No abstract

A potentially tetradentate pyridyl–thiazole ligand chain and an additional “external” crown ether binding site connect the two halves of a new ditopic ligand. The pyridyl‐thiazole binding sites can be changed or “reprogrammed” by the addition of Ba2+: In the presence of Hg2+ and Na+ the ligand L1 forms a dinuclear double helicate ([Hg2(L1)2Na2]6+), whereas in the presence of Hg2+ and Ba2+ a mononuclear species is formed ([Hg(L1)Ba]4+).

Self assembly of the ditopic ligand L1 with Cu2+ gives the dinuclear double helicate [Cu2(L1)2]4+, which can further coordinate s-block cations. This coordination alters the helicate pitch to a variety of different lengths depending on the size and charge of the guest cation.

There are numerous examples in the field of metallosupramolecular chemistry that demonstrate that careful design of ligands can produce species that are selective to certain metal ions.[ [2] Another approach to enhance metal specificity is to introduce discrete binding domains within a ligand strand such that each domain is specific to a particular metal ion.[3] However, when using the latter strategies, the information contained within the ligand system, that is, its "programming", is finalized at the synthetic stage and cannot be altered thereafter. Herein, we describe a ditopic ligand L 1 , whose selectivity for different transition-metal ions can effectively be "reprogrammed" by the addition of the larger s-block-metal ions to the crown ether moiety. This approach is related to the allosteric effect demonstrated by Rebek et al., in which the ability of a crown ether to coordinate Group 1 metal ions is influenced by coordination of a remote bipyridine coordination domain. [4] In this case, however, the reverse occurs as coordination of the crown ether unit controls the ability of a remote nitrogendonor unit to act as either a tetradentate or bisbidentate domain. Other reprogrammable systems have been shown to control the formation of helicates [5] and modulate their pitch length. [6] The reaction of L 1 (Scheme 1) with an equimolar amount of [Cu(MeCN) 4 ]PF 6 in MeCN gave a dark-red solution, and ESI-mass-spectrometric analysis showed the formation of a dinuclear double helicate with an ion at m/z 1497 consistent with {[Cu 2 (L 1 ) 2 ](PF 6 )} + . In addition, the crown ether moiety

There are numerous examples in the field of metallosupramolecular chemistry that demonstrate that careful design of ligands can produce species that are selective to certain metal ions.[ [2] Another approach to enhance metal specificity is to introduce discrete binding domains within a ligand strand such that each domain is specific to a particular metal ion.[3] However, when using the latter strategies, the information contained within the ligand system, that is, its "programming", is finalized at the synthetic stage and cannot be altered thereafter. Herein, we describe a ditopic ligand L 1 , whose selectivity for different transition-metal ions can effectively be "reprogrammed" by the addition of the larger s-block-metal ions to the crown ether moiety. This approach is related to the allosteric effect demonstrated by Rebek et al., in which the ability of a crown ether to coordinate Group 1 metal ions is influenced by coordination of a remote bipyridine coordination domain. [4] In this case, however, the reverse occurs as coordination of the crown ether unit controls the ability of a remote nitrogendonor unit to act as either a tetradentate or bisbidentate domain. Other reprogrammable systems have been shown to control the formation of helicates [5] and modulate their pitch length. [6] The reaction of L 1 (Scheme 1) with an equimolar amount of [Cu(MeCN) 4 ]PF 6 in MeCN gave a dark-red solution, and ESI-mass-spectrometric analysis showed the formation of a dinuclear double helicate with an ion at m/z 1497 consistent with {[Cu 2 (L 1 ) 2 ](PF 6 )} + . In addition, the crown ether moiety