Bis[μ-O-isopropyl (4-ethoxyphenyl)dithiophosphonato-κ2 S:S′]bis{[O-isopropyl (4-ethoxyphenyl)dithiophosphonato-κ2 S,S′]mercury(II)}

The title compound, [Hg2(C11H16O2PS2)4], is a dinuclear complex with a distorted tetrahedral geometry around each HgII atom. Although the two HgII atoms are surrounded by the same ligand, two different coordination modes are observed: one is chelating and the other bridging. The Hg—S bonds form two distinct pairs of long and short bonds. One pair includes both chelating and bridging Hg—S bonds with approximately equal bond lengths of 2.4042 (8) and 2.3997 (7) Å, respectively. The other pair is significantly longer at 2.9361 (9) and 2.8105 (8) Å, respectively. This pattern forms a center of inversion through the molecule with an equal and opposite effect occurring at the other HgII atom. The S—Hg—S angles vary widely from 76.26 (2) to 154.65 (3)°, indicative of a distorted tetrahedral arrangement of the S atoms around the HgII atom. The P—S bond lengths are 1.9681 (10) and 2.0519 (11)°, clearly indicating partial double-bond character in the former. The molecule contains an inversion center situated between the two HgII atoms.


Related literature
For information on dithiophosphonate compounds, see: Van Zyl & Fackler (2000); Van Zyl (2010). For examples of mercury(II) dithiophosphonate complexes, see: Gray et al. General and convenient methods to prepare dithiophosphonate salt derivatives have been reported (Van Zyl & Fackler, 2000). The title complex was formed through the reaction between two Hg 2+ cations and four [S 2 P(4-C 6 H 4 OEt)(O i Pr)]¯ ligands, the formed complex feature an 8-membered Hg 2 P 2 S 4 metallo-ring. Two of the ligands bind in a chelating manner and two ligands bind in a bridging manner, both types are anisobidentate, however, due to short and long pairings of the P -S bond and especially the Hg-S bonds.

Experimental
A colorless methanol (40 ml) solution of NH 4 [S 2 P(O i Pr)(4-C 6 H 4 OEt)] (1.322 g, 4.506 mmol) was prepared. A second colorless solution of Hg(NO 3 ) 2 .H 2 0 (0.772 g, 2.253 mmol) in deionized water (20 ml) was prepared, and added to the ligand solution with stirring over a period of 5 min. This resulted in a white precipitate indicating the formation of the title complex. The precipitate was collected by vacuum filtration, washed with water (3 x 10 ml) to remove NH 4 NO 3 and allowed to dry under vacuum for a period of 3 hrs, yielding a dry, free-flowing white powder. Colourless crystals suitable for X-ray analysis were grown by the slow diffusion of hexane into a dichloromethane solution of the title complex.

Refinement
All hydrogen atoms were placed in idealized positions and refined with geometrical constraints and U eq of 1.20-1.50 of parent C atom.. The structure was refined to R factor of 0.0227.

Figure 1
The ORTEP molecular structure of the title complex, shown with 50% probability.

Bis[µ-O-isopropyl (4-ethoxyphenyl)dithiophosphonato-κ 2 S:S′]bis{[O-isopropyl (4ethoxyphenyl)dithiophosphonato-κ 2 S,S′]mercury(II)}
Special details Geometry. All e.s.d.'s (except the e.s.d. in the dihedral angle between two l.s. planes) are estimated using the full covariance matrix. The cell e.s.d.'s are taken into account individually in the estimation of e.s.d.'s in distances, angles and torsion angles; correlations between e.s.d.'s in cell parameters are only used when they are defined by crystal symmetry. An approximate (isotropic) treatment of cell e.s.d.'s is used for estimating e.s.d.'s involving l.s. planes. 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.