Luminescent detection by coordination polymers derived from a pre-organized heterometallic carboxylic building unit

Abstract

A tetranuclear heterometallic complex [Li2Zn2(piv)6(py)2] (piv− = pivalate, py = pyridine) could be viewed as an 8-connected node or a dimer of 3-connected binuclear {LiZn(RCOO)3} carboxylate complexes. A solvothermal reaction of c with biphenyldicarboxylic acid (H2bpdc) results in two layered MOFs [{LiZn}2(bpdc)3(dma)4]·3DMA·H2O (1a ⊃ DMA) and [{LiZn}2(bpdc)3(nmp)4]·4NMP (1b ⊃ NMP) in dimethylacetamide (DMA) or N-methyl-2-pyrrolidone (NMP) solvents, respectively. The reaction of [Li2Zn2(piv)6(py)2] with H2bpdc and diazabicyclo[2.2.2]octane (dabco) in dimethylformamide (DMF) affords a 3D MOF [Li2Zn2(bpdc)3(dabco)]·9DMF·4H2O (2 ⊃ DMF) with an open structure. The frameworks in 1a and 1b are based on 3-connected binuclear nodes, connected through linear bpdc2− anions into a twofold interwoven honeycomb (hcb) layers, packed in ABAB manner. The tetranuclear units in 2 are connected by both bpdc2− and dabco into a 3D non-interpenetrated net with body-centered cubic (bcu) topology. The solvent molecules in both 1 and 2 could be substituted to various aromatic species, which nature affects the photoluminescence properties of the framework in a different way. For example, the substitution to nitrobenzene completely quenches the luminescence while the inclusion of benzyl alcohol, anisole, acetophenone into porous channels of 2 results in a marked shift of the emission peak maxima as well as an enhancement of the quantum yields.