Reaction in solution and in the solid state of 18-crown[6] with Cs2CO3 and 5-substituted isophthalic acids yields the new organic–inorganic complexes 18-crown[6]·Cs[OH-isoH] (2), 18-crown[6]·Cs[CH3-isoH] (3), 18-crown[6]·Cs[Br-isoH] (4), 18-crown[6]·Cs[OCH3-isoH] (5), 18-crown[6]·Cs[NO2-isoH] (6) and 18-crown[6]·Cs[tert-Butyl-isoH] (8), which have all been characterized by X-ray diffraction. All compounds except the latter are isomorphous, in spite of the size, shape and chemical nature of the substituent and its ability to form hydrogen bonds.
![Graphical abstract: Surprising robustness of a unit cell: isomorphism in caesium 18-crown[6] complexes with aromatic polycarboxylate anions](http://hg.y866.cn/compound/lib/scimg/usr/1/C0CE00363H.jpg)
