Synthesis and properties of four coordination polymers built from a semi-rigid tripod carboxylic acid

Abstract

By using a semi-rigid multidentate carboxylate linker 4,4′,4′′-(((2,4,6-trimethylbenzene-1,3,5-triyl)tris(methylene))tris(oxy))tribenzoic acid (H₃L), four coordination polymers, namely, [Cd₃(L)₂(H₂O)₄]·(guest) (1), [Mn₃(L)₂(DMF)₂(H₂O)₂]·(guest) (2), [Co₇(L)₄(DMF)₆(COOH)₂]·(guest) (3), and [Zn₃(L)₂(DMF)₂(H₂O)₃]·(guest) (4), were obtained and characterized by single-crystal X-ray diffraction, thermogravimetric and photoluminescent studies. Compound 1 is a two-dimensional (2-D) hcb-type layered structure made of rare, interlocked double-layered honeycomb sheets. Compound 2 is a doubly-interpenetrating (3,6)-connected 3-D network, in which L and Mn₃ act as triangle and trigonal prismatic nodes, respectively. Compound 3 has a (4,12)-connecting 3-D polycatenated network made of a rare four-ladder 2-D sheet, in which the Co₇ cluster is considered as a 12-connecting node and the ligand L³⁻ is a 3-connecting node. Similar to 1, compound 4 also possesses a 2-D hcb-type layered structure, but it is built from two interpenetrating single sheets. Compounds 1 and 4 exhibited strong blue photoluminescent emissions at room temperature upon excitation, owing to a ligand-centered excited state. The emission intensities of the two compounds varied upon contact with different solvents or analytes, exhibiting selective emission quenching responses towards nitroaromatics.