Metal complexes with a chiral N4 symmetrical Schiff base. Crystal structures of the ligand and its Cu(ii) and Ni(ii) “mono-helicates”

Abstract

The N₄ Schiff base ligand N,N′-bis(2-tosylaminobenzylidene)-1,2-diaminocyclohexane (H₂cyTs) and its divalent metal (Fe, Co, Ni, Cu, Zn and Cd) complexes have been prepared. Of these compounds only Zn(trans-cyTs)·3H₂O can be considered as blue luminescent (λ = 435 nm, ϕ = 0, 12). Either demetallation or the absence of the tosyl groups, results in a loss of fluorescence. The X-ray crystal structures of a diastereoisomeric mixture of H₂cyTs and its (1R,2R)-enantiomer, as well as those corresponding to Cu(trans-cyTs)·MeCN and Ni(trans-cyTs)·MeCN have been solved. The Cu(II) and Ni(II) ions assume tetrahedrally distorted square planar coordination geometries, involving the four donor N-atoms of the dianionic ligand. The spatial disposition of both tosyl groups prevents global consideration as an usual symmetric helicand.