Flexible cofacial binuclear metal complexes derived from α,α-bis(salicylimino)-m-xylene

Abstract

The tetradentate Schiff-base ligand SIXH₂ (α,α-bis(salicylimino)-m-xylene), prepared from salicylaldehyde and m-xylylenediamine, forms cofacial binuclear complexes with Pd and Cu. Of the two isomers possible (trans-syn and trans-anti) for M₂(SIX)₂, these complexes crystallize exclusively as the trans-anti isomer. In ansolvous Pd₂(SIX)₂, the metal-containing planes are approximately parallel, with Pd⋯Pd 4.416(1) Å. Pd₂(SIX)₂ also forms a crystalline solvate, in which the molecules adopt a more open conformation with longer metal–metal distances (5.109(1) and 5.112(1) Å). The M⋯M distance is significantly longer in Cu₂(SIX)₂ (6.653(1) Å), because of conformational changes in the m-xylylene moieties and substantial tetrahedral distortion about Cu.