научная статья по теме SYNTHESES AND STRUCTURAL DETERMINATION OF MONONUCLEAR NINE-COORDINATE (MNH)[GDIII(EDTA)(H2O)3] · 4H2O AND 2D LADDER-LIKE BINUCLEAR NINE-COORDINATE (MNH)2[GD (H2TTHA)2] · 4H2O Химия

КООРДИНАЦИОННАЯ ХИМИЯ, 2014, том 40, № 9, с. 533-542

УДК 541.49

SYNTHESES AND STRUCTURAL DETERMINATION OF MONONUCLEAR NINE-COORDINATE (MnH)[GdIn(Edta)(H2O)3] • 4H2O AND 2D LADDER-LIKE BINUCLEAR NINE-COORDINATE

(MnH)2[ GdI2II(H2TTHA)2] • 4H2O

© 2014 C. C. Ma, Y. Li, J. Wang*, D. Y. Kong, C. Qin, and Q. Wu

Department of Chemistry, Liaoning University, Shenyang, 110036 P.R. China *E-mail: wangjuncomplex890@126.com Received January 20, 2014

Two title rare earth metal coordination compounds, (MnH)[GdIII(Edta)(H2O)3] ■ 4H2O (I) and

(MnH)2[Gd2II(H2Ttha)2] ■ 4H2O (II), where Mn = methylamine, H4Edta = ethylenediamine-N,N,N',N'-tet-raacetic acid, H6Ttha = triethylenetetramine-N,N,N',N",N"',N"'-hexaacetic acid), have been successfully synthesized through direct heating reflux and characterized by FT-IR spectroscopy, thermal analysis and single-crystal X-ray diffraction techniques. In complex I, the Gd3+ ion is nine-coordinated by an Edta ligand and three water molecules, yielding a pseudo-monocapped square antiprismatic (MC-SAP) conformation. Complex I crystallizes in the orthorhombic crystal system with space group Fdd2. The cell dimensions are as follows: a = = 19.5207(17), b = 35.387(3), c = 12.5118(11) A, and V = 8642.8(13) A3. The central Gd3+ ion of II is also nine-coordinate, forming tricapped trigonal prismatic (TC-TP) conformation with three amine nitrogen atoms and six oxygen atoms. Complex II crystallizes in the monoclinic crystal system with P2/c space group. The crystal data are as follows: a = 14.4301(13), b = 11.2400(11), c = 17.7102(16) A, в = 112.606(2)°, and V = 2651.8(4) A3. There retain outer-protonated and inner-protonated carboxyl oxygen atoms in the [GdI2II(H2Ttha)2]2- complex anion. In II, there are only one type of methylamine cation (MnH+) as the

III 2

counter ion, which connects [Gdi (H2Ttha)2] complex anions and lattice water molecules through hydrogen bonds, leading to the formation of 2D ladder-like layer structure.

DOI: 10.7868/S0132344X14080064

INTRODUCTION

Owing to the particular physical and chemical properties, rare earth metals are usually selected to synthesize the metal-organic frameworks used in gas storage, adsorption, catalysis and separation [1—8]. In addition, some radioactive rare earth metal ions, for instance, 165Dy3+ and 166Ho3+ ions, due to the desirable radioactive characteristics, their corresponding complexes become excellent candidates for radiation synovectomy and radioimmunotherapy [9—11]. The Er(III) complexes play an important role in the production and development of laser fields [12]. Tb3+ ion, with a variety of organic ligands, is very popular as luminescent probes for the development of fluoroimmu-no-assays [13, 14]. High energy p-emitter of Y3+ ion, represents significant superiority in the treatment of larger tumor [15, 16]. What's more, because there are seven high-spin single electrons in the /-orbits of Gd3+ ion, the most in all the rare earth metal ions [17—24], many Gd(III) complexes are used as contrast agents

for magnetic resonance imaging (MRI) diagnoses. Recently, much betterment has been made for developing to cellular and molecular level [25], such as Gd3+ ion contract agents, nanoparticles based on colloidal lipid systems have been employed successfully to do cell labeling, using Gd-DTPA and MnCl2 multiple MR contrast agents to reveal detailed cytoarchi-tecture [26, 27]. In general, when most Gd(III)-based contract agents were synthesized the aminopolycar-boxly acids would be taken as ligands, which can form extraordinarily stable and water-soluble complexes with metal ions [28—30]. It maks the Gd(III) complexes with aminopolycarboxylic acid ligands have more widely application in the field of medicine. Due to the major role of Gd(III) complexes played in biology activities, hence, we think it makes sense to study the molecular structure and coordinate structure of more Gd(III) complexes with aminopolycarboxylic acid ligands.

A series of Gd(III) complexes with edta and ttha ligands have been reported by our laboratory, such as K[GdIII(Edta)(H2O)3] ■ 5H2O (H4Edta = ethylene-diamine-N,N,N',N'-tetraacetic acid) [31],

Na6[GdI2II(Ttha)2] ■ 8H2O (H6Ttha = triethylenetet-ramine-N,N,N',N",N'",N"'-hexaacetic acid) [32] and (EnH2)3[GdIII(Ttha)]2 ■ 11H2O [32]. By comparative analysis, it was found that, either Gd-Edta or Gd-Ttha complex, the coordination number all is nine. However, the coordinate structure and molecular structure are entirely different. The K[GdIII(Edta)(H2O)3] ■ 5H2O has a mononuclear molecular structure with pseudo-mono-capped square antiprismatic (MC-SAP) conformation [31]. And the (EnH2)3[GdIII(Ttha)]2 ■ 11H2O has two independent mononuclear structural units, and the GdN4O5 part in each [Gdm(Ttha)]3- complex anion adopts a MC-SAP polyhedron [32]. However, the

Na6[Gd2(Ttha)2] ■ 8H2O has a binuclear molecular

structure, and the GdN3O6 part in each [Gd^Ttha^]6-complex anion adopts a pseudo-tricapped trigonal prismatic (TC-TP) geometry [32]. Therefore, our studies showed that the molecular structures and coordinate structures of rare earth metal complexes with aminopolycarboxylic acid ligands sometimes not only related to the shape of ligands but also the counter ion species. In order to make in-depth our research, we want to know how the organic amine ion and ligand species generate the effects upon coordination number, coordinate structure, space group, molecular structure and crystal structure. As well as known, the organic amine can be regarded as the part of the amino acid, the research of interactions between organic amine with rare earth metal complex anions is significant for the exploration of their bioactivities and targets.

It is well known, aminopolycarboxylic acid can form extraordinarily stable and water-soluble complexes with rare earth metal ions [33, 34]. So, in this article, two ami-nopolycarboxylic acids, H4Edta and H6Ttha, were chosen as ligands and methylamine as counter ion, two novel rare earth metal complexes with aminopolycarboxylic acid ligands, namely, (MnH)[GdIII(Edta)(H2O)3] ■ 4H2O (I)

and (MnH)2[GdIII(H2Ttha)2] ■ 4H2O (II), were successfully synthesized. As expected, they both adopt nine-coordinate structure. However, due to the different ligands, I and II have different molecular structures and coordinate structures. Complex I adopts a mono-nuclear nine-coordinate MC-SAP geometry and the binding between MnH+ with [GdIII(Edta)(H2O)3]- is reviewed, providing the basis for the interaction of Gd(III) complexes with various biomolecules. While the polymeric II, being different from complexe I, adopts a binuclear nine-coordinate TC-TP geometry. In addition, four protons do not dissociate from the carboxyl oxygen atoms of Ttha ligand and formed two outer-protonated and two inner-protonated carboxyl

oxygen atoms in the [Gd™(H2Ttha)2]2- complex anion. What's more, complex II adopts a 2D ladder-like network through hydrogen bonds formed between methylamine and [Gd™(H2Ttha)2]2- complex anions. Therefore, it can be conclused that the ligand structures and counter ions play a crucial role on the coordinate structure of rare earth metal complexes.

EXPERIMENTAL

Synthesis of I. H4Edta (A.R., Beijing SHLHT Science & Trade Co., Ltd., China) (1.4607 g, 5.0 mmol) was added to 100 mL warm water and Gd2O3 powder (99.999%, Yuelong Rare Earth Co., Ltd., China) (0.9062 g, 2.5 mmol) was added slowly to the above warm H4Edta solution. After the mixture had been stirred and refluxed for 15.0 h, the solution became transparent, and then the pH value was adjusted to 6.0 by dilute methylamine (Mn) solution. Finally, the solution was concentrated to 25 mL and placed in dark desiccator. A light yellow crystal appeared after three weeks at room temperature. The yield was 76%.

CnH32N3O15Gd (I)

anal. calcd., %: Gd, 34.79; C, 21.88; H, 5.34; N, 6.96. Found, %: Gd, 34.85; C, 21.89; H, 5.32; N, 6.98.

Synthesis of II. H6Ttha (A.R., Beijing SHLHT Science & Trade Co., Ltd., China) (2.4723 g, 5.0 mmol) was added to 100 mL warm water and Gd2O3 powder (99.99%, Yuelong Rare Earth Co., Ltd., China) (0.9062 g, 2.5 mmol) was added to above warm H6Ttha solution slowly. The solution became transparent after the mixture had been stirred and refluxed for 13.0 h. And then the pH value was also adjusted to 6.0 by dilute methylamine (Mn). Finally, the solution was concentrated to 25 mL and placed in dark desiccator. A yellow crystal appeared after three weeks at room temperature. The yield was 79%.

C38H72N10O28Gd2 (II)

anal. calcd., %: Gd, 22.75; C, 31.88; H, 5.06; N, 9.78. Found, %: Gd, 21.97; C, 31.88; H, 5.07; N, 9.78.

Elemental analyses (C, H, and N) were determined by THERMO flash EA 1112 type analyzer instrument, and the Gd(III) was analysized by means of oxalate titration and thermal analysis. FT-IR spectra were determined by a Schimadza-IR 408 spectrophotometer (samples were skived and pressed to the slices with KBr). TG curves of I and II samples were determined by Mettler-Toledo 851 thermogravimetric analyzer in the presence of air (20 mL min-1) from room temperature to 800°C at a heating rate of 20°C min-1.

Table 1. Crystal data and structure refinement for I and II

Parameter Value

I II

Formula weight 603.65 1431.56

Temperature, K 298(2) 298(2)

Wavelength, A 0.71073 0.71073

Crystal system Orthorhombic Monoclinic

Space group Fdd2 P2/c

Unit cell dimensions:

a, A 19.5207(17) 14.4301(13)

b, A 35.387(3) 11.2400(11)

c, A 12.5118(11) 17.7102(16)

P, deg 90 112.606(2)

Volume, A3 8642.8(13) 2651.8(4)

Z 16 2

Pcalcd mg/m3 1.856 1.793

Absorption coefficient, mm-1 3.146 2.578

/(000) 4848 1444

Crystal size, mm 0.45 x 0.40 x 0.27 0.12 x 0.06 x 0.04

9 Range for data collection, deg 2.38 to 25.02 2.94 to 25.02

Limiting indices -19 < h < 22 -40 < k < 41 -12 < l < 14 -17 < h < 17 -13 < k < 11 -20 < l < 20

Reflections collected 9375 12466

Independent reflec

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