Honeycomb lattice iridate on the verge of Mott-collapse

A new honeycomb lattice iridate (La,Na)IrO${}_3$ ($\approx$ LaNaIr${}_2$O${}_6$) is successfully synthesized from the spin-orbit coupled Mott insulator Na${}_2$IrO${}_3$ by replacing the interlayer Na${}^{+}$ ions with La${}^{3+}$ ions. (La,Na)IrO${}_3$ shows a finite Sommerfeld term in heat capacity and a $-\ln T$ dependence of resistivity, indicating a realization of a metallic state driven by a Mott collapse. Furthermore, crystal structure analysis reveals the formation of Ir zig-zag chains with metal-metal bonding, increasing kinetic energy resulting in the Mott collapse. This observation would be due to a Mott collapse induced in a $J_{\mathrm{e}\mathrm{f}\mathrm{f}}=1\mathrm{/}2$ spin-orbit coupling Mott insulator with an Ir honeycomb lattice by topochemical control of the ionic configuration.