Schegolev Memorial Symposium Chernogolovka, Russia, October 2009 Organic-Inorganic Layer Salts as Molecular Functional Materials: Multilayers and Chirality Peter Day UCL and Royal Institution, London, UK

Layered structures – foundation of micro-electronics (MOS etc) Fabricated by ‘top down’ methods Molecular beam epitaxy Laser ablation Spin coating etc etc But is it possible to make multilayers by self-assembly? YES

A self-assembled multilayer Insulating layer Metallic layer Insulating layer

An old story of layers – soluble ferromagnets Bellitto and Day 1978 (C n H 2n+1 NH 3 ) 2 CrX 4

Halide Layer Conductors – from metals to insulators Mitzi et al. 1995

Conducting multilayers – BEDT-TTF charge transfer salts The BEDT-TTF moleculeElectrochemical crystal growth

Organic-Inorganic Charge Transfer Salts First paramagnetic molecular superconductor  ”-(ET) 4 [(H 3 O)Fe(C 2 O 4 ) 3 ].C 6 H 5 CN Day, Kurmoo, Graham 1995

What we want to do next…. First objective - Superlattices of layers D + X - salts form layers: DXDXDX…. Make e.g. DXD’XDXD’X…. D, D’ – same molecule, different packing D, D’ – different molecules

Multi-layers means multi-functions…. An early example of DXD’X… stacking  ”(ET) 4 [(H 3 O)Ga(C 2 O 4 ) 3 ].PhCH 2 CN Akutsu, Day et al D XD’ X D

Different layers have different functions metallic proton conductor H 3 O + -crown ether layer:– proton conducting ET layer:– electron conducting Akutsu, Day et al. 2005

Superstructure with purely inorganic layer Na + and H 2 O Martin, Day et al 2007

Second objective - Chiral organic-inorganic multilayers Why? Maybe novel properties – magneto-chiral anisotropy (Rikken) chiral Fermi surface? chiral superconductor?? How? chiral anions chiral donor molecules chiral guest molecules chiral solvents

Chiral anions – [M(C 2 O 4 ) 3 ] 3-  ”-(ET) 4 [M(C 2 O 4 ) 3 ]C 6 H 5 CN Each anion layer contains one enantiomer Day, Kurmoo, Graham 1995

Chiral anions – [M(C 2 O 4 ) 3 ] 3- Two polymorphs of (ET) 4 [(H 3 O)M(C 2 O 4 ) 3 ]C 6 H 5 CN C2/c is superconducting; Pbcn is semiconducting! Anion layersCation layers Turner, Day, Howard et al 2001

Ferromagnetic Metallic chiral tetra(methyl)-BEDT-TTF  ”-(TM-ET) 2.7 [MnCr(C 2 O 4 ) 3 ]CH 2 Cl 2 Incorporating a chiral donor molecule Gomez-Garcia, Giminez-Sal, Wallis & Coronado 2007

Chiral guest molecules - DXD’X superstructure (R)- and (S)-sec-phenyl alcohol Martin, Day, Akutsu et al 2007

Anion layers contain NH 4 +, [Fe(C 2 O 4 ) 3 ] 3- and guest molecules Martin, Day, Akutsu et al 2007

Crystals with chiral (R)- or racemic (R,S)- guest molecules Disorder of guest molecules in (R,S)- crystal Single crystal resistivities Martin, Day, Akutsu et al 2007 (R) (R,S)

Chiral solvent Crystallising (NH 4 ) 3 [Fe(C 2 O 4 ) 3 ] with 18C6 gives chiral [(NH 4 )(18C6)] 3 [Fe(C 2 O 4 ) 3 ].9H 2 O containing only one enantiomer of the anion. Helical array of [(NH 4 )(18C6)] + [Fe(C 2 O 4 ) 3 ] 3- and H 2 O

In an achiral solvent the same reactants crystallize in a racemic polymorph with a different structure [(NH 4 )(18C6)] 3 [Fe(C 2 O 4 ) 3 ].6H 2 O Martin 2008

ET salts from chiral solvent: ET 3 [(Na)  -Cr(C 2 O 4 ) 3 ].CH 2 Cl 2 Martin, Day et al, 2009

ET 3 [(Na)  -Cr(C 2 O 4 ) 3 ].CH 3 NO 2 Polymorph I – P Anion layer ET layer MartinMartin Martin, Day et al 2009

ET 3 [(Na)  -Cr(C 2 O 4 ) 3 ].CH 3 NO 2 Polymorph 2 – P2 1 Anion layerET layer Martin, Day et al 2009

What have we learned? Multi-layers of alternating organic and inorganic components can be crystallized with defined superstructures. Each layer can have its own properties (metallic, superconducting, magnetic etc). Chirality can be built into the structures by crystal engineering.

Collaborators Hiroki Akutsu; Akane Akutsu-Sato, Hyogo University, Japan – structures and properties John Wallis, Nottingham Trent University, UK – new donor molecules Mike Hursthouse; Peter Horton; Sussex University, UK – crystal structures Carlos Gomez, Valencia University, Spain – physical properties Amalia Coldea, Bristol University, UK – magnetoresistance Lee Martin, NottinghamTrent University, UK - synthesis, structures and properties

Our funding Engineering and Physical Sciences Research Council (UK) European Commission: MAGMANet; COST D35 Royal Society (UK)-JSPS (Japan)