L- and d-[Ln(HCO2)(SO4)(H2O)]n (Ln = La, Ce, Pr, Nd, and Eu): Chiral Enantiomerically 3D Architectures Constructed by Double −[Ln–O]n– Helices

Abstract

A total of 10 three-dimensional chiral coordination compounds L- and D-[Ln(HCO(2))(SO(4))(H(2)O)](n) (Ln = La, Ce, Pr, Nd, and Eu) have been synthesized without any chiral auxiliary and characterized by IR, thermogravimetric, and elemental analyses. Their structures were determined by single-crystal X-ray structural analysis, which shows that L-[Ln(HCO(2))(SO(4))(H(2)O)](n) (Ln = La, Ce, Pr, Nd, and Eu) crystallize in space group P4(3) and are laevogyrate and isostructural. The chiral frameworks of L-[Ln(HCO(2))(SO(4))(H(2)O)](n) are constructed from L-helical Ln-O cluster chains, while adjacent L-type helical -[Ln-O](n)- chains are connected through O-Ln-O linkages to form chiral intertwined Ln-O double helices of left-handedness. D-[Ln(HCO(2))(SO(4))(H(2)O)](n) crystallize in space group P4(1), and their chiral frameworks consist of D-helical Ln-O cluster chains. The observed second-harmonic-generation efficiencies of [La(HCO(2))(SO(4))(H(2)O)](n), Ce(HCO(2))(SO(4))(H(2)O)](n), [Pr(HCO(2))(SO(4))(H(2)O)](n), [Nd(HCO(2))(SO(4))(H(2)O)](n), and [Eu(HCO(2))(SO(4))(H(2)O)](n) are 0.7, 0.8, 0.7, 0.5, and 0.7 times that of urea, respectively. It is particularly interesting that [Pr(HCO(2))(SO(4))(H(2)O)](n) shows good two-photon absorption.