ic7b02702_si_001.pdf (5.89 MB)
Thermochromic Uranyl Isothiocyanates: Influencing Charge Transfer Bands with Supramolecular Structure
journal contribution
posted on 2018-02-13, 12:50 authored by Robert G. Surbella, Lucas C. Ducati, Jochen Autschbach, Nicholas P. Deifel, Christopher L. CahillThe synthesis and
structural characterization of seven new [UO2(NCS)5]3–- and [UO2(NCS)4Cl]3–-containing materials charge balanced by 4-phenylpyridinium
or 4,4′-bipyridinium cations are reported. Assembly of these
materials occurs via a diverse set of noncovalent interactions, with
the most prevalent involving the terminal sulfur atoms, which can
both accept hydrogen bonds and/or form S···S and S···Oyl interactions. The electrostatic potential of the [UO2(NCS)5]3– and [UO2(NCS)4Cl]3– anions was calculated and
mapped on the 0.001 au isodensity surface to rationalize the observed
assembly modes and to provide an electrostatic basis to elucidate
the role of the S atoms as both donors and acceptors of noncovalent
interactions. Compounds 1–7 display
a range of colors (red to yellow) as well as pronounced thermochromism.
A computational treatment (time-dependent density functional theory,
TDDFT) of the absorbance properties supports the temperature dependence
on the ratio of inter- to intramolecular
ligand to metal charge transfer (LMCT) bands as obtained from UV–vis
diffuse reflectance analysis. Finally, the luminescence profiles of
these materials feature additional peaks atypical for most uranyl-containing
materials, and a combined spectroscopic (Raman, IR, and fluorescence)
and computational (harmonic frequency calculations) effort assigns
these as originating from vibronic coupling between the ν1 UO symmetric stretch and bending modes of the isothiocyanate
ligands.