Syntheses and structures of chiral tri- and tetranuclear Cd(II) clusters with luminescent and ferroelectric properties

Abstract

Two couples of chiral tri- and tetranuclear Cd(II) clusters, namely [Cd4(S-L1)6]·(ClO4)2 (1) and [Cd4(R-L1)6]·(ClO4)2 (2), and [Cd3(S-L2)4]·(ClO4)2 (3) and [Cd3(R-L2)4]·(ClO4)2 (4) (L1=1-(1-(2-pyridine)-ethylimino)-2-naphtho, L2=2-(1-(2-pyridine)-ethylimino)-5-bromo-6-methoxy-pheno) have been synthesized via the solution reaction of chiral Schiff-base ligands with Cd(ClO4)2·6H2O, and characterized by single-crystal X-ray analyses, IR and circular dichroism (CD) spectra. Complexes 1 and 2 are a couple of tetranuclear Cd(II) complex enantiomers crystallized in the chiral space group P4222, and 3 and 4 are also a couple of trinuclear Cd(II) complex enantiomers crystallized in another chiral space group P21. The CD measurements further confirmed that 1–2, and 3–4 are a pair of enantiomers with Cotton effects of the opposite sign at the same wavelengths, respectively. The strong solid-state fluorescence emissions were observed at around 465nm for 1 and 2, and 485nm for 3 and 4, respectively. Furthermore, complex 3 exhibits a ferroelectric behavior related to the polar point group C2.