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Two cadmium coordination polymers containing piperazine-1,4-diylbis(pyridine-4-ylmethanone): Highly selective luminescent recognition of Cu2+
Accepted Manuscript Two cadmium coordination polymers containing piperazine-1,4- diylbis(pyridine-4-ylmethanone): highly selective luminescent recognition of Cu2+ Liu Liu, Chen Lian, Yin-shuang Long, Xu Guo, Li-rong Yang PII: DOI: Reference:
S0020-1693(16)30427-3 http://dx.doi.org/10.1016/j.ica.2016.07.049 ICA 17184
To appear in:
Inorganica Chimica Acta
Received Date: Revised Date: Accepted Date:
14 December 2015 16 June 2016 28 July 2016
Please cite this article as: L. Liu, C. Lian, Y-s. Long, X. Guo, L-r. Yang, Two cadmium coordination polymers containing piperazine-1,4- diylbis(pyridine-4-ylmethanone): highly selective luminescent recognition of Cu2+, Inorganica Chimica Acta (2016), doi: http://dx.doi.org/10.1016/j.ica.2016.07.049
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Two cadmium coordination polymers containing piperazine-1,4diylbis(pyridine-4-ylmethanone):
highly
selective
luminescent
recognition of Cu2+ Liu Liua,b, Chen Liana, Yin-shuang Longa, Xu Guoa, Li-rong Yanga* a
Henan Key Laboratory of Polyoxometalate, Institute of Molecule and Crystal Engineering, College of Chemistry
and Chemical Engineering, Henan University, Kaifeng 475004, P. R. China b
Nanyang Tobacco Monopoly Bureau (Company), Nanyang 473000, P. R. China
ABSTRACT: Two novel coordination polymers, namely, {[Cd(pdpy)(H2O)2]·SUL· (H2O)0.5}n (I) and {[Cd(pdpy)(PTA)]·H2O}n (II) (pdpy = piperazine-1,4-diylbis(pyridine-4-ylmethanone), PTA = p-phthalic acid and SUL = 5-sulphosalicylic acid) have been designed and successfully prepared under hydro-thermal conditions and characterized by elemental analyses, IR spectroscopy, and single crystal X-ray diffraction. Structural analysis indicates that the pdpy ligands adopt three different coordination modes in the as-synthesized I-II, and thus result in diversity of the targeted coordination polymers. It is worth mentioning that, based on the hydrogen bonding, I-II are assembled from two-dimensional (2D) structures into three-dimensional (3D) frameworks. Luminescent properties of I and II have been studied at ambient temperature. Significantly, both I and II show highly selective response to Cu2+ cations through luminescence quenching effects, which may make them promising luminescent selective recognition sensors for Cu2+. Keywords: Coordination polymer; Intermolecular forces; Luminescent recognition; Metal–organic frameworks; Hydro-thermal synthesis
1. Introduction Coordination polymers (CPs) as well as metal–organic frameworks (MOFs), which are crystalline multifunctional materials that are often assemblies of the organic linkers and metal ions (or metal clusters), have attracted enormous interest of synthetic chemists. In general, CPs _____________________ *Corresponding author. E-mail address: [email protected]
have emerged as a promising kind of materials with a wide variety of potential
applications such as in gas storage, optoelectronics, molecular recognition, microelectronics, molecular magnetism, chemical separations, ion exchange, nonlinear optics and heterogeneous catalysis [1-15]. Luminescent probe is an excellent example of a field where the ability to introduce chemical functionalities into the structures with useful properties has had a substantial positive impact on society in various applications. Cheng and co-workers performed a study on two coordination polymers containing 1D channels as selective luminescent probes to Zn2+ [16]. In same year, Liu et.al investigated the preparation of a series of lanthanide coordination polymers which can be used as molecular devices for Ag+ sensor [17]. A. Thibon and V. C. Pierre reported a terbium coordination polymer framework with a highly selective luminescent sensor for K+ in 2008 [18]. Following our ongoing efforts towards the synthesis and isolation of coordination polymers, which may act as selective luminescent probes to some metal ions [19-22]. In this work, we describe the synthesis, structures, luminescent properties of two kinds of Cd(II) coordination polymers based on piperazine-1,4-diylbis(pyridine-4-ylmethanone), which are formulated as {[Cd(pdpy)(H2O)2]·SUL· (H2O)0.5}n (I) and {[Cd(pdpy)(PTA)]·H2O}n (II). The synthetic strategies of I-II are presented in Scheme 1. The coordination polymers I and II exhibit a highly luminescent selectivity towards Cu2+.
Scheme 1 Experimental routes for coordination polymers I-II.
Scheme 2 Coordination modes in coordination polymers I-II.
2. Experimental Section 2.1 Materials and physical measurements All chemicals were commercially purchased from Jinan Camolai Trading Company and used without further purification. Elemental analyses (C, H, and N) were performed with a Perkin-Elmer 240 CHN Elemental Analyzer. IR spectra in the range of 400-4000 cm-1 were recorded with an AVATAR 360 FT-IR spectrometer (KBr pellets were used). The crystal structure was determined with a Bruker Smart CCD X-ray single-crystal diffractometer. Excitation and emission spectra were obtained with an F-7000 FL spectrofluorometer at room temperature.
2.2 Synthesis of the coordination polymers I-II Synthesis of {[Cd(pdpy)(H2O)2]·SUL·(H2 O)0.5}n (I) . A mixture of piperazine-1,4-diylbis (pyridine-4-ylmethanone) (3.01 mg, 0.1 mmol), 5-sulphosalicylic acid (1.88 mg, 0.1 mmol), Cadmium perchlorate hydrate (8.38 mg, 0.2 mmol) and water (10 mL) was homogenized by stirring for 30 min, then transferred into 25 mL Teflon-lined stainless steel autoclave under autogenous pressure at 160
for 4 days. After cooling the reaction system to room temperature
at a rate of 5
/ h, the clear solution was stirred at room temperature for 30 days then clear block
orange crystals were isolated. Yield of 80.31% (based on Cadmium perchlorate hydrate). Calc. for C46H52N8 O21S2 Cd2(%): C, 41.25; H, 4.01.; N, 8.29; S, 4.69. Found: C, 41.17; H, 3.91; N, 8.35; S, 4.78. IR data (KBr pellet, cm-1): 3419(br), 3045(w), 2916(w), 2885(w), 1592(s), 1477(m), 1437(m), 1376(m), 1274(m), 1217(m), 1177(s), 1128(w), 1080(w), 1036(m), 1004(m), 901(w), 832(m), 748(w), 710(w), 676(m), 642(w), 579(s), 532(m), 393(w). Synthesis
of
{[Cd(pdpy)(PTA)]·H2O}n
(II).
A
mixture
of
piperazine-1,4-diylbis
(pyridine-4-ylmethanone) (3.01 mg, 0.1 mmol), p-phthalic acid (1.66 mg, 0.1 mmol), Cadmium perchlorate hydrate (8.38 mg, 0.2 mmol) and water (10 mL) was homogenized by stirring for 30 min, then transferred into 25 mL Teflon-lined stainless steel autoclave under autogenous pressure at 140
for 3 days. After cooling the reaction system to room temperature at a rate of 5
/ h,
clear block white crystals were isolated. Yield of 40.93% (based on Cadmium perchlorate hydrate). Calc. for C16H18N2O8Cd(%): C, 40.09; H, 3.81.; N, 5.73. Found: C, 40.14; H, 3.79; N, 5.85. IR data (KBr pellet, cm-1 ): 3414(br), 3051(w), 2929(w), 1614(s), 1656(s), 1504(m), 1445(w), 1389(s), 1289(m), 1265(w), 1159(w), 1093(w), 1007(s), 891(w), 841(s), 753(s), 771(w), 649(w), 603(w), 530(m), 442(w), 388(w).
2.3 Crystallographic data collection and refinement Single-crystal diffraction data I-II were collected suitable single crystals of the coordination polymers on a Bruker Smart CCD X-ray single-crystal diffractometer with graphite monochromated MoKα-radiation (λ = 0.71073 Å) at 296(2) K. All independent reflections were collected in a range of 1.76-25.00º for coordination polymer I and 1.87-25.00º for coordination polymer II (determined in the subsequent refinement). Multi-scan empirical absorption corrections were applied to the data using the SADABS. The crystal structure was solved by direct methods and Fourier synthesis. Positional and thermal parameters were refined by the full-matrix least-squares method on F2 using the SHELXTL software package. A summary of the key crystallographic information is given in Table 1. Selected bond lengths and band angles for the coordination polymers I-II are listed in Table S1. Hydrogen-bond lengths (Å) and angles (°) for I-II are listed in Table S2.
Table 1 Summary of crystallographic data for coordination polymers I-II. Date
I
II
Empirical formula
C46H52Cd2N8O21S2
C 16H 18CdN2O 8
Formula weight
1341.87
478.72
Temperature / K
296(2)
296(2)
Crystal system
monoclinic
monoclinic
Space group
P21/m
P21/n
a/Å
7.6280(7)
6.0366(4)
b/Å
16.3673(16)
21.3977(16)
c/Å
11.2597(10)
13.7507(10)
α/°
90
90
β/°
104.3191(14)
92.0375(12)
90
90
1362.1(2)
1775.0(2)
1
4
1.636
1.791
0.942
1.279
680.0
960.0
0.38 × 0.28 × 0.26
0.42 × 0.18 × 0.16
Radiation
MoKα (λ = 0.71073)
MoKα (λ = 0.71073)
2θ range for data collection / °
3.734 to 49.998
3.522 to 49.998
-9 ≤ h ≤ 5, -19 ≤ k ≤ 16,
-7 ≤ h ≤ 7, -24 ≤ k ≤ 25,
-13 ≤ l ≤ 13
-15 ≤ l ≤ 16
6857
8983
2490 [Rint = 0.0227,
3123 [Rint = 0.0202,
Rsigma = 0.0271]
Rsigma = 0.0220]
2490 / 12 / 204
3123 / 0 / 244
1.320
1.211
R1 = 0.0527,
R1 = 0.0278,
wR2 = 0.1312
wR2 = 0.0886
R1 = 0.0557,
R1 = 0.0348,
wR2 = 0.1325
wR2 = 0.1085
1.32 / -0.66
1.15 / -0.83
γ/° Volume / Å
3
Z 3
ρcalc g / cm -1
µ / mm F(000)
Crystal size / mm
3
Index ranges Reflections collected Independent reflections Data / restraints / parameters 2
Goodness-of-fit on F
Final R indexes [I>=2σ (I)] Final R indexes [all data] Largest diff. peak / hole / eÅ-3
3. Results and discussion 3.1 FT-IR spectroscopy The structures of the coordination polymers are identified by satisfactory elemental analysis as well as FT-IR (See Fig. S1). The coordination polymer I-II have broad band in the ranges of
3431-3414 cm-1 and peak at 935-891 cm-1, which are due to water molecules in coordination and lattice forms [23, 24]. The absorption band of coordination polymers I at 1592 cm-1 represents the characteristic skeleton vibration of the pyridine ring, and the absorption related to the Cd–N and Cd–O stretching vibrations are observed at 523-430 cm-1 [25]. For coordination polymer II, there are strong absorption bands in the region of 1663 cm-1 and 1473 cm-1 that may be ascribed to the asymmetric (COO-) and symmetric (COO-) stretching of carboxyl groups of ligands [26-28], The values of ∆[νas -νs] of polymer II is 169 cm-1, which indicate that the carboxyl groups are coordinated with the metal ions via bidentate-chelating mode. The absence of the characteristic band around 1700 cm-1 shows that the ligands are completely deprotonated upon the coordination with Cd(II) ion [29].
3.2 Structural description of coordination polymers I-II Crystal Structures of {[Cd(pdpy)(H2O)2]·SUL·(H2O)0.5}n (I). The single-crystal X-ray diffraction analysis reveals that I crystallizes in monoclinic with the space group P21/m. The coordination environment of Cd(II) center is six-coordinated by two oxygen atoms (O6 and O6a) belonging to two molecules of pdpy ligands, two nitrogen atoms (N2 and N2a) from another two pdpy ligands, together with two terminal water molecules (O1W and O1Wa) to give rise to a slightly distorted {CdN2O4} octahedral coordination geometry with the equatorial plane occupied by O6, O6a, O1W and O1Wa. The axial sites are occupied by N2 and N2a atoms, as shown in Fig.1a. The pdpy displays µ4-(η1-N), (η1-N’),(η1 -O),(η1-O’) tetradentate coordination mode (mode I-a, see Scheme 2). The Cd–O distance is 2.315(4) Å, the Cd–OW distance is 2.248(4) Å and that of Cd–N is 2.318(4) Å, respectively, which are consistent with those in previous work covering Cd(II) coordination polymers [30-32].
Fig. 1 (a) Diagram showing the coordination environment for Cd(II) center in I. (b) The 2D layer structure include ring A and ring B. (c) The 3D architecture connected through hydrogen bonds between the adjacent 2D layers in I.
Based on the building block of [Cd2(pdpy)2(H2O)4] motif, coordination polymer I is covalently bonded into a 2D corrugated layer framework, which is orderly composed by two types of closed rings, namely, 24-membered rings Cd2C14N6O2 (ring A, with approximate dimension of 11.937 × 8.717 Å2) and 14-membered rings Cd2C8N2O2 (ring B, 7.628 × 7.179 Å2), as illustrated in Fig. 1b. Obviously, this 2D layer may also be regarded as being constructed by 1D ribbons involving ring A and those involving ring B, which are alternately arrayed. It is worth mentioning that, the dissociative SUL molecules are linearly and head-to-end arranged and sandwiched between two adjacent parallel 2D layers. More specifically, one sulfo group in one SUL molecule connects up-down layers together through hydrogen bonding with two coordinated water molecules coming from up-down layers, respectively. Simultaneously, similar cases occur for the carboxyl groups in each SUL molecule. Thus, the head-to-end arranged sulfo group and carboxyl group are linked into a 10-membered ring based on four hydrogen bonds (see Table S2), in which one guest water molecule is encapsulated, consequently, 3D architecture framework of I is taken shape, as shown in Fig. 1c.
Crystal Structures of {[Cd(pdpy)(PTA)]· H2O}n (II). The results of crystallographic analysis show that coordination polymer II crystallizes in the monoclinic system with space group P21/n. As illustrated in Fig. 2a, the central Cd(II) atom presents a distorted {CdO7} pentagonal bipyramid configuration coordinated by seven oxygen atoms including one oxygen atom deriving from one pdpy ligand, four oxygen atoms from two different chelating PTA2- ligands and two oxygen atoms from coordinating water molecules, respectively, in which five vertexes of equatorial plane are occupied by O1, O2, O3, O4 and O1W, while O5 and O2W atoms locate in the axial positions. In the asymmetric unit of II, the pdpy ligand adopts mode II-a coordination mode (µ2-(η1-O),(η1 -O’)), and PTA2- ligands display µ2-(η2-O,O’),(η2-O’’,O’’’) bidentate chelating mode (mode II-b), as shown in Scheme 2. The Cd–O distances are in the range of 2.315(3)-2.446(3) Å and those of Cd–OW lie in the range of 2.279(4)-2.298(3) Å (see Table S1), which are consistent with those in previous work covering Cd(II) coordination polymers [33-35].
Fig. 2 (a) Diagram showing the coordination environment for Cd(II) center in II. (b) View of the 2D (6, 6) chair-like sheet in I. (c) The 3D architecture connected through hydrogen bonds between the adjacent 2D layers in II.
In coordination polymer II, chelating PTA2- ligands (in µ2-(η2-O,O’),(η2-O’’,O’’’) mode II-b) and Cd(II) centers are connected to produce an infinite 1D (-Cd-PTA-Cd-PTA-)∞ sinusoid-shaped chain. Thereafter, these chains are bridged into 2D layer pattern with (6,6) network topology by the pdpy pillars in a trans arrangement along the a axis, in which the grid size is 27.287 × 20.072 Å2, as shown in Fig. 2b. Furthermore, two uncoordinated water molecules dwell in every grid unit which are connected with two axial coordinated water molecules, belonging to two {CdO7} motifs in the adjacent up-down chains by hydrogen bonding, respectively, as shown in Figure 3b. Ultimately, the coordinated apical water molecules of equatorial plane deriving from {CdO7} motifs in one layer are engaged in hydrogen bonding interactions with two apical oxygen atoms of {CdO7} motifs coming from the adjacent layer, resulting in a 3D non-interpenetrating architecture, as shown in Fig. 2c (O1W–H1WA···O3=1.97 Å and O1W–H1WB···O1=1.94 Å). Six-membered rings resulting from these hydrogen bonding interactions may contribute to the stabilization of the skeleton of II. The O···O contacts arising from hydrogen bonding are in the range of 2.769(4)-2.858(8) Å. In the past years, a series of Cd-pdpy coordination polymers have been reported by Robert L. LaDuca [36-42]. Compared with these coordination polymers, both I and II have different structures: For coordination polymer I, the dissociative SUL molecules provide the hydrogen bonding necessary for construction of the crystal structure and there is no other interaction force between two adjacent parallel 2D layers. For coordination polymer II, the Cd(II) atom shows pentagonal bipyramid configuration purely with seven O atoms and the N atoms from pbpy do not participate the coordination.
3.3 Luminescent properties Recent studies reveal that some coordination polymers constructed by d10 metal ions and π-conjugated organic ligands have been proposed as probes for metal ions, in molecular sensors, in electroluminescent displays and other photoactive materials [43]. We infer that the as-synthesized coordination polymers in this report may be conceivable to be acted as probes for certain metal ions. Therefore, the luminescent properties of coordination polymers I and II were investigated at room temperature, the coordination polymer I shows main emission peak at 400 nm (λex = 294 nm) and II shows a main emission peak at 337 nm (λex = 283 nm). Since the Cd(II) ions are difficult to oxidize or to reduce because of the d10 configuration, these emissions are
mainly assigned to the π-π* or n-π* transition [44-45]. To investigate the possibilities of luminescent selective recognition of coordination polymers I and II towards certain metal cations, the solid samples of I and II were immersed in water containing various metal cations to produce water solutions of I and II, respectively. The tested metal cations were as follow, namely, Co2+(Co(CH3COO)2), Zn2+(Zn(CH3COO)2), Ni2+(Ni(CH3COO)2),
Cd2+(Cd(CH3COO)2), Sr2+(SrCl2), Hg2+(HgSO4),
Ba2+(BaCl2),
Ag+(AgNO3),
Pb2+(Pb(CH3COO)2), Fe2+(FeSO4)
and
Ca2+(CaCl2),
Mn2+(Mn(CH3 COO)2),
Cu2+(Cu(CH3COO)2),
with
the
concentration of the metal cations of 1.0 × 10−4 M.
Fig. 3 (a) Comparisons of luminescent intensities of I in different metal ions. (b) Emission spectra of I in diverse metal ions.
For coordination polymer I (Fig. 3), the luminescent emission intensities are sharply decreased upon the addition of Cu2+ at 400 nm (from 6059 a.u. to 2061 a.u.), where the luminescent intensities in the presence of Cu2+ are about one-third as strong as those without Cu2+. Different from the above-mentioned, the introduction of Co2+, Cd2+, Ba2+, Ag+, Ca2+, Zn2+, Sr2+,
Pb2+, Mn2+, Ni2+, Hg2+, and Fe2+ cations into the water solution of coordination polymer I cause only minor changes of the emission intensities with unchanged position of the emission bands. As a result, coordination polymer I displays good selectivity towards Cu2+ and it can be considered as promising selective luminescent probes for Cu2+.
Fig. 4 (a) Comparisons of luminescent intensities of II in different metal ions. (b) Emission spectra of II in diverse metal ions.
For coordination polymer II (Fig. 4), particularly, the luminescent intensity of II is significantly decreased about ninefold (from 3861 a.u. to 421 a.u.) by addition of the Cu2+ at 337 nm (λex = 283 nm) and red-shift occurs in the emission spectrum of II (from 337nm to 362nm), as shown in Fig. 4b. Compared to Cu2+, the emission spectra of II in water containing other tested metals (including Mn2+, Ca2+, Ba2+, Pb2+, Zn2+, Co2+, Cd2+, Ag+, Hg2+, Ni2+, Fe2+, and Sr2+ cations) exhibit emission bands with unchanged position. The results suggest that coordination polymer II displays good selectivity towards Cu2+ and it may be considered as selective luminescent probes for Cu2+.
4. Conclusion In a word, we have successfully synthesized two novel coordination polymers through the flexible piperazine-1,4-diylbis(pyridine-4-ylmethanone) (pdpy) ligand by adopting the strategy of constructing carboxyl-containing auxiliary ligands. Structural analysis demonstrate that coordination modes of the title ligand together with the adoption of the auxiliary ligands can effectively tune the final structures of the as-synthesized coordination polymers I-II. Coordination polymer I shows a 2D corrugated sheet-like network assembled by a 1D ribbons involving two types of multiple closed rings. Coordination polymer II exhibits a 2D layer pattern with (6,6) network topology by the pdpy pillars in a trans arrangement. I-II are assembled from 2D structures into 3D frameworks, suggesting that intermolecular forces are of effective strategies in the assembly of the three-dimensional coordination polymers. Luminescent properties of I and II indicate that both I and II present highly selective response to Cu2+ through luminescence quenching effects, which may be acted as potential luminescent recognition sensors towards Cu2+.
Acknowledgments This research is financially supported by the Natural Science Foundation of Henan Province of China (Nos.13A150056, and 15NB005).
Supplementary Information CCDC: 1006871 for I and 1025153 for II contain the supplementary crystallographic data for this
paper.
These
data
can
be
obtained
free
of
charge
via
http://www.ccdc.cam.ac.uk/conts/retrieving. html or from CCDC, 12 Union Road, Cambridge CB2 1EZ, UK, E-mail: [email protected].
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Captions for Tables Table 1 Summary of crystallographic data for coordination polymers I-II. Table S1 Selected bond lengths(Å) and bond angles(°)for the coordination polymers I-II. Table S2 Hydrogen-bond lengths (Å) and angles (°) for coordination polymers I-II.
Captions for Figures and Scheme Scheme 1 Experimental routes for coordination polymers I-II. Scheme 2 Coordination modes in coordination polymers I-II. Fig. 1 (a) Diagram showing the coordination environment for Cd(II) center in I. (b) The 2D layer structure include ring A and ring B. (c) The 3D architecture connected through hydrogen bonds between the adjacent 2D layers in I. Fig. 2 (a) Diagram showing the coordination environment for Cd(II) center in II. (b) View of the 2D (6, 6) chair-like sheet in I. (c) The 3D architecture connected through hydrogen bonds between the adjacent 2D layers in II. Fig. 3 (a) Comparisons of luminescent intensities of I in different metal ions. (b) Emission spectra of I in diverse metal ions. Fig. 4 (a) Comparisons of luminescent intensities of II in different metal ions. (b) Emission spectra of II in diverse metal ions. Fig. S1 The IR spectra of I-II. Fig. S2 The lifetime measurements of I (at 400 nm) and II (at 337 nm) Fig. S3 The powder X-ray diffraction of I-II. Fig. S4 The absorption band of I.
Two cadmium coordination polymers containing piperazine-1,4diylbis(pyridine-4-ylmethanone):
highly
selective
luminescent
recognition of Cu2+ Liu Liu, Chen Lian, Yin-shuang Long, Xu Guo, Li-rong Yang*
Two novel three-dimensional coordination polymers with highly selective luminescent recognition of Cu2+ have been prepared based on low-dimensional architectures through intermolecular forces under hydrothermal conditions and characterized.
Research highlights： ⋅
Coordination polymers I-II have been synthesized together with three auxiliary ligands.
⋅
I-II are assembled form low-dimensional structures into three-dimensional frameworks.
⋅
I and II display highly selective recognition towards Cu2+.
S0020-1693(16)30427-3 http://dx.doi.org/10.1016/j.ica.2016.07.049 ICA 17184
To appear in:
Inorganica Chimica Acta
Received Date: Revised Date: Accepted Date:
14 December 2015 16 June 2016 28 July 2016
Please cite this article as: L. Liu, C. Lian, Y-s. Long, X. Guo, L-r. Yang, Two cadmium coordination polymers containing piperazine-1,4- diylbis(pyridine-4-ylmethanone): highly selective luminescent recognition of Cu2+, Inorganica Chimica Acta (2016), doi: http://dx.doi.org/10.1016/j.ica.2016.07.049
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Two cadmium coordination polymers containing piperazine-1,4diylbis(pyridine-4-ylmethanone):
highly
selective
luminescent
recognition of Cu2+ Liu Liua,b, Chen Liana, Yin-shuang Longa, Xu Guoa, Li-rong Yanga* a
Henan Key Laboratory of Polyoxometalate, Institute of Molecule and Crystal Engineering, College of Chemistry
and Chemical Engineering, Henan University, Kaifeng 475004, P. R. China b
Nanyang Tobacco Monopoly Bureau (Company), Nanyang 473000, P. R. China
ABSTRACT: Two novel coordination polymers, namely, {[Cd(pdpy)(H2O)2]·SUL· (H2O)0.5}n (I) and {[Cd(pdpy)(PTA)]·H2O}n (II) (pdpy = piperazine-1,4-diylbis(pyridine-4-ylmethanone), PTA = p-phthalic acid and SUL = 5-sulphosalicylic acid) have been designed and successfully prepared under hydro-thermal conditions and characterized by elemental analyses, IR spectroscopy, and single crystal X-ray diffraction. Structural analysis indicates that the pdpy ligands adopt three different coordination modes in the as-synthesized I-II, and thus result in diversity of the targeted coordination polymers. It is worth mentioning that, based on the hydrogen bonding, I-II are assembled from two-dimensional (2D) structures into three-dimensional (3D) frameworks. Luminescent properties of I and II have been studied at ambient temperature. Significantly, both I and II show highly selective response to Cu2+ cations through luminescence quenching effects, which may make them promising luminescent selective recognition sensors for Cu2+. Keywords: Coordination polymer; Intermolecular forces; Luminescent recognition; Metal–organic frameworks; Hydro-thermal synthesis
1. Introduction Coordination polymers (CPs) as well as metal–organic frameworks (MOFs), which are crystalline multifunctional materials that are often assemblies of the organic linkers and metal ions (or metal clusters), have attracted enormous interest of synthetic chemists. In general, CPs _____________________ *Corresponding author. E-mail address: [email protected]
have emerged as a promising kind of materials with a wide variety of potential
applications such as in gas storage, optoelectronics, molecular recognition, microelectronics, molecular magnetism, chemical separations, ion exchange, nonlinear optics and heterogeneous catalysis [1-15]. Luminescent probe is an excellent example of a field where the ability to introduce chemical functionalities into the structures with useful properties has had a substantial positive impact on society in various applications. Cheng and co-workers performed a study on two coordination polymers containing 1D channels as selective luminescent probes to Zn2+ [16]. In same year, Liu et.al investigated the preparation of a series of lanthanide coordination polymers which can be used as molecular devices for Ag+ sensor [17]. A. Thibon and V. C. Pierre reported a terbium coordination polymer framework with a highly selective luminescent sensor for K+ in 2008 [18]. Following our ongoing efforts towards the synthesis and isolation of coordination polymers, which may act as selective luminescent probes to some metal ions [19-22]. In this work, we describe the synthesis, structures, luminescent properties of two kinds of Cd(II) coordination polymers based on piperazine-1,4-diylbis(pyridine-4-ylmethanone), which are formulated as {[Cd(pdpy)(H2O)2]·SUL· (H2O)0.5}n (I) and {[Cd(pdpy)(PTA)]·H2O}n (II). The synthetic strategies of I-II are presented in Scheme 1. The coordination polymers I and II exhibit a highly luminescent selectivity towards Cu2+.
Scheme 1 Experimental routes for coordination polymers I-II.
Scheme 2 Coordination modes in coordination polymers I-II.
2. Experimental Section 2.1 Materials and physical measurements All chemicals were commercially purchased from Jinan Camolai Trading Company and used without further purification. Elemental analyses (C, H, and N) were performed with a Perkin-Elmer 240 CHN Elemental Analyzer. IR spectra in the range of 400-4000 cm-1 were recorded with an AVATAR 360 FT-IR spectrometer (KBr pellets were used). The crystal structure was determined with a Bruker Smart CCD X-ray single-crystal diffractometer. Excitation and emission spectra were obtained with an F-7000 FL spectrofluorometer at room temperature.
2.2 Synthesis of the coordination polymers I-II Synthesis of {[Cd(pdpy)(H2O)2]·SUL·(H2 O)0.5}n (I) . A mixture of piperazine-1,4-diylbis (pyridine-4-ylmethanone) (3.01 mg, 0.1 mmol), 5-sulphosalicylic acid (1.88 mg, 0.1 mmol), Cadmium perchlorate hydrate (8.38 mg, 0.2 mmol) and water (10 mL) was homogenized by stirring for 30 min, then transferred into 25 mL Teflon-lined stainless steel autoclave under autogenous pressure at 160
for 4 days. After cooling the reaction system to room temperature
at a rate of 5
/ h, the clear solution was stirred at room temperature for 30 days then clear block
orange crystals were isolated. Yield of 80.31% (based on Cadmium perchlorate hydrate). Calc. for C46H52N8 O21S2 Cd2(%): C, 41.25; H, 4.01.; N, 8.29; S, 4.69. Found: C, 41.17; H, 3.91; N, 8.35; S, 4.78. IR data (KBr pellet, cm-1): 3419(br), 3045(w), 2916(w), 2885(w), 1592(s), 1477(m), 1437(m), 1376(m), 1274(m), 1217(m), 1177(s), 1128(w), 1080(w), 1036(m), 1004(m), 901(w), 832(m), 748(w), 710(w), 676(m), 642(w), 579(s), 532(m), 393(w). Synthesis
of
{[Cd(pdpy)(PTA)]·H2O}n
(II).
A
mixture
of
piperazine-1,4-diylbis
(pyridine-4-ylmethanone) (3.01 mg, 0.1 mmol), p-phthalic acid (1.66 mg, 0.1 mmol), Cadmium perchlorate hydrate (8.38 mg, 0.2 mmol) and water (10 mL) was homogenized by stirring for 30 min, then transferred into 25 mL Teflon-lined stainless steel autoclave under autogenous pressure at 140
for 3 days. After cooling the reaction system to room temperature at a rate of 5
/ h,
clear block white crystals were isolated. Yield of 40.93% (based on Cadmium perchlorate hydrate). Calc. for C16H18N2O8Cd(%): C, 40.09; H, 3.81.; N, 5.73. Found: C, 40.14; H, 3.79; N, 5.85. IR data (KBr pellet, cm-1 ): 3414(br), 3051(w), 2929(w), 1614(s), 1656(s), 1504(m), 1445(w), 1389(s), 1289(m), 1265(w), 1159(w), 1093(w), 1007(s), 891(w), 841(s), 753(s), 771(w), 649(w), 603(w), 530(m), 442(w), 388(w).
2.3 Crystallographic data collection and refinement Single-crystal diffraction data I-II were collected suitable single crystals of the coordination polymers on a Bruker Smart CCD X-ray single-crystal diffractometer with graphite monochromated MoKα-radiation (λ = 0.71073 Å) at 296(2) K. All independent reflections were collected in a range of 1.76-25.00º for coordination polymer I and 1.87-25.00º for coordination polymer II (determined in the subsequent refinement). Multi-scan empirical absorption corrections were applied to the data using the SADABS. The crystal structure was solved by direct methods and Fourier synthesis. Positional and thermal parameters were refined by the full-matrix least-squares method on F2 using the SHELXTL software package. A summary of the key crystallographic information is given in Table 1. Selected bond lengths and band angles for the coordination polymers I-II are listed in Table S1. Hydrogen-bond lengths (Å) and angles (°) for I-II are listed in Table S2.
Table 1 Summary of crystallographic data for coordination polymers I-II. Date
I
II
Empirical formula
C46H52Cd2N8O21S2
C 16H 18CdN2O 8
Formula weight
1341.87
478.72
Temperature / K
296(2)
296(2)
Crystal system
monoclinic
monoclinic
Space group
P21/m
P21/n
a/Å
7.6280(7)
6.0366(4)
b/Å
16.3673(16)
21.3977(16)
c/Å
11.2597(10)
13.7507(10)
α/°
90
90
β/°
104.3191(14)
92.0375(12)
90
90
1362.1(2)
1775.0(2)
1
4
1.636
1.791
0.942
1.279
680.0
960.0
0.38 × 0.28 × 0.26
0.42 × 0.18 × 0.16
Radiation
MoKα (λ = 0.71073)
MoKα (λ = 0.71073)
2θ range for data collection / °
3.734 to 49.998
3.522 to 49.998
-9 ≤ h ≤ 5, -19 ≤ k ≤ 16,
-7 ≤ h ≤ 7, -24 ≤ k ≤ 25,
-13 ≤ l ≤ 13
-15 ≤ l ≤ 16
6857
8983
2490 [Rint = 0.0227,
3123 [Rint = 0.0202,
Rsigma = 0.0271]
Rsigma = 0.0220]
2490 / 12 / 204
3123 / 0 / 244
1.320
1.211
R1 = 0.0527,
R1 = 0.0278,
wR2 = 0.1312
wR2 = 0.0886
R1 = 0.0557,
R1 = 0.0348,
wR2 = 0.1325
wR2 = 0.1085
1.32 / -0.66
1.15 / -0.83
γ/° Volume / Å
3
Z 3
ρcalc g / cm -1
µ / mm F(000)
Crystal size / mm
3
Index ranges Reflections collected Independent reflections Data / restraints / parameters 2
Goodness-of-fit on F
Final R indexes [I>=2σ (I)] Final R indexes [all data] Largest diff. peak / hole / eÅ-3
3. Results and discussion 3.1 FT-IR spectroscopy The structures of the coordination polymers are identified by satisfactory elemental analysis as well as FT-IR (See Fig. S1). The coordination polymer I-II have broad band in the ranges of
3431-3414 cm-1 and peak at 935-891 cm-1, which are due to water molecules in coordination and lattice forms [23, 24]. The absorption band of coordination polymers I at 1592 cm-1 represents the characteristic skeleton vibration of the pyridine ring, and the absorption related to the Cd–N and Cd–O stretching vibrations are observed at 523-430 cm-1 [25]. For coordination polymer II, there are strong absorption bands in the region of 1663 cm-1 and 1473 cm-1 that may be ascribed to the asymmetric (COO-) and symmetric (COO-) stretching of carboxyl groups of ligands [26-28], The values of ∆[νas -νs] of polymer II is 169 cm-1, which indicate that the carboxyl groups are coordinated with the metal ions via bidentate-chelating mode. The absence of the characteristic band around 1700 cm-1 shows that the ligands are completely deprotonated upon the coordination with Cd(II) ion [29].
3.2 Structural description of coordination polymers I-II Crystal Structures of {[Cd(pdpy)(H2O)2]·SUL·(H2O)0.5}n (I). The single-crystal X-ray diffraction analysis reveals that I crystallizes in monoclinic with the space group P21/m. The coordination environment of Cd(II) center is six-coordinated by two oxygen atoms (O6 and O6a) belonging to two molecules of pdpy ligands, two nitrogen atoms (N2 and N2a) from another two pdpy ligands, together with two terminal water molecules (O1W and O1Wa) to give rise to a slightly distorted {CdN2O4} octahedral coordination geometry with the equatorial plane occupied by O6, O6a, O1W and O1Wa. The axial sites are occupied by N2 and N2a atoms, as shown in Fig.1a. The pdpy displays µ4-(η1-N), (η1-N’),(η1 -O),(η1-O’) tetradentate coordination mode (mode I-a, see Scheme 2). The Cd–O distance is 2.315(4) Å, the Cd–OW distance is 2.248(4) Å and that of Cd–N is 2.318(4) Å, respectively, which are consistent with those in previous work covering Cd(II) coordination polymers [30-32].
Fig. 1 (a) Diagram showing the coordination environment for Cd(II) center in I. (b) The 2D layer structure include ring A and ring B. (c) The 3D architecture connected through hydrogen bonds between the adjacent 2D layers in I.
Based on the building block of [Cd2(pdpy)2(H2O)4] motif, coordination polymer I is covalently bonded into a 2D corrugated layer framework, which is orderly composed by two types of closed rings, namely, 24-membered rings Cd2C14N6O2 (ring A, with approximate dimension of 11.937 × 8.717 Å2) and 14-membered rings Cd2C8N2O2 (ring B, 7.628 × 7.179 Å2), as illustrated in Fig. 1b. Obviously, this 2D layer may also be regarded as being constructed by 1D ribbons involving ring A and those involving ring B, which are alternately arrayed. It is worth mentioning that, the dissociative SUL molecules are linearly and head-to-end arranged and sandwiched between two adjacent parallel 2D layers. More specifically, one sulfo group in one SUL molecule connects up-down layers together through hydrogen bonding with two coordinated water molecules coming from up-down layers, respectively. Simultaneously, similar cases occur for the carboxyl groups in each SUL molecule. Thus, the head-to-end arranged sulfo group and carboxyl group are linked into a 10-membered ring based on four hydrogen bonds (see Table S2), in which one guest water molecule is encapsulated, consequently, 3D architecture framework of I is taken shape, as shown in Fig. 1c.
Crystal Structures of {[Cd(pdpy)(PTA)]· H2O}n (II). The results of crystallographic analysis show that coordination polymer II crystallizes in the monoclinic system with space group P21/n. As illustrated in Fig. 2a, the central Cd(II) atom presents a distorted {CdO7} pentagonal bipyramid configuration coordinated by seven oxygen atoms including one oxygen atom deriving from one pdpy ligand, four oxygen atoms from two different chelating PTA2- ligands and two oxygen atoms from coordinating water molecules, respectively, in which five vertexes of equatorial plane are occupied by O1, O2, O3, O4 and O1W, while O5 and O2W atoms locate in the axial positions. In the asymmetric unit of II, the pdpy ligand adopts mode II-a coordination mode (µ2-(η1-O),(η1 -O’)), and PTA2- ligands display µ2-(η2-O,O’),(η2-O’’,O’’’) bidentate chelating mode (mode II-b), as shown in Scheme 2. The Cd–O distances are in the range of 2.315(3)-2.446(3) Å and those of Cd–OW lie in the range of 2.279(4)-2.298(3) Å (see Table S1), which are consistent with those in previous work covering Cd(II) coordination polymers [33-35].
Fig. 2 (a) Diagram showing the coordination environment for Cd(II) center in II. (b) View of the 2D (6, 6) chair-like sheet in I. (c) The 3D architecture connected through hydrogen bonds between the adjacent 2D layers in II.
In coordination polymer II, chelating PTA2- ligands (in µ2-(η2-O,O’),(η2-O’’,O’’’) mode II-b) and Cd(II) centers are connected to produce an infinite 1D (-Cd-PTA-Cd-PTA-)∞ sinusoid-shaped chain. Thereafter, these chains are bridged into 2D layer pattern with (6,6) network topology by the pdpy pillars in a trans arrangement along the a axis, in which the grid size is 27.287 × 20.072 Å2, as shown in Fig. 2b. Furthermore, two uncoordinated water molecules dwell in every grid unit which are connected with two axial coordinated water molecules, belonging to two {CdO7} motifs in the adjacent up-down chains by hydrogen bonding, respectively, as shown in Figure 3b. Ultimately, the coordinated apical water molecules of equatorial plane deriving from {CdO7} motifs in one layer are engaged in hydrogen bonding interactions with two apical oxygen atoms of {CdO7} motifs coming from the adjacent layer, resulting in a 3D non-interpenetrating architecture, as shown in Fig. 2c (O1W–H1WA···O3=1.97 Å and O1W–H1WB···O1=1.94 Å). Six-membered rings resulting from these hydrogen bonding interactions may contribute to the stabilization of the skeleton of II. The O···O contacts arising from hydrogen bonding are in the range of 2.769(4)-2.858(8) Å. In the past years, a series of Cd-pdpy coordination polymers have been reported by Robert L. LaDuca [36-42]. Compared with these coordination polymers, both I and II have different structures: For coordination polymer I, the dissociative SUL molecules provide the hydrogen bonding necessary for construction of the crystal structure and there is no other interaction force between two adjacent parallel 2D layers. For coordination polymer II, the Cd(II) atom shows pentagonal bipyramid configuration purely with seven O atoms and the N atoms from pbpy do not participate the coordination.
3.3 Luminescent properties Recent studies reveal that some coordination polymers constructed by d10 metal ions and π-conjugated organic ligands have been proposed as probes for metal ions, in molecular sensors, in electroluminescent displays and other photoactive materials [43]. We infer that the as-synthesized coordination polymers in this report may be conceivable to be acted as probes for certain metal ions. Therefore, the luminescent properties of coordination polymers I and II were investigated at room temperature, the coordination polymer I shows main emission peak at 400 nm (λex = 294 nm) and II shows a main emission peak at 337 nm (λex = 283 nm). Since the Cd(II) ions are difficult to oxidize or to reduce because of the d10 configuration, these emissions are
mainly assigned to the π-π* or n-π* transition [44-45]. To investigate the possibilities of luminescent selective recognition of coordination polymers I and II towards certain metal cations, the solid samples of I and II were immersed in water containing various metal cations to produce water solutions of I and II, respectively. The tested metal cations were as follow, namely, Co2+(Co(CH3COO)2), Zn2+(Zn(CH3COO)2), Ni2+(Ni(CH3COO)2),
Cd2+(Cd(CH3COO)2), Sr2+(SrCl2), Hg2+(HgSO4),
Ba2+(BaCl2),
Ag+(AgNO3),
Pb2+(Pb(CH3COO)2), Fe2+(FeSO4)
and
Ca2+(CaCl2),
Mn2+(Mn(CH3 COO)2),
Cu2+(Cu(CH3COO)2),
with
the
concentration of the metal cations of 1.0 × 10−4 M.
Fig. 3 (a) Comparisons of luminescent intensities of I in different metal ions. (b) Emission spectra of I in diverse metal ions.
For coordination polymer I (Fig. 3), the luminescent emission intensities are sharply decreased upon the addition of Cu2+ at 400 nm (from 6059 a.u. to 2061 a.u.), where the luminescent intensities in the presence of Cu2+ are about one-third as strong as those without Cu2+. Different from the above-mentioned, the introduction of Co2+, Cd2+, Ba2+, Ag+, Ca2+, Zn2+, Sr2+,
Pb2+, Mn2+, Ni2+, Hg2+, and Fe2+ cations into the water solution of coordination polymer I cause only minor changes of the emission intensities with unchanged position of the emission bands. As a result, coordination polymer I displays good selectivity towards Cu2+ and it can be considered as promising selective luminescent probes for Cu2+.
Fig. 4 (a) Comparisons of luminescent intensities of II in different metal ions. (b) Emission spectra of II in diverse metal ions.
For coordination polymer II (Fig. 4), particularly, the luminescent intensity of II is significantly decreased about ninefold (from 3861 a.u. to 421 a.u.) by addition of the Cu2+ at 337 nm (λex = 283 nm) and red-shift occurs in the emission spectrum of II (from 337nm to 362nm), as shown in Fig. 4b. Compared to Cu2+, the emission spectra of II in water containing other tested metals (including Mn2+, Ca2+, Ba2+, Pb2+, Zn2+, Co2+, Cd2+, Ag+, Hg2+, Ni2+, Fe2+, and Sr2+ cations) exhibit emission bands with unchanged position. The results suggest that coordination polymer II displays good selectivity towards Cu2+ and it may be considered as selective luminescent probes for Cu2+.
4. Conclusion In a word, we have successfully synthesized two novel coordination polymers through the flexible piperazine-1,4-diylbis(pyridine-4-ylmethanone) (pdpy) ligand by adopting the strategy of constructing carboxyl-containing auxiliary ligands. Structural analysis demonstrate that coordination modes of the title ligand together with the adoption of the auxiliary ligands can effectively tune the final structures of the as-synthesized coordination polymers I-II. Coordination polymer I shows a 2D corrugated sheet-like network assembled by a 1D ribbons involving two types of multiple closed rings. Coordination polymer II exhibits a 2D layer pattern with (6,6) network topology by the pdpy pillars in a trans arrangement. I-II are assembled from 2D structures into 3D frameworks, suggesting that intermolecular forces are of effective strategies in the assembly of the three-dimensional coordination polymers. Luminescent properties of I and II indicate that both I and II present highly selective response to Cu2+ through luminescence quenching effects, which may be acted as potential luminescent recognition sensors towards Cu2+.
Acknowledgments This research is financially supported by the Natural Science Foundation of Henan Province of China (Nos.13A150056, and 15NB005).
Supplementary Information CCDC: 1006871 for I and 1025153 for II contain the supplementary crystallographic data for this
paper.
These
data
can
be
obtained
free
of
charge
via
http://www.ccdc.cam.ac.uk/conts/retrieving. html or from CCDC, 12 Union Road, Cambridge CB2 1EZ, UK, E-mail: [email protected].
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Captions for Tables Table 1 Summary of crystallographic data for coordination polymers I-II. Table S1 Selected bond lengths(Å) and bond angles(°)for the coordination polymers I-II. Table S2 Hydrogen-bond lengths (Å) and angles (°) for coordination polymers I-II.
Captions for Figures and Scheme Scheme 1 Experimental routes for coordination polymers I-II. Scheme 2 Coordination modes in coordination polymers I-II. Fig. 1 (a) Diagram showing the coordination environment for Cd(II) center in I. (b) The 2D layer structure include ring A and ring B. (c) The 3D architecture connected through hydrogen bonds between the adjacent 2D layers in I. Fig. 2 (a) Diagram showing the coordination environment for Cd(II) center in II. (b) View of the 2D (6, 6) chair-like sheet in I. (c) The 3D architecture connected through hydrogen bonds between the adjacent 2D layers in II. Fig. 3 (a) Comparisons of luminescent intensities of I in different metal ions. (b) Emission spectra of I in diverse metal ions. Fig. 4 (a) Comparisons of luminescent intensities of II in different metal ions. (b) Emission spectra of II in diverse metal ions. Fig. S1 The IR spectra of I-II. Fig. S2 The lifetime measurements of I (at 400 nm) and II (at 337 nm) Fig. S3 The powder X-ray diffraction of I-II. Fig. S4 The absorption band of I.
Two cadmium coordination polymers containing piperazine-1,4diylbis(pyridine-4-ylmethanone):
highly
selective
luminescent
recognition of Cu2+ Liu Liu, Chen Lian, Yin-shuang Long, Xu Guo, Li-rong Yang*
Two novel three-dimensional coordination polymers with highly selective luminescent recognition of Cu2+ have been prepared based on low-dimensional architectures through intermolecular forces under hydrothermal conditions and characterized.
Research highlights： ⋅
Coordination polymers I-II have been synthesized together with three auxiliary ligands.
⋅
I-II are assembled form low-dimensional structures into three-dimensional frameworks.
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I and II display highly selective recognition towards Cu2+.