Multifunctional polythreading coordination polymers: Spontaneous resolution, nonlinear-optic, and ferroelectric properties

The reactions of methylenediisophthalic acid (H₄L) and N-auxiliary ligands (1,2-bis(4-pyridyl)ethylene, 1,2-bis(4-pyridyl)ethane) with transition-metal centers (Co²⁺/Mn²⁺) have given rise to four unprecedented polythreading coordination polymers. Single-crystal X-ray diffraction analyses revealed that the compounds can be described as 3D ^2-2[1D²⁺]+2D^6- for 1, 3D^4-1D ²⁺+1D^6- for 2, and 2D^4-0D ²⁺+2[1D^3-] for 3 and 4. All the polymers are formed through the assembly of two kinds of motifs with opposite charges. Noncentrosymmetric structures and multifunctionality in 2-4 are established by varying ligands and metal centers. Spontaneous resolution upon crystallization occurred in compounds 3 and 4 in the absence of any chiral source. The enantiomers of 3 and 4 consist of three chiral building blocks of L ^4-/HL^3- and Mn²⁺ centers. In the solid state, polar compounds 2-4 exhibit nonlinear-optic (NLO) and ferroelectric properties at room temperature. The assembly of two kinds of motifs with opposite charges provides a useful method for the preparation of multifunctional compounds.