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

Abstract

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 Mg(2+), 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 Mg(2+), 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 Fe(II)(d)/cyano N(p) orbital to a phenanthroline pi* 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 Fe(II)(d)/cyano N(p) orbitals as a result of specific interactions with water solvent molecules or Mg(2+) 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.

Empirical Parameters for Solvent Acidity, Basicity, Dipolarity, and Polarizability of the Ionic Liquids [BMIM][BF4] and [BMIM][PF6]

“…Table SI3 in SI) the dipolarity term produces a bathochromic band shift (positive solvatochromism) of the electronic transition.From Eq. (6), the gas-phase transition appears to be at ν = 17100 cm -1 , which is in good accord with the most intense transition, the B3LYP vertical excitation energy in vacuum at 2.19 eV (567 nm) or 17637 cm -1 44. Hence, the pure solvent scales yield a good gas-phase electronic transition for [Fe(phen) 2 (CN) 2 ].…”

Structure, Dynamics, and Computational Studies of Lanthanide‐Based Contrast Agents

“…The use of large core ECPs has been justified by the fact that 4f orbitals do not significantly contribute to bonding due to their limited radial extension as compared to the 5d and 6s shells [45,46]. This approach avoids many problems associated with the computational treatment of open-shell systems, and despite its approximate nature is an efficient computational tool that has proven to give good results in studies that focus on the structural features or the estimates of relative energies for Ln 3+ complexes at both the HF and DFT level [47][48][49][50][51][52][53][54][55][56][57].…”

Progress and Challenges in the Calculation of Electronic Excited States

“…[213] Interestingly, the low-lying states of Fe(phen) 2 (CN) 2 , mainly of MLCT character, are described well with both pure (PBE) and hybrid (B3LYP) functionals. [214] Moreover, the agreement in the presence of a continuum solvent or microsolvation improves slightly with the use of PBE and not the B3LYP functional. The reason behind the striking good performance of the pure functional in such a situation is probably due to the mixing of the d-based orbitals with ligand-based orbitals, leading to an overlapping of the orbitals involved in the state and a hence to a loose CT character.…”