  We report the structures and physical properties of two new iridates,
NaIrO$_3$ and Sr$_3$CaIr$_2$O$_9$, both of which contain continuous
two-dimensional honeycomb connectivity. NaIrO3 is produced by room temperature
oxidative deintercalation of sodium from Na$_2$IrO$_3$, and contains
edge-sharing IrO6 octahedra that form a planar honeycomb lattice.
Sr$_3$CaIr$_2$O$_9$, produced via conventional solid-state synthesis, hosts a
buckled honeycomb lattice with novel corner-sharing connectivity between IrO6
octahedra. Both of these new compounds are comprised of Ir$^{5+}$ (5$d^4$) and
exhibit negligible magnetic susceptibility. They are thus platforms to
investigate the origin of the nonmagnetic behavior exhibited by Ir$^{5+}$
oxides, and provide the first examples of a $J$ = 0 state on a honeycomb
lattice.
