Synthesis, structure and property of diorganotin complexes with chiral N-(5-chlorosalicylidene)valinate ligand

Abstract

Six new diorganotin N-[(5-chloro-2-oxyphenyl)methylene]valinates, R2SnL (R = Me, 1; Et, 2; L = 5-Cl-2-OC6H3CH = NCH(i-Pr)COO: (S)-, a; (R)-, b; (RS)-, c), have been synthesized from the reaction of R2SnCl2 with the chiral ligand KHL (potassium salt of HL) in different solvents and characterized by elemental analysis, IR, NMR (1H, 13C and 119Sn) spectra. In benzene, the configuration of the chiral ligand was retained. (S)-Enantiomers (1a and 2a) and (R)-enantiomers (1b and 2b) display discrete molecular structures with distorted trigonal bipyramidal geometries in which two C atoms of organic groups (R) and the imino N atom occupy the equatorial positions and a phenoxide O and an unidentate carboxylate group O atom are in the axial orientation. In the methanol, the chiral ligand was racemized. 1c⋅MeOH is a centrosymmetric dimers formed by (R)- and (S)- enantiomers through two SnO⋅⋅⋅Sn bridges. The coordination geometry of the Sn atom can be described as a distorted pentagonal bipyramid with two methyl groups in axial positions. The crystal of 2c is composed of two threefold symmetric trimers, a [Et2SnL-(R)]3 and a [Et2SnL-(S)]3, with a macrocyclic 12-membered ring structure formed by the bidenate bridging coordination of carboxylate group to tin atoms. Each tin atom is six-coordinated in distorted [SnC2NO3] octahedron geometry. The fluorescence properties of ligand KHL and complexes 1 (1a-1c) and 2 (2a-2c) have been measured. The results show the complexes may be explored for potential luminescent materials.