Synthesis and crystal structure of ( Nitrato-O , O ' )-bis ( triphenylphosphine )-silver ( I ) toluene mono-solvate

The reaction of Ag(I) nitrate with triphenylphosphine in methanol in 1:1 molar ratios and recrystallization in toluene resulted in complex of the formula [Ag(PPh3)2NO3]∙C7H8. The compound is a mononuclear neutral complex in which the Ag atom is in a tetrahedral environment consisting of two triphenylphosphine ligands and a nitrate ion acting as a bidentate ligand. The compound crystallizes in the triclinic P1 space group and the molecular structure of the compound contained a distorted toluene solvent of crystallization.


INTRODUCTION
Silver nitrate forms complexes with many phosphoruscontaining ligands.In these, the phosphorus-containing ligand to silver ratio can be 1:1, 2:1, 3:1 or 4:1 (Trávnícek, 1998;Caruso et al., 1995;Cassel, 1981;Barron et al., 1986).Tertiary phosphine complex of Ag(I) salts display rich diversity of structural types due to the geometrical flexibility, bite angle, electronic properties of phosphine and the coordination modes of the supporting ligands which often renders predictions concerning the structural properties of silver phosphine complexes difficult (Trávnícek, 1998;Caruso et al., 1995;Cassel, 1981;Barron et al., 1986).The Ag(I) ion can exist in a variety of molecular polyhedron with coordination number of 2 to 4 but overall geometry depends on the bulkiness of the phosphine ligand, the solvent and the counter ions (Camalli and Caruso, 1988;Meijboom et al., 2009;Fenske et al., 2007).
The interaction between Ag(I) and triphenylphosphine has attracted great interest and many have been structurally characterized (Aslanidis et al., 1997;Othman et al., 1996;Venter et al., 2009;Housecroft, 1996).Predicting the structural properties of Silver-phosphine complexes are quite difficult because crystallization of some complexes have resulted in more than one polymorph (Meijboom et al., 2009).This warrants more research into factors that govern the formation of particular structural types.In this paper, the synthesis and crystal structure of Silver-phosphine complex of the type [AgXL 2 ] is presented (X = NO 3 , L = triphenylphosphine).

MATERIALS AND METHODS
The complex was obtained by the reaction of Silver nitrate with triphenylphosphine in 1:2 mole ratio.White crystals of the complex suitable for X-ray crystallography were isolated by slow evaporation of solvent at room temperature in toluene.Single-crystal X-ray diffraction data were collected on a Bruker KAPPA APEX II DUO diffractometer.Cell refinement and data reduction were performed using the program SAINT (Cortez and Raptis, 1997).The data were scaled and empirical absorption corrections were performed using SADABS (SAINT Version, 2006).The structure was solved by direct methods using SHELXS-97 (SAINT Version, 2006) and refined by full-matrix least-squares methods based on F 2 using SHELXL-97 (SAINT, 2006) with the graphic interface program X-Seed (Sheldrick, 1997).The programs X-Seed and POV-Ray (Barbour, 2001;Atwood and Barbour, 2003) were both used to prepare molecular graphic images.The parameters for crystal data collection and structure refine-ments, the bond lengths and angles are shown in Tables 1 and 2.

RESULTS AND DISCUSSION
The Ag complex [Ag(PPh 3 ) 2 NO 3 ]•C 7 H 8 crystallize in the triclinic space group P1 with a = 11.2113(7)Å, b =12.2868(7)Å and c = 16.1679(10)Å.The crystal structure of the compound (Figure 1) shows that the complex is a mononuclear species in which the Ag atom  [51.09(6)°].The bond lengths and angles around the metal ion are similar to those reported in the literature (Harker and Tiekink, 1989).
For Silver-phosphine 1:2 complexes of the type [AgXL 2 ], structural determination have shown that the complexes are dimeric and most often with halides bridges (Bowmaker et al., 1997;Cassel, 1979;Bowmaker et al., 1993).Inference from nuclear magnetic resonance (NMR) studies showed that some complexes may be monomeric with trigonal geometries (Muetterties and Alegranti, 1972;Bowmaker et al., 1996), while with some non-coordinating anion such as ClO 4 , NO 3 , two coordinate cationic complexes were obtained (Alyea et al., 1982;Goel and Pilon, 1978).In the present study, the NO 3 anion acts as a chelating bidentate ligand.The P-C and C-C bond length did not show any significant variations.The Ag-P bond lengths lie within the normal range for bis(triphenylphosphine) complexes, while the Ag-O distance is shorter than those obtained from complexes in which the NO 3 is a counter ion (Goliè et al., 1983).The observed changes in bond distances and angles are due to the interplay of various parameters (Camalli and Caruso, 1988;Meijboom et al., 2009;Fenske et al., 2007) such as the geometrical flexibility of Ag(I), the bite angles and the electronic properties of the phosphine.
The crystal packing of the compound contained two molecules in the unit cell and each crystallizes with a distorted toluene solvent molecule that is disordered over two positions with site occupancy factors of 61 and 39%, respectively.No classical hydrogen bonds exist between the molecules but they interacted through short contacts between one bonded oxygen atom and the H-atom of the triphenylphosphine.
In conclusion, [Ag(PPh 3 ) 2 NO 3 ]•C 7 H 8 has been synthesized and characterized by single crystal X-ray crystallography.Single crystal X-ray structure of the compound revealed that it exist in a distorted tetrahedral geometry and crystallized with a molecule of toluene in the crystal lattice.

Figure 1 .
Figure 1.Molecular structures of [Ag(PPh 3 ) 2 NO 3 ]•C 7 H 8 showing the atomic labelling scheme.All H atoms are omitted for clarity.All non-hydrogen atoms are presented with ellipsoidal model with probability level 30%.Only one toluene molecule with site occupancy factor 61% is shown.