Pr@C₇₄(C₆H₃Cl₂), a novel dichlorophenyl-functionalized derivative of the Pr-containing monometallofullerene Pr@C₇₄, was successfully prepared and isolated. Its molecular structure was determined as Pr@D_3h(14246)-C₇₄(C₆H₃Cl₂) by a combined mass spectrometry (MS), UV-visible-near-infrared (UV-vis-NIR) absorption spectroscopy, and quantum-mechanics characterization. Using the computed theoretical data, we evaluated the isomeric structures, metal-to-cage electron transfer, and metal-cage interactions of Pr@C₇₄(C₆H₃Cl₂) and the pristine Pr@C₇₄. Furthermore, the relative reactivity of C₇₄, Pr@C₇₄, and Pr@C₇₄(C₆H₃Cl₂) was estimated by the calculated electronic structures and bandgaps, and the results indicated that the open-shell structure and relatively small bandgap should be responsible for the unsuccessful isolation of C₇₄ and Pr@C₇₄.