Counteranion-controlled water cluster recognition in a protonated octaamino cryptand

Structural aspects of binding of water cluster and halides in the octaamino cryptand L (1,4,11,14,17,24,29,36-octaazapentacyclo[l 2.12.12.2(.6,9)2.(19,22)2(31.34)]tetratetraconta-6(43),7,9(44),19(41),20,22(42),31 (39),32,34(40)nonaene, N(CH2CH2NHCH2-p-xylyl-CH2NHCH2CH2)(3)N) in a protonated state were examined. Crystallographic results show binding of the acyclic quasiplanar water tetramer [H4L(H2O)(4)](I)(4)center dot-2.57H(2)O (1) in a tetraprotonated cryptand L having an iodide counteranion, where two water molecules reside inside the two tren-based cavity, bridged by a third water molecule, and a fourth external water molecule is hydrogen bonded to the bridged water molecule. In the case of complexes [H6L(Br)][(Br)(6)H]center dot 4H(2)O center dot 2HBr (2) and [H6L(Cl)][(Cl)(6)H]center dot 10.86H(2)O (3), a single bromide and chloride occupied, respectively, the inside of the cryptand cavity, where L is in a hexaprotonated state. Monotopic recognition of bromide/chloride was observed at the center of the cryptand cavity where halides show C-H center dot center dot center dot halide interactions instead of the N-H center dot center dot center dot halide interactions reported in the ditopic complexes of halides with the same cryptand, 5 and 6. Thermal analyses on 1-3 were carried out, and the data obtained distinctly differentiate water cluster complex 1 from the anion-encapsulated cryptates 2 and 3. This study represents the first example of anion-controlled cluster formation inside the cavity of a cryptand.