Series of coordination polymers based on 4-(5-sulfo-quinolin-8-yloxy) phthalate and bipyridinyl coligands: Structure diversity and properties

Journal of Solid State Chemistry 230 (2015) 80–89

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Series of coordination polymers based on 4-(5-sulfo-quinolin-8-yloxy) phthalate and bipyridinyl coligands: Structure diversity and properties Xun Feng a, Jing Liu b,a, Jin Li a, Lu-Fang Ma a, Li-Ya Wang a,c,n, Seik-Weng Ng d,e, Guo-Zhan Qin a a

College of Chemistry and Chemical Engineering, Luoyang Normal University, Luoyang 471022, China College of Chemistry and Molecular Engineering, Zhengzhou University, Zhengzhou 450001, China c College of Chemistry and Pharmacy Engineering, Nanyang Normal University, Nanyang 473601, China d Department of Chemistry, University of Malaya, Kuala Lumpur 50603, Malaysia e Chemistry Department, Faculty of Science, King Abdulaziz University, Jeddah 80203, Saudi Arabia b

art ic l e i nf o

a b s t r a c t

Article history: Received 29 March 2015 Received in revised form 23 May 2015 Accepted 7 June 2015 Available online 23 June 2015

Reactions between later metal salts and conjugational N-hetrocyclic sulfonate/ carboxylic acid under the presence of bipyridyl auxiliary ligands afforded a series of manganese, nickel, zinc, silver, cadmium coordination polymers bearing with phenyl pendant arm attached to quinoline skeletons, and they have been characterized by elements analysis, thermogravimetry, infrared spectroscopy and single-crystal X-ray diffraction studying. The series of polymers show interesting structural diversity in coordination environment, dimensions and topologies. They are all built from 2-D networks constructed from metal cluster through sulfonate or carboxylate groups, as the secondary building unit (SBU). The thermalgravimetric analyses show that they display framework stabilities in solid state. Variable-temperature magnetic susceptibility studies reveal the existence of antiferromagnetic interactions between adjacent Mn (II) ions in 1, and ferromagnetic interactions between Ni(II) ions for 2, respectively. The photo-luminescence properties of 3-5 have also been investigated systemically. & 2015 Elsevier Inc. All rights reserved.

Keywords: 4-(5-Sulfo-quinolin-8-yloxy) Phthalic acid Sulfate bridging Photo–luminescence Ferromagnetic interaction

1. Introduction During the last decades, the design, synthesis and self-assembly of later transition metal coordination polymer (CP) as functional materials for applications in electronic, magnetic, and optical devices is one of the most rapidly developing and exciting areas of inorganic chemistry [1–5]. The intense interesting in this field and one of the major goals of crystal engineering are targeted at predictable assembly of molecular species into extended architectures, and the potential applications, such as biological assays, catalysis, porosity, magnetism, light-emitting diodes and optical fibers for telecommunications [6–9], among which, later transition metal ions such as nickel, zinc, cadmium, silver are found to adopt a wide variety of geometries and exhibit interesting physical property [10–16]. Flexible ligands, especially, those N, O, S -containing donors possess rich structural information [17]. The quinoline and pyridine based ligands are particularly appealing because of their versatile coordination modes and variable conformations compared with simple rigid ligands [18–22]. Owing to their ability to affect the properties and strength of organic n

Corresponding author. E-mail address: [email protected] (L.-Y. Wang).

http://dx.doi.org/10.1016/j.jssc.2015.06.018 0022-4596/& 2015 Elsevier Inc. All rights reserved.

materials, the syntheses of metal coordination polymers by the judicious choice of conjugated organic spacers and transition-metal centers can be an efficient method for obtaining new types of functional materials [23]. However, it has been seldom reported for the combined biphenyl mutli-carboxylate/sulfate acid with pyridine as new kind of organic ligand with introduction an extended δ-π conjugated or π-conjugated system [24], by applying compartmental ligand 4-(5sulfo-quinolin-8-yloxy) phthalic acid (abbreviation as sqpa) in this contribution. It may result in possible novel structures and magnetic /luminescence properties. Esthetically pleasing structures can be produced upon the partially deprotonation or unsymmetrical coordination, free rotation of the aromatic ring of two carboxylic and sulfate groups to metal ions. Meanwhile, 4, 4′-bipyridine (abbreviated as bipy), as the N donor rigid ligand has been proved to be a good candidate for pillar ligand due to its’ various bridging fashions and strong coordination tendency to generate 1D to 3D moderately robust networks, exhibiting strong luminescence [25–27]. As a continuation of our previous investigation [28], as well as the elucidation of structures of substituted aromatic dicarboxylate, we also change ligand bipy as conjugational 1,2-bis(4-pyridyl) ethylene (abbreviated as bpe). Series of later transitional metal complexes with varisized and varishaped based on the sqpa as major ligand, bipyridinyl skeletons as auxiliary ligands, {bpe [Mn(bpe) (sqpa) (H2O)]2
2(H2O}n (1), {[Ni2(bipy)2

X. Feng et al. / Journal of Solid State Chemistry 230 (2015) 80–89

(sqpa)2 (bipy) Ni(bipy)2
8H2O]
7H2O}n (2), {(sqpa)2 [Zn(bipy) (H2O)]2
[Zn(bipy)2
(H2O)4](H2O)4}n (3), [(sqpa)2Ag2(bpe)]n (4) and {[(sqpa)2 Cd(bipy) (H2O)]2
[Cd(bipy)2
(H2O)2]
2(H2O}n(5), are successfully assembled. The structures, photo luminescence, thermal, magnetic properties are discussed in details, herein.

81

molecular and the hydrogen atoms in pyridine for 1, and sulfur atom and carbon atom of sulfo-quinolin for 5 were restrained in order to obtain reasonable thermal parameters. The details of the crystal parameters, data collection and the refinements for polymers are summarized in Table 1. The selected bond lengths and angles are listed in Table S1, respectively.

2. Experimental section 3. Results and discussion

2.1. General remarks All reagents used in the syntheses were of analytical grade and used as received. Elemental analyses for carbon, hydrogen and nitrogen atoms were performed on a Vario EL III elemental analyzer. The infrared spectra (4000–400 cm˗1) were recorded by using KBr pellet on an Avatar TM 360 E.S.P. IR spectrometer. Thermogravimetry (TG), differential thermalanalysis (TGA) were recorded using a SDT 2960 simultaneous thermal analyzer (DTA Instruments, New Castle, DE) in N2 atmosphere at a heating rate of 10 °C min˗1 in the temperature range of 25–900 °C. The temperature dependent magnetic susceptibilities for the complexes at a magnetic field of 2000 Oe are measured over the range of 2–300 K. Diamagnetic corrections were made with Pascal’s constants for all constituent atoms. Solid luminescence spectra were performed at the room temperature on a Hitachi F-4500 spectro-photometer with xenon arc lamp as the light source. The solution luminescent spectra in a 1 cm quartz spectrophotometer fluorescence cell (Starna) in methanol were run on a Cary Eclipse fluorescence spectrophotometer.

3.1. IR spectra of polymers IR spectra of 1–5 show features attributable to compositions of the polymers. The observed strong signals between 3200 and 3450 cm–1 in spectra are attributed to the O–H and/or N–H stretching vibrations. The broad and intense spectra appearing around 1600 and 1400 cm  1 in the IR spectra correspond to asymmetric and symmetric stretching vibrations of carboxylic groups, respectively [31]. The peaks at ca. 1580 cm  1 are assigned to the stretching vibrations of benzene ring in sqpa ligand [32–34]. The absorption about 1110 cm  1 indicate that existence of ether groups in substituted ligands [35]. Due to complexes 1, 2, 4, 5 are partially deprotonation, the absorptions about 1680–1700 cm  1 may exist stretching vibrations of the –COOH in ligand. 3.2. Structural descriptions for polymers 1–5

{bpe⎡⎣Mn(bpe) (sqpa) (H O)⎤⎦ ·2(H O} 2

2

2

n

(1)

2.2. Syntheses of conjugational ligand of sqpa The preparation of ligand sqpa was given in Electronic Supporting Information. 2.3. Preparation of the polymers The similar procedures were employed in preparation of the complexes 1–5, and synthesis of 1 will be described in detail herein. Sqpa (0.039 g, 0.2 mmol) and bpe (0.037 g, 0.2 mmol) were mixed in a solution of water/alcohol (v/v ¼ 1.2, 10 mL). Then an aqueous solution (10 mL) of Mn(AcO)2 2H2O (0.2 mmol
0.042 g) was added. After stirring for 30 min in air, the pH value was adjusted to 5.5. The mixture was placed into 25 mL Teflon-lined autoclave under autogenous pressure being heated at 150 °C for 72 h, and then the autoclave was cooled over a period of 24 h at a rate of 5 °C/h. After filtration, the product was washed with distilled water and then dried, yellow crystals of 1 were obtained suitable for X-ray diffraction analysis. For (1), yield: 0.0621 g (41%) based on manganese element. Elemental analysis (%): calcd for C35H28MnN4O10S: C 55.92, H 3.75, N 7.45, found: C 55.54, H 3.66, N 7.49. IR: 3481s, 3180br, 2947s, 2168s, 1613s, 1579s, 1441vs, 1121s, 1088s, 807s, 662m. Processes of preparation of 2–5, IR spectra for series of polymers are given in Electronic Supporting Information (Fig. S1), etc.




2.4. Crystallographic data collection and refinement The single crystals of the polymers 1–5 were mounted on a Bruker SMART APEX II CCD diffractometer equipped with a graphite monochromated MoΚα radiation (λ ¼0.71073 Å) at room temperature. The structures were solved by direct methods with SHELXS-97 [29]. The hydrogen atoms were assigned with a common isotropic displacement factor and included in the final refinement by the use of geometrical restraints. An empirical absorption correction was applied using the SADABS program. A full-matrix least-squares refinement on F2 was carried out using SHELXL-97 [30]. The solvate

Single crystal X-ray diffraction reveals that polymers 1–5 are all based on sqpa ligand and they all crystallize in monoclinic system. As depicted in Fig. 1(a), there are one Mn(II) ion, one sqpa dianion ligand, half bpe ligands and one coordinated water as well as one lattice water, in addition a free bpe in the asymmetry unit of 1. Mn(II) ion adopts octahedral coordination mode with a N2O4 donor set. The carboxylic group chelates and bridges adjacent Mn ions with Mn


Mn distance of 5.397 Å. Rigid bpe links adjacent Mn(II) ions, with the distance between two Mn(II) of 13.68 Å, and dihedral angle between benzenes ring within one molecule is just 0.64°. The [Mn-spqa] units were propagated into one-dimensional (1D) chains along ab plane. Meaning while, bpe interlinks Mn-sqpa units into 1D double chain along bc plane (Fig. 2a). Moreover, the bpe cross linked these chains into 2D irregular grid lattice array (Fig. S2). Compound 1 has a highly puckered 2D (4, 4) sheet and is further stack via hydrogen bonding to form a 3D supramolecular structure. The network of 1 can be further analyzed by the topological approach, which reveal that is corrugated shape 4-connected topology [17], as shown in Fig. 2b. The free bpe moieties project into the interlayer space between adjacent layers. {[Ni2(bipy)2 (sqpa)2 (bipy) Ni(bipy)2
8H2O]
6H2O}n

(2)

For 2, there are two crystallographically independent Ni(II) ions, two sqpa dianion ligands, three bipy ligands and eight coordinated water molecules as well as six lattice water molecules in basic unit. The Ni(1) ion is located on a twofold rotation axis and is six coordinated with three nitrogen atoms from bipy and three carboxylic oxygen atoms from sqpa ligands (Fig. 3a). Meanwhile, Ni(2) ion is accompanied by the O4N2 donor set in another octahedral environment with four water oxygen and two nitrogen atoms from bipy moieties completed a distorted octahedral geometry. Each carboxylic group of isophthalate adopts the anti–syn mode to connect adjacent Ni(1) ion forming a dimer unit with Ni

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X. Feng et al. / Journal of Solid State Chemistry 230 (2015) 80–89

Table 1 Crystal data and structure refinements for polymers 1–5. Empirical formula

C35H20MnN4O10S

Formula weight 751.65 Temperature (K) 293(2) Wavelength (Å) 0.71073 Crystal system Monoclinic Space group C2/c Unit cell dimensions (Å, a ¼32.067(4) deg) b ¼ 8.4473(9) c ¼ 26.724(3) β ¼ 99.912(2) Volume (Å3), Z 7130.9(14), 8 3 Dcaled, (g/cm ) 1.467 Absorption coefficient 0.498 (mm–1) Index ranges –41 rh r 40 0 rk r 10 0 rl r 34 F(000) 3256 θ Range for data collec- 1.55–27.50 tion (deg) Independent reflections 8116 Observed reflections 21,419 Refinement method Full-matrix least-squares on F2 Data/restraints/ 8116/06/460 parameters 2 1.008 Goodness-of-fit on F R index (I 4 2s(I)) R1 ¼ 0.0549 wR2 ¼ 0.1490 R index (all data) R1 ¼ 0.1150 wR2 ¼ 0.1700 Largest diff. peak / hole 0.722/–0.391 3 (e Å )

C74H66N10Ni3O32S2

C64H38N8O26S2Zn3

C46H30Ag2N4O16S2

C66H50Cd3N6O21S2

1847.62 296(2) 0.71073 Monoclinic P2/c a¼ 15.291(15) b ¼11.235(12) c ¼24.984(18) β ¼115.28(4) 3881(6), 2 1.581 0.871

1595.25 293(2) 0.71073 Monoclinic, P2(1)/c a¼ 20.198(3) b ¼10.4281(14) c ¼16.582(2) β ¼99.854(3) 3441.0(8), 2 1.540 1.186

1174.60 293(2) 0.71073 Monoclinic P2(1)/n a¼ 9.0395(6) b ¼10.5638(7) c ¼22.1117(14) β ¼98.0540(10) 2090.7(2), 2 1.866 1.122

1664.44 293(2) 0.71073 Monoclinic P2(1)/n a¼ 19.50(3) b ¼10.935(15) c ¼16.27(2) β ¼93.730(16) 3461(8), 2 1.597 1.051

–18r h r15 –12r k r 13 –27r l r30 1904 1.47–25.50

–24r h r 22 –11r k r 12 –17r l r 19 1352 2.49–25.50

–10r h r 11 –13r k r13 –28r l r 19 1176 2.14–27.50

–23r h r 23 –13r k r 12 –19r l r 9 1176 2.14–27.50

7216 19,573 Full-matrix least- squares on F2 7216/0/549

6034 17,122 Full-matrix least-squares on F2 6034/80/481

4780 12,517 Full-matrix least-squares on F2 4780/59/313

5970 19,173 Full-matrix least-squares on F2 5970/372/572

0.988 R1 ¼0.0872 wR2 ¼0.1938 R1 ¼0.1907 wR2 ¼0.2485 0.784/–0.856

1.083 R1 ¼0.0904 wR2 ¼0.1879 R1 ¼0.1441 wR2 ¼0.2052 1.484/–0.728

1.065 R1 ¼0.0601 wR2 ¼0.1696 R1 ¼0.0725 wR2 ¼0.1810 1.843/–1.215

0.883 R1 ¼0.0823 wR2 ¼0.1850 R1 ¼0.1737 wR2 ¼0.2244 1.547/–1.155

R = ∑ F0 − Fc / ∑ F0 ,

WR

1/2 ⎧ ⎡ 2⎫ 2⎤ = ⎨ ∑ ⎢ F02 − Fc 2 ⎥/ ∑ F02 ⎬ ⎦ ⎣ W ⎭ ⎩

(

)

( )

Fig. 1. Coordination environment of Mn(II) ion in 1. The hydrogen. atoms are omitted for clarity.






(1) Ni(1) shortest separations of 4.688 Å, and bipy propagate these dimer unit to give rise to an alternate 1D chain, with Ni (1)


Ni(1) distance of 11.09 Å (Fig. S3a). On the other hand for Ni (2) ion, the Ni(H2O)4 fragments are further linked by bipy into 1D double chain, and the chains parallel each other along bc plane with the Ni(2)


Ni(2) separation of 11.23 Å, as displayed in Fig. S3b. This is compared to the reported 1D chain structure of the complexes based on 2,5-dimethyl-1,3,4-thiodiazole3 [36], and this is distinguished from the 1D liner chain in 1. The chains mentioned above are further crosslinked into regular 2D network by rigid bpe ligands, as displayed in Fig. 3b. {(sqpa)2 [Zn(bipy) (H2O)]2
[Zn(bipy)2
(H2O)4] (H2O)4}n

(3)

Fig. 2. (a) View of a 1D ribbonlike chain composed of Mn atoms pillared by bpe. (b) Showing the 4-connected topology for 1; red spheres represent the Mn(II) unit nodes, and blue bonds represent the bpe bridges. (For interpretation of the references to color in this figure legend, the reader is referred to the web version of this article.)

X. Feng et al. / Journal of Solid State Chemistry 230 (2015) 80–89

83

Fig. 3. (a) Coordination environment of Ni(II) ion in 2. (b) A perspective view of 1D chains pillared by rigid ligands into a 2D network containing parallelogram windows. The hydrogen atoms, free bipy ligand and water are omitted for clarity.

As shown in Fig. 4a, there are two crystallographically independent Zn(II) ions, two sqpa dianion ligands, three bipy ligands and six coordinated water molecules as well as four lattice water molecules in asymmetry unit of 3. Both Zn(1) and Zn(2) display distorted octahedronal coordination environments with N2O4 donor set. Zn(1)-sqpa units were linked by carboxylic oxygen into 1D zig-zag chain (see Fig. S4). This is compared to the reported 1D chain structure of d10 complex based on anthracene-based dicarboxylic ligands [37, 38], but this is distinguished from the 1D liner chain in 1. The adjacent [Zn(isophthalate)] chains are further linked by bipy coligands and are extended into a 2D wave-like layer structure. Moreover, these layers are cross-linked by carboxylic group of the sqpa ligands and extended into a 3D pillaredlayer structure (see Fig. S5). Void space between neighboring layers is about 9.79(2)  23.85(6) Å, which are occupied by sulfonylquinolin moieties and free water molecules. The adjacent sets of parallel noninterpenetrating (4, 4) nets are joined together through sqpa ligands, as shown in Fig. 4c. The sqpa2– anion ligand adopts a μ2– kO, O′: kO″ modes connecting two Zn(II) centers in chelating and monodentate bridging modes (Scheme 1(a)) in 3, and connects two adjacent Zn(II) atoms to form a dimer in an anti– anti fashion. The Zn(2) lies on an inversion center with an octahedral geometry, which is coordinated by two N-atoms from bipy (Zn2–N1: 2.086(6)–2.174(6) Å) and four water O donors (Zn–O:

Fig. 4. (a) View of the coordination environments of Zn in asymmetric unit of 3 (some of hydrogen atoms have been omitted for clarity). (b) 1D zigzag chain composed of Zn(1)- isophathlate units connected along b-axis. (c) Schematic illustration of 1D double chains are extended into a wavelike 2D sheet via bipy moieties along a c plane.

2.022(5)–2.242(5) Å), which are also close to the values found in reported d10 metal complexes [39–41]. [(sqpa)2Ag2(bpe)]n

(4)

The asymmetry unit of 4 is consisted of one silver ion, one sqpa and a half bpe as auxiliary ligand. The Ag(I) is in a three-coordination geometry with an ON2 donor set, resulting in “T”- like configuration, as described in Fig. 5a. It is remarkable in 4 that Ag (I) ion is coordinated to N from bpe and oxygen atoms of sqpa, contrast with that in structure 5, in which Cd(2) ion is also coordinated to the oxygen from carboxylic oxygen O(9) of the sqpa ligand. Such coordination diversity is indicative of silver is prefer to be coordinated with N atoms, and this results in the formation of final 1-D double chain networks based on rail like array, as depicted in Fig. 5b. The bond distance of Ag(1)–N(1) and Ag(1)–N (2) are 2.208(4) and 2.251(5) Å, respectively, and bond distance of

84

X. Feng et al. / Journal of Solid State Chemistry 230 (2015) 80–89

OH

Ni

O

O

O O

HO3S

O

Mn

O

Mn

O

OH HO3S

O N

N

O

OH

Zn O

O

O H O

HO3S

Ni

Zn

OH HO3S

O

O N

N

O

OH

Ag

N

N

Cd O

OH

Cd O O S O

O

Cd

O N Scheme 1. The coordination fashions of ligand observed in 1–5.

which is weak interaction compared with the silver (I) complex with benzo[e] acephenanthrylene [44] or the metal-organic networks based on terphenyl carboxyli ligand [45,46]. The flexible nature of sqpa can be confirmed by the fact that armies of the ligands are bent outward. Benzene and pyridyl rings of spqa anion are noncoplanar, but are twisted with each other, with dihedral angle of 65.47° between the hydroxylquinoline plane and benzene plane from isophthalate moiety. They are closely similar to those found in other reported Ag(I) complex [47], or the other observed three-coordinated Ag(1) ion with N donor ligands [48,49]. Interestingly, for Ag(1)–O bond length 2.75 Å is also close to the values found in Ag(1) complexes bearing bpe and adamantanedicarboxylate ligands [50]. Rigid bpe acts as bidentate linker as in 4 just to bridge two Ag(I) centers to form a dimer unit rather than 1D column chain. Additional hydrogen bonding interactions are found between adjacent sulfate and carboxylic groups such as O(1)–H(1) ⋯O(6)#2 and O(3)–H(3)⋯O(4)#3, the hydrogen-bonding interactions further gives rise to a 3D inorganic–organic hybrid network, and contributing to stabilizing the crystal. This array cannot be comparable with Ag(I) complexes based on 2,5-dimethyl-1,3,4 thiodiazole3 ligand [51]. The significant feature of the structure is that there are no water molecules participating in the coordination to Ag(1) ion, although it is crystallized from the ethanol–water media. {[(sqpa)2 Cd(bipy) (H2O)]2
[Cd(bipy)2
(H2O)2]
2(H2O}n Fig. 5. (a) Description of coordination environment for sqpa ligand and silver atom in 4. (b) Stick model of the 2D ribbon-like network formed from bipy along a b plane.

Ag–O6 is 2.635 Å, falling within normal range, and they are comparable to those observed in the related silver (I) compounds [42,43]. While, bond distance of Ag–O5 is observed for 2.7659 Å,

(5)

As displayed in Fig. 6a, both Cd(1) and Cd(2) in 5 are six coordinated with N2O4 donor set, which the N atoms are provided from bipy and O atoms are from sqpa, as displayed in Scheme 1. The noticeable feature of the structures above mentioned is that sqpa ligand exhibits two kinds of coordination fashions, and this

X. Feng et al. / Journal of Solid State Chemistry 230 (2015) 80–89

85

results in the more complex array for 5 than others. The sqpa ligand acts as a μ2– bridging ligand in 3, while in 5 it exhibits both chelating and bridging μ3 modes linking adjacent three Cd(II) ions into trimeric unit. The carboxylic group connect them into 2D layer, as shown in Fig. S6. The 2D sheet further stack via O/O intermolecular interaction (carboxylate oxygen) from sqpa ligand to form a 3D supramolecular open framework along the b c plane leaving 1D tunnel, as illustrated in Fig. 6b. The incipient void space is found for the 3D framework to be 384.1 Å3 per cell volume assuming the remove of solvate (accounting for 11.1% of the total unit cell system, as volume for 3461.0 Å3, calculated using the Platon programmers) [52]. The network topology of 5 can be further analyzed by the topological approach. In this context, each Cd (1) center is considered as a three-connected node connecting two bipy and one sqpa ligand, with vertex symbol of (11.12(2).13(3), while Cd(2) center is regarded as four-connected node linking two bipy and two sqpa fragments with vertex symbol of (3(2).11.12 (4).14(4)), and the sqpa is treated as a three-connected node. From the viewpoint of topology, the structure is a trinodal (3, 3, 4) connected network, with vertex Schlafli symbol of {6.82}{104}, which represents a new network topology [53], as displayed in Fig. 6c. Cd(1) is attached to bipy exhibiting interval block array, while Cd(2) coordinated sqpa and bipy shows 1D chain. They interpret each other and this results in the 2D sheet aggregate. The structure is different from the polymers based on weaved layer consisting of Cd–Me4bpz helical chains [54], or is also different from the 3D framework containing cadmium(II)–phosphonatophenyl-sulfonate clusters, which crystallizes in the different space group [55]. It represents a 3-D extended network with two different kinds of channels, exhibiting window sizes of 12.12  12.0 or 7.2  4.1 Å, respectively. It is notable that the suitable ligand/ coligand are also crucial in formation of the diversity framework and property. 3.3. Thermogravimetric analysis and powder X-ray diffraction To study the thermal stability of compounds, thermo-gravimetric analysis (TGA) and differential thermogravimetric analysis (DTA) were performed (N2 atmosphere) on their polycrystalline samples. As illustrated in Fig. 7, for polymer 1, there are three obvious weight-loss steps with increasing temperature. An initial weight loss started at about 100 °C (4.82% loss), corresponding to the removal of two water molecules per formula unit (4.76% calcd.). The second strikingly weight loss step began from 390 to

Fig. 6. (a) Illustration of coordination environment of sqpa ligand and Cd(II) atom in 5. (b) Perspective view of the 3D framework of 5 bearing the 1-D channel down a-axis. (hydrogen atoms and free water molecules were omitted for clarity). (c) Schematic illustration of the topology of 5. Blue and green blocks represent Cd(1)–O and Cd(2)–O bonds, respectively.(For interpretation of the references to color in this figure legend, the reader is referred to the web version of this article.)

Fig. 7. The TG curves for polymers 1–5.

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X. Feng et al. / Journal of Solid State Chemistry 230 (2015) 80–89

510 °C, which is attributed to the release of three bpe moieties (exp. 24.3%; calcd. 24.6%). The third strikingly clean weight loss step takes place beyond 500 °C, corresponding to decomposition sqpa organic skeleton, respectively. TG results of 1–4 reported above are in consistence with the crystal structure analysis. It can be perceived from TGA diagraph that polymer 5 is little more thermally stable than others because it has more coordination number and fewer lattice water molecules. The purities and crystallinities of the bulk products of 1–5 were determined by comparison of the simulated and experimental X-ray powder diffraction patterns, and the results are reported in Fig. S7. The peak positions of the experimental patterns are nearly matched with the corresponding simulated ones generated from single crystal X-ray diffraction data, although some minor Bragg peak positions have been shifted in comparison to the simulated ones. 3.4. Magnetic property of polymers 1 and 2 The magnetic susceptibilities of 1 and 2 were measured in the temperature range of 2–300 K, which are shown as χMT and χM versus T plots. The results are depicted in Fig. 8. For 1, as displayed in Fig. 8a, the χMT value at room temperature is 8.92 cm3 K mol–1, which is larger than the expected one for two uncoupled Mn(II) ion with Si ¼ 5/2 and gi ¼ 2 [56,57]. As the temperature is lowered to 2 K, the χM T values decrease first slowly and then rapidly to the

Fig. 8. Temperature dependence of χMT (□) and χM (○) for 1 (a) and 2 (b). Open points are the experimental data, and the solid line represents the best fit obtained from the Hamiltonian given in the text.

value 1.55 cm3 K mol–1. This behavior is typical for weak antiferromagnetic interactions between the Mn(II) centers carboxylate bridge mediated. As stated above, the structure of 1 consists of binuclear Mn(II) units linked by carboxylic oxygen bridge, the binuclear units are interlinked to give a 2D system, and coupling through substituted bipyridine bridging can be ignored. The experimental magnetic data can be properly fitted using the following equation, where N, g, β and k have their usual meanings.

χMn2 =

Ng 2β 2 ⎡ A ⎤ ⎢ ⎥ 4KT ⎣ B ⎦

(6)

(

A = 8 e2x + 5e6x + 14e12x + 30e20x +55e 30x B = (1 + 3e

2x

6x

+ 5e

12x

+ 7e

+ 9e

20x

)

+ 11e 30x)

where x ¼| J | /KT. An additional coupling parameter, zJ′, was added in Eq. (7) to take into account the magnetic behavior between the 1-D chains as a molecular field approximation [58].

χM =

χbi 1−

2zJ / χ Nβ 2g 2 bi

(7)

The least-squares analysis of magnetic susceptibilities data led to J ¼–0.79 cm–1, zJ ¼–0.17 cm–1, g(Mn) ¼2.0493, g(ff) ¼0 and R¼5.3  10–4 for 1. The J values suggest that very weak anti-ferromagnetic interactions between the neighboring Mn(II) ions through the carboxylate, due to larger separation between Mn(II) ions, which are comparable to those reported for other similar Mn (II) species [59, 60]. The magnetic properties of polymer 2 in the form of the χMT versus T plots are shown in Fig. 9b. The χMT values of 2 at room temperature are 2.41 cm3 mol–1 K which is slightly larger than the spin-only value (2.0 cm3 K mol–1) expected for two coupled highspin Ni(II) ion systems with g ¼ 2.1–2.3 [61], which indicates that the orbital contribution is involved. As the temperature is lowered, the χMT value increases to a maximum of 3.71 cm3 K mol–1 at 18 K, and then decrease rapidly till to the lowest temperature upon further cooling. The increase of χMT with decreased temperature clearly indicates ferromagnetic coupling interactions between the metal centers. According to the structure of 2, it could be presumed that the main magnetic interactions between the Ni(II) centers might happen in doubly bridged carboxylic oxygen, whereas the super exchange interactions between Ni(II) ions

Fig. 9. The excitation spectra of polymers 3–5 at room temperature.

X. Feng et al. / Journal of Solid State Chemistry 230 (2015) 80–89

87

through the bipy bridging can be ignored because of the long distances of Ni…Ni separation. The magnetic susceptibility data were thus approximately analyzed by an isotropic dimer mode of spin S ¼ 1. Heisenberg–Hamiltonian was employed as following:

^^ ^ H = − JS1S2

(8)

where exchange constant J presents magnetically coupling within carboxylate-bridged dinuclear unit [62,63]. The least-squares analysis of magnetic susceptibilities data led to J ¼ 0.81 cm–1, g ¼ 2.07, R ¼ 1.1  10–5 for 2 (see Fig. 8b). The J value indicates a ferromagnetic exchange between the syn–anti carboxylatebridged Ni(II) binuclear unit. Although magnetostructural studies on carboxylate-bridged Ni (II) with the carboxylate are seldom reported, ferromagnetic interactions through this exchange pathway have been known [64]. In this case, 1D chain based on Ni-pipy unit along b-axis and the anti–syn configuration may reduce drastically the overlap between the magnetic orbitals, thus diminishing the anti-ferromagnetic coupling and enhancing the ferromagnetic pathway [65–67]. Finally, a point which deserves a brief comment is the fact that the magnetic coupling between the Mn(II) and nickel(II) ions through the carboxylate bridge is antiferro- (1) and ferromagnetic (2). The different electronic configuration of the metal ions involved with five (1) and two (2) unpaired electrons t2g3eg2 for Mn(II), and t2g6eg2 for Ni(II), Oh symmetry would account for that [68]. 3.5. Photoluminescence properties of the polymers 3–5 The solid-state luminescence properties of compounds 3–5 as well as the free ligands of sqpa were investigated at room temperature, as reported in Figs. 9, 10 and S8. For free sqpa ligand, upon excitation of λmax ¼ 340 nm, it shows a fluorescence medium strong emission band maximum at λmax ¼ 468 nm, which may be assigned to the intraligand transition of the ligand. As reported in Fig. 10a, excitation through the band λmax ¼ 348 nm, polymer 3 shows emission at 494 nm, which is similar on profile of the emission spectrum of free sqpa ligand, indicative of intraligand (π–π*) transitions of ligand in nature, which is similar to reported complex [Zn2(pytpy)2 (ox)2]n[69]. Unfortunately, Cd(II) compound 5 containing sqpa ligand exhibits very weak emission, as shown in Fig. 10a. Notably, band at 518 nm, the weakened emission peak in 5 may be the result from the weakened conjugacy after coordination. This is essentially not comparable to Cd (II) complexes based on BCbpy ligand (BCbpy ¼1-(4-carboxybenzyl)-4,4′-bipyridinium) [70]. For polymer 4, a lower energy emission at 546 nm was observed in green region upon the radiation maximum at 460 nm (in indigo region), as displayed in Fig. 10a and b. It is proposed that metal–ligand bonding could lead to the red-shift of emission bands, Hence, ligand-to-ligand charge transfers (LLCT) in the absorption transition of 4 is unreasonable, and thus it is reasonable to attribute the low-energy emission peaks to the p–π* to Ag(I) ion transition according to the reported theoretical calculation [71]. Compared to the free sqpa ligand, the enhancement of luminescence intensity for 4 is perhaps a result of the metal  ligand coordination, which effectively increases the rigidity of the ligand and reduces the non-radioactive decay of the intraligand (π  π*) excited state [72,73]. Remarkably, the silver-cluster composites exhibit high photo- and chemical stability making them very attractive, for instance, as phosphor applications, fluorescent lamps and upconverter materials. Being distinct from 3 and 5, polymer 4 is favorable for the reduction of the energy of the π  π* or n  π* transition to some extent, in which the pair pyridyl rings of the coligand are nearly coplanar. This is different essentially from the previous reports assigned a red/orange emission to a Ag6n + cluster in heat-treated LTA zeolites with high silver loading whereas the

Fig. 10. (a) Emission spectra of the free spqa ligand and polymers 3–5 under different excitation. (b) The CIE chromaticity diagram for 4.

green emission at lower silver loadings was attributed to a Ag n3 +− 4 cluster [74]. However, the differences of excitation profiles between free ligands and complexes, indicates the possibility for dye molecules transferring photon energy to silver centers [75–77]. Considering the sheet array of 4, we monitored changes of ionic zinc (II) concentration by using luminescent chemosensory. This is investigated upon adding zinc (II) nitrate solid. As displayed in Fig. 11, upon addition of Zn (II) (in 0–6 equiv.), a gradually enhancement fluorescence occurred at emission of 546 nm. This is perhaps due to the chelating to Zn and steric effect after introducing Zn ion entering into the 2D lattice gap, followed by enhancement of fluorescence intensity [78,79]. Furthermore, on increasing the equality, the emission band in 4 shows slightly blue shift, which is attributed to approach the maximum emission of polymer 3.

4. Conclusions Series of new types Mn, Ni, Zn, Ag and Cd polymers assembled from the substituted conjugational nitrogen-heterocyclic ligand have been successfully achieved, and the bidentate N containing

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[8] [9] [10] [11] [12] [13] [14] [15] [16] [17] [18] [19] [20] [21] [22] [23] Fig. 11. Fluorescence photoemission intensity of 4 as a function upon addition Zn2 þ (0–6% equiv. of Zn(NO3)3), λex ¼ 358 nm at room temperature.

ligand was applied as the second linker. They show diversity of structures with different topology from 2-D network to 3-D framework, due to the electron configuration of central ion and auxiliary ligands. Magnetic studies reveal that there are antiferromagnetic interactions between the transition metal ions in the polymeric Mn (II), while ferromagnetic interactions in the Ni (II) polymer. Remarkably, the silver-cluster composite exhibits high chemical stability and chemosensor for zinc ion. The results obtained here will be of usage in establishing a design strategy for other high-dimensional coordination polymers with interesting structural, topologies and functional properties.

[24] [25] [26] [27] [28] [29] [30] [31] [32] [33] [34] [35]

Acknowledgments This work was supported by the National Natural Science Foundation of China (Nos. 21273101 and 21271098). Foundation for Science & Technology Innovation Talents and Research Team in Universities of Henan (No. 2014HASTIT014 and 4IRTSTHN008), Tackle Key Foundation of Science and Technology of Henan Province, China (No. 142102310483) and Foundation for University of Malaya (UM.C /625/1/HIR/247). We are indebted to Dr. S.Z. Zhan, Department of Chemistry, Shantou University for kindly helping with the topology analysis.

Appendix A. Supplementary material Supplementary data associated with this article can be found in the online version at http://dx.doi.org/10.1016/j.jssc.2015.06.018.

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