Stabilization of the Anionic Metalloligand, [Ag₆(mna)₆]^6– (H₂mna = 2‑Mercapto Nicotinic Acid), in cor, α‑Po, and sql Nets Employing Alkaline Earth Metal Ions: Synthesis, Structure, and Nitroaromatics Sensing Behavior

Three new heterometallic metal organic frameworks, [{[Ca₆(H₂O)₁₈]­[Ag₆(mna)₆]₂}­·[Ag₆(Hmna)₆]­·20H₂O], 1, {[Sr₃(H₂O)₁₀]­[Ag₆(mna)₆]­·12H₂O}, 2, and {[Ba₃(H₂O)₁₀]­[Ag₆(mna)₆]­·8H₂O}, 3, have been synthesized following hard–soft acids–bases principle. Compounds 1 and 2 have three-dimensional structures with cor and pcu (α-Po) topology, whereas compound 3 has a two-dimensional sql topology. Smaller calcium and strontium ions form a simple dimer (Ca2/Sr2, 1/2) and tetramer units (Sr4, 2), whereas the larger barium ion forms infinite Ba–O–Ba chains. The presence of the electron-rich mna ligand in all the compounds paved the way for the detection of electron-deficient hazardous nitroaromatics employing photoluminescence quenching methods. The luminescence intensities of the compounds are strongly quenched by picric acid, p-nitro phenol, and 2-nitro toluene at low concentration, which indicates that these compounds are excellent materials for the detection of these nitroaromatics in solution.