Coordination properties of ,'-bis(5-methylsalicylidene)-2-hydroxy-1,3-propanediamine with d- and f-electron ions: crystal structure, stability in solution, spectroscopic and spectroelectrochemical studies.

Template reaction between 5-methylsalicylaldehyde and 2-hydroxy-1,3-propanediamine in the presence of copper ion led to dinuclear and mononuclear copper(ii) complexes [CuL(CHCOO)(CHOH)](CHOH) (1) and [CuHL](CHOH) (2), where HL is ,'-bis(5-methylsalicylidene)-2-hydroxy-1,3-propanediamine. The result of the reactions between 5-methylsalicylaldehyde and 2-hydroxy-1,3-propanediamine in the presence of lanthanide ions and/or copper(ii) ion was ,'-bis(5-methylsalicylidene)-2-hydroxy-1,3-propanediamine (HL B) or [CuHL](CHOH) (2), respectively. Structures of the compounds were determined by single-crystal X-ray diffraction and physicochemical methods. The microstructures and phase compositions of crystals were studied by scanning electron microscopy (SEM). In dinuclear complex [CuL(CHCOO)(CHOH)](CHOH) (1), two copper(ii) ions are bond to one HL ligand and one acetate ion. Coordination modes of the two copper centers are different: the geometry of copper 1 is almost ideal square-planar, while that for copper 2 can be described as tetragonal pyramidal. In complex [CuHL](CHOH) (2), the copper(ii) ion is four coordinated and the coordination, rather than square-planar, can be described as flattened tetrahedral. Formation of complexes between copper(ii) or lanthanide ions with ,'-bis(5-methylsalicylidene)-2-hydroxy-1,3-propanediamine (HL) was also studied in solution by pH potentiometry. It should be mentioned that the complexes of lanthanide ions exist only in solution. Additionally, the salen-type ligand HL and its dinuclear and mononuclear copper(ii) complexes were studied by cyclic voltammetry, and their spectroelectrochemical properties were examined.