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Mixed‐Valence, Mixed‐Spin‐State, and Heterometallic [2×2] Grid‐type Arrays Based on Heteroditopic Hydrazone Ligands: Synthesis and Electrochemical Features
Author(s) -
Uppadine Lindsay H.,
Gisselbrecht JeanPaul,
Kyritsakas Nathalie,
Nättinen Kalle,
Rissanen Kari,
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.200401224
Subject(s) - chemistry , steric effects , redox , hydrazone , electrochemistry , spin crossover , crystallography , ligand (biochemistry) , metal , metal ions in aqueous solution , valence (chemistry) , stereochemistry , inorganic chemistry , organic chemistry , electrode , biochemistry , receptor
An extended family of heterometallic [M 1 2 M 2 2 (L − ) 4 ] n + [2×2] grid‐type arrays 1 – 9 has been prepared. The three‐tiered synthetic route encompasses regioselective, redox and enantioselective features and is based on the stepwise construction of heteroditopic hydrazone ligands A – C . These ligands contain ionisable NH and nonionisable NMe hydrazone units, which allows the metal redox properties to be controlled according to the charge on the ligand binding pocket. The 2‐pyrimidine (R) and 6‐pyridine (R′) substituents have a significant effect on complex geometry and influence both the electrochemical and magnetic behaviour of the system. 1 H NMR spectroscopic studies show that the Fe II ions in the grid can be low spin, high spin or spin crossover depending on the steric effect of substituents R and R′. This steric effect has been manipulated to construct an unusual array possessing two low‐spin and two spin‐crossover Fe II centres (grid 8 ). Electrochemical studies were performed for the grid‐type arrays 1 – 9 and their respective mononuclear precursor complexes 10 – 13 . The grids function as electron reservoirs and display up to eight monoelectronic, reversible reduction steps. These processes generally occur in pairs and are assigned to ligand‐based reductions and to the Co III /Co II redox couple. Individual metal ions in the heterometallic grid motif can be selectively addressed electrochemically (e.g., either the Co III or Fe II ions can be targeted in grids 2 and 5 ). The Fe II oxidation potential is governed by the charge on the ligand binding unit, rather than the spin state, thus permitting facile electrochemical discrimination between the two types of Fe II centre in 7 or in 8 . Such multistable heterometallic [2×2] gridlike arrays are of great interest for future supramolecular devices incorporating multilevel redox activity.