Temperature Dependent Assembly, Structural Diversity and Luminescent Property in Two Novel Cd Coordination Polymers①

WANG JianLIN PingDU Shao-Wu(State Key Laoratory of Structural Chemistry, Fujian Institute of Research on the Structure of Matter, Chinese Academy of Sciences, Fuzhou 350002, China)(Graduate University of Chinese Academy of Sciences, Beijing 100049, China)

Temperature Dependent Assembly, Structural Diversity and Luminescent Property in Two Novel Cd Coordination Polymers①

WANG Jiana,bLIN Pinga②DU Shao-Wuaa(State Key Laboratory of Structural Chemistry, Fujian Institute of Research on the Structure of Matter, Chinese Academy of Sciences, Fuzhou 350002, China)b(Graduate University of Chinese Academy of Sciences, Beijing 100049, China)

Temperature dependent assembly of two novel Cd coordination polymers with the phen and H2MIP ligands (phen = 1,10-phenanthrolion and H2MIP = 5-methyl-isophthalic acid), formulated as Cd2(MIP)2(phen)2(1) and Cd3(MIP)3(H2MIP)(phen)2(2).They have been structurally characterized by single-crystal X-ray diffraction, elemental analysis, FT-IR spectra and TGA.1 crystallizes in the monoclinic space group P2/n, while 2 crystallizes in the triclinic space group P1.1 shows a 2D (two-dimensional) plane and 2 shows a 1D (one-dimensional) chain.In addition, their solid-state luminescent properties have also been investigated.

temperature dependent assembly, 2D, 1D, luminescent;

Many polymers formed by one kind of ligand have been reported.However, relatively less interest has been paid into the research of Cps synthesized by at least two different ligands.Compared with polymers formed by only one kind of ligand, these synthesized by at least two different ligands may have novel topology structures which provide opportunities for better properties[10-16].

Many factors affect the synthesis of Cps, such as pH value[5], ligand configuration[11]and reaction temperature[17,18].Especially, the reaction temperature is a crucial factor in the synthesis of Cps.Theoretically, the reaction temperature has a direct effect on the reaction energy barrier in reaction thermodynamics and the reaction rate in the reaction kinetics.In addition, the reaction temperature has an important effect on the solubility, conformation and the coordination modes of organic ligands, so multidimensional architectures may be obtained by adjusting the reaction temperature purposefully[17,18].

In our previous studies, we focused our attention on the mixture of carboxylic and N-donor ligands[21].In this paper, we apply the same method to synthesize novel Cps with mixed ligands of H2MIP and 1,10-phenanthrolion.Herein, we report polymers 1 and 2.The structure changes from 1D to 2D are effected by the reaction temperature.

2 EXPERIMENTAL

2.1 Materials and instruments

All the chemicals were purchased commercially and used as received.Thermogravimetric analysismass spectrometry analysis (TGA-MS) experiments were performed using a TGA/NETZSCH STA449C instrument heated from 30 to 800 ℃ (heating rate of 10 ℃/min, nitrogen stream).The powder X-ray diffraction (XRD) patterns were recorded on crushed single crystals in the 2q range of 5～50o using Cu-Kα radiation.The XRD were measured on a PAN alytical X’pert PRO X-ray diffractometer.IR spectra using the KBr pellet technique were recorded on a Spectrum-One FT-IR spectrophotometer.Elemental analyses (C, H, and N) were measured with an Elemental Vairo ELIII Analyzer.Fluorescence spectra for the solid samples were performed on an Edinburgh Analytical instrument FLS920.

2.2 Synthesis

Cd2(MIP)2(phen)2(1) A mixture of Cd(NO3)2·4H2O (0.040 g, 0.13 mmol), phen (0.014 g, 0.075 mmol) and H2MIP (0.024 g, 0.13 mmol) in the mixture of water (6.5 mL) and acetonitrle (1.5 mL) was stirred at room temperature for a few minutes.The resulting slurry was transferred into a 20 mL Teflon-lined stainless-steel vessel, which was heated at 180 ℃ and maintained at this temperature for 72 h at a rate of 3.125 ℃/h.After that, the system was cooled to room temperature.Yellow massive crystals of 1 were obtained and washed with water and dried in air (yield 65% based on Cd).Elemental Anal.Calcd.for 1 C42H28Cd2N4O8(941.48): C, 53.53; H, 2.97; N, 5.95%.Found: C, 53.40; H, 2.85; N, 5.89%.IR (KBr, cm?1): 3385m, 3048s, 2855vw, 1613s, 1595vs,1565s,1430s,1363vs, 1246w, 1102s, 1018w, 894w, 785s, 736s, 595w, 515s.

Cd3(MIP)3(H2MIP)(phen)2(2) A mixture of Cd(NO3)2·4H2O (0.040 g, 0.13 mmol), phen (0.014 g, 0.075 mmol) and H2MIP (0.024 g, 0.13 mmol) in the mixture of water (6.5 mL) and acetonitrle (1.5 mL) was stirred at room temperature for a few minutes.The resulting slurry was transferred into a 20 mL Teflon-lined stainless-steel vessel, which was heated at 150 ℃ and maintained at this temperature for 72 h at a rate of 3.125 ℃/h.The system was cooled to room temperature.Yellow strip crystals of 2 were obtained which were washed with water and dried in air (yield 60% based on Cd).Elemental Anal.Calcd.for 2 C60H40Cd3N4O16(1410.16): C, 51.06; H, 2.84; N, 3.97%.Found: C, 50.96; H, 2.79; N, 3.85%.IR (KBr, cm?1): 3410m, 3048s, 2854vw, 1625 s, 1595 vs,1571s,1431s,1367vs, 1246w, 1108s, 1018w, 894w, 774s, 728s, 598w, 515s.

2.3 Structure determination

Single-crystal X-ray diffraction data were collected on a Rigaku diffractometer equipped with a Mercury CCD area detector (MoKα, λ = 0.71073 ?) at room temperature.Empirical absorption corrections were applied to the data using the Crystal Clear program.The structures were solved by direct methods and refined by full-matrix least-squares on F2using the SHELXTL-97 program[19,20].Metal atoms in each compound were located from the E-maps and other non-hydrogen atoms were located in successive difference Fourier syntheses.All non-hydrogen atoms were refined anisotropically.Selected bond lengths (?) and bond angles (o) are listed in Tables 1 and 2, respectively.

3 RESULTS AND DISCUSSION

3.1 Structural description

Cd2(MIP)2(phen)2(1) Crystal data for 1: (C42H28Cd2N4O8, Mr= 941.48, monoclinic, P2/n, a = 10.186(3), b = 14.296(4), c = 24.778(8) ?, β = 93.425(6)°, V = 3601.5(18) ?3, Z = 4, Ra= 0.0370 and wRb= 0.1296.The asymmetric unit of 1 consists of two Cd(II) ions, two MIP2-ligands and two 1,10-phenanthrolion molecules.As depicted in Fig.1(a),Cd(1) is seven-coordinated by five carboxylate oxygen atoms (O(1a), O (2), O(4), O(7), O(8)) from three MIP2-ligands and two nitrogen atoms (N(3), N(4)) from 1,10-phenanthrolion to show a badly distorted {Cd1O5N2}.Cd(2) is also seven-coordinated by five carboxylate oxygen atoms (O(1a), O(3a), O(5b), O(6b), O(8)) from three MIP2-ligands together with two nitrogen atoms (N(1), N(2)) from 1,10-phenanthrolion to form a seriously distorted {Cd1O5N2}.The Cd–O distances are in the range of 2.222(3)～2.414(3) ? and the Cd–N lengths vary from 2.334(4) to 2.373(4) ?, all within the normal ranges[13].In the bind of MIP2-ligands and Cd2+, 1 shows a 2D plane (Fig.1(b)).

Fig.1.(a) View of the coordination environment of metal ions and the coordination modes of the CH3-m-BDC2－ligands in 1.(b) Polyhedral view of the 2D framework for 1.Symmetry codes: (a) ?x+2, ?y+1, ?z; (b) ?x+5/2, y?1/2, ?z+1/2; (c) ?x+5/2, y+1/2, ?z+1/2

Table 1.Selected Bond Lengths (?) and Bond Angles (°) for 1

Table 2.Selected Bond Lengths (?) and Bond Angles (°) for 2

Cd3(MIP)3(H2MIP)(phen)2(2) Crystal data for 2: C60H40Cd3N4O16, Mr= 1410.16, triclinic, P1, a = 9.979(2), b =11.477(3), c = 13.994(4) ?, α = 96.837(11), β = 110.401(7), g =102.488(8)°, V = 1433.2(6) ?3, Z = 1, R = 0.03700.046 and wR = 0.1464.The asymmetric unit of 2 consists of two Cd(II) ions, two MIP2-ligands and one 1,10-phenanthrolion molecule.As depicted in Fig.2(a), Cd(1) is coordinated by six carboxylate oxygen atoms (O(1), O(1a), O(6), O(6a), O(8b), O(8c)), as can be described as {Cd1O6}.Cd(2) is surrounded by four carboxylate oxygen atoms (O(1), O(2), O(5), O(7c)) from two MIP2-ligands and two nitrogen atoms (N(1), N(2)) from 1,10-phenanthrolion, which can be described as a seriously distorted {Cd1O4N2}.The Cd–O distances are in the range of 2.223(4)～ 2.642(4) ? and the Cd–N distances fall in the 2.3262(4)～2.331(4) ? region, all within the normal ranges[13].In the bind of MIP2-ligands and Cd2+, 2 shows a 1D chain (Fig.2(b)).

It is noteworthy that the coordination modes of MIP2-ligands are different in 1 and 2, as shown in Fig.1(a) and Fig.2(a).When the dimensionality of the frameworks is increased from 1D to 2D, the carboxylate group tends towards an increase both in the coordination number of metal ions and the formation the M-O-M linkage mode[17], which is caused by the deprotonation of H2MIP ligands with increasing the reaction temperature.It shows that the reaction temperature plays a crucial role in the architecture of the final products.

Fig.2.(a) View of the coordination environment of metal ions and the coordination modes of CH3-m-BDC2－ligands in 2.(b) Polyhedral view of the 1D framework for 2.Symmetry codes: (a)–x+1,–y+2,1-z; (b)–x,–y+2, 1-z; (c) x+1, y, z; (d)x–1,y, z

3.2 Spectral and thermal analyses

The powder X-ray diffraction patterns of 1 and 2 are given in Fig.3 with the pattern simulated on the basis of single-crystal structures.The positions of diffraction peaks in both patterns correspond well, which indicates that the synthesized samples 1 and 2 are both pure.In order to examine the stability of the frameworks, thermal gravimetric analyses (TGA) for 1 and 2 were carried out in nitrogen gas from 30 to 1000 ℃ (Fig.4).The TGA curves for 1 and 2 both show almost no weight loss before the decomposition of the framework.The frameworks of 1 and 2 begin to collapse at the temperature of 300 ℃ and 290, respectively.In the IR spectra of 1 and 2, the absence of strong absorption associated with the carboxyl group at around 1701 cm-1indicates complete deprotonation of 5-methylisophthalic acid.The characteristic absorption bands of thecarboxylate groups are shown in the range of 1565～1635 cm-1for the asymmetric stretching vibration nas(COO-) and 1345～1430 cm-1for the symmetric stretching vibration ns(COO-).The above results are all confirmed by single-crystal X-ray diffraction analysis.

Fig.3.Simulated and experimental XRD powder patterns of 1 and 2

Fig.4.View of the TGA curves of 1 and 2

3.3 Luminescent properties

The solid-state luminescent spectra of 1 and 2 in the solid state at room temperature have also been studied.As shown in Fig.5, the free ligands exhibit emissions at 374 nm for H2MIP (λex= 280 nm) and 390 nm for phen (λex= 290 nm).As shown in Fig.6, the emission bands are 510 nm (λex= 390nm) for 1 and 512 nm (λex= 400 nm) for 2, respectively.1 shows one broad emission band with the maximum intensity at 510 nm upon excitation at 390 nm, which is red-shifted by 120 nm relative to the emission wavelength of free ligand phen.2 shows one broad emission band with the maximum intensity at 512 nm upon 340 nm excitation, which is red-shifted by 112 nm relative to the emission wavelength of free ligand phen.The red-shift suggests that the Cd(II) ions coordinate to the ligand phen, which evokes the ligand-to-metal charge transfer (LMCT)[21].

Fig.6.Luminescent spectra of 1 and 2 at room temperature

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1 INTRODUCTION

ion polymers (Cps) have

much attention in the fields of supramolecular chemistry and crystal engineering because of their intriguing variety of topologies and structural diversities[1-4].Various metal centers and multifunctional organic ligands have been used for the design and construction of Cps due to their potential applications as functional materials in the fields of gas absorption and separation, ion-exchange, catalysis, luminescence and magnetism[5-9].

10.14102/j.cnki.0254-5861.2011-0605

Received 15 December 2014; accepted 6 March 2015 (CCDC 1033239 for 1 and 1033240 for 2)

① This work was supported by the National Basic Research Program of China (973 Program, 2012CB821702), the National Natural Science Foundation of China (21233009 and 21173221) and the State Key Laboratory of Structural Chemistry

② Corresponding author.E-mail: pinglin@fjirsm.ac.cn