Phosphonates containing 8-hydroxyquinoline moiety and their metal complexes: structures, fluorescent and magnetic properties

Abstract

Two kinds of solid-state structures of 5-phosphonomethyl-8-hydroxyquinoline (5pm8hqH₃) have been obtained, namely 1·HCl·H₂O and 1·H₂O, involving different hydrogen bonds and/or aromatic stacking interactions. As a derivative of 5pm8hqH₃, 5-phosphonomethyl-8-(carboxymethoxy)quinoline (5pm8cmoqH₃) was synthesized. Based on 5pm8hqH₃ and 5pm8cmoqH₃, three new metal phosphonates have been hydrothermally prepared, including Zn(5pm8hqH)(H₂O)·H₂O (2), Cu(5pm8cmoqH)·2H₂O (3) and Fe(5pm8cmoqH) (4), exhibiting layered structures for 2 and 4, and a three-dimensional open framework for 3. The 8-hydroxyquinoline moieties in 1·H₂O and 2–4 exhibit three kinds of interesting aromatic stacking modes, including pyridine ring–pyridine ring stacking between a pair of moieties, double benzene ring–pyridine ring stacking between a pair of moieties and alternating benzene ring–benzene ring and pyridine ring–pyridine ring stacking among a number of moieties in the layered structure. The solid-state fluorescence measurements indicate the emissions of 1·HCl·H₂O and 1·H₂O are significantly different due to their distinct packing structures. Compound 2 exhibits both ligand-centered (LC) and ligand-to-metal charge transition (LMCT) emissions. Magnetic studies reveal dominant antiferromagnetic interactions in 3 and 4.