Ab Initio Powder Diffraction Structure Analysis of a Host-Guest Network: Short Contacts between Tetrathiafulvalene Molecules in a Pore

Abstract

Many crystal structures of porous coordination networks have been solved by single-crystal X-ray crystallography, providing detailed molecular structural information on framework, guest arrangement, and even reactive intermediates generated in situ. Such detailed structural analysis facilitated the explosive development of porous coordination networks in the last 15 years. On the other hand, although there are many examples of ab initio powder X-ray diffraction (PXRD) analysis of inorganic materials, organic solids, nonporous coordination networks, and discrete small molecules, there are only few reports of ab initio PXRD analysis of porous coordination networks describing guest behavior (guest exchange, gas adsorption, etc.). This is because ab initio PXRD analysis is considerably more challenging than singlecrystal structure determination. Porous coordination networks usually have large unit cells and often low symmetry that contribute to severe peak overlap which hampers accurate structure determination. By using high-resolution synchrotron PXRD and the simulating annealing method, we have now succeeded in solving the crystal structure of a biporous coordination network having an unprecedented arrangement of tetrathiafulvalene (TTF) molecules and a unit cell larger than 15000 . The PXRD analysis revealed very short intermolecular S···S contacts between TTF molecules (3.370 ) that have a nonplanar shape indicating a neutral form. Those findings agree with solid-state spectroscopic features. A key issue in inducing intriguing physical properties in TTF is how to arrange the molecules. We tried to achieve a unique arrangement of TTF molecules by using the pores of a porous coordination network. We used the previously reported network [(ZnI2)3(1)2(2)]n·xC6H5NO2·yCH3OH (3, where 1 is 2,4,6-tris(4-pyridyl)-1,3,5-triazine (TPT) and 2 is triphenylene; x 4 and y 2) and prepared new isostructural ZnBr2 network 4 (Scheme 1) by instant synthesis. [3b]