Ultrathin Films of 2D Hofmann-Type Coordination Polymers: Influence of Pillaring Linkers on Structural Flexibility and Vertical Charge Transport

Searching for novel materials and controlling their nanostructuration into electronic devices is a challenging task ahead of chemists and chemical engineers. Even more so when this new application requires an exquisite control over the morphology, crystallinity, roughness, and orientation of the films produced. In this context, it is of critical importance to analyze the influence of the chemical composition of perspective materials on their properties at the nanoscale. We report the fabrication of ultrathin films (thickness < 30 nm) of a family of Fe^II Hofmann-like coordination polymers (CPs) by using an optimized liquid-phase epitaxy (LPE) set up. The series [Fe(L)₂{Pt(CN)₄}] (L = pyridine, pyrimidine, and isoquinoline) conform an ideal platform for correlating the effect of the axial nitrogenated ligand with changes to their structural response to guests or electrical resistance. All film properties relevant to device integration have been thoroughly analyzed with complementary surface techniques for a meaningful comparison. Our results reveal that changes to this ligand can hinder the structural transformation triggered by the absorption of guest molecules previously reported for the pyridine phase. Also important, it can substantially hinder vertical charge transport across the layers, even at the ultrathin film limit.