DiffTMC: Structure- and Property-Guided Diffusion Models for Designing Transition Metal Complexes

Transition metal (TM) complexes are functional systems composed of metal centres coordinated by ligand molecules. Their three-dimensional structural characteristics, including shape, symmetry, and coordination number, play a critical role in determining their physicochemical properties. In this work, we present DiffTMC, an equivariant diffusion model for the targeted design of TM complexes with specified structural features and properties. We introduce structure-aware guidance for connectivity, coordination number, and shape, enabling DiffTMC to generate TM complexes with desired coordination environments. To explicitly control symmetry, we further propose a tessellation-based strategy that allows DiffTMC to generate strictly symmetric TM complexes belonging to a prescribed point group. In addition, we incorporate property conditioning, using the HOMO--LUMO gap as a representative example. Density functional theory (DFT) calculations indicate that 76 of 100 randomly sampled complexes fall below the prescribed HOMO-LUMO gap threshold. Overall, these results demonstrate that the proposed structural and property guidance effectively enables the controlled and targeted design of transition metal complexes.