Multi-phase Spin crossover in Fe(ptz) 6 (BF 4 ) 2

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1 Multi-phase Spin crossover in Fe(ptz) 6 (BF 4 ) 2 Neutron diffraction & optical investigations under pressure collaboration with C. Ecolivet (GMCM, Rennes) J. Jeftic (ENSCR, Rennes) J.F. Létard (ICMCB, Bordeaux) P. Rosa (ICMCB, Bordeaux) B. Ouladdiaf (ILL, Grenoble) F. Moussa (LLB, Saclay) ECRYS, Cargèse 2008 INSTITUT MAX Institut VON Max von LAUE Laue - -PAUL Paul Langevin LANGEVIN

2 Guidelines General features on the spin crossover The complex Fe(ptz) 6 (BF 4 ) 2 Structural aspects Pressure effects - Low pressure - High pressure Pressure vs Light INSTITUT MAX VON LAUE -

3 Transition-metal complexes and Spin-crossover: - Kahn Molecular Magnetism Topics in Current Chemistry, Spin crossover in transition metal compounds I, II, III Springer 2004 L = complex organic ligand Intermediate ligand field oct ~ k B T Low Spin High Spin Strong ligand field L=CN - Low Spin t 2g e g Low Spin High Spin S LS < S HS e g t 2g Weak ligand field L=H 2 O High Spin V LS < V HS Order Parameter: concentration of LS species non-symmetry breaking // liquid-gas transition HS phase: stabilization by the entropy (configuration and vibrational)

4 Molecular multistability and industrial perspectives: materials with ~ room temperature spin crossover Threshold sensors: temperature, pressure, light... Data storage, holography photo and magneto active switches Fe(pyrazine)[Pt(CN) 4 ] Reversible LS-HS transition by 8ns laser pulse (532nm) in the hysteresis loop Bousseksou et al, Angewandte Chemie 2005 INSTITUT MAX VON LAUE - Létard et al, ICMCB Bordeaux (Olikrom ANVAR program)

5 Pressure effects on spin crossover complexes: - favor the LS state [Fe(bpym)(NCS) 2 ] 2 bpym - LS-LS HS-LS HS-HS - magnetic ordering (when LS 0) Fe(phen) 2 (NCS) 2 LS HS Gütlich et al, J. phys:condmat (2004)

6 The spin crossover transition of Fe(ptz) 6 (BF 4 ) 2 : a model system high symmetry of ligands around the Fe II atom Decurtins, Gütlich, Köhler, Spiering, Hauser, Chem. Phys. Lett At equilibrium transition (T, P) - Out of equilibrium transition photo-induced by long light pulses (LIESST and reverse-liesst) Wiehl et al, J. Appl. Cryst 1990, Acta Cryst B 1993 LS S=0 HS S=2 Jeftic et al, Polyhedron 2003

7 Spin crossover transition of Fe(ptz) 6 (BF 4 ) 2 : at equilibrium or out-of-equilibrium? Influence of the cooling rate Jung et al. Z. Phys.B100(1996)517 HS concentration : in the supercooled phase R 3, by undergoing the structural transition R 3 P 1

8 Fe II (ptz) 6 (BF 4 ) 2 at atmospheric pressure R 3, Z=3 Fe interconnection via potential H bonding restricted in the (a,b) plane Wiehl et al. Appl. Cryst.(1990) 23,151 projection in (a+b, c) plane Projection along 3 (a,b) plane c~34å a~11å Poster on Hydrogen bonding as spin crossover mediator in Fe(L222(NO 3 O 2 ))(CN) 2 H 2 O

9 Fe(ptz) 6 (BF 4 ) 2 Transition at atmospheric pressure at low temperature ( 130K) Spin crossover Ferroelastic transition R 3 P 1 Wiehl, Spiering, Gütlich, Knorr, J. Appl. Cryst (1990) 23, 151

10 Fe(ptz) 6 (BF 4 ) 2 transition at atmospheric pressure by Brillouin scattering =676 nm Kr + laser 100mw Continuous illumination P 1 Ecolivet et al, to be published R 3 Spectra fitted with coupled susceptibilities of the longitudinal acoustic mode with relaxation (quasielastic component)

11 Fe(ptz) 6 (BF 4 ) 2 Chemical PRESSURE effects Influence of dilution of a non-magnetic atom: Zn 1-x HS concentration in [Fe x Zn 1-x (ptz) 6 ](BF 4 ) x Fe < Fe 2+ 3d 6 atomic radius 1.56Å Zn 2+ 3d 10 atomic radius 1.42 Å negative pressure effect T open symbols T solid symbols Jung et al. Z. Phys.B100(1996) Arrows indicate the structural transition (T ) - HS =1/2 indicates the spin crossover INSTITUT MAX VON LAUE -

12 T (K) Fe II (ptz) 6 (BF 4 ) 2 : LS-HS transition under pressure at equilibrium High pressure studies at low temperature: He gas for - high pressure even at low T - a perfect pressure control - a good transparency Neutrons, Raman Solidification of He 50 Temperature evolution of the HS concentration obtained from optical density measured at different hydrostatic pressures. Jeftic et al, J. Phys. Chem. Sol. 57 (1996) 1743 Jeftic et al, High Pressure Research 23 (2003) P (MPa)

13 Fe(ptz) 6 (BF 4 ) 2 4F2 at LLB triple-axes spectrometer (a*,b*) reciprocal plane HS from the optical density Jeftic et al, J. Phys. Chem. Sol. 57 (1996) 500 bars 1000 bars 1bar

14 Fe II (ptz) 6 (BF 4 ) 2 at low pressure (optical absorption) T = 160K HS LS 350bar 1200bar INSTITUT MAX VON LAUE -

15 Fe(ptz) 6 (BF 4 ) 2 (P,T) phase diagram Low pressure

16 Fe(ptz) 6 (BF 4 ) 2 Photo-induced effects (LIESST effects) HS LS Light Slow cooling (at equilibrium) HS disordered phase P-1 LS disordered phase P-1 phase Fast cooling (out of equilibrium) HS phase R-3 LS phase R-3 Moussa, Molnar et al, Chem. Phys. Lett. 402 (2005) 503 INSTITUT MAX VON LAUE -

17 Fe II (ptz) 6 (BF 4 ) 2 at higher pressure neutron scattering ILL P = 60MPa but above 200MPa reconstructive phase transition T ( 179.5K) FWHM ( ) ~ 5 T ( K) FWHM ( ) ~ 20

18 Fe II (ptz) 6 (BF 4 ) 2 at high pressure (optical absorption) T=245K, P=100 MPa T=245K, P=210 MPa

19 T (K) Fe II (ptz) 6 (BF 4 ) 2 under hydrosatic pressure - the LS-HS transition is decoupled from the ferroelastic transition - Hysteresis ferroelastic transition Fe II (ptz) 6 (BF 4 ) 2 - Pure Spin instability: the 1 st order spin transition becomes a continuous spin crossover - "negative pressure" effect R-3 HS R-3 HS P-1 HS P-1 LS? Magnetic susceptibility Neutron scattering D15, D10 at ILL 4F2 at LLB Optical density R-3 LS P-1 P-1 LS LS P (MPa) INSTITUT Institut MAX Max VON von Laue LAUE - Paul - PAUL Langevin LANGEVIN