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

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)nH(2)O (1), [Pr-2(3,5-pdc)(3)(H2O)(2)](n)2n(H2O) (2), [Sm-2(3,5-pdc)(3)(H2O)(3)](n)nH(2)O (3), {[Eu-2(3,5-pdc)(3)(H2O)(3)(CH3CHO)](n)n[2(H2O)(DMF)]} (4), {[Gd-2(3,5-pdc)(3) (H2O)(2)](n)2nH(2)O} (5) and [Er(3,5-pdc)(adip)(0.5)(H2O)](n) (6) (where 3,5-pdc(2-) = fully deprotonated; 3,5-pdcH(-) = partially deprotonated 3,5-pyridinedicarboxylic acid; adip(2-) = 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 P1 space group, whereas CPs 3, 4 and 6 crystallize in the monoclinic P2(1)/n, P2(1)/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 ((4)-O:O,O:O:O,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.