American Chemical Society
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Solvatochromic and Ionochromic Effects of Iron(II)bis(1,10-phenanthroline)dicyano: a Theoretical Study

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journal contribution
posted on 2010-02-15, 00:00 authored by Ivelina Georgieva, Adélia J. A. Aquino, Natasha Trendafilova, Paulo S. Santos, Hans Lischka
Solvatochromic and ionochromic effects of the iron(II)bis(1,10-phenanthroline)dicyano (Fe(phen)2(CN)2) complex were investigated by means of combined DFT/TDDFT calculations using the PBE and B3LYP functionals. Extended solvation models of Fe(phen)2(CN)2 in acetonitrile and aqueous solution, as well as including interaction with Mg2+, were constructed. The calculated vertical excitation energies reproduce well the observed solvatochromism in acetonitrile and aqueous solutions, the ionochromism in acetonitrile in the presence of Mg2+, and the absence of ionochromic effect in aqueous solution. The vertical excitation energies and the nature of the transitions were reliably predicted after inclusion of geometry relaxation upon aqueous micro- and global solvation and solvent polarization effect in the TDDFT calculations. The two intense UV−vis absorption bands occurring for all systems studied are interpreted as transitions from a hybrid FeII(d)/cyano N(p) orbital to a phenanthroline π* orbital rather than a pure metal-to-ligand-charge transfer (MLCT). The solvatochromic and ionochromic blue band shifts of Fe(phen)2(CN)2 were explained with preferential stabilization of the highest occupied FeII(d)/cyano N(p) orbitals as a result of specific interactions with water solvent molecules or Mg2+ ions in solution. Such interactions occur through the CN groups in the complex, and they have a decisive role for the observed blue shifts of UV−vis absorption bands.