Nanoporous molecular crystals

Abstract

Nanoporous Molecular Crystals (NMCs) are nanoporous materials composed of discrete molecules between which there are only non-covalent interactions-i.e. they do not possess an extended framework composed of covalent or coordination bonds. They are formed from removing guest molecules from inclusion compounds (ICs) a process that for most ICs usually results in the collapse of the open structure of the crystals but in the case of NMCs the packing of the host molecules is retained and nanoporosity obtained. In recent years a number of NMCs have been confirmed by the technique of gas adsorption and these materials are surveyed in this feature article. In addition, the reasons for stability of these crystals are discussed. It is the author's belief that many more ICs, the structures of which are readily obtainable from the Cambridge Structural Database (CSD), may act as precursors to NMCs.

Porous organic molecular solids by dynamic covalent scrambling

“…There has been less focus here in comparison with the preparation of ordered porous solids using crystal engineering [10][11][12][13][14][15][16][17][18][19][20][21][22][23][24][25][26][27][28][29] . Polymers of intrinsic microporosity (PIMs), for example, form amorphous microporous solids-that is, amorphous solids with pore dimensions smaller than 2 nm-as a result of their rigid and contorted chain structures 30,31 .…”

“…Calixarenes, in particular, can exhibit 'porosity without pores' 10,11 : that is, the solid materials can adsorb guests by cooperative diffusion, despite having isolated voids rather than interconnected pore structures. Permanent, interconnected porosity in discrete organic molecules with low molar mass is rarer 11 and is typically confined to certain ordered molecular crystals [12][13][14][15][16][17][18][19][20][21][22][23][24] . Examples include modified calixarenes [12][13][14] , 3,3′,4,4′-tetra(trimethylsily lethynyl)biphenyl 15 , tris-o-phenylenedioxycyclotriphosphazene 16 , 4-hydroxyphenyl-2,3-4-trimethylchroman 17 , cucurbit [6]uril 18 , some dipeptides 19 , diyne macrocycles 20 and imine-linked porous organic cages 21,22 .…”

The unexpected formation of a dihydroisobenzofuran derivative from the addition of a Grignard reagent to a 1,3-indanedione

“…The organic layers were evaporated under reduced pressure to give the crude product which was purified by column chromatography (hexane/EtOAc, 9:1) to give the title compound (0.84 g, 30%) as a white solid, mp 193 -195 °C. 1 Crystals of 4 were prepared by the slow diffusion of MeOH into a CHCl 3 solution of the complex. Single-crystal XRD data were collected at 150 K using graphite monochromated MoKα radiation on a Bruker-Nonius Kappa CCD diffractometer with an Oxford Cryosystems cooling apparatus.…”

“…However, molecules with 'awkward' structures do not pack space efficiently and form clathrate crystals containing solvent. In theory, removal of the included solvent can result in a crystalline nanoporous crystal 1 or an amorphous material that could possess microporosity, like that found in macromolecular systems such as the Polymers of Intrinsic Microporosity (PIMs). 2 In PIMs, the microporosity arises from the rigid and contorted nature of the polymer chains.…”

Hydrophobic dipeptide crystals: a promising Ag-free class of ultramicroporous materials showing argon/oxygen adsorption selectivity

“…Such a material should have highly hydrophobic and less than 0.5 nm-wide pores, and a porosity of, at least, 20 %. With the large numbers of organic microporous solids discovered in recent years, there are plenty of candidates to be tested 65,66 .…”