Synthesis , Crystal Structure , and Fluorescent Property of a Zn ( II ) Complex with N-Nicotinoylglycine Ligand

A new Zn(II) complex, [ZnL2(H2O)4]·2H2O (1) (HL = N-nicotinoylglycine), was synthesized by Zn(OAc)2·2H2O with N-nicotinoylglycine in 95% ethanol solution. Its structure has been determined by single-crystal X-ray diffraction, elemental analysis, and infrared spectrum. The crystal analysis show that complex 1 crystallizes in triclinic, space group P1. The Zn(II) ion, located on an inversion center, is coordinated by two N-nicotinoylglycine ligands through pyridine nitrogen and four water molecules. The crystal packing indicates 1D polymeric chains which expand into a 3D network structure by hydrogen bonds and π···π stacking. The luminescent properties of Zn(II) complex in solid state and in ethanol have also been investigated.


Structural Description of Zn(II) Complex (1)
Zn(II) complex 1 crystallizes in triclinic system, space group P1, and the crystallographic independent unit contains one N-nicotinoylglycine anion ligands, two coordinated water molecules, a lattice water molecule and one Zn(II) ion located on symmetry center.The coordination environment of the Zn(II) ion in 1 is shown in Figure 1, and a selection of bond lengths (Å) and angles ( • ) is listed in Table 1.From Figure 1, it can be seen that the Zn(II) ion is six-coordinated by the pyridine-N atoms of two N-nicotinoylglycine anion ligands and by four O atoms of water molecules, thus adopting an octahedral coordination geometry.The COO-groups of N-nicotinoylglycine ligand does not coordinate with Zn(II) ion, and the coordination environment in complex 1 is the same as that reported in literature for the nicotinoyl-glycine Mn(II) complex [21].Complex 1 is linked by O-H•••O hydrogen bonds to form 1D chained structure (Figure 2).The 1D chains further expand into a 3D network structure by hydrogen bonds and π•••π stacking interactions (Figure 3).Details of the hydrogen bonds geometry for the Zn(II) complex are given in Table 2. Table 1.Selected bond lengths (Å) and bond angles ( • ) for Zn(II) complex.

Fluorescent Properties
The fluorescent behaviors of Zn(II) complex in solid state and in ethanol solution have been investigated.The fluorescent spectra are shown in Figure 5.The Zn(II) complex exhibits fluorescent maximum peak at 461 nm (in solid state) and 441 nm (in ethanol solution) upon excitation at 391 nm.However, the N-nicotinoylglycine ligand does not have luminescent peak [23].Indicating that the Zn(II) takes part coordination with N-nicotinoylglycine ligand and Zn (II) complex can stably exist in ethanol solution.

Crystal Data Collection and Structure Determination
The intensity data of single crystal of [ZnL 2 (H 2 O) 4 ]•2H 2 O (1) were collected on a Brucker Smart Apex CCD diffractometer using graphite-monochromated MoKα radiation (λ = 0.71073 Å) at 293 (2) K. Diffraction data were collected using φ-ω scan mode.Cell parameters were refined using Bruker SMART program.The Bruker SAINT program was used for data reduction.The structure was solved by direct method using the SHELXS-97 program [24], and refined on F 2 by full-matrix least squares with the SHELXL-97 program [24].The key information of the crystal structure solutions and refinements is listed in Table 3. Crystallographic data for the structure reported in this paper has been deposited with the Cambridge Crystallographic Data Centre as supplementary publication No. CCDC 1540290.Copy of the data can be obtained free of charge on application to CCDC, 12 Union Road, Cambridge CB2 1EZ, UK (Fax: +44-1223-336-033; E-Mail: deposit@ccdc.cam.ac.uk).

Conclusions
In summary, a new Zn(II) complex has been synthesized by Zn(OAc) 2 •2H 2 O with N-nicotinoylglycine in 95% ethanol solution.The complex 1 formd 1D chained structure and 3D network structure by hydrogen bonds and π•••π stacking.The Zn(II) complex showed blue fluorescence both in solid state and in ethanol.

Figure 1 .
Figure 1.The coordination environment of Zn(II) ion, where the thermal ellipsoids were drawn at 30% possibility.

Figure 5 .
Figure 5.The fluorescent spectra of Zn(II) complex in solid and in ethanol.The excitation and emission slit widths were 5 nm.