Anion binding with two polyammonium macrocycles of different dimensionality

A comparative study of the binding of nitrate and sulfate with a polyammonium monocycle L(1), (3,6,9,17,20,23-hexaazatricyclo[23.3.1.1(11,15)]-triaconta-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)]-tetratetraconta-6,7,9,20(43),21,23,33(42),34,36-nonaene), is reported. Potentiometric studies indicated negligible binding for L(1) and nitrate, but high affinity was observed for sulfate (log K(H5L(SO4)/H5L-SO4) = 3.53(1), log K(H6L(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 nitrate (1) and sulfate (2) salts of L(1), the free base (3) of L(2), and the nitrate (4) and tosylate (5) salts of L(2). Structural results for L(1) indicate relatively planar monocycles with cis and trans orientations of the phenyl groups for 2 and 1, respectively, with the anions above and below the monocycle rings. For L(2), key features include an encapsulated water and intricate water network in 3, two encapsulated and four external nitrates and two external water molecules in 4, and six external tosylates with sulfonate groups pointing into the cavity and eight external waters in 5.