Bulk spin-crossover in the complex [FeL(NCS)2] of a tris(pyridyl)ethane-derived N4-ligand-a temperature-dependent crystallographic studyElectronic supplementary information (ESI) available: Additional figures, data of tensor analyses, CIFs of crystal structures and variable-temperature diffraction. CCDC 960951-960957. For ESI and crystallographic data in CIF or other electronic format see DOI: 10.1039/c3dt53070a

• Main Authors: Wiedemann, Dennis, Grohmann, Andreas
• Format: Journal Article
• Language: English
• Published: 14.01.2014
• ISSN: 1477-9226; 1477-9234
• DOI: 10.1039/c3dt53070a

We have recently shown that the vacuum-deposited complex [Fe II L(NCS) 2 ] (L: 1-{6-[1,1-di(pyridin-2-yl)ethyl]-pyridin-2-yl}- N , N -dimethylmethanamine) is capable of a thermally induced spin crossover (SCO) in direct contact with a graphite surface. The SCO significantly differs from the transition behaviour in the bulk phase (powder). In the present work, the assumption of virtually no intermolecular interaction in the powder is confirmed by comparison with the spin transition in acetone solution ( T 1/2 = 234[3] K, Δ T 80 = 58[4] K), as monitored by temperature-dependent UV/Vis spectroscopy. The complex crystallises from chlorocarbons in the form of a number of pseudopolymorphs. Amongst these, the sufficiently stable solvate [Fe II L(NCS) 2 ]·CHCl 3 is investigated by variable-temperature single-crystal X-ray diffractometry. Its SCO behaviour ( T 1/2 = 240[3] K, Δ T 80 = 35[4] K) correlates with features of molecular structure that are unambiguously identified by analysis of the tensor of thermal expansion. Following comprehensive comparison of spin-transition properties in different states of aggregation (also in relation to the newly synthesised high-spin iron( ii ) and iron( iii ) complexes [Fe II Cl 2 L] and [Fe III Cl 2 L]PF 6 ), a mode of adsorption on graphite surfaces is proposed, that complies with all previous findings. Differences in the spin-crossover behaviour of [FeL(NCS) 2 ] in the crystalline state vs . on a graphite surface are rationalised by a study of variation in the thermal-expansion tensor.