Ionic liquids for Inorganic 1. Introduction and Materials ... · Ionic liquids for Inorganic and...

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Peter Nockemann, Leuven Summer School Ionic Liquids 2010

Ionic liquids for Inorganic

and Materials Chemistry

K.U.Leuven, Summer School Ionic Liquids

August 24, 2010

Peter Nockemann

Queen‘s University of Belfast

QUILL Research Centre

E-mail: [email protected]


Ionic Liquids for Inorganic and Materials Chemistry

Outline

1. Introduction

2. Solvation & Solubility of Metal Salts in Ionic Liquids

3. Speciation of Metals in Ionic Liquids

4. Ionic Liquids for Nanomaterials Synthesis

5. Summary and Outlook


Applications of ILs in inorganic & materials

chemistry

Catalysis

Zeolithe synthesis

Shaped nanoparticles

Metal-organicframeworks

Coordination chemistry

Introduction


1. Introduction

What are the features of ionic liquids that make them interesting for

inorganic and materials synthesis?

• ILs possess a high polarity and high dipole moment

• Tunable functionalities

• Reactions in the liquid phase are possible at high temperatures -compared

to convential solvents, or low temperatures compared to solid state

chemistry

• Negligible vapour pressure – e.g. water can be reversibly removed

• Large electrochemical window & chemical stability

• Preorganised solvent structures


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Solvothermal

Solvent chemistryCoordination chemistry

Solid-state chemistry

Temperature

„Ionothermal Synthesis“

A „temperature gap“

Novel inorganic synthetic pathways in coordination & materials chemistry

Towards low temperature solid state chemistry in ILs



2. Solvation and Solubility of Metal Salts in Ionic Liquids

2.1. Considerations on Metal Salt Solubility

2.2. Coordination Chemistry in ILs

2.3. Metal-Containing Ionic Liquids

2.4. Conlusions




Selected reviews:



• Solubility of metal salts in ionic liquids depends strongly on the nature of

the ionic liquid

• The solubility can be very poor in certain ionic liquids

• Especially weakly coordinating anions of the ionic liquids result in low

solubilities

• Functionalised ionic liquids can increase the solubility due to the

coordinating ability of the functional group

• Solubility of metal salts is strongly dependent on the water content –

traces of water can have a huge effect on solubility – especially

hydrophilic Ils often contain significant amounts of water

• The high viscosity of ionic liquids means often slow mass transfer


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Ways to improve the solubility of metal salts:

• Strongly coordinating anions can form anionic complexes – ionic nature

of the metal complex increases compatibility with the ionic liquid

• Mimic the cation of an ionic liquid – e.g. imidazolium instead of sodium

• Addition of poly (ethylene glycol) (PEG) increases usually the solubility of

inorganic metal salts

• Rule of thumb: solubility increases with temperature (and chance of

crystallisation upon cooling)

• Trick: use co-solvent (e.g. methanol) to dissolve the metal salt first – then

evaporate the volatile solvent


Peter Nockemann, Leuven Summer School Ionic Liquids 2010 Peter Nockemann

P. Nockemann et al. Chem. Commun. 2005 (34): 4354-4356.

Lanthanide spectroscopy in ionic liquids


• Strongly coordinating anions can form

anionic complexes – ionic nature of the

metal complex increases compatibility with

the ionic liquid

• Mimic the cation of an ionic liquid – e.g.

imidazolium instead of sodium


2.2 Coordination Chemistry in Ionic Liquids, Example 1:

• Coordination in an ionic liquid with a strongly coordinating anion

• Dissolved metal complexes form anionic species

• Conceptually suitable for extraction of metals



CoO / Co2O3

+ HTf2N + IL

H2O

IL + CoCo(Tf2N)x

Co(Tf2N)x

Ionic Liquid + [Co(hfac)3]-

in H2O

in H2OIonic liquid

Concept for metal extraction using ionic liquids

Example: extraction of a cobalt(II) solution using an ionic liquid

NNF3C CF3

O OAqueous solution of Co(Tf2N)2

[BMIM][hfac]

No contamination of the aqueous phase with residues of the ionic liquidH. Mehdi et al., Chem. Commun., 2010, 113, 234-236.


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Interactions in the structure of [C18MIM][hfac]

Crystal structure of [C18

MIM][hfac]



+

(a) Nd(Tf2N)3 in H2O(b) Ionic liquid

Neodymium extraction using an ionic liquid

NNF3C CF3

O O

(a)

(b)

Aqueous solution of Nd(Tf2N)3

[BMIM][hfac]

Peter Nockemann



Structure of a neodymium(II) complex obtained after extraction

[C4mim][Nd(hfac)4]

Nd(Tf2N)3,aq + 4[C4mim][hfac]org

-> [C4mim][Nd(hfac)4]org + 3[C4mim][Tf2N]org

Crystallised from a

concentrated solution



Na

O

O

F3C

F3C

3

N

N

2

Surprising result: structure of [BMIM] 2[Na(hfac) 3]

→ extraction of alkaline metals?

H. Mehdi et al., Chem. Commun., 2010, 113, 234-236.


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• Coordination of a cobalt(II) salt in a nitrile functionalised ionic liquid

• Example for tunable coordinating abilities and solvent interaction

• Cationic ‘solvent coordination’


Chemistry – A European Journal 2010, 16, 1849-1858.


S

O

NS

OO

CF3

O

F3C

N

CN

HH

Structure of a nitrile functionalised ionic liquid

P. Nockemann et al. Chemistry – A European Journal 2010, 16, 1849-1858.

2.2 Coordination Chemistry in Ionic Liquids, Example 2


1 2 3 4 5

-0,30

-0,27

-0,24

-0,21

-0,18

part

ial c

harg

e

chain length

Alkyl analogue Pyrrolidinium IL

O r i g i n D e m o O r i g i n D e m o O r i g i n D e m o






Calculation of the charge distribution of nitrile functionalized ionic liquids

A natural bond orbital analysis was performed. The partialcharge of the nitrile function (N1 and C1) was determined by thenatural charge (NPA) of the natural atomic orbitals.(S. Zahn/ B. Kirchner, Leipzig)



Co

SO

N

SO

O

O

CF3

CF3

S O

N

S O

O

O

F3C

F3C

S

O

N

S

O

O

O

CF3

CF3

S

O

N

S

O

O

O

F3C

F3C

N2+

2


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Co

Tf2N

Tf2NNTf2

N

Tf2N

C

N

N C

N



Co

N

N

N

N

C

N

N CN

NC

N

C

N

C

N

C

N

+8



Co

Tf2N

Tf2NNTf2

N

H2O

NS

S

O

O

O

O

F3CF3C

C

N

N C

N

Crystal structure of

[Co(Tf2N)

3(H

2O)(C

2NMPyr)

2](Tf

2N)

Hydration of a solvate – but reversible!




• A protic betaine based functionalised ionic liquid

• Dissolution of metal oxides

• Dissolution of oxides & subsequent crystallisation as a synthetic

pathway to unusual coordination compounds


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J. Phys. Chem. B, 2006, 110, 20978 – 20992.

N+

COOH

CF3S

N-

SCF3

O

O

OO

Betainium ionic liquid [Hbet][Tf2N]

Stripping of metal ions from the ionic liquid

[Hbet][Tf2N] can solubilize large

quantities of metal oxides

Inorg. Chem., 2008, 47, 9987 - 9999.



Solubility of metal oxides in the task-specific ionic liquid [Hbet][Tf2N]

formation of pentameric Ni-clusters

potential magnetic material

high solubility of the complexesin ionic liquidsP. Nockemann et al., Crystal Growth & Design, 2008, 8, 1353 – 1363.

[Ni5(bet)12(H2O)6][Tf2N]10

[Cu3(bet)8(H2O)4][Tf2N]6



Solubility of metal oxides in the task-specific ion ic liquid [Hbet][Tf 2N]

soluble

not soluble

not tested



Structure of [Ni5(bet)

12(H

2O)

6][Tf

2N]

10obtained from an ionic liquid

Cation [Ni5(bet)

12(H

2O)

6]+10

P. Nockemann et al., Crystal Growth & Design, 2008, 8, 1353 – 1363.


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Packing in the structure of [Ni5(bet)

12(H

2O)

6][Tf

2N]

10



O

Pb

Pb

PbPb

O

Pb

H N

S

SO

O

OO

CF3

CF3

N

S

S O

O

O

O

F3C

F3C

NS S

O

O

O

O

CF3 CF3

O

ON

OO

N

OO

NOO

N

OO

N

OO

N

OO

NO

O

N

H2O

Structure of [(Pb4O)Pb(OH)(bet)

8(Tf

2N)

3][Tf

2N]

4obtained from an ionic liquid

Cationic [(Pb4O)Pb(OH)(bet)8(Tf2N)3]4+ cluster



Pathway provides access to new classes of compounds and materials

Indication of the high potential of synthesis from ionic liquids


Metal oxidesdissolved in a task-

specific ionic liquid

PbNiMn

ZnCo

P. Nockemann et al., Inorg. Chem., 2008, 47, 9987 - 9999.



2.3 Metal-Containing Ionic Liquids:

• Metals can be part of the ionic liquids

• Properties of ionic liquids with additional intrinsic properties of the metal

• Versatile applications in catalysis, catalyst precursors, reagents for

chemical reactions or for nanomaterials synthesis

• Functional materials with luminescent of magnetic properties


Review paper:

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2.3 Metal-Containing Ionic Liquids, Example 2

Depending on the type of boron cluster anions, these compounds

exhibit a high thermal stability up to 480°C (type [Cnmim]

2[B

12Cl

12], n =

2, 4, 8, 10, 12, 14, 16, 18) and low glass transition temperatures (type

[Cnmim][Co(C

2B9H11

)2], n = 2, 4, 6, 8, 10, 12, 14).


2.3 Metal-Containing Ionic Liquids, Example 3


N N

5

Ln(NCS)8

Structure of [BMIM]5[Ln(NCS)8] (BMIM = 1-butyl-3-methylimidazolium; Ln = La –Yb)

Lanthanide-containing ionic liquids

Miscibility with other ionic liquids like [BMIM][Tf2N] or [BMIM][PF6]

P. Nockemann et al. J. Am. Chem. Soc. 2006, 128, 13658.



3. Speciation of metals in ionic liquids:

• Basic question: What is surrounding of a metal in IL-solution? How is it

coordinated? What about IL-metal interactions?

• Methods to probe the surrounding of a metal ion in an ionic liquid

• Methods should work in the liquid state

• Equilibria or mixtures of different species of metal complexes are possible

• Solid state structure can be different from liquid state species

• Speciation is extremely important for the further progress of inorganic and

materials chemistry in ionic liquids


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Some techniques & methods for metal speciation

UV-Vis absorption spectroscopy

Luminescence and excitation spectroscopy (steady state and dynamic

measurements, visible & near-infrared spectroscopy)

Extended X-ray Absorption Fine Structure (EXAFS)

NMR spectroscopy (1H, 13C, diamagnetic metal cores)

Infrared & Raman spectroscopy of metal complexes

XPS; neutron diffraction

3. Metal speciation in ionic liquids


3. Metal speciation in ionic liquids, Example 1


Speciation of lanthanide-containing ionic liquids

Optical absorption& emission spectroscopy(Lanthanide as symmetry probes)

EXAFS

Extended X-Ray

Absorption

Fine Structure

89Y- and 139La-NMR

Speciation in the liquid state

Bond lengths & coord. numb.

Number of species (sites) present

FT-IR and FT-RamanSpectroscopybond lengths / angles,coordination mode

Initial models for speciationfrom crystallography

Models for speciation from theoryDFT, molecular dynamics simulations



Speciation of Rare-Earth Betaine Bistriflimide Complexes

Dissolved in Ionic Liquids

[Eu2(bet)8(H2O)4][Tf2N]6

18000 17000 16000 15000 14000

600 650 700

Inte

nsi

ty (

a.u

.)

Wavenumber (cm-1)

Wavelength (nm)

0 1 2 3 4 5 60,0

0,5

1,0

1,5

2,0

2,5

(b)

FT

R + ∆ / Å

89Y- and 139La-NMRFT-IR and FT-Raman

Spectroscopybond lengths / angles,

coordination mode

Optical absorption

& emission spectroscopy

(Lanthanide as

symmetry probes)

EXAFSExtended X-Ray

Absorption

Fine Structure

Luminescence

decay curve:Bi-exponential

components:

657 ± 40 ms (61%)

1225 ± 142 ms (39%)


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∆T

- 2 H2O



17300 17280 17260 17240 17220 17200

578,5 579 579,5 580 580,5 581

Inte

nsity

(a.u

.)

Wavenumber (cm-1)

17 240 cm-1

17 245 cm-1

Wavelength (nm)

Indication for two species fromoptical spectroscopy

→ At least two different speciespresent in the ionic liquid solution

P. Nockemann et al., Chemistry – A European Journal, 2009, 15, 1449 – 1461.



Beam line 11-ID-B at APS

MAR 345 Image Plate

X-ray scatteringThe scattering experiment

at APS

Monochromator: Si (511)E = 90.48 keV,λ = 0.13702 Å.

D = 277 mm



CeO2 powder 0.5 M U(VI) 1 M HClO4

Image plate screenings of MAR 345 detector

Bragg Scattering Diffuse Scattering



1 2 3 4 5 6

0.0

0.5

1.0

1.5

2.0

2.5

3.0 1.42 Å

2.63 Å

2.50 Å

4.01 Å

g(r)

r [Å]

500 mM Eu [Hbet] [Tf2N]

pure [Hbet] [Tf2N]

crystalline dimer

HEXS of the solid and liquid samplesPair distribution function


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Solid state Solution

P. Nockemann et al., Chemistry – A European Journal, 2009, 15, 1449 – 1461.



P. Nockemann et al. Inorg. Chem. 2007, 46, 11335-11344.

Speciation of uranyl complexes in ionic liquids

D4h

D3h

[UO2(NO3)3]-

[bmim]2[UO2Br4]





4. Ionic liquids for nanomaterials synthesis:

4.1 Nanoparticles & shaped nanomaterials

4.2 Porous framework materials


Review papers:

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What is the role of ionic liquids in nanomaterials synthesis?

• Nanoparticle can be synthesised in-situ in ionic liquids

• Ionic liquids can stabilise nanoparticles

• NPs with small diameters and a narrow size distribution

• Stable colloidal systems can be generated which can be used for high

turnover rates e.g. in catalytic hydrogenations

• Preorganised solvent structure





• Tunable surface tensions:

• Low suface tensions result in high nucleation rates – generation of very small particles

• ILs with low interface energies for larger objects – good stabilisation / solvatisation of

molecular species

• Inorganic Synthesis under ambient conditions – also anhydrous or water-

poor conditions are possible

• Hydroxide / oxihydrate formation can be suppressed – low generation of

amorphous species, so condensed systems are likely to crystallise





• Extended hydrogen-bond systems and therefore highly structured –

induces structural directionality (IL effect)


[EMIM][PF6] [OMIM][PF6]

Segregation of polar and

non-polar domains in

imidazolium ILs




• Extended hydrogen-bond systems and therefore highly structured –

induces structural directionality (IL effect)

• High self-organisation in the liquid state as “entropic driver” for

spontaneous, well defined and extended ordering of nanoscale structures


Different gold nanoparticle morphologies from different IL conditions.

Y. Qin, Y. Song, N. J. Sun, N. Zhao, M. X. Li, L. M. Qi, Chem. Mater. 2008, 20, 3965.

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Ionic precursor

Polar

region

Apolar metal-

organic precursor

Non-polar Tail of ionic liquid



• Preferential solubility of the nanomaterials precursor determines in which domain of

the IL it will be preferentially distributed

• So one approach to control size & shape is to modulate the volumes of the polar /

non-polar domains in the ionic liquid




Synthesis of iron oxide nanorods and nanocubes in an imidazolium ionic liquid Yong Wang, Hong YangChemical Engineering Journal, 2009, 147, 71–78.




A. Taubert, Angew. Chem. Int. Ed. 2004, 43, 5380.

Copper(I) chloride nanoplatelets from a copper-containing ionic liquid precursor

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Interaction of metal nanoparticles with the ionic liquids

There are indications that the interaction of metal NPs with anions or cations is size-dependent.



Photoinduced Oxidation of Water to Oxygen in the Ionic Liquid BMIM BF4 as the Counter Reaction in the Fabrication of Exceptionally Long Semiconducting Silver

Tetracyanoquinodimethane Nanowires Chuan Zhao and Alan M. Bond, J. Am. Chem. Soc. 2009.





4.2 Ionic Liquids for Porous Materials

Ionothermal synthesis for framework materials

• Ionic liquids act as solvents and template provider

• Usually temperatures between 150°C -220°C

• In theory, the ionic liquids act as space fillers during the zeolithe synthesis

• Long range correlations (structuring) within the ionic liquids is believed to

increase the likelihood of transferring chemical information from the

template cation to the framework

• Reactions in an ionic environment

• Small quantities of water can have huge influence on resulting structure


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SIZ-1 (St Andrews Ionothermal Zeolite-1) and

SIZ-6 (Figure 2) are new zeotype structures

and were produced without the addition of

fluoride. Both structures have hanging P–O

bonds and aluminium coordinated to more

than four oxygens.19,24 SIZ-3 (AEL) and SIZ-4

(CHA) were produced with the addition of HF

and consist of fully condensed frameworks.

SIZ-5 (AFO) was produced with the addition of

water and can be classified as hydrothermal

synthesis due to the quantity of water used

being greater in molar terms than the

quantity of ionic liquid.

Parnham, E. R.; Morris, R. E. 1-Alkyl-3-methylimidazolium bromide ionic liquids in the ionothermal synthesis of aluminium

phosphate molecular sieves. Chem. Mater. 2006, 18, 4882–4887.

Ionothermal synthesis of porous alumophosphate molecular sieves

-> reaction conditions lead to

different structure types



5. Summary and Outlook (1):

• Ionic liquids open new frontiers in inorganic and materials chemistry

• Ionic liquids themselves can be considered as ‘advanced’ or hybrid

materials (see applications in dye sensitised solar cells, lithium ion

batteries, sensors, new composite materials, etc.)

• ILs allow interesting possibilities in coordination- and possibly metal-

organic chemistry -> e.g. stabilisation of unusual oxidation states

• Great potential for controlled growth of nanoporous, nanoparticular or

nanoshaped materials



„Ionothermal Synthesis“Access to new

classes of compounds

and materials

New possiblities for

speciation-, process and

reaction control

Chemistry at the interface

of coordination- and

solid state chemistry

Basic research:

Fundamental issues in a

new solution chemistry

= Synthesis in ionic liquids

at elevated temperature





• IL-containing composite materials are an emerging field!

A flexible dye-sensitized solar cell with a

solvent-free ionic liquid

electrolyte.(courtesy G24i Ltd.)

Flexible nanocomposites for energy

storage in supercapacitors. PNAS 2007,

34, 13574.


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5. Summary and Outlook: still some work to do…!

• Solubility has only been studied for some selected examples

• More fundamental data on coordination of metals in ionic liquids required

• More detailed speciation studies in the liquid state on a variety of metals

in ionic liquids would be desirable

• The fundamentals of nanoparticle / nanoshapes with controlled and

predictable growth is still in its infancy – a lot of trial and error

• Lack of understanding the ‘nanostructured liquids’

• Great potential for controlled growth of nanoporous, nanoparticular or

nanoshaped materials



• Queen’s University Belfast• The QUILL Research Centre• Prof. Ken Seddon• Dr. Małgorzata Swadźba-Kwaśny, Léa Chancelier, David Bailie• Dr. Paul Nancarrow, Moira Lewis• EPSRC

• K.U.Leuven (Belgium)• Prof. Koen Binnemans• Dr. Ben Thijs, Dr. Kyra Lunstroot, Michael Pellens• Dr. Kristof Van Hecke, Prof. Luc Van Meervelt

Acknowledgement

Ionic liquids for Inorganic 1. Introduction and Materials ... · Ionic liquids for Inorganic and...

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