Structure and fluorescent properties of mercury(ii) pyridine-2,3-dicarboxylate coordination polymers tuned by ancillary ligands and alkaline-earth metal ions

Abstract

The reactions of pyridine-2,3-dicarboxylic acid (2,3-PyDCH₂) with Hg(CH₃COO)₂, tuned by ancillary ligands and alkaline-earth metal ions, gave [Hg₂(2,3-PyDC)₂]_n (1), {[Hg(phen)(2,3-PyDC)]·2H₂O}_n (2), [CaHg(2,3-PyDC)(SCN)₂(H₂O)]_n (3), [SrHg(2,3-PyDC)(SCN)₂(H₂O)]_n (4) and [BaHg(2,3-PyDC)(SCN)₂(H₂O)]_n (5). Compound 1 presents a three-dimensional topological network with the Schläfli symbol (4².6⁴)(4².6³.8)(4³.6⁶.8) (4.6²), formed by two kinds of 2,3-PyDC²⁻ ligands (five-connecting and three-connecting) and two kinds of four-connecting Hg(II) ions. The introduction of chelating 1,10-phenanthroline ancillary ligands in 2 gave one-dimensional chains. The addition of alkaline-earth metal ions and the ancillary ligand SCN⁻ to the Hg²⁺–2,3-PyDC²⁻ system gave a three-dimensional topological network with the Schläfli symbol (4⁶.6⁹.8⁴)(3².4².5.6⁵)(3².4.6³)(4⁶.6²) for 3 and two-dimensional structures formed by the connection of one-dimensional Sr(II)/Ba(II)–carboxylate chains via dinuclear units [Hg₂(SCN)₂]²⁺ with the Schläfli symbol (3.8²)(3⁴.4⁵.5.6⁴.7)(3.4².5.6.7) for compounds 4 and 5. The photoluminescent properties of free 2,3-PyDCH₂ and complexes 1–5 were investigated. They reveal no fluorescent emission (fluorescence “off” state) for free 2,3-PyDCH₂ in the absence of metal ions. However, an emission band (fluorescence “on” state) was found upon the coordination of 2,3-PyDC²⁻ to Hg²⁺ in 1 to giva a 3D structure. Interestingly, the addition of ancillary ligands and alkaline earth metal ions to the Hg²⁺–2,3-PyDC²⁻ system results in the disappearance of the fluorescence (fluorescence “off” state) in compounds 2–5.