Homochiral zinc phosphonates with layered and open framework structures using polycarboxylate as second linkers

Abstract

Reactions of zinc sulfate and (R)- or (S)-(1-phenylethylamino)methylphosphonic acid (pempH₂) in the presence of 1,4-benzenedicarboxylic acid (H₂bdc) result in homochiral enantiomers (R)- and (S)-[Zn₄(pempH)₄(bdc)₂]·2H₂O (1). When H₂bdc is replaced by 1,2,4,5-benzenetetracarboxylic acid (H₄btec), enantiomers (R)- and (S)-[Zn₃(pempH)₂(btec)(H₂O)₂]·H₂O (2) are obtained. Compounds 1 have a layer structure in which the chiral inorganic double chains, made up of corner-sharing {ZnO₄} and {PO₃C} tetrahedra, are connected by bdc²⁻. While in compounds 2, chiral chains of zinc phosphonate are each connected to their four equivalent neighbors through btec⁴⁻ linkages, resulting in an open framework structure. All these compounds are optically active, exhibiting second harmonic generation (SHG) responses 0.2 or 0.8 times that of urea.