D.L. Reger et al. / Polyhedron 25 (2006) 2616–2622
2617
that for a given ligand coordination environment, the more
highly organized structure will have lower spin-state cross-
over temperatures and more abrupt crossovers than those
with less highly or more ‘‘loosely’’ organized structures.
In contrast, we have shown that differences in the molecu-
lar, rather than supramolecular, structure of the two
crystallographically independent molecules in Fe[(p-HC„
CC H )B(3-Mepz) ] can have an impact on the tempera-
single symmetric quadrupole doublet and the estimated rel-
ative errors of the fitting parameters are ± 0.005 mm/s for
the isomer shifts and ± 0.01 mm/s for the quadrupole split-
tings and line widths. The absolute errors are approxi-
mately twice as large.
2.2. Na[(C H )B(3-Mepz) ] (1)
6
5
3
6
4
3 2
ture and abruptness of the observed spin-state crossover.
Herein we report the synthesis, solid-state structure,
and magnetic and M o¨ ssbauer spectral properties of
Fe[(C H )B(3-Mepz) ] , the parent complex of the Fe-
In the drybox, neat BBr (3.76 g, 15.0 mmol. Caution.
3
The vapors of neat boron tribromide are very corrosive
toward stopcock grease and plastics) was added by pipette
to neat phenyltrimethylsilane (2.04 g, 13.6 mmol) con-
tained in a PTFE-stopcock Schlenk flask and was capped
with a PTFE-taped glass stopper. The stopper of the
Schlenk flask was reinforced with rubber bands, taken
out of the dry box, and placed in a 60 ꢁC oil bath, with
the stopcock closed, for 4.5 h (Caution. Adequate shielding
must be used at this point because a closed system is being
heated; the rubber bands, in conjunction with the glass
stopper, act as a check valve for pressure build-up). After
the reaction was complete, the volatile components were
removed by vacuum distillation at room temperature to
yield 3.16 g (94%) of crude C H BBr as an off-white solid.
6
5
3 2
[
(p-R-C H )B(3-Mepz) ] complexes referred to above.
6 4 3 2
Analyses of these results provide interesting new insight
into the factors that control the spin-crossover behavior
of this class of compounds.
2
. Experimental
2
.1. General considerations
Unless otherwise specified, all operations were carried
out under a nitrogen atmosphere by using either stan-
dard Schlenk techniques or a Vacuum Atmospheres
HE-493 inert atmosphere dry box. Solvents for synthetic
procedures and spectroscopic studies were dried by con-
6
5
2
The glass stopper was replaced with a rubber septum, and
the C H BBr (3.16 g, 12.8 mmol) was dissolved, in situ, in
6
5
2
50 mL toluene. The C H BBr solution was added via can-
6
5
2
ventional methods and distilled under a N atmosphere
nula to a solution of 3-methylpyrazole (3.14 g, 38.3 mmol)
2
immediately prior to use. All chemicals were purchased
from Aldrich Chemicals. 3-Methylpyrazole was distilled
under vacuum before use. Robertson Microlit Laborato-
ries performed all elemental analyses. Melting point
determinations were made on samples contained in glass
capillaries using an Electrothermal 9100 apparatus and
are uncorrected. Mass spectrometric measurements
recorded in ESI(± ) mode were obtained on a Micromass
Q-Tof spectrometer. NMR spectra were recorded by
using a Varian Gemini 300. Chemical shifts were refer-
and NEt (3.55 mL, 25.6 mmol) in toluene (150 mL). After
3
the resulting cloudy suspension was stirred at room tem-
perature overnight, the toluene solution [presumably con-
taining (C H )B(3-Mepz) (3-MepzH)] was transferred to
6
5
2
a 500 mL Schlenk flask by cannula filtration thereby
removing the colorless precipitate of (HNEt )Br (4.38 g,
3
t
94%). A solution of NaO Bu (1.23 g, 12.8 mmol) in 1:1 tol-
uene/THF (50 mL) was added by cannula to the solution
of ‘‘(C H )B(3-Mepz) (3-MepzH)’’ and the resulting sus-
6
5
2
pension was stirred for 12 h. The colorless solid was sepa-
rated by filtration, washed with hexanes (2 · 100 mL) and
was dried under vacuum to leave 4.00 g (85%, from phenyl-
trimethylsilane) of Na[(C H )B(3-Mepz) ] as a white solid.
enced to solvent resonances at dH 7.26 for CDCl , and
3
dH 3.31 for CD OD.
3
Magnetic susceptibilities were measured between 4 and
6
5
3
1
3
00 K in an applied field of 0.5 T using a Quantum Design
Mp, 282 ꢁC sinters; 300 ꢁC dec. black liquid. H NMR
(300 MHz, CD OD, 25 ꢁC): d = 7.25 (m, 2H, meta-H),
MPMS XL SQUID magnetometer. The sample was mea-
sured in a gelatin capsule whose very small diamagnetic
susceptibility made a negligible contribution to the overall
observed susceptibility. The molar magnetic susceptibility
of Fe[(C H )B(3-Mepz) ] was calculated with a molecular
3
7.11 (m, 3H, ortho-H and para-H), 7.05 (d, J = 1.5 Hz,
3H, H -pz), 5.86 (d, J = 1.5 Hz, 3H, H -pz), 2.23 (s, 9H,
5
4
1
3
CH3);
C
NMR (125.79 MHz, CD OD, 25 ꢁC):
3
d = 149.23, 136.78, 135.14, 134.14, 127.28, 125.74 (C3-
6
5
3 2
mass of 718.26 g/mol and was corrected by
and C -pz, aryl) 103.67 (C -pz), 13.44 (–CH ) High Res.
5
4
3
ꢂ6
ꢂ364.5 · 10 emu/mol for the diamagnetism of the com-
ESI(ꢂ)MS, Calc. (Obs.) for anion: 331.1843 (331.1844).
2.3. Fe[(C H )B(3-Mepz) ] (2)
plex, a value which was obtained from tables of Pascal’s
constants.
6
5
3 2
2
The M o¨ ssbauer spectral absorber contained 42 mg/cm
of crushed but unground crystals of Fe[(C H )-
Under inert atmosphere, the addition of an aqueous
6
5
B(3-Mepz) ] mixed with boron nitride. The spectra were
solution (50 mL) of FeCl Æ 4H O (0.153 g, 0.77 mmol) to
3
2
2
2
measured at 4.2, 78, and 295 K on a constant-acceleration
spectrometer which utilized a room temperature rhodium
matrix cobalt-57 source and was calibrated at room tem-
perature with a-iron foil. The spectra have been fit with a
a methanol solution (20 mL) of 1 (0.546 g, 1.54 mmol)
yielded a copious amount of colorless solid that was iso-
lated by filtration. The solid was then taken up in CH Cl ,
2
2
the solution was dried over MgSO , filtered, and the
4