Spherical versus linear anion encapsulation in the cavity of a protonated azacryptand

Grams scale synthesis of an octaaminocryptand L(2) with high yield is obtained in one-pot by low-temperature [2 + 3] condensation of tris(2-aminoethyl)amine with isophthalaldehyde, followed by sodium borohydride reduction. Structural aspects of octaaminocryptand L(2) x MeOH, binding of iodide (spherical) and bichloride (linear) in L(2), (1,4,11,14,17,24,29,36-octa-azapentacyclo-[12.12.12..2(6,9).2(19,22).2(31,34)]-tetratetraconta 6(43),7,9(44),19(41),20,22(42),31(39),32,34(40)-nonane, N(CH2CH2NHCH2-m-xylyl-CH2NHCH2CH2)3N), in the hexaprotonated and tetraprotonated states, respectively, are examined. Crystallographic results show binding of single iodide [H6L(2)I](I)5 x 4 H2O, (2), in a hexaprotonated cryptand L(2). Monotopic recognition of iodide is observed via (N-H)(+)...iodide interactions. The tetraprotonation of L(2) by hydrochloric acid showed the formation and encapsulation of a bichloride inside the cavity, which is examined from the single-crystal X-ray study. Encapsulation and binding of a proton-bridged linear bichloride inside the cavity of tetraprotonated L(2), [H4L(2)(ClHCl)](Cl)3 x nH2O (3), via (N-H)(+)...chloride interactions is observed in the structural investigation. This study shows that degree of protonation and its distribution in the receptor architecture play an important role in guest encapsulation. Further, it represents the first example of an encapsulated bichloride inside the cavity of an organic host.