10.1021/acs.inorgchem.8b00352.s001
Po-Jung Huang
Po-Jung
Huang
Yoshiki Natori
Yoshiki
Natori
Yasutaka Kitagawa
Yasutaka
Kitagawa
Yoshihiro Sekine
Yoshihiro
Sekine
Wataru Kosaka
Wataru
Kosaka
Hitoshi Miyasaka
Hitoshi
Miyasaka
One-Dimensional
Chains of Paddlewheel-Type Dichromium(II,II) Tetraacetate Complexes:
Study of Electronic Structure Influenced by σ- and π‑Donation
of Axial Linkers
American Chemical Society
2018
HOMO
σ- donor strength
Cr
RCO
p K b
L ax
II
Electronic Structure Influenced
2018-04-11 16:48:37
Journal contribution
https://acs.figshare.com/articles/journal_contribution/One-Dimensional_Chains_of_Paddlewheel-Type_Dichromium_II_II_Tetraacetate_Complexes_Study_of_Electronic_Structure_Influenced_by_-_and_Donation_of_Axial_Linkers/6128180
Paddlewheel-type
carboxylate-bridged dichromium(II,II) complexes possess intriguing
properties such as high redox activity and thermally assisted paramagnetism.
However, the relationship of their structures with electronic states
and physical properties has not been extensively studied. In this
work, we investigated a series of one-dimensional chain complexes
based on the paddlewheel-type dichromium(II,II) tetraacetate complex
([Cr<sub>2</sub><sup>II,II</sup>(OAc)<sub>4</sub>] = [Cr<sub>2</sub><sup>II,II</sup>]) with pyridine/pyrazine-type organic linkers
(μ<sub>2</sub>-L<sub>ax</sub>) having different σ- and
π-donating abilities to clarify the electronic structure of
[Cr<sub>2</sub><sup>II,II</sup>] assemblies. The chain compounds are
stable in air, probably owing to their robust polymerized forms. X-ray
crystallographic studies and magnetic measurements revealed that the
basicity (p<i>K</i><sub>b</sub>) of L<sub>ax</sub>, which
quantitatively correlates with the σ-donor strength of L<sub>ax</sub>, modulates the Cr–Cr and Cr–L<sub>ax</sub> distances and the energy separation (<i>E</i><sub>S–T</sub>) between the diamagnetic (singlet) and thermally populated paramagnetic
(triplet) states. The Cr–Cr and Cr–L<sub>ax</sub> distances
are strongly influenced by σ- and π-donation from L<sub>ax</sub>, while the frontier δ orbital makes only a small contribution
to the structural features. Density functional theory calculations
were conducted to clarify this issue. The calculations produced the
following unanticipated results against the long-known model: (i)
the σ bonding orbital is the HOMO and dominates bonding in the
[Cr<sub>2</sub><sup>II,II</sup>] unit, (ii) the total Cr–Cr
bond order is less than 1.0, and (iii) the δ orbital electron
density is almost completely localized on the chromium sites. The
computational results accurately predict the magnetic behavior and
provide evidence for a new configuration of frontier orbitals in [Cr<sub>2</sub><sup>II,II</sup>(RCO<sub>2</sub>)<sub>4</sub>(L<sub>ax</sub>)<sub>2</sub>].