Construction of Mononuclear Macrocyclic and Dinuclear Acyclic Schiff Base Complexes via Cadmium(II)–Ion Template: Synthesis, Characterisation, and Crystal Structures

Abstract Using a metal template approach a series of mono and dinuclear cadmium(II) were synthesized by Schiff base condensation of a pendant armed dialdehyde, i.e. 2-[3-(2-formylphenoxy)-2-hydroxypropoxy] benzaldehyde (PL) with selection of different diamines, diethylenetriamine, dipropylenetriamine, 1,2-diaminopropane and 1,2-diaminoethane. Depending on the nature of the diaminoalkane spacers and metal ion, 1:1 (metal:ligand) macrocyclic (L1OH and L2OH) or 2:1 (metal:ligand) acylic (L3O − and L4O − ) complexes of cadmium(II) were obtained. With the longer spacers diethylenetriamine and dipropylenetriamine ring closure around the cadmium ion was observed and [1+1] macrocyclic Schiff base ligands (L1OH and L2OH) were formed. With the shorter spacers 1,2-diaminopropane and 1,2-diaminoethane ring closure was not observed. Interestingly, the dialdehyde PL reacted with two molecules of diamine, forming intermediate product acyclic Schiff base [1+2] ligands (L3O − and L4O − ) that are coordinated to two cadmium ions to form dinuclear complexes. Crystal structures indicated that the complex [CdL1(NO 3 )]. NO 3 contains a hexadentate macrocyclic ligand and a bidentate NO 3 − anion with an eight-coordinated cadmium in distorted dodecahedron geometry. The molecular structures of the complexes [Cd 2 (L3O)(NO 3 ) 3 (H 2 O)] and [Cd 2 (L4O)(NO 3 ) 3 ], on the other hand, exhibit of two seven-coordinated cadmium centers, which are bridged by the deprotonated hydroxyl group. The coordination geometries of the cadmium ions can be described as a capped trigonal prism and/or capped octahedron.