Halide-Mediated Modification of Magnetism and Electronic Structure of α‑Co(II) Hydroxides: Synthesis, Characterization, and DFT+U Simulations

The
present study introduces a comprehensive exploration in terms of physicochemical
characterization and calculations based on density functional theory
with Hubbard’s correction (DFT+U) of the whole family of α-Co­(II)
hydroxyhalide (F, Cl, Br, I). These samples were synthesized
at room temperature by employing a one-pot approach based on
the epoxide route. A thorough characterization (powder X-ray diffraction,
X-ray photoelectron spectroscopy, thermogravimetric analysis/mass
spectroscopy, and magnetic and conductivity measurements) corroborated
by simulation is presented that analyzes the structural, magnetic,
and electronic aspects. Beyond the inherent tendency of intercalated
anions to modify the interlayer distance, the halide’s nature
has a marked effect on several aspects. Such as the modulation
of the CoOh to CoTd ratio, as well as the inherent
tendency towards dehydration and irreversible decomposition. Whereas
the magnetic behavior is strongly correlated with the CoTd amount reflected in the presence of glassy behavior with high magnetic
disorder, the electrical properties depend mainly on the nature of
the halide. The computed electronic structures suggest that the CoTd molar fraction exerts a minor effect on the inherent conductivity
of the phases. However, the band gap of the solid turns out to be
significantly dependent on the nature of the incorporated halide,
governed by ligand to metal charge transfer, which minimizes the gap
as the anionic radius becomes larger. Conductivity measurements of
pressed pellets confirm this trend. To the best of our knowledge,
this is the first report on the magnetic and electrical properties
of α-Co­(II) hydroxyhalides validated with in silico descriptions,
opening the gate for the rational design of layered hydroxylated phases
with tunable electrical, optical, and magnetic properties.