Three isostructural metal–organic frameworks ([Ln₂(phen)₂(NO₃)₂(chdc)₂]·2DMF (Ln³⁺ = Y³⁺ for 1, Eu³⁺ for 2 or Tb³⁺ for 3; phen = 1,10-phenanthroline; H₂chdc = trans-1,4-cyclohexanedicarboxylic acid) were synthesized and characterized. The compounds are based on a binuclear block {M₂(phen)₂(NO₃)₂(OOCR)₄} assembled into a two-dime nsional square-grid network containing tetragonal channels with 26% total solvent-accessible volume. Yttrium (1)-, europium (2)- and terbium (3)-based structures emit in the blue, red and green regions, respectively, representing the basic colors of the standard RGB matrix. A doping of Eu³⁺ and/or Tb³⁺ centers into the Y³⁺-based phase led to mixed-metal compositions with tunable emission color and high quantum yields (QY) up to 84%. The bright luminescence of a suspension of microcrystalline 3 in DMF (QY = 78%) is effectively quenched by diluted cinnamaldehyde (cinnamal) solutions at millimolar concentrations, suggesting a convenient and analytically viable sensing method for this important chemical.

Four new gadolinium(III) metal-organic frameworks containing 2,2′-bipyridyl (bpy) or 1,10-phenanthroline (phen) chelate ligands and trans-1,4-cyclohexanedicarboxylate (chdc²⁻) were synthesized. Their crystal structures were determined by single-crystal X-ray diffraction analysis. All four coordination frameworks are based on the binuclear carboxylate building units. In the compounds [Gd₂(bpy)₂(chdc)₃]·H₂O (1) and [Gd₂(phen)₂(chdc)₃]·0.5DMF (2), the six-connected {Ln₂(L)₂(OOCR)₆} blocks form a 3D network with the primitive cubic (pcu) topology. In the compounds [Gd₂(NO₃)₂(phen)₂(chdc)₂]·2DMF (3) and [Gd₂Cl₂(phen)₂(chdc)₂]·0.3DMF·2.2dioxane (4), the four-connected {Ln₂(L)₂(X)₂OOCR)₄} units (where X = NO₃⁻ for 3 or Cl⁻ for 4) form a 2D square-grid (sql) network. The solid-state luminescent properties were investigated for the synthesized frameworks. Bpy-containing compound 1 shows no luminescence, possibly due to the paramagnetic quenching by Gd³⁺ cation. In contrast, the phenathroline-containing MOFs 2–4 possess yellow emission under visible excitation (λ_ex = 460 nm) with the tuning of the characteristic wavelength by the coordination environment of the metal center.