In situ complexation of 8-hydroxyquinoline and 4,4′-bipyridine with zinc(II) in the interlayer space of montmorillonite

A series of mixed-ligand zinc complexes was prepared by coordination of 8-hydroxyquinoline and 4,4′-bipyridine to interlayer zinc(II) ion of montmorillonite through solid–solid reactions at room temperature. The intercalation of the ligands and the in situ formation of the mixed-ligand zinc complexes in the interlayer spaces of montmorillonite were confirmed by powder XRD, TG-DTA, as well as FT-IR, UV-Vis and photoluminescence spectroscopies. The intense photoluminescence of zinc(8-hydroxyquinoline)(4,4′-bipyridine)-montmorillonite hybrids appeared at 503 nm while photoluminescence of zinc(4,4′-bipyridine)(8-hydroxyquinoline)-montmorillonite hybrids was seen at 511 nm. The blue- and red-shifts of the luminescent bands of the hybrids compared with that of zinc(8-hydroxyquinoline)2-montmorillonite (506 nm) suggested that the different types and/or microstructure of the mixed-ligand zinc complexes formed in the interlayer spaces of montmorillonite. The photoluminescence intensities of the as-prepared mixed-ligand zinc complexes in montmorillonite decreased in the order of zinc(8-hydroxyquinoline)(4,4′-bipyridine)2-montmorillonite > zinc(8-hydroxyquinoline)(4,4′-bipyridine)-montmorillonite > zinc(4,4′-bipyridine)(8-hydroxyquinoline)2-montmorillonite > zinc(4,4′-bipyridine)(8-hydroxyquinoline)-montmorillonite > zinc(8-hydroxyquinoline)-montmorillonite. The sequence of ligand loading affected the molecular structure and/or packing of the formed complex to control the photoluminescence efficiencies of the hybrids.