Reactive Species Unveiled by Ab Initio Powder Structure Analysis

Porous coordination network has been the subject of explosive development because of their fascinating properties. However, there is still an unexplored research field in self-assembly of porous materials. There are many metastable states before reaching the thermally most stable state. By controlling the weak intermolecular interactions, we can trap various metastable coordination networks which will not be obtained by conventional thermodynamic control. Kinetically trapped metastable networks were not paid much attention, because firstly it is very difficult to analyze crystal structures. We demonstrated that it is possible to perform ab initio powder structure determination of porous coordination networks using low resolution data; totally different coordination networks can be selectively prepared from the same starting materials by thermodynamic and kinetic control; a robust porous coordination network can be prepared from the kinetic product which can be prepared instantly and in a large scale.[1] We also demonstrated that a pore in porous networks can be used as a crystalline molecular flask.[2] The robust networks maintain crystallinity and enable direct observation of reactive species by X-ray diffraction. It is still challenging to observe reactive species in a pore with clear structural evidence. In this talk, we will report ab initio powder structure analysis of reactive species trapped in a porous coordination network and their unique chemistry.[3]

Gas Phase Single Crystal Growth of Coordination Networks

Organic ligands and metal ions can produce several kinds of networks depending on experimental conditions, such as solvent, temperature, reaction speed, and so on.1, 2 While many MOF chemists have used solution phase reaction, recently some unique networking methods have been investigated, e.g. mechanochemical solid state reactions. Here we report a new method for single crystal growth of porous coordination networks via gas phase. In our previous work, we found that heating of interpenetrated network [(ZnI2)3(TPT)2]n (solvent) forms a crystalline powder, [(ZnI2)3(TPT)2]n (1, TPT = 2,4,6-tris(4-pyridyl)triazine).3 We determined a porous saddle-type structure of 1 by ab initio PXRD analysis. Interestingly, we could not prepare 1 by grinding and heating the starting powder materials of ZnI2 and TPT. Therefore, we attempted to prepare coordination networks via gas phase. On heating of ZnI2 and TPT together under reduced pressure in a glass ample at high temperature, single crystal growth of 1 was observed. The single crystal X-ray structure analysis revealed that 1 has the same structure as microcrystalline powder of 1. In gas phase, because there is no solvation effect, network topology is purely based on ligand interactivity and geometry of metal coordination. Therefore, saddle-type network is one of the possible patterns on the basis of geometry of only TPT and ZnI2 without guest molecules. To the best of our knowledge, this is the first example of single crystal growth of porous coordination network via gas phase. In summary, we successfully demonstrated the first gas phase single crystal growth of porous coordination network formation. In this presentation, we will discuss network design by gas phase reaction based on ligand interactivity focusing on weak intermolecular interaction.

Kinetic Assembly of a Thermally Stable Porous Coordination Network

The advantage of porous coordination network synthesis is designability by changing metal sources and ligands.[1] Therefore, not only many commercially available ligands but also newly synthesized ones were used for networking. On the other hand, most of metal sources are common reagents or stable metal moieties because they can be more predictable as a metal connector. So far, there is no report focusing on usage of labile metal sources for selective network formation. One of the promising methods to produce unique networks with such labile metal sources is kinetic control[2] because labile metal sources produce various species in solution. In this talk, we will introduce selective syntheses of thermally stable porous coordination networks using a labile Cu4I4 cubane cluster [Cu4I4(PPh3)4] (1) and a rigid tetradentate Td-symmetry ligand tetra-(4-(4-pyridyl)phenyl)methane (2) by kinetic and thermodynamic control.[3] On heating the mixture of 1 and 2 in DMSO at 453 K, a homogenous colorless solution was obtained. Rapid cooling (~20 Kmin-1) of the solution produced yellow needle crystals, {[(CuI)2(2)]·solvent}n (3a) that shows novel CuI helical chain unit, in 99% yield (Fig. A). On the other hand, slow cooling (~3 Kmin-1) produced orange block crystals, {[(Cu2I2)(2)]·solvent}n (3b) that shows rhombic Cu2I2 dimer unit, in 95% yield. Both the network crystals can keep the crystallinity up to 673 K under N2 atmosphere. In kinetic product 3a, due to the unique structure, iodides of the CuI chains facing to 1D channel, the network crystal shows chemisorption of I2 by making a covalent bond with an iodide of part of the CuI chains to form an I3- group (Fig. B). On the other hand, in thermodynamic product 3b, Cu2I2 dimer units are hindered by bridging ligand 2. That is why network crystal 3b shows only physisorption of I2, even though network has 1D channel similar to 3a.