Pd(II) complexes with thiacalix[4]-arene and -aniline; subtle, but distinct influences of phenol and aniline units on the 3-D structure

The Pd(II) complexes of thiacalix[4]aniline (TCAn) and thiacalix[4]arene (TCAr), in which four aniline and phenol units are linked by four sulfides at the o,o′-positions, respectively, were prepared by simply heating the ligands with Pd(II)(OAc)₂ in CHCl₃ or benzene at reflux and structurally characterized by X-ray diffraction methods. In TCAn, two thiacalix ligands adopting a pinched-cone conformation are fused at the narrower rims to coordinate to two Pd(II) ions by amide NH^- and the adjacent S atoms. In contrast for TCAr, two ligands coordinate to two Pd(II) ions with phenolate O^- and thioether S atoms at the narrower rims. Four sets of hydrogen bonding between the O^- and free OH cause a deviation of the Pd(II) centers from the square coordination plane and also lead the conformation of the calix to be more cone-like to provide enough space to accommodate guest CH₃CN molecules.