Water as a modifier in a hybrid coordination network glass

Chemical diversification of hybrid organic-inorganic glasses remains limited, especially compared to traditional oxide glasses, for which continuous composition variation and thus property tuning is possible through addition of weakly bonded modifier cations. In this work, we show that water addition can depolymerize polyhedra with labile metal-ligand bonds in a cobalt-based coordination network, yielding a series of non-stoichiometric glasses. Based on calorimetric, spectroscopic, X- ray absorption fine structure, and ab initio simulation studies, we demonstrate that the added water molecules promote breakage of cobalt-oxygen bonds, which leads to lower melting and glass transition temperatures. These structural changes also modify both the physical and chemical properties of the melt-quenched glass, with strong parallels to the network modifier concept in oxide glasses. We show that this approach also applies to other transition metal-based coordination networks, and it will thus enable diversification of hybrid glass chemistry, including non- stoichiometric glass compositions, continuous tuning of physical and chemical properties, and a significant rise in the number of glass-forming hybrid systems by allowing them to melt before they thermally decompose.