научная статья по теме A NOVEL PHOTO AND THERMAL STABLE DYSPROSIUM COMPLEX WITH TETRAPHENYLIMIDODIPHOSPHINATE ACID Химия

Текст научной статьи на тему «A NOVEL PHOTO AND THERMAL STABLE DYSPROSIUM COMPLEX WITH TETRAPHENYLIMIDODIPHOSPHINATE ACID»

КООРДИНАЦИОННАЯ ХИМИЯ, 2014, том 40, № 3, с. 188-192

УДК 541.49

A NOVEL PHOTO AND THERMAL STABLE DYSPROSIUM COMPLEX WITH TETRAPHENYLIMIDODIPHOSPHINATE ACID

© 2014 S. J. Li and K. Li*

Department of Chemistry, Zhoukou Normal University, Zhoukou, 466001 P.R. China *E-mail: shujinglike@163.com Received March 29, 2013

The first Dy(III) tetraphenylimidodiphosphinate complex Dy(Tpip)3 was synthesized and characterized by elemental analysis, IR, TG, and X-ray diffraction analysis. The aryl-functionalised imidodiphosphinate lig-and (Tpip) provides a bidentate anionic site that leads to a hexa-coordinate dysprosium complex [Dy(Tpip)3]. The X-ray single-crystal structural analysis indicates that the structure crystallizes to a trigonal system with a space group P 3, a = 23.4638(17) , c = 21.3207(18) A , and Z = 6. It shows excellent thermal stability with no obvious weight loss below 400°C. The luminescence experiment shows that the complex exhibits the typical luminescence of Dy3+ ion in the visible region. The photo stability of Dy(Tpip)3 is very good and the emission intensity remains above 94% as it of before excited upon excitation for 3600 s.

DOI: 10.7868/S0132344X14020066

INTRODUCTION

In recent years, the design and synthesis of lanthanide complexes (RE) are a research focus not only because of the intriguing variety of architectures and topologies in supramolecular chemistry and crystal engineering [1, 2], but also the special photo/electroluminescence [3—6], magnetism [7—9], and photoca-talysis [10, 11]. Particularly, optical properties of lanthanide coordination complexes become a highly active and fast-growing research field owing to the strong fluorescence deriving from f—f transitions, which lead to long fluorescence lifetimes, large Stokes' shift and shark emission peaks. The intra-configuration of 4f— 4f transitions in lanthanide ions are Laporte-forbid-den, but organic ligands called as "antennas" [12] can absorb the excitation light and transfer the energy from their lowest triplet state energy level (T) to the resonance level of RE(III) ions, which makes the luminescence intensity of RE(III) ions stronger. By employing different organic ligands, large amount of rare earth complexes bearing unique luminescent properties have been synthesized, especially Sm(III), Eu(III), Tb(III) and Dy(III) complexes. A series of lanthanide metal-organic frameworks [Ln(L)(Bpdc)0.5(Phen)]OT (Ln = Eu, Gd, Tb, Dy; L = 4,4'-to(2-sulfonatostyr-yl)biphenyl; Bpdc = 4,4'-biphenyldicarboxylate; Phen = 1,10-phenanthroline) were prepared in [13]. These compounds display intriguing fluorescent properties including strong intensity, bathochromic-shift and the variable and versatile emission bands. The Sm, Eu,

Tb, and Dy complexes of the type [Ln(Hfaa)3(Phen)] (Hfaa = hexafluoropentanedione) were successfully synthesized, and the quantum yields (O = 46, 32, 2.7 and 2.1% for Eu, Tb, Sm and Dy, respectively) of the complexes indicate that energy transfer from ligands (Hfaa and Phen) to Ln(III) is efficient [14].

We are interested in the development of neutral lanthanide complexes with ligands that completely encapsulate the ion forming a hydrophobic shell around the metal ion. In order to achieve this, we need strong binding sites that coordinate to the lanthanide and bulky aromatic units that are "independent/remote" from the binding site and which form the hydrophobic shell. We have chosen tetraphenylimidodiphosphinate (Tpip) as an ideal ligand, which can be regarded as the "inorganic analog" of 1,3-diketones providing O=P—N—P=O binding site [15]. We envisage that complexes with Tpip may have higher thermal stability due to its inorganic nature. The structure and luminescence properties of Eu(Tpip)3 • 0.67H2O and Tb(Tpip)3 were reported in [16]. Two interesting ¿¿s-cyclometalated iridium complexes using Tpip as the ancillary ligand were synthesized in [17] and they are good green and blue-green phosphorescent materials having potential applications in OLEDs, particularly at high luminance and high current density. In this work, we used the lig-and tetraphenylimidodiphosphinate acid (HTpip) to construct the compound Dy(Tpip)3 (I). The structure of the Dy(III) complex was characterized by single

A NOVEL PHOTO AND THERMAL STABLE DYSPROSIUM COMPLEX

crystal X-ray diffraction, the themal property and PL spectra of it were investigated too.

EXPERIMENTAL

Materials and methods. All chemicals of analytical grade were purchased from Sigma-Aldrich and used as received. Elemental analyses for C, H, and N were performed on a PerkinElmer 240C analyzer. Solid infrared spectrum was recorded on a \fector22 Bruker Spectrophotometer with KBr pellets in the 400—4000 cm-1 region. TG analyse was collected on a PerkinElmer Pyris 1 TG-DSC STA 499F3 analyzer from room temperature to 800°C with a heating rate of 10°C/min under nitrogen. The powder XRD pattern was recorded on a Shimadzu XD-3A X-ray diffractometer. Solid-state luminescence spectra were recorded on HITACHI F-4600 Fluorescence Spectrophotometer.

Synthesis. The ligand HTpip was synthesized by the reaction of chlorodiphenylphosphine and hexameth-yldisilazane followed by oxidation with H2O2. KTpip was prepared by dissolving HTpip in methanolic KOH

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solution and then adding diethyl ether [15]. One equivalent of DyCl3 • 6H2O was added drop by drop to three equivalents of KTpip to afford complex I. The synthetic route of complex I is shown in Scheme 1. Colorless block crystals suitable for X-ray structure analysis were obtained in 76% yield by evaporation of a concentrated solution of complex I in dichlorometh-ane and ethanol.

For C72H6oN3O6P6Dy

anal. calcd., %: C, 61.26; H, 4.28; N, 2.98. Found, %: C, 61.30; H, 4.33; N, 2.95.

The IR spectrum of Dy(Tpip)3 shows strong absorptions at 1223 and 1127 cm-1, which can be assigned to the stretching of the group P-N-P. And the v(P-O) stretch appears at 1089 and 1064 cm-1. No obvious absorptions in the region between 3100 and 4000 cm-1 indicates there are no water moleculars coordinated to Dy(III).

Scheme 1. The synthetic route of complex I.

X-ray crystallography. The crystal structure of I has been solved by X-ray diffraction analysis. Intensity data were collected on a Bruker SMART CCD diffractometer using monochromated Mo-Ka radiation (X = = 0.71073 A) at room temperature. The collected frames were processed with the software SAINT [18]. The structure was solved by the direct method and refined by full-matrix least-squares on F2 using the program SHELXTL-97 [19]. Non-hydrogen atoms were refined anisotropically. Hydrogen atoms were placed in calculated position or found in the difference Fou-

rier maps. The main crystallographic data are summarised in Table 1. Selected bond lengths and angles are listed in Table 2. Crystallographic data for structure I has been deposited in the Cambridge Crystallographic Data Centre (no. 92707; deposit@ccdc.cam.ac.uk or http://www.ccdc.cam.ac.uk).

RESULTS AND DISCUSSION

The crystal structure of I is shown in Fig. 1. There are three Dy(Tpip)3 molecules in each unit cell. The

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S. J. LI, K. LI

Table 1. Crystallographic data and structure refinement for complex I

Parameter Value

Formula weight 1411.55

Temperature, K 296(2)

Crystal system Trigonal

Space group P 3

a, A 23.4638(17)

b, A 23.4638(17)

c, A 21.3207(18)

a, deg 90

ß, deg 90

Y, deg 120

Volume, A3 10165.5(13)

Z 6

Pcalcd mg m-3 1.383

Absorption coefficient, mm-1 1.297

/(000) 4302

9 Range for data collection, deg 1.00-27.55

Index ranges -30 < h < 29,

-27 < k < 30,

-21 < l < 27

Reflections collected/unique 70183/15657

Rint 0.0339

Absorption correction None

Max and min transmission 0.7814 and 0.7127

Data/restraints/parameters 15 657/0/793

Goodness-of-fit on F2 1.027

Final R indices (I> 2a(I)) Rx = 0.0310, wR2 = 0.0846

R indices (all data) R1 = 0.0463, wR2 = 0.0945

Largest diff. peak and hole, e A-3 2.472 and -0.718

center atom dysprosium coordinates to six oxygen atoms from the three Tpip ligands with mean Dy—O bond length 2.26 A. The geometry around dysprosium is a distorted octahedron with ODyO angles 156.148(69)° and 80.837(69)°—112.424(72)°. The center dysprosium bonds with three sets of skeleton atoms O—P—N—P—O to form three six-numbered rings, and the twelve phe-nyl groups surround them to construct a hydrophobic cage. In the powder XRD patterns for I, the diffraction peaks of simulated and experimental patterns match well at the relevant positions, indicating the phase purity. The difference in reflection intensities between the simulated and experimental patterns is due to the preferred orientation of the crystals in the powder sample.

The thermogram of complex I was recorded under nitrogen atmosphere at a heating rate of 10°C/min (Fig. 2). Before 400°C, the thermogram does not display any inflexion point, which indicates that it does not contain any kind of water (crystalliferous or coordinated). The complex has excellent thermal reliability, probably due to the high binding energy of O=P and N=P bonds. At 400°C, it begins to decompose and loses a fraction of weight corresponding to the decomposition of the ligands. The decomposition takes place in two stages, and the total weight loss for the complex is 72.6%.

Considering the excellent luminescent properties of Dy(III), the solid-state photoluminescent spectra were measured at room temperature. The solid-state excitation and emission spectra of I are shown in Fig. 3. Dy(Tpip)3 exhibits emission bands at 487, 576, and 667 nm (^ex = 274 nm), which correspond to the

F9/2 ^ H15/2, 4F/2^ H13/2, 4F/2 ^ H11/2 transitions, respectively. These are characteristic of Dy(III) and result in the typical yellow luminescence [20].

Table 2. Selected bond lengths (A) and angles(deg) for I*

Bond d, A Bond d, A

Dy(1)-O(1) 2.2593(19) Dy(1)-O(2) 2.2656(18)

O(1)-P(1) 1.518(2) O(2)-P(2) 1.5140(18)

N(1)-P(1) 1.591(3) N(1)-P(2) 1.594(2)

Angle ro, deg Angle ro, deg

O(1)

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