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  0   Introduction

  Currently, quite a few novel coordination compl-exes are reported ^[1-2]. With the rapid development of coordination complexes, complexes with closed-shell d10 metals have attracted considerable attention due to important applications in catalysis ^[3-4] and biochemis-try ^[5-6]. In particular, complexes bearing the Ag-S bond have raised continuously increasing interest, owing to their use in pharmacology ^[7] and thin films ^[8], as well as glass and ceramic technology ^[9]. In coordination chem-istry, it is one of the most interesting phenomena that two or more stable products are synthesized by the same reactions. The success of designed synthesis and separation of materials still look upon as something of challenge ^[10-11].

  Herein, we set out to design, prepare, and characterize silver (Ⅰ) complexes of silver halides AgX (X=Cl, Br), using same phosphine moieties and taking into account the coordination versatility of the thiol ligand (Scheme 1), namely [AgCl (PPh₃)₂(BTZT)]·CH₃OH (1), [AgCl (PPh₃)₂(BTZT)]₂ (2) ^[12], and [AgBr (PPh₃)₂(BTZT)]·CH₃OH (3), [AgBr (PPh₃)₂(BTZT)]₂ (4) ^[13] (PPh₃=triphenylphosphine; BTZT=benzothiazoline-2-thione). The BTZT ligand was transformed from MBT ligand in different chemical environment because of chemically active groups of MBT (MBT=2-mercaptob-enzothiazole) ^[14]. Complexes 1 and 3 have been synth-esized and characterized by IR, elemental analysis, ¹H NMR spectroscopy and single-crystal X-ray diffraction.

  Figure Scheme 1.  Routine of synthesis for complexes 1~4

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  1   Experimental

  1.1   Materials and measurements

  All chemical reagents are commercially available and used without furthermore treatment. FT-IR spectra (KBr pellets) were measured on a Perkin-Elmer Infrared spectrometer. C, H and N elemental analysis were carried out on an ElementarVario MICRO CUBE (Germany) elemental analyzer. ¹H NMR was recorded at room temperature with a Bruker DPX 600 spectrometer.

  1.2   Synthesis of [AgCl (PPh₃)₂(BTZT)]·CH₃OH (1)

  A mixture of AgCl (0.2 mmol, 0.0291g), PPh₃ (0.4 mmol, 0.104 9 g) and MBT (0.2 mmol, 0.033 3 g) were dissolved in a mixture of CH₃OH (5 mL) and CH₂Cl₂ (5 mL), stirred for 6 h and filtered. Colorless crystal 1 was obtained from the filtrate after standing at the room temperature for several days. Yield: 56%. Element analysis Calcd. for C₄₄H₃₉AgClNOP₂S₂(%): C, 60.89; H, 4.50; N, 1.61; Found (%): C, 61.08; H, 4.39; N, 1.52. IR data (KBr pellets, cm^-1): 3 418w, 3 049w, 2 937w, 2 815w, 1 598w, 1 583w, 1 495m, 1 478m, 1 432 s, 1 328m, 1 092m, 1 077w, 1 028m, 1 012w, 743s, 693s, 604w, 512m. ¹H NMR (600 MHz, CDCl3, 298 K): δ 7.51~7.23(m, CH_benzene).

  1.3   Synthesis of [AgBr (PPh₃)₂(BTZT)]CH₃OH (3)

  Complex 3 was prepared in a manner similar to that described for 1, using AgBr (0.2 mmol, 0.037 0 g), PPh₃ (0.4 mmol, 0.104 8 g) and MBT (0.2 mmol, 0.033 2 g) as starting materials. Yield: 51%. Element analysis Calcd. for C₄₄H₃₉AgBrNOP₂S₂(%): C, 57.92; H, 4.27; N, 1.53. Found (%): C, 57.81; H, 4.02; N, 1.46. IR data (KBr pellets, cm^-1): 3 434w, 3 052w, 3 001w, 2 935w, 2 875w, 2 825w, 1 596w, 1 492m, 1 478m, 1 432s, 1 323m, 1 093m, 1 076w, 1 030m, 1 012w, 996w, 743s, 694s, 606w, 513m. ¹H NMR (600 MHz, CDCl3, 298 K): δ 7.51~7.23(m, CH_benzene).

  1.4   Structure determination

  Single crystals of the title complexes were mounted on a Bruker Smart 1000 CCD diffractometer equipped with a graphite-monochromated Mo Kα (λ=0.071 073 nm) radiation at 298 K. Semi-empirical absorption corrections were applied using SADABS program ^[15a]. All the structures were solved by direct methods using SHELXS program of the SHELXTL-97 package and refined with SHELXL-97 ^[15b]. Metal atom centers were located from the E-maps and other non-hydrogen atoms were located in successive difference Fourier syntheses. The final refinements were performed by full matrix least-squares methods with anisotropic thermal parameters for non-hydrogen atoms on F ². The hydrogen atoms were generated geometri-cally and refined with displacement parameters riding on the concerned atoms.

  Crystallographic data and experimental details for structural analysis are summarized in Table 1, and selected bond lengths and angles of complexes 1 and 3 are summarized in Table 2. The bond lengths and angles of hydrogen bonds of complexes 1 and 3 are listed in Table 3.

  Table 1.  Crystallographic data for complexes 1 and 3

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  Table 1.  Crystallographic data for complexes 1 and 3
  Table 2.  Selected bond distances (nm) and bond angles (°) for complexes 1 and 3

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  Table 2.  Selected bond distances (nm) and bond angles (°) for complexes 1 and 3
  Table 3.  Hydrogen bonds of complexes 1 and 3

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  Table 3.  Hydrogen bonds of complexes 1 and 3

  CCDC: 1407305, 1; 1407306, 3.

  2   Results and discussion

  2.1   Synthesis of complexes

  As is known to all, many factors can influence the structures of the compounds, such as temperature, solvent and molar ratio of the starting materials. We obtain two kinds of complexes 1 and 2 by the reactions of AgCl, PPh₃, and BTZT in 1: 2: 1 molar ratio in mixed solvent (CH₃OH/CH₂Cl₂). Complex 1 crystallizes in the monoclinic system with space group P2₁/n, while 2 ^[12] crystallizes in the triclinic system with space group P1.

  3 and 4 were obtained by the reactions of AgBr with PPh₃ in the presence of 2-mercaptobenzothiazole (MBT) in 1: 2: 1 molar ratio in mixed solvent (CH₃OH/CH₂Cl₂). 3 crystallizes in the monoclinic system with space group P2₁/n, while 4 ^[13] crystallizes in the triclinic system with space group P1.

  Complexes 2 and 4 were synthesized in winter, but 1 and 3 were obtained in summer. So we think that the temperature of volatilization may influence the structures of the compounds.

  2.2   Infrared spectroscopy

  The infrared spectra of complexes 1 and 3 show the absorption around 1 459~1 495 cm^-1 due to C-C stretch vibration of the phenyl rings and the middle absorption around 3 049 or 3 052 cm^-1 is caused by C-H vibration of the phenyl rings. The C-H out-of-plane bending vibrations of the phenyl rings are found around 743 and 694 cm^-1. The absorption of the N-H stretch vibration is in the range of 3 418~3 434 cm^-1.The C=N bond vibration is found in 1 432 cm^-1.

  2.3   Description of the crystal structure

  Single-crystal X-ray diffraction analysis of 1 reveals the Ag (Ⅰ) metal adopts four-coordinated mode, which is bonded to two P atoms from two PPh₃ ligands, one chlorine atom and one S atom from the C=S fragment of the BTZT ligand peripherally establishing a distorted tetrahedral geometry about the metal. In particular, the complex 2 contains two same moieties in each asymmetric unit ^[12].

  In complex 1 (Fig. 1), the Ag-P bond distance is sim-ilar to that in previous literature. The Ag-Cl bond dist-ance is comparable with those observed in related com-plexes [AgCl (κ¹-S-C₃H₅NS (NeMe))(PPh₃)₂] (0.257 0(1) nm) ^[16] and [AgCl (κ1-S-C₃H₅NS (NePrn)(PPh₃)₂)] (0.257 51(5) nm) ^[16]. The Ag-S bond distance is longer than that found in [Ag (imdt) Cl]_n ^[17] (0.248 66(14) nm), but it is shorter than that of complex 2 ^[12]. The angles around the Ag atom are in the range of 100.50(3)°~129.27(3)°. The Cl-Ag-S bond angle is smaller than that of [AgCl (TPP)₂(MTZD)] (102.68(3)°) and {[AgCl (TPP)₂(MBZT)]·(MBZT)·2(toluene)} (104.91(4)°) ^[18].

  Figure 1.  Perspective view of complex 1 with thermal ellipsoids drawn at the 30% probability level

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  Moreover, intramolecular N-H…Cl hydrogen bonds are observed (N…Cl 0.311 6(3) nm, N-H…Cl 170.0°) in the complex 1. The main structure of 1 links free CH₃OH by hydrogen bonding interactions.

  In complex 3 (Fig. 2), the angles around the Ag atom are in the range of 101.13(4)°~129.04(5)°.The coordination geometry around each Ag atom indicates a distorted tetrahedron. The Ag-P bond length is typical Ag-P distance ^[19]. The Ag-Br distance is found in good agreement with the reported values ^{[16, 20]}, but is longer than those of complex 4. The Ag-S bond length is longer than that observed in [Ag₂(μ-S-pySH)₂(PPh₃)₂ Br₂] (0.260 8(1) nm) ^[14]. The P-Ag-P bond angle is all longer than those in another similar complex ^[21]. Moreover, intramolecular N-H…Br hydrogen bonds are observed (N…Br 0.326 9(5) nm, N-H…Br 169.2°) in the complex 3. The main structure of 3 links free CH₃OH by hydrogen bonding interactions. The O-H…Br hydrogen bond to link free CH₃OH and NO₃^- anion is observed (O…Br 0.332 9(7) nm, O-H…Br 171.2°) in the complex 3.

  Figure 2.  Perspective view of complex 3 with thermal ellipsoids drawn at the 30% probability level

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  Compared to complex 3, the complex 4 contains two same structures in each asymmetric unit. Each Ag atom adopts four-coordinated mode, which is coor-dinated with two P atoms from two PPh₃, one Br atom and one S atom from benzothiazoline-2-thione ligand (BTZT).

  Figure 3.  Solid-state excitation and emission spectra of 1 and 3 at 298 K

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  2.4   Fluorescence spectra

  The luminescent excitation and emission spectra of complexes 1, 3 and MBT ligand in the solid state at room temperature are obtained. The emission peak of PPh₃ is at 402 nm (λ_ex=372 nm) ^[19]. In the fluore-scence emission spectrum of MBT ligand, the emission peak is found at 419 nm (λ_ex=342 nm). When excited at 365 nm, a fluorescence emission peak of complex 1 is found at 431 nm. The complex 3 exhibits fluorescence signal centered at 423 nm with an excitation maximum at 353 nm. The red-shift of emission peaks of 1 and 3 are derived from ligand-centered π-π^* transition.

  3   Conclusions

  In summary, two kinds of silver (Ⅰ) halide com-plexes based on triphenylphosphine and benzothia-zoline-2-thione, [AgCl (PPh₃)₂(BTZT)]·CH₃OH (1), and [AgBr (PPh₃)₂(BTZT)]·CH₃OH (3), were synthesized and characterized by IR, elemental analysis, ¹H NMR spectroscopy, luminescent spectra and single-crystal X-ray diffraction. However, by the same reactions two different products 2 (The reaction condition was same as 1) and 4 (The reaction condition was same as 3) were synthesized. Single-crystal X-ray diffraction analysis reveals that 1 and 3 crystallize in the monoclinic system with space group P2₁/n, while 2 and 4 crystallize in the triclinic system with space group P1. The luminescent spectra show that 1 and 3 emission peaks were assigned to the ligand centered π-π^* transition.

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  Scheme 1  Routine of synthesis for complexes 1~4

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  Figure 1  Perspective view of complex 1 with thermal ellipsoids drawn at the 30% probability level

  A part of hydrogen atoms are omitted for clarity

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  Figure 2  Perspective view of complex 3 with thermal ellipsoids drawn at the 30% probability level

  A part of hydrogen atoms are omitted for clarity

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  Figure 3  Solid-state excitation and emission spectra of 1 and 3 at 298 K

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  Table 1.  Crystallographic data for complexes 1 and 3

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  Table 2.  Selected bond distances (nm) and bond angles (°) for complexes 1 and 3

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  Table 3.  Hydrogen bonds of complexes 1 and 3

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