Metal naphthalenedicarboxylates with diverse network architectures: Synthesis, crystal structures and properties

Polyhedron 28 (2009) 3759–3768

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Metal naphthalenedicarboxylates with diverse network architectures: Synthesis, crystal structures and properties Xiu-Juan Jiang a,b, Jian-Hua Guo a, Miao Du a,b,*, Jin-Shan Li b,* a b

College of Chemistry and Life Science, Tianjin Key Laboratory of Structure and Performance for Functional Molecule, Tianjin Normal University, Tianjin 300387, PR China State Key Laboratory of Elemento-Organic Chemistry, Nankai University, Tianjin 300071, PR China

a r t i c l e

i n f o

Article history: Received 26 July 2009 Accepted 26 August 2009 Available online 1 September 2009 Keywords: Metal naphthalenedicarboxylate Network architecture Structural regulation Thermal stability Fluorescence

a b s t r a c t Reactions of 1,4-naphthalenedicarboxylic acid (1,4-H2nda) and a bent dipyridyl co-ligand 4-amino-3,5bis(4-pyridyl)-1,2,4-triazole (4bpt) with CoII, ZnII, or CdII acetate afford four coordination polymers, [Co(1,4-nda)(4bpt)(H2O)]n (1), {[Co(1,4-nda)2(4bpt)(H2O)2][Co(4bpt)(H2O)4](H2O)1.5}n (2), {[Zn(1,4nda)2(4bpt)(H2O)2][Zn(4bpt)(H2O)4](H2O)1.5}n (3), and {[Cd2(1,4-nda)2(4bpt)2(H2O)2](DMF)1.5(H2O)3}n (4). In the structure of the CoII complex 1, the polycatenation of inclined 2-D (4,4) coordination layers leads to the formation of a 3-D supramolecular framework, whereas two types of 1-D polymeric chains are observed in another CoII coordination species 2, which are interconnected via H-bonding to result in an unusual 3-D host–guest lattice. Notably, complexes 1 and 2 have been prepared under similar hydrothermal conditions and their structural discrepancy can only be ascribed to a subtle change of basicity for the reaction solution. The ZnII complex 3 is isostructural to 2, and the CdII complex 4 displays a 2-fold parallel interpenetrating array of undulating (4,4) coordination layers. By using the conventional solvent evaporation method, two PbII naphthalenedicarboxylates [Pb(1,4-nda)(DMF)]n (5) and {[Pb2(2,6nda)2(DMF)2](DMF)}n (6) have also been prepared (2,6-nda = 2,6-naphthalenedicarboxylate). Complex 5 has a unique 5-connected 3-D coordination architecture, whereas 6 represents a 3-fold interpenetrating framework of 4-connected diamond topology. Their structural difference suggests the significant isomeric effect of the naphthalenedicarboxylate tectons on structural assemblies. Thermal stability of these crystalline materials has been investigated by thermogravimetric and differential thermal analysis (TG– DTA) technique and solid-state luminescent properties of the ZnII, CdII, and PbII complexes have also been explored. Ó 2009 Elsevier Ltd. All rights reserved.

1. Introduction Currently, metal–organic frameworks (also called coordination polymers or coordination polymer networks) have received considerable attention due to their interesting network structures and potential applications [1–3]. Aromatic polycarboxyl compounds have been extensively used as the bridging building blocks to construct metal–organic framework solids [4–12] in virtue of their structural rigidity and chemical robustness, which will result in the high thermal stability of such hybrid crystalline materials that is comparable to purely inorganic zeolites [13–16]. These versatile tectons also display several interesting features that are advantaged to produce various coordination networks. First, the carboxylate group may have multiform coordination modes such

* Corresponding authors. Address: College of Chemistry and Life Science, Tianjin Key Laboratory of Structure and Performance for Functional Molecule, Tianjin Normal University, Tianjin 300387, PR China (M. Du). E-mail addresses: [email protected] (M. Du), [email protected] (J.-S. Li). 0277-5387/$ - see front matter Ó 2009 Elsevier Ltd. All rights reserved. doi:10.1016/j.poly.2009.08.022

as monodentate, chelating, and bridging upon metalation. Second, a much wider variation in the degree of deprotonation for such ligands can influence not only their coordination ability but also electrovalence, which thus will determine the compositions and supramolecular architectures of the resulting complexes. Last, the carboxyl group is always involved in intermolecular H-bonding, which may further consolidate or extend the coordination arrays. In this regard, as the analogs of the most familiar linear terephthalate linker, 1,4-naphthalenedicarboxylate (1,4-nda) [17–23] and 2,6-naphthalenedicarboxylate (2,6-nda) [24–31] have also been confirmed to act as nice candidates for preparing coordination polymer networks. Notably, the carboxylate groups in the substituted terephthalate tectons such as 1,4-nda will not be co-planar to the attached aromatic ring due to the steric hindrance, which consequently may extend the metal centers in different directions to result in new coordination networks. It is well-known that the rod-like connectors generally direct grid- or cubic-type coordination frameworks with large voids or channels, among which the aromatic dicarboxylate ligands tend to afford robust crystalline materials owing to the possible

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bidentate binding of carboxylate [32–39]. However, network interpenetration or entanglement often occurs in this connection to prevent the generation of desired microporous metal–organic frameworks [40–45], although in some conditions interpenetration has been proposed as a means of increasing the dimensionality and structural rigidity of the coordination networks. According to these points, it can be anticipated that the building blocks 1,4-nda and 2,6-nda will potentially facilitate the formation of interesting coordination polymers with available channels or interpenetrating motifs. On the other hand, the rational assembly of structurally defined coordination polymers using the mixed-ligand strategy has currently demonstrated a remarkable success. In this manner, we have exploited a variety of coordination frameworks with interesting architectures and properties based on the polycarboxylate tectons and a 4,40 -dipyridyl derivative 4-amino-3,5-bis(4-pyridyl)-1,2,4triazole (4bpt), which has an angular backbone in contrast to the linear 4,40 -bipyridyl ligand and thus, imposes profoundly steric effect on assembling the coordination networks [46–48]. For instance, a systematic study on coordination frameworks with benzenedicarboxylate isomers and 4bpt indicates that their structural diversity can be well regulated by the metal ions and positional isomerism of the ligands [46,48], whereas the crystalline products of CoII and CdII coordination polymers with 4bpt and trimesate significantly rely on the reaction conditions [47]. As a continuation of this attractive project, we have extended the dicarboxylate tectons from terephthalate to 1,4-nda, which has a larger conjugated backbone by introducing the fused phenyl group and thus may significantly affect the coordination assembly. Herein, we will describe four CoII, ZnII, and CdII mixed-ligand complexes with 4bpt and 1,4-nda, which display diverse network structures. In addition, this work reveals the significant isomeric effect of 1,4-nda and 2,6-nda on constructing the PbII coordination polymers, which display different 3-D architectures with a rare 5-connected topology and a three-fold interpenetrating diamond lattice, respectively. Thermal stability of these crystalline materials and solid-state fluorescent properties of the ZnII, CdII, and PbII species will also be presented. 2. Experimental 2.1. Materials and general methods With the exception of the ligand 4bpt that was prepared according to the literature method [49], all reagents and solvents for synthesis and analysis were commercially available and used as received. Fourier transform (FT) IR spectra (KBr pellets) were taken on an AVATAR-370 (Nicolet) spectrometer. Elemental analyses were carried out on a CE-440 (Leemanlabs) analyzer. X-ray powder diffraction (XRPD) patterns were recorded on a Rigaku D/max2500 diffractometer for Cu Ka radiation (k = 1.5406 Å), with a scan speed of 2°/min and a step size of 0.02° in 2h. Thermogravimetric and differential thermal analysis (TG–DTA) experiments were performed on a Rigaku Thermoflex analyzer from room temperature to 600 °C under N2 atmosphere at a heating rate of 10 °C/min. Solid-state fluorescence spectra were recorded on a WGY-10 spectrofluorometer at room temperature. 2.2. Synthesis of complexes 1–6 2.2.1. [Co(1,4-nda)(4bpt)(H2O)]n (1) A mixture of Co(OAc)24H2O (25.0 mg, 0.10 mmol), 4bpt (12.0 mg, 0.05 mmol), 1,4-H2nda (10.8 mg, 0.05 mmol), NaOH (1 mL, 0.1 M, water solution), and H2O (10 mL) was heated at 160 °C for 3 days in a sealed Teflon-lined stainless steel vessel

(20 mL) under autogenous pressure. Slow cooling of the reaction mixture to room temperature at a rate of 5 °C/h produced the red strip crystals of 1 in 38% yield (10.1 mg, based on 4bpt). Anal. Calc. for C24H18N6O5Co (1): C, 54.45; H, 3.43; N, 15.88. Found: C, 54.36; H, 3.52; N, 15.96%. IR (cm1): 3441bs, 1608s, 1460m, 1407m, 1369m, 1220w, 1073w, 999w, 940w, 834s, 773m, 737m, 702m, 664m, 607m, 568m, 513m. 2.2.2. {[Co(1,4-nda)2(4bpt)(H2O)2][Co(4bpt)(H2O)4](H2O)1.5}n (2) The same synthetic procedure as that for 1 was used except that sodium hydroxide was not included in the starting reagents. Red block crystals of complex 2 were obtained in 52% yield (15.1 mg, based on 4bpt). Anal. Calc. for C48H47N12O15.5Co2 (2): C, 49.79; H, 4.09; N, 14.52. Found: C, 49.85; H, 4.00; N, 14.35%. IR (cm1): 3431bs, 1617s, 1559s, 1457m, 1407s, 1361s, 1258w, 1213w, 1160w, 1023w, 983w, 789m, 745m, 671m, 613m, 574m, 514m. 2.2.3. {[Zn(1,4-nda)2(4bpt)(H2O)2][Zn(4bpt)(H2O)4](H2O)1.5}n (3) The same synthetic method as that for 2 was used except that Co(OAc)24H2O was replaced by Zn(OAc)22H2O, affording pale-yellow strip crystals of complex 3 in a yield of 51% (14.6 mg, based on 4bpt). Anal. Calc. for C48H47N12O15.5Zn2 (3): C, 49.25; H, 4.05; N, 14.36. Found: C, 49.05; H, 4.15; N, 14.28%. IR (cm1): 3412bs, 3292bs, 1617vs, 1551vs, 1460s, 1408vs, 1360vs, 1257m, 1164w, 1066w, 1019w, 985w, 802s, 745s, 699s, 578s, 513s. 2.2.4. {[Cd2(1,4-nda)2(4bpt)2(H2O)2](DMF)1.5(H2O)3}n (4) A CH3OH/DMF (5 mL, v/v = 4/1) solution of 4bpt (12.0 mg, 0.05 mmol) and 1,4-H2nda (10.8 mg, 0.05 mmol) was carefully layered onto a DMF (3 mL) buffer, below which a water (2 mL) solution of Cd(OAc)22H2O (27.0 mg, 0.10 mmol) was placed in a straight glass tube. Colorless block crystals of complex 4 were obtained after one week upon slow evaporation of the solvents. Yield: 15.9 mg (48%, based on 4bpt). Anal. Calc. for C52.5H52.5Cd2N13.5O14.5 (4): C, 47.43; H, 3.98; N, 14.22. Found: C, 47.55; H, 3.88; N, 14.20%. IR (cm1): 3432bs, 1657s, 1614s, 1562s, 1461m, 1409s, 1363s, 1259w, 1220w, 1097w, 1069w, 1011w, 836m, 782m, 740m, 665m, 611m, 579m. 2.2.5. [Pb(1,4-nda)(DMF)]n (5) To a DMF (10 mL) solution of 1,4-H2nda (10.8 mg, 0.05 mmol) was added a CH3OH/H2O (10 mL, v/v = 4/1) solution of Pb(NO3)2 (16.8 mg, 0.05 mmol) with vigorous stirring for ca. 30 min. Then, the solution was filtered and left to stand at room temperature. Colorless block crystals of complex 5 were obtained after one week in 63% yield (15.5 mg, based on 1,4-H2nda). Anal. Calc. for C15H13NO5Pb (5): C, 36.44; H, 2.65; N, 2.83. Found: C, 36.55; H, 2.40; N, 2.90%. IR (cm1): 1649s, 1588w, 1559s, 1539m, 1509w, 1460m, 1412s, 1364s, 1258m, 1205w, 1101w, 823m, 798m, 669w, 571m. 2.2.6. {[Pb2(2,6-nda)2(DMF)2](DMF)}n (6) The same synthetic method as that for 5 was used except that 1,4-H2nda was replaced by 2,6-H2nda (10.8 mg, 0.05 mmol), forming well-shaped colorless block crystals of 6 after ca. one week in 39% yield (10.4 mg, based on 2,6-H2nda). Anal. Calc. for C33H33N3O11Pb2 (6): C, 37.32; H, 3.13; N, 3.96. Found: C, 37.45; H, 3.05; N, 4.05%. IR (cm1): 1655s, 1603m, 1541s, 1490m, 1398s, 1355s, 1198w, 1096w, 920m, 785s, 754w, 665w, 642w, 543m, 479m, 443m. 2.3. X-ray crystallography Single-crystal X-ray diffraction data for 1–6 were collected on a Bruker Apex II CCD diffractometer with Mo Ka radiation (k = 0.71073 Å) at room temperature. There was no evidence of

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crystal decay during data collection. In each case, a semi-empirical absorption correction was applied (SADABS) and the program SAINT was used for integration of the diffraction profiles [50]. All structures were solved by direct methods using SHELXS and refined with SHELXL [51]. The final refinements were carried out by full-matrix least-squares methods with anisotropic thermal parameters for all non-H atoms on F2. As a role, C- and N-bound H atoms were placed geometrically and refined as riding. The water H atoms were first located in difference Fourier syntheses and then fixed at the calculated positions. Isotropic displacement parameters of H were derived from their parent atoms. The H atoms of one lattice water (O16 with half occupancy) in 2 and 3 as well as those of all water molecules in 4 were not located. Standard geometry constraints were used for one lattice DMF molecule (with half occupancy) in 4 in order to improve the refinement stability, on which the ‘‘FLAT” and soft ‘‘SADI” constraints were also imposed. In 6, one coordinated and one lattice DMF molecules were treated using a disorder model by locating their C atoms in two equivalent sites. Further crystallographic details are listed in Table 1. Selected bond parameters and H-bonding geometries are shown in Tables S2 and S3, respectively. 3. Results and discussion 3.1. Synthesis and general characterization Three synthetic methods were applied to prepare complexes 1– 6, in which 1–3 were synthesized under hydrothermal condition, 4 was obtained by layered diffusion, and 5 and 6 were isolated directly from a CH3OH/DMF/H2O solution. For the CoII complexes 1 and 2, the pH value of the reaction solution is crucial to generate different crystalline products. In the initial preparation of the PbII complexes 5 and 6, the 4bpt ligand was also added to the reaction system, which however was not included in the final crystalline products. Further related experiments reveal that both complexes can be obtained under the same condition without the presence of 4bpt. Complexes 1–6 are air stable with the maintenance of their crystallinity for at least several weeks and are insoluble in water and common organic solvents. The compositions of all complexes

were identified by single-crystal X-ray diffraction, microanalysis, and IR techniques. Their phase purities of the bulk samples were also confirmed by the X-ray powder diffraction (XRPD) patterns (see Fig. S1), which show essential similarity to those of the calculated ones. In the IR spectra of 1–6, the absence of characteristic absorption bands of carboxyl indicates the complete deprotonation of the naphthalenedicarboxylic acids. As a result, the antisymmetric and symmetric stretching vibrations of carboxylate are observed in the range of 1541–1617 and 1360–1412 cm1, respectively. Additionally, the strong absorption bands appearing at 1649–1657 cm1 in the IR spectra of 4–6 suggest the presence of DMF molecules. 3.2. Structural description of 1–6 3.2.1. [Co(1,4-nda)(4bpt)(H2O)]n (1) Complex 1 crystallizes in the acentric space group Pna21 with the flack parameter of 0.01(1), showing a 3-D supramolecular architecture via the inclined polycatenation of 2-D (4,4) coordination layers. In this structure, each CoII center takes a distorted octahedral geometry (see Table S1 for detailed bond parameters), comprising four oxygen atoms from two 1,4-nda and one water ligand in the equatorial plane as well as two axial pyridyl nitrogen donors of a pair of 4bpt (see Fig. 1a). In each 1,4-nda ligand, two carboxylate groups adopt the chelating and monodentate coordination modes (I, see Chart 1), respectively, which deviate by 7.8(2)° from co-planarity and take the dihedral angles of 71.8(1)° and 64.8(1)° with the attached phenyl ring. As for 4bpt, the triazolyl plane forms the dihedral angles of 36.3(1)° and 16.0(1)° with the terminal pyridyl rings, which are inclined to each other by 26.4(1)°. As a result, the CoII centers are extended by 4bpt and 1,4-nda building blocks along the [1 0 0] and [0 1 1] directions to form a 2-D (4,4) coordination layer (see Fig. 1b), with the adjacent Co  Co separations of 14.886(1) and 10.529(1) Å. The void space of each rectangle grid is so large that it can be threaded by one equivalent grid from another layer. Thus, each 2-D net is entangled with an infinite number of other parallel layers in an inclined fashion (with the dihedral angle of 42.8(1)°), forming a 2-D ? 3-D polycatenated framework (see Fig. 1c). Furthermore, multiple H-bonding

Table 1 Crystallographic data and structural refinement summary for complexes 1–6.

Chemical formula Formula weight Crystal size (mm3) Crystal system Space group a (Å) b (Å) c (Å) a (°) b (°) c (°) V (Å3) Z qcalc (g cm3) l (mm1) F(0 0 0) Total/independent reflections Parameters Rint Ra, Rwb Goodness-of-fitc a b c

1

2

3

4

5

6

C24H18N6O5Co 529.37 0.24  0.12  0.11 orthorhombic Pna21 14.8855(6) 19.4823(8) 7.6427(3) 90.00 90.00 90.00 2216.4(2) 4 1.586 0.826 1084 10904/3733 325 0.0246 0.0261, 0.0603 1.036

C48H47N12O15.5Co2 1157.84 0.18  0.16  0.12 triclinic  P1

C48H47N12O15.5Zn2 1170.72 0.25  0.12  0.10 triclinic  P1

C52.5H52.5N13.5O14.5Cd2 1329.38 0.24  0.22  0.18 triclinic  P1

12.245(4) 14.439(5) 14.821(5) 87.581(5) 85.595(5) 70.548(5) 2463(1) 2 1.561 0.758 1194 12646/8581 703 0.0154 0.0379, 0.0930 1.051

12.2639(4) 14.4397(5) 14.8293(5) 87.633(1) 85.596(1) 70.426(1) 2466.7(1) 2 1.576 1.057 1206 12758/8661 703 0.0157 0.0341, 0.0775 1.015

12.042(2) 13.406(2) 19.474(3) 92.830(2) 92.253(3) 107.732(2) 2985.8(8) 2 1.479 0.786 1348 14779/10261 770 0.0199 0.0767, 0.1904 1.135

C15H13NO5Pb 494.45 0.24  0.22  0.18 orthorhombic P212121 6.9810(5) 13.4564(9) 15.756(1) 90.00 90.00 90.00 1480.1(2) 4 2.219 11.421 928 7586/2605 201 0.0273 0.0193, 0.0481 1.094

C33H33N3O11Pb2 1062.00 0.22  0.20  0.18 monoclinic P21/c 12.4663(5) 18.3331(7) 16.0996(6) 90.00 107.603(1) 90.00 3507.2(2) 4 2.011 9.651 2016 17741/6176 498 0.0255 0.0220, 0.0448 1.042

R = R||Fo||Fc||/R|Fo|. Rw = [R[w(Fo2Fc2)2]/Rw(Fo2)2]1/2. GOF = {R[w(Fo2Fc2)2]/(np)}1/2.

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presence of NaOH [17], which shows a similar 2-D layered coordination network to that of 1. However, in this case, these layers are further extended to a 3-D supramolecular architecture via hydrogen bonding. Such a structural discrepancy may be ascribed to the dissimilar backbones of bipy and 4bpt, which lead to different sizes of the grid for the 2-D layers (14.886  10.529 Å2 for 1 and 11.288  11.484 Å2 for {[Co(1,4-nda)(bipy)(H2O)2]H2O}n). 3.2.2. {[M(1,4-nda)2(4bpt)(H2O)2][M(4bpt)(H2O)4](H2O)1.5}n (M = CoII for 2 and ZnII for 3) Complexes 2 and 3 are isostructural (see Table 1) and thus herein, only the crystal structure of 2 is described in detail. In this case, two types of 1-D infinite coordination chains with different compositions are found, which are further interconnected via hydrogen bonds to afford an unusual 3-D supramolecular architecture. As shown in Fig. 2a, the asymmetric unit consists of two crystallographically independent CoII centers with different coordination environments. The Co1 ion is coordinated by four equatorial water ligands and two axial pyridyl groups of 4bpt, whereas the octahedral sphere of Co2 is defined by two axial pyridyl nitrogen donors of 4bpt and four equatorial oxygen atoms from two water and two 1,4-nda ligands. In each 1,4-nda, one carboxylate is unidentate and the other is uncoordinated (II, see Chart 1). The carboxylate groups of O5–C37–O6 and O7–C42–O8 are inclined to each other by 24.8(4)° and make the dihedral angles of 40.7(2)° and 51.5(1)° with the phenyl plane (the corresponding parameters in the other 1,4nda are 83.6(2)°, 61.5(2)°, and 35.6(2)°, respectively). The two 4bpt ligands also show different backbone geometries. In 4bpt involving N1 and N6, the two pyridyl groups deviate by 16.0(1)° from co-planarity and form the dihedral angles of 7.5(1)° and 23.4(1)° with the central triazolyl plane, whereas the corresponding values in the other 4bpt (involving N7 and N12) are 51.2(1)°, 16.1(1)°, and 35.2(1)°, respectively. Along the [0 0 1] direction, the CoII centers are extended by the 4bpt spacers to generate two types of 1-D coordination chains (see Fig. 2b), in each of which the adjacent Co  Co distance is 14.821(5) Å. Interestingly, the Co2 chains are interconnected via H-bonds such as N5–H5AO3, N5–H5BO5, and O10–H10AO7 to afford a 3-D framework with available 1-D channels, in which the Co1 chains are captured to constitute a host–guest lattice (see Fig. 2c). This supramolecular architecture is further consolidated by multiple hydrogen bonds between two types of 1-D chains as well as those between the chains and included lattice water molecules (see Table S2 for details). Notably, small potential solvent accessible voids (51.4 Å3, 2.1% of the unit cell volume) are found as calculated by PLATON program. In this regard, a related ZnII complex {[Zn(1,4-nda)(bipy) (H2O)2]H2O}n [23] has been prepared at room temperature in a CH3OH/DMF solution, which is isostructural to its CoII analogue {[Co(1,4-nda)(bipy)(H2O)2]H2O}n [17] that is discussed above. This result also reveals the distinct tectonic functions of the linear bipy and bent 4bpt building blocks.

Fig. 1. Views of 1. (a) Coordination environment of CoII with atom labeling of the asymmetric unit. (b) 2-D (4,4) coordination layer. (c) Schematic representation of the 3-D polycatenated supramolecular framework.

interactions (O5–H5B  N2, O5–H5B  N3, N5–H50   O1, and N5– H500   O2) between the adjacent entangled layers as well as that between the parallel layers (O5–H5A  O4) are observed to sustain the final 3-D supramolecular network (see Table S2 for details of hydrogen bonding). A closely related complex {[Co(1,4-nda)(bipy)(H2O)2]H2O}n (bipy = 4,40 -bipyridine) has been hydrothermally prepared in the

3.2.3. {[Cd2(1,4-nda)2(4bpt)2(H2O)2](DMF)1.5(H2O)3}n (4) Complex 4 has similar (4,4) layered coordination arrays to those of 1, which however are of 2-fold parallel interpenetration in this structure. There exist two crystallographically independent CdII ions in the asymmetric unit with similar pentagonal-bipyramidal geometries, both of which are hepta-coordinated to five oxygen atoms from two chelating carboxylates and one water as well as a pair of axial pyridyl nitrogen donors from 4bpt (see Fig. 3a). The carboxylate groups of O1–C23–O2 and O3–C24–O4 in one 1,4-nda are inclined to each other by 24.3(8)°, which make the dihedral angles of 51.6(6)° and 29.3(7)° with the affiliated phenyl group, whereas the corresponding values in the other 1,4-nda are 14.5(9)°, 48.6(5)°, and 39.5(7)°, respectively. As far as the 4bpt

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Chart 1. Coordination modes of the naphthalenedicarboxylate ligands in complexes 1–6.

spacer involving N1 and N6, the two pyridyl rings are inclined by 78.7(4)° from co-planarity and make the dihedral angles of 45.6(4)° and 34.8(5)° with the central triazolyl plane, whereas the corresponding values in the other 4bpt molecule are 68.1(4)°, 15.4(4)°, and 53.0(4)°, respectively. As illustrated in Fig. 3b, the CdII ions are interlinked by 1,4-nda  0] and [1 1 0] (mode III, Chart 1) and 4bpt spacers along the [1 1 axes to afford a 2-D (4,4) layer with large rectangular grids, in which the Cd  Cd distances separated by 4bpt and 1,4-nda are 15.046(2) and 13.302(2)/11.343(2) Å, respectively. Notably, a pronounced bend at the two 1,4-nda around each metal center results in the undulating character of the 2-D layer, and the undulation of two adjacent such 2-D arrays is out-of-phase, which leads to the formation of a 2-fold interpenetrating pattern to greatly decrease the potential voids (see Fig. 3c). Analysis of the crystal packing indicates that such two-fold interpenetrating patterns adopt the anti-parallel arrangement along the [0 0 1] axis with some offset, among which the lattice DMF and H2O guests are included (see Fig. 3c). As expected, H-bonding interactions involving the coordination layers and/or lattice solvents are found to further stabilize this structure (see Table S2). In addition, there exist very small voids of 38.0 Å3 (1.3% of the unit cell volume) in this case. Two related CdII coordination polymers with terephthalate and 4bpt have been reported in our recent work [46,48], which also show similar (4,4) layered frameworks of 2-fold interpenetration to that of 4. However, in these two structures, there exist large channels to accommodate the lattice solvents in despite of network interpenetration, which are not available in the structure of 4. This structural discrepancy can be ascribed to the bulk naphthalene backbone of 1,4-nda in 4, which occupies most of the space voids. 3.2.4. [Pb(1,4-nda)(DMF)]n (5) and {[Pb2(2,6-nda)2(DMF)2](DMF)}n (6) PbII is an interesting component for the construction of unusual network solids due to its large ion radius, flexible coordination environment and the possible occurrence of the stereochemically active lone pair of electrons [52–55]. Notably, the crystal structure of 5 (space group P212121 with the flack parameter of 0.003(2)) has been reported recently, but without a clear analysis of its complicated 3-D chiral framework [56]. Thus here, we will mainly focus on its intriguing structural feature by using the topological approach to illustrate the infrequent network connectivity. With regard to 1,4-nda, the two carboxylate groups are inclined to the

conjunctive phenyl ring by 36.0(4)° and 60.6(3)°, respectively, which are almost perpendicular to each other with a dihedral angle of 85.9(4)°. Each PbII ion is coordinated by five 1,4-nda and each 1,4-nda dianion is linked to five PbII centers via two bridging carboxylate groups (IV, Chart 1), as depicted in Fig. 4a. Thus, a 3-D coordination framework is formed with both PbII and 1,4-nda serving as the five-connected nodes (see Fig. 4b), which however are not topologically equivalent. In fact, each PbII center is a trigonalbipyramidal node with the vertex symbol of (4.4.4.4.4.4.63.63.63.66), whereas each 1,4-nda acts as a planar pentagonal node with the vertex symbol of (42.42.42.6.6.64.64.66.827.827), constituting a binodal 5-connected framework with the Schläfli symbol of (43.65.82)(46.64). So far, a variety of 3-D coordination nets with 3-, 4-, and 6-connected nodes have been presented [57–64]. However, coordination polymers with 5-connected structural prototypes are quite limited due to the difficulty in achieving such connectivity for the metal ion nodes as well as the crystallographic problem caused by 5-fold symmetry [65–67]. Remarkably, the 3-D framework of 5 represents an unprecedented 5-connected topology, which also reveals that the 5-fold symmetry is not necessary to establish a network with such an unusual connectivity [62]. To further investigate the influence of isomeric effect of ligand tecton on structural assembly, a longer rigid isomer 2,6-nda in comparison with 1,4-nda was applied to construct a completely different 3-D PbII complex 6 with a 3-fold interpenetrating diamondoid framework. Fig. 5a displays the similar octahedral spheres of two crystallographically independent PbII centers, coordinating to six oxygen donors of three 2,6-nda and one DMF. In this case, the carboxylate groups in each 2,6-nda are almost co-planar with the naphthalene backbone, which is different to that in 1,4-nda. The carboxylate groups of O1–C1–O2 and O8–C22–O9 in two centrosymmetric 2,6-nda ligands adopt the chelating fashion, whereas those of O4–C10–O5 and O6–C17–O7 in another 2,6-nda take the g-O, O0 -l-O, O mode (V and VI, see Chart 1). As a result, the PbII ions are linked by these 2- and 4-connected ligands to afford a 3-D coordination framework. In this structure, two adjacent Pb1 and Pb2 centers are bridged by a pair of carboxylate oxygen atoms to form a dimeric unit with the Pb  Pb distance of 4.087(1) Å (see Fig. 5a). Viewing from the topological standpoint, such dinuclear motifs can be considered as the tetrahedral secondary building units (SBUs) to constitute a familiar 3-D diamondoid network. Further analysis of the crystal packing reveals that three such identical networks are mutually entangled to afford a 3-fold interpenetrating

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Fig. 2. Views of 2. (a) Coordination environments of two crystallographically independent CoII centers. (b) Two different 1-D polymeric chains extended by the 4bpt spacers. (c) 3-D host–guest crystalline lattice (blue for hydrogen bonding host consisting of Co2 chains and pink for Co1 chains as guests). (For interpretation of the references to colour in this figure legend, the reader is referred to the web version of this article.)

3-D lattice (see Fig. 5b). Even after interpenetration, large triangular channels are found along [0 0 1], which are occupied by the coordinated and lattice DMF molecules (see Fig. 5c). The effective free volumes of 6 before and after the elimination of all DMF components are 51.7 and 1571.4 Å3, respectively, corresponding to 1.5% and 44.8% of the unit cell volume.

3.3. Influence factors on ligand binding and network assembly The experimental results suggest that the network structures of coordination polymers presented in this work can be significantly affected by several factors such as the metal ion, tecton isomerism, and even basicity of the reaction system. And as expected, the

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Fig. 3. Views of 4. (a) Coordination environments of two crystallographically independent CdII ions. (b) Two-fold parallel interpenetrating structure of the 2-D (4,4) coordination layers. (c) Packing diagram of the interpenetrating arrays with the inclusion of lattice DMF molecules.

naphthalenedicarboxylate building blocks display various coordination modes with the metal ions (see Chart 1), which thus play different roles in network construction and are responsible for

their structural diversity. For instance, the basicity of solution is critical to produce the distinct CoII coordination species 1 and 2. As a consequence, the 1,4-nda ligands in 1 serve as spacers to

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Fig. 4. Views of 5. (a) Connectivity of PbII and 1,4-nda in the 3-D coordination network. (b) Schematic representation of the 5-connected network with (43.65.82) (46.64) topology.

bridge the CoII ions via two terminal carboxylate groups, whereas those in 2 are only unidentate ligation. Although complexes 1 and 4 display similar 2-D (4,4) networks, the different coordination geometries of CoII and CdII may be responsible for their distinct entangled fashions between the 2-D layers. That is to say, for each pentagonal-bipyramidal CdII center in 4, the angle between two chelated carboxylate groups within the equatorial plane is smaller than that in 1, which leads to the corrugated feature and thus 2fold interpenetration of the layers, whereas the 2-D sheets in 1 are polycatenated to construct a 3-D architecture. As for the PbII species 5 and 6, they display distinct 5-connected compact lattice and three-fold interpenetrating diamond framework with 1-D channels. This significant structural discrepancy can be ascribed to the positional difference of two carboxylate groups on the naphthyl backbone for the isomeric 1,4-nda and 2,6-nda tectons, which leads to the variety of their length, steric effect, and binding mode. 3.4. Thermal stability Thermal properties of the coordination polymers have been studied by TG–DTA technique (see Fig. S2 for TG–DTA curves)

[68]. The TG result indicates that complex 1 is thermally stable to 226 °C, upon which pyrolysis of the coordination framework occurs and ends at 426 °C. Correspondingly, one endothermic and one exothermic peaks are observed at 300 and 418 °C in the DTA curve. No weight loss is found upon further heating to 600 °C. In the TG curve of 2, a series of consecutive weight loss occurs in the temperature range of 31–410 °C, with two endothermic peaks and one exothermic peak at 132/243 and 397 °C in the DTA curve. No weight loss is found upon further heating to 600 °C. For 3, the first weight loss of 6.73% in 44–115 °C corresponds to the elimination of four and a half water molecules (calc: 6.92%), with one endothermic peak at 117 °C in DTA. The residual framework starts to decompose at 282 °C, which stops at 529 °C with one exothermic peak observed at 514 °C in the DTA curve. No weight loss is found upon further heating to 600 °C. In the TG curve of 4, the first weight loss of all lattice water and DMF molecules is observed in the range of 86–290 °C (found: 11.08% and calc: 12.31%), with one endothermic peak at 110 °C in DTA. With that, pyrolysis of the residual species occurs and stops at 485 °C, with two exothermic peaks at 332 and 470 °C in DTA. No weight loss is observed upon further heating to 600 °C. As for 6, the weight loss in

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mic peak at 501 °C in the DTA curve. No weight loss is found upon further heating to 600 °C. 3.5. Photoluminescence properties Coordination polymers with d10 metal centers and conjugated organic ligands are promising candidates for photoactive inorganic–organic hybrid materials [69,70]. Therefore, solid-state luminescent properties of the polymeric ZnII, CdII, and PbII complexes 3–6 were studied. The free ligands show the maximum emissions at 380 nm for 4bpt (kex = 319 nm), 484 nm for 1,4H2nda (kex = 400 nm), and 469 nm for 2,6-H2nda (kex = 386 nm), which can be attributed to the p ? p* and/or n ? p* transitions. For complex 3, the maximum emission band is weak and observed at ca. 413 nm, whereas no obvious emission peak is found for 4 (kex = 319 nm, see Fig. S3a), probably due to the quenching effect of solvent molecules. For complexes 5 and 6, the maximum emission bands appear at ca. 389 and 454 nm (kex = 400 and 386 nm, see Fig. S3b), respectively, which may originate from the intraligand transition of naphthalenedicarboxylate [70]. Additionally, the significant blue shift of the emission peak for complex 5 in comparison with that of 1,4-H2nda may be assigned to the incorporation effect of metal–ligand interaction and deprotonation of the ligand. 4. Conclusions and perspective A series of CoII, ZnII, and CdII coordination polymers with 1,4naphthalenedicarboxylate and a bent dipyridyl co-ligand 4-amino-3,5-bis(4-pyridyl)-1,2,4-triazole are presented, which display multifarious supramolecular structures such as the 2-D ? 3-D polycatenated network, H-bonding host–guest lattice consisting of two types of coordination chains, and 2-fold parallel interpenetrating array of (4,4) coordination layers. This result reveals the effect of basicity for the reaction solution and coordination geometry for the metal center on structural construction of these coordination networks. On the other hand, the remarkable isomeric effect of naphthalenedicarboxylate tectons on directing such crystalline networks has also been indicated by a pair of PbII complexes with 1,4-nda and 2,6-nda, which show distinct 3-D 5-connected and three-fold interpenetrating diamond frameworks. In these complexes, the naphthalenedicarboxylate ligands exhibit versatile binding fashions, which will be ultimately responsible for structural diversity of the resulting coordination polymers. Significantly, the twist of carboxylates in 1,4-nda arising from the space hindrance of bulk naphthyl group in comparison with that of terephthalate may result in different connecting modes with the metal centers and thus, benefit for constructing unusual coordination networks. The present work also confirms that the mixed-ligand synthetic strategy is reliable to design and synthesize new coordination polymers and further systematic investigations on such network-based crystalline materials with 4bpt and other aromatic polycarboxylate tectons are our ongoing projects. Acknowledgements Fig. 5. Views of 6. (a) Coordination environments of two crystallographically independent PbII ions. (b) Schematic representation of the 3-fold interpenetrating diamondoid framework. (c) Packing diagram showing the triangular channels with the inclusion of lattice DMF molecules.

97–416 °C range (found: 13.51% and calc: 13.77%) in the TG curve may be ascribed to the exclusion of one lattice and one coordinated DMF molecules, with two endothermic peaks at 152 and 181 °C and one exothermic peak at 365 °C in DTA. Subsequently, the residue starts to decompose, which ends at 526 °C with one exother-

This work was financially supported by the National Natural Science Foundation of China (No. 20671071), Program for New Century Excellent Talents in University (No. NCET-07-0613), Tianjin Normal University, and SRF for ROCS, SEM. Appendix A. Supplementary data CCDC 721408, 721409, 721410, 721411, 721412 and 721413 contains the supplementary crystallographic data for complexes

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