Synthesis , Crystal Structure , Catalytic Properties , and Luminescent of a Novel Eu ( III ) Complex Material with 4-Imidazolecarboxaldehyde-pyridine-2-carbohydrazone

A novel Eu(III) complex, [Eu(L)2(H2O)4]·(NO3)·(H2O)4 (1) (H2L = 4-imidazolecarboxaldehyde-pyridine-2carbohydrazide), was synthesized. Its structure has been characterized by elemental analysis, IR, and X-ray single crystal diffraction analysis. Complex 1 is of orthorhombic, space group Fdd2 with a = 29.471(6) A ̊, b = 10.287(2) A ̊, c = 24.340(5) A ̊, V = 7379(3) A ̊3, Z = 8, Mr = 902.58, Dc = 1.625 μg·m-3, μ = 1.789 mm-1, F(000) = 3656, GOOF = 1.099, the final R = 0.0517, ωR = 0.1292 for 3043 observed reflections with I > 2σ(I). The A3 coupling reaction has been investigated using the complex 1 as catalyst. The luminescent spectrum of the complex 1 gives two weak peaks (448 nm and 491 nm) and two strong peaks (596 nm and 620 nm) from excitation at 279 nm. Copyright © 2017 BCREC Group. All rights reserved.


Introduction
Increasing studies have been focused on the europium complexes, because they show rich coordination model, biological activity, catalytic activity and strong red luminescence [1][2][3][4].So far, various Eu(III) complexes with multipodal ligands, such as diketonate [5], Schiff-base [6], carboxylate [7], and bipyridyl [8] have been reported.Meanwhile, hydrazone compounds are excellent multipodal ligands [9], and their me-tal complexes have also shown good properties in cytotoxic activity [10], luminescence [11], and catalytic application [12].Syntheses of propargylamines under heterogeneous catalysis are particularly attractive as they allow the production and ready separation of large quantities of products using small amounts of catalysts.So the development of heterogeneous catalysts for preparing propargylamines by the A 3 coupling reaction remains an active research area [13][14][15][16][17].However, so far, there is little research on the catalytic activity of Eu(III) complexes.As part of our research interest, in this paper, a novel Eu(III) complex was reported.Moreover,

Materials and measurements
4-Imidazolecarboxaldehyde (A.R.), pyridine-2-carbohydrazide (A.R.) and Eu(NO3)3•6H2O (A.R.) were purchased from Aladdin Reagent Company.The analyses of C, H, and N were made on a Elementar Vario EL III elemental analyzer.Infrared spectra (KBr pellets, 4000-400 cm -1 ) were recorded on a Nicolet NEXUS 670 spectrophotometer.The X-ray singlecrystal data collection for complex 1 was per-formed on a Bruker Smart-1000 CCD diffractometer.The luminescent emission spectrum of complex 1 in solid state was measured on a PE LS-55 spectrometer.

Crystal data and structure determination
X-ray diffraction analysis of complex 1 was carried out at 293 (2) K on a Bruker Smart-1000 CCD diffractometer by using a φ~ω scan mode.The structure was solved by direct methods with SHELXL-97 program package [18] and refined with SHELXTL-97 [19].The most crystal data of complex 1 are listed in Table 1.

General procedure for the three component coupling reaction (A 3 )
The coupling of benzaldehyde, piperidine and phenylacetylene with 1,4-dioxane as solvent was selected as a model reaction.The reaction was conducted by heating Eu(III) complex catalyst (70 mg), benzaldehyde (0.13 mmol), piperidine (0.15 mmol), and phenylacetylene (0.17 mmol) in 1,4-dioxane (1.5 g) without any additives or an inert atmosphere at 120 °C for 5 h.The yield of propargylamine is equal to the conversion of benzaldehyde, and was determined by using a by GC (GC1100, Capillary Column, SE-54) analysis.

Structural description
The complex 1 crystallizes in orthorhombic space group FDD2.The crystal structure of complex 1 is constructed by a central Eu(III) ion, two 4-imidazolecarboxaldehyde-pyridine-2carbohydrazide anions, a isolated NO3 -counter anion, four coordinated water molecules and four lattice water molecules (Figure 2  The complex molecules form 3D network structure by the aid of intermolecular hydrogen bonds and intramolecular hydrogen bonds (Table 2 and Figure 3).

Catalytic studies
The prepared complex was used as a catalyst for A 3 coupling reaction of aldehyde, amine and terminal alkyne (Figure 4).The yield of propargylamine was determined by using GC (GC1100, Capillary Column, SE-54) analysis.The results exhibit that only a trace amount of propargylamine was obtained when do not use any catalyst.A yield of 2.8 % was obtained at 120 °C for 5 h.The yield of propargylamine was reached 16 % for 5 h at 120 °C using complex 1 as a catalyst.It can be seen that the complex has a higher yield of propargylamine than blank.However, the activity of complex is still less than those of Au/MOF and Cu(II) complex material [6,15].

Luminescent property
The luminescent properties of Eu(III) complexes have been received more interest because of their strong red luminescence emission [21].Figure 5 displays the luminescence emission spectrum of complex 1 in solid state, it can be seen that the complex 1 gives two weak peaks (448 nm and 491 nm) and two strong peaks (596 nm and 620 nm) from excitation at 279 nm.

Conclusions
In summary, a new Eu(III) complex has been synthesized and its structure has been determined by elemental analysis, IR, luminescent and X-ray single crystal diffraction analysis.The catalytic activity for A 3 coupling reaction using Eu(III) complex as catalyst is a higher yield of propargylamine than blank.

Figure 4 .
Figure 4.A 3 coupling reaction of benzaldehyde, piperidine, and phenylacetylene using Eu(III) complex as catalyst

Figure 5 .
Figure 5.The emission spectrum of 1.The excitation and emission slit widths were 5 nm

Table 1 .
The most crystal data of complex 1

Table 2 .
Hydrogen bonds for complex 1