As the gas adsorption isotherms and the ex situ PXRD patterns indicate the changes of the material, in situ PXRD measurements in parallel to the adsorption of various gases should provide a clear image of the structural transitions occurring during gas adsorption. The results are in agreement with the previous observations as the reflections show the characteristic pattern of DUT-76(Cu) but the intensity rapidly decreases in the pressure range p/p0 = 0.1 -0.19, which is when the smallest kinds of pores -the cuboctahedral MOPs -are filled and the bigger tetragonal and ultimately the cubic pores fill up (see Figure ). In the desorption branch a further decrease in reflection intensities is observed. Subtle changes in the diffraction pattern are visible namely a transient increase of a peak at 2θ = 3.7° from p/p0 = 0.0 -0.039. In the higher angles range of 2θ > 8.0° reflection intensity drops and then increases again with a minimum at p/p0 = 0.0054. However, the formation of new crystalline phases was not observed. In situ PXRD, measured in parallel to physisorption of propane and n-butane show comparable results (see Figures ). The decrease in reflection intensity can be caused by either decomposition or amorphization.