葉行培 吳偉娜 李飛飛 蔡紅新 王 元

(河南理工大學(xué)物理化學(xué)學(xué)院，焦作 454000)

0 Introduction

Recently, quinolinyloxyl acetamide ligands and their fluorescence properties with rare earth ions have attracted much more attention due to their strong antenna effect to Eu(Ⅲ)or Tb(Ⅲ) ion[1-5]. On the other hand, such ligands could form stable complexes with transition metal ions and thus to act as fluorescent sensor for Cd(Ⅱ)or Zn(Ⅱ)ion[6-8]. In addition, Cd(Ⅱ)ion with d10configuration can adopt a variety of coordination geometries and is particularly useful for the construction of coordination[6-7]. Thus, in this work,a Cd (Ⅱ) complex containing a quinolin-8-yloxyl acetamide ligand L (L=N-methyl-N-phenyl-2-(quinolin-8-yloxy)acetamide) was synthesized and characterized by X-ray diffraction. In addition, the fluorescence spectra of the ligand and complex 1 in CH3CN solution were investigated.

1 Experimental

1.1 Materials and measurements

Solvents and starting materials for synthesis were purchased commercially and used as received.Elemental analysis was carried out on an Elemental Vario EL analyzer. The1H NMR spectra were recorded with a Bruker AV400 NMR instrument in deuterated acetone with TMS as internal standard.The mass spectrum was obtained on a TRACE DSQ GC/MS. The IR spectra (ν=4 000 ～400 cm-1) were determined by the KBr pressed disc method on a Bruker V70 FT-IR spectrophotometer. The UV spectra were recorded on a Purkinje General TU-1901 spectrophotometer. Fluorescence spectra were determined on a Varian CARY Eclipse spectrophotometer. In the measurements of emission and excitation spectra the pass width is 5 nm.

1.2 Preparations of the ligand L and [CdL(H2O)(NO3)]NO3·CH3COCH3(1)

The ligand L was synthesized according to the literature procedure[9]. M.p. 117～118 ℃;1H NMR(CD3COCD3, ppm)： δ 3.48 (3H, s,CH3), 4.78 (2H, s,CH2), 7.05～8.88 (11H, m, phenyl and quinoline); MS,m/z：293[M+1]+.IR(KBr,cm-1)：ν(C=O)1 681,ν(C=N)1 618, ν(Ar-O-C) 1 258.

The ligand L (0.029 2 g,0.1 mmol)was dissolved in acetone (3 ml), then an acetone solution (2 ml)containing cadmium nitrate tetrahydrate (0.031 8 g,0.1 mmol) was added dropwise at room temperature.After stirring for 2 h, the mixture was filtered and set aside to crystallize for several days, giving colorless block crystals of 1, which were collected by filtration,washed with Et2O and dried in air. Yield ca. 52%based on L. Anal. calc. for C21H22N4O10Cd (%)： C,41.84; H, 3.68; N, 9.29. Found(%)： C, 41.57; H, 3.42;N, 9.00. IR (KBr, cm-1)： ν(OH) 3 428, ν(C=O) 1 634,ν(C=N)1 588,ν(Ar-O-C)1 218, ν4(NO3)1 478,ν1(NO3)1 326, ν(OH) 618.

1.3.1 X-ray crystallography

The X-ray diffraction measurement for 1 was performed on a Bruker SMART APEX ⅡCCD diffractometer equipped with a graphite monochromatized Mo Kα radiation (λ=0.071 073 nm) by using φ-ω scan mode. Semi-empirical absorption correction was applied to the intensity data using the SADABS program[10].The structures were solved by direct methods and refined by full matrix least-square on F2using the SHELXTL-97 program[11].All non-hydrogen atoms were refined anisotropically. H atoms for the water molecules are located from difference Fourier map and refined with restraints in bond length and thermal parameters. All the other H atoms were positioned geometrically and refined using a riding model.Details of the crystal parameters, data collection and refinements for 1 are summarized in Table 1.

CCDC： 958121.

Table 1 Crystal data and structure refinement for 1

2 Results and discussion

2.1 Crystal structure of complex 1

Fig.1 Molecular structure of the title complex shown with 10% probability displacement ellipsoids

As shown in Fig.1, the title complex contains one solvate acetone molecule, with a composition of [CdL(H2O)(NO3)]NO3·CH3COCH3. Selected bond lengths and angles are summarized in Table 2. It can be confirmed that the Cd (Ⅱ) center possesses a coordination geometry closer to a distorted octahedral geometry with the donor centers of two O atoms and one N atom from the ligand, two O atoms from two mono-dentate nitrate anions and one O atom from one water molecule. The bond angles of O6-Cd1-O1 and O9-Cd1-O3 are 151.54 (6)° and 167.10 (7)° ,respectively; confirming that in 1, the four atoms O1(from the ligand L), O3, O6 (from two nitrate groups)and O9 (from water molecule) are in the basal plane.The axial positions are occupied with N1 atom and O2 atom from the ligand L. In complex 1, most bond angles are highly deviated from those of the ideal geometry. Although the coordination behavior of the organic ligands is similar, the structure of 1 is different from that of [Cd(L1)2(NO3)]NO3·0.5H2O[7]and[Cd(L2)(NO3)2(CH3OH)][6](L1=N-benzyl-2-(quinolin-8-yloxy)acetamide; L2=N-(quinolin-8-yl)-2-(quinolin-8-yloxy)acetamide). In both literature complexes, the Cd(Ⅱ)ion is eight-coordinated. However, the Cd(Ⅱ)ion is coordinated by a N2O6donor set in the former (two NO2sets from two L1ligands and two O atoms from a bidendate nitrate group) and a NO7donor set in the latter (one NO2set from the ligand L2, four O atoms from two bidendate nitrate groups and one O atom from methanol).

In the crystal of 1, intramolecular O-H … O hydrogen bonds between the coordinated water molecule and free nitrate O atoms link the complexes into chains along the a axis (Fig.2). In addition, the intramolecular O -H … O between the coordinated water molecule and solvate acetone O atoms are also present.

Fig.2 Intramolecular hydrogen bonds of extended chain-like structure along the a axis

2.2 IR spectra

Table 2 Selected bond lengths (nm)and angles (°) in the title complex

The IR spectra of L show strong band at 1 681 cm-1, which are attributable to stretch vibrations of the carbonyl group of amide (ν(C=O)). The peak at 1 618 m-1should be assigned to the ν(C=N), and the peak at 1 258 cm-1to ν(Ar-O-C). Upon coordination with Cd(Ⅱ)ion, the ν(C=O), ν(C=N) and ν(Ar-O-C) shift by 47, 30 and 40 cm-1, respectively; indicating that carbonyl oxygen atom, ethereal oxygen atom and quinoline nitrogen atom take part in coordination to the metal ion[7-8]. The aqueous ν(OH) bands appear at 3 428 cm-1and ρ(OH) bands at 618 cm-1showing that there is coordinative water molecule in 1[8]. In addition, two intense absorption bands in the spectra associated with the asymmetric stretching appear at 1 478 cm-1(ν1) and 1 326 cm-1(ν4), clearly establishing that the NO3-groups (C2v) take part in coordination. The difference between the two bands is 1 52 cm-1,suggesting that the NO3-groups in 1 are mono-dentate ligands[7-8,12]. It is in accordance with the result of the crystal structure study.

2.3 UV spectra

The UV spectra of L and 1 in CH3CN solution(concentration： 1×10-5mol·L-1) was measured at room temperature (Fig.3). The spectra of L feature three main bands located around 200 (ε=106 538 L·mol-1·cm-1), 239 (ε=74 512 L·mol-1·cm-1) and 298 nm (ε=8 103 L·mol-1·cm-1)[13]. The bands could be assigned to characteristic π-π* transitions centered on naphthalene, quinoline ring and the acetamide unit, respectively. They shift to 201 (ε=56 623 L·mol-1·cm-1),240 (ε=25 041 L·mol-1·cm-1) and 299 nm (ε=2 619 L·mol-1·cm-1) in complex 1, respectively. The hypochromicities indicate that the ligand L takes part in the coordination in complex 1.

Fig.3 UV spectra of L and 1 in CH3CN solution at room temperature

2.4 Fluorescence spectra

The fluorescence spectra of the ligand L and 1 in CH3CN solution (concentration： 1×10-5mol·L-1) was measured at room temperature. The excitation and emission wavelengths of both compounds are at 240 and 390 nm, respectively (Fig.4). It also can be seen that the emission intensity of 1 is much lower than that of the ligand L. This is probably due to the coordination of Cd(Ⅱ)ion influencing the fluorescence emission of the ligand L[14].

Fig.4 Fluorescence emission spectra of L and 1 in CH3CN solution at room temperature

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