This paper reported on a new type of in situ metal/ligand, or copper-mediated organic reaction under hydrothermal conditions, which led to the generation of two new metal-organic frameworks (MOFs) with unprecedented molecular topologic nets.

Two possible reasons for the high citation rate are as follows:

1) Hydrothermal reactions, being conducted in sealed tubes—or autoclaves—in elevated temperature (compared to ambient temperature) and pressure (compared with open air) are a powerful technique for preparation of insoluble inorganic materials, but they have been exploited in the discovery of new metal/ligand reactions only since the late 1990s, although metal/ligand reactions have been known for over 80 years. Some unusual organic reactions that are inaccessible via conventional methods may be facilitated under hydrothermal conditions, thus it may represent a new bridge between coordination chemistry and synthetic organic chemistry.

2) Such in situ metal/ligand reactions may be utilized as a practical strategy in the crystal engineering of functional MOF materials with desired structures.

This paper describes a new discovery, and also a new methodology for preparing MOF materials, which led to our making progress in developing strategies for the construction of MOFs with desired structures.

Compared with the conventional hydrazine-based synthetic method for 1,2,4-triazoles, which have wide applications in pharmaceuticals, specialty explosives, photography, information recording systems and agriculture, as well as in precursors to a variety of heterocycles, the copper-assisted cycloaddition of organonitriles and ammonia under hydrothermal condition is a new, one-pot synthesis.

Meanwhile, the copper triazolate frameworks synthesized by in situ metal/ligand reactions not only open up a new synthetic strategy for crystal engineering, because this kind of MOFs is very difficult to be crystallized, but also provide novel structural information for the designed assembly of some interesting networks.

The work not only presents a discovery of a new organic reaction, but also implies a new synthetic strategy in the crystal engineering of structurally interesting MOFs with possible properties.

It was consequence of our ongoing investigations on the discovery of new solvothermal in situ metal/ligand reactions and crystal engineering of functional MOF materials. In fact, after the discovery of some oxidative hydroxylation of aromatic compounds, or hydrothermal in situ metal/ligand reactions in 2001—published in Angew. Chem. Int. Ed. 41: 1029, 2002— we intensified our efforts toward discovering new solvothermal in situ metal/ligand reactions. Because the reactions could hardly be "seen" in the one-pot, "black-box-like" reactor, we encountered great difficulty in finding new in situ metal/ligand reactions under solvothermal conditions. In other words, these types of reactions are somewhat illusory!

Moreover, the complexities involved in the organic reactions or supramolecular assemblies obstruct an in-depth investigation on the mechanism or pathways of a multi-step organic ligand reaction. Fortunately, we have been successful in trapping some of the important reaction intermediates and byproducts mainly through the crystal engineering approach, thereby giving a closer picture of the reactions—for example, see J. Am. Chem. Soc. 127: 5495, 2005. Therefore, the current progress substantiates our expectation that a new bridge has been created between coordination chemistry and synthetic organic chemistry.