  The metal-hydride-based topochemical reduction process has produced novel
thermodynamically unstable phases across various transition metal oxide series
with unusual crystal structures and non-trivial ground states. Here, by such an
oxygen (de-) intercalation method we synthesis a novel samarium nickelate with
ordered nickel valences associated with tri-component coordination
configurations. This structure, with a formula of Sm$_{9}$Ni$_{9}$O$_{22}$ as
revealed by four-dimensional scanning transmission electron microscopy, emerges
from the intricate planes of {303}$_{\text{pc}}$ ordered apical oxygen
vacancies. X-ray spectroscopy measurements and ab-initio calculations show the
coexistence of square-planar, pyramidal and octahedral Ni sites with mono-, bi-
and tri-valences. It leads to an intense orbital polarization, charge-ordering,
and a ground state with a strong electron localization marked by the
disappearance of ligand-hole configuration at low-temperature. This new
nickelate compound provides another example of previously inaccessible
materials enabled by topotactic transformations and presents a unique platform
where mixed Ni valence can give rise to exotic phenomena.
