Synthesis and characterisation of palladium(II) complexes of mixed thioether/oxa ionophores. Crystal structures of [PdCl2([18]aneS2O4)], [Pd([18]aneS2O4)2][PF6]2([18]aneS2O4= 1,4,7,10-tetraoxa-13,16-dithiacyclooctadecane) and [Pd([18]aneS3O3)2][PF6]2([18]aneS3O3= 1,4,7-trioxa-10,13,16-trithiacyclooctadecane)

Abstract

The palladium(II) complexes cis-[PdCl₂([18]aneS₂O₄)], [Pd([18]aneS₂O₄)₂][PF₆]₂([18]aneS₂O₄= 1,4,7,10-tetraoxa-13,16-dithiacyclooctadecane), [Pd([18]aneS₃O₃)₂][PF₆]₂([18]aneS₃O₃= 1,4,7-trioxa-10,13,16-trithiacyclooctadecane) and [PdCl([20]aneS₃O₃)]BPh₄([20]aneS₃O₃= 1,4,7-trioxa-10,14,18-trithiacycloicosane) have been synthesised and characterised. Reaction of PdCl₂ with 1 molar equivalent of [18]aneS₂O₄ afforded cis-[PdCl₂([18]aneS₂O₄)]; addition of a second equivalent gave the bis complex cation [Pd([18]aneS₂O₄)₂]²⁺. The crystal structure of cis-[PdCl₂([18]aneS₂O₄)] showed the Pd^II in a square-planar co-ordination geometry with mutually cis Cl^– ligands, Pd–S(1) 2.276(2), Pd–S(4) 2.2786(14), Pd–Cl(1) 2.307(2), Pd–Cl(2) 2.3100(14)Å, Cl(1)–Pd–Cl(2) 92.12(5), Cl(1)–Pd–S(1) 176.33(5), Cl(1)–Pd–S(4) 87.76(5), Cl(2)–Pd–S(1) 91.19(4) Cl(2)–Pd–S(4) 179.24(4) and S(1)–Pd–S(4) 88.96(4)°. The near-planar macrocycle co-ordinates as a bidentate chelating ligand via the exo oriented S-donor atoms leaving the endo oriented O atoms free. The SCH₂CH₂S moiety adopts a gauche conformation [S(1)–C(2)–C(3)–S(4)–58.3(4)°] with the ethylene bridge occupying part of the macrocyclic cavity. The crystal structure of [Pd([18]aneS₂O₄)₂][PF₆]₂ showed the Pd^II occupying a crystallographic inversion centre, with square-planar co-ordination by the [18]aneS₂O₄ ionophores through the thioether S donors, Pd–S(1) 2.3217(14), Pd–S(4) 2.3102(13)Å and S(1)–Pd–S(4) 88.71(5)°. The conformation of the macrocycle is very similar to that found in cis-[PdCl₂([18]aneS₂O₄)], with the O atoms in endo orientations. Reaction of PdCl₂ with 2 equivalents of [18]aneS₃O₃ afforded [Pd([18]aneS₃O₃)₂][PF₆]₂ which has the Pd^II occupying a crystallographic inversion centre, with square-planar co-ordination by the [18]aneS₃O₃ ligands via two of their three thioether S-donor atoms, Pd–S(1) 2.308(2), Pd–S(4) 2.319(2)Å, S(1)–Pd–S(4) 88.33(8)°. The structure exhibits some disorder in the polyether/thioether chain which was modelled in terms of two half-occupied orientations. In one component of the disorder the third S-donor atom of each ligand exhibits a long-range apical interaction with the Pd^II, Pd ⋯ S(16) 3.290(2)Å. Reaction of PdCl₂ with 1 equivalent of [20]aneS₃O₃ afforded the monocation [PdCl([20]aneS₃O₃)]⁺.