Calix[4]pyrrole: An Old yet New Ion-Pair ReceptorThe Southampton Group thanks the EPSRC/Crystal Faraday for a studentship to G.W.B. and the EPSRC for a DTA studentship to S.J.B. Additionally, we would like to thank Professor Mike Hursthouse and the EPSRC for access to the crystallography facilities at the University of Southampton. P.A.G. thanks the Royal Society for a University Research Fellowship. The work in Austin was supported by the US Department of Energy Office of Science (grant no. DE-FG02-04ER63741 to J.L.S.). The research at ORNL was sponsored by the Division of Chemical Sciences, Geosciences, and Biosciences, Office of Basic Energy Sciences, US Department of Energy, under contract no. DE-AC05-00OR22725 with Oak Ridge National Laboratory, managed and operated by UT-Battelle, LLC.