X-ray single-crystal diffraction (SCD) analysis has the intrinsic limitation that the target molecules must be obtained as single crystals. Here we report a protocol for SCD analysis that does not require the crystallization of the sample. In our method, tiny crystals of porous complexes are soaked in a solution of the target, such that the complexes can absorb the target molecules. Crystallographic analysis clearly determines the absorbed guest structures along with the host frameworks. Because the SCD analysis is carried out on only one tiny crystal of the complex, the required sample mass is of the nanogram-microgram order. We demonstrate that as little as about 80 nanograms of a sample is enough for the SCD analysis. In combination with high-performance liquid chromatography, our protocol allows the direct characterization of multiple fractions, establishing a prototypical means of liquid chromatography SCD analysis. Furthermore, we unambiguously determined the structure of a scarce marine natural product using only 5 micrograms of the compound.
Many molecular cages selectively bind guests in solution, but in the solid state close packing often prevents guest entry, which renders the cages inactive. We envisioned that coordination networks constructed from well-known molecular cages could transfer the richness of solution-state host-guest chemistry into the solid state. We report a crystalline coordination network generated from an infinite array of octahedral M(6)L(4) cage subunits (M = metal, L = ligand). This coordination network is a 'crystalline molecular sponge' engineered on the molecular level and retains similar guest recognition properties to those found in solution. The network crystallinity is robust and thus X-ray diffraction analysis can be used to unambiguously observe single-crystal to single-crystal guest inclusion. The void spaces define alternating M(12)L(8) and M(12)L(24) cuboctahedral molecular cages and these large cages absorb up to 35 weight per cent of C(60) or C(70) by simply soaking the crystals in a toluene solution of the fullerene. When the crystals are immersed in fullerene mixtures, C(70) is preferentially absorbed.
We recently reported a new method for single-crystal X-ray diffraction (SCD) analysis that does not require the crystallization of the target compound. In this 'crystal-free' crystallography, a tiny crystal of a porous complex is soaked in the solution of the target guest. The guest molecules are absorbed and oriented in the crystal pores and can be analyzed by X-ray diffraction. We describe here a detailed synthetic protocol for the preparation of uniform single crystals of the porous host complex and for the subsequent guest uptake. The protocol describes our most versatile porous complex, which is prepared from commercially available ZnI2 and 2,4,6-tri(4-pyridyl)-1,3,5-triazine. The host complex has large pores with a cross-section of 8 × 5 Å(2). Single crystals of the complex are grown from layered solutions of the two components. The pores of the as-synthesized complex are filled with nitrobenzene, which is replaced with the inert solvent cyclohexane. This solvent exchange is essential for the rapid and effective inclusion of target compounds. The most crucial and delicate step is the selection of high-quality single crystals from the mixture of crystals of various shapes and sizes. We suggest using the facial indices of the single crystals as a criterion for crystal selection. Single-crystal samples for X-ray analysis can be prepared by immersing the selected crystals in a cyclohexane/dichloromethane solution of target compound. After a very slow evaporation of the solvent, typically over 2 d, the final crystal can be picked and directly subjected to SCD analysis. The protocol can be completed within ∼16 d.
Previously unnoticed ambiguities in the crystallographic data in our Article (specifically, non-negligible disorder of the miyakosyne A molecule), along with further work by three of the authors (Y.H., K.T. and S.M.) have revealed that the stereochemistry we assigned at C14 of miyakosyne A is incorrect. Our new investigations confirm that we can indeed determine the molecular skeleton of miyakosyne A. However, we can only tentatively and not unambiguously identify all of the stereochemistry of miyakosyne A based on the data included in the original paper. A future publication will confirm the stereochemistry at the C14 moiety of miyakosyne A. The other conclusions of our paper are not affected by this correction.
Chiral crystalline sponges with preinstalled chiral references were synthesized. On the basis of the known configurations of the chiral references, the absolute structures of guest compounds absorbed in the pores of the crystalline sponges can be reliably determined without crystallization or chemical modification.
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