Synthesis and Reaction of [HC(CMeNAr)2Mn]2
A R T I C L E S
filtration, the solution was concentrated to ca. 10 mL. Dark-red crystals
were obtained after 1 week at 4 °C. Yield: 0.07 g, 15%. Mp 154-156
°C. Anal. Calcd for C58H82Mn2N4 (945.16): C, 73.65; H, 8.68; N, 5.93.
Found: C, 73.62; H, 8.67; N, 5.74. EI-MS: m/z (%) 944 (5) [M]+,
472 (100) [1/2M]+. IR (KBr, Nujol mull, cm-1): ν˜ 1698 (w), 1654
(w), 1624 (w), 1577 (w), 1555 (w), 1261 (s), 1092 (s), 1019 (s), 937
(w), 866 (w), 799 (s), 762 (w), 722 (w), 667 (w), 614 (w), 568 (w).
curve. The best fitting parameters are J ) 109.8(2) and F )
0.031(4)% (F being the percentage of paramagnetic impurity
assumed to have a spin S ) S1). The Zeeman g factor and the
temperature-independent paramagnetism were kept constant at
g ) 2.00 and TIP ) 830 × 10-6 cm3 mol-1 27
. The agreement
factor R (R ) ∑i|øi° - øic|/∑iøi°) was 0.88%. The computed J
value is in good agreement with the experimental one, and with
the B3LYP results in better quantitative agreement as often
found in the literature. Equivalent fits of the magnetic data were
obtained for S1 ) S2 ) 3 (J ) 109.9(2), F ) 0.023(4)%, TIP )
830 × 10-6 cm3 mol-1, R ) 0.88%) and S1 ) S2 ) 2 (J )
109.7(2), F ) 0.045(4)%, TIP ) 830 × 10-6 cm3 mol-1, R )
0.95%).
[{HC(CMeNAr)2}Mn(µ-O)]2 (3). Route a: KMnO4 (0.5 g, 3.2
mmol) was added to a solution of 2 (0.2 g, 0.2 mmol) in toluene (20
mL) at room temperature. The mixture was stirred at room temperature
for 2 days. Unreacted KMnO4 was removed by filtration. The solvent
was removed in vacuum, and the residue was extracted with diethyl
ether. Red crystals were obtained after 4 days at 4 °C. Yield: 0.14 g,
72%. Mp 213-215 °C. Anal. Calcd for C58H82Mn2N4O2 (977.16): C,
71.23; H, 5.94; N, 5.73. Found: C, 70.92; H, 5.67; N, 5.54. EI-MS:
m/z (%) 976 (100) [M]+. IR (KBr, Nujol mull, cm-1): ν˜ 1659 (w),
1623 (w), 1592 (w), 1552 (w), 1528 (w), 1261 (s), 1094 (s), 1025 (s),
936 (w), 919 (w), 842 (w), 801 (s), 761 (w), 720 (w), 699 (w), 668
(w), 607 (w), 514 (w), 467 (w). Route b: Dry O2 was introduced into
a solution of 2 (0.2 g, 0.2 mmol) in toluene (20 mL) at -78 °C instead
of N2. The solution was kept at this temperature for 2 h and slowly
warmed to room temperature and stirred for 12 h. All volatiles were
removed in vacuum, and the residue was extracted with diethyl ether.
Red crystals were obtained after 7 days at 4 °C. Yield: 0.12 g, 63%.
Magnetic Measurement of 3. The magnetic data of 3 were
recorded in the temperature range of 4-300 K. The magnetic
behavior is indicative of an antiferromagnetic coupling between
the two manganese(III) centers, S1 ) S2 ) 2 in a pseudo-
tetrahedral chromophore, mediated by the two oxo-bridges. The
µeff (4.7 µB) at room temperature is much lower than the spin-
only value expected for two noninteracting S ) 2 spins (µeff
)
6.9 µB). The µeff steadily decreases to ∼0 µB at about 24 K
(Figure S1). This behavior is consistent with the geometry and
the type of bridging atoms. The temperature dependence of the
magnetic susceptibility was fitted as described in the Experi-
mental Section. The best fit values are J ) 91.5(5), g ) 1.99-
(2), and R ) 0.98%.
X-ray Crystallography. Crystallographic data of complexes 2 and
3 were collected on a Stoe IPDS II-array detector system with graphite-
monochromated Mo KR radiation (λ ) 0.71073 Å). The structures were
solved by direct methods (SHELXS-97) and refined against F2 using
SHELXL-97.28 All non-hydrogen atoms were located by difference
Fourier synthesis and refined anisotropically. The hydrogen atoms were
included at geometrically calculated positions and refined using a riding
model.
Conclusions
In summary, we have prepared [{HC(CMeNAr)2}Mn]2 (Ar
) 2,6-iPr2C6H3) (2), the first complex with three-coordinate
manganese(I), by the Na/K alloy reduction of [{HC(CMeNAr)2}-
Computational Details. All of the calculations were performed in
the framework of the density functional theory (DFT) with the
NWChem4.6.29 Single-point calculations of the experimental X-ray
structure were performed using the B3LYP functional.30 Calculations
with the Becke-Perdew (BP) functional31,32 were also done for
comparison. All electron double-ú basis set proposed by Ahlrichs was
applied to all of the atoms except for Mn, which was treated with the
Ahlrichs triple-ú basis set.33
2+
Mn(µ-I)]2 (1). Compound 2 has a Mn2 core with a Mn-Mn
bond. The reaction of 2 with KMnO4 or O2 affords a Mn2O2
core compound [{HC(CMeNAr)2}Mn(µ-O)]2 (3). The latter
oxidation with O2 of the two Mn(I) centers involves a homolytic
cleavage of the Mn-Mn bond, indicating the interesting
reactivity of 2 for further investigations.
Population analysis based on natural atomic orbitals (NAO) and
natural bond orbitals (NBO)23 was performed using the NBO 5.0
program34 implemented in NWChem.
Experimental Section
General Considerations. All reactions were performed using
standard Schlenk and drybox techniques. Solvents were appropriately
dried and distilled under dinitrogen prior to use. Elemental analyses
were performed by the Analytisches Labor des Instituts fu¨r Anorga-
nische Chemie der Universita¨t Go¨ttingen. Mass spectra were obtained
on a Finnigan Mat 8230. IR spectra were recorded on a Bio-Rad Digilab
FTS-7 spectrometer as Nujol mulls between KBr plates. Magnetic
measurements were performed by using a Cryogenic S600 SQUID
magnetometer operating with an applied field of 1 Torr. The sample
was prepared in a glovebox by grinding freshly filtered crystals. The
powder was wrapped in a Teflon tape placed in a special sample holder
and placed inside the SQUID without any contact with air. Magnetic
susceptibilities were corrected for diamagnetism by using Pascal’s
constants. [{HC(CMeNAr)2}Mn(µ-I)]2 (1) was synthesized as previ-
ously reported in the literature.9
Calculations of the exchange coupling constant were performed using
the broken symmetry formalism19 with the working equation, J ) 2/25
[E(HS) - E(BS)], where E(HS) and E(BS) are the SCF energies of
the high spin (S ) 5) and broken symmetry (MS ) 0) states,
respectively. The ø versus T curve was fitted using the standard
procedure35 by minimizing the squares’ sum of the differences between
computed and measured molar susceptibilities with the MINUIT
program package.36 The best fit values are reported in the text.
(28) (a) Sheldrick, G. M. Acta Crystallogr. A 1990, 46, 467-473. (b) Sheldrick,
G. M. SHELXL-97, Program for Crystal Structure Refinement; Universita¨t
Go¨ttingen: Go¨ttingen, Germany, 1997.
(29) High-performance computational chemistry group, NWChem: A Compu-
tational Chemistry Package for Parallel Computers, version 4.6, Pacific
Northwest National Laboratory: Richland, WA, 2004.
(30) Becke, A. D. J. Chem. Phys. 1990, 98, 5648-5652.
[{HC(CMeNAr)2}Mn]2 (2). At room temperature, a suspension of
1 (0.60 g, 0.5 mmol) in toluene (30 mL) was added to a Na/K alloy
(Na 0.01 g, 0.5 mmol; K 0.04 g, 1 mmol). The mixture was stirred at
room temperature for 4 days, and a red solution was obtained. After
(31) Becke, A. D. Phys. ReV. A 1988, 38, 3098-3100.
(32) Perdew, J. P. Phys. ReV. B 1986, 33, 8822-8824.
(33) Schafer, A.; Horn, H.; Ahlrichs, R. J. Chem. Phys. 1992, 97, 2571-2577.
(34) NBO 5.0. Glendening, E. D.; Badenhoop, J. K.; Reed, A. E.; Carpenter, J.
E.; Bohmann, J. A.; Morales, C. M.; Weinhold, F. Theoretical Chemistry
.wisc.edu/-nbo5.
(27) Due to the high variance-covariance between F and TIP (0.87), we
performed a series of calculations for various values of TIP between 600
× 10-6 and 900 × 10-6 cm3 mol-1. The value shown in the text gave the
better agreement.
(35) (a) Kahn, O. Molecular Magnetism; VCH Publishers: New York, 1993.
(b) O’Connor, C. J. Prog. Inorg. Chem. 1982, 29, 203-283.
(36) James, F. MINUIT, version 94.1; CERN Program Library; CERN Geneva,
Switzerland.
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