Intercalation of Neutral Guests in Pillared Salt Cocrystals of 5-Ureidosalyclic Acid

The salts of 5-ureidosalyclic acid (5-USA) form a range of pillared salt inclusion complexes from basic solvents, namely, triethylamine, piperidine, morpholine, and 4-ethylpyridine. The triethylamine derivative is unsolvated, while the other salts include 1-3 solvent molecules of formula XH⁺(5-USA-H)^-·nX (X = morpholine, n = 1, 2, and 3 (2a - 2c); X = 4-ethylpyridine, n = 1 (3) and X = piperidine, n = 2.5 (4)). The morpholine salt expands the layered structure to include 1, 2, or 3 guests. The 5-USA anion can also act as a bidentate ligand for manganese(III), again forming highly solvated inclusion complex anions [Mn(5-USA-H)₂(Solv)₂]^-. When interacting strongly with the countercation, the 5-USA anions adopt an unusual cis carboxylate isomer form, whereas the morpholinium salt solvate (H-morpholine)[Mn(5-USA-H)₂(morpholine)₂]·2(morpholine) (5c) is trans. The soft, plastic crystals of this complex gradually desolvate, losing channel morpholine and ultimately spontaneously recrystallizing as the 5-USA salt dimorpholine inclusion complex 2b. The complex hydrogen-bonded, pillared 5-USA salts illustrate a design concept for intercalated materials of forming charged, planar layers that leave the charge-balancing counterion exposed, such that interlayer guest species must be incorporated to effectively solvate the charged moieties.