Issue 40, 2012

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

Abstract

We report the syntheses, characterisations, and spin state behaviours of salts of the tripodal-ligated Fe(II) complex [FeL6-OH]X2 (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 (L2 = 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 > 3 > 2); the triflate salt 1 (T1/2 = 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.

Graphical abstract: Anion dependence in the spin-crossover properties of a Fe(ii) podand complex

Supplementary files

Article information

Article type
Paper
Submitted
06 Jun 2012
Accepted
15 Aug 2012
First published
07 Sep 2012

Dalton Trans., 2012,41, 12577-12585

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

C. M. Klug, A. M. McDaniel, S. R. Fiedler, K. A. Schulte, B. S. Newell and M. P. Shores, Dalton Trans., 2012, 41, 12577 DOI: 10.1039/C2DT31213A

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