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

Abstract

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 [Cu₂L(CH₃COO)(CH₃OH)](CH₃OH) (1) and [CuHL](CH₃OH) (2), where H₃L is N,N′-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 N,N′-bis(5-methylsalicylidene)-2-hydroxy-1,3-propanediamine (H₃L B) or [CuHL](CH₃OH) (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 [Cu₂L(CH₃COO)(CH₃OH)](CH₃OH) (1), two copper(II) ions are bond to one H₃L 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](CH₃OH) (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 N,N′-bis(5-methylsalicylidene)-2-hydroxy-1,3-propanediamine (H₃L) 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 H₃L and its dinuclear and mononuclear copper(II) complexes were studied by cyclic voltammetry, and their spectroelectrochemical properties were examined.