research infrastructure at the department of chemistry neil brooks
TRANSCRIPT
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
• 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
TXRF example: [Br] and [Cl] in ionic liquids
[Br] in [C4mim][Tf2N] (ppm)
Recovery rates (%)
RSD (%)
10000 105 6
4000 105 9
2000 113 4
1000 100 6
100 100 60 2000 4000 6000 8000 10000
0
2000
4000
6000
8000
10000
12000
Mea
sure
d B
r co
nc. i
n [C
4mim
][Tf 2N
] (pp
m)
Expected Br conc. in [C4mim][Tf
2N] (ppm)
0 2000 4000 6000 8000 10000
0
2000
4000
6000
8000
10000
Mea
sure
d C
l con
c. in
[C4m
im][O
Ac]
(pp
m)
Expected Cl conc. in [C4mim][OAc] (ppm)
[Cl] in [C4mim][OAc] (ppm)
Recovery rates (%)
RSD (%)
10000 92 74000 90 82000 94 141000 97 5400 91 10200 96 10100 98 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• 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
1H-benzotriazole (0.1 M)Pure Ag-LMS
Pure Ag-LMS
Pure benzotriazole
0.1M benzotriazole in Ag-LMS (bulk)
0.1M benzotriazole in Ag-LMS on Ag surface
DSC – Differential Scanning Calorimetry
DSC: technique
• 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
• Contact me by email: [email protected] to notify interest– Set up meeting to discuss how to proceed
• Tom Vander Hoogerstraete (Chemistry)• M. Ganapathi (MTM)
Practicalities
Acknowledgements