pH modulated assembly in the mixed-ligand system Cd(ii)–dpstc–phen: structural diversity and luminescent properties

Abstract

Hydrothermal reaction of cadmium salt, 3,3′,4,4′-diphenylsulfonetetracarboxylic acid (H₄dpstc) and 1,10-phenanthroline (phen) under different pH conditions have afforded four novel supramolecular complexes, in which the pH value of the reaction solution plays a crucial structure-directing role. [Cd(H₂dpstc)(phen)]_n (1) formed in a neutral reaction environment exhibits a 1D infinite chain structure containing partially deprotonated H₂dpstc²⁻ as the H-bond donors and acceptors. Whereas [Cd₂(dpstc)(phen)₂]_n·4.5nH₂O (2), [Cd₂(dpstc)(phen)₂]_n·nH₂O (3) and [Cd₂(dpstc)(phen)₄(H₂O)₂]·6H₂O (4) contain fully deprotonated dpstc⁴⁻ ligands due to the alkaline reaction conditions. Complex 2 possesses a unique 2D layered structure with 1D channels. The most striking feature of 2 is that its 2D holed (4,4)-water-net is constructed from hexameric water clusters and two types of dimeric water clusters. Surprisingly, the water net and the metal–organic skeleton are interpenetrated to form a fascinating 3D metal–organic–water supramolecular architecture. A further increase of the pH value leads to another 2D layered framework of 3 containing dumbbell-shaped rings as subunits. Reaction at a strongly alkaline solution leads to a discrete molecule of 4. Meanwhile solid-state properties such as thermal stability and the photoluminescence properties at room temperature for these complexes have also been systematically investigated.