An evidence for a chain to network transformation during the microwave hydrothermal crystallization of an open-framework zinc terephthalate

A 3-D open-framework and a chain-structured zinc terephthalate are obtained by hydrothermal crystallization under microwave heating at 180°C. The study shows that these structures have rather similar principal building units, which facilitates the structure transformation from the low-dimensional to the open-framework one during crystallization. The transformation involves the formation of new coordinative bonds between a Zn atom in a chain and two terephthalate groups from two different chains: one from the same stack and the other from the neighboring stack. Also, one water molecule coordinated to the Zn atom in the chain-like structure is lost and the zinc atom expands its coordination number to five. A considerable shift of the chains as well as bond twisting in them are necessary to occur prior to the formation of the network.