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 Ir^III anions are oxidised by chlorine in CCl₄ to red-brown Ir^IV 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 Rh^III 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)Å, 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)Å.