Synthesis, structure and spectroscopic studies on hydroxo-bridged heterotrinuclear complexes of cobalt(III) with ethane-1,2-diamine and ammonia as terminal ligands

Abstract

Hydroxo-bridged homo- and hetero-trinuclear cobalt(III) complexes of the type [M^II(H₂O)₂{(OH)₂Co^III(N₄)}₂]X₂·nH₂O [M^II= a divalent metal ion such as Co^II, Ni^II or Zn^II; N₄=(en)₂(en = ethane-1,2-diamine) or (NH₃)₄; X = SO₄ or (ClO₄)₂; n= 3 or 5] have been prepared and spectroscopically characterized. The structure of [Cu{(OH)₂Co(en)₂}₂][SO₄]₂·2H₂O 1 has been determined. The geometry around copper atom is a pseudo-square-based pyramid, with the basal sites occupied by four bridging hydroxide oxygens and the apical site is occupied by a weakly co-ordinated sulfate anion [Cu–O 2.516(4)Å]. The hydroxo groups bridge pairs of cobalt(III) ions which are in near-octahedral environments. The ethylenediamine chelate rings have the twist conformation. In the crystal structure of [Cu{(OH)₂Co(en)₂}₂][ClO₄]₄·2H₂O 2 the perchlorate ion is not co-ordinated and the en ligands have ‘envelope’ conformations. The sulfate ion in [Cu{(OH)₂Co(NH₃)₄}₂][SO₄]₂·4H₂O 3 is not co-ordinated to the central copper ion. Electronic, infrared and variable-temperature EPR spectral data are discussed.