Excellent self-assembly properties of Iron Phthalocyanines on alumina for locally ordered single-atom catalysts

In a biomimetic approach, metal Phthalocyanines (Pcs) can be considered to efficiently model single atom catalysts (SACs), hosting catalytically active single metal atoms in their macrocyclic cages. An ordered 2D array of SACs can thus be obtained when metal Pcs are assembled in a regular framework. In this work we consider in particular Iron Pcs (FePcs) on an ultra-thin alumina film grown on the Ni₃Al(111) surface. Intrinsic modulations in the potential energy surface related with the oxide film structure drive the self-assembly of FePc molecules into a regular array, with molecular vacancies forming a hexagonal Bravais lattice with the same periodicity of the substrate, i.e. with a lattice parameter of about 4 nm. The symmetry of the supramolecular structure is dictated by the template rather than by the C_4v symmetry of the individual molecules, thus indicating prevalence of molecule-substrate interactions with respect to intermolecular forces. The same hexagonal periodicity extends also to the multilayer, which starts forming already before completion of the first, interfacial monolayer. The latter exhibits a local definite chirality, also propagating to the multilayer in a determined stacking sequence.