We note that the two Co-O octahedra shown in Figure are crystallographically equivalent and thus fully equivalent reactivity with water should be expected. While the [CoBr4] 2-centers generally behave similarly as in the water-free state, the Co-O(hmba) bonds break much more easily in the hydrated system and some hmba are ultimately replaced by water molecules in the glassy state (Figure ). As such, when water replaces the oxygens of hmba, dangling organic motifs (i.e., hmba only coordinating to one Co-center) are created as shown by the significant reduction in the Tg from 16 ºC to -15 ºC for the fully polymerized and fully depolymerized glass structures, respectively. Lastly, when adding more water than what causes full depolymerization, it is found that water bonds less tightly, suggesting that water is placed in structural cavities and not in direct vicinity of the Co-polyhedra (Figure ). We note that only octahedral configurations are presented in Figure , but that these are most likely accompanied by four-and five-fold coordinated Co-O centers. Such non-stoichiometric distribution in hydration and coordination numbers are generally not accepted in the crystalline state, but are well-recognized in glasses (e.g., oxides 15 ). The fundamental melting (and glass formation) mechanism is similar to that of other known hybrid systems, namely ZIFs and hybrid perovskites, involving the breakage (and full or partial reformation) of the coordination network upon melting and subsequent quenching into the glassy state. As such, water addition limits the reformation of the initial network-connecting species -in oxide glass science, such elements are termed as "modifiers". The effect observed in this work, as studied in detail for Co(hmba)3[CoBr4] but also confirmed for Co(hmba)3[Co(SCN)4] and Mn(hmba)3[MnBr4] systems, is therefore mechanistically different from the recent work of vitrification by desolvation. We believe the proposed structural mechanism is not unique to the systems studied in this work and may also find usefulness for e.g., the much-studied ZIFs where much work has been devoted to lowering the melting temperature and viscosity and, as such, a modifier would be of great usefulness to push the field forward. As reflected from the observed water-induced decrease in Tm and Tg (Figs. and), the resulting glass properties are expected to exhibit similar large changes upon inclusion of water. From traditional rigidity considerations, the depolymerization of a network greatly reduces, e.g., its hardness and elastic moduli. Water (or other "modifier") addition may thus serve as a method for tweaking the mechanical properties of hybrid glasses, similarly to the case of oxide glasses. Moreover, such depolymerization could allow more hybrid and MOF crystals to melt before they thermally decompose, thus dramatically expanding the range of hybrid glass formation.