A series of 3D lanthanide coordination polymers decorated with a rigid 3,5-pyridinedicarboxylic acid linker: syntheses, structural diversity, DFT study, Hirshfeld surface analysis, luminescence and magnetic properties

Abstract

Single crystal X-ray diffraction studies reveal the formation of six new coordination polymers (CPs) with the general formulas [Dy(3,5-pdc)(3,5-pdcH)(H₂O)₂]_n·nH₂O (1), [Pr₂(3,5-pdc)₃(H₂O)₂]_n·2n(H₂O) (2), [Sm₂(3,5-pdc)₃(H₂O)₃]_n·nH₂O (3), {[Eu₂(3,5-pdc)₃(H₂O)₃(CH₃CHO)]_n·n[2(H₂O)(DMF)]} (4), {[Gd₂(3,5-pdc)₃ (H₂O)₂]_n·2nH₂O} (5) and [Er(3,5-pdc)(adip)_0.5(H₂O)]_n (6) (where 3,5-pdc²⁻ = fully deprotonated; 3,5-pdcH⁻ = partially deprotonated 3,5-pyridinedicarboxylic acid; adip²⁻ = fully deprotonated adipic acid; and DMF = dimethylformamide) by solvothermal self-assembly of lanthanide ions with rigid 3,5-pyridinedicarboxylic acid as a linker and adipic acid as an auxiliary flexible spacer (only coordinated in CP 6). CPs 1 and 2 crystallize in the triclinic P space group, whereas CPs 3, 4 and 6 crystallize in the monoclinic P2₁/n, P2₁/c and C2/c space groups, respectively. CP 5 exhibits the trigonal R3 space group. The 3,5-pdc ligand exhibits eight diverse coordination modes in CPs 1–6, whereas the adipic acid spacer in CP 6 shows only one coordination mode (μ₄–κO:κO,O:κO:κO,O). The organic ligands interconnect with metal ions to generate 3D metal–organic frameworks with a variety of intriguing topologies. Theoretical studies, DFT calculations and Hirshfeld surface analysis support the structures adopted by the various CPs. CPs 3 (Sm) and 4 (Eu) emit strong ligand-sensitized characteristic f–f luminescence. Weak ferromagnetic interactions have been studied at low temperatures for CP 1 and CP 5.