Allosteric‐Controlled Metal Specificity of a Ditopic Ligand

Abstract

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

Allosteric deprogramming of a trinuclear heterometallic helicate

“…Residual peaks in the electron density map were assigned and refined as a ca. half-site occupancy perchlorate moiety [ClO 4 (7)]. The latter may simply be due to a small quantity of perchloric acid co-crystallate.…”

“…For example, we developed a ditopic ligand that forms a dinuclear double-stranded helicate with Hg(II), but may be reprogrammed to form a mononuclear complex following binding of Ba 2+ or Sr 2+ ions to an external crown ether site. 6 This approach may also be employed to modify (i) a ligand's preference for different metal ions, 7 (ii) helical pitch-length 8 and (iii) gross molecular structure. 9 In the last case, ligand reprogramming causes a dicopper(I) double-stranded helicate to adopt a side-by-side configuration.…”

Electrostatic control of the formation of heteroleptic transition metal helicates

“…4 The ability to reprogramme this ligand strand also changes its metal specificity; thus the ligand's preference for Cu(I) ions can be changed to Zn(II) ions by addition of either Sr 2+ or Ba 2+ . 5 Other, more subtle effects have been reported such as the ability to modulate the pitch length of a Cu(II)-containing helicate by addition of various s-block metals ions to the crown ether unit. 6 In this paper we report a potentially hexadentate ditopic ligand L 1 which forms a dinuclear double helicate with Zn(II) ([Zn 2 (L 1 ) 2 ](ClO 4 ) 4 ) and demonstrate that the formation of heteroleptic transition metal helicates, with a ligand containing the same potentially hexadentate N-donor domain, can be controlled by addition of barium ions.…”

Organic−Inorganic Hybrid Compounds of Li with Bisimidazole Derivatives: Li Ion Binding Study and Topochemical Properties

“…The design and synthesis of molecular inorganic−organic hybrid materials is an area of hot pursuit because of their distinctive topology and functional architectural frameworks and potential applications in energy storage devices, catalysis, etc. − There is a wealth of information available on coordination polymers with metal ion connectors and organic linkers incorporated into their frameworks, which may be attributed to their distinctive topology, as well as to their utility. − Although the neutral ditopic nitrogen-containing ligands, such as pyrazine, 4,4‘-bipyridine, and 1,10-phenanthroline, have been extensively employed, ,− the scope of preparing coordination polymers from the ditopic bisimidazoles remains largely unexplored. Recently, efforts have been made to incorporate bisimidazolium into naphthalene and pyridine macrocyclic calix structures, which function as anion receptors. − Imidazole−lithium complexes are also of importance because they have applications in electrical devices, olefin polymerizations, etc. − Room-temperature ionic liquids derived from imidazole, being nonflammable and nonvolatile, are widely employed as conductive nonaqueous electrolytes in high-power-density lithium batteries …”