Synthesis and Computational Study of a Pyridylcarbene Fe(II) Complex: Unexpected Effects of fac/mer Isomerism in Metal-to-Ligand Triplet Potential Energy Surfaces

• Published in: Inorganic chemistry 2018-08, Vol.57 (16), p.10431-10441
• Main Authors: Francés-Monerris, Antonio, Magra, Kevin, Darari, Mohamed, Cebrián, Cristina, Beley, Marc, Domenichini, Edoardo, Haacke, Stefan, Pastore, Mariachiara, Assfeld, Xavier, Gros, Philippe C, Monari, Antonio
• Format: Article
• Language: English
• Subjects: Chemical Sciences; Coordination chemistry; or physical chemistry; Theoretical and
• ISSN: 0020-1669; 1520-510X
• DOI: 10.1021/acs.inorgchem.8b01695

The synthesis and the steady-state absorption spectrum of a new pyridine-imidazolylidene Fe­(II) complex (Fe-NHC) are presented. A detailed mechanism of the triplet metal-to-ligand charge-transfer states decay is provided on the basis of minimum energy path (MEP) calculations used to connect the lowest-lying singlet, triplet, and quintet state minima. The competition between the different decay pathways involved in the photoresponse is assessed by analyzing the shapes of the obtained potential energy surfaces. A qualitative difference between facial (fac) and meridional (mer) isomers’ potential energy surface (PES) topologies is evidenced for the first time in iron-based complexes. Indeed, the mer complex shows a steeper triplet path toward the corresponding 3MC minimum, which lies at a lower energy as compared to the fac isomer, thus pointing to a faster triplet decay of the former. Furthermore, while a major role of the metal-centered quintet state population from the triplet 3MC region is excluded, we identify the enlargement of iron–nitrogen bonds as the main normal modes driving the excited-state decay.