We have a worked example for geologically stable carbon sequestration without any novel chemical bonding, and that's storing carbon in compounds that are mostly unhydrogenated carbon by mass, deep underground:

Charcoal. If you aim to sequester carbon without some kind of reactant (and most reactants are incredibly energy intensive to make & stage, burning more CO2 than captured), you have to effectively make charcoal. Growing a forest, pyrolyzing it, and burying the charcoal, is the inverse process of coal mining, and is the default comparator on cost, effort, and materials for any sort of carbon sequestration scheme.