This report focuses on heat capacity and thermodynamic properties of crystalline perovskite-like layered oxides: protonated titanate H2Nd2Ti3O10 and its n-butoxy derivative, designated as H2Nd2Ti3O10 × BuOH, in the temperature range from 5 to 340 K. Isobaric heat capacity of the compounds was measured using precise adiabatic vacuum calorimetry. Standard
thermodynamic properties of the oxides were estimated based on the temperature dependencies of the experimental heat capacity. The data obtained allowed us to verify the applicability of the additivity principle for predicting the thermodynamic properties of layered organic–inorganic hybrids. As a result of the experiments, it was established that the principle of additivity is not realized in the case of covalent bonding between the inorganic matrix and organic molecules, which indicates the impossibility of calculating the heat capacity of the hybrid material as the sum of the values for the oxide and organic components, confirming the presence of a covalent bond between them.