Structure and luminescence variations in Cd(II) mixed-ligands coordination compounds influenced by coordination modes of naphthalene-1,5-disulfonate and configuration of flexible bis(pyridyl) ligands

Abstract

Hydrothermal reaction of Cd(OAc)2, naphthalene-1,5-disulfonic acid (1,5-H2NDS) and different flexible bis(pyridyl) ligands in water or mixed ethanol–water solution gives rise to the formation of five new Cd(II) coordination compounds, [Cd(L1)2(H2O)2]n·n(1,5-NDS) (1), [Cd(1,5-NDS)(L2)2]n (2), [Cd(HL3)2(H2 O)4]n·2n(1,5-NDS)·2nH2O (3), [Cd(1,5-NDS)(L4)2]n (4) and [Cd(1,5-NDS)(L5)2]n (5) [L1=N-(pyridin-4-ylmethyl)pyridin-3-amine, L2=N-(pyridin-3-ylmethyl)pyridin-3-amine, L3=N-(pyridin-3-ylmethyl) pyridin-2-amine, L4=N,N′-(1,4-phenylenebis(methylene))bis(pyridin-3-amine), L5=N,N′-(1,3-phenylenebis (methylene))bis(pyridin-3-amine)], which have been characterized by elemental analysis, infrared (IR) spectroscopy, thermogravimetric (TG) analysis, photoluminescence (PL) spectroscopy, powder and single-crystal X-ray diffraction. In compounds 1 and 2, the short bis(pyridyl) ligands L1 and L2 join adjacent Cd(II) cations into “8” shaped chains while the short protonated L3 ligand in compound 3 only coordinates to Cd(II) cation in terminal mode. In contrast, the long bis(pyridyl) ligands L4 and L5 in compounds 4 and 5 connect adjacent Cd(II) cations into 44 layer motifs. The 1,5-NDS2− acts as counter-anions in compounds 1, 3 and bridging anions in compounds 2, 4 and 5, giving rise to diverse supramolecular network (1 and 3), 44 (2) and 36 (4) layers, as well as pcu net (5). Moreover, solid-state luminescent properties demonstrate that compounds 1–5 exhibit strong emissions varying from 387 to 468nm.