Unsymmetrical ligands still make one Pd2L4 cage isomer
Steric and geometric ligand design plus solvent polarity steer unsymmetrical dipyridyl ligands into a single cis or trans Pd2L4 cage rather than a statistical isomer mix.
Source
Conformational control of Pd<sub>2</sub>L<sub>4</sub> assemblies with unsymmetrical ligands
Study at a glance
- Design
- Other — Unsymmetrical bis-pyridyl ligands assembled with Pd(II) to control cis/trans Pd2L4 isomers
- N
- Coordination-cage synthesis/DFT — no sample N
- Population
- Pd2L4 coordination cages in MeCN/DMSO
- Outcome
- Ligand sterics locking preferred Pd2L4 cage isomers
Structured fields used in claim comparison tables when every cited study has a complete layer.
Inspect source passages
Unsymmetrical ligands still make one Pd2L4 cage isomer
These passages occur verbatim in the stored paper text. They support the points listed below; they do not verify every statement in the explanation.
DFT favoured trans-[Pd2(1)4]4+ by 6.1 kJ mol−1.
These calculations suggested that the trans -Pd 2 L 4 cage was the thermodynamically favoured species by 6.1 kJ mol −1 (), and thus the likely product.
cis-[Pd2(4)4]4+ was lowest in energy by 4.4–26.8 kJ mol−1 versus other isomers.
DFT calculations (Table S2) supported the cis -[Pd 2 ( 4 ) 4 ] 4+ isomer as being the lowest energy species by 4.4–26.8 kJ mol −1 compared to the other three potential isomers.
What they did
Authors synthesised unsymmetrical bis-pyridyl ligands, assembled them with [Pd(CH3CN)4](BF4)2 in acetonitrile or DMSO, and assigned cage isomers by 1H/DOSY NMR, MS, variable-temperature NMR, SCXRD and DFT relative energies.
What they found
Methyl steric bias and non-coplanar donors can lock a single cis-Pd2L4 isomer; ligand 1 gives trans in MeCN but a cis/trans mix in DMSO; DFT ranked isomers by several kJ mol−1.
The limits
What it doesn't show
The work does not demonstrate guest binding, catalysis, or multifunctional cavities inside these isomerically pure cages.
Key terms
- Pd2L4 cage
- Dinuclear palladium assembly of four ditopic ligands around two square-planar Pd(II) ions.
- cis vs trans isomer
- Relative arrangement of unsymmetrical ligands around the Pd2 core (like vs unlike ends clustered).
- DOSY NMR
- Diffusion-ordered NMR used to estimate hydrodynamic radius of the assembly.
- SCXRD
- Single-crystal X-ray diffraction confirming solid-state ligand arrangement.
- Naked Pd(II)
- Palladium precursor with labile acetonitrile ligands, [Pd(CH3CN)4]2+.
Flashcards
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Quiz yourself
Pd2L4 cages here are assembled from:
Common questions
What metal precursor was used?
[Pd(CH3CN)4](BF4)2.
How fast did ligand 2 form a single cage?
Within 2 h at room temperature in d6-DMSO.
What did DFT say about trans-[Pd2(1)4]4+?
It was favoured by 6.1 kJ mol−1 over the cis isomer.
Why does solvent change ligand-1 products?
Polar DMSO stabilises the more polar cis cage; MeCN gives trans only.
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