научная статья по теме AN ERBIUM-ORGANIC POLYMER INCORPORATING 2-(HYDROXYL)-6-METHYLISONICOTINIC AND OXALATE COLIGAND WITH 63 TOPOLOGY Химия

Текст научной статьи на тему «AN ERBIUM-ORGANIC POLYMER INCORPORATING 2-(HYDROXYL)-6-METHYLISONICOTINIC AND OXALATE COLIGAND WITH 63 TOPOLOGY»

КООРДИНАЦИОННАЯ ХИМИЯ, 2014, том 40, № 12, с. 755-761

УДК 541.49

AN ERBIUM-ORGANIC POLYMER INCORPORATING 2-(HYDROXYL)-6-METHYLISONICOTINIC AND OXALATE COLIGAND WITH 63 TOPOLOGY

© 2014 A. Q. Tian1, 2, J. L. Chen3, X. Feng2, *, X. M. Lang2, and L. Y. Wang2, 3

1Basic Courses Education Department, Henan Forestry Vocational College, Luoyang, 471002 P.R. China 2College of Chemistry and Chemical Engineering, Luoyang Normal University, Luoyang, 471022 P.R. China 3College of Chemistry and Pharmacy Engineering, Nanyang Normal University, Nanyang, 473601 P.R. China

*E-mail: fengx@lynu.edu.cn Received June 2, 2014

A new lanthanide—organic framework incorporating both substituted isonicotinic acid and oxalate coligand has been fabricated successfully through solvo-thermal reaction, namely, {[Er(p.2-H2Minca)](p.2-C2O4 ■ ■ 2H2O] ■ 2H2O}n (I) (H3Minca = 2-(hydroxyl)-6-methyl-isonicotinic acid, H2C2O4 = oxalate acid). Complex I exhibits two dimensional (2D) corrugated networks with a 63 topology, in which {LnO8} polyhedron units are alternately linked through carboxylate and oxalate oxygen atoms into the 2D sheet layer (CIF file CCDC no. 948026). Thermogravimetric and different thermal analysis measurements indicate that I displays high thermal stability. Complex I also shows characteristic f-f transition luminescence emission in NIR region.

DOI: 10.7868/S0132344X14120135

INTRODUCTION

Over the last decades, the construction of lanthanide carboxylate based metal-organic frameworks (Ln-MOFs) has been a field of rapid growth not only for their intriguing architectures and topologies but also for their applications in areas of catalysis, sorption, separation, luminescence, magnetism, non-linear optical property, etc. [1, 2], because of their special chemical and physical properties arising from the unique spectroscopic and 4f electronic. A large part of these studies is concerned with homo- and het-eropolymetallic compounds obtained using compart-mental polydentate ligands and is motivated by optical or magnetic properties or biological interest, and a variety of multicarboxylate pyridimine /imidazoline/py-ridine-based ligands have been extensively employed for exhibiting various coordination fashions with magnetic and luminescent properties, and so on [3, 4]. At the same time, oxalate, as the smallest dicarboxylate, is rigid and coplanar, has a small stereo effect which is beneficial for constructing MOFs [5]. Meanwhile, ox-alate has been proved to be a good candidate for pillar ligand due to its various bridging abilities and strong coordination tendency to generate 1D to 3D moderately robust networks, exhibiting tunable ferro or anti-ferro-magnetic exchanges [6]. The oxalate within lanthanide carboxylate system can reduce or eliminate water molecules from the coordination sphere of the central ions, hence increasing the luminescent intensity and lifetime of the materials [7]. The introduction the electron donating species (e.g., methyl group) to

isonicotinic acid is expected to enhance the coordination ability of ligand and facilitate the electron transfer within the compounds [6]. As a continuation of our previous investigation [8], and in order to better understand the coordinating behavior and role of the ox-alate in the self—assembly processes and the properties in these systems, a new erbium-organic framework has been isolated through the lanthanide salts reaction with isonicotinic acid derivative under hydrothermal synthesis condition.

EXPERIMENTAL

Materials and physical measurements. 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. Thermogravimetric analyses (TGA) were performed under atmosphere with a heating rate of 10°C/min-1 using TGa/s DTA8 51 e. The powder X-ray diffraction (PXRD) patterns were measured using a Bruker D8 Advance powder diffrac-tometer at 40 kV, 40 mA for CuZ"a radiation (X = = 1.5418 A) with a scan speed of 0.2 s/step and a step size of 0.02 (29). Luminescence spectra of the complexes in solid state were carried out on a Cary Eclipse fluorescence spectrophotometer.

Synthesis of {[Er(^2-H2Minca)](^2-C2O4) • 2H2O] • • 2H2O}„ (I). Organic ligand H3Minca (0.039 g,

0.2 mmol) and sodium oxalate dihydrate (0.029 g, 0.2 mmol) in a solution of water—DMF (V/V = 2.0, 10 mL) were mixed with an aqueous solution (10 mL) of 0.1 mmol, (0.0439 g) Er(NO3)3 ■ 6H2O. After stirring for 20 min in air, the pH value was adjusted to 5.5 with nitric acid, and the mixture was placed into 25 mL Teflon-lined autoclave under autogenous pressure being heated at 150°C for 72 h, then the autoclave was cooled over a period of 24 h at a rate 5°C/h. After filtration, the product was washed with distilled water and then dried, colorless crystals of I were obtained suitable for X-ray diffraction analysis. For I, the yield was 0.0144 g (34%) based on Er.

For C9H10NO9Er

anal. calcd., %: C, 25.34; H, 2.36; N, 3.28. Found, %: C, 25.26; H, 2.49; N, 3.21.

IR (KBr; v, cm-1): 3402 br, 3342 s, 2946 s, 1621 s, 1532 s, 1413 m, 1374 s, 1087 s, 929 v.s, 747 m, 668 s, 457 m.

X-ray structure determination. A single crystal of the title complex (0.25 x 0.21 x 0.17 mm) was mounted on a Bruker SMART APEX II CCD diffractometer equipped with a graphite-monochromatized MoZ„ radiation (A = 0.71073 A) by using a 9/® scan mode at room temperature in the range of 2.35o < 9 < 25.49°. Corrections for Lp factors were applied and all non-hydrogen atoms were refined with anisotropic thermal parameters. The structure was solved by direct methods with SHELXS-97 [9]. The hydrogen atoms were assigned with common isotropic displacement factors and included in the final refinement by use of geomet-

rical restrains. A full-matrix least-squares refinement on F2 was carried out using SHELXL-97 [10]. The final R1 = 0.0211, wR2 = 0.0520, (w = 1/[a2(Fo2) +

+ (0.0296P2) + 1.5268P], where P = (Fo2 + 2Fc2/3), S= = 0.998, (Ap)max = 0.876 and (Ap)min = -1.594 e/A3. Crystallographic and experimental details are summarized in Table 1. The selected bond lengths and bond angles are listed in Table 2.

Supplementary material for structure I has been deposited with the Cambridge Crystallographic Data Centre (no. 948026; deposit@ccdc.cam.ac.uk or http:// www.ccdc.cam.ac.uk).

RESULTS AND DISCUSSION

In the IR spectra of compound I, the presence of the broad and strong characteristic stretches in frequency region of 3200—3450 cm-1 are assigned to the characteristic peaks of OH vibration of free water molecules. The strong vibrations appeared around 1640 and 1390 cm-1 correspond to the asymmetric and symmetric stretching vibrations of the carboxylic group [11]. The strong absorption at ~2950 cm-1 indicates the existence of methyl group. In IR spectra, the peaks at ~1590 cm-1 are assigned to the coordinated

C2o4- anions [12]. The absence of strong bands ranging from 1690 to 1710 cm-1 indicates that the completely deprotonation of carboxylic groups of pyridine carboxylic tectonic. The binuclear units linked by H3Minca and oxalate ligands in compound I are illustrated in Scheme:

(a)

Er'

V

'O,

O--O

(b)

\

Er

Single X-ray diffraction analysis reveals that complex I is crystallizing in triclinic system with space

group of P1. They are all found to be lanthanide-or-ganic polymers based on discrete binuclear lanthanide carboxylate aggregates and one free water molecule. As illustrated in Fig. 1, the asymmetric unit of I is composed of an eight-coordinated Er3+ cation, two H3Minca ligands, two oxalate and one coordinated waters, as well as one uncoordination water molecule. In this unit, each H3Minca ligand provides two O atoms from the one carboxylic group to connect two adjacent Er3+ ions (see Scheme). The oxalate ligand acts as bidentate and chelating ligand linking to two metal

nodes. The dihedral angle between the neighboring oxalate ligands sharing the common erbium(III) ion is 73.02°. Interestingly, the pyridine-N and hydroxyl-O do not coordinate to central ion. The remaining two sites were occupied by oxygen atom of water molecules, completing the distorted dodecahedral coordination. Bond Er-O distances involving the central ion (2.250(3) and 2.440(3) A) are closely similar to those observed in several related lanthanide species [13].

The H3Minca has been deprotonated for carboxyl groups, but an H atom was added to pyridine N bearing one positive charge, and the hydroxyl group has been deprotonated, so it is denoted as H2Minca-, cor-

KOOP^HH^HOHHAtf XHMHfl TOM 40 № 12 2014

respondingly. All H2Minca-anion ligands have the same coordination mode with dangling lateral methyl arms, employing carboxylic group doubly connecting two Er3+ ions to form a binuclear unit with the shortest distance Er(III)-Er (III) of 5.109 A. The two carbox-lylate connected two Er3+ions, resulting in an eight remembered chair-like ring. There is a unique bridging oxalate ligand chelating the two adjacent Er3+ ions in binuclear unit via its oxygen atoms, connecting these eight remembered rings, giving rise to a 1D ribbon infinite chain along the xz plane, as displayed in Fig 2a. At the same time, the two neighboring Er3+ ions are also connected via oxalate oxygen to form a Er2 diun-clear unit with the Er—Er separation of 6.245 A. These binuclear segments are further grafted on to the 1D infinite ribbon zigzag chain array along the crystallo-graphic z axis (Fig. 2b). Moreover, the carboxlylate from next H3Minca ligand acts as a linker, alternately connecting these 1D chains into an interesting corrugated 2D lamellar sheet along xy plane, as displayed in Fig. 3. The individual nets are undulated and sinusoidal in nature [14].

In this sheet, six Er3+ ions were alternately connected by four oxalate and two carboxylates from H3Minc

Для дальнейшего прочтения статьи необходимо приобрести полный текст. Статьи высылаются в формате PDF на указанную при оплате почту. Время доставки составляет менее 10 минут. Стоимость одной статьи — 150 рублей.

Показать целиком