Supramolecular Architecture Modulated by Positional Isomerism: Synthesis, Structure, and Fluorescence Properties of Ionic Systems Containing 1,8-Naphthalimide Derivatives and Tetrahalometallate Anions

Abstract

Tetrahalometallate salts of organic compounds are a class of organic–inorganic hybrid materials formed through electrostatic interactions between the organic cations and inorganic frameworks. In this study, the structures of 13 new tetrahalometallate salts of N-(n-picolinium)-1,8-naphthalimide (n = 2, 3) and three N-(n-picolinium)-1,8-naphthalimide halide salts (n = 2, 3) are reported. The ionic compounds, formed from N-(n-picolinium)-1,8-naphthalimide (n = 2, 3) and divalent metal halides, contain two isolated organic cations and a distorted tetrahalometallate anion in the asymmetric unit, with molecular formula 2(C18H13N2O2)+[MX4]2–, where M = Zn, Co, and Cu and X = Cl and Br, while the reaction of N-(n-picolinium)-1,8-naphthalimide (n = 2, 3) with FeCl3 yields a complex with one organic cation and a [FeCl4]− anion in the asymmetric unit, with molecular formula (C18H13N2O2)+[FeCl4]−. The effect of changing the position of the nitrogen atom in the picolinium cation on the hydrogen bonding pattern, supramolecular assembly, and crystal-packing motif was systematically investigated. Solid-state fluorescence of these ionic compounds reveals that both the metal center and the halido ligands affect the emission intensity and wavelength of the complexes, although no coordination exists between the organic cation and the tetrahalometallate anion. A structure–property relationship is presented.