On-Surface Synthesis of Spin Crossover Polymeric Chains

We report on the successful on-surface polymerization reaction of codeposited zwitterionic quinones with Fe atoms on Au(110) at an appropriate temperature. The resulting covalent one-dimensional polymer chains arrange in a well-ordered two-dimensional (2D) structure as proven by scanning tunneling microscopy and low-energy electron diffraction. The ordered regions can reach the micrometer size. Furthermore, the electronic and magnetic properties of the zwitterionic quinoidal polymers on Au(110) were investigated using the density functional theory with an explicit inclusion of the Hubbard U term. The spin-polarized generalized gradient approximation plus U method (SGGA + U) has been used, and the freestanding isolated polymer chain, the 2D arrangement, and the adsorbed polymers have been calculated. From ab initio calculations, we predict the zwitterionic quinoidal polymer chains to be a one-dimensional spin crossover compound. For the freestanding chains, we find two local minima with comparable energies...