From two-dimensional trapezoid-like layer to three-dimensional porous indium-4,4′-biphenyldicarboxylate MOFs

Three new indium coordination polymers formulated as In(phen)(BPDA) _1.5 (1), In(OH)(H₂O)(BPDA) (2), and In(BPDA) ₂·Me₂NH₂·H₂O (3) (phen = 1,10-phenanthroline, C₁₂N₂H₈; H ₂BPDA = 4,4′-biphenyldicarboxylic acid, C₁₄O ₄H₁₀; Me₂NH = dimethylamine, C ₂H₇N), have been synthesized under hydro(solvo)thermal conditions and characterized by infrared (IR), thermal gravimetric analysis (TGA) and luminescence studies. In the two-dimensional (2D) trapezoid-like layer of 1, three BPDA^2- anions and one phen group bind to a seven-coordinated In³⁺ ion with the distorted pentagonal bi-pyramid geometry. In 2, the extended -In-OH-In- chains are connected through BPDA ^2- to form a 3D framework. Complex 3 possesses a two-fold interpenetrating structure, which consists of two independent infinite diamond-like frameworks with point symbol 6⁶. All three samples exhibit varied solid-state fluorescence: emissions at 468 nm (intense blue), 559 nm (greenish-yellow), and 577-645 nm (broad intense orange band with a maximum at 611 nm, λ_ex = 257 nm) for 1, 567 nm (weak greenish-yellow, λ_ex = 344 nm) for 2, and 480 nm (intense greenish-blue, λ_ex = 385 nm) for 3.