Synthesis and characterization of trinuclear Schiff-base complexes containing sulphur dioxide or hydrogensulphite ions as bridging groups. Crystal structure of [Zn{(µ-CH3CO2)(salpd-µ-O,O′)Cu}2][salpd = propane-1,3-diylbis(salicylideneiminate)]

Abstract

Trinuclear complexes of general formulas [MCu₂(CH₃CO₂)₂(salpd)₂](M = Mg^II, Mn^II, Co^II, Ni^II, Cu^II, or Zn^II) and [MNi₂(CH₃CO₂)₂(salpd)₂](M = Mg^II, Mn^II, Co^II, or Ni^II) were prepared, where H₂salpd represents propene-1,3-diylbis(salicylideneimine). Further reactions of the complexes of the former series with sulphur dioxide yielded [MCu₂(CH₃CO₂SO₂)₂(salpd)₂](M = Mg^II, Mn^II, Co^II, or Ni^II) and [Cu₃(HSO₃)₂(salpd)₂(H₂O)₂]. Cryomagnetic measurements (77.4–295 K) have shown that a weak or negligible antiferromagnetic spin coupling (J=–46 to 0 cm^–1) is operating between the terminal and central metal ions in the complexes except for [Cu₃(HSO₃)(salpd)₂(H₂O)₂] which showed a strong antiferromagnetic coupling (J=–186 cm^–1) between neighbouring copper(II) ions. X-Ray crystal analysis was carried out for [Zn{(µ-CH₃CO₂)(salpd-µ-O,O′)Cu}₂]. It crystallizes in the monoclinic space group P2₁/a with a= 16.228(5), b= 11.971 (2), c= 9.239(3)Å, β= 100.15(3)°Z= 2, and R=–0.0887. The complex consists of a linear Cu^II–Zn^II–Cu^II trinuclear unit which has an inversion centre. The Cu^II and Zn^II are bridged by the two phenolate oxygens of the salpd and the oxygens of the acetate ion.