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Advanced Inorganic

Topics Class-Dr. Brian Barry

if you think you synthesized "something" new or interesting or know a compound, how do you convince someone else that you know what you made? look in literature; use an array of necessary/appropriate analysis methods to make your case
chemical analysis is key for quantitative information on atomic compositions and chemical reactivity
chemical analysis of metals atomic absorption/emission spectroscopy (AA/AE)
chemical analysis of gases/organic compounds oxygen-based combustion analysis (CHN converted to CO2, H2O, N2 gases)
chemical analysis of ions classical ion-selective detection (ex. flame tests)
most chemical analysis methods require the destruction of the chemical uniqueness and atomic connectivity of your inorganic/organic materials (aka sample)
what types of "physical" analyses are applicable to inorganic chemistry? that depends strongly on what type of inorganic structure/material you are studying
which is easier to study molecules or extended materials molecules because they are easier to dissolve
when the nuclear spin quantum number (I) value = 0 the nuclei is unaffected by a magnetic field (ex. 12C)
as the atom size increases the Larmor frequency decreases because it takes longer to turn over
T1 is the relaxation time also described as the time required for the nuclei to come back up after being knocked down; different rate for each nuclei
1 T is how many MHz 42.6 MHz
a magnetic field of 1T induces a Larmor frequency of how much in a proton 42.6 MHz
for a given nucleus with a nuclear spin, I there are how many degenerate states possible 2I +1
NMR is a super conductor containing electrons rotating counterclockwise
in NMR a constant magnetic field is generated from electricity, the stronger the field is it easier or harder to flip an electron harder
free induction decay wavelength released from a charged electron as it flips back to it's relaxed mode
Fourier transforms changes the RF signal (intensity vs. time) to x-axis of ppm
how does ppm relate to frequency range is roughly 15-0 ppm for 1H NMR but different standards can be chosen (scaling factor)
absorption of energy by nucleus with a nuclear magnetic moment is called resonance (spin changes relative to applied magnetic field). The change in energy is dependent on magnetic field strength
a brief (microsecond) RF pulse causes transitions from ground nuclear spin state to excited nuclear spin state transition (M (I)= +1/2, -1/2)
sensitive RF detector coil records the time spectrum that is converted to frequency domain by FT
most modern magnets are not perfectly stable, so they need to maintain a lock on a specific nucleus and then adjust the field slightly to keep the resonance energy of this nucleus unchanged
since energy increases as the magnetic field increases recording absorption processes on different instruments will lead to different frequency values
since only ppm differences exist with different resonance frequencies, it is crucial that all nuclei see the same external magnetic field; how do we make it homogeneous a. spin a dissolved solution sample very fast (~20 Hz) b. fine tune imperfections in applied magnetic field and glass tube by electronic shimming
why do peaks appear at different relative resonance energies/frequencies? define Heff=net magnetic field implying on the nucleus of interest
chemical shift is dimensionless but is generally reported in ppm to make it the same on different NMR
EPR sample is held in a very strong magnetic field while electromagnetic radiation is applied monochromatically
Magnetic susceptibility is a dimensionless proportionality constant that indicates the degree of magnetization of a material in response to an applied magnetic field (k)
diamagnetism materials create an induced magnetic field in a direction opposite to an externally applied magnetic field, and are repelled by the applied magnetic field.
paramagnetism a form of magnetism whereby certain materials are attracted by an externally applied magnetic field, and form internal, induced magnetic fields in the direction of the applied magnetic field.
ferromagnetism the basic mechanism by which certain materials (such as iron) form permanent magnets, or are attracted to magnets
units for u (mu) magnetic moment; A(m^2) or J (T^-1)
CHNS beings by wrapping a sample in aluminum foil
CHNS sample is dropped into a chamber with 5% He (carrier gas) and 95% O2 (combustion) and the sample hits a heated filament
CHNS the sample is combusted and the volitle components are carried away by He
In CHNS we need to decrease oxygen to the point that it is out of the gas stream and we do this with high surface area copper catalyst
how to we get rid of the oxygen in CHNS high surface area copper catalyst; CuO forms on surface and you are left with He, CO2, H2O, N2, and SO2 which enter the GC
what components of CHNS enter the GC He, CO2, H2O, N2, and SO2
using standards in GC we can relate peak intensity to the concentration/mass of the sample
what are somethings that can go wrong in CHNS? not all of it combusts; metal carbides form
if carbides form in CHNS the GC readout will have a low levels of carbon because not all of it reacts
how do you counteract the formation of carbides in CHNS add WO3 and/or Ta2O5 catalysts which catalyze the combustion (make the reaction happen so fast that the metal carbides can't form)
what does CHNS detect? carbon, hydrogen, nitrogen, and sulfur
solid state chemistry deals with extended materials held together by ionic or covalent bonds
in extended materials where are the electrons shared over the whole material; not localized
extended materials have a higher boiling point and a lower volatility than molecules
solid-state chemistry is the study of well-ordered crystals, often flawless on near (mm) length scale; syntheses target new compositions with often complex structures and new physical properties
materials chemistry is the synthesis & study of extended solids (ex. highly disordered structures, low dimensional polymers, solids with nanoscale dimensions); often manipulate known solids to achieve new & useful physical or chemical properties
4 general characteristics of molecules and molecular solids discrete units (usually under 10 covalently bonded atoms), valence e-s localized bonds or MOs, synthesis often at low temperatures, may be soluble
3 general characteristics of solid-state structure large number of interconnected atoms or ions held together by covalent and/or ionic forces, bonding by valence e-s in orbitals that are dispersed in bands, synthesis at high temps
the ceramic method is also known as "heat and beat" or "shake and bake"; mix and heat to react; directly react the components at high temperatures
Thin film growth chemical vapor deposition (CVD); A(g) + B(g) = C(s)film + byproduct gases
solution nanoparticle growth (<100 nm particle sizes) particle growth (nucleation and precipitation) from eated solution of reactive precursors-AB compounds may require a subsequent high-temperature annealing (or use very hot solutions) step to complete reaction and form crystalline product
we need a reaction vessel that removes air/O2 from reaction how do we solve this load both reagents into a sealed, evacuated glass ampoule
remember PV= nRT calculation for gaseous reagents, intermediates, and byproducts
stable solid reagents (e.g. Ti Metal) require substantial external energy to react; so we need to heat the elements in a furnace and the thermal limits of the reactor need to be considered
ampoules for heating air-sensitive reactions are made from pyrex (use up to ~550 degrees C in a vacuum); silica (pure SiO2 up to ~1200 degrees C)
SiO2 will not crack upon rapid cooling (drop in water) but Pyrex will (thermally expansion coefficient is large)
what are the experimentally determined "best" reaction conditions for TI and S8 mix powders in a sealed evacuated Pyrex ampoule; heat at 400 degrees C, intermittently cool, remove partially reacted powder, grind it to expose reactive Ti surfaces, and reheat in an ampoule; heat in a silica vessel at high Ts for a week
problems with glass ampoules reagent attack on glass walls; ampoule explosions due to gas pressure release
how do you solve reagents sticking to the glass ampoules walls add a second protective liner to the sealed glass ampoule (dual containment)
how do you solve an ampoule explosion due to gas pressure release use a glass tube with flowing inert gas
resistively heated components (controlled current/voltage through metal wire) heating tape or mantles; lab tube or box furnaces; furnaces with special heating elements; resistive heating (inert conditions) of graphite or a metal foil
exotic heating methods induction heating; electric arc/discharge; high wattage halogen bulb or infrared bulb heaters
grinding helps maximize the surface area of compounds
two solids can "diffuse" into each other but they would take an incredibly long time to do this by themselves
NMR is a resonance technique involving absorption of what type of frequency energy radio frequency energy
the magnetic environment of a nucleus affects its resonance frequency and allows what type of information to be deduced (hint NMR) structural information
to be NMR active the nuclei must poses a nuclear spin (nuclear angular momentum) (I) that does not equal 0
In the absence of an applied magnetic field, the different nuclear spin states of a nucleus are degenerate
Are the nuclear spin states of a nucleus degenerate in the presence of an applied magnetic field? no
With nearly 100% abundance the 1H NMR spectrum is contributed by how many hydrogen atoms in the sample virtually every one
Which nuclei are suitable for NMR spectroscopic studies? ones with an I value that doesn't equal 0; helpful if it exists in high abundance; helpful if the T1 (relaxation time) is relatively short
possession of a quadrupole moment leads to short values of T1 but tend to cause the peak to broaden
a particular nucleus absorbs characteristic radiofrequencies (it resonances at the frequency). If an NMR spectrometer is tuned to a particular resonance frequency only a selected NMR active nucleus is observed
ex. only 1H nuclei are observed if a 400 MHz spectrometer is tuned to 400 MHz, but if the same spectrometer is returned to 162 MHz, only 31P nuclei are observed (just like tuning a radio and receiving one station at a time)
Nonequivalent nuclei of the same element resonate at different frequencies and therefore have different chemical shifts
although chemical shift does not technically have units it is recorded in ppm so as to show that the value was multiplied by 10^6; it was multiplied because the values were so small
different reference compounds can be used to place 0 ppm; one example is TMS; CD3Cl
the closer a ppm value is to 0, is the frequency higher or lower lower
deuterated solves are used so that the 1H NMR spectra are not swamped with unnecessary hydrogen signals
integration of a peak is proportional to the number of nuclei giving rise to the signal (ex. 1:3)
Coupling results from one hydrogen's magnetic field being associated with another hydrogen's magnetic field
coupling constant J is measured in Hz and describes the distance between two coupled peaks
proton-decoupled is represented as {1H}, what are decoupled experiments NMR experiments where certain nuclei are "hidden" on the radiofrequency
What is the Larmor frequency of a 31P in 3T magnetic field? (note in 100 MHz NMR 31P=40.5 MHz) 51.8 MHz
Created by: 530848841



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