Schegolev Memorial SymposiumChernogolovka, Russia, 12-15 October

2009

Organic-Inorganic Layer Salts

as Molecular Functional Materials:

Multilayers and ChiralityPeter DayUCL and Royal Institution, London, UK

Layered structures – foundation of micro-electronics

(MOS etc)• Fabricated by ‘top down’ methods

Molecular beam epitaxyLaser ablationSpin coating etc etc

• But is it possible to make multilayers by self-assembly? YES

A self-assembled multilayer

Insulatinglayer

Metalliclayer

Insulatinglayer

An old story of layers – soluble ferromagnets

Bellitto and Day 1978

(CnH2n+1NH3)2CrX4

Halide Layer Conductors –from metals to insulators

Mitzi et al. 1995

Conducting multilayers – BEDT-TTF charge transfer salts

The BEDT-TTF molecule Electrochemical crystal growth

Organic-Inorganic Charge Transfer Salts

First paramagnetic molecular superconductor

”-(ET)4[(H3O)Fe(C2O4)3].C6H5CN

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 packingD, D’ – different molecules

Multi-layers means multi-functions….

An early example of DXD’X… stacking”(ET)4[(H3O)Ga(C2O4)3].PhCH2CN

Akutsu, Day et al. 2003

D X D’ X D

Different layers have different functions

metallic proton conductorH3O+-crown ether layer:– proton conducting

ET layer:– electron conducting

Akutsu, Day et al. 2005

Superstructure with purely inorganic layer

Na+ and H2O

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 moleculeschiral guest moleculeschiral solvents

Chiral anions – [M(C2O4)3]3-

”-(ET)4[M(C2O4)3]C6H5CN

Each anion layer contains one enantiomer

Day, Kurmoo,Graham 1995

Chiral anions – [M(C2O4)3]3-

Two polymorphs of (ET)4[(H3O)M(C2O4)3]C6H5CN

C2/c is superconducting; Pbcn is semiconducting!

Anion layers Cation layers

Turner, Day, Howard et al 2001

16.6 Å

Ferromagnetic

Ferromagnetic

Metallic

S S

SS

SS

S S

chiral tetra(methyl)-BEDT-TTF

”-(TM-ET)2.7[MnCr(C2O4)3]CH2Cl2

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 NH4+,

[Fe(C2O4)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 (NH4)3[Fe(C2O4)3] with 18C6 gives chiral [(NH4)(18C6)]3[Fe(C2O4)3].9H2O containing only one enantiomer of the anion.

Helical array of[(NH4)(18C6)]+[Fe(C2O4)3]3- and H2O

In an achiral solvent the same reactants crystallize in a

racemic polymorph with a different structure

[(NH4)(18C6)]3[Fe(C2O4)3].6H2O

Martin 2008

ET salts from chiral solvent:ET3[(Na)-Cr(C2O4)3].CH2Cl2

Martin, Day et al, 2009

ET3[(Na)-Cr(C2O4)3].CH3NO2

Polymorph I – P212121

Anion layer ET layer

Martin

Martin, Day et al 2009

ET3[(Na)-Cr(C2O4)3].CH3NO2

Polymorph 2 – P21

Anion layer ET 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)