Double‐Decker Coordination Cages

Abstract

Bis(pyridin‐3‐ylmethyl) pyridine‐3,5‐dicarboxylate (L) possessing one internal and two terminal pyridine moieties displayed differential coordination ability when combined with suitable PdII components. The compound L acted as a bidentate chelating ligand to form mononuclear complexes when combined with cis‐[Pd(tmeda)(NO3)2] or Pd(NO3)2 in calculated ratios. The combination of Pd(NO3)2 with L in a ratio of 3:4, however, afforded the trinuclear “double‐decker” cage [(NO3)2⊂Pd3(L)4](NO3)4, in which L acts as a nonchelating tridentate ligand and the counter anion (i.e., NO3–) acts as template. The encapsulated NO3– can be replaced by F–, Cl–, or Br– but not by I–. The F–‐encapsulated cage could not be isolated due to its reactivity, whereas the Cl– or Br– encapsulated cages could be isolated. Although anionic guests such as NO3–, Cl–, or Br– stabilized the cages, the presence of excess Cl– or Br– (not NO3–) facilitated decomplexation reactions releasing the ligand. The complexation of Pd(Y)2 (Y = BF4–, PF6–, CF3SO3–, or ClO4–) with L afforded the corresponding mononuclear complexes under appropriate conditions. However, these counter anions could not act as templates for the construction of double‐decker cages.

Multicavity Metallosupramolecular Architectures

“…In 2014, Chand, Hanan and co-workersutilised flexible tripyridyl ligandst op roduced multicavity self-assembled architectures ( Figure 8). [23] Complexation of a tris-monodentate tripyridyl ligand with palladium(II) ions in a4:2 ratio gave 2m olecules of a" spiro-type"[ PdL 2 ] 2 + system (similar to that observed by McMorran and Steel) ( Figure 8a). However,w hen a4:3 ratio of Pd II ions and the ligand were mixed, a[ Pd 3 L 4 ] 6 + linear double cavity system was generated (Figure 8b).…”

“…Mass spectral analysis of the system with three methylene units displayed signals [21] and b) the proposed methodtoadouble cavity cage system by linearextension of the "parent" ligand. [22] An X-raystructure of the double molecule [23] a) the X-ray structure of the "spiro-type" system [PdL 2 ] 2 + complex and b) the X-ray structure of the double cavity system [Pd 3 L 4 ] 6 + architecture with two chloride guestbound in the cavities. Hydrogena toms, solvent molecules and the rest of the counterionsh ave been omitted for clarity.Conditions for formationo fd isplayed structures:( i) Pd(NO 3 ) 2 arising from the loss of three, four and five BF 4 À counterions, as wella sp eaks where the BF 4 À anions had been exchanged for Cl À ions.…”

Self-assembled conjoined-cages

“…We have also demonstrated the use of AgCl where the Cl − ion displaced bound NO 3 − ion from the cavity of some coordination cages whereupon the more soluble AgNO 3 remained in solution 49 . The requirement of the encapsulated anions in the creation of these assemblies was realized when attempts toward synthesizing…”

Design of a double-decker coordination cage revisited to make new cages and exemplify ligand isomerism

“…We report here a Pd 3 L 4 -type cage prepared from Pd(NO 3 ) 2 and pyridine-3,5-diylbis(methylene) dinicotinate ( L1 ) . We reported earlier the first Pd 3 L 4 -type double-decker coordination cage using a simple tridentate “E” shaped ester-based ligand bis(pyridin-3-ylmethyl)pyridine-3,5-dicarboxylate ( L2 ) [22–23]. An additional feature in our design using L2 is the stoichiometrically controlled formation of PdL 2 -type spiro and Pd 3 L 4 -type double-decker complexes that is reversible under appropriate conditions.…”

“…We reported a family of Pd 2 L 4 -type complexes that fits under the definition of ligand isomerism [34]. In the pursuit of ligand isomerism in Pd 3 L 4 -type double-decker cages we intended to include our reported cage (prepared from palladium(II) and L2 ) [22–23] and construct a new isomeric Pd 3 L 4 -type complex. The complexation study of cis -protected and bare palladium(II) components with the new tridentate ligand, i.e., pyridine-3,5-diylbis(methylene) dinicotinate ( L1 ) is the focus of this work.…”