Autocatalytic Surface Explosion Chemistry of 2D Metal–Organic Frameworks

Metal–organic
frameworks are a combination of inorganic
constituents and organic ligands with a high degree of variability
which are, as coordination compounds in homogeneous catalysis, potentially
highly selective heterogeneous catalysts. The synthesis and thermal
stability of monolayer thin Cu-, Ni-, and Fe-squarate 2D MOFs are
studied using X-ray photoelectron spectroscopy, scanning tunneling
microscopy, and temperature-programmed reaction spectroscopy on a
Cu(100) surface in ultrahigh vacuum. Highly ordered 2D squarate MOFs
are obtained by mild annealing of squarate multilayers. Upon annealing
at higher temperatures, the Ni- and Fe-squarate layers undergo autocatalytic
surface explosion chemistry with carbon monoxide as a desorbing product
in a very narrow temperature interval. Despite the different stabilities
of Ni- and Fe-based MOFs, mixed {Ni + Fe}-MOFs also decompose in a
narrow single temperature interval. Such autocatalytic behavior is
explained by a numerical model whichunlike rate equation-based
kineticsexplicitly considers the chemical nature of nearest
neighbors.