Synthesis, Crystal Structures, and Solid-State Luminescent Properties of Diverse Ln–Pyridine-3,5-Dicarboxylate Coordination Polymers Modulated by the Ancillary Ligand

Nine members of the novel Ln–pyridine-3,5-dicarboxylate
coordination polymer family, namely, [Ln­(PDC)­(GA)]n (Ln = Gd (1), Tb (2),
Dy (3), Er (4)), [Ln­(PDC)­(OAc)­(H2O)]n·nH2O (Ln = Sm (5), Eu (6), Gd (7)), [Gd­(PDC)­(OAc)­(H2O)2]n·nH2O (8), and [Tb­(PDC)1.5­(H2O)]n (9) (PDC = pyridine-3,5-dicarboxylate,
GA = glycolate, OAc = acetate), have been successfully obtained by
carefully regulating the ancillary ligand or reaction temperatures.
Complexes 1–4 are isomorphous two-dimensional
networks generated by Ln–glycolate chains and bridging PDC
ligands. When the HOAc was utilized instead of glycolic acid, isomorphic
three-dimensional compounds 5–7 were
isolated. The Ln3+ atoms are first bridged by acetate anions
to give dinuclear clusters, which are extended by nearby six PDC ligands
forming a 3D (3,6)-connected flu-topological framework.
Notably, the increase of reaction temperature from 160 to 180 °C
during the synthesis of compound 7 led to compound 8, the other 3D (3,6)-connected structure on the base of dinuclear
subunits with rtl topology. Furthermore, the absence
of HOAc introduced the formation of compound 9, in which
each binuclear cluster links adjacent eight PDC anions to give a 3D
(3,8)-connected tfz-d topological structure. The
elemental analyses, XRPD, FT-IR, and TGA were also investigated to
characterize compounds 1–9. Furthermore,
solid-state photoluminescence measurements show that these Ln–pyridine-3,5-dicarboxylate
coordination polymers produce strong emissions at room temperature.