Anion dependence in the spin-crossover properties of a Fe(II) podand complex

作者：Klug Christina M; McDaniel Ashley M; Fiedler Stephanie R; Schulte Kelsey A; Newell Brian S; Shores Matthew P^*

来源：Dalton Transactions, 2012, 41(40): 12577-12585.

DOI：10.1039/c2dt31213a

We report the syntheses, characterisations, and spin state behaviours of salts of the tripodal-ligatedFe(II) complex [FeL6-OH]X-2 (L6-OH = tris{4-[(6-methanol)-2-pyridyl]-3-aza-3-butenyl}amine, X = OTf- (1), Br- (2), I (-)(3), BPh4- (4)). Covalent linking of the ligand arms is imperative as a high-spin bis(tridentate) complex (5) is formed when a non-tethered ethyl iminopyridine ligand (L-2 = 4-[(6-methanol)-2-pyridyl]-3-aza-3-butenyl) is used. For salts 1-4, thermally-induced spin-crossover (SCO) is observed in the solid state, with dependence on anion and solvate molecules. Salts with larger anions show more complete SCO centred at higher temperatures (1 %26gt; 3 %26gt; 2); the triflate salt 1 (T-1/2 = 173 K) also shows the strongest cooperativity of the compounds examined. Hydrogen bonding appears to be critical to SCO in this family of salts: limiting interactions by use of tetraphenylborate produces a high-spin complex down to 5 K. In protic solvents such as methanol, spectra of [FeL6-OH](2+) are largely unchanged over a period of three days, but dissociate when interrogated with strong field bidentate ligands. Compounds 1-3, and 5 remain high spin in solution down to 180 K, consistent with the data obtained in the solid state.

• 出版日期2012