Transcript Research infrastructure at the Department of Chemistry

Research Infrastructure at the
Department of Chemistry
Neil Brooks
Outline
• Overview, basics and examples of core infrastructure
– Total X-ray Fluoresence Spectroscopy – TXRF
– IR/Raman spectroscopy
– Differential Scanning Calorimetry (DSC)
– Nuclear Magnetic Resonance (NMR)
– Single Crystal X-ray Crystallography (SC-XRD)
• Summary
• Assorted other equipment
TXRF – Total X-ray Fluoresence Spectroscopy
TXRF: key parameters
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Two Bruker S2 Picofox TXRF spectrometers in the group
Key information: accurate elemental compositions/ratios
Fast and easy
Low detection limit possible (e.g. ppb)
Multi-element sample analysis
Difficult to detect elements lighter than chlorine
– Ejected X-rays from lighter elements low in energy (matrix effects)
TXRF: technique
TXRF: technique
Measured Cl conc. in [C4mim][OAc] (ppm)
Measured Br conc. in [C4mim][Tf2N] (ppm)
TXRF example: [Br] and [Cl] in ionic liquids
[Br] in
Recovery RSD
[C4mim][Tf2N] (ppm) rates (%) (%)
12000
10000
8000
6000
4000
2000
0
0
2000
4000
6000
8000
10000
Expected Br conc. in [C4mim][Tf2N] (ppm)
10000
105
6
4000
105
9
2000
113
4
1000
100
6
100
100
6
[Cl] in
Recovery RSD
[C4mim][OAc] (ppm) rates (%) (%)
10000
8000
6000
4000
2000
0
0
2000
4000
6000
8000
10000
Expected Cl conc. in [C4mim][OAc] (ppm)
10000
4000
2000
1000
400
200
100
92
90
94
97
91
96
98
7
8
14
5
10
10
13
IR/Raman Spectroscopy
IR: technique
• FT-IR spectrometer Bruker Vertex 70 with Raman module Bruker
RAM II
• Vibrational spectroscopy
– Key information: identification of particular bond vibrations
IR: technique
• FT-IR spectrometer Bruker Vertex 70 with Raman module Bruker
RAM II
• Vibrational spectroscopy
– Key information: identification of particular bond vibrations
• Spectral range 4500 to 400 cm-1
– Transmittance mode (sample prep necessary)
– Attenuated total reflection
• Diamond or ZnSe crystal
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Fast (ca. 1-2 minutes)
Far infrared (400 to 40 cm-1) also possible
Variable resolution (e.g. 1, 2, 4 cm-1)
Required sample: <5 mg
Raman: technique
• FT-IR spectrometer Bruker Vertex 70 with Raman module Bruker
RAM II
• Different selection rules to IR
• Nd-YAG laser λ = 1064 nm
– Variable laser power (1-500 mW)
– Fluoresence can be problem
• Spectral range 3600 to 40 cm-1
• Variable resolution (e.g. 1, 2, 4 cm-1)
• Sample dependent collection time (typically 2 minutes – 2 hours)
– No background collection
• Liq. N2 cooled Ge CCD detector
• Required sample: 50-500 mg
• Surface Enhancement possible (SERS)
Raman example: adsorption of 1H-benzotriazole
on silver substrate in [Ag(MeCN)4]2[Ag(Tf2N)3]
• text
Pure Ag-LMS
0.1M benzotriazole in Ag-LMS on Ag surface
0.1M benzotriazole in Ag-LMS (bulk)
Pure benzotriazole
Pure Ag-LMS
1H-benzotriazole (0.1 M)
DSC – Differential Scanning Calorimetry
DSC: technique
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Mettler-Toledo DSC822e module
Key information: phase transition temperatures/energetics
Required sample: 2-5 mg
Temperature range -60 to 250 °C
Variable heating rate (typically 10 °C/min)
• Complimented with polarised optical microscopy (thermomicroscopy)
on an Olympus BX-60 polarising microscope equipped with a Linkam
THMS 600 hot stage. Temperature range: -196°C - 600°C.
DSC example: eutectic behaviour of
DMSO2/acetamide mixtures
DSC traces of DMSO2/acetamide mixtures
Tamman plot
NMR – Nuclear Magnetic Resonance Spectroscopy
NMR: technique
• Energy states of spin active nuclei split from degeneracy inside a
magnetic field
– E/M radation applied to populate the higher energy state
– Difference in energy of higher and lower states measured is a
function of the nucleus and its environment
• Key information: chemical information about nucleus environment
• 300, 400 and 600 MHz spectrometers available
• Nucleus must be NMR active
– Most common nuclei: 1H, 13C, 31P, 19F
– Can not have unpaired electrons
– Must have sufficient natural abundance
• Liquid state: sample must be a liquid or disolved in a solvent
• Required sample: 5-20 mg
Single Crystal X-ray Crystallography (SC-XRD)
SC-XRD: technique
• Key information: absolute three-dimensional crystal structure
– Allows the resolution of atom positions up to ±0.001 Å
– Accurate bond and intermolecular distances
• Scattering (diffraction) of X-rays from ordered array of molecules in a
crystal leads to diffraction pattern (Bragg’s law: nλ=2dsinθ)
• Diffraction pattern is directly related to the three-dimensional electron
density pattern
– Phase problem
– Imperfect crystals
SC-XRD: practicalities
• Must have (good quality) single crystal!
• Crystal size (each dimension) must be 0.05 to 0.5 mm
– Larger crystals can be cut to size
– Smaller crystals may be possible but will take longer
• Crystal growth
– Evaporation of saturated solution
– Addition of antisolvent
– Growth from melt by slow cooling
• What can be determined?
– Can be used for phase identification
• Crystal structure already known (unit cell check)
– New structure determination
– Elemental composition (on specific lattice sites)
SC-XRD example: structure of Ag-LMS
• First synthesised a Cu-LMS of formula [Cu(MeCN)4][Tf2N]
– Melting point 65 °C
• New Ag-LMS of formula [Ag(MeCN)~2][Tf2N]
– Melting point 18 °C
• Slow cooling of Ag-LMS gave good quality crystals
• Structure determined as [Ag(MeCN)4]2[Ag(Tf2N)3]
SC-XRD: case study structure of Ag-LMS
• If [Ag(MeCN)4]2[Ag(Tf2N)3] is heated at 50 °C for a period of time new
crystals appear
• Crystal structure analysis shows the new compound is [Ag(MeCN)Tf2N]
– One-dimensional polymeric structure
– Melting point 90 °C
Overview
Sample prep
required
Amount
sample
Experiment
time
Analysis
time
Difficulty
TXRF
Yes
ppm
<1 hour
1 hour
Easy
IR
No
<5 mg
2-5 minutes
15 minutes
Easy
Raman
No
50-500mg
0.5-4 hours
1 hour
Medium
DSC
No
2-5 mg
Several hours
15 minutes
Easy
NMR
Yes
5-20 mg
0.5-4 hours
1 hour
Medium
SC-XRD
Yes
one crystal
1 day
1+ week
Hard
Assorted other equipment
• Mass spectrometry
• Absorption spectroscopy (UV-VIS-IR)
– Varian Cary 5000: UV-VIS-NIR spectrophotometer (175-3300 nm)
• Luminescence spectrometers
• Viscosimetry
– Brookfield cone plate viscosimeter (LVDV-II+ Programmable
Viscometer) with cone spindle CPE-40
• X-ray powder diffraction setup with rotating Mo-anode
– SAXS and WAXS
• CHN microanalysis
– CE Instruments EA-1110 CHN elemental analyser
Practicalities
• Contact me by email: [email protected] to notify interest
– Set up meeting to discuss how to proceed
Acknowledgements
• Tom Vander Hoogerstraete (Chemistry)
• M. Ganapathi (MTM)