  The degree of electron correlations remains a central issue in the iron-based
superconductors. The parent iron pnictides are antiferromagnetic, and their
bad-metal behavior has been interpreted in terms of proximity to a Mott
transition. We study such a transition in multi-orbital models on modulated
lattices containing an ordered pattern of iron vacancies, using a slave-rotor
method. We show that the ordered vacancies lead to a band-narrowing, which
pushes the system to the Mott insulator side. This effect is proposed to
underlie the insulating behavior observed in the parent compounds of the newly
discovered (K,Tl)yFexSe2 superconductors.
