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)^-·<i>n</i>X (X = morpholine, <i>n</i> = 1, 2, and 3 (<b>2a</b> - <b>2c</b>); X = 4-ethylpyridine, <i>n</i> = 1 (<b>3</b>) and X = piperidine, <i>n</i> = 2.5 (<b>4</b>)). 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 <i>cis</i> carboxylate isomer form, whereas the morpholinium salt solvate (H-morpholine)[Mn(5-USA-H)₂(morpholine)₂]·2(morpholine) (<b>5c</b>) is <i>trans</i>. The soft, plastic crystals of this complex gradually desolvate, losing channel morpholine and ultimately spontaneously recrystallizing as the 5-USA salt dimorpholine inclusion complex <b>2b</b>. 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.