MOF matrix likely exerts a decrease in pore symmetry, leading to splitting of the relevant diffraction peaks. For example, local electrostatic interaction could cause a displacement of the copper nodes similar to Zn 2+ in ZIF-8, or a collective distortion of the Cu paddle-wheel units. To unveil the potential lattice change at local scale after the incorporation of the IL into the CuBTC pores X-ray total scattering experiments using the pair distribution function (PDF) were collected at room temperature (Figure ). PDF data using the D(r) function showed the expected atomatom correlations for the CuBTC using a previously reported structure (CCDC: 755080) (Figure , Figures ). IL correlations were also elucidated (Figure ). IL@CuBTC D(r) function exhibited contributions from both materials but predominantly from CuBTC (Figure ). Differential PDF (dPDF) of the CuBTC and composite D(r) functions resulted in a dPDF pattern containing features of the pristine IL, verifying the presence of the IL in the MOF and revealing other unidentified correlations (Figure ). Despite the wide employment of dPDF to observe phase transitions and the presence of metal-oxoclusters at a local scale, the presence of three components (CuBTC, IL and the interface) complicates the precise determination of atompair correlations using this methodology. Recently, the use of the principal component analysis (PCA) and multilinear regression (MLR) analysis of PDF data has been employed in MOF-glass composites to successfully unveil the potential interactions at the interface. PCA of the pristine materials and the composite has resolved three principal components (PCs) (Figure ); PC1 (58.85%) and PC2 (33.38%) correspond to CuBTC and IL, respectively (Figure ). The weighting of PC1 in the composite is greater than both parent materials, while the PC2 weighting decreases with IL content (Figure ). However, the weightings of PC3 have a lower contribution (in absolute value) for the composite than the pristine materials. The negative weighting to PC3 for the composites suggests that -PC3 may be the more physically relevant function. The MLR approach fits the composite PDF function using proportions of the pristine CuBTC and IL D(r) functions (see Supporting Information) (Figure ). The residual difference between the experimental and the fitted composite PDFs, may reveal any potential IL-CuBTC correlations as they cannot be present in the pristine CuBTC and IL D(r) functions. Comparing the three different approaches, the negative PC3 and the residual obtained in the MLR exhibit very similar features, that might corresponding with the atom-atom interactions between the IL and CuBTC (Figure ). Two main features at 1.99 and ). These interactions have also been previously proposed in other IL-MOF composites. Ex situ Raman spectra of CuBTC and IL@CuBTC taken in the frequency range of 100-600 cm -1 are presented in Figure , with a range of vibrations related to the to the Cu paddle-wheel units in CuBTC. These spectra were collected after being subjected to a variable number of thermal cycles according to the above DSC studies.