Syntheses, crystal structures and optical properties of six homochiral coordination networks based on phenyl acid-amino acids

Abstract

Six homochiral metal–organic coordination networks based on two new phenyl acid-amino acids, [ZnL¹1₂(H₂O)₂] (1), [Cu₂L¹1₂(H₂O)₃] (2), [Zn₂L¹1₂] (3), [CuL²2(H₂O)₂]·2H₂O (4), [ZnL²2] (5) and [Cd₃NaL²2₃(ClO₄)]·3H₂O·DMF (6), where L¹1 = (S)-4-((1-carboxy-2-methylpropylamino)methyl)benzoic acid, and L²2 = (S)-4-((1-carboxy-2-hydroxyethylamino)methyl)benzoic acid, have been synthesized and characterized. Compound 1 is a supramolecular network of hydrogen bondings linking up discrete zinc coordination units, and compound 2 presents a 2D lattice motif of water molecules linking up polymeric chains, while compound 3 is a 3D network constructed of interesting left-hand triple helices. Compound 4 consists of 1D coordination polymeric chains, while compound 5 adopts an intriguing 2D diamondoid network built from two kinds of left-handed helices, and compound 6 is a 3D framework constructed from homochiral cages. In addition, the second-order nonlinear optics (NLO) properties of compounds 1–6 were investigated. Compound 1 has a powder SHG intensity of 3.4 versus a-quartz, and the powder SHG intensities of compounds 2–4 approximate to that of a-quartz, while the powder SHG intensities are 7.8 and 8.4 versus a-quartz for compounds 5 and 6, respectively. Compounds 1, 3, 5 and 6 in the solid state exhibit blue fluorescent emissions at room temperature, mainly attributed to the ligand-centered transitions.