Homochiral coordination polymers of Zn(II) and Pb(II) with interesting three-dimensional helicates

Abstract

Based on a designed enantiomerically pure chiral ligand H3L, two interesting homochiral metal−organic frameworks (HMOFs), namely {[Zn3(L)2(H2O)2]∙2H2O}n (1) and {[Pb(HL)(H2O)]∙H2O}n (2), have been solvothermally synthesized (H3L = (S)-4'-(((1-carboxyethyl)amino)methyl)-[1,1′-biphenyl]-3,5-dicarboxylic acid). Complexes 1 and 2 are novel three-dimensional metal−organic helicates with different structural motifs. In 1, anionic (L)3− ligands bridge trimetallic Zn-clusters to form a [3,6]-connected architecture of (63)2(612·83) topology. In particular, each trimetallic Zn-cluster is the node of six strand 21 helical chains consisting of four right-handed helical chains and two left-handed helical chains. In 2, zwitterionic (HL)2− ligands link PbII ions into a 3-connected 103-topological helicate composed of 21 helical chains extending along three crystal axes, and two thirds of which are left-handed. Interesting enough, the chiral ligand H3L not only transferred its inherent chirality to the synthesized complexes 1 and 2, but also induced unexpected helical chirality. Furthermore, the morphologies, thermal stabilities and solid-state optical properties including CD spectra, and nonlinear optical and luminescent properties of compounds 1 and 2 were also carried out. Compounds 1 and 2 exhibit interesting fluorescence emissions and obvious second-order nonlinear activity in addition to the excellent thermal stability of their dehydrated frameworks, indicating that the HMOF materials have great potential in optical devices.