Bromidotris(triphenylphosphane)silver acetonitrile monosolvate monohydrate

In the title compound, [AgBr(C18H15P)3]·C2H3N·H2O, the coordination of the Ag atom is close to ideal tetrahedral, with the three Ag—P bond lengths almost equal [2.5441 (10), 2.5523 (9) and 2.5647 (10) ° A] and the Ag—Br bond slightly longer [2.7242 (5) Å]. The coordination tetrahedron is slightly flattened, the Ag atom is closer to the PPP plane; the P—Ag—P angles are wider than the Br—Ag—P angles. The voids in the crystal structure are filled with ordered acetonitrile solvent molecules. The remaining electron density was interpreted as a water molecule, disordered over three alternative positions. Neither of the solvent molecules is connected by any directional specific interactions with the complex.


Related literature
For general background to silver complexes and their biological activity, see: Blower & Dilworth (1987); Zartilas et al. (2009). For a similar complex without the solvent molecules, see: Engelhardt et al. (1987). For a description of the Cambridge Structural Database, see: Allen (2002).

Experimental
Crystal data [AgBr(C 18  complexes have also been studied for their antitumor activity (e.g. Zartilas et al., 2009 and references therein). This makes the study of silver(I) chemistry very attractive, since the molecular design and structural characterization of silver(I) complexes with particular properties is therefore an intriguing aspect. In this context, our research has been focused for some time on coordination compounds of silver(I) with a large range of heterocyclic thiones containing triarylphosphines as bulky p-acceptor co-ligands such as triphenylphosphine, whereby particular emphasis has been placed on the determination of the factors causing variations of silver(I) geometry.
In the crystal structure of the titled compound the coordination of silver atom is tetrahedral. All Ag-P bond lengths are almost equal, mean value is 2.554 (10) Å, while Ag-Br is slightly longer, of 2.7242 (5)  tetrahedron is slightly flattened, the Ag atom is closer to the PPP plane. It might be seen also from the X-Ag-X angle pattern: all P-Ag-P angles are larger than the Br-Ag-P angles.
In the crystal structure the voids are filled with the ordered acetonitrile molecule and with a remaining electron density which was interpreted as a water molecule, disordered over three alternative positions. Due to the lack of the directional interactions the crystal packing are probably determined by Weak π···π interactions (the separation between parallel C13···C18 phenyl rings related by the center of symmetry is 3.46 Å) and some van der Waals-type dispersion interaction. The presence of the solvent -acetonitrile and the residual electron density which fills the voids (and was interpreted as the disorder water molecules causes that the complex looses its C 3 symmetry which was reported for the unsolvated structure (Engelhardt et al., 1987).

Experimental
All solvents used were of reagent grade, while silver bromide, triphneylphosphine and 5-chloro-2-mercaptobenzothiazole (Aldrich, Merck) were used with no further purification. The IR spectra of the ligands and the complexes were recorded on the Perkin-Elmer spectrum GX FT-IR spectrophotometer in the range, 4000-370 cm -1 (using KBr pellets).

Refinement
Hydrogen atoms were located geometrically (C(methyl)-H 0.98 Å, C(ar)-H 0.95 Å) and refined as a riding model; the U iso values of H atoms were set at 1.2 (1.5 for methyl groups) times U eq of their carrier atom. The significant residual electron density observed in the voids was interpreted as the disordered water molecule which might come from the not dried solvent.
The site occupation factors of disordered water molecule were constrained to sum up to unity; weak constraints were applied to the ADP's of these partially occupied atoms. The 12 reflections were probably obscured by the beamstop, and therefore the SQUEEZE procedure was not used. Fig. 1. Anisotropic ellipsoid representation of molecule 1 together with atom labelling scheme. The ellipsoids are drawn at 50% probability level, hydrogen atoms are omitted for clarity.

Special details
Geometry. All s.u.'s (except the s.u. in the dihedral angle between two l.s. planes) are estimated using the full covariance matrix. The Refinement. Refinement of F 2 against ALL reflections. The weighted R-factor wR and goodness of fit S are based on F 2 , conventional R-factors R are based on F, with F set to zero for negative F 2 . The threshold expression of F 2 > σ(F 2 ) is used only for calculating Rfactors(gt) etc. and is not relevant to the choice of reflections for refinement. R-factors based on F 2 are statistically about twice as large as those based on F, and R-factors based on ALL data will be even larger.