Postsynthetic adsorption of stable nitroxide radical probes in diamagnetic nano/mesoporous metal-organic frameworks (MOFs) allows application of electron paramagnetic resonance (EPR) for studying structure, functions, and corresponding guest-host interactions in such MOFs. This approach was recently demonstrated using (2,2,6,6-tetramethylpiperidin-1-yl)oxyl (TEMPO) embedded in structurally flexible MIL-53(Al), with the mobility and reactivity of TEMPO reflecting structural dynamics of MOF. In the present work we embed three derivatives of TEMPO (4-oxo-TEMPO, 4-hydroxo-TEMPO, 4- acetamido-TEMPO) in MIL-53(Al) and investigate structural "breathing" of this MOF with temperature to gain deeper understanding of underlying guest-host interactions. Different substituents in the piperidine ring lead to different mobility and reactivity of corresponding nitroxides. The obtained EPR data and molecular dynamics calculations show that the efficiency of nitroxide radical reaction with μ2-hydroxo group of MIL-53(Al) strongly correlates with the character of its molecular motion, and the reversibility of this reaction upon structural "breathing" is a general phenomenon. On the basis of these findings, practical suggestions on selecting spin probes for in-MOF EPR studies are formulated.