Similar to the MOF identification scheme (MOFid) of Bucior et al., we use a string representation that captures the chemistry of MOF building blocks and some of the structural information through topology encoding. However, our representation differs from MOFid in two notable ways: (1) we consider MOF building blocks as secondary building units (SBUs) -which are defined by their connection points to other SBUs within a topological net 9 -while MOFid's chemistry-focused syntax retains organic linkers as discrete building blocks, including any carboxylate groups; (2) the chemistry of MOF building blocks is described here using SELFIES (a 100% robust molecular string representation) rather than SMILES 36,37 (for which a large proportion of strings do not map to a valid molecular graph). Specifically, Group SELFIES is used to represent the edge SBUs (i.e., the linkers) while SELFIES is used for the node SBUs. This choice is motivated by the observation that chemical moiety important for MOF linker design, such as functional groups or aromatic rings, are rarely preserved when the SELFIES representation of edge SBUs are perturbed.