Fluoride sensors

Thioureas-binding site can be introduced to molecules like anthraquinone and is for use in various kinds of anion or fluoride sensors. Thiourea-based sensor are generally designed to recognize anion through an intermolecular hydrogen bonding.167 171... 

Arimori, S., Davidson, M. G., Fyles, T. M., Hibbert, T. G., James, T. D., Kociok-Kohn, G. I., Synthesis and structural characterisation of the first bis(bora)calixarene a selective, bidentate, fluorescent fluoride sensor. Chem. Commun. 2004, 1640-1641. 

The reaction of anionic [l,8]naphthaborate 30 with dialkyl- or diarylhaloborane electrophiles leads to the formation of 1,8-diborylnaphthalenes 31 (Scheme 3) sulfur-bridged 31e proved to be a very selective calorimetric fluoride sensor, functioning by coordination of fluoride to both boron centers <2004CC1284>. 

Fluoride anion strongly interacts with various inorganic and organic boron and silicon compounds. These reactions are the basis for several fluoride sensors. Interaction of fluoride with boron compounds results in electron density redistribution and may also induce structural changes. Formation of fluoride complex by ferrocene derivative (Figure 16.19a) results in a decrease of oxidation potential by 200 mV... 

A series of multifunctional anthrylboranes with up to six boron centers and divergently extended itt-conjugation have been reported. Trianthrylborane itself is bright orange, whereas the extended system (157) is dark red colored. This bathochromic shift was attributed to the more extended delocalization in the starbust oligomer (157). Two reversible reduction waves were found for the two different boron environments in (157). The anthrylboranes have also been studied as fluorescent fluoride sensors (see Section 7.2.1). 

Liu, Z.Q., Shi, M., Li, F.Y., etal. (2005) Highly selective two-photon fluorescent fluoride sensor derived from organic boranes. Organic Letters, 7, 5481-5484. 

H. Ohji and P. J. French, Single step electrochemical etching in ammonium fluoride. Sensors Actuators 74, 109, 1999. 

Shinkai and coworkers reported that ferroceneboronic acid 17 (Fig. 3) acts as an electrochemical anion sensor.It exhibits excellent selectivity for fluoride ions in the presence of other halides and anions such as SCN , S04, and H2PO4 . A i ox value of 1000 M in MeOH/H20 was found for fluoride, compared to values of less than 2 M for chloride and bromide. The fluoride ion is a hard base and. therefore, interacts considerably with the hard boron atom. Oxidation results in the ferrocene group becoming more electron withdrawing. The electron density of the boron atom decreases therefore, the strength of the fluoride complex increases. A biden-tate Z7/ s(boronate) Lewis acid was also shown to act as a fluoride sensor. 

An easily visualised example is the multidentate Lewis-acid host 2.77, a colourimetric fluoride sensor. The receptor contains a non-irmocent ferrocenyl linker between the boronate groups. Reaction of 2.77 with n-Bu4N+F in CHCI3... 

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