Comprehensively Understanding Isomorphism and Photoluminescent Nature of Two-Dimensional Coordination Polymers of Cd(II) and Mn(II) with 1,1′-Ethynebenzene-3,3′,5,5′-tetracarboxylic Ligand

Four isomorphic two-dimensional (2D) homo- and heterometallic coordination polymers (CPs), [(Cd_xMn_1-x)₃(HEBTC)₂(DMSO)₆] with x = 1 (1), 1/3 (2), 0.5 (3), and 2/3 (4) were prepared by conventional one-pot self-assembly approach, using Cd²⁺ or mixtures of Cd²⁺ and Mn²⁺ with 1,1′-ethynebenzene-3,3′,5,5′-tetracarboxylic (H₄EBTC) under solvothermal conditions. The crystal structures of four isomorphic CPs are composed of center-symmetric trinuclear metal clusters building units linked by HEBTC^3- ligands, extending into (3, 6)-connected topological 2D nets. Four CPs are isomorphic to the Mn-CP, [Mn₃(HEBTC)₂(DMSO)₆], we recently reported. The solid-state photoluminescence of 1-4 shows dual emissions at ambient condition, where the emission bands centered at ca. 390 and 562 nm in 1 are assigned to the fluorescence and phosphorescence within HEBTC^3- ligand, respectively; however, the emission bands centered at around 397 and 470 nm in 2-4 are attributed to fluorescence, corresponding to electron transition within HEBTC^3- ligand and MLCT transition between HEBTC^3- ligand and Mn²⁺ ion. In addition, the origin of isomorphism between 1 and Mn-CP is also discussed.