Structural variations in polynuclear copper (II) complexes based on salicylaldimine type ligands along with dicyanamido co-ligand

Abstract

Two new polynuclear complexes of Cu(II), [(CuL¹)Cu(N₃C₂)₂]_n (1) and [(CuL²)₂)Cu(N₃C₂)₂]•H₂O (2), have been synthesized by reacting the “ligand complexes”, [CuL¹] and [CuL²] respectively with copper perchlorate and sodium dicyanamide (NaN₃C₂) in ethanol–water, where the di-Schiff base ligands H₂L¹ = N,N′-bis(salicylidene)-1,3-propanediamine and H₂L² = N,N′-bis(α-methylsalicylidene)-1,3-propanediamine. Structural analysis shows that complex 1 is a 2D polymer formed by linking the dinuclear units through a μ_1,5-dicyanamido bridge. It contains alternating helical chains of P and M types. Complex 2 is a discrete bent trinuclear species where phenoxido groups of two terminal “ligand complexes” coordinate to a central Cu( II) along with terminally coordinated dicyanamido anions. Both complexes exhibit irreversible reductive Cu (II)/Cu (I) and quasi-reversible oxidative Cu (II)/Cu (III) responses in cyclic voltammetry. The electrochemically generated Cu (I) species for both complexes are unstable and undergo disproportionation to Cu0 and Cu²⁺.