been achieved in the last decade,1–4 however, the crystal engineering of coordination frameworks with desired topologies and specific properties still remains a difficult challenge since it depends on a variety of factors that can influence the self-assembly process.5 Basically, the design of proper ligands as “building blocks”, together with the coordination preferences of the metal centers as “nodes”, is undoubtedly the most rational synthetic strategy in manipulating the framework topologies and thus modifying the properties of these materials. In our attempt to investigate the design and control of the selfassemblies of inorganic–organic coordination architectures, we have initiated a synthetic program for the construction of various supramolecular complexes with interesting extended frameworks based on the angular dipyridyl rigid ligands.6 In this work, we chose 4pyridylthioacetic acid (Hpyta) as a flexible multifunctional building block considering its following advantages compared with the usual rigid ligands: (i) it has two possible configurations (gauche and anti, see Chart 1 below) and possesses flexible connection modes that will lead to novel topological architectures upon metal complexation under appropriate conditions. One of the rare and interesting phenomena occurring during self-assembly is a conformational change of a flexible building block, especially for leading to show a supra† Electronic supplementary information (ESI) available: Fig. S1. Calculated and experimental XRPD patterns for complexes 1, 2, 3, 5 and 6, respectively (from bottom to top). Fig. S2. View of the SS interactions between adjacent coordination chains in 2. Fig. S3. The stacking diagram (space-filling model) of the parallel coordination frameworks along [100] direction showing the cavities for 4. Fig. S4. 3-D hydrogen-bonding supramolecular architecture view along [010] direction for 5. Fig. S5. View of the 2-fold interpenetrating 2-D supramolecular architecture in 6. See http://www.rsc.org/suppdata/dt/b4/b403498h/
molecular isomerism by altering the geometry of the ligand,1e which results in an increase of enthalpy; (ii) it has three potential binding sites when coordinating to a metal center. A carboxylate binding group exhibiting a variety of coordination modes7 usually makes the ligand anionic and the framework neutral. The sulfide group, as a soft base, generally prefers to coordinate to the soft metal such as AgI. Meanwhile, the free sulfide groups in the complexes often act as chemical interaction sites, which is attractive for developing new catalytic systems (for example, the moiety can catalyse the transfer of oxygen atoms to produce hydroxy groups).8a A pyridyl-type group that is able to satisfactorily complete the coordination sphere of the metal center usually leads to the formation of novel coordination polymers;9 (iii) it has a strong capability of forming hydrogen bonding or SS weak interactions that play an important role in the assembly of supramolecular compounds. Only limited compounds of this ligand, including [Zn(pyta)(OH)]n and [Zn(pyta)2]n, which show unique 2-D homo-chiral helices8a or 1-D coordination chain8b patterns, are documented to date.10 Considering all the aspects stated above, thus, we herein describe the synthesis, characterization and crystal structures of a series of novel metal complexes of pyta, including [Co(pyta)2(H2O)4] (1), {[Cu(pyta)2(H2O)]·0.5H2O}n (2), [Ag(pyta)]n (3), {[Zn(pyta)2]·4H2O}n (4), {[Mn(pyta)2(H2O)]}n (5) and [Pb(pyta)2]n (6), in which a variety of coordination modes and different configurations of pyta were observed.
Chart 1
Experimental Materials and physical measurement All the starting materials and solvents for syntheses were obtained commercially (ACROS) and used as received. FT-IR spectra (KBr
This journal is © The Royal Society of Chemistry 2004
Dalton Trans., 2004, 2065–2072
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pellets) were taken on a FT-IR 170SX (Nicolet) spectrometer. Carbon, hydrogen, and nitrogen analyses were performed on a Perkin–Elmer 240C analyzer. Thermal stability (TGA) experiments were carried out on a Dupont thermal analyzer from room temperature to 800 °C under a nitrogen atmosphere at a heating rate of 10 °C min-1. X-ray powder diffraction (XPRD) patterns were recorded on a Rigaku RU200 diffractometer at 60 kV, 300 mA for Cu K radiation ( = 1.5406 Å), with a scan speed of 2° min−1 and a step size of 0.02° in 2. The calculated XRPD patterns were produced using the SHELXTL-XPOW program and single-crystal reflection data. Synthesis of [Co(pyta)2(H2O)4] (1) To a solution of Hpyta (34 mg, 0.2 mmol) in hot water (10 mL) was added a dilute aqueous solution of 1,4-diazacycloheptane with stirring to adjust the pH value of the mixture to ca. 7. Then, a water solution (5 mL) of CoCl2·6H2O (43 mg, 0.18 mmol) was added slowly to the above solution under refluxing conditions for ca. 10 min. The resultant orange solution was filtered after cooling to room temperature. Block pink single-crystals suitable for X-ray diffraction were obtained by slow evaporation of the solvents within one week in 85% yield. Anal. calc. for C14H20CoN2O8S2: C, 35.98; H, 4.31; N, 5.99%. Found: C, 35.71; H, 4.66; N, 5.87%. IR (cm−1): 3315br (O–H for H2O), 1598vs and 1379vs (as and s for COO−), 1534m, 1488s, 1425s (skeletal vibrations for pyridyl ring).
Synthesis of [Pb(pyta)2]n (6) To a solution of Hpyta (34 mg, 0.2 mmol) in hot water (10 mL) was slowly added a water solution (5 mL) of Pb(OAc)2·3H2O (76 mg, 0.2 mmol) under refluxing conditions for ca. 30 min. The resultant white precipitate was filtered off and the colorless solution was left to stand at room temperature. Block colorless single-crystals suitable for X-ray diffraction were obtained by slow evaporation of the solvents within one day in 80% yield. Anal. calc. for C14H12N2O4PbS2: C, 30.93; H, 2.23; N, 5.15%. Found: C, 30.90; H, 2.11; N, 5.24%. IR (cm−1): 1579vs and 1368s (as and s for COO−), 1551s, 1534m, 1485s, 1417s and 1402s (skeletal vibrations for pyridyl ring).
Synthesis of {[Cu(pyta)2(H2O)]·0.5H2O}n (2)
X-ray crystallographic data collections and refinement
Hpyta (85 mg, 0.5 mmol) was dissolved in hot water (20 mL). To the above solution was added a dilute aqueous solution of CuCl2·2H2O (52 mg, 0.3 mmol) and a large amount of blue precipitate was formed immediately. The slurry mixture was further vigorously stirred under heating for ca. 30 min, and then filtered after cooling to room temperature. The blue powder product of 2 was collected and washed with anhydrous methanol. The light-blue filtrate was allowed to stand at room temperature, and blue block single-crystals suitable for X-ray diffraction were obtained by evaporation of the solvents within one day. Total yield: 95%. Anal. calc. for C14H15CuN2O5.5S2: C, 39.38; H, 3.54; N, 6.56%. Found: C, 39.30; H, 3.87; N, 6.45%. IR (cm−1): 3446br (O–H for H2O), 1602vs and 1371vs (as and s for COO−), 1535w, 1489s, 1425s (skeletal vibrations for pyridyl ring).
Single crystal X-ray diffraction measurements of 1 (pink, 0.18 × 0.12 × 0.08 mm), 2 (blue, 0.22 × 0.18 × 0.12 mm), 3 (colorless, 0.28 × 0.18 × 0.14 mm), 4 (colorless, 0.24 × 0.18 × 0.16 mm), 5 (colorless, 0.16 × 0.14 × 0.10 mm) and 6 (colorless, 0.16 × 0.14 × 0.12 mm) were carried out with a Bruker Smart 1000 CCD diffractometer equipped with a graphite crystal monochromator situated in the incident beam for data collection at 293(2) K. The lattice parameters were obtained by least-squares refinement of the diffraction data of 667 (for 1), 857 (for 2), 793 (for 3), 832 (for 4), 733 (for 5) and 995 (for 6) reflections, respectively, and data collections were performed with Mo-K radiation ( = 0.71073 Å) by scan mode in the range of 1.80 < < 25.03° (for 1), 1.63 < < 25.03° (for 2), 2.58 < < 26.42° (for 3), 2.38 < < 25.01° (for 4), 2.55 < < 26.40° (for 5) and 3.58 < < 26.51° (for 6). No evidence was found for crystal decay during data collection of complexes 1–3, 5 and 6, and crystals of 4 which are air sensitive were thus measured in a sealed capillary. All the measured independent reflections were used in the structural analysis, and semi-empirical absorption corrections were applied using the SADABS program. The program SAINT11 was used for integration of the diffraction profiles. All the structures were solved by direct methods using the SHELXS program of the SHELXTL package and refined with SHELXL.12 Metal atoms were located from the E-maps and other non-hydrogen atoms were located in successive difference Fourier syntheses. The final refinement was performed by full-matrix least-squares methods with anisotropic thermal parameters for all the non-hydrogen atoms on F2. All the hydrogen atoms were first found in difference electron density maps, and then placed in the calculated sites and included in the final refinement in the riding model approximation with displacement parameters derived from the parent atoms to which they were bonded. A summary of the crystallographic data and structure refinements are listed in Table 1. CCDC references numbers 233041–233046. See http://www.rsc.org/suppdata/dt/b4/b403498h/ for crystallographic data in CIF or other electronic format.
Synthesis of [Ag(pyta)]n (3) Hpyta (68 mg, 0.4 mmol) was dissolved in hot water (20 mL). To the above solution was added an aqueous solution of AgNO3 (85 mg, 0.5 mmol) and a little brown precipitate was observed. The resulting solution was filtered, and the filtrate was allowed to stand at room temperature. Prismatic colorless crystals suitable for X-ray diffraction were obtained by evaporation of the solvents within one day in 65% yield. Anal. calc. for C7H6AgNO2S: C, 30.46; H, 2.19; N, 5.07%. Found: C, 30.32; H, 2.21; N, 4.89%. IR (cm−1): 1593vs and 1395vs (as and s for COO−), 1536m and 1484s (skeletal vibrations for pyridyl ring). Synthesis of {[Zn(pyta)2]·4H2O}n (4) Hpyta (102 mg, 0.6 mmol) and Zn(OAc)2·2H2O (88 mg, 0.4 mmol) were mixed in aqueous solution (40 mL). The mixture was heated for ca. 30 min with stirring and then filtered after cooling to room temperature. Upon slow evaporation of filtrate at room temperature, well-shaped colorless crystals of 4 suitable for X-ray diffraction were obtained within one week in 70% yield. Anal. calc. for C14H20ZnN2O8S2: C, 35.49; H, 4.25; N, 5.91%. Found: C, 35.67; H, 3.81; N, 6.13%. IR (cm−1): 3463br (O–H for H2O), 1604vs and 1373vs (as and s for COO−), 1535m, 1492s, 1432s and 1387s (skeletal vibrations for pyridyl ring). Synthesis of {[Mn(pyta)2(H2O)]}n (5) To a solution of Hpyta (34 mg, 0.2 mmol) in hot water (10 mL) was added an aqueous solution (5 mL) of MnCl2·4H2O (40 mg, 2066
0.2 mmol). Then, a dilute aqueous solution of 1,4-diazacycloheptane was added dropwise with stirring to the above mixture until the pH was ca. 7. Further stirring of the solution resulted in a small quantity of brown precipitate, which was filtered off. The resultant colorless filtrate was left to stand at room temperature. Block colorless single-crystals suitable for X-ray diffraction were obtained by slow evaporation of the solvents within three days in 70% yield. Anal. calc. for C14H14MnN2O5S2: C, 41.08; H, 3.45; N, 6.84%. Found: C, 40.91; H, 3.79; N, 6.77%. IR (cm−1): 3388br (O–H for H2O), 1594vs, 1579vs and 1416vs (as and s for COO−), 1484s and 1395s (skeletal vibrations for pyridyl ring).
Dalton Trans., 2004, 2065–2072
Results and discussion Preparation of compounds 1–6 Compounds 1–6 were obtained as neutral molecular complexes in the water system by combination of Hpyta with different metal salts, respectively. Compound 1 could also be isolated according to the same synthetic procedure, however, using Co(ClO4)2, Co(NO3)2 or
Table 1
Crystal data and structure refinement parameters for complexes 1–6
Empirical formula M Crystal system Space group a/Å b/Å c/Å /° /° /° V/Å3 Z calcd./g cm−3 µ/cm−1 No. observations Ra Rwb
Empirical formula M Crystal system space group a/Å b/Å c/Å /° V/Å3 Z calcd./g cm−3 µ/cm−1 No. observations Ra Rwb a
1
2
3
C14H20CoN2O8S2 467.37 Triclinic P-1 6.437(2) 7.053(3) 11.717(5) 93.101(6) 102.501(5) 114.759(6) 465.3(3) 1 1.668 11.92 1644 0.0411 0.1025
C14H15CuN2O5.5S2 426.94 Triclinic P-1 8.056(3) 8.506(3) 12.785(5) 102.049(6) 91.166(5) 100.076(6) 842.1(5) 2 1.684 15.75 2946 0.0429 0.1024
C7H6AgNO2S 276.06 Monoclinic P21/c 8.156(3) 10.102(4) 10.085(4) 90 104.952(5) 90 802.8(5) 4 2.284 27.21 1645 0.0237 0.0595
4
5
6
C14H20ZnN2O8S2 473.81 Monoclinic P21/c 13.243(8) 17.090(10) 8.978(5) 108.489(11) 1927(2) 4 1.633 15.35 3325 0.0590 0.1149
C14H14MnN2O5S2 409.33 Monoclinic C2/c 15.993(6) 6.392(2) 15.682(6) 93.781(6) 1599.6(10) 4 1.700 11.14 1635 0.0344 0.0786
C14H12N2O4PbS2 543.57 Monoclinic C2/c 11.434(6) 21.768(11) 7.710(4) 126.711(6) 1538.3(14) 4 2.347 112.60 1271 0.0171 0.0373
R = ∑||Fo| − |Fc|| / ∑|Fo|. b Rw = [∑[w(Fo2 − Fc2)2] / ∑w(Fo2)2]1/2.
Co(OAc)2 as the source of cobalt (confirmed by X-ray diffraction, IR spectra and elemental analyses). Similar cases were also observed for CuII, ZnII, AgI, MnII and PbII complexes, which indicates that the final products are independent of the counter-anions of the metal salts. Complexes 1, 2, 4, 5 and 6 have the 2 : 1 ligand/metal compositions, and for 3, a 1 : 1 ligand/metal coordination polymer is achieved. Indeed, in these specific self-assembled processes, the products do not depend on the ligand-to-metal ratio (the results were confirmed by X-ray diffraction, IR spectra and elemental analyses). However, increasing the metal-to-ligand ratio results in a somewhat higher yield and crystal quality. Complexes 1–3, 5 and 6 are air stable and can retain their structural integrity at room temperature for a considerable length of time, and their phase purities were confirmed by X-ray powder diffraction (Fig. S1, ESI†). For the ZnII complex 4, well-shaped crystals decomposed gradually after being taken away from the mother liquor as stated above. The resultant substance is amorphous and insoluble in water or common organic solvents, the composition of which is [Zn(pyta)2]·2H2O according to the results of the elemental analyses. Exposing this material to water vapor for 120 h to examine if the lost molecule including water could be re-introduced, however, it did not succeed. It is worthwhile to point out that the other two ZnII–pyta coordination polymers have been isolated under different conditions: (i) the reaction of Hpyta and Zn(NO3)2·6H2O in water in the presence of triethylamine as the proton scavenger through diffusion approach yields a novel twodimensional coordination polymer [Zn(pyta)(OH)]n (4a), which contains two types of homo-chiral helices;8a (ii) combination of Hpyta with Zn(OAc)2·2H2O in the presence of NaOH under hydrothermal conditions affords a one-dimensional polymeric coordination chain [Zn(pyta)2]n (4b).8b Considering the result of 4 described here, it is clear to see that different reaction conditions/mechanism plays a key role in controlling the solid structures of Zn–pyta coordination polymers. Furthermore, the building block pyta adopts
different coordination modes/configurations in these complexes, which is discussed in detail as below. X-ray single-crystal structures of complexes 1–6 Structure description of [Co(pyta)2(H2O)4] (1). In the centrosymmetric mononuclear compound 1, each CoII ion, locating at the inversion center, coordinates to two pyridyl nitrogen atoms from distinct pyta moieties (Co–N distance: 2.144(3) Å) and four water molecules (Co–O lengths: 2.122(3) and 2.091(3) Å) as shown in Fig. 1(a), adopting an approximate octahedral geometry (CoN2O4). For pyta taking the anti-configuration, it coordinates to the CoII center with only the pyridyl N atom (behaving as a monodentate ligand), and thus results in this unexpected mononuclear structure. Two C–O bond distances of the carboxylic group are equivalent (see Table 2), agreeing with its uncoordinated structural geometry. The shortest intermolecular Co(1)O(1) and Co(1)O(2) distances (symmetry code: x + 1, y, z + 1) are 4.066 and 4.142 Å, respectively. Analysis of the crystal packing of 1 reveals the existence of three types of intermolecular O–HO hydrogen bonds, including O(3)–H(3A)O(2)i (i = −x + 2, −y, −z + 1), O(4)–H(4B)O(2)ii (ii = −x + 2, −y + 1, −z + 1) and O(4)–H(4C)O(1)iii (i = x − 1, y, z − 1), between the water ligands and the uncoordinated carboxylic groups. Four intermolecular O–HO hydrogen bonds between the O(4) water ligands and the carboxylate oxygen atoms from four adjacent complex molecules result in a closed hydrogenbonded ring that could be described as N4 = R44(12) pattern.13 The OO separations are in the 2.663–2.961 Å range with HO distances of 1.880–2.445 Å, and the bond angles are in the region of 118.9–152.5°, being in the normal range of such non-covalent interactions.14 Therefore, these mononuclear subunits are connected through these hydrogen bonds to form a two-dimensional layered supramolecular pattern, as depicted in Fig. 1(b). Dalton Trans., 2004, 2065–2072
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Table 2
Selective bond lengths (Å) and angles (°) for complex 1
Bond lengths
Table 3
Selective bond lengths (Å) and angles (°) for complex 2
Bond lengths
Co(1)–O(3) Co(1)–N(1) C(7)–O(1)
2.122(3) 2.144(3) 1.249(5)
Co(1)–O(4) S(1)–C(6) C(7)–O(2)
2.091(3) 1.800(4) 1.251(5)
93.91(12) 87.89(12) 88.39(13) 103.6(2)
O(4)–Co(1)–O(3)a O(4)–Co(1)–N(1)a O(3)–Co(1)–N(1)a C(7)–C(6)–S(1)
86.09(12) 92.11(12) 91.61(13) 110.4(3)
Bond angles O(4)–Co(1)–O(3) O(4)–Co(1)–N(1) O(3)–Co(1)–N(1) C(3)–S(1)–C(6)
Symmetry code: 1 − x, −y, −z. a
Cu(1)–O(1)a Cu(1)–O(5) Cu(1)–N(1) S(1)–C(2) C(1)–O(1) C(14)–O(3)
1.964(3) 2.414(3) 1.999(4) 1.775(5) 1.252(5) 1.222(6)
Cu(1)–O(4)b Cu(1)–O(3)b Cu(1)–N(2) S(2)–C(13) C(1)–O(2) C(14)–O(4)
1.979(3) 2.723(7) 2.000(3) 1.793(5) 1.227(6) 1.272(5)
172.91(13) 91.08(13) 90.46(14) 101.07(13) 94.63(14) 103.5(2) 103.6(2)
O(1)a–Cu(1)–N(2) O(1)a–Cu(1)–N(1) N(2)–Cu(1)–N(1) O(4)b–Cu(1)–O(5) N(1)–Cu(1)–O(5) C(1)–C(2)–S(1) C(14)–C(13)–S(2)
88.43(14) 89.21(14) 173.10(16) 86.01(12) 92.18(14) 118.2(3) 117.5(3)
Bond angles O(1)a–Cu(1)–O(4)b O(4)b–Cu(1)–N(2) O(4)b–Cu(1)–N(1) O(1)a–Cu(1)–O(5) N(2)–Cu(1)–O(5) C(3)–S(1)–C(2) C(10)–S(2)–C(13)
Symmetry codes: a −x, 2 − y, −z. b −x, 1 − y, 1 − z.
Fig. 1 (a) View of the mononuclear structure of 1 (hydrogen atoms are omitted for clarity); (b) view of the 2-D hydrogen-bonding supramolecular layer (irrelevant hydrogen atoms are omitted for clarity).
Structure description of {[Cu(pyta)2(H2O)]·0.5H2O}n (2). Xray single-crystal determination indicates that complex 2 is a neutral 1-D coordination polymer, in which the CuII centers are bridged via gauche-pyta ligands. As shown in Fig. 2(a), each CuII center is coordinated by two pyridyl nitrogen donors and two carboxylic oxygen atoms from two crystallographically independent pyta moieties, and a water ligand completes the coordination polyhedron around CuII from the apical position. The coordination geometry of the pentacoordinated CuII center (CuN2O3) can be described as an almost perfect square-pyramid, which is reflected by the value (0.002) defined by Addison et al. ( = 0 for an ideal square-pyramid, and = 1 for an ideal trigonal bipyramid)15 and further developed by O’Sullivan et al. recently.16 The central CuII ion is ca. 0.36 Å above the basal least-squares plane defined by N(1), N(2), O(1) and O(4) toward the apical water molecule. Two Cu–Npyridyl bond lengths are nearly the same (see Table 3), both being normal for such Cu–N coordination bonds.17 Two Cu–Ocarboxylic bond distances are also similar and slightly/significantly shorter than the Cu–Npyridyl/ Cu–Owater bonds. In addition, a rather weak Cu(1)–O(3) coordination interaction with the distance of 2.723(7) Å is observed in this structure, and thus, the coordination mode of this carboxylic group can also be described as asymmetric bidentate chelate. For both carboxylic groups, the coordinated C–O bond lengths (1.252(5) and 1.272(5) Å) are significantly longer than those of the uncoordinated/ weak coordinated cases (1.227(6) and 1.222(6) Å), being consistent with their structural features. Fig. 2(a) exhibits the one-dimensional framework of 2 in which two adjacent CuII ions are linked through two centrosymmetric gauche-pyta ligands to form a tetragonal unit with a size of 4.97 × 6.52 Å2 (4.99 × 6.53 Å2 for the neighboring unit consisting of CuII and another crystallographically independent pyta molecule) and the CuCu distance of 8.55(2) Å (8.34(2) Å for the neighboring unit). The shortest CuCui (i = −x, −y + 2, −z + 1) separation between the adjacent chains is 6.00(2) Å. 2068
Dalton Trans., 2004, 2065–2072
Fig. 2 (a) 1-D coordination framework for 2 with atom labeling of the asymmetric unit (hydrogen atoms and disordered water molecules are omitted for clarity); (b) perspective diagram of the two-dimensional hydrogenbonding sheet along crystallographic (011) plane (irrelevant hydrogen atoms are omitted for clarity).
Analysis of the crystal packing of 2 reveals the existence of two types of O–HO hydrogen bonds and weak inter-chain SS interactions. As depicted in Fig. 2(b), a pair of inter-chain head-totail O(5)–H(5A)O(4)i (i = x, y + 1, z) hydrogen bonds (described as N2 = R22 (8) pattern)13 between the coordination water molecule in each chain and the carboxylic oxygen atom from the adjacent chain are observed, resulting in a 2-D sheet architecture along the crystallographic (011) plane. Within each coordination chain, one uncoordinated carboxylic O(2) atom acts as the acceptor of one O(5)–H(5B)O(2)ii (ii = −x, −y + 2, −z) hydrogen bond with the adjacent coordinated water molecule, forming a six-membered hydrogen-bonding ring with a flattened-boat configuration. For two such types of O–HO interactions stated above, the OO separations are 2.931 and 2.687 Å with the HO distances of 2.092 and 1.889 Å, and the bond angles are 174.6 and 156.0°, being in the normal range of such non-covalent interactions.14 In addition, the nonbonding S(1)S(1) distance between two adjacent 1-D frameworks is 3.430(9) Å, which is less than the sum of the van der Waals’ radii of two S atoms and indicates a weak SS interaction.18 Fig. S2 (ESI†) shows the 2-D supramolecular motif through such interactions. Thus, combining the hydrogen-bonding and SS interactions, these 1-D coordination chains are further extended into a 3-D supramolecular network. Structure description of [Ag(pyta)]n (3). In the structure of 3, each AgI center is four-coordinated to three distinct pyta ligands,
adopting an AgO2SN distorted tetrahedral coordination sphere. Selected bond distances and angles for 3 are listed in Table 4. For pyta exhibiting the gauche-configuration, it binds to the AgI center with the pyridyl N atom, S donor and a syn–anti bridging carboxylic group, and thus, a five-membered chelated ring Ag(1)–S(1)– C(6)–C(7)–O(1) is formed as depicted in Fig. 3(a). Two C–O bond distances of the carboxylic group are almost equivalent, agreeing with its structural feature (syn–anti coordination). Thus, each AgI atom coordinates to three distinct pyta ligands and each pyta bridges three AgI centers to form a 2-D coordination polymer with (6,3) topology19 along the crystallographic (110) plane, as illustrated in Fig. 3(a). The shortest closed circuit contains six AgI centers and has a nonplanar geometry. Within each coordination sheet, the neighboring AgAg separations along x and y directions are 8.156(3) and 5.426(2) Å, respectively. Additionally, the shortest AgAgi (i = −x + 1, −y + 1, −z) distance between the adjacent sheets is 4.888(3) Å. Analysis of the crystal packing of 3 shows that these 2-D coordination layers are parallel stacked with an A(−A)A(−A) sequence (the neighboring layers are centrosymmetric to each other), as depicted in Fig. 3(b), and such a closed packing mode leaves no free space to accommodate guest molecules.
Table 4
Selective bond lengths (Å) and angles (°) for complex 3
Bond lengths Ag(1)–O(2)a Ag(1)–S(1) S(1)–C(6) C(7)–O(2)
2.281(2) 2.548(1) 1.798(3) 1.252(3)
Ag(1)–N(1)b Ag(1)–O(1) C(7)–O(1)
2.302(2) 2.559(2) 1.243(4)
103.56(8) 117.59(7) 99.78(8) 102.65(13)
O(2)a–Ag(1)–S(1) O(2)a–Ag(1)–O(1) S(1)–Ag(1)–O(1) C(7)–C(6)–S(1)
133.64(6) 120.47(7) 74.21(5) 113.47(19)
Bond angles O(2)a–Ag(1)–N(1)b N(1)b–Ag(1)–S(1) N(1)b–Ag(1)–O(1) C(3)–S(1)–C(6)
Symmetry codes: a −x + 1, y + 1/2, −z + 1/2. b −x + 1, y, z.
described as asymmetric bidentate chelate. Meanwhile, the antipyta building blocks further extend such dinuclear nodes through the coordination of pyridyl N atoms and monodentate carboxylic groups with ZnII to form a 2-D coordination polymer with the most common (4,4) topology.19 Fig. 4(b) shows the lamellar network of 4, in which the adjacent [Zn2(pyta)2] nodes are linked by bridging anti-pyta ligands with the ZnZn separation of 11.241(4) Å to form large and nearly square repeating grids. For carboxylic groups in either gauche- or anti-pyta, the coordinated C–O bond lengths (1.278(8) and 1.265(6) Å) are significantly longer than those of the weak coordinated/uncoordinated bonds (1.221(8) and 1.239(6) Å), being consistent with their structural features.
Fig. 3 (a) 2-D (6,3) coordination sheet in 3 which is the projection viewing along the (110) plane with atom labeling of the asymmetric unit (hydrogen atoms are omitted for clarity); (b) The stacking diagram of the parallel coordination sheets along the [100] direction.
Structure description of {[Zn(pyta)2]·4H2O}n (4). The crystal structure of 4 has a 2-D infinite coordination pattern and four guest water molecules. As shown in Fig. 4(a), each ZnII center coordinates to four distinct pyta moieties, forming a ZnN2O2 tetrahedral environment. Two Zn–Npyridyl bond lengths are nearly the same, and slightly longer than two similar Zn–Ocarboxylic distances (see Table 5). It is interesting that each independent unit contains both gauche- and antipyta ligands. For the former type, two centrosymmetric pyta linking units bridge two ZnII atoms to form a dinuclear motif with pyridyl N atoms and monodentate carboxylic groups, and the ZnZn distance is 8.353(6) Å. Similar to 2, a rather weak Zn(1)–O(1) coordination interaction (2.778(5) Å) is observed in this case, and thus, the coordination mode of this carboxylic group can also be
Fig. 4 (a) Dinuclear ZnII motif bridged by two centrosymmetric gauchepyta ligands with atom labeling of the asymmetric unit in 4 (hydrogen atoms are omitted for clarity); (b) View of the 2-D (4,4) coordination network (water moieties and hydrogen atoms are omitted for clarity) with dinuclear nodes.
Analysis of the crystal packing of 4 indicates that these 2-D coordinated sheets are closely stacked along the (100) direction with an ABAB sequence, offset by approximate 0.5 (y + z) along the (011) plane, as illustrated in Fig. S3 (ESI†). The shortest inter-sheet ZnZn separation is 5.516(2). The including water molecules (four Dalton Trans., 2004, 2065–2072
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Table 5
Selective bond lengths (Å) and angles (°) for complex 4
Table 6
Bond lengths Zn(1)–O(2)a Zn(1)–N(2)b S(1)–C(6) C(7)–O(1) C(14)–O(3)
Bond lengths 1.962(4) 2.017(5) 1.786(7) 1.221(8) 1.265(6)
Zn(1)–O(3) Zn(1)–N(1) S(2)–C(13) C(7)–O(2) C(14)–O(4)
1.971(4) 2.019(5) 1.786(7) 1.278(8) 1.239(6)
Mn(1)–O(3) Mn(1)–N(1) S(1)–C(6) C(7)–O(2)
2.220(3) 2.275(2) 1.791(3) 1.250(3)
Mn(1)–O(1)a Mn(1)–O(2)a C(7)–O(1)
2.295(2) 2.325(2) 1.239(3)
91.08(6) 87.87(7) 90.51(7) 84.91(5) 169.82(10) 56.37(7) 102.71(12)
N(1)–Mn(1)–N(1)b N(1)–Mn(1)–O(1)a N(1)–Mn(1)–O(2)a O(3)–Mn(1)–O(2)a O(2)c–Mn(1)–O(2)a O(2)c–Mn(1)–O(1)a C(7)–C(6)–S(1)
177.85(11) 92.32(7) 87.81(7) 141.15(5) 77.70(9) 133.80(7) 115.56(18)
Bond angles
Bond angles O(2)a–Zn(1)–O(1) O(3)–Zn(1)–N(2)b O(3)–Zn(1)–N(1) C(3)–S(1)–C(6) C(7)–C(6)–S(1)
Selective bond lengths (Å) and angles (°) for complex 5
106.5(2) 100.3(2) 107.3(2) 104.1(3) 116.9(5)
O(2)a–Zn(1)–N(2)b O(2)a–Zn(1)–N(1) N(2)b–Zn(1)–N(1) C(10)–S(2)–C(13) C(14)–C(13)–S(2)
111.7(2) 114.5(2) 115.0(2) 101.1(3) 112.1(4)
Symmetry codes: a −x + 2, −y + 1, −z + 2. b −x + 1, y + 1/2, −z + 1/2.
O(3)–Mn(1)–N(1) N(1)–Mn(1)–O(1)c N(1)–Mn(1)–O(2)c O(3)–Mn(1)–O(1)a O(1)c–Mn(1)–O(1)a O(1)a–Mn(1)–O(2)a C(3)–S(1)–C(6)
Symmetry codes: a x + 1/2, y + 1/2, z. b −x + 1, y, −z + 1/2. c −x + 1/2, y + 1/2, −z + 1/2.
per formula unit) are incorporated in the cavities and form three/five O–HO hydrogen bonds with the uncoordinated carboxylic oxygen donors of the host frameworks/each other, which further stabilize the 3-D supramolecular packing. For these hydrogen bonding interactions, the HO separations are in the 1.866–2.242 Å range with the OO distances in the region of 2.597–2.849 Å, and the smallest bond angle is 127.1°, being in the normal range of such interactions.14 It should be noted that although the offset packing mode significantly reduces the size of the porous channels compared with the overlap packing mode, an analysis of the voids of the host networks of 4 still shows a value of 409.9 Å3 of the channel space,20 corresponding to 21.3% of the unit cell volume, which was occupied by the guest water molecules. Structure description of {[Mn(pyta)2(H2O)]}n (5). The polymeric structure of 5 was revealed by X-ray single-crystal structure determination, in which the MnII center coordinates to two carboxylic groups with symmetry bidentate chelate mode, two pyridyl nitrogen donors and a water ligand, as shown in Fig. 5(a). The local coordination geometry around the MnII atom (MnO5N2) can be best described as a slightly distorted pentagonal-bipyramid. Two pyridyl N atoms occupy the axial positions, and the MnII center lies approximately in the pentagonal least-squares plane defined by O(3)–O(1)i–O(2)i–O(1)ii–O(2)ii (the oxygen atoms are symmetrically equivalent through Mn(1)–O(3), see Table 6 for details of symmetric codes) with a deviation of only 0.052 Å. Selected bond distances and angles for 5 are listed in Table 6. Two C–O bond distances of the carboxylic group are nearly equivalent, agreeing with its structural feature (symmetry bidentate chelate). For the pyta ligand with gauche-configuration, each bridges two MnII atoms with its pyridyl N atom and carboxylic group (the neighboring MnMn separation is 8.612(3) Å), forming a 2-D coordination pattern with (4,4) topology19 consisting of the [Mn4(pyta)4(H2O)4] repeating unit (the diagonal MnMn distances are 6.392(2) and 15.993(6) Å, respectively), as depicted in Fig. 5(b). Within the 2-D pattern, each coordinated water molecule forms two O(3)–H(3)O(2)iv, v (iv = x + 1/2, y − 1/2, z; v = −x + 1/2, y − 1/2, −z) hydrogen bonds with two opposite carboxylic oxygen atoms (along the [010] direction): the HO separation is 2.016 Å with the OO distance of 2.775 Å, and the bond angle is 148.2°, being in the normal range of such weak interactions.14 Additionally, due to the flexible feature of pyta, these 2-D coordination motifs are not planar, but with a flexuous arrangement (see side-view from the [010] direction in Fig. S4 (ESI)†). Analysis of the crystal packing of 5 shows that these 2-D coordination patterns have the parallel stack and the shortest inter-layer MnMn (symmetry codes: −x + 1, −y + 2, −z; or −x + 1, −y + 2, −z + 1) distance is 7.847(4) Å. A pair of C(6)– H(6A)O(1)vi (vi = −x, −y + 1, −z) hydrogen bonds are observed between the methylene and the carboxylic groups from two adjacent 2-D layers, forming a N2 = R22 ring (CO and HO distances: 3.282 and 2.351 Å, C–HO angle: 160.8°).13 Thus, these 2-D 2070
Dalton Trans., 2004, 2065–2072
Fig. 5 (a) View of the metal coordination environment in 5 with atom labeling of the asymmetric unit (hydrogen atoms are omitted for clarity); (b) 2-D coordination network along the (110) plane (hydrogen atoms are omitted for clarity).
patterns are further extended into a 3-D supramolecular network through these weak interactions, as depicted in Fig. S4 (ESI†). Structure description of [Pb(pyta)2]n (6). The crystal structure of 6 shows a neutral 1-D coordination chain motif, as depicted in Fig. 6(a), in which each crystallographically independent PbII center coordinates to two pyridyl N atoms and two carboxylic O donors from distinct pyta ligands, adopting the tetrahedral coordination geometry. The Pb–Ocarboxylic bond length is significantly shorter than that of Pb–Npyridyl (see Table 7), and a weak Pb(1)–O(1) coordination bond is also observed (2.788(6) Å). For the carboxylic group exhibiting asymmetric bidentate chelate mode coordinated to PbII ion, the C(7)–O(2) bond length is significantly longer than that of C(7)–O(1), being consistent with its structural feature. Two neighboring PbII centers are bridged through two C2-symmetric gauche-pyta ligands to result in a tetragonal unit with a size of 4.45 × 7.94 Å2 and a PbPb distance of 9.208(5) Å. In addition, the shortest PbPb (symmetry codes: −x + 2, −y + 2, −z + 2; −x + 2, −y + 2, −z + 3) separation between the adjacent coordination chains is 4.522(7) Å.
Table 7
Selective bond lengths (Å) and angles (°) for complex 6
Bond lengths Pb(1)–O(2) S(1)–C(6) C(7)–O(2)
2.462(3) 1.798(4) 1.260(4)
Pb(1)–N(1)ab C(7)–O(1)
2.635(3) 1.237(4)
88.91(13) 72.61(9) 104.73(19)
O(2)c–Pb(1)–N(1)a N(1)a–Pb(1)–N(1)b C(7)–C(6)–S(1)
74.16(9) 132.77(15) 115.4(3)
Bond angles O(2)–Pb(1)–O(2)c O(2)c–Pb(1)–N(1)b C(3)–S(1)–C(6)
Symmetry codes: a x + 1, y, z + 1. b x, y, −z + 1/2. c −x + 2, y, −z + 5/2.
As stated in the Introduction, pyta has three potential bind sites (Npyridyl, S and COO−), which also make it a versatile building block in construction of novel coordination polymers. In all the pyta-containing complexes, the pyridyl N atom takes part in the coordination with the metal center. The anionic nature of the carboxylic group makes the coordination framework neutral, except in [Pd(dppp)(Hpyta)](CF3SO3)2. For the mononuclear complex 1, the COO− group is free and does not bind to the CoII center, and in most other cases, it exhibits the monodentate and/or asymmetric/symmetric bidentate chelate modes. Several unique structural points of pyta are observed in [Ag(pyta)]n (3): it behaves as a tri-connected block using Npyridyl, S and a syn–anti bridging COO− group. The sulfur atom, known as a soft base, coordinates to the AgI center that is not found in any other reported complexes, and thus a five-membered chelated ring is formed in this structure. Additionally, weak SS interactions were observed in the CuII and PbII complexes, which extend the 1-D coordination frameworks to higher dimensional supramolecular networks. The coordination modes of pyta observed in the reported structures are illustrated in Fig. 7, and we believe other trends will emerge with the increasing number of pyta coordination frameworks.
Fig. 7 Coordination modes of pyta in the reported structures.
Thermogravimetric analysis Fig. 6 (a) 1-D coordination framework of [Pb(pyta)2]n (hydrogen atoms are omitted for clarity) with atom labeling of the asymmetric unit; (b) view of the SS interactions between the adjacent coordination chains.
As described above, the coordination framework of 6 is somewhat similar to that of 2. Analysis of the crystal packing of 6 shows the existence of weak inter-chain SS interactions, which is also observed in 2. The nonbonding S(1)S(1) distance between two adjacent 1-D frameworks is 3.546(4) Å, which is less than the sum of the van der Waals’ radii of two S atoms and indicates a very weak SS interaction.18 These weak interactions extend the coordination chains to result in a 2-D supramolecular sheet, as illustrated in Fig. 6(b). Furthermore, these 2-D frameworks are wave-like and a pair of such opposite 2-D motifs insert into each other to form a novel 2-fold interpenetrating architecture, as shown in Fig. S5 (ESI†). The features of pyta From the above descriptions, we can clearly see that the coordination modes of pyta, behaving quite differently under the inducement when binding to a special metal center, are critical in determining the solid structures of its metal complexes. Thus, it is very interesting and essential to compare the structural data of this flexible building block in these complexes and other related compounds reported before. As listed in Table 8, the pyta ligand usually adopts the gauche configuration, which could be reflected by the torsion angle () between the central C–S bond, and the pyridyl and carboxylic groups (in the range from 60.0(2) to 81.2(6)° in these cases). The anti configuration of pyta was observed in the mononuclear CoII complex 1, and 2-D ZnII coordination polymer 4, in which the angles are 178.5(3) and −171.6(5)°, respectively. It is noteworthy that both gauche- and anti-pyta ligands exist in the structure of 4, which is different to those in the other two ZnII–pyta coordination polymers [Zn(pyta)(OH)]n (4a) and [Zn(pyta)2]n (4b) (gauche-configuration) obtained under different reaction mechanisms.
High thermal stability is an important precondition in the conversion of porous coordination frameworks from laboratory curiosities to practical materials. Thus, thermogravimetric analyses (TGA) were conducted to determine the thermal stability of complexes 1–6. For 1, the first weight loss of 15.61% from 80 to 170 °C (peak: 131 °C) corresponds to the loss of four coordinated aqua ligands (calculated: 15.42 %). The remaining substance does not lose weight upon further heating until a rapid weight loss occurs in the 300–345 °C region (peak: 334 °C), corresponding to the removal of one and half pyta ligands (observed: 54.25%, calculated: 53.97%). Further heating to 800 °C of the sample indicates a continuous and slow weight loss. For 2, the first weight loss of 6.69% from 75 to 150 °C (peak: 126 °C) corresponds to the release of half lattice water and one coordinated aqua ligand (calculated: 6.33%). The remaining coordinated framework does not lose weight upon further heating until three consecutive weight losses occur in the 200–280 °C region (peak: 218, 231 and 266 °C, total weight: 64.61%). Further heating to 800 °C of the sample only indicates a continuous and slow weight loss. For 3, the coordination framework remains intact until three consecutive weight losses occur in the 170–280 °C region (peak: 176, 201 and 272 °C, total weight: 54.40%). Further heating to 800 °C of the sample only indicates a continuous and slow weight loss. For 4 (fresh sample), the first weight loss of 14.78% from 60 to 88 °C (peak: 76 °C) corresponds to the release of four guest water molecules (calculated: 15.20%). The coordination framework remains intact until the second weight loss (66.01%) occurs in the 200–440 °C broad region (peak: 318 °C). Further heating to 800 °C of the sample only indicates a continuous and slow weight loss. For the 2-D coordination framework 5, the first weight loss of 4.63% from 180 to 205 °C (peak: 190 °C) corresponds to the expulsion of a coordinated water moiety. The coordination network starts to decompose until heating to 310 °C with a rapid weight loss of 59.60% in the 310–360 °C region (peak: 342 °C). Further heating to 800 °C of the sample shows a continuous and slow weight loss. It should be noted that the coordination polymer with such a high thermal stability is rare. For 6, the coordination framework remains intact until two consecutive weight losses Dalton Trans., 2004, 2065–2072
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Table 8
Comparison of the structural parameters of pyta in the metal complexes Compound
Configuration
Coordination mode
/°a
Refs.
[Co(pyta)2(H2O)4] (1) {[Cu(pyta)2(H2O)]·0.5H2O}n (2)
anti gauche gauche gauche anti gauche gauche gauche gauche gauche gauche gauche
178.5(3) −71.4(4) −68.5(4) −60.0(2) 71.0(6) −171.6(5) 77.3(4) 77.4(3) 69.5(2) 75.9(3) 66.6(5)b 81.2(6)
This work This work
[Ag(pyta)]n (3) {[Zn(pyta)2]·4H2O}n (4)
1 (Npy) , 2 (Npy, OCOO ) , 3 (Npy, O,O′as, COO ) 3, 4 (Npy, S, Osyn,O′anti, COO ) , 3 (Npy, O,O′as, COO ) , 2 (Npy, OCOO ) , 2 (Npy, OCOO ) , 3 (Npy, O,O′as, COO ) , 3 (Npy, O,O′sym, COO ) , 3 (Npy, O,O′as, COO ) , 2 (Npy, OCOO ) 1 (Npy) , 2 (Npy, OCOO ) −
−
[Zn(pyta)(OH)]n (4a) [Zn(pyta)2]n (4b) {[Mn(pyta)2(H2O)]}n (5) [Pb(pyta)2]n (6) [(Ph)3Sn(pyta)]n (7) [Pd(dppp)(Hpyta)](CF3SO3)2 (8) [Mn(SALEN)(pyta)]n (9)
−
−
− −
−
−
−
−
−
c
This work This work ref. 8a ref. 8b This work This work ref. 10a ref. 10b ref. 10c
The torsion angle between the central C–S group, and the pyridyl and carboxylic groups. b This is an average value due to the existence of two crystallographically independent molecules in the asymmetric unit. c No data available. a
occur in the 220–315 °C region (peak: 233 and 302 °C, total weight: 47.85%). Just like other compounds, further heating to 800 °C of the sample only shows a continuous and slow weight loss.
Conclusions and perspectives A series of novel inorganic–organic coordination supramolecular networks have been generated from a multidentate organic ligand 4-pyridylthioacetic acid (Hpyta) and inorganic CoII, CuII, AgI, ZnII, MnII and PbII salts, and structurally characterized by X-ray diffraction analysis. These compounds show mononuclear, 1-D and 2-D coordination frameworks, respectively, and different supramolecular networks were further observed through hydrogen bonding or SS weak interactions. That is, we have succeeded in the assemblies of supramolecular architectures from low to higher dimensionality by altering the selection of the metal ions. The present study demonstrates that the flexible pyta anion is capable of coordinating to metal centers with Npyridyl, S donors or the COO− group and exhibits either gauche- or anti-configuration, which were fully embodied in these new materials. We are currently extending this result by preparing new multifunctional ligands of this type with different coordination groups instead of pyridyl (for example, pyrazine or imidazole), having different orientations of the nitrogen donor on the pyridyl rings, or containing longer length spacers. We anticipate that this new type of organic ligands will result in a variety of coordination polymers or supramolecules with unique topologies and interesting properties.
Acknowledgements This work was financially supported by the Natural Science Foundation of Tianjin (No. 033609711) and the Starting Funding of Tianjin Normal University (to M. Du). We also thank Dr Hai-Bin Song for X-ray data collection of these compounds.
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