Organoselenium/Tellurium-Bearing Macroacyclic and Cyclic Ligand Systems and Their Complexation Reactions

Abstract

A series of phenol-substituted acyclic Schiff bases, 2,6-{RE(CH₂) _n N═C(CH₃)}₂-C₆H₂(4-CH₃)(OH), (E = Te: R = C₆H₅, n = 2(L _a), 3(L _b); R = C₆H₄-4-OCH₃, n = 2(L _c), 3(L _d); E = Se: R = C₆H₅, n = 2(L _e), 3(L _f)), of the type E₂N₂O have been synthesized by condensation of 2,6-diacetyl-4-methylphenol with arylchalcogenoalkylamines. This ligand framework is useful for designing molecular complexes with a variety of coordination modes depending upon the nature of the central metal atom. The reactivity of the tellurium-bearing macroacyclics ligands towards Zn(II), Cd(II), and Hg(II) has been examined. The ligands L _a?L _d with Zn(II) and Cd(II), and only L _a and L _b with Hg(II) form complexes of composition M₂X₄L, (X = Cl or Br), whereas L _c and L _d with Hg(II) give products of composition HgBr₂L. The modes of ligand interaction with Zn(II) and Cd(II) are different than that with Hg(II).

Following a multistep reaction involving abstraction of bridged Br atoms and subsequent addition of more ligand, the mercury complex, Hg₂Br₄L has been used for developing metallocyclic system of the type Hg₂Br₂L₂]²⁺. The latter has been found to encapsulate Zn(II) and Cd(II) to give multimetallic systems.