Pseudohalide-Controlled Assemblies of Copper-Schiff Base Complexes with an Encapsulated Sodium Ion: Synthesis, Crystal Structure, and Computational Studies

Three new hetero-bimetallic coordination complexes [Na((CuL1)-L-II)(2)](ClO4)center dot 0.5H(2)O (1), [Na((CuL2)-L-II)(2)][Cu-2(I)(mu(1,3)-NCS)(3)](n) (2), and {[Na((CuL3)-L-II)(2)](mu(1,5)-dca)}(n) (3; dca = dicyanamide) have been synthesized by using different Schiff base ligands [e. g., (LH2)-H-1 = N,N'-bis(3-methoxysalicylidenimino)-1,3-diaminopentane, (LH2)-H-2 = N, N'-bis(3-ethoxysalicylidenimino)-1,3-diaminopropane, and (LH2)-H-3 = N,N'-bis(5-bromo-3-methoxysalicylidenimino)- 1,3-diaminopropane] in the presence of pseudohalide coligands N-3(-), SCN-, and N(CN)(2)(-) (dca), respectively. The ligands and the complexes have been characterized by microanalytical and spectroscopic techniques. The structures of the complexes, determined by single-crystal X-ray diffraction studies, show that in all cases a trinuclear Na((CuL)-L-II)(2) unit is formed, but of different configurations. 1 does not include N-3(-) anions. In contrast, in 2, SCN- extrudes partial in situ reduction of Cu-II to lead to the formation of an infinite [Cu-2(I)(mu(1,3)-NCS)(3)](n) anionic chain; and in 3, N(CN)(2)(-) bridges the metal-ligand assemblies to form a 1D polymeric chain. ESI-MS, UV/Vis spectroscopy, and cyclic voltammetry were performed to investigate the solution-state behavior of the complexes. Theoretical calculations of the optimized geometries of the complexes were carried out at the BLYP/DNP level to determine their relative stabilities from the HOMO-LUMO gap and chemical softness values.