Implications of Coordination Chemistry to Cationic Interactions in Honeycomb Layered Nickel Tellurates

Honeycomb layered tellurates represent a burgeoning class of multi-functional materials with fascinating crystal-structural versatility and a rich composition space. Despite their multifold capabilities, their compositional diversity remains underexplored due to complexities in experimental design and syntheses. Thus, in a bid to expand this frontier and derive relevant insights into allowed metastable compositions, we employ a density functional theory ($\rm DFT$) approach to predict $in$ $silico$ the crystal structures of new honeycomb layered tellurates embodied by the composition, $A\rm_2 Ni_2TeO_6$ ($A$ = alkali, hydrogen or coinage-metal cations). Here, alkali-metal atoms with vastly larger radii than $\rm K$ ($\rm Rb$ and $\rm Cs$) are found to engender a prismatic coordination with the oxygen atoms from the honeycomb slabs whilst coinage-metal atoms ($\rm Ag$, $\rm Au$ and $\rm Cu$) display a propensity for linear coordination. Further, $\rm H_2 Ni_2TeO_6$ is found to also render a linear coordination wherein the hydrogen atom preferentially establishes a stronger coordination with one of the oxygen atoms to form hydroxyl groups. All $A$ cations in the studied $A\rm_2 Ni_2TeO_6$ compositions form a honeycomb lattice. Conclusions on the possibility of a monolayer-bilayer phase transition in coinage metal atom tellurates can be drawn by considering the implications of conformal symmetry of the cation honeycomb lattice and metallophilicity. This work not only propounds new honeycomb layered tellurate compositions but also provides novel insight into the rational design of multifunctional materials for applications ranging from energy storage, catalysis and optics to analogue condensed matter systems of gravity.