Highly selective detection of Hg2+ and MeHgI by di-pyridin-2-yl-[4-(2-pyridin-4-yl-vinyl)-phenyl]-amine and its zinc coordination polymer

Abstract

Solvothermal reaction of Zn(NO₃)₂·6H₂O with di-pyridin-2-yl-[4-(2-pyridin-4-yl-vinyl)-phenyl]-amine (ppvppa) and 1,4-naphthalenedicarboxylic acid (1,4-H₂NDC) in H₂O and MeCN at 150 °C yielded a two-dimensional (2D) coordination Zn(II) polymer [Zn(ppvppa)(1,4-NDC)]_n (1). Compound 1 was characterized by elemental analysis, IR spectroscopy, powder X-ray diffraction, single-crystal X-ray diffraction and thermogravimetric analysis. Compound 1 consists of dimeric [Zn₂(ppvppa)₂] units linked by 1,4-NDC bridges to generate a 2D honeycomb network. Either compound 1 or ppvppa alone can detect Hg²⁺ or MeHgI selectively and with good sensitivity. Upon addition of Hg²⁺ ions to a MeCN solution of ppvppa, marked changes in the UV-vis and fluorescence spectra are observed, associated with colour changes, which are easily identified by the naked eye. The pyridinyl rings of ppvppa are coordinated to the Hg²⁺ ion. This motif in the presence of NO₃⁻ ions forms a binuclear complex [Hg₂(ppvppa)₂(NO₃)₄] (2), which has been characterized as the solvate [Hg₂(ppvppa)₂(NO₃)₄]·H₂O·4MeCN (2·H₂O·4MeCN) by single-crystal X-ray diffraction studies. In aqueous solution, compound 1 emits pale orange light at ambient temperature and the addition of Hg²⁺ or MeHgI induces an change of fluorescence color from pale orange to blue. Compound 1 is a promising candidate as a sensitive naked-eye indicator for Hg²⁺ or MeHgI in water under a UV lamp.

Prof. Lang and Prof. Brammer met with each other in Nanjing, China when Prof. Brammer taught lectures at Nanjing Tech University last November. Prof. Lang's research involves metal sulfide cluster chemistry, design and development of new coordination complex-based catalysts, bioinorganic chemistry related to mimicking metal sites of enzymes and proteins, and so on. Prof. Brammer's research interest covers supramolecular chemistry and crystal engineering, in particular host–guest chemistry and catalysis in metal–organic frameworks, reactions in molecular solids and fundamentals of intermolecular interactions. Both professors recognised their many mutual research interests and decided to initiate an international collaborative project in the area of coordination polymers. Both will visit the partner's lab in China and UK in the near future and expand this project to a higher level.