An iron(ii) complex exhibiting five anhydrous phases, two of which interconvert by spin-crossover with wide hysteresisElectronic supplementary information (ESI) available: synthetic and crystallographic experimental procedures; additional crystallographic figures and tables; TGA and powder diffraction data. CCDC reference numbers 836761836763 and 836792. For ESI and crystallographic data in CIF or other electronic format see DOI: 10.1039/c1sc00584g

• Main Authors: Roberts, Thomas D, Tuna, Floriana, Malkin, Tamsin L, Kilner, Colin A, Halcrow, Malcolm A
• Format: Journal Article
• Language: English
• Published: 10.01.2012
• ISSN: 2041-6520; 2041-6539
• DOI: 10.1039/c1sc00584g

[FeL 2 ][BF 4 ] 2 2H 2 O (L = 2,6-di{5-methylpyrazol-3-yl}pyridine) adopts a 1:1 high:low spin state population, and can be converted into different high-spin anhydrous phases by recrystallisation (phase 1 A ) or by thermal dehydration (phase 1 B ). Upon cooling in vacuo , the latter undergoes a thermal spin-state transition centred near T 1/2 = 205 K. The transition has a thermal hysteresis width of 65 K in freshly prepared samples, although this gradually narrows to 37 K on repeated scanning. X-Ray powder diffraction measurements performed in vacuo show that 1 B , initially formed at 375 K, exhibits two consecutive crystallographic phase changes near 300 and 270 K, before undergoing a third phase change concomitant with its spin-state transition. None of these new phases is isostructural with 1 A , which itself undergoes a thermal spin-crossover on cooling without a change in crystal symmetry. Mixed-spin [FeL 2 ][BF 4 ] 2 2H 2 O (L = 2,6-di{5-methylpyrazol-3-yl}pyridine) can be converted into different high-spin anhydrous phases by recrystallisation or thermal dehydration. The latter undergoes a spin-state transition on cooling with up to 65 K thermal hysteresis, via a sequence of three crystallographic phase changes.