Anion binding with two polyammonium macrocycles of different dimensionality

A comparative study of the binding of nitrate and sulfate with a polyammoni um monocycle L-1, (3,6,9,17,20,23-hexaazatricyclo[23.3.1.1(11,15)]-triacont a-1(29),11,13,15(30),25,27-hexaene), and the corollary bicycle L-2, (1,4,12 , 15,18,26,31,39-octaazapentacyclo-[13.13.13.1(6,10).1(20,24).1(33,37)]-tet ratetraconta-6,7,9,20(43),21,23,33-(42),34,36-nonaene), is reported. Potent iometric studies indicated negligible binding for L-1 and nitrate, but affi nity was observed for sulfate (log K-H5L(SO4)/H5L . SO4 = 3.53(1), log K-H6 L(SO4)/H6L . SO4 = 4.36(1)). Stronger binding was observed for the cryptand L-2 with both nitrate and sulfate (log K-H6L(NO3)/H6L . NO3 = 3.11(5), log K-H7L(NO3)/H7L . NO3 = 3.55(5); log K-H6L(SO4)/H6L . SO4 = 4.43(1), log K- H7L(SO4)/H7L . SO4 = 4.97(5)). Five crystal structures are reported: the ni trate (1) and sulfate (2) salts of L-1, the free base (3) of L-2, and the n itrate (4) and tosylate (5) salts of L-2. Structural results for L-1 indica te relatively planar monocycles with cis and trans orientations of the phen yl groups for 2 and 1, respectively, with the anions above and below the mo nocycle rings. For L-2, key features include an encapsulated water and intr icate water network in 3, two encapsulated and four external nitrates and t wo external water molecules in 4, and six external tosylates with sulfonate groups pointing into the cavity and eight external waters in 5.