Novel metal-organic and supramolecular 3D frameworks constructed from flexible biphenyl-2,5,3′-tricarboxylate blocks: Synthesis, structural features and properties

Journal of Molecular Structure 1145 (2017) 339e346

Contents lists available at ScienceDirect

Journal of Molecular Structure journal homepage: http://www.elsevier.com/locate/molstruc

Novel metal-organic and supramolecular 3D frameworks constructed from flexible biphenyl-2,5,30 -tricarboxylate blocks: Synthesis, structural features and properties Ao You a, Yu Li a, **, Ze-Min Zhang a, Xun-Zhong Zou b, Jin-Zhong Gu c, *, Alexander M. Kirillov d, Jin-Wei Chen e, Yun-Bo Chen f a

College of Environmental Engineering, Guangdong Industry Polytechnic, Guangzhou, 510300, China School of Traditional Chinese Medicine/School of Pharmacy, Guangdong Pharmaceutical University, Guangzhou, 510006, China Key Laboratory of Nonferrous Metal Chemistry and Resources Utilization of Gansu Province and College of Chemistry and Chemical Engineering, Lanzhou University, Lanzhou, 730000, China d Centro de Química Estrutural, Complexo I, Instituto Superior T
ecnico, Universidade de Lisboa, Av. Rovisco Pais, 1049-001, Lisbon, Portugal e College of Light Chemistry Engineering, Guangdong Industry Polytechnic, Guangzhou, 510300, China f Guangzhou Shanhe Chemical Co,. Ltd., Guangzhou, 510440, China b c

a r t i c l e i n f o

a b s t r a c t

Article history: Received 2 December 2016 Received in revised form 10 May 2017 Accepted 16 May 2017 Available online 17 May 2017

Biphenyl-2,5,30 -tricarboxylic acid (H3L) was selected as an unexplored tricarboxylate building block and applied for the hydrothermal synthesis of three novel coordination compounds, namely a 0D tetramer [Co4(HL)2(m3-HL)2(phen)6(H2O)2]$3H2O (1) and two 3D metal-organic frameworks (MOFs) [Cd3(m5-L)(m6L)(py)(m-H2O)2(H2O)]n$H2O (2) and [Zn3(m4-L)2(2,20 -bpy)(m-4,40 -bpy)]n$2H2O (3). These products were easily generated in aqueous medium from the corresponding metal(II) chlorides, H3L, and various Ndonor ancillary ligands, selected from 1,10-phenanthroline (phen), pyridine (py), 2,20 -bipyridine (2,20 bpy), and 4,40 -bipyridine (4,40 -bpy). Compounds 1e3 were isolated as stable crystalline solids and were fully characterized by IR and UVevis spectroscopy, elemental, thermogravimetric (TGA), powder (PXRD) and single-crystal X-ray diffraction analyses. Compound 1 possesses a discrete tetracobalt(II) structure, which is extended into a 3D H-bonded network with the pcu topology. In contrast, MOF 2 discloses a very complex trinodal 4,5,12-connected net with an undocumented topology, while MOF 3 features the nce/I topological framework. The magnetic (for 1) and luminescence (for 2 and 3) properties were also studied and discussed. The present study thus widens a still very limited family of metal-organic and supramolecular frameworks driven by flexible biphenyl-2,5,30 -tricarboxylate building blocks. © 2017 Elsevier B.V. All rights reserved.

Keywords: Biphenyl-2,5,30 -tricarboxylic acid Coordination compound Magnetic properties Luminescent properties

1. Introduction The design of novel metal-organic frameworks (MOFs) has seen a tremendous popularity in recent years due to not only their fascinating architectures and topologies but also because of their notable applications as functional materials in different areas [1e12]. Nevertheless, it is still a considerable challenge to control the structural and functional characteristics of MOFs during their assembly processes, since a high diversity of factors can alter the structure of resulting products. Examples of such factors include

* Corresponding author. ** Corresponding author. E-mail addresses: [email protected] (Y. Li), [email protected] (J.-Z. Gu). http://dx.doi.org/10.1016/j.molstruc.2017.05.075 0022-2860/© 2017 Elsevier B.V. All rights reserved.

the coordination geometry of metal nodes, interconnectivity of organic spacers, reaction conditions and stoichiometry, and presence of ancillary ligands [13e18]. It is thus particularly interesting to test various flexible organic building blocks containing modifiable backbones and connectivity information as spacers along with the metal centers having different coordination preferences. Many aromatic polycarboxylic acids are frequently applied for this purpose [2,14,18e23]. Aiming at extending our general research line in this field [19,20,22,24,25], we have searched for relatively simple but yet little explored aromatic polycarboxylic acids with a potential to generate complex and topologically unique metal-organic or supramolecular frameworks. Hence, in the present work we selected biphenyl-2,5,30 -tricarboxylic acid (H3L) as a promising and flexible building block on account of the following considerations.

340

A. You et al. / Journal of Molecular Structure 1145 (2017) 339e346

(1) H3L contains three COOH groups that may be completely or partially deprotonated, depending on the pH. (2) This is a flexible ligand due to possible rotation of phenyl rings around the CeC single bond. (3) This carboxylic acid has been very little explored toward the synthesis of MOFs [26e28], as confirmed by a search of the Cambridge Structural Database. Hence, we report herein the hydrothermal synthesis, full characterization, crystal structures, topological classification, thermal stability, and magnetic and luminescent properties of three novel coordination compounds; their structures range from a 3D supramolecular framework [Co4(HL)2(m3-HL)2(phen)6(H2O)2]$3H2O (1) to 3D metal-organic frameworks [Cd3(m5-L)(m6-L)(py)(m-H2O)2(H2O)]n$H2O (2) and [Zn3(m4-L)2(2,20 -bpy)(m-4,40 -bpy)]n$2H2O (3). 2. Experimental 2.1. Materials and physical measurements All chemicals and solvents were of A.R. grade and used without further purification. Elemental (C, H, N) analyses were performed on an Elementar Vario EL elemental analyzer. IR spectra were recorded in KBr pellets on a Bruker EQUINOX 55 spectrometer. UV/ Vis absorption spectra were determined on a Varian UV-Cary100 spectrophotometer. Thermogravimetric analyses (TGA) were carried out under a N2 stream with a heating rate of 10  C/min on a LINSEIS STA PT1600 thermal analyzer. Powder X-ray diffraction patterns (PXRD) were determined with a Rigaku-Dmax 2400 diffractometer using Cu-Ka radiation (l ¼ 1.54060 Å) with a step of 0.01, in which the X-ray tube was operated at 40 kV and 40 mA. Excitation and emission spectra of solid samples were recorded at room temperature on an Edinburgh FLS920 fluorescence spectrometer. 2.2. Synthesis and analytical data 2.2.1. [Co4(HL)2(m3-HL)2(phen)6(H2O)2]·3H2O (1) CoCl2$6H2O (0.2 mmol, 47.3 mg), H3L (0.2 mmol, 48.7 mg), phen (0.3 mmol, 59.4 mg), and NaOH (0.4 mmol, 16.0 mg) were mixed in H2O (10 mL) with continuous stirring at room temperature for 15 min, and then sealed in a 25 mL Teflon-lined stainless steel vessel. This was heated at 160  C for 3 days, followed by cooling to room temperature at a rate of 10  C/h. Pink needle-shaped crystals of 1 were isolated manually and washed with distilled water. Yield: 70.3 mg, 55% based on cobalt(II) chloride. Elemental analysis (%) for C132H90N12Co4O29: calcd, C, 62.32; H, 3.56; N, 6.61; found, C, 62.15; H, 3.60; N, 6.52. IR (KBr, cm1): 3466 m, 3058 w, 1711 m, 1590 s, 1568 m, 1517 m, 1495 m, 1426 s, 1405 m, 1385 m, 1289 w, 1220 m, 1146 w, 1130 w, 1104 w, 1084 w, 1045 w, 984 w, 929 w, 868 w, 852 m, 844 m, 827 m, 773 m, 726 s, 701 w, 687 w, 645 w, 517 w. 2.2.2. [Cd3(m5-L)(m6-L)(py)(m-H2O)2(H2O)]n·H2O (2) A mixture of CdCl2$6H2O (0.30 mmol, 60.3 mg), H3L (0.2 mmol, 48.7 mg), and py (6.3 mmol, 0.5 mL) in H2O (10 mL) was stirred at room temperature for 15 min and then sealed in a 25 mL Teflonlined stainless steel vessel. This was heated at 160  C for 3 days, followed by cooling to room temperature at a rate of 10  C/h. Colorless block-shaped crystals of 2 were isolated manually and washed with distilled water. Yield: 63.3 mg, 60% based on cadmium(II) chloride. Elemental analysis (%) for C35H27NCd3O16: calcd, C, 39.85; H, 2.58; N, 1.33; found: C, 39.71; H, 2.55; N, 1.36. IR (KBr, cm1): 3349 m, 1563 s, 1517 s, 1423 m, 1398 s, 1365 s, 1294 w, 1262 w, 1221 w, 1148 w, 1081 w, 1065 w, 1035 w, 987 w, 914 w, 857 w, 837 w, 764 m, 726 w, 702 m, 671 w, 634 w, 572 w.

2.2.3. [Zn3(m4-L)2(2,20 -bpy)(m-4,40 -bpy)]n·2H2O (3) ZnCl2 (0.3 mmol, 40.9 mg), H3L (0.2 mmol, 48.7 mg), 2,20 -bpy (0.15 mmol, 23.4 mg), 4,40 -bpy (0.15 mmol, 23.4 mg), and NaOH (0.6 mmol, 24.0 mg) were mixed in H2O (10 mL) with continuous stirring at room temperature for 15 min, and then sealed in a 25 mL Teflon-lined stainless steel vessel. This was heated at 160  C for 3 days, followed by cooling to room temperature at a rate of 10  C/h. Colorless block-shaped crystals of 3 were isolated manually and washed with distilled water. Yield: 61.1 mg, 55% based on zinc(II) chloride. Elemental analysis (%) for C50H34N4Zn3O14: calcd, C, 54.05; H, 3.08; N, 5.04; found, C, 54.27; H, 3.05; N, 5.10. IR (KBr, cm1): 3437 m, 3079 w, 1610 m, 1548 s, 1506 w, 1449 m, 1423 s, 1382 s, 1262 w, 1221 w, 1174 w, 1112 w, 1070 w, 1050 w, 1019 w, 972 w, 914 w, 863 w, 806 w, 784 m, 733 w, 702 w, 676 w, 640 w, 604 w, 572 w. 2.3. X-ray crystallography The single-crystal data for compounds 1e3 were collected at 293 K on an Bruker APEX-II CCD diffractometer with Mo-Ka radiation (l ¼ 0.71073 Å). The structures were solved using direct methods, which yielded the positions of all non-hydrogen atoms. These were refined first isotropically and then anisotropically. All the hydrogen atoms (except for those bound to water molecules) were placed in calculated positions with fixed isotropic thermal parameters and included in structure factor calculations at the final stage of full-matrix least-squares refinement. The hydrogen atoms of the water molecules were located by difference maps and constrained to ride on their parent O atoms. All calculations were performed using the SHELXTL-97 system [29]. The crystallographic data are summarized in Table 1. Selected bond lengths and angles are listed in Table S1, whereas hydrogen bonds are given in Table S2 (Supplementary Material). 3. Results and discussion 3.1. Hydrothermal self-assembly synthesis To explore biphenyl-2,5,30 -tricarboxylic acid as a flexible building block with three carboxylic acid groups toward the synthesis of Co, Cd, or Zn containing metal-organic or supramolecular 3D frameworks, we have attempted several hydrothermal reactions by treating the corresponding metal(II) chlorides with H3L in the presence of some standard ancillary ligands or potential linkers; these were selected from 1,10-phenanthroline, pyridine, 2,20 bipyridine, or 4,40 -bipyridine (Scheme 1). These reactions resulted in the generation of three novel products formulated as [Co4(HL)2(m3-HL)2(phen)6(H2O)2]$3H2O (1), [Cd3(m5-L)(m6-L)(py)(m(2), and [Zn3(m4-L)2(2,20 -bpy)(m-4,40 H2O)2(H2O)]n$H2O bpy)]n$2H2O (3). The structural differences in the obtained products suggest that their assembly process depends on the type of central metal ion and N-donor ancillary ligand, thus resulting in a 0D tetracobalt(II) compound 1 and 3D metal-organic frameworks 2 and 3. All compounds were isolated as stable crystalline solids and were characterized by standard methods, namely by elemental analysis, IR and UVevis spectroscopy, thermogravimetric analysis, single crystal and powder X-ray diffraction (PXRD). In fact, the PXRD patterns of the bulk samples of 1e3 are in good agreement with the calculated ones from the single crystal X-ray diffraction data (Figs. S1eS3, Supplementary Material), thus indicating the phase purity of the obtained products. 3.2. Crystal structure of [Co4(HL)2(m3-HL)2(phen)6(H2O)2]·3H2O (1) Compound 1 crystallizes in the triclinic space group P1 and its

A. You et al. / Journal of Molecular Structure 1145 (2017) 339e346

341

Table 1 Crystallographic data and structure refinement summary for 1e3. Compound

1

2

3

Formula Mr Crystal system Space group a (Å) b (Å) c (Å) a ( ) b ( ) g ( ) V (Å3) Z T (K) Dcalc (g cm3) Crystal size (mm3) F(000) m (Mo-Ka)/mm1 q ( ) Reflections collected Rint Independent reflections(I  2s(I)) Max. and min. transmission Limiting indices

C132H90N12Co4O29 2543.88 Triclinic Pe1 12.4427(5) 14.2268(8) 16.6929(9) 95.608(4) 96.172(4) 108.610(4) 2756.8(2) 1 293(2) 1.532 0.28  0.20  0.16 1306 0.682 3.28e25.05 18426 0.0345 9725 0.8988/0.8321 14  h  14, 16  k  16, 19  l  19 803 0.392, 0.441 1.054 R1 ¼ 0.0509, wR2 ¼ 0.1148 R1 ¼ 0.0770, wR2 ¼ 0.1306 1470611

C35H27NCd3O16 1054.77 Triclinic Pe1 10.843(2) 12.833(2) 14.064(4) 63.97(2) 70.45(2) 69.181(16) 1606.0(7) 2 293(2) 2.181 0.19  0.15  0.14 1032 2.055 3.277e26.022 8973 0.0582 8973 0.697/1.000 13  h  13, 15  k  15, 17  l  17 517 1.33, 0.95 0.839 R1 ¼ 0.0505, wR2 ¼ 0.0928 R1 ¼ 0.0939, wR2 ¼ 0.1008 1470612

C50H34N4Zn3O14 1110.92 Monoclinic C2/c 31.879(2) 18.2009(11) 7.8060(8) 90 96.830(9) 90 4497.1(6) 4 293(2) 1.641 0.25  0.23  0.20 2256 1.664 3.27e25.05 9016 0.0610 3984 0.7319/0.6811 37  h  32, 21  k  21, 9  l  9 321 0.458, 0.769 1.035 R1 ¼ 0.0590, wR2 ¼ 0.1339 R1 ¼ 0.1016, wR2 ¼ 0.1588 1470613

Parameters D(r)(e$Å3) Goodness-of-fit Final R indices [I > 2s(I)] R indices (all data) CCDC No.

CoCl2 HOOC

COOH

NaOH, phen CdCl2 py

COOH

[Co4(HL)2( 3 -HL)2(phen)6 (H2O)2]·3H2 O (1) 0D

3D H-bonded net

[Cd3( 5-L)( 6-L)(py)( -H2O)2(H2O)]n·H2O (2) 3D MOF

ZnCl2 NaOH 4,4 -bpy, 2,2 -bpy

[Zn3 ( 4-L)2 (2,2 -bpy)( -4,4 -bpy)]n·2H2O (3) 3D MOF

Scheme 1. Structural formula of H3L and simplified scheme of the synthesis of 1e3.

asymmetric unit contains two Co(II) atoms, two HL2 blocks (one terminal and one m3-bridging), three phen moieties, one H2O ligand, and one and a half of lattice H2O molecule per formula unit. As depicted in Fig. 1a, both Co1 and Co2 atoms are six-coordinate and possess distorted octahedral {CoN2O4} and {CoN4O2} environments, respectively. The Co1 center is coordinated by two carboxylate O atoms from two individual m3-HL2e blocks and four N atoms from two phen ligands. The Co2 center is bound by three carboxylate O atoms from one m3-and one terminal HL2 ligands, an O atom from H2O ligand, and two N atoms from the phen moiety. The CoeO bonds range from 2.039(4) to 2.307(4) Å, whereas the CoeN distances vary from 2.110(5) to 2.171(5) Å, which are comparable to those found in other related Co(II) compounds [8,10,18,19]. In 1, the HL2 blocks act either as m3-spacers or terminal ligands (Scheme 2, modes I and II), in which the carboxylate groups show the m-bridging bidentate and the terminal mono- and bidentate modes, respectively. The dihedral angles between the two phenyl rings in the HL2 ligands are 51.93 and 39.33 . As shown in Fig. 1b, two crystallographically equal Co1 centers are bridged by 2-carboxylate groups of two different m3-HL2e blocks, giving rise to a tetranuclear unit. Such tetracobalt(II) units are further assembled

into a 3D H-bonded framework (Fig. 1c). For the sake of its topological analysis [30], only strong DH…A hydrogen bonds were considered [H…A <2.50 Å, D … A <3.50 Å, and :(DH…A) > 120 ; D and A stand for donor and acceptor atoms]. After reduction of the tetracobalt(II) blocks to their centroids, the generated underlying net (Fig. 1d) can be topologically classified as a uninodal 6connected framework with the pcu [alpha-Po primitive cubic] topology and point symbol of (412.63). 3.3. Crystal structure of [Cd3(m5-L)(m6-L)(py)(m-H2O)2(H2O)]n·H2O (2) The asymmetric unit of 2 consists of three crystallographically independent Cd(II) atoms, two different m5-and m6-L3e blocks, one py moiety, three coordinated and one lattice H2O molecules. As depicted in Fig. 2a, the six-coordinate Cd1 center possesses a distorted octahedral {CdO6} environment, filled by three carboxylate O atoms from three different L3 ligands (two m6-and one m5-L3e) and three O atoms from three H2O ligands (including one m-H2O linker); the axial sites are taken by the O1 and O14ii atoms. The sevencoordinate Cd2 atom adopts a distorted {CdO7} pentagonal

342

A. You et al. / Journal of Molecular Structure 1145 (2017) 339e346

(a)

(c)

(b)

(d)

Fig. 1. Structural fragments of 1. (a) Coordination environment of the Co(II) atom (H atoms except those of COOH groups are omitted for clarity). Symmetry codes: i: x, y þ 1, z. (b) View of the tetranuclear unit (phen ligands are omitted for clarity). Symmetry codes: i: x, y þ 1, z. (c) Perspective of a 3D supramolecular framework along the ac plane (blue dashed lines represent hydrogen bonds). (d) Topological representation of the underlying 3D H-bonded network showing a uninodal 6-connected net with the pcu [alpha-Po primitive cubic] topology; rotated view along the c axis; color code: centroids of 6-connected tetracobalt(II) molecular nodes (cyan balls). (For interpretation of the references to color in this figure legend, the reader is referred to the web version of this article.)

Scheme 2. Coordination modes of the HL2/L3 blocks and N-donor ligands (phen, 2,20 -bpy, and 4,40 -bpy) in 1e3.

bipyramid geometry taken by five carboxylate O atoms from four L3 moieties (two m5-and two m6-L3e) and two O atoms from two H2O ligands. The Cd3 center is also seven-coordinate and possesses a distorted pentagonal bipyramid {CdO6N} environment, occupied by six carboxylate O atoms from four individual L3 blocks (two m5and two m6-L3e) and one N atom from a py ligand. The lengths of the

CdeO bonds are in the 2.169(7)e2.771(6) Å range, while the CdeNpy bond is 2.266(7) Å; these are within normal ranges reported for related Cd(II) compounds [2,18e20,22,27]. In 2, the L3 spacers act as m6-or m5-blocks (Scheme 2, modes III and IV), in which the carboxylate groups show the terminal monodentate, mbridging bidentate, or m-bridging tridentate modes. The dihedral angles between the two phenyl rings in the L3 ligands are 53.01 and 52.36 . The carboxylate groups of m5-L3e, m6-L3e, and m-OH2 bridge alternately six Cd(II) atoms to produce hexacadmium(II) motifs (Fig. 2b). These motifs are further interlinked by the L3 blocks to form a very complex 3D open framework (Fig. 2c). It features channels [6.11  12.6 Å measured by atom-to-atom distances], which are filled with guest water molecules. Upon their removal, we computed by the PLATON an effective free volume that is 11.5% of the crystal volume [31]. However, after eliminating both coordinated and guest water molecules, the effective free volume attains 18.7% of the crystal volume of 2. Aiming at getting further insight into the intricate 3D metal-organic framework, we performed its topological analysis [30,32]. After simplification procedure (terminal ligands were eliminated and all bridging blocks were contracted to their centroids), an underlying 3D net was obtained. In this net, one can observe the presence of [Cd4(m-H2O)4]8þ secondary building units (SBUs) that are composed of two pairs of Cd1 and Cd2 atoms. These SBUs were reduced to their centroids and treated as the 12-connected cluster nodes which, along with the 4-connected Cd3 nodes and 5-connected m5-L nodes, form a further simplified 3D underlying net (Fig. 2d). The topological analysis [30] of this net revealed a trinodal 4,5,12-connected framework with the unique topology. It is described by the point

A. You et al. / Journal of Molecular Structure 1145 (2017) 339e346

(a)

343

(b)

(c)

(d)

Fig. 2. Structural fragments of 2. (a) Coordination environment of the Cd(II) atoms (H atoms are omitted for clarity). Symmetry codes: i: x þ 1, y þ 1, z; ii: x þ 1, y þ 1, z þ 1; iii: x þ 1, y, z þ 1; iv: x þ 1, y, z þ 1; v: x, y þ 1, z; vi: x þ 2, y þ 1, z. (b) Hexacadmium(II) motif. Symmetry codes: i: x þ 1, y þ 1, z þ 1; ii: x þ 1, y þ 1, z; iii: x þ 1, y, z þ 1; iv: x  1, y, z þ 1. (c) Perspective of the 3D porous metal-organic framework along the ac plane. (d) Topological representation of the underlying 3D metalorganic framework (after second round of simplification) showing a trinodal 4,5,12-connected net with the unique topology defined by the point symbol of (428.630.88)(46)2(48.62)4; view along the b axis; color codes: centroids of 12-connected [Cd4(m4-H2O)4]8þ cluster nodes based on Cd1/Cd2 atoms (pale green balls), 4-connected Cd3 nodes (turquoise balls), centroids of 5-connected m5-L nodes (gray). (For interpretation of the references to color in this figure legend, the reader is referred to the web version of this article.)

symbol of (428.630.88)(46)2(48.62)4, wherein the (428.630.88), (46), and (48.62)4 notations are those of the [Cd4(m-H2O)4]8þ cluster nodes, Cd3 and m5-L nodes, respectively. An undocumented character of the present topology was confirmed by a search of different databases [30,32,33]. 3.4. Crystal structure of [Zn3(m4-L)2(2,20 -bpy)(m-4,40 -bpy)]n·2H2O (3) The crystal structure of 3 is composed of two Zn(II) atoms (Zn1 with half occupancy and Zn2 with full occupancy), one m4-L3e block, a half of 2,20 -bpy moiety, a half of 4,40 -bpy ligand, and one lattice H2O molecule per formula unit (Fig. 3a). The six-coordinate Zn1 center possesses a distorted octahedral {ZnN2O4} environment, filled by four O atoms from the two different m4-L3e spacers, and two N atoms from 2,20 -bpy moiety. The six-coordinate Zn2 atom is surrounded by five carboxylate O atoms from three independent m4-L3e blocks and one N atom from a m-4,40 -bpy ligand, thus forming a distorted octahedral {ZnNO5} geometry. The ZneO [2.003(4)e2.570(4) Å] and ZneN [2.090(4)e2.092(6) Å] bond distances are in good agreement with those observed in some related Zn(II) compounds [18,20,22,23,28]. In 3, the L3 block acts as a m4spacer (Scheme 2, mode V), in which the three carboxylate groups

show the terminal bidentate and m-bridging tridentate modes. The dihedral angle between the two phenyl rings in the m4-L3e ligand is 64.08 . The 4,40 -bpy moiety acts as a m-linker (Scheme 2, mode VIII) and its pyridyl rings are not coplanar showing a dihedral angle of 4.68 . The m4-L3e spacers and m-4,40 -bpy linkers alternately assemble the adjacent Zn(II) centers to form a very complex 3D open framework (Fig. 3b). This features channels [9.70  10.8 Å measured by atom-to-atom distances], which are filled with guest water molecules. Upon their removal, we computed by the PLATON an effective free volume that is 9.4% of the crystal volume [31]. For the sake of topological classification of this network [30,34], we generated a simplified underlying net (Fig. 3c) by omitting terminal phen ligands and reducing all the bridging ligands to centroids maintaining their connectivity. The resulting net is composed of the 4-connected Zn2 and m4-L nodes (these are topologically equivalent) and the 2-connected Zn1 atoms and m-4,4’-bpy linkers. This net can be classified as a uninodal 4-connected framework with the nce/I topology and point symbol of (42.63.8). 3.5. Thermogravimetric analysis Thermal stability of compounds 1e3 was evaluated by thermogravimetric analysis (TGA) under nitrogen atmosphere. As

344

A. You et al. / Journal of Molecular Structure 1145 (2017) 339e346

(a)

(b)

(c)

Fig. 3. Structural fragments of 3. (a) Coordination environment of the Zn(II) atoms (H atoms are omitted for clarity). Symmetry codes: i: x þ 1, y, z þ 3/2; ii: x þ 1/2, y þ 3/ 2, z þ 1; iii: x þ 1/2, y  1/2, z þ 1/2. (b) Perspective of the 3D porous metal-organic framework along the ab plane. (c) Topological representation of the underlying framework showing a uninodal 4-connected net with the nce/I topology; view along the c axis; color code: 4-connected Zn2 nodes and 2-connected Zn1 atoms (cyan balls), centroids of 4connected m4-L nodes (gray), centroids of 2-connected m2-4,4’-bpy linkers (blue). (For interpretation of the references to color in this figure legend, the reader is referred to the web version of this article.)

shown in Fig. 4, compound 1 loses its three lattice and two coordinated water molecules (exptl, 3.3%; calcd, 3.5%) in the 155e236  C temperature range. The dehydrated sample remains stable up to 261  C followed by the decomposition. For MOF 2, there

is one distinct thermal effect in the 37e140  C range that corresponds to the removal of one lattice and three coordinated H2O molecules (exptl, 6.7%; calcd, 6.8%). A dehydrated sample remains stable up to ~350  C. Similarly, MOF 3 shows the loss of two lattice water molecules between 64 and 166  C (exptl, 3.3%; calcd, 3.2%) and a dehydrated sample remains stable up to ~360  C. 3.6. UVevisible spectra The UVevis spectra of compounds 1e3 and biphenyl-2,5,30 tricarboxylic acid (H3L) were measured at room temperature in the solid state using microcrystalline samples (Fig. S4). The absorption peaks at 267 nm (for H3L) or at 232, 341, and 473 nm (for compound 1), 300 nm (for compound 2), and 303 nm (for compound 3) were observed in the respective spectra. The absorption bands in the ranges of 232e341 and 473 nm can be attributed to the p*/n or p*/p transitions as well as the ded transition of the d7 (Co2þ) cation, respectively [35e37]. 3.7. Luminescent properties

Fig. 4. TGA curves of compounds 1e3.

The emission spectra of compounds 2 and 3, as well as biphenyl2,5,30 -tricarboxylic acid (H3L) were measured in the solid state at room temperature (Fig. 5). The organic H3L block displays a weak photoluminescence with an emission maximum at 472 nm upon excitation at 321 nm. For metal-organic frameworks 2 and 3, the

A. You et al. / Journal of Molecular Structure 1145 (2017) 339e346

345

magnetically isolated spin-only high-spin Co(II) ions (S ¼ 3/2, g ¼ 2.0). This is a common phenomenon for Co(II) ions due to their strong spin-orbit coupling [8,10,19,20]. The cMT values decrease steadily on lowering the temperature and reach the minimum of 5.60 cm3,mol1,K at 2.00 K. The overall magnetic behavior is due to the single ion effects for Co ions and/or weak antiferromagnetic interactions [40]. Because of a long separation between the Co1 and Co2 (9.505(2) Å), only the coupling interactions within the {Co2} unit are considerable (Fig. 1b). Based on the molecular structure, we analyze the magnetic data by a model combining two mononuclear models and one dinuclear model. We apply an Empirical model for a cobalt(II) ion in a distorted octahedral geometry developed by F. Lloret and co-workers [41] and the magnetic susceptibility is expressed in Eq. (1).

cMT ¼

2

Nb ½GðTÞ2 4k

(1)


factor in the G(T) is a temperature dependent function of Lande whole temperature range,

P4

Fig. 5. Solid state emission spectra of H3L (lex. ¼ 321 nm) and compounds 2 and 3 (lex. ¼ 321 nm) at room temperature.

3.8. Magnetic properties Variable-temperature magnetic susceptibility measurements were performed using a powder sample of 1 in the 2e300 K temperature range (Fig. 6). The cMT value of 9.90 cm3,mol1,K at 300 K is much larger than the value (7.48 cm3,mol1,K) expected for four

3 2 Y X

k¼0

GðTÞ ¼ emission bands are significantly more intense and have a maximum at 413 or 482 nm, respectively (lex was 321 nm in both cases). These emission bands may be attributed to the p*/n (for 2) or p*/p (for 3) transitions [19,20,22,23,38,39]. The enhancement of luminescence in 2 and 3 in comparison with H3L can be related to the binding of the L3 blocks to Cd(II) and Zn(II) centers. This can result in the increase the ligand rigidity, thus possibly reducing the loss of energy by radiationless decay [19,20,22,23].

"

P4

"

j¼1

k¼0

3

Ai;j;k xij T k 5

i¼0

3 2 Y X j¼1

!

!

3

(2)

Bi;j;k xij T k 5

i¼0

where x1 ¼ a (orbital reduction factor), x2 ¼ D (axial distortion parameter) and x3 ¼ l (spin-orbit coupling parameter), D and l being given in cm1 and T in Kelvin. The coefficients obtained for this expression are given by F. Lloret. The dinuclear model is derived from the Lines model [41,42], giving the susceptibility expression

cMT ¼

2

Nb ½GðTÞ2 Fdim 3k

(3)

Fdim is the magnetic exchange function,

Fdim ¼

6

  3 þ exp 25J 9kT

(4)

Therefore, the full €I‡MT for 1 is expressed by Eq. (5).

cMT ¼

2

2

Nb Nb ½GðTÞ2 þ ½GðTÞ2 Fdim 2k 3k

(5)

Assuming all four cobalt ions are magnetically identical, the best fit for the magnetic susceptibility data (Fig. 6) gives the following parameters: a ¼ 0.78, D ¼ 522 cm1, l ¼ 179 cm1, J ¼ 0.68 cm1, c2 ¼ 0.01681. The a, D and l parameters are within the range of usual values. The J value indicates the presence of intradimer antiferromagnetic exchanges in 1. 4. Conclusions

Fig. 6. Temperature dependence of cMT vs. T for compound 1. The blue line represents the best fit to the equation in the text. (For interpretation of the references to color in this figure legend, the reader is referred to the web version of this article.)

The present work achieved the synthesis and full characterization of a new series of supramolecular or metal-organic 3D frameworks assembled from biphenyl-2,5,30 -tricarboxylic acid (H3L) as a little explored tricarboxylate building block, thus broadening its still limited application toward the synthesis of multinuclear complexes or MOFs. The versatility of this building block is evident from the variety of its coordination modes observed in compounds 1e3. In fact, apart from acting as the monoprotonated HL2 or fully deprotonated L3 blocks, these

346

A. You et al. / Journal of Molecular Structure 1145 (2017) 339e346

flexible tricarboxylate moieties can behave as terminal ligands (in 1) or act as m3- (in 1), m4- (in 3), and m5- and m6- (in 2) spacers. As a result, the topologically distinct supramolecular (in 1) or metalorganic (in 2 and 3) 3D frameworks can be generated. Their analysis disclosed uninodal 6- or 4-connected nets with the pcu and nce/I topologies in 1 and 3, respectively, whereas a very complex trinodal 4,5,12-connected net with an undocumented topology was identified in 2. These findings show that the use of different metal(II) precursors with H3L and ancillary N-donor ligands can result in the formation of structurally different networks, which also show interesting luminescent or magnetic properties. Future studies toward exploring H3L and related tricarboxylate building blocks for the generation of supramolecular and metal-organic frameworks will be pursued. Acknowledgements This work was supported by Guangdong Province Higher Vocational Colleges & Schools Pearl River Scholar Funded Scheme (2015), the Natural Science Foundation of Guangdong Province, China (Project No. 2016A030313761), the Pearl River Scholar Foundation of Guangdong Industry Polytechnic (Project No. RC2015-001), the Opening Foundation of MOE Key Laboratory of Bioinorganic and Synthetic Chemistry School of Chemistry Sun YatSen University (2016), Science and Technology Planning Project of Guangzhou (Project No. 201510010170) and Polymer Teaching Resources Library Project in Vocational Education of the National Ministry of Education (Project No.:2015-17). AMK acknowledges the FCT (UID/QUI/00100/2013, SFRH/BSAB/114190/2016). Appendix A. Supplementary data Supplementary data related to this article can be found at http:// dx.doi.org/10.1016/j.molstruc.2017.05.075. References [1] [2] [3] [4]

X.D. Zheng, T.B. Lu, CrystEngComm 12 (2010) 324. W.G. Lu, C.Y. Su, T.B. Lu, L. Jiang, J.M. Chen, J. Am. Chem. Soc. 128 (2006) 34. S. Horike, D. Umeyama, S. Kitagawa, Acc. Chem. Res. 46 (2013) 2376. L. Chen, Q.H. Chen, M.Y. Wu, F.L. Jiang, M.C. Hong, Acc. Chem. Res. 48 (2015) 201. [5] L.E. Kreno, K. Leong, O.K. Farha, M. Allendorf, R.P.V. Duyne, J.T. Hupp, Chem. Rev. 112 (2012) 1105. [6] A.H. Chughtai, N. Ahmad, H.A. Younus, A. Laypkov, F. Verpoort, Chem. Soc. Rev.

44 (2015) 6804. [7] M.H. Zeng, Y.L. Zhou, M.C. Wu, H.L. Sun, M. Du, Inorg. Chem. 49 (2010) 6436. [8] M.H. Zeng, Z. Yin, Y.X. Tan, W.X. Zhang, Y.P. He, M. Kurmoo, J. Am. Chem. Soc. 136 (2014) 4680. [9] C. He, K. Lu, D. Liu, W. Jin, J. Am. Chem. Soc. 136 (2014) 5181. [10] M.H. Zeng, Y.X. Tan, Y.P. He, Z. Yin, Q. Chen, M. Kurmoo, Inorg. Chem. 52 (2013) 2353. [11] B. Ding, S.X. Liu, Y. Cheng, C. Guo, X.X. Wu, J.H. Guo, Y.Y. Liu, Y. Li, Inorg. Chem. 55 (2016) 4391. [12] Y.Y. Wang, Q. Jin, S.X. Liu, C. Guo, Y.Y. Liu, B. Ding, X.X. Wu, Y. Li, Z.Z. Zhu, RSC Adv. 5 (2015) 35238. [13] L.N. Zhang, C. Zhang, B. Zhang, C.X. Du, H.W. Hou, CrystEngComm 17 (2015) 2837. [14] X.X. Xu, Y. Lu, E.B. Wang, Y. Ma, X.L. Bai, Cryst. Growth Des. 6 (2006) 2029. [15] A.M. Stepenson, D. Ward, Chem. Commun. 48 (2012) 3605. [16] R. Singh, P.K. Bharatdwaj, Cryst. Growth Des. 13 (2013) 3722. [17] X.M. Chen, M.L. Tong, Acc. Chem. Res. 40 (2007) 162. [18] S. Pal, T.K. Pal, P.K. Bharadwaj, CrystEngComm 18 (2016) 1825. [19] J.Z. Gu, Z.Q. Gao, Y. Tang, Cryst. Growth Des. 12 (2012) 3312. [20] Y.L. Shao, Y.H. Cui, J.Z. Gu, A.M. Kirillov, J. Wu, Y.W. Wang, RSC Adv. 5 (2015) 87484. [21] J.J. Sezer, O.Z. Yessilel, H. Erer, O. Sahin, J. Solid State Chem. 233 (2016) 463. [22] Y.L. Shao, Y.H. Cui, J.Z. Gu, J. Wu, Y.W. Wang, A.M. Kirillov, CrystEngComm 18 (2016) 765. [23] S.S. Chen, L.Q. Sheng, Y. Zhao, Z.D. Liu, R. Qiao, S. Yang, Cryst. Growth Des. 16 (2016) 229. [24] J.Z. Gu, Y.H. Cui, J. Wu, A.M. Kirillov, RSC Adv. 5 (2015) 78889. [25] J.Z. Gu, A.M. Kirillov, J. Wu, D.Y. Lv, Y. Tang, CrystEngComm 15 (2013) 10287. [26] J. Zhao, L.Q. Xie, Y.M. Ma, A.J. Zhou, W. Dong, J. Wang, Y.C. Chen, M.L. Tong, CrystEngComm 16 (2014) 10006. [27] Z.Q. Gao, H.J. Li, K.M. Alexander, J.Z. Gu, Chin. J. Struct. Chem. 33 (2014) 888. [28] W.P. Wu, B. Liu, G.P. Yang, H.H. Miao, Z.P. Xi, Y.Y. Wang, Inorg. Chem. Commun. 56 (2015) 8. [29] G.M. Sheldrick, Acta Crystallogr. (A64) (2008) 112. [30] (a) V.A. Blatov, IUCrCompComm Newsl. 7 (2006) 4; (b) V.A. Blatov, A.P. Shevchenko, D.M. Proserpio, Cryst. Growth Des. 14 (2014) 3576. [31] P. Van der Sluis, A.L. Spek, Acta Crystallogr. Sect. A Found. Crystallogr. 46 (1990) 194. [32] The reticular Chemistry structure resource (RCSR) database M. O'Keeffe, M.A. Peskov, S.J. Ramsden, O.M. Yaghi, Acc. Chem. Res. 30 (2008) 1782. [33] See the Cambridge Structural Database (CSD, Version 5.36, 2015) F.H. Allen, ActaCrystallogr B58 (2002) 380. [34] (a) M. O'Keeffe, O.M. Yaghi, Chem. Rev. 112 (2012) 675; (b) M. Li, D. Li, M. O'Keeffe, O.M. Yaghi, Chem. Rev. 114 (2014) 1343. [35] Z.Q. Shi, Y.Z. Li, Z.J. Guo, H.G. Zheng, Cryst. Growth Des. 13 (2013) 3078. [36] P. Manna, B.K. Tripuramallu, S.K. Das, Cryst. Growth Des. 12 (2012) 4607. [37] L. Qin, Y.Z. Li, Z.J. Guo, H.G. Zheng, Cryst. Growth Des. 12 (2012) 5783. [38] B. Ding, P. Yang, Y.Y. Liu, Y. Wang, G.X. Du, CrystEngComm 15 (2013) 2490. [39] Y.Y. Xu, X.X. Wu, Y.Y. Wang, X.M. Su, S.X. Liu, Z.Z. Zhu, B. Ding, Y. Wang, J.Z. Huo, G.X. Du, RSC Adv. 4 (2014) 25172. [40] O. Kahn, Molecular Magnetism, VCH, New York, 1993. [41] F. Lloret, M. Julve, J. Cano, R. Ruiz-Garcia, E. Pardo, Inorg. Chim. Acta 361 (2008) 3432. [42] M.E. Lines, J. Chem. Phys. 55 (1971) 2977.