This article marks the 20 th year of coverage of anion receptor chemistry by this series of reviews. In the first review, published in Coordination Chemistry Reviews in 2000 (and covering highlights in anion coordination and anion directed assembly in 1997 and 1998),[1] it was noted that "Anion coordination has received little attention over the last 30 years when compared to that devoted to the coordination chemistry of cations." Now as we look back over the last 50 years we see that this has changed and that many real world applications for anion complexation have emerged.[2] Although this review has moved between publications over the last two decades;[1, 3-11]-it is appropriate for it return to Coordination Chemistry Reviews to mark both this milestone and the special issue devoted to Coordination Chemistry in Australia. 2. Fundamental studies This section covers the development of new receptors and understanding the fundamentals of anion interactions, ranging from classic hydrogen-bond systems to more exotic halogen and chalcogen bond-based receptors. In 2016, we have seen examples of anion receptors that advance our understanding of aromatic, hydrophobic and ion-pair interactions, and the development of photo-switchable receptors and multivalent systems. 2.1. Hydrogen-bond based receptors A number of groups have exploited C-H hydrogen bonds for the recognition of anions. Amendola and coworkers [12] reported the C-H hydrogen bonding receptor 1•(PF6)3 based on a tripodal 1,3,5-trimethylbenzene scaffold and incorporating imidazolium and 2,3,4,5-tetrafluorobenzene moieties as C-H hydrogen-bond donors. Proton NMR titrations in CD3CN and

The anion transport properties of a range of alkyl-substituted phenylthioureas were tested in vesicles of different lipid composition. Although changes in the bilayer affected the rate of transport for all compounds in the series, the 'ideal' log P for peak activity did not change depending on the composition of the bilayers tested.

A series of fluorinated tripodal tris-thioureas function as highly active anion transporters across lipid bilayers and cell membranes.

The anion-bindinga nd transport properties of an extensive library of thiophene-based molecules are reported. Seventeen bis-urea positional isomers, with different binding conformationsa nd lipophilicities, have been synthesized by appending a-o rb-thiopheneo ra-, b-, or g-benzo[b]thiophene moieties to an ortho-phenylenediamine central core, yielding six subsets of positional isomers. Through 1 HNMR, X-ray crystallography, molecular modelling,a nd anion efflux studies, it is demonstrated that the most active transporters adopt ap re-organized binding conformation capable of pro-moting the recognition of chloride, using urea and CÀH bindingg roups in ac ooperative fashion.A dditional large unilamellar vesicle-based assays, carriedo ut under electroneutral and electrogenic conditions, together with N-methyld-glucamine chloride assays,h ave indicated that anion efflux occurs mainly through an H + /Cl À symportm echanism. On the other hand, the most efficient anion transporter displays cytotoxicity against tumor cell lines, while having no effects on acystic fibrosis cell line.

Dedicated to Prof. Jerry Atwood on the occasion of his 75 th birthday. A tripodal tris-selenourea anion transporter matches the activity of its thioanalogue but shows distinct selectivity We report the synthesis of a tripodal tris-selenourea transporter scaffold. The Cland NO3transport activity of the compound has been compared extensively with the analogous oxo-and thiourea compounds. We found that the selenourea demonstrates remarkably similar transport efficacy and mechanistic properties to the equivalent thiourea, but demonstrates flipped selectivity for Clover NO3- .