The thermodynamics of hydrogen interaction with coordinatively unsaturated Sc(III) cationic sites in the metal organic framework MIL-100(Sc) was studied by variable temperature infrared spectroscopy. Simultaneous measurement of the hydrogen equilibrium pressure ( inside a closed IR cell) and the integrated IR absorbance over the temperature range 80-125 K led to the determination of the corresponding values of standard adsorption enthalpy and entropy, which resulted to be Delta H(0) = -11.2 (+/- 1) kJ mol(1) and Delta S(0) = -120 (+/- 10) J mol(1) K(1). The enthalpy value is among the largest reported so far for hydrogen adsorption on MOFs. (C) 2011 Elsevier B. V. All rights reserved.