Exceptionally high temperature spin crossover in amide-functionalised 2,6-bis(pyrazol-1-yl)pyridine iron(ii) complex revealed by variable temperature Raman spectroscopy and single crystal X-ray diffraction

Attwood, Max; Akutsu, Hiroki; Martin, Lee; Blundell, Toby J.; Le Maguere, Pierre; Turner, Scott S.

Abstract

The synthesis of a novel amide-functionalised 2,6-bis(pyrazol-1-yl)pyridine-4-carboxamide ligand (bppCONH2) is described. The complex salts [Fe(bppCONH2)2](BF4)2 and [Fe(bppCONH2)2](ClO4)2 were synthesised and characterised by SQUID magnetometry, differential scanning calorimetry, variable temperature Raman spectroscopy and single crystal X-ray diffraction. DSC measurements of [Fe(bppCONH2)2](BF4)2 indicate a spin-crossover (SCO) transition with T↑ at 481 K and T↓ at 461 K, showing a 20 K hysteresis. DSC for the perchlorate salt shows an SCO transition with T↑ at 459 K and T↓ at 445 K with a 14 K hysteresis. For the BF4− salt analysis of low and high-spin state crystal structures at 101, 290 and 500 K, suggest stabilisation of the low spin state due to the formation of 1D hydrogen-bonded cationic chains. Variable temperature Raman studies of the BF4 salt support the presence of a high temperature SCO. It is speculated that the presence of hysteresis may be attributed to differences in the inter-molecular hydrogen bonding in the low spin and high spin states.

Citation

Attwood, M., Akutsu, H., Martin, L., Blundell, T. J., Le Maguere, P., & Turner, S. S. (2021). Exceptionally high temperature spin crossover in amide-functionalised 2,6-bis(pyrazol-1-yl)pyridine iron(ii) complex revealed by variable temperature Raman spectroscopy and single crystal X-ray diffraction. Dalton Transactions, 50(34), 11843-11851. https://doi.org/10.1039/d1dt01743h

• Journal Article Type: Article
• Acceptance Date: Jul 28, 2021
• Online Publication Date: Aug 2, 2021
• Publication Date: Sep 14, 2021
• Deposit Date: Nov 30, 2023
• Journal: Dalton Transactions
• Print ISSN: 1477-9226
• Electronic ISSN: 1477-9234
• Publisher: Royal Society of Chemistry
• Peer Reviewed: Peer Reviewed
• Volume: 50
• Issue: 34
• Pages: 11843-11851
• DOI: https://doi.org/10.1039/d1dt01743h
• Public URL: https://durham-repository.worktribe.com/output/1963787