Synthesis and Characterization of Mercury(Ii) Complexes Containing Mixed Ligands of Mono or Diphosphines and Saccharinate

Introduction

Saccharin{o-sulfobenzimide; 1,2-benzothiazol-3(2H)-one-1,1-dioxide; Hsac}, most widely used as an artificial sweetening agent Interaction of saccharin. with different biologically relevant cations attracted great interest due to the suspected carcinogenicity of this compound [1-3] which was definitively ruled out in 2001      [3-4]. Saccharin ligand has three potential donor sites, it is not expected to use all three towards the same metal because of geometrical constraints. It is therefore likely to acts as a monodentate or a bidentate . Metal Complexes of this ligand with transition and non transition metals have been studied extensively these have been comprehensively revied [5] and a large number of papers published every year in this field. Saccharinate interacts with some heavy non.-transition metal cations such as Cd(II) and Hg(II) to yield of [Cd(sac)₂(H₂O)₂].2H₂O. [6] and [Hg(sac)₂] [7] respectively. Mixed ligands Hg(II) complexes containing saccharinato and nitrogen donor ligands have been reported [8-14]. However mixed ligand complexes of Hg(II) with saccharin and mono or diphosphine seems to be unexplored although such mixed ligand complexeshave been reported for some other transition metals [15-17] We expect that mixed ligands complexes of tertiary phosphines and saccharin to be an important class of complexes and exhibit synergic effect attributed to the mixed ligands.

In the present paper we report the synthesis and characterization of some mercury(II) complexes containing mixed ligands, tertiary, mono or diphosphines and saccharin.

Experimental

General

The experimental techniques were the same as those used in our recent paper from this laboratory [18].

Starting materials

The compounds HgCl₂, Hg(OAc)₂, dppm, dppe, dppp, dppb, PPh₃ and Nasac were commercial products and were used as supplied. The compounds [HgCl(sac)] and [Hg(sac)₂] were prepared according to literature methods [19,20].

Preparation of complexes

[HgCl(Sac)(dppm)]₂(1)

A solution of dppm (0.07g, 1.9 mmol.) in warm EtOH (7ml) was added to a suspension of  [Hg(sac)Cl] (0.08g, 1.9 mmol.)  in hot EtOH (10ml). The mixture was stirred at room temperature for 1h.  The pale white solid thus formed was filtered off washed with EtOH, dried under vacuum (yield 67%).The following complexes were prepared and isolated by a similar method; (2),(3) and (4).

[Hg(sac)₂(dppm)] (5)

A solution of dppm (0.05g, 0.1 mmol.) in warm EtOH (7ml) was added to a suspension of  [Hg(sac)₂] (0.08g, 0.1 mmol.)  in hot EtOH (7ml). The resulting clear solution was filtered off and evaporated. The pale white solid thus formed was filtered off washed with EtOH, dried under vacuum and recrystalized from DMSO, (yield 95%)

[Hg(sac)₂(dppe)] (6)

A solution of dppe (0.07g, 0.18 mmol.) in warm EtOH (7ml) was added to a suspension of  [Hg(sac)₂] (0.1g, 0.18 mmol.)  in hot EtOH (10ml). The mixture was stirred at room temperature for 1h. The pale white solid thus formed was filtered off washed with EtOH, dried under vacuum (yield 66%). The following complexes were prepared and isolated by a similar method; (7) and (8).

[Hg(sac)₂(dppe)₂] (9)

A solution of dppe (0.079g, 0.17 mmol.) in warm EtOH (10ml) was added to a suspension of  [Hg(sac)₂] (0.059g, 0.088 mmol.)  in hot EtOH (10ml). The resulting clear solution was filtered off and evaporated to near dryness. n-Hexane (10ml) was added, The pale white solid thus formed was filtered off washed with EtOH, dried under vacuum (yield 89%). The following complexes were prepared and isolated by a similar method; (10), (11) and (12).

Table 1: Color, Yield, Elemental analysis and conductivity of complexes (1) – (12)

 

Infrared spectra

Selected infrared spectroscopic data of the prepared complexes (1)–(12) are listed in Table2. All complexes display a sharp strong bands between (1620-1697cm^-1) attributed to the u(C=O) of the saccharin ligand coordinated as monodentate though the nitrogen atom [29,30]. Two strong bonds at around (1240-1294) and (1147-1153cm^-1) are characteristic for the u_as SO₂ and u_s SO₂ modes of sac, respectively. Whereas the bands at ca. (1325-1342) and (949-968cm^-1) are assigned to the symmetric and asymmetric stretching of the CNS moiety in the sac ion. Additional bands between 332-352cm^-1 assigned to u(P-C).The u(C-H) aliphatic appeared at ca. 2906-2935cm^-1 while the u(C-H) aromatic appeared at ca. 3051-3059cm^-1.

Conclusion

In summery reaction of the linear mercury(II) complex [HgCl(sac)] with mono or diphosphine resulted in the formation of tetrahedral complexes of the type [HgCl(sac)(diphos)]. Reaction of  [Hg(sac)₂] with one mole equivalent of diphos. gave tetrahedral complexes of the type [Hg(sac)₂(diphos)] while reaction with two mole equivalent gave octahedral complexes of the type [Hg(sac)₂(diphos)₂].

Acknowledgment

We would like to thank the nmr department Institute for Anorganische Chemic, Martin- luther- University, Halle, Germany for measuring the nmr spectra.

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