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

Two new polynuclear complexes of Cu(II), [(CuL1)Cu(N3C2)2]n (1) and [(CuL2)2Cu(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 μ1,5-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+.

Graphical abstractThe synthesis, crystal structure and electrochemical properties of two polynuclear copper(II) complexes, [(CuL1)Cu(N3C2)2]n (1) and [(CuL2)2Cu(N3C2)2]·H2O (2), obtained from two different di-Schiff base ligands, H2L1 = N,N′-bis(salicylidene)-1,3-propanediamine and H2L2 = N,N′-bis(α-methylsalicylidene)-1,3-propanediamine, are reported. Complex 1 is a 2D coordination polymer with a μ1,5-dicyanamido bridge and complex 2 is a rare type of bent trinuclear species with terminally coordinated dicyanamide co-ligands.Figure optionsDownload full-size imageDownload as PowerPoint slideHighlights► Synthesis and crystal structure of two Cu(II) complexes with a di-Schiff base and dicyanamide as ligands. ► Complex 1 is a 2D coordination polymer formed by a μ1,5-dicyanamido bridge. ► Complex 2 is a rare type of bent trinuclear complex containing a terminal dicyanamide ligand. ► Both compounds exhibit irreversible reductive and quasi-reversible oxidative responses in cyclic voltammetry.