ABSTRACT
Four different ruthenium(ii) complexes were incorporated into the metal-organic framework (MOF) UiO-67 using three different synthetic strategies: premade linker synthesis, postsynthetic functionalization, and postsynthetic linker exchange. One of these complexes was of the type (N-N)3Ru2+, and three of the complexes were of the type (N-N)2(N-C)Ru+, where N-N is a bipyridine-type ligand and N-C is a cyclometalated phenylpyridine-type ligand. The resulting materials were characterized by PXRD, SC-XRD (the postsynthetic functionalization MOFs), N2 sorption, TGA-DSC, SEM, EDS, and UV-Vis spectroscopy, and were digested in base for subsequent 1H NMR analysis. The absorption profiles of the MOFs that were functionalized with cyclometalated Ru(ii) complexes extend significantly further into the visible region of the spectrum compared to the absorption profiles of the MOFs that were functionalized with the non-cyclometalated reference, (N-N)3Ru2+.
ABSTRACT
The syntheses and characterization of nine new cyclometalated ruthenium complexes are reported. These structures consist of Ru(ii) with bipyridine and phenylpyridine ligands which are substituted with ester or carboxylate groups. Two of the complexes were extensively studied and their properties were compared to those of two previously reported structures. The identities of the compounds were confirmed by NMR, HR-MS and single crystal XRD, and the electronic properties were investigated by UV-Vis spectroscopy. DFT and TD-DFT calculations showed that the intense absorbances in the visible region of the spectrum of these cyclometalated complexes are due to electronic excitations to virtual orbitals located on the carboxylated ligands. These results indicate that the compounds are promising candidates as sensitizers for more efficient photocatalysis with sunlight. Further, the carboxylate groups should facilitate their use as linkers in metal-organic frameworks.
