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Chem Sci. 2017 May 1;8(5):3949-3959. doi: 10.1039/c6sc05317c. Epub 2017 Mar 23.

Solvent modified spin crossover in an iron(iii) complex: phase changes and an exceptionally wide hysteresis.

Author information

1
Functional Materials and Nanotechnology Centre of Excellence (FuNTech) , Walailak University , Thasala , Nakhon Si Thammarat 80160 , Thailand . Email: hdavid@g-mail.wu.ac.th.
2
MacDiarmid Institute for Advanced Materials and Nanotechnology , Institute of Fundamental Sciences , Massey University , Palmerston North , New Zealand.
3
School of Chemistry , Monash University , Clayton , Melbourne , Victoria 3800 , Australia.
4
Australian Synchrotron , 800 Blackburn Rd , Clayton , Victoria 3168 , Australia.
5
Department of Chemistry & MacDiarmid Institute for Advanced Materials and Nanotechnology , University of Otago , PO Box 56 , Dunedin , 9054 , New Zealand.

Abstract

Solvent effects in a series of Fe(iii) spin crossover (SCO) complexes [Fe(qsal-I)2]OTf·sol (sol = MeOH 1, EtOH 2, n-PrOH 3, i-PrOH 4, acetone 5 and MeCN 6) are explored. SCO is abrupt in 1 (following MeOH loss) and 2, gradual for 3 (T1/2 = 199 K) and 4 (T1/2 = 251 K) and incomplete, even up to 350 K, for 5 and 6. In [Fe(qsal-I)2]OTf SCO occurs at T1/2↓ = 225 K and T1/2↑ = 234 K (ΔT = 9 K), while aged samples of 2 exhibit an exceptionally wide hysteresis of 80 K (T1/2↓ = 139 K and T1/2↑ = 219 K). In contrast, fresh samples of 2 exhibit stepped SCO with hysteresis varying from 2 to 42 K. VT-PXRD (variable temperature powder X-ray diffraction) studies indicate a new phase, 2b, is formed upon cooling below 180 K along with a minor LS phase 2c. Phase 2c and the HS phase 2a undergo a spin transition at T1/2↓ = 180 K and T1/2↑ = 215 K with phase 2b exhibiting two-step SCO. Structural studies in both spin states, except 6, show the cations are linked through extensive π-π interactions to form 1D chains. A combination of P4AE (parallel fourfold aryl embrace) and I···X (X = I, O, π) interactions create tightly packed 3D supramolecular networks. This study emphasizes that while solvent may result in only small structural changes SCO characteristics can be impacted dramatically.

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