Transcript List of users: JK, years 2008/2009 1. 2. 3. 4. 5. 6. 7. 8. 9. 10. 11. 12. 13. 14. 15. 16. 17. 18. 19. 20. 21. 22. Juan Bartolome, Institute of Material Science of Aragon, University of Zaragoza, Span; Terry Collins, Dept.

List of users: JK, years 2008/2009
1.
2.
3.
4.
5.
6.
7.
8.
9.
10.
11.
12.
13.
14.
15.
16.
17.
18.
19.
20.
21.
22.
Juan Bartolome, Institute of Material Science of Aragon, University of Zaragoza, Span;
Terry Collins, Dept. of Chemistry, Carnegie Mellon University;
Betty Gaffney, Dept. of Biology, Florida State University;
Radovan Herchel, Palacky U., Olomouc, Czech Republic;
Hua-Fen Hsu, Dept. of Chemistry, National Cheng Kung University, Tainan, Taiwan;
Alvin Holder, University of Southern Mississippi;
Jos de Jongh, Institute of Physics, Leiden University, The Netherlands;
Miguel Julve, Institute of Molecular Science, University of Valencia, Spain;
Martin Kirk, Dept. of Chemistry, New Mexico State University;
Masaaki Kojima, Dept. of Chemistry, Okayama University, Japan;
Panayotis Kyritsis, Dept. of Chemistry, National and Kapodistrian University of Athens, Greece;
Susan Latturner, Dept. of Chemistry, Florida State University;
Craig McLachlan, Dept. of Chemistry, Southern Illinois State University,
Dan Mindiola, Dept. of Chemistry, Indiana University;
Ademir Neves, Dept. of Chemistry, Federal University of Santa Catalina, Florianopolis, Brasil;
Hanka Przybylinska, Institute of Physics, Polish Academy of Sciences, Warsaw, Poland;
Jan Reedijk, Institute of Chemistry, Leiden University, The Netherlands;
Jeremy Smith, Dept. of Chemistry, New Mexico State University;
Al Stiegman, Dept. of Chemistry, Florida State University;
Joshua Telser, Dept. of Biological, Chemical and Physical Sciences, Roosevelt University, Chicago;
Ming-Liang Tong, Dept. of Chemistry, Sun-Yat Sen University, Guangzhou, China;
Sergei Zvyagin, Dresden High Magnetic Field Laboratory, Germany;
List of publications: AO/JK, year 2008
1.
3.
4.
5.
Aromí, G.; Bouwman, E.; Burzurí, E.; Carbonera, C.; Krzystek, J.; Luis, F.; Schlegel, C.; van Slageren, J.; Tanase,
S.; Teat, S. J., Chem. Eur. J., 2008, 14, 11158-11166.
Cizmar, E; Ozerov, M; Ignatchik, O.; Papageorgiou, T. P.; Wosnitza, J.; Zvyagin, S. A.; Krzystek, J.; Zhou, Z.;
Landee, C. P.; Landry, B. R.; Turnbull, M. M.; Wikaira, J. L., New J. Phys., 2008, 10, 033008.
Dinse, A.; Ozarowski, A.; Hess,C.; Schomäcker, R. and Dinse, K.P., J. Phys. Chem. C, 112, 17664–1767
Drabent, K.; Ciunik, Z. and Ozarowski, A. Inorg. Chem., 2008, 47, 3358-3365.
Erdem, E.; Drahus, M.; Eichel, R. A.; Ozarowski, A.; van Tol, J. and Brunel, L. C., Ferroelectrics, 2008, 363, 39-49.
6.
Erdem, E.; Eichel, R. A.; Kungl, H.; Hoffmann, M. J.; Ozarowski, A.; van Tol, J.; Brunel, L. C., IEEE Trans.
2.
Ultrasonics Ferroelectrics and Frequency Control, 2008, 55, 1061-1068.
7.
8.
9.
10.
11.
12.
13.
14.
Karadas, F.; Schelter, E. J.; Shatruk, M.; Prosvirin, A. V.; Bacsa, J.; Smirnov, D.; Ozarowski, A.; Krzystek, J.; Telser,
J.; Dunbar, K. R., Inorg. Chem., 2008, 47, 2074-2082.
Krzystek, J.; England, J.; Ray, K.; Ozarowski, A.; Smirnov, D.; Que Jr., L.; Telser, J., Inorg. Chem., 2008, 47, 38433845.
Makhankova, V. G.; Beznischenko, A.O.; Kokozay, V. N.; Zubatyuk, R. I.; Shishkin, O. V.; Jezierska, J. and
Ozarowski, A., Inorg. Chem., 2008, 47, 4554-4563
Nesterova, O.V.; Petrusenko, S. R.; Kokozay, V .N.; Skelton, B.W.; Jezierska, J.; Linert, W. and Ozarowski,
A., Dalton Transactions, 2008, 1431-1436.
Ozarowski, A., Inorg. Chem., 2008, 47, 9760-9762.
Pregelj, M.; Arcon, D.; Zorko, A.; Zaharko, O.; Brunel, L.-C.; van Tol, H.; Ozarowski, A.; Nellutla,S. and Berger,
H., Physica B, 2008, 403, 950.
Szyczewski, A.; Lis, S.; Krzystek, J.; Staninski, K.; Klonkowski, A.; Kruczynski, Z.; Pietraszkiewicz, M. J. Alloys
Compd., 2008, 451, 182-185.
Zvyagin, S. A.; Batista, C. D.; Krzystek, J.; Zapf, V. S.; Jaime, M.; Paduan-Filho, A.; Wosnitza, J., Physica B, 2008,
403, 1497-1499.
List of publications: AO/JK, year 2009
1.
2.
3.
4.
5.
6.
7.
8.
9.
10.
11.
12.
Dinse,K.-P.; van Tol, J.; Ozarowski, A.; Corzilius, B., App. Magn. Reson., accepted.
Martinez-Lillo, J.; Armentano, D.; De Munno, G.; Wernsdorfer, W.; Clemente-Juan, J.; Krzystek, J.; Lloret, F.;
Julve, M.; Faus, J., Inorg. Chem. 2009, 48, 3027-3038.
Moomaw, E. W.; Angerhofer, A.; Moussatche, P.; Ozarowski, A.; Garcia-Rubio, I. and Richards, N. G.
J., Biochemistry, 2009, 48, 6116-6125.
Nesterova, O.V.; Petrusenko, S.R.; Nesterov, D.S.; Kokozay, V.N.; Skelton, B.W.; Jezierska, J.; Linert, W.;
Ozarowski, A., New Journal of Chemistry, submitted.
Nieto, I.; Bontchev, R. P.; Ozarowski , A.; Smirnov, D.; Krzystek , J.; Telser , J.; Smith, J. M., Inorg. Chim. Acta,
2009, 362, 4449–4460.
Ozarowski, A.; Szymanska, I. B.; Muziol, T. and Jezierska, J., J. Am. Chem. Soc., 2009, 131, 10279-10292
Stoll, S.; Gunn, A.; Brynda, M. ; Sughrue, W.; Kohler, A. C.; Ozarowski, A.; Fisher, A. J.; Lagarias, J. C. and Britt,
R. D., J. Am. Chem. Soc., 2009, 131, 1986-1995
Telser, J.; Wu, C.-C.; Chen., K.-Y.; Hsu, H.-F.; Smirnov, D.; Ozarowski, A.; Krzystek, J., J. Inorg. Biochem., 2009,
103, 487-495.
Witwicki, M.; Jezierska, J. and Ozarowski, A., Chem. Phys. Letters, 2009, 473, 160-166.
Witwicki, M.; Jerzykiewicz, M.; Jaszewski, A.; Jezierska, J.; Ozarowski, A., J. Phys. Chem. submitted.
Xavier, F.; Neves, A.; Casellato, A.; Peralta, R.; Bortoluzzi, A.; Szpoganicz, B.; Cardoso Severino, P.; Terenzi, H.;
Tomkowicz, Z.; Ostrovsky, S.; Haase, W.; Ozarowski, A.; Krzystek, J.; Telser, J.; Schenk, G., Inorg. Chem., 2009,
48, 7905–7921.
Ye, S.; Neese, F.; Ozarowski, A.; Smirnov , D.; Krzystek, J.; Telser, J.; Liao, J.-H.; Hung, C.-H.; Chu, W.-C.; Tsai,
Y.-F; Wang, R.-C.; Chen, K.-Y.; Hsu, H.-F., Inorg. Chem., under review.
JK’s Highlight #1:
Synthesis and spectroscopic investigations of four-coordinate nickel
complexes supported by a strongly donating scorpionate ligand.
(Collaboration with Jeremy Smith, New Mexico State U.)
H
B
N
N
N N
t
t
Bu
N
Ni
Br
Bu
t
Bu
A molecular structure (left) and an ORTEP diagram (right) of
HB(tBuIm)3NiBr (“N-confused scorpionate”)
Motivation
• Fragment of a larger synthetic work concentrated on the
tris(carbene)borates;
• Measurement of the donor properties (strength) via various
spectroscopic techniques; in this case HFEPR;
• Understanding the correlation of electronic and magnetic properties
of HS Ni(II) complexes (still in process).
Field-frequency dependence of EPR spectra of HB(tBuIm)3NiBr
-1
Energy (cm )
0
694
2
4
6
8
10
12
14
16
18
20
22
24
25
660
634
614
593
572
20
Magnetic Field (T)
522
499
479
457
432
406
379
352
15
10
5
321
300
277
253
0
228
199
0
100
200
300
400
500
600
700
Frequency (GHz)
154
123
0
5
10
15
20
Magnetic Field (T)
A multifrequency set of HFEPR spectra of microcrystalline 3
recorded at 4.2 K using optical modulation (i.e., in absorptive
mode). The frequencies (in GHz) are given adjacent to each
spectrum.
25
2D (field vs. frequency or energy) map of turning
points recognized in the HFEPR spectra of 3 shown
in Figure 3. Squares are experimental resonances
while curves were generated using best-fitted spin
Hamiltonian parameters: S = 1, |D| = 2.49 cm–1, |E| =
0.54 cm–1, gx = 2.22, gy,z = 2.21. Red curves
correspond to turning points with B0 || x, blue curves
– with B0 || y, and black curves – with B0 || z.
Single-frequency data and the sign of D:
T = 30 K:
HFEPR spectra recorded using magnetic
modulation (i.e., in derivative mode) at 222.4
GHz at 5 K (lower black trace) and 30 K (upper
black trace) accompanied by powder-pattern
simulations using the following spin
Hamiltonian parameters: S = 1, |D| = 2.52, |E| =
0.63 cm–1, giso = 2.22. Red traces were
calculated using positive values of the zfs
parameters, while blue traces – using negative
values. The sharp peak at g ~ 2.2 (~7.2 T) in
the experimental spectra is the so-called
“double-quantum transition”, which is not
simulated.
T = 5 K:
2
3
4
5
6
7
8
Magnetic Field (T)
9
10
11
Unexpected result: hyperfine structure
 = 112 GHz
 = 202 GHz
 = 305 GHz
 = 432 GHz
 = 624 GHz
-1.0
-0.5
0.0
0.5
1.0
Relative Magnetic Field (T)
The hyperfine structure superimposed on the Bmin turning point in the
EPR spectra of 3 recorded using magnetic modulation at 30 K and
various frequencies, as indicated. Zero on the magnetic field scale
corresponds to 1.004 T at 112 GHz, 3.315 T at 202 GHz, 4.730 T at 305
GHz, 6.870 T at 432 GHz, and 10.012 T at 624 GHz.
Experimental HFEPR spectrum of 3 recorded using magnetic
modulation at 30 K and at 432 GHz (black trace) along with a
simulation (red trace), generated as the sum of three individual
spectra with slightly varying giso values: 2.230, 2.215, 2.200. Each
simulation otherwise uses the following identical parameter set: S =
1, D = +2.49 cm-1, E = +0.54 cm-1; isotropic Gaussian linewidth
(hwhh), 1.2 GHz; Aiso(81Br) = 1.50 GHz (Aiso(79Br) = 1.39 GHz),
P||(81Br) = (3/2)Pz = 33 MHz (P||(79Br) = 40 MHz). Simulations were
calculated for each Br isotope and then summed in the abundance
ratio.
Results/Discussion
• The HB(tBuIm) ligand is a stronger σ-donor than the “regular”
scorpionate;
• The same ligand has also π-donating properties;
• LFT calculations semi-quantitatively successful in correlating
electronic and magnetic properties;
• LFT problematic in determining the sign of D;
• This is probably due to spin delocalization to a heavy atom (Br) as
proved by the observed hyperfine structure due to Br isotopes.
Published in:
Nieto, I.; Bontchev, R. P.; Ozarowski , A.; Smirnov, D.; Krzystek , J.; Telser , J.; Smith, J. M.,
Inorg. Chim. Acta, 2009, 362, 4449–4460.
JK’s Highlight #2:
Aminocarboxylate Complexes of Vanadium(III): Electronic Structure
Investigation by HFEPR Spectroscopy
(Collaboration with Hua-Fen Hsu, National Cheng Kung U. Taiwan)
[V(trdta)]-
O
O
N
N
O V O
O
O
[V(edta)(H2O)]-
O O
O
O
N
N
O V O
O
O
OH2
[V(nta)(H2O)3]
O
O O
O
O
N
O
O
H2O
V
H2O
O
OH2
Complexes investigated in this study (as powders and aqueous solutions)
Motivation
• Aminocarboxylate complexes of vanadium(III) are of interest as
models for biologically and medicinally relevant forms of this
interesting and somewhat neglected ion;
• Obtaining EPR spectra from this ‘EPR-silent’ ion, particularly in
aqueous solutions;
• Characterize magnetic properties via spin Hamiltonian formalism;
• Characterize electronic structural properties combining electronic
spectra and magnetic response using LFT;
Typical FFD in solid form (Na[V(trdta)]·3H2O)
-1
Energy (cm )
0
2
4
6
8
10
12
14
16
18
20
22
24
24
Magnetic Field (T)
20
16
12
8
4
0
0
100
200
300
400
Frequency (GHz)
500
600
700
Field vs. frequency map of EPR
resonances recorded at 5 K for solid
Na[V(trdta)]·3H2O. Red squares
represent experimental resonances
attributed to the dominant triplet state
of somewhat larger zfs parameters
than that represented by the blue
circles. Red curves were simulated
using S = 1, |D| = 5.60 cm–1, |E| = 0.85
cm–1, giso = 1.95, and blue curves
using S = 1, |D| = 5.15 cm–1, |E| = 0.23
cm–1, giso = 1.95, with dotted lines
represent turning points with B0 || x,
dashed lines with B0 || y and solid lines
with B0 || z. Black crosses at low
frequencies/fields represent
resonances that could not be attributed
to either triplet state; their appearance
suggests a presence of yet another
species characterized by a smaller zfs.
Green triangles are resonances
originating from a V(IV) impurity as
proved by the green line, which is a
simulation using S = 1/2 and giso =
1.95.
Single-frequency spectra of aqueous [V(trdta)]-
HFEPR spectrum of aqueous [V(trdta)]recorded at 305 GHz and 20 K (solid trace)
together with a simulation (dashed trace)
assuming an ideal powder pattern, which is
the sum of equal amounts of three individual
triplet species. Spin Hamiltonian parameters
used in the simulations: all S = 1; one species
with: D = +0.68 cm–1, E = 0, gx,y = 1.98, gz =
1.95, 50 mT isotropic single-crystal linewidth;
one species with D = +0.87 cm–1, E = 0, gx,y
= 1.98, gz = 1.95, 50 mT linewidth; one
species with: D = +2.35 cm–1, E = 0, giso =
1.95, 200 mT linewidth.
0
2
4
6
8
Magnetic Field (T)
10
12
14
Aqueous HFEPR spectrum of [V(edta)(H2O)]-
D<0
Expt.
D>0
2
3
4
5
6
7
8
Magnetic Field (T)
9
10
11
HFEPR spectrum of aqueous
[V(edta)(H2O)]- recorded at 218 GHz
and 20 K. Central (solid) trace:
experiment; upper dashed trace:
simulation using parameters: S = 1, D
= -2.01 cm–1; E = 0, giso = 1.95; lower
dashed trace: simulation using the
same value but a positive sign of D.
Isotropic single-crystal linewidth used in
the simulations for the ΔMS = 1
transitions: 200 mT; for the ΔMS = 2
transition: 50 mT. The intensities of the
simulated spectra are scaled so as to
match exactly the experimental turning
point at 6.8 T, demonstrating that the
intensities of the features at 5.9, 9 and
10 T are matched by the simulation
only for D > 0. The peak near 8 T
originates from a trace amount of V(IV)
Comparison of HFEPR and X-band
Main figure: [V(edta)(H2O)]- in aqueous solution
shows spectra even at X-band (at 9.7 GHz and 20
K; upper, solid trace is experiment; lower, dashed
trace is simulation using the spin Hamiltonian
parameters obtained from HFEPR experiments,
with the single-crystal linewidth of 100 mT for the
perpendicular turning point, and 25 mT for the
parallel one; these linewidths are of the same
order of magnitude as those required at high
frequencies). The group of resonances centered
on 350 mT belongs to the well-known hyperfine
pattern of the VO2+ ion. The single narrow line at
ca. 180 mT, indicated by the asterisk, originates
from the dielectric resonator used in this
experiment. Inset: the origin of the 218 GHz, and
9.7 GHz resonances in the 2D field/frequency
representation such as in Figure 1 (solid lines are
with the field parallel; dashed lines with the field
perpendicular to the molecular axes). The field
range of the HFEPR experiment (see Figure 3) is
represented by the vertical dotted line, while the
circle indicates the X-band EPR conditions used
here.
Results/discussion
•
First ever successful EPR detection of V(III) in aqueous solution;
•
In combination with very insightful previous studies of the electronic
absorption which provided ligand-field parameters, it has been possible to
describe the electronic structure of V(III) in [V(trdta)]- and [V(edta)(H2O)]- ;
•
Qualitative conclusions as to the relationship between coordination and
optical and magnetic properties: 6-coordinate V(III) complexes with O,N
donor atoms show no electronic absorption band in the NIR region, and
exhibit relatively large magnitude zfs (D  5 cm-1), while analogous 7coordinate complexes do have a NIR absorption band and show relatively
small magnitude zfs (D < 2 cm-1).
Published in:
Telser, J.; Wu, C.-C.; Chen., K.-Y.; Hsu, H.-F.; Smirnov, D.; Ozarowski, A.; Krzystek, J., J.
Inorg. Biochem., 2009, 103, 487-495.
AO’s Highlight #1:
Structure of the biliverdin radical intermediate in PcyA
identified by high-field EPR
(Collaboration with David Britt, UC Davis)
Motivation:
The cyanobacteria employ the pigment phycocyanobilin (PCB) in
light-energy conversion (photosynthesis). PCB is produced by the
enzyme phycocyanobilin : ferredoxin oxidoreductase (PcyA) from
biliverdin (BV). The mechanism of PcyA's catalysis is poorly
understood. With HFEPR, the nature of the radical intermediate can
be determined, thus helping to elucidate the reaction mechanism.
Reaction mechanism
endo
exo
biliverdin IXα
(BV)
radical
intermediate
radical
intermediate
2H+, 2e-
2H+, 2e-
181,182-dihydrobiliverdin
(DHBV)
3Z/3E-phycocyanobilin
(PCB)
EPR spectra (406 GHz)
Radical intermediates of various mutants of
the enzyme were obtained by freezequenching, and EPR spectra at 406.4 GHz
were measured and the g tensors were
obtained. The g tensor of a radical,
characterized by three values gx, gy, and
gz, is a sensitive probe for the protonation
state of the radical. It can be predicted
theoretically by density functional theory
(DFT) calculations based on the X-ray
crystal structure of the enzyme-substrate
complex. There are six possible
protonation sites in biliverdin. The g tensors
of all 42 possible protonation states were
computed.
Conclusions
• Comparison with the experimental g
tensor reveals that the biliverdin
radical is in a bis-lactim form,
protonated at the two carbonyl
oxygens.
• The resolution power of EPR has
been spectacularly demonstrated.
Published in:
Stoll, S.; Gunn, A.; Brynda, M. ; Sughrue, W.; Kohler, A. C.; Ozarowski, A.; Fisher,
A. J.; Lagarias, J. C. and Britt, R. D., J. Am. Chem. Soc., 2009, 131, 1986-1995
AO’s Highlight #2
HFEPR and Magnetic Studies on (novel) Tetrameric and Dimeric
Quinoline Adducts of Copper Trifluoroacetate (some induced by
Florida air)
An unusually rich source of polynuclear complexes was discovered while investigating the
quinoline adducts of copper(II) trifluoroacetate. Two previously unknown green benzene and
toluene solvates containing a μ4-oxo core, Cu4O(CF3COO)6(quin)4 , were synthesized and found
to be ferromagnetic with a ground state S=2. When exposed to Florida air,* they convert
irreversibly to a blue complex of unknown structure which is antiferromagnetic and exhibits
triplet state EPR spectra. Magnetic susceptibility measurements revealed that the blue complex
was also tetrameric. Moreover, exposure of a previously known dimeric complex
Cu2(CF3COO)4(quin)2 to humid air resulted in a reversible formation of yet another tetrameric
system, {[Cu2(OH)(CF3COO)4(quin)]-(quinH+)}2 in which two quinoline molecules are coordinated
to copper, while another two are protonated and play a role of cations.
Published in:
Ozarowski, A.; Szymanska, I. B.; Muziol, T. and Jezierska, J., J. Am. Chem. Soc., 2009, 131, 10279-10292
Results
2.5
3
2.0
m eff per 1 Cu, B.M.
2a
1.5
2
2
2a
3
1.0
0.5
Temperature, K
0.0
0
•
100
200
300
Structures and magnetic properties:
2: Green dimer Cu2(CF3COO)4(quin)2
2a: Blue Tetramer {[Cu2(OH)(CF3COO)4(quin)]-(quinH+)}2
3: Green Tetramer Cu4O(CF3COO)6(quin)4
Z
The green benzene and toluene solvates containing a m 4-oxo core,
MS= 3
Cu4O(CF3COO)6(quin)4 are ferromagnetic with a ground state S=2. The EPR
spectra were analyzed in terms of the spin Hamiltonian
Z
Z
MS= 2
MS= 4
*
Z
H = mBB·g·S + D{Sz2-S(S+1)/3} + E(Sx2- Sy2) + B40O40 + B42O42 + B44O44
Z
A blue species formed from the green tetramers exhibits triplet state (S=1)
EPR spectra.
Y
gx
gx
gx
D, cm-1 E, cm-1
B40,
cm-1
2
B42,
cm-1
B44,
cm-1
*
20 K, 333.6 GHz
2.168
2.173 2.066 -0.827 -0.114 0.000 -0.0114 0.0012
Green benzene
solvate, S=2
2.169
2.175 2.067 -0.875 -0.049 0.000 -0.009 -0.006
X
2.263 2.112 -1.636 -0.0187
-
-
-
A Hamiltonian
H=J1(S1S2+S3S4) + J2(S1S3+S1S4+S2S3+S2S4)
was used to describe the magnetic properties of the green and
blue tetramers. EPR parameters had to be taken into account to
reproduce magnetic susceptibility of the ferromagnetic tetramers
at the lowest temperatures.
J1 = -100 cm-1, J2 = -39 cm-1 were found for the green
tetramers, while J1 = J2= +88 cm-1 was determined for the blue
tetramer. The EPR spectrum observed for the latter species
comes from an excited S=1 state.
Red solid lines in the figure to the right were simulated with
these parameters.
12
14
*
Z
6
7
8
9
10
11
Magnetic Induction, T
12
13
EPR spectra of the green tetramers (top, 324 GHz, 10K) and
of the blue tetramer (bottom)
5
Magnetic Moment, m
2.049
Z
X
5
Blue tetramer, S=1
Z
Y
Z
Green toluene
solvate, S=2
The copper coordination and
the system of bridges in the
green tetramers
4
6
8
10
Magnetic Induction, Tesla
Z
4
3
2
1
0
0
50
100
150
200
Temperature, K
250
Magnetic moments of the green and blue tetramers
The blue complex [Cu4(OH)2(CF3COO)8(quin)2]2-(quinH+)2 (right)
formed on Florida air from the previously known solid dimeric
[Cu(CF3COO)2∙(quin)]2 (left), is antiferromagnetic and shows no
EPR spectrum at any frequency and temperature.
‘Broken symmetry’ DFT calculations were performed to estimate the
exchange integrals in all three tetranuclear complexes of known
structure, showing surprisingly good agreement with experimental
2000
10 , cgs units
results.
1000
6
Green Dimer Cu2(CF3COO)4(quin)2
80 K, 406.4 GHz
1500
500
Simulated with:
gx=gy = 2.084, gz= 2.412
D = - 0.433 cm-1, E = 0
11.5
12.0
12.5
0
0
13.0
13.5
50
100
150
200
Temperature, K
250
Blue circles: magnetic susceptibility of
14.0
Green Dimer
[Cu4(OH)2(CF3COO)8(quin)2]2-(quinH+)2 The
red line was calculated with J1=0, J2=81cm-1,
g=2.17. Green circles are the literature data for
the green dimer [Cu(CF3COO)2∙(quin)]2. The
solid line was calculated for a dimer with J=310
cm-1 and g=2.27 (literature data).
Blue Tetramer
Development of a New Mössbauer Facility at the NHMFL
Mossbauer Spectra of a 'Spin-Crossover' Iron(II) Complex
100
14.4 keV Gamma Transmission %
A Mössbauer instrument equipped with a 57Co source, suitable for
57Fe-containing samples was installed several months ago and the
low-temperature extension has been added recently.
Some practical experiments have already been performed (A.
Ozarowski’s UCGP grant).
98
96
290 K, paramagnetic
130 K, paramagnetic
4.2 K, diamagnetic
4.2 K LIESST
94
92
-1.0
-0.5
0.0
0.5
1.0
1.5
2.0
2.5
3.0
Source velocity, mm / s
The nuclear processes
occurring in a Mössbauer
source. The Mössbauer effect
relies on the 14.4 keV gamma
radiation (red arrow)
Some iron(II) complexes of ligands of intermediate
strength are paramagnetic at the room temperature
(S=2) but undergo an abrupt ‘spin crossover’
transition when the temperature is lowered (105 K in
this particular case). The resulting diamagnetic state
(S=0) is stable down to the lowest temperatures.
However, when a diamagnetic sample kept at 4.2 K
was irradiated with green light, a so-called LightInduced Excited Spin State Trapping process
(LIESST) occurred and the sample was converted to
the paramagnetic state (S=2), which is then stable
for unlimited time below 50K. In this way, the
Mössbauer spectra of both the diamagnetic state
(red line) and paramagnetic state (green line) were
recorded at 4.2 K. The sample was provided by an
external user (Dr. K. Drabent, Wroclaw University).
Development of an FDMR spectrometer at NHMFL
(Frequency Domain Magnetic Resonance)
FDRMS: an alternative way of doing EPR: sweeping frequency instead
of field.
(A) [Fe(H2O)6](ClO4)2 (B) (NH4)2[Fe(H2O)6](SO4)2,
0
100
Frequency (GHz)
200
300
400
500
Frequency (GHz)
600
0
700
100
200
300
400
500
600
700
24
20
A
A
12
8
4
0
2
4
6
8
10
12
14
16
18
20
22
20
B
16
Transmission (a.u.)
Magnetic Field (T)
16
2
4
6
8 10 12 14 16 18 20 22
12
8
B
4
0
2
4
6
8
10
12
14
16
-1
Energy (cm )
Field domain
18
20
22
2
4
6
8 10 12 14 16 18 20 22
-1
Energy (cm )
Frequency domain
Experimental FDMRS setup
Exp. setup in Stuttgart, Germany (Dressel)
The BWO range (needs updating)
Practical need for FDMRS:
0
2
4
6
8
10
12
Magnetic Field (T)
Powder 224 GHz spectrum of Ni(II)(tacn)2(ClO4)2 at T = 10 K.
Practical need for FDMRS:
|D| or |D+E| ?
0
1
2
3
4
5
6
7
8
Magnetic Field (T)
Powder 98 GHz spectrum of Ni(II)(tacn)2(ClO4)2 at T = 10 K.
Practical need for FDMRS:
Spin Hamiltonian para.
S = 1;
|D| = 3.2; |E| = 0.32 T;
giso = 2.15.
0
2
4
6
8
10
12
14
Magnetic Field (T)
Powder 224 GHz spectrum + simulation of Ni(II)(tacn)2(ClO4)2 at T = 10 K.