Structural Analysis and Electronic Properties of Negatively Charged TCNQ: 2D Networks (TCNQ)2Mn Assembled on Cu(100)

A compound two-dimensional monolayer mixing Mn atoms and 7,7,8,8-tetracyanoquinoclimethane (TCNQ) molecules was synthesized by supramolecular assembly on a Cu(100) surface under ultrahigh-vacuum conditions. The interactions in the Mn(TCNQ)(2) network and in the full system arc analyzed from a molecular orbital perspective and in the light of scanning tunneling microscopy (STM) imaging and simulations. Structural, electronic, and magnetic properties are studied in detail using density functional theory (DFT) calculations. In the absence of Cu and depending on the theoretical method used, the TCNQ species can be formally described as either dianions TCNQ(2-) interacting with Mn4+ cations according to ligand held theory (using GGA calculations) or, alternatively, as radical monoanions interacting with Mn2+ cations in a high spin state (using GGA+U calculations). In the complete system including a Cu substrate, whatever theoretical method is used, TCNQs appear as dianions interacting with both Mn2+ cations in a high spin state (d(5)) and charged copper surface atoms.