научная статья по теме SYNTHESES, CRYSTAL STRUCTURES, AND THERMAL PROPERTIES OF TWO COMPLEXES BUILT BY IMIDAZOLE-BASED MULTI-CARBOXYLATE LIGANDS Химия

Текст научной статьи на тему «SYNTHESES, CRYSTAL STRUCTURES, AND THERMAL PROPERTIES OF TWO COMPLEXES BUILT BY IMIDAZOLE-BASED MULTI-CARBOXYLATE LIGANDS»

КООРДИНАЦИОННАЯ ХИМИЯ, 2015, том 41, № 8, с. 474-481

УДК 541.49

SYNTHESES, CRYSTAL STRUCTURES, AND THERMAL PROPERTIES OF TWO COMPLEXES BUILT BY IMIDAZOLE-BASED MULTI-CARBOXYLATE LIGANDS

© 2015 F. Wang1, 2, Z. N. Chen1, Z. F. Li1, and G. Li1, *

1College of Chemistry and Molecular Engineering, Zhengzhou University, Zhengzhou, Henan, 450001 P.R. China 2Department of Chemistry, Henan Institute of Education, Zhengzhou, Henan, 450014 P.R. China

*E-mail: gangli@zzu.edu.cn Received December 24, 2014

Based on two promising p-CPhH4IDC and o-CPhH4IDC ligands, one 2D coordination polymer, [Ca(p-CPhH2IDC)(H2O)]n (p-CPhH4IDC = 2-(4-carboxylphenyl)-1H-imidazole-4,5-dicarboxylic acid) (I) and one novel dimeric complex, [Cd2(o-CPhH2IDC)2(H2O)6] • 4H2O (o-CPhH4IDC = 2-(2-carboxylphenyl)-1H-imidazole-4,5-dicarboxylic acid) (II) have been hydrothermally synthesized and structurally characterized by elemental analyses, IR spectroscopy, and single crystal X-ray diffraction (CIF files CCDC nos. 929826 (I), 959841 (II)). Polymer I exhibits a graceful 2D grid sheet structure. Polymer II is a binuclear complex in which two Cd2+ ions are bridged by two carboxyates from two o-CPhH2IDC2- ligands. Four and two types of coordination environments around the Ca and Cd atoms, respectively can be observed. Furthermore, the solid-state photoluminescence and thermal properties of the two complexes have been investigated.

DOI: 10.7868/S0132344X15080071

INTRODUCTION

In recent years, the design of functional complexes via metal ions and various organic ligands has become a hot research field. However, it is still a far-reaching challenge to predict the assembly of complexes owing to various influence factors such as pH values, molar ratios of raw materials, reaction solvents and temperatures [1—3]. As one might expect, the key is to select a powerful multifunctional organic ligand to build up useful complexes. For example, the types of organic linkers with N- or O-donors have led to a wide range of complexes with numerous interesting bridging modes [4—6]. That is to say, one of the best building bricks that can be used to attain such complexes is the imidazole-based dicarboxylate ligand, which can adopt different bonding modes to metals. Our laboratory has introduced 2-carboxyphenyl and 4-carbox-yphenyl groups into the 2-position of the imida-zole-4,5-dicarboxylic acid (H3IDC) system respectively so as to synthesize two promising ligands,

2-(2-carboxylphenyl)-1#-imidazole-4,5-dicarboxy-lic acid (o-CPhH4IDC), and 2-(4-carboxylphenyl)-1#-imidazole-4,5-dicarboxylic acid (p-CPhH4IDC). More importantly, a series of fascinating structures bearing o-CPhH4IDC or ^-CPhH4IDC have been obtained [7, 8].

This prompted us to prepare more similar complexes to explore their properties. To us excitement, two complexes: polymer [Ca(p-CPhH2IDC)(H2O)]„ (I) and dimer [Cd2(o-CPhH2IDC)2(H2O)6] • 4H2O (II) have been synthesized successfully (Scheme 1). In this paper, single-crystal X-ray diffractions reveal that the ^-CPhH4IDC and o-CPhH4IDC ligands show a variety of coordination modes severally (Fig. 1). The structural analyses of the complexes have been discussed in detail. Moreover, the thermal and solid-state photoluminescence properties of the complexes have also been investigated. The syntheses of complexes I and II are given below:

HOOC COOH

NH4^N

CaCl2

H2O Et3N l6o°C72 h [Ca^CPhH2IDC)(H2O)]„

(I)

COOH ^-CPhH4IDC

HOOC^_^COOH

NH ..J. N CdCi2 ■ 6h2o

[Cd2(0-CPhH2lDC)2(H2O)6] • 4H2O

H2O Et3N 160°C 96 h

COOH (II)

o-CPhH4IDC

Scheme.

EXPERIMENTAL

Materials and methods. All chemicals were of reagent grade quality obtained from commercial sources and used without further purification. The organic ligands o-CPhH4IDC and ^-CPhH4IDC were prepared according to the literature procedure [9]. Elemental analyses (C, H, and N) were performed on a FLASH EA 1112 analyzer. IR Spectra were recorded on a BRUKER TENSOR 27 spectrophotometer as KBr pellets in the 400-4000 cm-1 region. TG measurements were performed by heating the crystalline sample from 20 to 1100°C at a rate of 10°C min-1 in the air on a Netzsch STA 409PC differential thermal

analyzer. Fluorescence spectra were characterized at room temperature by a F-7000 fluorescence spectrophotometer (240 nm/min).

Synthesis of I. A mixture of ^-CPhH4IDC (27.4 mg, 0.1 mmol), CaCl2 (11.1 mg, 0.1 mmol), H2O (7 mL), triethylamine (Et3N) (0.028 mL, 0.2 mmol) was sealed in a 25 mL Teflon-lined stainless steel autoclave, heated at 160°C for 72 h, and then cooled to room temperature at a rate of 10°C/h. The colorless long-strip crystals of I were isolated, washed with distilled water, and dried in air (51% yield based on Ca).

(a)

(b)

^4-p-CPhH2IDC2- p.2-o-CPhH2IDC2-

Fig. 1. Coordination modes of p-CPh^IDC2- and o-CPh^IDC2- anions in polymers I (a) and II (b). КООРДИНАЦИОННАЯ ХИМИЯ том 41 № 8 2015

Table 1. Crystallographic data and structure refinement information for compounds I and II

Parameter Value

I II

Temperature, K 296(2) 296(2)

Fw 332.28 953.34

Crystal system Monoclinic Monoclinic

Crystal size, mm 0.21 x 0.20 x 0.19 0.21 x 0.19 x 0.18

Space group P2(1)/c C2/c

a, A 8.801(5) 23.29(3)

b, A 16.932(10) 11.190(13)

c, A 9.013(5) 17.10(4)

P 100.480(7) 128.951(10)

V, A3 1320.8(13) 3466(10)

Pcalcd mg m-3 1.671 1.321

Z 4 4

p., mm-1 0.515 1.321

9 Range, deg 2.35-28.48 2.14-27.10

Reflections mesured/unique (Rjnt) 7274/2318 (0.0285) 11056/3810 (0.0293)

Reflections with I > 2a(I) 8828 11056

Data/restraints/parameters 2318/0/212 3810/12/271

GOOF on F2 1.037 1.086

R, wR (I> 2ct(I)) 0.0373, 0.0936 0.0269, 0.0620

R, wR (all data) 0.0512, 0.1030 0.0367, 0.0663

Apmax and Apmjn e AT3 0.262 and -0.257 0.636 and -0.480

IR (KBr; v, cm-1): 3438 s, 3106 m, 2944 w, 1589 s, 1568 s, 1525 s, 1402 s, 1269 m, 1116 w, 1017 w, 973 m, 856 m, 796 m, 733 m, 663 w, 568 w, 453 w.

IR (KBr; v, cm-1): 3357 m, 1715 m, 1551 s, 1450 m, 1401 s, 1292 m, 1228 w, 1146 m, 979 m, 849 s, 801 m, 765 m, 729 w, 677 w, 544 m, 424 w.

For C12H8N2O7Ca

anal. calcd., %: C, 43.34; H, 2.41; N, 8.43. Found, %: C, 43.62; H, 2.75; N, 8.72.

For C^^O^Cd,

anal. calcd., %: C, 30.21; H, 3.36; N, 5.87. Found, %: C, 30.57; H, 3.64; N, 6.15.

Synthesis of II. A mixture of o-CPhH4IDC (27.6 mg, 0.1 mmol), CdCl2 • 6H2O (10.9 mg, 0.1 mmol), Et3N (0.028 mL, 0.2 mmol) and H2O (7 mL), was sealed in a 25 mL Teflon-lined autoclave and heated at 160°C for 96 h. Then the reaction mixture was allowed to cool to room temperature at a rate of 10°C/h. The colorless crystals of II were collected in 43% yield (based on Cd), washed with distilled water and dried in air.

X-ray crystallography. Measurements of compounds I and II were made on a Bruker smart APEXII CCD diffractometer with a graphite-monochromated MoZa radiation (X = 0.71073 A). Single crystals of I and II were selected and mounted on a glass fiber. All data were collected at room temperature 296(2) K using the ®—29 scan technique and corrected for Lorenz-polarization effects. A correction for secondary extinction was applied. The two structures were

Table 2. Selected bond distances (A) and angles (deg) for the complexes I and II*

Bond d, A Bond d, A Bond d, A

Ca(1)—O(6)#1 Ca(1)-O(1) Ca(1)-N(1) 2.2845(17) 2.4237(16) 2.546(2) I Ca(1)-O(2) Ca(1)-O(12)#2 II Cd(1)-O(5)#1 Cd(1)-O(7) 2.332(2) 2.4802(18) Ca(1)-O(7) Ca(1)-O(7)#3 2.3647(16) 2.5173(17)

Cd(1)—O(8) Cd(1)—O(9) 2.275(3) 2.334(3) 2.275(3) 2.339(5) Cd(1)-N(2) Cd(1)-O(1) 2.289(4) 2.422(3)

Angle ro, deg Angle ro, deg Angle ro, deg

O(6)#1Ca(1)O(2) O(6)#1Ca(1)O(1) O(6)#1Ca(1)O(12)#2 O(1)Ca(1)O(12)#2 O(7)Ca(1)O(7)#3 O(6)#1Ca(1)N(1) O(1)Ca(1)N(1) 88.41(7) 87.41(6) 82.02(7) 162.64(5) 75.49(7) 153.97(6) 67.45(6) I O(6)#1Ca(1)O(7) O(2)Ca(1)O(1) O(2)Ca(1)O(12)#2 O(6)#xCa(1)O(7)#3 O(1)Ca(1)O(7)#3 O(2)Ca(1)N(1) O(12)#2Ca(1)N(1) II O(8)Cd(1)N(2) O(5)#1Cd(1)O(9) O(8)Cd(1)O(1) O(9)Cd(1)O(1) 93.09(6) 84.04(7) 81.93(7) 121.65(6) 144.24(5) 82.59(6) 120.44(6) O(2)Ca(1)O(7) O(7)Ca(1)O(1) O(7)Ca(1)O(12)#2 O(2)Ca(1)O(7)#3 O(12)#2Ca(1)O(7)#3 O(7)Ca(1)N(1) O(7)#3Ca(1)N(1) 167.06(6) 83.18(6) 111.00(6) 114.49(8) 52.43(5) 90.58(5) 84.20(5)

O(8)Cd(1)O(5)#1 O(8)Cd(1)O(9) O(9)Cd(1)O(7) N(2)Cd(1)O(1) 93.99(10) 84.41(10) 87.9(2) 71.99(9) 111.96(10) 177.79(8) 174.58(7) 92.06(10) O(5)#1Cd(1)N(2) N(2)Cd(1)O(9) O(5)#xCd(1)O(1) O(7)Cd(1)O(1) 93.05(19) 88.97(19) 89.42(9) 84.03(11)

* Symmetry transformations used to generate equivalent atoms: #1 x + 1, y, z; #2 —x + 2, —y + 2, — z + 1; #3 — x + 2, —y + 2, — z (I). #1 -x + 1/2, -y + 1/2, -z + 1 (II).

solved by direct methods and expanded using the Fourier technique. The non-hydrogen atoms were refined with anisotropic thermal parameters. Hydrogen atoms were included but not refined. All calculations were performed using the SHELX-97 crystallographic software package [10]. Crystal data and experimental details for compounds I and II are contained in Table 1. Selected bond lengths and angles are listed in Table 2.

Supplementary material for structures I and II has been deposited with the Cambridge Crystallographic Data Centre (nos. 929826 (I), 959841 (II); depos-it@ccdc.cam.ac.uk or http://www.ccdc.cam.ac.uk).

RESULTS AND DISCUSSION

X-ray single crystal diffraction analyses reveal that compound I is a 2D network. The asymmetrical unit of I consists of a crystallographic independent Ca2+ cation which surrounded by four ^-CPhH2IDC2-ligands and one coordinated H2O molecules. As shown in Fig. 2a, the central Ca2+ ion has a seven-coordinate environment occupied by five O atoms and one N atom of carboxy groups from four individual ^-CPhH2IDC2- ligands and the remaining one site

occupied by one O atoms from one coordinated water molecule. The Ca—O bond lengths are in the range of 2.2845(17)-2.5173(17) A, while the Ca-N bond lengths are 2.546(2) A are in good with the bond lengths observed in other Ca(II) compounds [11-14].

The ligand ^-CPhH2IDC2- in I adopts the coordination mode linking f

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