Interpenetrated 3D polymeric metal-radical networks built from a tetranitroxide radical and bis(hexafluoroacethylacetonato) manganese(II) [22]

Full text of DOI:10.1021/ja016133h

J. Am. Chem. Soc. 2001, 123, 7465-7466
7465
We report herein the crystal structure and magnetic properties
of {[Mn(hfac)2]2(tetranitroxide)}n (hfac ) hexafluoroacetylac-
etonate) obtained by slow interdiffusion of a heptane solution
containing dehydrated MnII(hfac)2 in a dichloromethane solution
of the tetranitroxide18
Interpenetrated 3D Polymeric Metal-Radical
Networks Built from a Tetranitroxide Radical and
Bis(hexafluoroacethylacetonato) Manganese(II)
Fabrice Mathevet and Dominique Luneau*
{Mn(hfac)2]2(Tetranitroxide)}n crystallizes in the tetragonal
P41212 space group.19 The asymmetric unit which comprises one
tetranitroxide ligand and two Mn(hfac)2 units is shown in Figure
1. Both MnII(hfac)2 units coordinate two nitroxide groups in a
cis conformation, but the two crystallographically independent
maganese(II) ions Mn1 and Mn2 have opposite octahedral
configuration respectively ∆ and Λ. The crystal structure is shown
in Figure 2; it consists of two independent and neutral 3D
polymeric metal-radical networks of the diamond type, which
interpenetrate in a fashion similar to those found for Zn(CN)2.14,15
Each Mn(hafc)2 unit bound two nitroxide groups to have the
Mn(II) ions octahedral and act as an anchorage node for two
tetranitroxide units which promote the three-dimensional building.
Each of the two interpenetrated networks are built separately from
four of the eight independent positions of the crystal group.20 The
interpenetrated networks have the effect to fill partially the large
cavities induced by the 3D structure and increase the crystal
packing. However, the density is still very low (d ) 1.269 g cm-3)
if compared with other hexafluoroacetylacetonato derivatives
(dmean ) 1.60 g cm-3). As has already been mentioned, the crystal
structure is reminiscent of catenane compounds in the way that
the two infinite networks interlock.
Laboratoire de Chimie Inorganique et
Biologique (UMR 5046), DRFMC
CEA-Grenoble, 17 rue des Martyrs
38054 Grenoble Cedex 09, France
ReceiVed May 3, 2001
ReVised Manuscript ReceiVed June 20, 2001
Physical properties in molecular-based materials depend mainly
on intermolecular cooperation. Therefore, any progress in master-
ing the assembly of molecules in the solid state is of general
concern to numerous fields such as magnetism as well as
electronic or nonlinear optical materials for example.
In the field of molecular-based magnets most of the chemical
routes aim to the building of 3D networks as a prerequisite to
high Curie temperatures (Tc) below which a material behaves like
a magnet.,1-5 In this frame, the metal-radical approach, in which
radicals are used as bridging ligands for metal ions, is particularly
appealing for it combines both the versatility of organic and
inorganic spin carriers, which moreover interact generally strongly.4,6
Following this way, and using chelating nitronyl nitroxide radicals,
we successfully synthesized and characterized layered 2D com-
pounds with honeycomb structures and Tc below 50 K.7,8 In an
other approach K. Inoue and H. Iwamura, using polynitroxide
radicals, have succeeded to synthesize 2D and 3D metal-radical
coordination polymers with Tc up 50 K.9-11 The latter was, to
now, the unique example of 3D network among this class of
compound.
(12) Tetrakis[4-(N-tert-butyl-N-oxyamino)phenyl]methane: To a solution
of tetrakis(4-bromophenyl)methane (1.3 g, 2 mmol) in freshly distilled THF
(50 mL) was added n-butyllithium (2.5 M in hexane, 4 mL, 10 mmol) at -78
°C. The mixture was warmed slowly at room temperature over a period of 1
h and then cooled again at -78 °C prior to addition of 2-methyl-2-
nitrosopropane (800 mg, 4.5 mmol of the dimer). After warming and stirring
for 12 h at room temperature, a saturated NH4Cl aqueous solution (20 mL)
was added to the resulting mixture. The THF solution was separated, and the
aqueous phase was extracted with ethyl ether. After gathering the organic
phases, they were washed with water, dried over Na2SO4, and evaporated.
The residue containing tetrakis[4-(N-tert-butyl-N-hydroxyamino)phenyl]-
methane was dissolved in CH2Cl2 (100 mL) and cooled over ice. An aqueous
solution of NaIO4 (900 mg, 4 mmol) was then added and the mixture turned
red. After strong stirring for 30 min the organic phase containing a mixture
of unreacted material with mono-, bis-, tris- and tetraradicals was separated
and the aqueous phase extracted with dichloromethane. The organic phases
were gathered and evaporated. The residue was chromatographed on silica
with a mixture (1:1) of diethyl ether and petroleum ether. The mono-, bis-,
tris-, and tetranitroxide were identified by EPR spectroscopy. The tetrani-
troxide, was then twice recrystallized by vapor diffusion of ethyl ether in a
dichloromethane-saturated solution to give red needlelike crystals which are
stable for long period of time. (300 mg, 23%). FW ) 664.9 mp ) 220-225
°C.
Taking advantage of these works we synthesized the tetrakis-
[4-(N-tert-butyl-N-oxyamino)phenyl]methane (tetranitroxide).12
Indeed, several publications have shown that the use of molecular
blocks based on the substituted tetraphenylmethane unit lead
efficiently to the building of organic and inorganic 3D frame-
works.13-17
(13) Simard, M.; Su, D.; Wuest, J. D. J. Am. Chem. Soc. 1991, 113, 4696.
(14) Reddy, D., S.; Craig, D., C.; Desiraju, G. R. J. Am. Chem. Soc. 1996,
118, 4090.
(15) Hoskins, B., F.; Robson, R. J. Am. Chem. Soc. 1989, 111, 5962.
(16) Hoskins, B., F.; Robson, R. J. Am. Chem. Soc. 1990, 112, 1546.
(17) Robson, R. Dalton. Trans 2000, 3735.
(18) {[Mn(hfac)2]2(tetranitroxide)}n. (hfac ) hexafluoroacetylacetonate)
Mn(hfac)2‚2H2O (50 mg, 0.01 mmol) was dissolved in 10 mL of boiling
heptane to azeotropically remove hydratation water molecules. After complete
dissolution a few drops of dichloromethane were added to avoid crystalliza-
tion upon cooling at room temperature. The resulting solution was put in
a test tube (10 × 200 mm) on the top of a solution of the tetranitroxide (33
mg, 0.005 mmol) in 10 mL of dichloromethane. Small dark crystals were
obtained after 10 days of interdiffusion of the solutions. Anal. Calcd for
Mn2C61H56F24N4O12: Mn, 6.85; C, 45.71; H, 3.52; F, 28.45; N, 3.50; O, 11.98.
Found: Mn, 6.80; C, 45.65; H, 3.57; F, 28.63; N, 3.48.
* Author for correspondence. E-mail: luneau@drfmc.ceng.cea.fr.
(1) Kahn, O. Molecular Magnetism; VCH: New York, 1993.
(2) Miller, J. S. Inorg. Chem. 2000, 39, 4392.
(3) Miller, J. S.; Drillon, M. MagnetoScience: Molecules to Materials;
Wiley-VCH: Weinheim, 2000.
(4) Lahti, P. M. Magnetic Properties of Organic Materials; Marcel
Dekker: New York, 1999.
(5) Verdaguer, M.; Bleuzen, A.; Marvaud, V.; Vaissermann, J.; Seuleman,
M.; Desplanches, C.; Scuiller, A.; Train, C.; Garde, R.; Gelly, G.; Lomenech,
C.; Rosenman, I.; Veillet, P.; Cartier, C.; Villain, F. Coord. Chem. ReV. 1999,
190-192, 1023.
(19) Crystallography: Data collected at room temperature on a Bruker
SMART CCD diffractometer (λ ) 0.71073?) were processed through the
SAINT reduction software to give 67398 measured reflections and 21301
independent. The structure was solved and refined on F2 using the SHELXTL
software. C61H56N4O12F24Mn2, MW ) 1602.98, dark red, parallelepiped crystal,
tetragonal, P41212 (No 92), a ) 20.1716(5) and c ) 41.230(2) Å, V ) 16776.2-
(9) Å3, Z ) 8, R(int) ) 0.1053, R(F) ) 0.0761 [I < 2σ(I)], wR(F2) ) 0.2495
(all data).
(6) Caneschi, A.; Gatteschi, D.; Rey, P. Prog. Inorg. Chem. 1991, 30, 331.
(7) Fegy, K.; Luneau, D.; Ohm, T.; Paulsen, C.; Rey, P. Angew. Chem.,
Int. Ed. 1998, 37, 1270.
(8) Fegy, K.; Lescop, C.; Luneau, D.; Rey, P. Mol. Cryst. Liq. Cryst. Sci.
Technol., Sect. A 1999, 334, 521.
(9) Inoue, K.; Iwamura, H. J. Am. Chem. Soc. 1994, 116, 3173.
(10) Inoue, K.; Hayamizu, T.; Iwamura, H.; Hashizume, D.; Ohashi, Y. J.
Am. Chem. Soc. 1996, 118, 1803.
1
1
1
1
1
1
(20) (x, y, z; -x, -y, z + /2; -y + /2, x + /2, z + /4; y + /2, -x + /2,
z + 3/41) and (y, x, -z; -y, -x, -z + 1/2; -x + 1/2, y + 1/2, -z + 1/4; x + 1/2,
3
(11) Iwamura, H.; Inoue, K.; Koga, N. New. J. Chem 1998, 201.
-y + /2, -z + /4).
10.1021/ja016133h CCC: $20.00 © 2001 American Chemical Society
Published on Web 07/07/2001

7466 J. Am. Chem. Soc., Vol. 123, No. 30, 2001
Communications to the Editor
Figure 3. Temperature dependence of the magnetic susceptibility ømol
(b) and of its product with temperature ømolT (9). The solid lines represent
the best-fit curves.
3
suggests that the resulting spin S ) /2 are weakly and antifer-
Figure 1. Molecular building block {[Mn(hfac)2]2(tetranitroxide)}. The
fluorine atoms are omitted for clarity. Selected bonds (Å) and angles
(deg). O-N ) 1.288(4)-1.302(4), Mn1-O3i ) 2.096(2), Mn1-O1 )
2.105(2), Mn2-O4ii ) 2.098(2), Mn2-O2 ) 2.098(2)‚, Mn1-O(hfac)
) 2.131(3)-2.161(4), Mn2-O(hfac) ) 2.106(3)-2.142(4), Mn-O-N
) 128.5(3)-131.1(3). i ) y - 1/2, -x + 1/2, z - 1/4, ii ) y + 1/2, -x +
romagnetically coupled in the solid state which prevents any
magnetic behavior. Accordingly, the temperature dependence of
the magnetic susceptibility was fitted considering three spin units
5
S2-S1-S3 (S1 )
/
and S2 ) S3 ) 1/2) in which S1 is
2
antiferromagnetically coupled (J) with S2 and S3 [F(J,T)].22 An
additional coupling (Z′J′) based on the molecular field approxima-
tion was introduce in the fitting process (øfit) to take into account
the magnetic behavior at low temperature.23,24 The best fit was
obtained for J ) -200 cm-1, Z′J′ ) -0.1 cm-1, g ) 2.05. A
value of -200 cm-1 for the manganese(II)-nitroxide interaction
is in agreement with previous finding.6 The -0.1 cm-1 value for
Z′J′ could be reasonably attributed to through-space intermolecular
interactions rather than the coupling through the tetranitroxide.
Indeed, the shortest intramolecular distance between the manga-
nese(II) ions through the tetranitroxide bridging ligand calculated
by summing all of the bond lengths is 20.907(3) Å, while the
shortest intermolecular distance is 10.027(3) Å. Moreover the
central sp3 carbon (C1) is not expected to mediate strong
superexchange interactions.
1
1/2, z - /4.
Figure 2. The crystal structure showing the two interpenetrated 3D
networks projected along [010] direction. The hfac and tert-butyl groups
are omited for clarity.
Despite the lack of spontaneous magnetization the present
compound is a rare example of 3D metal-radical coordination
polymer. Furthermore, it highlights the strength and usefulness
of metal coordination chemistry in supramolecular engineering.
The product of the magnetic susceptibility with tempera-
ture (ømolT) is 4.0 emu K mol-1 at 300 K for the molecular unit
{[Mn(hfac)2]2(tetranitroxide)}21 (see Figure 3). Upon cooling it
decreases only a little down to 60 K (3.75 emu K mol-1), and
more abruptly below. The value at 300 K is smaller than expected
Acknowledgment. This work was supported by the Centre National
de la Recherche Scientifique (CNRS), the Commissariat a` l’Energie
Atomique (CEA), the Grenoble University Joseph Fourier (UJF) and the
3MD Network of the TMR program of the E.U. (Contract ERBFM-
RXCT980181).
5
if the two manganese(II) ions (S ) /2) and the four nitroxide
radicals (S ) 1/2) were magnetically independent (ømolT ) 10.50
emu K mol-1). Furthermore, in the range 300-60 K ømolT
is consistent with strong antiferromagnetic couplings between
the manganese(II) ions and the two coordinated nitroxide
radicals.
Supporting Information Available: Crystallographic data for com-
pounds in CIF format. This material is available free of charge via the
Internet at http://pubs.acs.org.
JA016133H
This leads to a ground spin state S ) 3/2 (ømolT ) 3.75 emu K
mol-1 for two S ) 3/2). The decrease observed below 60 K
(22) Gruber, S. J.; Harris, C. M.; Sinn, E. J. Chem. Phys. 1968, 49, 2183.
F(J,T) ) (Ng2â2/4kT){[35 + 84 exp(5J/kT) + 35 exp(-2J/kT) + 10 exp(-
7J/kT)]/[3 + 4 exp(5J/kT) + 3 exp(-2J/kT) + 2 exp(-7J/kT)]}.
(23) Ginsberg, A. P.; Lines, M. E. Inorg. Chem. 1972, 11, 2289.
(24) øfit ) 2{F(J,T)/[1 - (2Z′J′/Ng2â2)F(J,T)]} with F(J,T) defined in ref
22.
(21) The magnetic susceptibilities were measured on the polycrystalline
sample in the temperature range 2-300 K with a Quantum Design MPMS
SQUID magnetometer at a field strength of 0.5 T. The data were corrected
for atomic diamagnetism using Pascal constants.