Self-Assembly of the First Discrete 3d−4f−4f Triple-Stranded Helicate

Abstract

The connection of an additional bidentate chelating unit at the extremity of a segmental bis-tridentate ligand in L5 provides an unprecedented sequence of binding sites for the self-assembly of heterometallic 3d-4f triple-stranded helicates. Thorough thermodynamic and structural investigations in acetonitrile show the formation of intricate mixtures of complexes when a single type of metal (3d or 4f) is reacted with L5. However, the situation is greatly simplified when Zn(II) (3d-block) and Lu(III) (4f-block) are simultaneously coordinated to L5, thus leading to only two identified species: the target C 3 -symmetrical trinuclear triple-stranded d-f-f helicate HHH-[ZnLu 2 (L5) 3 ] 8+ and a tetranuclear doublestranded complex [Zn 2 Lu 2 (L5) 2 ] 10+ . Interestingly, the removal of Zn(II) from the former triple-helical complex has only a minor effect on the coordination of Lu(III), and translational autodiffusion coefficients show a simple reduction of the length of the molecular rigid cylinder from L = 2.7 nm in HHH-[ZnLu 2 (L5) 3 ] 8+ to L = 2.3 nm in HHH-[Lu 2 (L5) 3 ] 6+ . Finally, the complete thermodynamic picture provides five novel stability macroconstants containing information about shortrange (ca. 9 A ˚) and long-range (ca. 18 A ˚) intramolecular intermetallic d-f and f-f interactions.

Understanding, Controlling and Programming Cooperativity in Self‐Assembled Polynuclear Complexes in Solution

“…the condition u L;L triÀ;triÀ ¼ u L;L biÀ;biÀ ¼ u L;L biÀ;triÀ ¼ u L;L complies). Granting the two standard assumptions pertinent to helicate assemblies based on semi-rigid ligands that i) no hairpin or strained structures are formed and ii) the principle of maximum siteoccupancy prevails, [9c,d] application of Equation (10) to, for example, the Equilibrium (11) leading to the recently reported bimetallic trinuclear complex HHH-A C H T U N G T R E N N U N G [Lu 2 Zn(L1) 3 ] 8 + [24] gives the corresponding Equation (12…”

“…As is often the case for this type of system, a number of other (homometallic) species were also identified as key intermediates in the self-assembly of HHH-A C H T U N G T R E N N U N G [Lu 2 Zn(L1) 3 ] 8 + . [24] Within the precincts of the criteria discussed above, similar treatment for these Equilibria (15), (17) and (19) thus gives a corresponding set of Equations (16), (18) and (20) ( Figure 2). Note that apart from the stoichiometries inferred from ESI-MS and UV/Vis titrations, very little structural information is available for the intermediate species [24] and their cumulative macroscopic stability constants are modelled by the sum of the microscopic formation constants characterising the different conceivable structural isomers (or microspecies) present at equilibrium ( Figure 2 and Appendix I in the Supporting Information).…”

“…Recently, we reported on the structural and thermodynamic investigations of the first directional triple-stranded heterometallic helicate HHH-[Lu 2 Zn(L1) 3 ] 8 + , based on segmental pyridyl-benzimidazole ligand L1 (Scheme 1). [24] The mere preparation of this complex is perhaps not overwhelmingly noteworthy in its own right, given the now widespread appreciation for the importance of stereoelectronic matching between metal ion and ligand binding site in metallosupramolecular design, but its detailed thermodynamic investigation has presented an opportunity to address previously inaccessible intermetallic interactions in solution. The complex features a linear arrangement of two Lu 3 + trications and one Zn 2 + dication, separated by regular intervals of about 9 .…”

Control of metallo-supramolecular assemblies via steric, hydrogen bonding and argentophilic interactions; formation of a 3-dimensional polymer of circular helicates

“…25,26 One such example of higher orders of self-assembly has been demonstrated by Ward et al 6 In this work they demonstrate the formation of triple helix comprised of three infinite chains of double helicates. The basic unit is a bis-bidentate ligand which forms a dinuclear double helicate with Ag(I) (e.g.…”

AgI‐Directed Triple‐Stranded Helicates with meta‐Ethynylpyridine Ligands

“…For instance, N ‐oxide binaphthol derived ligands wrap around three independent Na + or Li + ions to form trinuclear triple‐stranded helicates 7a. Additionally, recent studies demonstrated that transition‐metal ions [Co(II/III),8a,8c,8d Ga III ,8c In III ,8c Fe(II/III),8d–8h Cu(I/II),8h,8i,10 Zn II ,8b,8j,8k Mn II ,8k,8l Ag I[9i,11] ] and Ln III[8b,9] (Ln = La, Eu, Ce, Tb, Lu) also play a very important role in the formation of triple‐stranded helicates. The metallo centers in the helicates impart a cationic charge, which is expected to enhance the potential use of such triple‐stranded helicates in chemical and biochemical domains, particularly, in DNA labeling and recognition 8d,9d.…”