Structural diversity in the complexes based on a hetero-trimetallic Cu₂Cd node and dicyanamide spacer: a hexanuclear cluster, a 1D stair polymer and a 1D zigzag chain as supramolecular isomers, and a 3D network

Abstract

Four new hetero-metallic copper(II)–cadmium(II) complexes [{(CuL)₂Cd}₂ (μ_1,5-N(CN) ₂)₂](ClO₄)₂•(H₂O) ₂ (1), {[{(CuL) ₂Cd}₂ (μ_1,3,5-N(CN) ₂)₂](ClO₄)₂}_n (2), {[(CuL) ₂Cd(μ_1,5-N(CN) ₂)](ClO₄)}_n (3) and [(CuL) ₂Cd(μ_1,5-N(CN) ₂)₂]_n (4) have been synthesized using a trinuclear hetero-metallic node, [(CuL) ₂Cd]²⁺ (where H₂L = N,N′-bis(salicylidene)-1,3-propanediamine) and a dicyanamido spacer by varying the ratios of the reactants and temperature. The hetero-trinuclear node is formed in situ by the reaction of the “metalloligand” [CuL], cadmium perchlorate and sodium dicyanamide. All the complexes are structurally characterized. Complex 1 is a discrete hexanuclear cluster where two trinuclear nodes are connected through the Cd centres by convergent double μ_1,5-dicyanamido spacers. Complex 2 is a 1D stair coordination polymer, in which the hexanuclear units are joined by the coordination of the central nitrogen atom of a μ_1,3,5-dicyanamido ligand to the Cu atom of another unit. In contrast, complex 3 is a 1D zigzag chain, formed by connecting the Cd centre of trinuclear nodes via divergent μ_l,5-dicyanamido spacers. These three complexes contain a common [(CuL) ₂Cd(N(CN) ₂)]ClO₄ trinuclear unit as the molecular building block. They represent an example of “supramolecular isomerism” of 0D/1D coordination polymers. On the other hand, replacement of the perchlorate ions from this trinuclear unit by another dicyanamido spacer results in complex 4, which is a 3D network, constructed by joining the trinuclear nodes through both Cd and Cu centers with the help of divergent dicyanamido spacers in the μ_l,5 mode.