Anion Recognition and Templation in Coordination Chemistry

Abstract

The selective recognition of anionic species by molecular receptors is an area of increasing interest due to the important roles played by anions in biological systems and the environment. An attractive approach for the recognition of anions is to use metal‐based receptors, which provides some important advantages over purely organic hosts. Metallo‐hosts can combine the structural and functional properties of metal centres with the recognition capabilities of organic ligands to selectively bind anionic guests. In our group we have developed different approaches for the synthesis of this type of metallo‐receptors. One of these approaches is based on the use of the anion of interest as a templating agent to link together different organic and metal‐containing building blocks into assemblies that have high selectivity for the templating anion. This microreview aims to give an overview of the research carried out in the author's group in this area over the past few years. Relevant examples from other groups are discussed and, where appropriate, compared to the work carried out in our group.(© Wiley‐VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2008)

Pre-organisation or a hydrogen bonding mismatch: silver(I) diamide ligand coordination polymers versus discrete metallo-macrocyclic assemblies

“…Strategies to selectively complex anions require the synthesis of hosts utilising one or more of a toolbox of interactions, 11 including hydrogen bonding donor groups, 10,12 π-acidic heteroarene scaffolds, [14][15][16][17] cationic groups for electrostatic interactions 11,18 and Lewis acidic moieties. 11 The investigation of metallo-supramolecular assemblies 5,[19][20][21][22] and coordination polymers [23][24][25] as anion receptors and for anion separation or sequestration has also received attention. In the context of developing such systems for anion inclusion, the use of a metallo-supramolecular species to bind anions can provide a number of advantages over neutral organic receptors.…”

“…In the context of developing such systems for anion inclusion, the use of a metallo-supramolecular species to bind anions can provide a number of advantages over neutral organic receptors. 5,[20][21][22] Firstly, the anion binding and encapsulating aspects of a self-assembled system can be readily explored by combining a number of relatively simple organic ligands, which display moieties capable of interacting with anions with different metal ions; the structural complexity required to bind an anion of interest is controlled by the choice of metal ion, 26 Figure 1(a). Altering the affinity for a particular anion could be achieved by substituting in a different, but structurally similar ligand (Figure 1b) or changing the metal ion.…”

Anion-induced conformational changes in 2,7-disubstituted indole-based receptors

“…[1][2][3][4][5] Potential applications in the separation and extraction of anionic species, in the development of new sensing systems and in the design of new compounds that may have potential biological activity has driven the synthesis of a plethora of receptors 25 containing amides and thioamides, pyrroles and indoles, ureas and thioureas, ammonium, guanidinium and imidazolium moieties. 6,7 Indole is employed by Nature in sulfate binding protein 8 and in the enzymatic active site of haloalkane dehalogenase 9 30 to bind anions, however research in area of indole-based anion receptors [10][11][12][13][14][15][16][17][18][19][20] is still at an early stage compared to the range of anion receptors based on pyrrole.…”

“…Regrettably, negative NOEs in 3⋅ AcO -complex NOEs thwarted a conformational study of this complex. 5 The conformational preorganization of 4, where H2β and H7α point away from indole H1 proton, is supported by strong {H2β}-H3 and {H7α}-H6 NOEs as well as weak NOE enhancements between H1-H2β and H1-H7α. The addition of chloride or bromide anions triggers conformational changes in 10 4, which were clearly indicated by decreased {H2β}-H3 and {H7α}-H6 NOEs and increased NOEs between indole H1 and both H2β and H7α protons ( respectively.…”

Control of metal-directed self-assembly by metal–amine interactions

“…Template effects were observed in the guest-dependent formation of MOFs, 12-16 crystallization processes, 17 metal counter-anion dependent self-assembly, 3, 18 and templation through p-p-stacking interactions.…”