Self‐assembly and Cycling of a Three‐state Pd_xL_y Metallosupramolecular System

Abstract

The use of stimuli to induce reversible structural transformations in metallosupramolecular systems is of keen interest to chemists seeking to mimic the way that Nature effects conformational changes in biological machinery. While a wide array of stimuli have been deployed towards this end, stoichiometric changes have only been explored in a handful of examples. Furthermore, switching has generally been between only two distinct states. Here we use a simple 2‐(1‐(pyridine‐4‐methyl)‐1H‐1,2,3‐triazol‐4‐yl)pyridine “click” ligand in combination with PdII in various stoichiometries and concentrations to quantitatively access and cycle between three distinct species: a [PdL2]2+ monomer, a [Pd2L2]4+ dimer, and a [Pd9L12]18+ cage.

Directing metallo-supramolecular assembly through complementarity

“…At a 2 : 2 ratio between metal ion and ligand, a 2 + 2 dimer, [Pd 2 ( 2 AD -pyridine ) 2 (solvent) 2 ] 4+ , was formed instead. 85 Interestingly, the head-to-tail complementarity was broken here, with the coordination sphere of each metal ion consisting of a 2 AD site, a monodentate pyridine from the other ligand, and solvent (Fig. 15b).…”

“…As mentioned earlier, 84,85 the pyridyl arm of 2 AD -pyridine is free to coordinate to other metals, which could enable added functionality beyond guest binding. Investigations with Ag + showed it was clear that neither metallo-ligand coordinated to silver(I) through the pyridyl arm to produce extended systems in solution.…”

Metallo‐Supramolecular Self‐Assembly with Reduced‐Symmetry Ligands

“…In this structure each Pd(II) ion possesses a square planar coordination geometry; however, six of the ions are coordinated by two bidentate triazolylpyridine units, whilst the other three bind to four monodentate pyridines (Figure 9d). [48] Exploitation of the different coordinating propensities of the bidentate and monodentate fragments of 18 enabled precision synthesis of a mixed-metal architecture. Initial coordination of the ligand with Pt(II) gave the homologous mononuclear complex [Pt(18)] 2 + ; subsequent addition of Pd(II) to this kinetically inert complex yielded the heteronuclear cage [Pt 6 Pd 3 (18) 12 ] 18 + , isostructural with its homonuclear analogue.…”

“…Above 14 mM a single structure emerged, identified as the nona‐nuclear cage [Pd 9 ( 18 ) 12 ] 18+ . In this structure each Pd(II) ion possesses a square planar coordination geometry; however, six of the ions are coordinated by two bidentate triazolylpyridine units, whilst the other three bind to four monodentate pyridines (Figure d) …”

Using Complementary Ligand Denticity to Direct Metallosupramolecular Structure about Metal Ions with Square‐Planar Geometry

“…They next reported a ligand with a tridentate 2‐(1H‐pyrazol‐1‐yl)‐6‐(1H‐1,2,3‐triazol‐4‐yl)‐pyridine site and a single monopyridyl arm ( L17 , Figure ) . In 2 : 2 combination with Pd II or Pt II in DMSO, dinuclear [M 2 L17 2 ] 4+ complexes were formed at low concentrations.…”