Co-ordination chemistry of higher oxidation states. Part 18. Bidentate selenoether complexes of the tetravalent platinum metals. Crystal and molecular structure of [Pt{o-C6H4(SeMe)2}Cl4

Abstract

Osmium(IV) complexes [Os(L–L)Cl4][L–L =e.g. MeSe(CH2)nSeMe (n= 2 or 3) or PhSeCH2CH2SePh] have been prepared from [OsCl6]2– and L–L in 2-methoxyethanol. The same ligands and iridium trichloride produce polymeric [{Ir(L–L)Cl3}n], which are converted into [NMe4][Ir(L–L)Cl4] by excess [NMe4]Cl. These IrIII anions are oxidised by chlorine in CCl4 to red-brown IrIV complexes [Ir(L–L)Cl4]. Halogen (X2) oxidation of [Pt(L–L)X2](X = Cl or Br) produces stable [Pt(L–L)X4]. Complexes trans[M(Me2Se)2Cl4](M = Pt, lr, or Os) are also described. Ruthenium(III) complexes, [AsPh4][Ru(MeSeCH2CH2SeMe)Cl4], [{Ru(MeSeCH2CH2SeMe)Cl3}n], and [{Ru2(MeSeCH2CH2SeMe)3Cl6}n] have been prepared, but these, the RhIII analogues, and [Pd(L–L)Cl2] cannot be oxidised to the tetravalent state. The complexes have been characterised by analysis, i.r., u.v.-visible, 1H, 77Se, and 195Pt n.m.r. spectroscopy and magnetic measurements as appropriate. The 77Se n.m.r. spectra of the [Ir(L–L)Cl4]–, [Pt(L–L)X4], [Pt(Me2Se)X5]– and (prepared in situ)[Pd(Me2Se)X5]–(X = Cl or Br) complexes have been recorded and the values of δ(Se) and 1J(PtSe) discussed. The structure of [Pt{o-C6H4(SeMe)2}Cl4] has been determined by a single-crystal X-ray study and shown to be monoclinic, space group P21/n, with a= 7.926(5), b= 14.545(3), c= 12.307(4)A, β= 99.88(4)°, and z= 4. The structure was refined to R= 0.052 from 1 927 reflections. The structure contains discrete six-co-ordinate Pt and the selenium ligand adopts the meso conformation, Pt–Cl 2.299(4)–2.344(4), Pt–Se 2.432(2) and 2.441(1)A.