Subcomponent Exchange Transforms an Fe^II₄L₄ Cage from High- to Low-Spin, Switching Guest Release in a Two-Cage System

Abstract

Subcomponent exchange transformed new high-spin FeII4L4 cage 1 into previously-reported low-spin FeII4L4 cage 2: 2-formyl-6-methylpyridine was ejected in favor of the less sterically hindered 2-formylpyridine, with concomitant high- to low-spin transition of the cage’s FeII centers. High-spin 1 also reacted more readily with electron-rich anilines than 2, enabling the design of a system consisting of two cages that could release their guests in response to combinations of different stimuli. The addition of p-anisidine to a mixture of high-spin 1 and previously-reported low-spin FeII4L6 cage 3 resulted in the destruction of 1 and the release of its guest. However, initial addition of 2-formylpyridine to an identical mixture of 1 and 3 resulted in the transformation of 1 into 2; added p-anisidine then reacted preferentially with 3 releasing its guest. The addition of 2-formylpyridine thus modulated the system’s behavior, fundamentally altering its response to the subsequent signal p-anisidine.

Dynamic Complex‐to‐Complex Transformations of Heterobimetallic Systems Influence the Cage Structure or Spin State of Iron(II) Ions

“…These aldehydes were also used to develop 3D architectures with different shapes and sizes that show complex‐to‐complex transformations upon replacement of 2‐formyl‐6‐methylpyridine with less bulky 2‐formylpyridine. These transformations resulted in a change of the spin state of iron(II) cations from high spin to low spin, due to shortening of the Fe−N bonds . The decrease of steric strain might be responsible for the preferential incorporation of 2‐formylpyridine over 2‐formyl‐6‐methylpyridine …”

“…These transformations resulted in a change of the spin state of iron(II) cations from high spin to low spin, due to shortening of the Fe−N bonds . The decrease of steric strain might be responsible for the preferential incorporation of 2‐formylpyridine over 2‐formyl‐6‐methylpyridine …”

“…The steric strain in ML‐1 , BP‐1 , and CU‐1 results in an elongation of the Fe−N bond lengths and the stabilization of the paramagnetic high‐spin state . Still the situation is energetically unfavourable, and hence, can be exploited in thermodynamically driven complex‐to‐complex transformations during which the steric strain is reduced.…”

No, Not That Way, the Other Way: Creating Active Sites in Self-Assembled Host Molecules

“…Again, it should be noted here that the Nitschke lab has performed an extensive series of studies on these processes in larger, more complex systems as well. 53 2-Formylpyridines with groups at the 5-position have no steric clash with the metal centers, and any differences in assembly are merely based on donor ability. If species such as 6-methyl formylpyridine (MePyCHO) are used (or 2-formylquinoline), the assembly behavior is quite different.…”

Selective Encapsulation and Separation of Dihalobenzene Isomers with Discrete Heterometallic Macrocages

“…[4] Due to their remarkables olubility in aw ide variety of solvents, self-assembled metallamacrocyclesand metallacages have found application in several research areas, [5,6] includ-ing catalysis, biosciences,s eparation processes andt he development of advanced sensors. [7,8] Haloarenes are valuable starting materials for cross-coupling reactions, ak ey step in the synthesis of drugs and conjugated organic compounds. [9,10] Due to their similarc hemical and physicalp roperties, traditional methods either have great difficultiesi ns eparating of haloarenei somers or effect the separation with high cost.…”