The interaction of citrate with kite-like Fe \(_2\) O \(_3\) and tetranuclear Fe \(_4\) O \(_6\) molecules was investigated across seven dielectric environments at the UB3LYP-D3(BJ) level with def2-TZVP and 6-31+G(d) basis sets. Water was described with the Solvation Model based on Density (SMD), while five ionic liquids were represented with the generalized ionic-liquid SMD parameterization (SMD-GIL) across dielectric constants from 11.40 to 41.00. For Fe \(_2\) O \(_3-\) Citrate \(^{3-}\) , citrate binds through a bidentate O6/O7 carboxylate anchor that is preserved across the dielectric series, whereas Fe \(_4\) O \(_6\) engages two carboxylate arms through shorter monodentate contacts. The protonated central hydroxyl does not coordinate Fe directly, but stabilizes the bound citrate conformation through an intramolecular O–H \(\cdots \) O hydrogen bond. Natural bond orbital (NBO) analysis assigns this interaction mainly to LP(2) O14 \(\rightarrow \) \(\sigma ^*\) (O18–H19) donation, with \(E^{(2)}\) values of 3.65–5.46 kcal mol \(^{-1}\) across the dielectric sweep. Hybrid explicit-continuum tests with six water molecules and explicit [CH \(_3\) NH \(_3\) ][HCOO] ion pairs retain the same inner-sphere Fe2–O6/O7 attachment, showing that first-shell hydrogen bonding and ion-pair orientation refine rather than overturn the continuum description. The antiferromagnetic singlet is the ground state of Fe \(_2\) O \(_3-\) Citrate \(^{3-}\) in all environments, while one-electron oxidation favors a ferromagnetic dectet. BSSE-estimated coordination energies decrease from \(-144.90\) kcal mol \(^{-1}\) in the gas phase to \(-19.31\) kcal mol \(^{-1}\) in water, confirming strong dielectric attenuation while preserving stabilizing carboxylate binding. Formal deprotonation analysis shows that hydroxyl deprotonation of free citric acid is less favorable than carboxyl deprotonation by 22.09 kcal mol \(^{-1}\) in SMD water. Imposed Cit \(^{4-}\) binding opens a mixed alkoxide/carboxylate coordination channel, best viewed as a model for hydroxyl-deprotonating conditions rather than the dominant citrate form. Bond-dissociation scans give Fe–O(citrate) well depths of 24–39 kcal mol \(^{-1}\) and demonstrate cooperative bidentate stabilization.
