The 9-anthryltriphenylstibonium cation, [1](+), has been synthesized and used as a sensor for the toxic fluoride anion in water. This stibonium cation complexes fluoride ions to afford the corresponding fluorostiborane 1-F. This reaction, which occurs at fluoride concentrations in the parts per million range, is accompanied by a drastic fluorescence turn-on response. It is also highly selective and can be used in plain tap water or bottled water to test fluoridation levels.

Turn on the lantern! The stibine donor ligand of a cationic palladium complex acts as a Lewis acid and reacts with a fluoride anion to afford the corresponding fluorostiboranyl-palladium species (see scheme). Bindung of the fluoride anion to the antimony center induces a change in denticity of the triphosphine unit and leads to a bright-orange trigonal-bipyramidal d(8) lantern complex.

BiZness as usual? Not exactly! The bismuth atom of the tridentate diphosphinobismuthine (o-(Ph(2)P)C(6)H(4))(2) BiCl behaves as a Z rather than L ligand when in the coordination sphere of late transition metals such as gold. The σ-acceptor behavior of Bi is supported by its disphenoid coordination geometry and theoretical studies, which show a Au→Bi interaction.

In search for new examples of σ-acceptor ligands, we have investigated the tridentate ligands (o-(iPr2P)C6H4)2SbPh) (L(Ph)) and (o-(iPr2P)C6H4)2SbCl) (L(Cl)) which react with (tht)AuCl (tht = tetrahydrothiophene) to afford L(Ph)AuCl (1) and L(Cl)AuCl (2), respectively. As suggested by the structure of these complexes, which confirm complexation of the SbP2 ligands to the gold chloride fragment, and in agreement with the results of the density functional theory (DFT) and natural bond orbital (NBO) calculations, the gold and antimony atom of 1 and 2 are involved in a Au→Sb donor-acceptor interaction. The magnitude of this interaction is higher in complex 2 which possesses a chlorinated and thus more Lewis acidic antimony center. We have also compared the strength of the Au→Sb interaction present in 2 with the Au→Bi interaction observed in the newly prepared bismuth analogue [(o-(iPr2P)C6H4)2BiCl]AuCl (3). This comparison reveals that 2 possesses a stronger Au→Pn bond (Pn = pnictogen), an observation reconciled by invoking the greater Lewis acidity of antimony(III) halides. Finally, complexes 1 and 2 undergo a clean antimony-centered oxidation when treated with ortho-chloranyl. These oxidation reactions afford complexes [(o-(iPr2P)C6H4)2(o-C6Cl4O2)SbPh]AuCl (5) and [(o-(iPr2P)C6H4)2(o-C6Cl4O2)SbCl]AuCl (6). Structural and computational studies of 5 show that the Au→Sb bond becomes shorter and more covalent upon oxidation of the antimony atom. Although the structure of 6 has not been experimentally determined, spectroscopic and computational results show a similar effect in this complex. Complex 5 and 6 constitute rare examples of metalated six coordinate antimony compounds.

The tetravalent platinum stiboranyl complex [(o-(Ph2P)C6H4)2(o-C6Cl4O2)Sb]PtCl2Ph (2) has been synthesized by reaction of [(o-(Ph2P)C6H4)2SbClPh]PtCl (1) with o-chloranil. In the presence of fluoride anions, the stiboranyl moiety of 2 displays non-innocent behavior and is readily converted into a fluorostiborane unit. This transformation, which is accompanied by elimination of a chloride ligand from the Pt center, results in the formation of [(o-(Ph2P)C6H4)2(o-C6Cl4O2)SbF]PtClPh (3). Structural, spectroscopic, and computational studies show that the conversion of 2 into 3 is accompanied by a cleavage of the covalent Pt-Sb bond present in 2 and formation of a longer and weaker Pt→Sb interaction in 3. These results show that this new Pt-Sb platform supports the fluoride-induced metamorphosis of a stiboranyl X ligand into a stiborane Z ligand.