Synthesis, structures and photoluminescence properties of a series of alkaline earth metal-based coordination networks synthesized using thiophene-based linkers

Three new 3-D coordination networks were synthesized using alkaline-earth metal centers, calcium, and strontium, with 2,5-thiophenedicarboxylate (TDC) as the organic linker. [Ca₂(TDC-2H)₂(DMF)₂] _n [1, space group P2₁/n, a = 10.0704(3) Å, b = 14.2521(3) Å, c = 17.5644(6) Å, β = 94.281(2) ] is composed of tetrameric calcium polyhedral clusters, which are connected by the organic linkers. Coordinated DMF molecules are present within the 1-D channel along the [010] direction. [Ca(TDC-2H)]_n [2, space group Pbcm, a = 5.3331(5) Å, b = 6.8981(4) Å, c = 18.141(2) Å] consists of chains of edge-sharing calcium octahedra, connected by organic linkers, to form a dense network. [Sr(TDC-2H)(DMF)]_n [3, space group P2₁/n, a = 5.9795(3) Å, b = 17.058(1) Å, c = 11.3592(6) Å, β = 91.257(1) ] forms a structural topology almost identical to compound 1 except that the chains are built by combinations of edge- and face-sharing polyhedra. Compounds 1 and 3 were synthesized using DMF as solvent, whereas compound 2 crystallizes using ethanol. Photoluminescence studies reveal that the topologies of the networks and the presence of the coordinated solvent molecules control the luminescence properties of the compounds.