Two cadmium coordination polymers based on tris(p-carboxyphenyl) phosphane oxide with highly selective sensing of nitrobenzene derivatives and Hg2+ cations

Abstract

Two coordination polymers (CPs), namely, [Cd_1/2(L)_1/3(bib)_1/2(H₂O)]_n (1) and {[Cd₂(HL)₂(bibp)₂]·3H₂O}_n (2), have been assembled from the tripodal ligand tris(p-carboxyphenyl)phosphane oxide (H₃L) with the help of 1,4-bis(imidazol-1-yl)benzene (bib) or 4,4′-bis(imidazol-1-yl)biphenyl (bibp). Structural analyses revealed that complex 1 is an unprecedented (3,4)-connected {10³}₂{10⁶}₃ net with 2D [Cd₃(L)₂]_n sheets arranged in an ABCA′B′C′A′′B′′C′′ fashion. Complex 2 exhibits 3-fold interpenetrated sheets with a 4-connected {4⁴·6²}-sql sheet. Structural comparison reveals that the length of bis(imidazole) ancillary linkers plays a critical role in determining the structures and topologies. To our delight, fluorescence measurements show that the two Cd(II) CPs can selectively and sensitively detect Hg²⁺ cations and nitrobenzene derivatives (nitrobenzene, p-nitrotoluene, p-nitroaniline, and p-nitrophenol), which suggests that the two Cd(II) CPs are promising bifunctional luminescence sensor materials that could sense metal ions and small organic molecules.