In UOV, the germanium distribution is significantly affected by the presence of three crystallographically inequivalent D4R units in the framework. In particular, across all the Si/Ge ratios we observe significant heterogeneity in the occupation of the three types of D4R units (SI Figure ), with the "T3-T6" D4R unit (composed of T-sites T3 and T6) being the most attractive on average and "T14-T18" D4R unit the least attractive for Ge atoms. But even the occupation of the "T3-T6" D4R unit peaks only at about four germanium atoms for Si/Ge < 6 (see Figures and), with a strong preference for the germanium clustering in one of the S4R sub-units in D4R (SI Figures S14 S31 S32 S33 ). For Si/Ge < 6 other-than-D4R T-sites become on average more populated than D4R sites with the majority of germanium found in adjacent and framework T-sites in-between the "T3-T6" D4R units, i.e., approx. along the [0b0] direction (see Figure for Si/Ge = 2.7). Also, some spillover of germanium (up to 2-3 Ge atoms) to the "T17-T19" D4R unit is observed at higher germanium loading. These trends strengthen with increasing germanium content as germanium atoms approximately phase-separate into isolated thin "slices" of T-sites stretching approximately along the [0b0] direction, neither spreading through the columns formed from D4R and lau CBU (along [a00] direction) nor extending through the whole [a00] plane (SI Figures S32 S33).