Combined Effect of Hydrogen Bonding and π···π Stacking Interactions in the Assembly of Indium(III) Metal–Organic Materials: Structure-Directing and Aggregation-Induced Emission Behavior

Abstract

Six novel luminescent materials In(III)-2,3-H2qldc/phen metal–organic assemblies (MOAs), namely, [In2(phen)3Cl6]·CH3CN (In1), [In2(phen)3Cl6]·CH3CN·2H2O (In2), [In2(phen)2Cl6] (In3), [In(3-qlc)2(phen)Cl] (In4), [In(3-qlc)2(2,2′-bipy)Cl]·2H2O (In5) and [In(3-qlc)3(phen)]·H2O (In6) (2,3-H2qldc = quinoline-2,3-dicarboxylic acid; 3-Hqlc = quinoline-3-carboxylic acid, which is formed from the decarboxylation reaction of 2,3-H2qldc; phen = 1,10-phenanthrolin; 2,2′-bipy = 2,2′-bipyridine) have been hydro(solvo)thermally synthesized and characterized by single-crystal X-ray diffraction, infrared (IR), elemental analysis, 1H NMR spectra, and thermogravimetric analysis (TGA). The crystal structures of In1–In6 indicate that the hydrogen bonding and π···π stacking interactions play critical roles in the formation of the extended supramolecular array. In1 displays the rare hexatomic ring 3D (4,5)-connected supramolecular architecture through twofold interpenetrating of 2D cell membrane-like structures. In2 exhibits a 3D 4-connected sra supramolecular architecture. In3 is built from binuclear [In2Cl2] clusters and possesses an interesting 2D (4,4)-connected sql supramolecular network. Due to existing hydrogen bonds forming coplanar dimers, In4 and In5 show more extended π-conjugated system and appear as 3D diamond-like supramolecular architectures with point symbol 66. In6 is coordinated with four almost vertical ligands and further form a 3D diamond-like supramolecular architecture via hydrogen bonding and π···π stacking interactions. Complexes In1–In6 exhibit tunable luminescence with emission maxima containing deep blue, blue, light blue, green, and yellow green at 298 and 77 K both in DMSO solvent and in the solid state. It is worth noting that In4 and In5 exhibit good aggregation-induced emission (AIE) properties in the solid state. Both of them show very weak luminescence in dimethyl sulfoxide (DMSO, good solvent) while their intensity increased enormously by the addition of water (H2O, poor solvent) due to aggregation.