Effect of adlayer structure on the host-guest recognition between calcium and crown-ether-substituted phthalocyanine arrays on Au single-crystal surfaces

Adlayers of 15-crown-5-ether-substituted cobalt(II) phthalocyanine (CoCRPc) were prepared by immersion of either Au(111) or Au(100) substrate into benzene-ethanol (9:1 v/v) mixed solutions containing CoCRPc. In situ STM imaging was carried out after transferring the CoCRPc-modified Au crystals into aqueous HClO₄ solution. The packing arrangement of the CoCRPc array on Au(111) was determined to be p(8 × 4√3R - 30°), and the internal structure was clearly observed by high-resolution STM. Two adlayer structures of CoCRPc, (8 × 9) and (4√5 × 4√5)R26.7°, were found on the Au(100)-(1 × 1) terrace. In the presence of 1 mM Ca²⁺, two Ca²⁺ ions were trapped in two diagonally located 15-crown-5-ether moieties of each CoCRPc molecule on Au(111), whereas encapsulation of Ca ²⁺ ions was not seen in the CoCRPc arrays on the Au(100)-(1 × 1) surface. The present study demonstrates that the relationship between crown moieties of CRPc and the underlying Au lattice is important in the trapping of Ca²⁺ ions in crown rings.