Synthesis, Crystal Structure and Luminescent Property of Cd (II) Complex with N-Benzenesulphonyl-L-leucine

A new trinuclear Cd (II) complex [Cd3(L)6(2,2-bipyridine)3] [L = N-phenylsulfonyl-L-leucinato] has been synthesized and characterized by elemental analysis, IR and X-ray single crystal diffraction analysis. The results show that the complex belongs to the orthorhombic, space group P212121 with a = 16.877(3) Å, b = 22.875(5) Å, c = 29.495(6) Å, α = β = γ = 90°, V = 11387(4) Å3, Z = 4, Dc= 1.416 μg·m−3, μ = 0.737 mm−1, F (000) = 4992, and final R1 = 0.0390, ωR2 = 0.0989. The complex comprises two seven-coordinated Cd (II) atoms, with a N2O5 distorted pengonal bipyramidal coordination environment and a six-coordinated Cd (II) atom, with a N2O4 distorted octahedral coordination environment. The molecules form one dimensional chain structure by the interaction of bridged carboxylato groups, hydrogen bonds and π-π interaction of 2,2-bipyridine. The luminescent properties of the Cd (II) complex and N-Benzenesulphonyl-L-leucine in solid and in CH3OH solution also have been investigated.


Introduction
Investigation of the inorganic-organic hybrid materials with carboxylate ligands has gained considerable attention during the last decade due to their attractive structures and promising potential applications for catalysis, gas storage, magnetic, luminescence materials [1][2][3][4][5][6][7]. Structural studies have

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shown that the organic ligands containing multi-oxygen and nitrogen atoms can coordinate with metal ions in different ways, resulting in the formation of various metal-organic frameworks with specific topologies and useful properties. The Cd (II) complexes have gained considerable attention due to their luminescent properties [4]. We have been exploring the preparation of inorganic-organic hybrid materials by combining metal ions and organic ligands containing multi-oxygen and nitrogen atoms. We have now synthesized a new hybrid material, [Cd 3 (L) 6 (2,2-bipyridine) 3 ] [L= N-phenylsulfonyl-L-leucinato]. The luminescent properties of the Cd (II) complex and N-Benzenesulphonyl-L-leucine in solid and in CH 3 OH solution also have been investigated.

IR Spectra
The ν as (COOH), ν s (COOH) and ν (C=N) vibrations of free ligand are at 1,659 cm −1 and 1,436 cm −1 and 1587 cm −1 , respectively. For the Cd (II) complex, they shift to 1,587 cm −1 , 1,402 cm −1 and 1552 cm −1 , respectively, which suggest that the oxygen atoms of COOand the nitrogen atoms of 2,2-bipyridine coordinate to Cd (II) ions [8]. The difference between the ν as (COO − ) and ν s (COO − ) band is 185 cm −1 , indicating a bidentate carboxylate moiety, consistent with the X-ray structural analysis. The new band at 419 cm −1 is assigned to the ν (Cd-O) vibration.

Structure Description
The molecular structure and molecular packing arrangement are shown in Figures 1 and 2, respectively.

Luminescent Properties
Previous studies have shown that the Cd (II) complexes exhibit luminescent properties [11]. Hence, we investigated the luminescent properties of the Cd (II) complex in the solid-state and in CH 3 OH solution (1.06 × 10 −5 mol L −1 ) at room temperature. The emission spectra of the Cd (II) complex are shown in Figure 5. In the solid state, the Cd (II) complex displays strong luminescent emission bands at 442 nm when excited at 335 nm. And in CH 3 OH solution, the Cd (II) complex displays strong luminescent emission bands at 457 nm when excited at 335 nm. For excitation wavelengths between 280 and 420 nm, there is no obvious emission observed for the N-benzenesulphonyl-L-leucine ligand. Compared with the emission maximum of the Cd (II) complex in methanol solution, the emission maximum of the Cd (II) complex in solid was blue shifted, which may be due to the quenching effect of the methanol solvent.

Materials and Methods
The N-benzenesulphonyl-L-leucine ligand was prepared according to the method reported in the literature [5]. Other chemicals were of reagent grade and were used without further purification.
Carbon, hydrogen and nitrogen analyses were obtained using an Elementar Vario III EL elemental analyzer. Infrared spectra were recorded on a Nicolet AVATAR 360 FTIR spectrophotometer with KBr in the range of 400 cm −1 -4000 cm −1 . Mass spectrum was performed on a VG ZAB-HS Fast-atom bombardment (FAB) instrument. Excitation and emission spectra were obtained on a PE LS-55 spectrometer at room temperature. X-ray diffraction data of the Cd (II) complex was collected on a Bruker smart CCD diffractometer.

Synthesis of Cd (II) Complex
A methanol solution of 0.5 m mol (0.1543 g) cadmium nitrate tetrahydrate was added to a solution containing 1.0 m mol (0.2710 g) of N-benzenesulphonyl-L-leucine and 1.0 m mol (0.04 g) of sodium hydroxide in 10 mL CH 3 OH. The mixture was continuously stirred for 2 h at refluxing temperature. The mixture was cooled at room temperature, and was collected by filtration. By evaporation in air at room temperature, a single crystal suitable for X-ray determination was obtained from methanol solution after 15 days. Elementary analysis: calcd for C 102 H 120 Cd 3

X-Ray Crystallography
Single crystal X-ray diffraction data were collected on a Bruker smart CCD diffractometer at 153(2) K using graphite-monochromatic Mo Kα radiation (λ = 0.71073 Å). The structure was solved by the direct method and refined with full-matrix least-squares techniques using SHELXL-97 [12]. All non-hydrogen atoms were refined anisotropically, and all hydrogen atoms were put in calculated positions. Molecular graphics were drawn with the program package SHELXTL-97 crystallographic software package [13]. The main crystal data of the collection and refinement details of the Cd (II) complex are summarized in Table 1. Selected bond lengths and angles are listed in Table 2.