Synthesis and characterisation of selenoether macrocyclic complexes of CoIII, RhIII and IrIII: crystal structures of trans-[CoBr2([16]aneSe4)]BPh4 and trans-[IrBr2([16]aneSe4)]BPh4([16]aneSe4= 1,5,9,13-tetraselenacyclohexadecane)

Abstract

Reaction of CoX₂(X = Cl, Br or I) with [16]aneSe₄(1,5,9,13-tetraselenacyclohexadecane) and NH₄PF₆ under a dry oxygen atmosphere yielded the complexes [CoX₂([16]aneSe₄)]PF₆. The rhodium(III) and iridium(III) species [MX₂([16]aneSe₄)]⁺(M = Rh or Ir, X = Cl or Br) were obtained by reaction of MX₃·3H₂O with [16]aneSe₄ in refluxing aqueous ethanol, or for [RhBr₂([16]aneSe₄)]⁺, from [Rh(H₂O)₆]³⁺, LiBr and [16]aneSe₄, and isolated by the addition of either NaBF₄, NH₄PF₆ or NaBPh₄. The compound [RhCl₂([8]aneSe₂)₂]BF₄([8]aneSe₂= 1,5-diselenacyclooctane) was prepared from [{Rh(CO)₂Cl}₂], [8]aneSe₂ and HBF₄ in refluxing aqueous acetone. All complexes were characterised by IR, UV/VIS, ¹H and ⁷⁷Se-{¹H}(and ⁵⁹Co where appropriate) NMR spectroscopies, mass spectrometry and microanalyses. The UV/VIS and ⁵⁹Co NMR spectroscopy on [CoX₂([16]aneSe₄)]⁺ showed that for X = Cl and Br only the trans dihalide species is present (this is supported by ⁷⁷Se-{¹H} NMR data), whereas a mixture of cis and trans forms is present where X = I. The ⁷⁷Se-{¹H} NMR spectroscopic studies on [MX₂([16]aneSe₄)]⁺(M = Rh or Ir, X = Cl or Br) and [RhCl₂([8]aneSe₂)₂]⁺ showed the presence of both the cis and trans forms in dimethylformamide solution, although for [MCl₂([16]aneSe₄)]⁺ only the trans isomer is soluble in MeNO₂. The crystal structures of trans-[MBr₂([16]aneSe₄)]BPh₄(M = Co or Ir) each show endocyclic co-ordination of the metal to all four Se donor atoms of the macrocycle, with the mutually trans bromide ligands completing the distorted octahedron; Co–Br(1) 2.396(1), Co–Se(1) 2.393(1), Co–Se(2) 2.402(1); Ir–Br(1) 2.468(4), Ir–Br(2) 2.483(4), Ir–Se(1) 2.470(3), Ir–Se(2) 2.470(3), Ir–Se(3) 2.461(3), Ir–Se(4) 2.462(3)Å.