КООРДИНАЦИОННАЯ ХИМИЯ, 2013, том 39, № 5, с. 298-303
УДК 541.49
A YTTERBIUM POLYMER INCORPORATING ETHYL-4,5-IMIDAZOLE-DICARBOXYLATA AND FORMATE COLIGAND: STRUCTURE, LUMINESCENT, AND MAGNETIC PROPERTIES
© 2013 X. Feng1, Y. Zhao3, P. P. Lei1, J. J. Shang1, and L. Y. Wang1, 2, *
1 College of Chemistry and Chemical Engineering, Luoyang Normal University, Luoyang, 471022 P.R. China 2 College of Chemistry and Pharmacy Engineering, Nanyang Normal University, Nanyang, 473601 P.R. China 3 College of Physics and Electronic Information, Luoyang Normal University, Luoyang, 471022 P.R. China
*E-mail: wlya@lynu.edu.cn Received September 24, 2011
A new lanthanide-organic coordination polymer incorporating both substituted imdazole dicarboxylate and formate auxiliary ligand, namely {[Yb3(HEimda)4(^2-HCOO) ■ 4H2O] ■ 2H2O}n (I) (H3Eimda = Ш-2-ethyl-4,5-imidazole-dicarboxylic acid), has been prepared and was structurally characterized by elemental analysis, IR and X-ray diffraction. It crystallizes in the monoclinic system, space group of C2/c. The polymer I is built from two dimensional (2D) double decker networks based on the Ln4HEimda4 tetranuclear basic car-boxylate as secondary building unit. The extensive hydrogen bonds extend the 2D lamellar network into a 3D supramolecular aggregate. The emission spectrum of polymer I exhibits ligand-to-metal charge-transfer transition luminescence. Variable-temperature magnetic susceptibility measurement reveals that the end to end bridging fashion of formate group results in the depopulation of the stark levels for a single Yb3+ ion and/or possible antiferromagntic interactions between Yb3+ ions within the carboxylato bridged dinuclear unit.
DOI: 10.7868/S0132344X13050022
INTRODUCTION
In recent years, the design and construction of extended frameworks containing rare-earth metals bridged by carboxylic groups have attracted a great deal of interest in chemistry and materials science fields, owing to their extraordinary molecular architectures and fascinating chemical/physical properties [1—4]. Over the last decades, a variety of multicarbox-ylate triazine/imidazoline/pyridine-based ligands have been extensively employed for exhibiting various coordination fashions to accompany diversity of interesting structures with honeycomb, rectangular grid, bilayer lattice, 1D ladder and diamonds frameworks, with gas adsorptions, magnetic and luminescent properties, and so on [5]. However, among various strategies, most of the work has focused on the assembly of the af-block metal-organic frameworks, and the analogous chemistry of the lanthanide ions still remains less developed [6]. It has also been demonstrated that formate, being the smallest carboxylate, is cheap and with low toxicity, and it has a small stereo effect which is beneficial for constructing of metal-organic frameworks (MOFs) [7]. Meanwhile, formate ligand plays an important role in coordination chemistry, which may adopt a remarkable versatile three-atom binding modes such as monodentate, chelating, and bridging in the syn—syn, syn—anti, and anti—anti configurations [8, 9]. As a continuation of our previous investigation
and better understand the influence exerted by the formate auxiliary ligand on the structures and properties in these systems, we describe here the synthesis, structure, photoluminescence, and magnetic properties of a ytterbium-organic polymer {[Yb3(HEimda)4(^2-HCOO) • • 4H2O] • 2H2O}„ (I) based on the 1#-2-ethyl-4,5-im-idazole-dicarboxylate (HEimda) and formate ligand. It is also hoped that the combination of two types of ligands will enhance the energy-transfer efficiency from ligand to lanthanide ions [10].
EXPERIMENTAL
Materials and physical measurements. All reagents used in the syntheses were of analytical grade and used as received. Elemental analyses for C, H, and N were performed on a Vario EL III elemental analyzer. The infrared spectra (4000—400 cm-1) were recorded by using KBr pellet on an AvatarTM 360 E.S.P. IR spectrometer. Thermogravimetry-differential thermal analysis was 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 from 20 to 900°C. Luminescence spectra ofpolymer I in a 1 cm quartz spectrophotometer fluorescence cell (Starna) in methanol were run on a Cary Eclipse fluorescence spectrophotometer. Vriable-temperature magnetic susceptibilities were measured using a MPMS-7
SQUID magnetometer under a 0.2 T applied magnetic field and over the range of 2 to 300 K. Diamagnetic corrections were made with Pascal's constants for all constituent atoms.
Synthesis of the polymer I. H3Eimda acid (0.039 g, 0.2 mmol) and sodium formate dihydrate (0.021 g, 0.2 mmol) in a solution of water—alcohol (v/v = 1.2, 10 mL) were mixed with an aqueous solution (10 mL) ofYb(NO3)3 • 6H2O (0.089 g, 0.2 mmol). After stirring for 20 min in air, the pH value was adjusted to 3.5 with nitric acid, and the mixture was placed into 25 mL Teflon-lined autoclave under autogenous pressure being heated at 155°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. The yield was 0.0362 g (39%) based on lanthanide element.
For C29H37N8O24Yb3
anal. calcd., %: C, 26.14; H, 2.79; N, 8.41. Found, %: C, 26.25; H, 2.76; N, 8.28.
IR (KBr; v, cm-1): 3384 s, 3186 br, 2978 m, 1590 s, 1529 s, 1462 s, 1410 m, 1338 s, 1279 m, 1212 s, 867 m, 810 v.s, 793 s, 660 s, 569 m.
Crystallographic data collection and refinement.
Single-crystal diffraction data of complex I were collected on a Bruker SMART APEX CCD diffractome-ter with graphite-monochromated Mo^a radiation (k = 0.71073 A) at room temperature. The structure was solved using direct methods and successive Fourier difference synthesis (SHELXS-97) [11] and refined using the full-matrix least-squares method on F2 with anisotropic thermal parameters for all nonhydrogen atoms (SHELXL-97) [12]. The disordered ethyl carbon atoms of HEimda ligand and formate oxygen atoms were restrained in order to obtain reasonable thermal parameters. The hydrogen atoms of organic ligands were placed in calculated positions and refined using a riding on attached atoms with isotropic thermal parameters 1.2 times those of their carrier atoms. The summary crystallographic data and selected bond lengths and angles for polymer I are listed in Tables 1 and 2, respectively.
Supplementary material for structure I has been deposited with the Cambridge Crystallographic Data Centre (no. 845838; deposit@ccdc.cam.ac.uk or http:// www.ccdc.cam.ac.uk).
RESULTS AND DISCUSSION
Polymer I is a lanthanide-organic 3D framework based on lanthanide-organic square motifs. As illustrated in Fig. 1a, the asymmetric unit of I contains three crystallographically independent Yb3+ cations, three HEimda ligands, one formate group, and four
Table 1. Crystal data and structure refinement details for the polymer I
Parameter Value
Formula weight 1400.79
Temperature 296(2)
Crystal system Monoclinic
Space group C2/c
a, A 33.620(3)
b, A 9.1156(9)
c, A 12.9595(13)
P, deg 92.0560(10)
V, A3 3969.1(7)
Z 4
p, g cm-3 2.344
Crystal size, mm 0.23 x 0.18 x 0.15
F(000) 2676
p., mm-1 7.114
9 Range for data collection, 2.32-25.50
deg
Limiting indices range -40 < h < 40,
-11 < k < 11,
-15 < l < 15
Type of scan 9/ro
Reflections collected 14234
Independent reflections (Rint) 3684
Reflections with I > 2o(I) 3627
Max and min transmissions 0.4150 and 0.2915
Name of parameters 297
GOOF 1.041
R1, wR2 (I > 2ct(I)) 0.0359, 0.1224
R1, wR2 (all data) 0.0363, 0.1229
APmax and Apmjn e AT3 1.734 and -2.701
R = - j^WoiL Rw = ^iF2 - Fc2|2/Sw (i^i2) 2]1/2.
coordinated waters, as well as two lattice water molecules. All of three HEimda anion ligands have the same coordination mode with dangling lateral ethyl arms, chelating three Yb3+ ions. Interestingly, the asymmetric coordination pattern of the ligand led to a crystal structure belonging to a centric space group. There are two categories of Yb3+ ions in the unit and both categories of the Yb3+ ions are in an octacoordi-nate manner, exhibiting a slightly distorted square an-tiprism geometry, but with different coordination environments. The Yb(1) ion is coordinated with two imidazolyl nitrogen atoms from the HEimda ligands, five carboxylate oxygen atoms from the HEimda ligands, and the coordination sphere of the Yb(1) cation is completed by one oxygen atom from terminal
Table 2. Selected bond lengths (A) and bond angles (deg) for polymer I*
Bond d, A Bond d, A Bond d, A
Yb(1)-O(6)#2 2.232(6) Yb(1)-O(1) 2.344(5) Yb(2)-O(2)#4 2.243(6)
Yb(1)-O(7))#2 2.280(6) Yb(1)-O(9) 2.354(7) Yb(2)-O(12)#4 2.332(16)
Yb(1)-O(8) 2.304(5) Yb(1)-N(1) 2.506(6) Yb(2)-O(10)#4 2.336(7)
Yb(1)-O(4)#3 2.310(6) Yb(2)-O(10) 2.336(7) Yb(2)- O(3) 2.363(6)
Angle ro, deg Angle ro, deg Angle ro, deg
O(6))#2Yb(1)O(7))#2 77.2(2) O(7)#2Yb(1)O(9) 73.6(3) O(4)#3Yb(1)N(3) 121.8(2)
O(6))#2Yb(1)O(8) 106.4(2) O(8)Yb(1)O(9) 89.5(3) O(1)Yb(1)N(3) 75.8(2)
O(6))#2Yb(1)O(4)#3 79.1(3) O(4)#3Yb(1)O(9) 74.0(2) O(9)Yb(1)N(3) 143.4(2)
O(7))#2Yb(1)O(4)#3 76.8(2) O(1)Yb(1)O(9) 70.6(2) N(1)Yb(1)N(3) 81.5(2)
O(8)Yb(1)O(4)#3 75.0(2) O(6)#2Yb(1)N(1) 94.0(3) O(2)#4Yb(2)O(2) 89.8(4)
O(6))#2Yb(1)O(1) 144.6(2) O(7)#2Yb(1)N(1) 74.1(2) O(2)Yb(2)O(3)#4 144.9(2)
O(7))#2Yb(1)O(1) 121.4(2) O(8)Yb(1)N(1) 133.6(2) O(2)Yb(2)O(12')#5 84.1(5)
O(8)Yb(1)O(1) 72.9(2) O(1)Yb(1)N(1) 66.8(2) O(12)Yb(2)O(3) 128.9(4)
O(7))#2Yb(1)N(3) 138.9(2) O(6)#2Yb(1)N(3) 72.0(2) O(2)Yb(2)O(12')#1 76.6(5)
O(2)#4Yb(2)O(12) 72.8(6) O(8)Yb(1)N(3) 66.8(2) O(2)Yb(2)O(12)#4 72.8(6)
O(2)Yb(2)O(12) 67.6(5) O(7)#2Yb(1)O(8) 150.2(2) O(12)#4Yb(2)O(3) 77.4(5)
* Symmetry codes: #1 -x -z; #7 x, -y, z + 1/2.
+ 1, -y + 1, -z + 1; #2 x, -y, z - 1/2; #3 x, y
. #3 .
1, z; #4 -x + 1,
y, -z - 1/2
• #5 ,
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