Jiang Xuhong,^a,b Zhang Weiguang,^a Zhong Yun,^a Wang Suelein ^c
(^aDept. of Chem., South China Normal University，Guangzhou 510631; ^b Dept.of Foundation, Zhongkai Agrotechnical College, Guangzhou 510230; ^cDept.of Chemistry, National Tsing Hua University, Hsinchu, Taiwan 300, China)

Abstract The novel polymer: [Ag ( ⁿBu-XA) ]_n ( ⁿBu-XA=n-butylxanthate) was synthesized and crystallographically characterized. This polymer of silver ( I) with xanthate has different structural arrangement of the DTC, DDP ligands from that of Ag-DDT, Ag-DTC. The polymeric structure of this complex consists of two-dimensional corrugated plane of square. This complex crystallizes in the monoclinic system, space group P2(1)/c, with a=15.544(12)Å, b=6.206(5)Å, c=8.494(7)Å, b=96.358(1)^o, V=814.3ų, Z=4, R₁=0.0360, wR₂=0.0872.
Keyword Silver( I) complex, n-Butylxanthate, Two-dimensional polymer

1. INTRODUCTION       
Compounds formed from silver ( I) with dithiolate ligands such as the dialkyldithiocarbamates ( DTC) ^[1,2] and dithiophosphates ( DDP) ^[3-5] are well known. However, xanthate complexes of silver ( I) have been much less extensively studied than those dithiolate ligands and only some spectroscopic results about ( ROCS₂) ( Ph₃P) ₂Ag ( R=Me,Et,Pr,i-Pr) have been reported,^[6-8] In this paper we present the synthesis and crystal structure of the silver (I) complex with the n-butyl xanthate [Ag(ⁿBu-XA)]_n, which is a flaky polymeric complex involving bridging to adjacent metal through sulfur. It appears to be a novel mode of coordination.

2. EXPERIMENTAL
2.1 Reagents
All reagents are analytically pure and made in China.
2.2 Measurements
A yellow-green single crystal of [ Ag( ⁿBu-XA) ] _n with the dimensions 0.38×0.38× 0.37mm was mounted on glass fibers and data collections were performed on a Siemens P4 diffractometer with graphite-monchromated Mo-Ka radiation ( l =0.71073Å) at 296K, using the w /2q scan technique. The reflections were corrected for absorption by the Gaussian integration method, for Lorentz polarization and secondary extinction effects. The structure was solved by the Patterson method and subsequent difference Fourier techniques and refined by full-matrix least-squares method with anisotropic thermal factors for all non-hydrogen atom; a number of the hydrogen atoms were placed in calculated position. All calculations were performed using the SHELXTL system of computer programs.
    The IR spectra were recorded on a PE17300 FT-IR spectrometer in the region of 4000-400 cm^-1 in KBr pellet. Carbon and hydrogen were determined by using a Perkin-Elmer elemental analyzer.
2.3 Preparation of the complex        
The Na⁺[ⁿBu-XA] was synthesized by the reaction of n-butanol, sodium hydroxide and carbon disulfide. Then a solution of AgNO₃ in acetone-water was added in it. After the reaction, the precipitate was separated by filtration, and the filtrate was collected and allowed to evaporate slowly, while protected from light. The product was a rhombic yellow-green flake crystal, which was then used in the crystallographic study.

3. RESULTS AND DISCUSSION
3.1 IR spectra
Spectroscopic data IR ( KBr) :2960( m) 1469( m) 1224( m) 1191( s) 1128( m) 1035( s) 1024( s) 940( m) 741( w) 656( w) 564( vw) 499( w) cm^-1.The IR spectra showed characteristic bands of the complex. The band in the 2960 cm^-1 , belonging to the u( C-H) stretching vibration. The band in the 1469 cm^-1 , belonging to the d( C-H) bend vibration. The band in the 1250-1000 cm^-1, belonging to the u( C-O) stretching vibration, the band in the 740-560 cm^-1 ,belonging to the u( C-S) stretching vibration.^[9]
3.2 Elemental analysis
Elemental analysis on [Ag( ⁿBu-XA) ]_n Found: C23.33%, H3.52%；Calc.: C23.27%, H3.98%。
3.4 Crystal structural description         
Crystal data: C₅H₉AgOS₂, M=257.11, monoclinic, space group P2( 1) /c, Z=4, a=15.544( 12) Å, b=6.206( 5) Å, c=8.494( 7) Å, b=96.35( 1)^o , V=814.3( 11)ų, D_c=2.097 Mg/m³, F( 000) =504. The final values R₁=0.0360，wR₂=0.0872 were obtained. Selected Bond Lengths ( Å) and Bond Angles(o)are shown in Table 1.

Table 1 Selected Bond Lengths ( Å) and Bond Angles(^o)

Symmetry code，#1：-x+1,y-1/2,-z+3/2；#2：-x+1,-y-1,-z+1；#3：-x+1,y+1/2,-z+3/2；#4：x,-y-1/2,z-1/2；#5：x,-y-1/2,z+1/2

    The structure of [Ag ( ⁿBu-XA) ]_n is a polymer with eight- membered ring ( CS₂Ag) ₂ units. These eight- membered rings are parallel to each other. They are connected to one another by S-Ag bridging bond ( Fig.1) and formed corrugated two-dimensional polymer ( Fig.2) . The eight- membered ring is "chair" conformation and the terminal n-butyl groups of it take a trans-configuration. In the eight- membered ring, each n-butylxanthate ligand bridges two silver atoms to form the ring.

	Fig.1 The thermal ellipsoid drawing ( 50% probability) of [Ag( nBu-XA) ]n.The n-butyl groups were omitted for clarity.
	Fig. 2 Part of one of the extended polymer sheets present in  the crystals of [Ag( nBu-XA) ]n

   Each of the silver atoms is trigonally coordinated to three sulfur atoms from three ligands ( Fig.1) . Three sulfur atoms and one silver atom are almost coplanar. The bond angles of S( 1) -Ag-S( 2) , S( 1) #1-Ag-S( 2) and S( 1) -Ag-S( 1) #1 are 133.30( 4)^o, 119.47( 4) and 106.30( 2)^o respectively. Xanthate ligands are always bidentate to the bivalent or trivalent metals and form chelates with these metal atoms. In the case of the [Ag( ⁿBu-XA) ]_n, one sulfur atom [S( 2) ] of the ligand is monodentate and the other [S( 1) ] is bidentate. The bond length of the Ag( 1) -S( 1) #1 2.576( 2)Å is a little longer than those of Ag( 1) -S( 2) 2.492( 11)Å and Ag( 1) -S( 1) 2.501( 12)Å, due to S( 1) being a bridging atom. The sulfur atom [S( 1) #1] coordinated to another silver atom [Ag#] of the adjacent eight- membered ring. The Ag-S distances are in good agreement with those found in {Ag[S₂P( OC₃H_{7) 2}]}₆ [2.485( 2) ~2.572( 2) ]Å and {Ag[S₂C( OC₂H_{5) 2}]}₆ [2.471( 3) ~2.554( 3) ]Å. The S(1)-C(1) [1.704( 4)Å] and S(2)-C(1) [1.683( 4)Å] bond distances trend to average, it seems likely that the C-S distances show the double bond character-probably delocalized over the two C-S bonds. The O(1)-C(1) bond distances[1.337( 5)Å] is shorter than the O(1)-C(2) [1.453( 6)Å], which is a consequence of the hybridization of the carbon atom^[10]. So it can be deemed that n-butylxanthate adopts this novel mode of coordination.

     The Ag( 1) -Ag( 1) #2 distances ( 3.130 Å) are longer than Ag-Ag 2.886Å in silver metal,^[11] shorter than the Vander Waals diameter of silver 3.40Å.^[12] So there is no metal-metal bond in the polymer.
    In this polymer the adjacent polymeric sheets are parallel to each other. They are arranged to give a layer arrange ( Fig. 3) . The outer surfaces of each sheet were dominated by the hydrophobic n-butyl groups and thus there are no intersheet interaction other than normal Vander Waals. This absence of strong intermolecular interaction clearly contributes to the low melting point of the solid.
    Being a polymer,[ Ag( ⁿBu-XA) ]_n is not readily soluble in an organic solvent.

Fig. 3 View of the polymeric structure of [Ag(ⁿBu-XA)]_n

Crystal data for the title complex is available from the Cambridge Crystallographic Data Center ( CCDC No.170252 )

REFERENCE         
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