Iron complexes of bridging azo ligands in aqueous solution: changes in the thermal switching mechanism on coordination and oxidation state of metal centres

• Published in: Dalton transactions : an international journal of inorganic chemistry 2023-02, Vol.52 (6), p.172-173
• Main Authors: Bardají, Manuel, Font-Bardia, Mercè, Gallen, Albert, Garcia-Cirera, Beltzane, Ferrer, Montserrat, Martínez, Manuel
• Format: Article
• Language: English
• Subjects: Aqueous solutions; Coordination; Iron; Isomerization; Ligands; Oxidation; Valence
• ISSN: 1477-9226; 1477-9234
• DOI: 10.1039/d2dt03790d

Three azobenzenes CN(C 6 H 4 )-N&z.dbd;N-(C 5 H 4 N) ( py-iso ), CN(C 6 H 4 )-N&z.dbd;N-(C 6 H 4 )CN ( cyano-iso ) and CN(C 6 H 4 )-N&z.dbd;N-(C 6 H 4 )NC ( iso-iso ) with good coordinating groups (pyridine, phenylcyano or phenylisocyano) at the ends of the diazenyl unit have been synthesized and fully characterised. These compounds have been used as ligands in the synthesis of water-soluble metallic species by coordination to {Fe II (CN) 5 3− } units, either in one or two of the anchoring groups of the derivatives. Both the azo derivatives and their complexes are photochemically active with respect to their trans -to- cis isomerisation process. Their cis -to- trans reverse thermal reaction has been thoroughly studied as a function of the donor groups, solvent, temperature and pressure, in order to gain insight into the rotation or inversion mechanisms involved in the process. A comparison of the isomerisation mechanism between the iron complexes and the corresponding free ligands revealed an interesting fine tuning of the process on coordination of the {Fe II (CN) 5 3− } moieties, which may even produce, in some cases, non-photoswitchable species containing typically photoactive units. Isocyanide-appended azo derivatives have been designed as photoactive building blocks in assembly reactions; the rotation/inversion mechanistic tuning of the thermal cis -to- trans isomerisation has been analysed.