Copper co-ordination to thioether ligands. Chemical, spectroscopic, and crystallographic studies on copper(I) complexes of 2-(3,3-dimethyl-2-thiabutyl)pyridine and the 2-(3,3-dimethyl-2-thiabutyl)pyridinium cation

Abstract

The ligand 2-(3,3-dimethyl-2-thiabutyl)pyridine (L) and its protonated cation, 2-(3,3-dimethyl-2-thiabutyl)-pyridinium ion (LH⁺), have been used to prepare the copper(I) complexes [CuL_nBr](n= 1 or 2) and [Cu(LH)X₂](X = Cl or Br). Electronic and i.r. spectroscopic data for these complexes are presented, and the chemical relationships between them discussed. The crystal and molecular structures of [CuL₂Br] and [{Cu(LH)Br₂}₂] have been determined by single-crystal X-ray diffraction techniques, from diffractometer data. Crystals of [CuL₂Br] are monoclinic, space group P2₁/n, with a= 16.927(3), b= 8.867(1), c= 15.371(2)Å, β= 100.61(1)°, and Z= 4. Crystals of [{Cu(LH)Br₂}₂] are also monoclinic, space group P2₁/n, with a= 15.700(3), b= 9.038(3), c= 9.926(2)Å, β= 98.66(1)°, and Z= 2. After full-matrix least-squares refinement final R values are 0.066 (for 2 032 observed reflections) and 0.047 (for 1 538 observed reflections) respectively. The complex [CuL₂Br] is monomeric, the distorted tetrahedral geometry round the copper atom being completed by a bromide ion [Cu–Br 2.424(2)Å], the pyridyl nitrogen and thioether sulphur of a bidentate ligand L [Cu–N 2.109(9), Cu–S 2.357(3)Å], and the thioether sulphur of a unidentate ligand L [Cu–S 2.310(3)Å]. The complex [{Cu(LH)Br₂}₂] exists as a centrosymmetric dimer with the distorted tetrahedral copper(I) centres dibromo-bridged [Cu–Br 2.597(1)Å]. The two remaining co-ordination positions round each copper are occupied by a terminal bromide ion [Cu–Br 2.363(1)Å] and the thioether sulphur [Cu–S 2.276(2)Å] of an LH⁺ cation.