posted on 2024-03-13, 20:31authored byEmily Hruska, Quansong Zhu, Somnath Biswas, Matthew T. Fortunato, Dustin R. Broderick, Christine M. Morales, John M. Herbert, Claudia Turro, L. Robert Baker
The effects of temperature and chemical environment on
a pentanuclear
cyanide-bridged, trigonal bipyramidal molecular paramagnet have been
investigated. Using element- and oxidation state-specific near-ambient
pressure X-ray photoemission spectroscopy (NAP-XPS) to probe charge
transfer and second order, nonlinear vibrational spectroscopy, which
is sensitive to symmetry changes based on charge (de)localization
coupled with DFT, a detailed picture of environmental effects on charge-transfer-induced
spin transitions is presented. The molecular cluster, Co3Fe2(tmphen)6(μ-CN)6(t-CN)6, abbrev. Co3Fe2,
shows changes in electronic behavior depending on the chemical environment.
NAP-XPS shows that temperature changes induce a metal-to-metal charge
transfer (MMCT) in Co3Fe2 between a Co and Fe
center, while cycling between ultrahigh vacuum and 2 mbar of water
at constant temperature causes oxidation state changes not fully captured
by the MMCT picture. Sum frequency generation vibrational spectroscopy
(SFG-VS) probes the role of the cyanide ligand, which controls the
electron (de)localization via the superexchange coupling. Spectral
shifts and intensity changes indicate a change from a charge delocalized,
Robin-Day class II/III high spin state to a charge-localized, class
I low spin state consistent with DFT. In the presence of a H-bonding
solvent, the complex adopts a localized electronic structure, while
removal of the solvent delocalizes the charges and drives an MMCT.
This change in Robin-Day classification of the complex as a function
of chemical environment results in reversible switching of the dipole
moment, analogous to molecular multiferroics. These results illustrate
the important role of the chemical environment and solvation on underlying
charge and spin transitions in this and related complexes.