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Synthesis, Structural Features, Absorption Spectra, Redox Behaviour and Luminescence Properties of Ruthenium( II ) Rack‐Type Dinuclear Complexes with Ditopic, Hydrazone‐Based Ligands
Author(s) -
Stadler AdrianMihail,
Puntoriero Fausto,
Campagna Sebastiano,
Kyritsakas Nathalie,
Welter Richard,
Lehn JeanMarie
Publication year - 2005
Publication title -
chemistry – a european journal
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.687
H-Index - 242
eISSN - 1521-3765
pISSN - 0947-6539
DOI - 10.1002/chem.200401261
Subject(s) - chemistry , hydrazone , ligand (biochemistry) , crystallography , luminescence , absorption spectroscopy , metal , redox , ruthenium , bridging ligand , photochemistry , absorption (acoustics) , stereochemistry , crystal structure , inorganic chemistry , materials science , organic chemistry , catalysis , biochemistry , receptor , physics , optoelectronics , quantum mechanics , composite material
The isomeric bis(tridentate) hydrazone ligand strands 1 a – c react with [Ru(terpy)Cl 3 ] (terp y =2,2′:6′,2′′‐terpyridine) to give dinuclear rack‐type compounds 2 a – c , which were characterised by several techniques, including X‐ray crystallography and NMR methods. The absorption spectra, redox behaviour and luminescence properties (both in fluid solution at room temperature and in rigid matrix at 77 K) of the ligand strands 1 a – c and of the metal complexes 2 a – c have been studied. Compounds 1 a – c exhibit absorption spectra dominated by intense π–π* bands, which, in the case of 1 b and 1 c , extend within the visible region, while the absorption spectra of the rack‐type complexes 2 a – c show intense bands both the in the UV region, due to spin‐allowed ligand‐centred (LC) transitions, and in the visible, due to spin‐allowed metal‐to‐ligand charge‐transfer (MLCT) transitions. The energy position of these bands strongly depends on the ligand strand: in the case of 2 a , the lowest energy MLCT band is around 470 nm, while in 2 b and 2 c , it lies beyond 600 nm. Ligands 1 a – c undergo oxidation processes that involve orbitals based mainly on the CH 3 NN fragments. The complexes 2 a – c undergo reversible metal‐centred oxidation, while reductions involve the hydrazone‐based ligands: in 2 b and 2 c , the bridging ligand is reduced twice and in 2 a once before reduction of the peripheral terpy ligands takes place. Ligands 1 a – c exhibit luminescence from the lowest‐lying 1 π–π* level. Only for complex 2 a does emission occur; this may be attributed to a 3 MLCT state involving the bridging ligand. Taken together, the results clearly indicate that the structural variations introduced translate into interesting differences in the spectroscopic, luminescence and redox properties of the ligand strands as well as of the rack‐type metal complexes.