The selective detection of anions in complex multicomponent matrices remains challenging. Of particular interest is recognition of toxic and/or radioactive pertechnetate (TcO4−), a dominant environmental chemical form of the radioisotope 99Tc produced in the nuclear fuel cycle. The long half-life of 99Tc (2.13 × 105 years) and highly mobile subsurface transport properties of 99TcO4− generate considerable environmental and health concerns. Monitoring 99Tc in groundwater is challenging due to the requirement to meet low detection limits below the drinking water standard as well as presence of competing anions. This work focuses on square-planar, cationic, coordinatively unsaturated Pt(II) complexes that undergo a distinct spectroscopic change upon exposure to 99TcO4−. The spectroscopic response arises from the ability of these complexes to form quasi-one-dimensional stacked systems via noncovalent Pt---Pt interactions, which can be altered by varying the counter anion. In the parent solid material, Pt(II) units are arranged in a manner that does not result in a continuous chain of short Pt---Pt contacts. Substitution of an anion, that uniquely satisfy the requirements of lattice parameters needed for extended Pt---Pt overlap (as shown in attached scheme), result in distinct spectroscopic changes in the material. These form the basis of anion detection, and can be customized for TcO4− detection. Our studies identified the Pt(II) complex [Pt(tpy)Br]SbF6 (tpy = 2,2′;6′,2″-terpyridine) to undergo a dramatic colorimetric / luminescence response upon TcO4− exposure due to concomitant enhancement of Pt---Pt interactions. The spectroscopic response was highly selective for TcO4− among other competing anions (Cl−, CO32−, SO42−, NO3−) indicating TcO4- to uniquely satisfy the steric and electronic requirements for an extended chain of stacked square-planar [Pt(tpy)Br]+ units. The electronic spectroscopies were complimented by structural determination to elucidate the mechanism of this response at a molecular level.

Highly selective detection of aqueous pertechnetate using square-planar platinum(II) complexes

254th National Meeting (2017)

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