  Nearly two decades ago, Alexei Kitaev proposed a model for spin-$1/2$
particles with bond-directional interactions on a two-dimensional honeycomb
lattice which had the potential to host a quantum spin-liquid ground state.
This work initiated numerous investigations to design and synthesize materials
that would physically realize the Kitaev Hamiltonian. The first-generation of
such materials, such as Na$_{2}$IrO$_{3}$, $\alpha$-Li$_{2}$IrO$_{3}$, and
$\alpha$-RuCl$_{3}$, revealed the presence of non-Kitaev interactions such as
the Heisenberg and off-diagonal exchange. Both physical pressure and chemical
doping were used to tune the relative strength of the Kitaev and competing
interactions; however, little progress was made towards achieving a purely
Kitaev system. Here, we review the recent breakthrough in modifying Kitaev
magnets via topochemical methods that has led to the second-generation of
Kitaev materials. We show how structural modifications due to the topotactic
exchange reactions can alter the magnetic interactions in favor of a quantum
spin-liquid phase.
