Synthesis, Crystal Identification, and Thermal Studies of A New Organic-Inorganic Hybrid Yttrium(III) Complex With Squarate

Introduction

Metals-carboxylate family are one of the most important materials attracting researchers in the last decade [1][2][3][4][5] owing to their interesting molecular topologies[6]. They present a great interest follows their hybrid character and three-dimensional networks [7] [8] [9]. Recently, a large number of studies have been carried out on metal squarates with an open structure. The squarate dianion (C₄O₄^2-) can link metal ions in various coordination modes through the oxygen atoms [10].

In our own investigations, we are interested in the synthesis and characterization of complexes of yttrium square with templates such as ethylenediamine (Ed) [11], piperazine (pip), 1,4-diazabicyclo [ 2.2.2] octane (Dabco). The inking of the amines in the crystal lattices participates in the enlargement of the pores or the tunnels formed by the frameworks of these materials.

In the present study, we describe the synthesis, and spectroscopy, XDR identification and thermal behaviour of the new isotype.

Materials and Methods

All chemicals used were analytical reagents and purchased commercially. Diffraction powder experiments were performed at room temperature on a D8 Advence X-ray spectrometer. The sample for measurement was prepared by depositing the dried powder on a silicon sample holder. The structures were identified using DIFFRAC EVA V3.1 program [12]. The crystal lattice search was carried out with the Dicvol 06 program [13]. The program used for powder pattern simulation and molecular charts is a mercury program  [14]. The crystallographic data file used number is 1194867. Thermogravimetry analyses were carried out on a STA 449 F3 Jupiter. Thermal decomposition was recorded for 32 mg samples in (N₂) flow with a heating rate of 5°min^-1 up to 550°C.

Synthesis of Y(H₂O)₆(C₄O₄)(HC₄O₄).H₂O

A solution of yttrium nitrate hexahydrate (0.19 g) in water (5 ml) was added dropwise to a solution of (Ed) 0.4 ml or (Pip) 0.48 g or (Dabco) 0.22 g in distilled water (10 ml). The solutions immediately became turbid and were homogenized by the addition of a drop of HNO₃ with stirring for 5 minutes at 40 ° C. Then, 0.1 g of squaric acid in (10 ml) water was added dropwise. The clear solutions formed were stirred for 4 h at room temperature, and then colorless crystals formed were filtered and washed with water and dried in air.

Results and Discussion

X-Ray Diffraction (Xrd)

The XRD experimental data of the synthesized product agree with simulated diffractogram with mercury 3.8 software for Eu(H₂O)₆(C₄O₄)(HC₄O₄).H₂O[15] complex with a shift involving the difference between the ionic rays between europium and Yttrium. Fig 1

Figure 1: Parts of the experimental powder diffraction pattern of Y(H2O)6(C4O4)(HC4O4).H2O (red) and the powder pattern calculated from the atomic coordinates of the europium related compound black with part of Rietveld plot. Click here to View figure

 

Indexation Des Diagrammes De Diffraction de Y(H₂O)₆(C₄O₄)(HC₄O₄).H₂O

Indexing with DIVCOL 06 program leads in a monoclinic unit cell with parameters noted in Table 1 and figures of merit M (24) = 40.4, F (24) = 89.5 (0.0037, 73) revealing crystallization quality. The elemental cell in compound described by Jean-Francois Petit, and al is voluminous that we report. This justifies the shift noted in the diffractograms of Fig 2.

Table 1 : Cell parameters of M(H₂O)₆(C₄O₄)(HC₄O₄).H₂O    M = Eu, Y.

	a(Å)	b(Å)	c(Å)	α (°)	β (°)	γ(°)	V  (Å3)
Eu(H2O)6(C4O4)(HC4O4).H2O	15.263(2)	14.898(l)	6.354(l)	90	92.24(1)	90	1444
Y(H2O)6(C4O4)(HC4O4).H2O	15.1987	14.8094	6.3209	90	92.271	90	1421.6

 

in Table 2 are collected indexation data of  recorded diffractogram , showing the isotype of the two compounds.

Table 2 : Indexing data  of x-ray diffraction pattern for Y(H2O)6(C4O4)(HC4O4).H2O. Click here to View table

 

Figure 2: A packing plot of Eu(H2O)6(C4O4)(HC4O4).H2O[15] showing the intermolecular hydrogen-bonding scheme and tunnels encapsulates water molecules.   Click here to View figure

 

Thermal Analyses of Y(H₂O)₆(C₄O₄)(HC₄O₄).H₂O

The thermal behaviours of Y(H₂O)₆(C₄O₄)(HC₄O₄).H₂O show a three stage mass loss (FIG 3). The first stage between 90 and 113 correspond to elimination of the own water molecule, with a mass loss of 9.13, whereas in the second step the six water molecules coordinated to the metal atoms are emitted 115 and 260 with a mass loss of 19.33. In the last stage, decomposition of both squarate and mono hydrogen squarate ligands. The thermal decomposition product was identified as Y₂O₃. The final decomposition products of the complex was identified by powder RDX with the corresponding diffractogram obtained for the pure oxide

Figure 3: TG curve of Y(H2O)6(C4O4)(HC4O4).H2O Click here to View figure

 

Our work aim lies in hybrid materials preparation, intercalating amines in their crystal lattices. In our approach, several procedures were tested. The only resulting complex is {(C₂H₁₀N₂)_1.5[Y(C₄O₄)₃(H₂O)₄]}_n  [11]. To our knowledge, yttrium, squarate and amine complexes are less common. The structure of these materials with extensive networks including, the amine is specified from the viewpoint of properties of their analogue where the amine is not included in the network.

Catena-poly[sesqui(ethylenediammonium)[[tetraaquabis (squarato-қO) yttrium (III)]-μ-squarato-қ2O: O ‘]] [11] complex is characterized by a Two-dimensional crystalline structure. YO8 antiprisms formed constitute linear chains. The amines located between these chains participate, by hydrogen bonding, to interconnect these chains, thus forming layers which develop in parallel and stack along the axis c. They are located approximately 9° from each other. These layer arrangements reveal channels which develop parallel to the c axis and encapsulate protonated ethylenediamine (Fig 4).

Figure 4 : Cristal lattice showing porosity of {(C2H10N2)1.5[Y(C4O4)3(H2O)4]}n  [11]. Click here to View figure

 

The approach is to make varied the amine, by choosing templates with different carbon chains in their lengths, to favor the modifications of the properties of the material.

In Y(H₂O)₆(C₄O₄)(HC₄O₄).H₂O complex, crystal lattice is characterized by presence of the tunnels along the c axis encapsulating water molecules (zeolite property). FIG 2 is reproduced from the crystallographic data file of Complex Eu(H₂O)₆(C₄O₄)(HC₄O₄).H₂O [15] .

Conclusion

In the present work we have demonstrated that based on simple considerations concerning the nature of the metal atoms and coordination behaviour of the ligands the crystal structure of coordination polymers can be controlled to some extent. Whereas the occurrence of two-dimensional grids in these compounds was planned, the formation of the three-dimensional coordination network by interpenetration of these grids was not intended. However, compounds were obtained that contain channels in which additional water molecules are embedded. These channel water molecules can

-bipyridine metal squarates (Me=Mn, Fe, Co, Ni) showing the metal coordination in the hydrated compounds (left) and hypothetical structure of the fully dehydrated compounds (right).

reversibly be removed in a topotactic reaction. Surprisingly, also the removal of the water molecules which are coordinated to the metal atoms is reversible. The temperature of the steps and the energies involved depend on the nature of the metal atoms and can be understood on the basis of the slightly different crystal structures. The hydration and dehydration processes lead to continuous and significant changes of the optical properties of these compounds which can be attributed to a change of the coordination of the metal atoms.

Based on the structural data and the magnetic measurements a mechanism for the removal of the water molecules that are coordinated to the metal atoms is suggested. To prove this assumptions structural and spectroscopic investigations as well as theoretical calculations are planned. However, this will be the subject of further investigations.

Acknowledgments

We gratefully acknowledge the financial support by the State of Schleswig-Holstein. We are very thankful to Professor Dr. Wolfgang Bensch for helpful discussion, financial support and the facility to use his experimental equipment

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