A self-assembled coordination cage usually possesses one well-defined three-dimensional (3D) cavity whereas infinite number of 3D-cavities are crafted in a designer metal-organic framework. Construction of a discrete coordination cage possessing multiple number of 3Dcavities is a challenging task. Here we report the peripheral decoration of a trinuclear [Pd 3 L 6 ] core with one, two and three units of a [Pd 2 L 4 ] entity for the preparation of multi-3D-cavity conjoined-cages of [Pd 4 (L a) 2 (L b) 4 ], [Pd 5 (L b) 4 (L c) 2 ] and [Pd 6 (L c) 6 ] formulations, respectively. Formation of the tetranuclear and pentanuclear complexes is attributed to the favorable integrative self-sorting of the participating components. Cage-fusion reactions and ligand-displacement-induced cage-to-cage transformation reactions are carried out using appropriately chosen ligand components and cages prepared in this work. The smaller [Pd 2 L 4 ] cavity selectively binds one unit of NO 3 − , F − , Cl − or Br − while the larger [Pd 3 L 6 ] cavity accommodates up to four DMSO molecules. Designing aspects of our conjoined-cages possess enough potential to inspire construction of exotic molecular architectures.

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.

The complexation study of cis-protected and bare palladium(II) components with a new tridentate ligand, i.e., pyridine-3,5-diylbis(methylene) dinicotinate (L1) is the focus of this work. Complexation of cis-Pd(tmeda)(NO3)2 with L1 at a 1:1 or 3:2 ratio produced [Pd(tmeda)(L1)](NO3)2 (1a). The reaction mixture obtained at 3:2 ratio upon prolonged heating, produced a small amount of [Pd3(tmeda)3(L1)2](NO3)6 (2a). Complexation of Pd(NO3)2 with L1 at a 1:2 or 3:4 ratios afforded [Pd(L1)2](NO3)2 (3a) and [(NO3)2@Pd3(L1)4](NO3)4 (4a), respectively. The encapsulated NO3 – ions of 4a undergo anion exchange with halides (F–, Cl– and Br– but not with I–) to form [(X)2@Pd3(L1)4](NO3)4 5a–7a. The coordination behaviour of ligand L1 and some dynamic properties of these complexes are compared with a set of known complexes prepared using the regioisomeric ligand bis(pyridin-3-ylmethyl)pyridine-3,5-dicarboxylate (L2). Importantly, a ligand isomerism phenomenon is claimed by considering complexes prepared from L1 and L2.