A novel rhodium [Rh(NO3)5]2− anionic complex with mixed denticity of nitrato ligands was isolated in a form of its poorly soluble caesium salt. The structure of the salt was studied by an X-ray single crystal method. DFT-based theoretical studies were carried out to gain insights into the electronic structure and the properties of the [Rh(NO3)5]2− complex. The calculated 15N NMR chemical shifts of nitrato groups in [Rh(NO3)5]2− complex was found to become sensitive to the nitrate ligand coordination bonding mode upon ion-pairing with caesium cations. In good agreement with experimental findings, the DFT calculated free energies for the addition of H2O or NO3 − ligands to the [Rh(NO3)5]2− complex points to its low hydrolytic stability.