Molecular Magnetic Switches Dr. Marat M. Khusniyarov Department of Chemistry and Pharmacy Friedrich-Alexander-University of Erlangen-Nuremberg Erlangen, Germany

Spin-Crossover Metal Complexes eg eg DT, Dp, hn t2g t2g low-spin Fe(II) high-spin Fe(II) diamagnetic paramagnetic LS HS Switching: Application: magnetic properties, electrical conductivity, refractive index, color, … electronics, spintronics, sensors, memory units, … molecular

LIESST (Light-Induced Excited Spin State Trapping) LS HS LS HS Problem: photoinduced state is usually stable only at very low temperatures T < 50K! P. Gütlich, A. Hauser et al., Chem. Phys. Lett. 1984, 105, 1 A. Hauser, Top. Curr. Chem. 2004, 234, 155

LD-LISC (Ligand-Driven Light-Induced Spin Change) trans- planar cis- non-planar first evidence for photoswitching at RT M.-L. Boillot, J. Zarembowitch et al., Inorg. Chem. 1996, 35, 3975 spin change conversion  3% H. Nishihara et al., Dalton Trans. 2009, 280 2. liquid phase Limitations: 1. very low spin-change conversion

Spin-Crossover Molecular Photoswitch open-ring isomer closed-ring isomer Photocyclization UV, solution, RT Photocycloreversion visible light, solution, RT Multiple photoswitching extinction at 376 nm

Spin-Crossover Molecular Photoswitch Inorg. Chem. 2013, 52, 11585 HS S = 2 LS S = 0 NMR under UV irradiation solution, RT Multiple photoswitching HS  LS photoconversion: 40% at RT !

Reversible photocyclization in the solid state at RT UV Photocycloreversion visible light Multiple photoswitching abs. at 375 nm S 2p XPS 100% open-ring 68% open-ring 32% closed-ring UV Reversible photocyclization in the solid state at RT

Spin-Crossover Molecular Photoswitch NEXAFS at Fe L3 Angew. Chem. Int. Ed. 2015, 54, 12976 HS 100% HS 68% LS 32% HS 84% LS 16% UV visible RT HS S = 2 LS S = 0 room temperature ! solid state ! reversible ! molecular level !

Current Developments Modifications “1” “0” hn or electrically @ RT Au(111) Au(111)

Valence Tautomeric Metal Complexes strongly paramagnetic Intramolecular Electron Transfer coupled with Spin-Crossover at Co center LS-Co(III) HS-Co(II) weakly paramagnetic strongly paramagnetic St = 0 + 1/2 St = 3/2 + 1/2 + 1/2 meff = 1.73 mB meffRT = 5.12 mB A. L. Rheingold, D. N. Hendrickson et al., J. Am. Chem. Soc. 1993, 115, 8221 photoswitching requires T < 20 K! Problem:

Valence Tautomeric Molecular Switches cis-trans isomerizable systems

Valence Tautomeric Molecular Switches Variable temperature Evans NMR Variable temperature UV-VIS at RT: HS-Co(II): 44% LS-Co(III): 56% LS-Co(III) HS-Co(II) DG = DH – TDS DH = 43(5) kJ mol–1 DH = 56(1) kJ mol–1 DS = 144(16) J mol–1 K–1 DS = 190(5) J mol–1 K–1 Both ΔH and ΔS are too large for a valence tautomeric equilibrium !

Equilibria in Solution HS-Co(II) HS-Co(II) LS-Co(III)

Coordination-Induced Valence Tautomerism Titration with 4-styrylpyridine Chem. Eur. J. 2014, 20, 11149 UV-VIS-NIR Evans NMR IVCT Ka = 4(1)·103 L mol–1 Ka = 6(2)·103 L mol–1 Coordination-Induced Valence Tautomerism (CIVT) RT HS-Co(II) LS-Co(III)

Photomagnetic Molecular Switch Chem. Sci. 2015, 6, 4599 trans  cis photoisomerization (l = 320 nm) UV-VIS-NIR Evans NMR EPR Ligand-Driven Light-Induced Valence Tautomerism (LD-LIVT) RT LS-Co(III) HS-Co(II) l = 320 nm l = 272 nm

Overview Angew. Chem. Int. Ed. 2015, 54, 12976 Inorg. Chem. 2013, 52, 11585 Light-Induced Spin-Crossover at RT Chem. Eur. J. 2014, 20, 11149 Coordination-Induced Valence Tautomerism (CIVT) Dalton Trans. 2013, 42, 5237 Chem. Sci. 2015, 6, 4599 Supramolecular Magnetic Networks Ligand-Driven Light-Induced Valence Tautomerism (LD-LIVT)

Acknowledgements The Group: Magdalena Milek Alexander Witt Dr. Ghulam Abbas Prof. Rainer Fink Dr. Benedikt Rösner FAU Erlangen-Nuremberg (XPS, NEXAFS) Dr. Frank Heinemann FAU Erlangen-Nuremberg (crystallography)