Host–guest recognition of calcium by crown-ether substituted phthalocyanine array on Au(111): relationship between crown moieties and gold lattice

High-resolution scanning tunneling microscopy has revealed that, of the four crown-ether moieties of 15-crown-5-ed phthalocyanine array on Au (111) surface, only two crown-ether voids at diagonal positions, where the void centers and hollows surrounded by three gold atoms match exactly, trap two Ca^2+ ions.