Off-Lattice Coarse-Grained Model of Surface-Confined Metal-Organic Architectures

An off-lattice model of self-assembling surfaceconfined metal-organic nanostructures (SMONs) comprising tripod molecules has been developed. The model considers the directionality and saturability of coordination bonding. To parametrize the model, density functional theory methods have been used. Self-assembly of the SMONs has been simulated with Metropolis Monte Carlo method in the canonical ensemble. In this paper, we investigate how the directionality of metal-linker bonding and the linker/metal ratio affect the self-assembly of SMONs containing metal centers with different coordination numbers: M(II), M(III), and M(IV). The directionality of coordination bonding is determined by the functional group of the linker molecule and is defined in the model as the angular diameter of the interaction shell. Regardless of the preferred coordination number of the metal center, even a small change in the angular diameter significantly affects the structure of the SMONs. Depending on the angular diameter and composition of the metal-organic layer, various structures can appear. Using our model, we have simulated the self-assembly of the random porous (or defected honeycomb) and triangular structures, the set of hexagonal phases, amorphous structures of different densities, and metal- organic chains. Relative thermal stabilities of clusters of the main structures have been studied. The model reproduces correctly the main SMONs observed by scanning tunneling microscopy.