2D and 3D coordination networks of tetra(carboxyphenyl)-porphyrins with cerium and thulium ions

Reactions between tetra(4-carboxyphenyl)porphyrin and cerium nitrate, and between tetra(3-carboxyphenyl)porphyrin and thulium oxalate, in the presence of N,N-dimethylformamide, water and acidic environment, yielded under solvothermal conditions crystalline coordination networks of 2:3 and 1:1 stoichiometry, respectively. The hybrid cerium-porphyrin compound represents a single-framework coordination polymer of open three-dimensional architecture, sustained by a continuous coordination synthon throughout the crystal. Each of the bridging cerium ions coordinates simultaneously to several porphyrin moieties, while every tetradentate porphyrin unit associates through its four carboxylate groups to different cerium bridges. The structure is perforated by similar to 0.5 nm wide channel voids that accommodate uncoordinated solvent. The thulium-porphyrin compound consists of two-dimensional (rather than three dimensional) coordination networks with corrugated surfaces, wherein each metal ion associates with four different porphyrins while every porphyrin unit coordinates through its carboxyphenyl arms to four neighboring thulium sites. Stacking of these two-dimensional arrays along the third dimension is stabilized by porphyrin-porphyrin pi-pi dispersion forces and hydrogen bonds, but not coordination. This study, along with our earlier findings, confirm that the lanthanide ions are excellent coordination reagents for the tessellation of the multidentate carboxyporphyrin entities into two- and three-dimensional polymeric architectures. (C) 2008 Elsevier B.V. All rights reserved.