Bis[O-isopropyl (4-ethoxyphenyl)dithiophosphonato-κ2 S,S′]lead(II)

The title compound, [Pb(C11H16O2PS2)2], is a neutral four-coordinate mononuclear complex with a distorted square-pyramidal geometry of the PbS4 core. The apical PbII atom of each pyramid is 1.33059 (3) Å above the basal S4 plane. The metal atom is surrounded by two chelating dithiophosphonate ligands binding through the S-donor atoms. The ligands are anisobidentate as the pyramid is comprised of Pb—S bond lengths that vary substantially [2.6999 (7), 2.7128 (6), 2.8877 (7) and 2.9472 (7) Å], clearly indicating two short and two longer bond lengths. The P—S bond lengths are also paired as shorter [1.9959 (9) and 1.9877 (8) Å] and slightly longer [2.0115 (9) and 2.0245 (9) Å], indicating an anisobidentate nature of the ligand whereby the shorter P—S bond has more double-bond character than the other. The S—Pb—S (chelating) bond angles range from 71.841 (18) to 72.692 (19)°, whilst the Pb—S—P bond angles range from 84.70 (3) to 90.51 (3)°.

The title compound, [Pb(C 11 H 16 O 2 PS 2 ) 2 ], is a neutral fourcoordinate mononuclear complex with a distorted squarepyramidal geometry of the PbS 4 core. The apical Pb II atom of each pyramid is 1.33059 (3) Å above the basal S 4 plane. The metal atom is surrounded by two chelating dithiophosphonate ligands binding through the S-donor atoms. The ligands are anisobidentate as the pyramid is comprised of Pb-S bond lengths that vary substantially [2.6999 (7), 2.7128 (6), 2.8877 (7) and 2.9472 (7) Å ], clearly indicating two short and two longer bond lengths. The P-S bond lengths are also paired as shorter [1.9959 (9) and 1.9877 (8) Å ] and slightly longer [2.0115 (9) and 2.0245 (9) Å ], indicating an anisobidentate nature of the ligand whereby the shorter P-S bond has more double-bond character than the other. The S-Pb-S (chelating) bond angles range from 71.841 (18) to 72.692 (19) , whilst the Pb-S-P bond angles range from 84.70 (3) to 90.51 (3) .

Experimental
Crystal data [Pb(C 11  The title complex exhibits a structure that is built up of distorted square pyramids in dimeric pairs. The dimeric pair is characterised by intermolecular interactions between the Pb atom of one monomer with a S atom of adjacent unit, containing a Pb···S distance of 3.619 Å. Similar intermolecular interactions occur between the Pb atom of one monomeric unit and four carbon atoms in an adjacent aromatic ring in the Pb-Ar (Ar = aromatic ring) bond distance range of 3.421-3.597 Å. A related structure with a different alkoxy group was previously reported (Gray et al., 2004), showing similar inter Pb···S and Pb···Ar interactions, and intermolecular Pb-S bond lenghts. It was postulated that the aforementioned Pb···Ar interactions stabilized the dimeric structure. The structure reported by Gray et al. (2004) adopts a similar molecular unit, the lead also resides in the centre of a distorted pyramid, 1.30 Å above the basal S 4 plane. General and convenient methods to prepare dithiophosphonate salt derivatives have been reported (Van Zyl & Fackler, 2000).

Experimental
A colorless methanol (40 ml) solution of NH 4 [S 2 P(O i Pr)(4-C 6 H 4 OEt)] (1.010 g, 3.443 mmol) was prepared. Another solution of Pb(NO 3 ) 2 (0.570 g, 1.721 mmol) in deionized water (20 ml) was prepared, and added to the colorless solution with stirring over a period of 5 min. This resulted in a white precipitate, which proved to be the formation of the title complex. The precipitate was collected by vacuum filtration, washed with water (3 x 10 ml) and allowed to dry under vacuum for a period of 3 hrs, yielding a dry, free-flowing white powder. Colorless crystals suitable for X-ray analysis were grown by the slow diffusion of hexane into a dichloromethane solution of the title complex. Yield: 0.926 g, 71%.

Refinement
All non-hydrogen atoms were refined anisotropically. All hydrogen atoms were placed in idealized positions and refined with geometrical constraints and constrained to ride on their parent atoms, with C-H = 0.95-1 00 Å,and U iso (H aryl ) = 1.2×U eq C aryl and U iso (H methyl ) = 1.5×U eq C methyl .

Figure 1
The molecular structure of the title complex with displacement ellipsoids shown at the 50% probability level. H-atoms have been omitted for clarity.

Bis[O-isopropyl (4-ethoxyphenyl)dithiophosphonato-κ 2 S,S′]lead(II)
Crystal data [Pb(C 11   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 R-factors(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.