Metal complexes of Schiff bases derived from Thiophen-2-aldehyde

Abstract

A number of metal chelates of NN'-ethylenebis(2-thenylideneimine) (S-N-N-S) are described. The compounds [Cu(S-N-N-S)₂][CuX₂] (X = Cl, Br, I), Pd(S-N-N-S)X₂, (X = Cl, Br, NO₂) and the low-spin complex [Ni(S-N-N-S)₂]- (ClO₄)₂,2H₂O are unaffected by boiling water. On the other hand, the compounds M(S-N-N-S)X₂ (M = Co, Cu, Zn, Cd; X = Cl, Br, I, or NCS), which were prepared from alcoholic solution, are converted slowly in cold and rapidly in hot water into the corresponding metal bisethylenediamine complexes owing to hydrolysis of the coordinated Schiff base. Paramagnetic complexes Ni(S-N-N)₂X₂ (X = Br, I) containing the partially hydrolysed Schiff base N-2-aminoethyl-2'-thenylideneimine (S-N-N) were obtained when solutions of the nickel halides were treated with NN'-ethylenebis(2-thenylideneimine). Evidence is produced to show that in these metal complexes the ligand is coordinated through both nitrogen atoms and that the sulphur atom in the thiophene ring is not coordinated. except possibly in the polymeric palladium complexes. Some metal chelates of NN'-trimethylenebis(2-thenylideneimine) were also isolated. Complexes of palladium(II) and cobalt(11) with NN'-1,2-phenylenebis(2-thenylideneimine) were prepared; in these complexes the Schiff base acts as a unidentate ligand since coordination through both nitrogen atoms would require a gross deformation of the bond angles. Palladium(II) complexes of N-n-propyl-2-pyridylmethyleneimine and NS'-tri-methylenebis(2-thenylideneimine) were also characterized. However, attempts to isolate metal chelates of NN'-ethylenebis(2-pyrrolylmethyleneimine) were unsuccessful.