Binuclear coordination complex of open merocyanine form of photochromic spiropyran with MnII(hfac)2 having high spin (S = 5) ground state

• Published in: New journal of chemistry 2023-03, Vol.47 (11), p.5470-5476
• Main Authors: Osipov, Nikita G, Faraonov, Maxim A, Shestakov, Alexander F, Mikhailenko, Maxim V, Kuzmin, Alexey V, Khasanov, Salavat S, Otsuka, Akihiro, Yamochi, Hideki, Kitagawa, Hiroshi, Konarev, Dmitri V
• Format: Article
• Language: English
• Subjects: Coordination compounds; Coupling (molecular); Dimers; Exchanging; Ferromagnetism; Ligands; Manganese; Oxygen atoms; Photochromism; Spiropyrans
• ISSN: 1144-0546; 1369-9261
• DOI: 10.1039/d3nj00058c

Photochromic molecules can transform from colorless closed to colored open forms by coordination with metal ions. Interaction of photochromic 1,3,3-trimethylindolino-β-naphthopyrylospiran (TMI-NPS) with manganese(ii) hexafluoroacetylacetonate in o-dichlorobenzene results in the formation of deep red-violet solution indicating a coordination-induced transition from closed to colored open form. Precipitation of crystals yields {MnII(hfac)2·(μ2-TMI-NPS)}2 dimers (1) in which two Mn(ii) atoms of hexafluoroacetylacetonate are bridged by oxygen atoms of two TMI-NPS ligands in the open form. Magnetic studies show a weak ferromagnetic exchange between MnII spins through oxygen atoms of TMI-NPS with estimated exchange interaction (J) of +1.07 cm−1. A positive Weiss temperature of +8 K also supports ferromagnetic coupling. As a result, MnII spins arrange parallel to each other at 2 K, and correspondingly, these dimers transfer to a high spin (S = 5) state. DFT calculations support noticeable mixing of the metal and ligand orbitals and essential positive charge on the TMI-NPS ligands, which can provide ferromagnetic exchange between MnII spins.