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

Abstract

Two new heterobimetallic cages, a trigonal‐bipyramidal and a cubic one, were assembled from the same mononuclear metalloligand by adopting the molecular library approach, using iron(II) and palladium(II) building blocks. The ligand system was designed to readily assemble through subcomponent self‐assembly. It allowed the introduction of steric strain at the iron(II) centres, which stabilizes its paramagnetic high‐spin state. This steric strain was utilized to drive dynamic complex‐to‐complex transformations with both the metalloligand and heterobimetallic cages. Addition of sterically less crowded subcomponents as a chemical stimulus transformed all complexes to their previously reported low‐spin analogues. The metalloligand and bipyramid incorporated the new building block more readily than the cubic cage, probably because the geometric structure of the sterically crowded metalloligand favours the cube formation. Furthermore it was possible to provoke structural transformations upon addition of more favourable chelating ligands, converting the cubic structures into bipyramidal ones.

A Paramagnetic NMR Spectroscopy Toolbox for the Characterisation of Paramagnetic/Spin-Crossover Coordination Complexes and Metal-Organic Cages

“…However, the acquisition of two HMQC spectra was necessary to cover the large spectral range in both dimensions as non-uniform excitation resulted in a decrease in the intensity or complete loss of cross-peaks at the extremes of the spectral range ( Figure 4). Nevertheless, an overlay of the two HMQC spectra confirmed the assignments made using the selective 1 H-decoupling 13 C experiments ( Figures S42-S46). HMBC spectra were also acquired in an attempt to assign the quaternary carbons and the three spin systems within a particular ligand environment; however, no cross-peaks were observed due to the long delays resulting from the small magnitude of 3 J coupling constants in contrast to the large 1 J coupling constants utilised in the HMQC experiments.…”

“…HSQC and HMBC). The protoncoupled 13 C spectrum contained signals over almost a 900 ppm range ( Figure S41), making uniform excitation over this very wide spectral range difficult. Therefore, overlapping spectra of smaller spectral widths were acquired to cover the entire range.…”

“…NMR spectra were recorded on a Bruker Avance 200, a Bruker AvanceNeo 500, or a Bruker Avance 600 spectrometer, the latter being equipped with a cryogenically cooled triple-resonance probe head. Chemical shifts for 1 H, 13 C, and 19 F spectra are expressed in parts per million (ppm) and coupling constants (J) are reported in Hertz (Hz). 1 H and 13 C spectra of the diamagnetic compounds were referenced to TMS at 0.0 ppm and the chemical shifts of the paramagnetic complexes/cage are reported relative to the resonance of the residual methyl proton and carbon of CD3CN (δH = 1.94 ppm, δC = 1.32 ppm).…”

Better Together: Functional Heterobimetallic Macrocyclic and Cage‐like Assemblies

“…Another example of ad ynamic heterobimetallic system,c onsisting of ac ube andatrigonal bipyramid, that allows for cage-to-cage transformations could be presented by our group recently. [37] Ligand fragment exchanges were possible due to as terically strained coordination sphere around iron(II) cations,c aused by crowded ligandsw ith methyl groups.W hen 11 or 15 were treated with an analogous less bulky non-methylatedb uildingb lock, the systems incorporated the new buildingb lock releasing the less favorable subcomponent. The reduction of steric strain might be the driving force in this case and eventually resulted in ac hange of the spin state of iron(II) cations from high-spin in strained cages to low-spin.…”

Kinetic selection of Pd4L2 metallocyclic and Pd6L3 trigonal prismatic assemblies

“…These can provide either a strong or weak trans-effect, which can tune the metal-multitopic ligand interactions from labile to more inert. While there have been numerous separate reports that involve assemblies with either strong trans-effect ancillary ligands, such as the diphosphines commonly utilised by Stang and others, [7][8][9][10] or weaker transeffect ligands, usually nitrogen donors such as ethylene diamine and their derivatives, 6,11,12 studies that involve and simultaneously compare the two are relatively scarce. [13][14][15] In this study we provide a rare direct comparison, and show how careful selection can be used to control the formation of different architectures.…”