Synthesis, Structures, and Magnetic Properties of Novel Mononuclear, Tetranuclear, and 1D Chain MnIII Complexes Involving Three Related Asymmetrical Trianionic Ligands

Article abstract of DOI:10.1021/ic0348796

The manganese(III) complexes studied in this report derive from asymmetrical trianionic ligands abbreviated H₃Lⁱ (i = 4-6). These ligands are obtained through reaction of salicylaldehyde with half-units , the latter resulting from monocondensation of different diamines with phenylsalicylate. Upon deprotonation, Lⁱ (i = 4-6) possess an inner N₂O₂ coordination site with one amido, one imine, and two phenoxo functions, and an outer amido oxygen donor. The trianionic character of such ligands yields original neutral complexes with the L/Mn stoichiometry. The crystal and molecular structures of three complexes have been determined at 190 K (1) or 180 K (2 and 3). Complex 1 crystallizes in the triclinic space group P1 (No. 2): a = 7.8582(14) A, b = 10.9225(16) A, c = 12.4882(18) A, α = 67.231(14)°, β = 72.134(14)°, γ = 82.589(13)°, V = 940.6(3) A³, Z = 2. Complex 2 crystallizes in the orthorhombic space group Pbcn (No. 60): a = 23.8283(15) A, b = 11.1605(7) A, c = 26.152(2) A, V = 6954.8-(8) A³, Z = 8, while complex 3 crystallizes in the monoclinic space group P2₁/c (No. 14) with a = 11.7443(14) A, b = 7.5996(10) A, c = 18.029(2) A, β = 100.604(10)°, V = 1581.6(3) A³, Z = 4. Owing to hydrogen bonds and π-π stackings, the mononuclear neutral molecules of 1 are arranged in a 2D network while complexes 2 and 3 are tetranuclear and polymeric (1D chain) species; respectively, owing to the bridging ability of the oxygen atom of the amido function. The experimental magnetic susceptibilities of complexes 2 and 3 indicate the occurrence of similarly weak Mn^III-Mn^III antiferromagnetic interactions (J = -1.1 cm^-1). Single ion zero-field splitting of manganese(III) must be taken into account for satisfactorily fitting the data by exact calculation of the energy levels associated to the spin Hamiltonian through diagonalization of the full matrix for axial symmetry in 2 (J = - 1.1 cm^-1, D₁ = 2.2 cm ^-1, D₂ = -2.8 cm^-1), D₁ and D ₂ being associated to the six- and five-coordinate Mn ions, respectively. A weaker antiferromagnetic interaction (J = - 0.2 cm ^-1) operates through π-π stacking in complex 1. Complex 3 is a weak ferromagnet (ordering temperature ～7 K) as a result of the spin canting originating from the crystal packing.

Full text of DOI:10.1021/ic0348796

Inorg. Chem. 2004, 43, 2736−2744
Synthesis, Structures, and Magnetic Properties of Novel Mononuclear,
Tetranuclear, and 1D Chain MnIII Complexes Involving Three Related
Asymmetrical Trianionic Ligands
Jean-Pierre Costes,* Franc¸oise Dahan, Bruno Donnadieu, Maria-Jesus Rodriguez Douton,†
Maria-Isabel Fernandez Garcia,† Azzedine Bousseksou, and Jean-Pierre Tuchagues
Laboratoire de Chimie de Coordination du CNRS, UPR 8241, lie´e par conVentions a` l’UniVersite´
Paul Sabatier et a` l’Institut National Polytechnique de Toulouse, 205 route de Narbonne,
31077 Toulouse Cedex, France
Received July 25, 2003
i
The manganese(III) complexes studied in this report derive from asymmetrical trianionic ligands abbreviated H L
3
(i ) 4−6). These ligands are obtained through reaction of salicylaldehyde with “half-units”, the latter resulting from
i
monocondensation of different diamines with phenylsalicylate,. Upon deprotonation, L (i ) 4−6) possess an inner
N O coordination site with one amido, one imine, and two phenoxo functions, and an outer amido oxygen donor.
2
2
The trianionic character of such ligands yields original neutral complexes with the L/Mn stoichiometry. The crystal
and molecular structures of three complexes have been determined at 190 K (1) or 180 K (2 and 3). Complex 1
crystallizes in the triclinic space group P1h (No. 2): a ) 7.8582(14) Å, b ) 10.9225(16) Å, c ) 12.4882(18) Å, R
3
) 67.231(14)°, â ) 72.134(14)°, γ ) 82.589(13)°, V ) 940.6(3) Å , Z ) 2. Complex 2 crystallizes in the
orthorhombic space group Pbcn (Νï. 60): a ) 23.8283(15) Å, b ) 11.1605(7) Å, c ) 26.152(2) Å, V ) 6954.8-
3
(8) Å , Z ) 8, while complex 3 crystallizes in the monoclinic space group P21/c (No. 14) with a ) 11.7443(14) Å,
3
b ) 7.5996(10) Å, c ) 18.029(2) Å, â ) 100.604(10)°, V ) 1581.6(3) Å , Z ) 4. Owing to hydrogen bonds and
π−π stackings, the mononuclear neutral molecules of 1 are arranged in a 2D network while complexes 2 and 3
are tetranuclear and polymeric (1D chain) species, respectively, owing to the bridging ability of the oxygen atom
of the amido function. The experimental magnetic susceptibilities of complexes 2 and 3 indicate the occurrence of
III
III
-1
similarly weak Mn −Mn antiferromagnetic interactions (J ) −1.1 cm ). Single ion zero-field splitting of manganese-
(III) must be taken into account for satisfactorily fitting the data by exact calculation of the energy levels associated
to the spin Hamiltonian through diagonalization of the full matrix for axial symmetry in 2 (J ) − 1.1 cm-1, D )
1
2.2 cm-1, D ) −2.8 cm-1), D and D being associated to the six- and five-coordinate Mn ions, respectively. A
2
1
2
weaker antiferromagnetic interaction (J ) − 0.2 cm-1) operates through π−π stacking in complex 1. Complex 3
is a weak ferromagnet (ordering temperature ∼7 K) as a result of the spin canting originating from the crystal
packing.
Introduction
polynuclear alkoxo-, phenoxo-, carboxylato-, and oxo-
bridged manganese complexes are of current interest from a
variety of viewpoints, including molecular magnetic materials
and bioinorganic chemistry. In the former area, it has been
shown that some of these polynuclear species possess large
total spin values (ST) in their ground state. Large ST values
provide the possibility of obtaining new manganese-based
single-molecule magnets (SMMs).2 In the area of bioinor-
ganic chemistry, dinuclear and tetranuclear species may be
used as synthetic models of the active site of various non-
heme manganese proteins and enzymes such as catalases,3
An investigation area of increasing importance in con-
temporary chemistry concerns functional materials made up
from discrete molecules. Functionality depends on the
electronic structure of the constituent molecules. In this
regard, complexes of 3d transition metal ions provide a large
variety of unusual electronic structures.1 Dinuclear and
* To whom correspondence should be addressed. E-mail: costes@
lcc-toulouse.fr. Fax: 33 (0)5 61 55 30 03.
† Present address: Dpto de Quimica Inorganica, Universidad de Santiago
de Compostela, Santiago de Compostela, E15782 Spain.
2736 Inorganic Chemistry, Vol. 43, No. 8, 2004
10.1021/ic0348796 CCC: $27.50 © 2004 American Chemical Society
Published on Web 03/17/2004

MnIII Complexes with Asymmetric Trianionic Ligands
liver arginase,4 manganese ribonucleotide reductase (RNR),5
thiosulfate oxidizing enzyme,6 and the oxygen evolving
complex (OEC) of photosystem 2.7
solvents (propane-2-ol, dichloromethane, diethyl ether, acetone,
ethanol, and methanol) were used for the syntheses of ligands and
complexes.
Ligands. The method used to synthesize the half-unit trifunc-
tional ligands LiH2 (i ) 1-3) was adapted from the process
described earlier.9
Important to the future of the above areas is the develop-
ment of synthetic procedures that may yield new ligands from
which polynuclear manganese species with original structure
and properties may be obtained. Up to now, neutral
manganese complexes have essentially been obtained by
association of symmetrical neutral or mono- or dianionic
ligands (the later two being most often Schiff bases) with
halide, pseudohalide, carboxylato, hydroxo, and oxo anions
in the metal coordination sphere.8 This observation prompted
us to extend the synthesis, through stepwise processes, of
ligands including an inner asymmetrical trianionic tetraden-
tate N2O2 coordination site with one amide, one imine, and
two phenol functions, and an outer amido oxygen donor
atom.
L1H2. A mixture of phenyl salicylate (2.14 g, 1 × 10-2 mol)
and 1,2-diamino-2-methylpropane (0.88 g, 1 × 10-2 mol) in
propane-2-ol (40 mL) was refluxed for 30 min and then cooled to
room temperature with stirring. The white precipitate which
appeared upon cooling was filtered off, and washed with diethyl
ether. Yield: 1.8 g (86%). Anal. Calcd for C11H16N2O2: C, 63.4;
1
H, 7.7; N, 13.5. Found: C, 63.0; H, 7.5; N, 13.4. H NMR (250
MHz, 20 °C, DMSO-d6): δ 1.19 (s, 6H, CH3), 3.38 (s, 2H, CH2),
6.81 (t, J ) 8 Hz, 1H, C(5)H), 6.94 (d, J ) 8 Hz, 1H, C(3)H),
7.37 (td, J ) 1.8 and 8 Hz, 1H, C(4)H), 7.96 (dd, J ) 1.8 and 8
Hz, 1H, C(6)H), 9.55 (l, 1H, NH). 13C{1H} NMR (62.896 MHz,
20 °C, DMSO-d6): δ 27.0 (s, CH3), 49.5 (s, CH2), 51.4 (s, CH3C),
117.6 (s, ArC(3)H), 118.4 (s, ArC), 118.7 (s, ArC(5)H), 129.7 (s,
ArC(6)H), 132.7 (s, ArC(4)H), 162.5 (s, ArC(2)OH), 168.2 (s,
OCNH). Characteristic IR absorptions (Nujol mull): 3261,1617,
In this contribution, we describe the synthesis and full
characterization of three such asymmetrical trianionic ligands,
L4H3, L5H3, and L6H3, and the preparation, molecular
structure, and magnetic properties of the complexes obtained
by aerobic reaction of these ligands with manganese, [L6-
1559, 1536 cm-1
.
L2H2. This ligand was prepared as L1H2, using phenyl salicylate
(2.14 g, 1 × 10-2 mol) and 1,2-diaminopropane (0.74 g, 1 × 10-2
mol). Yield: 1.6 g (82%). Anal. Calcd for C10H14N2O2: C, 61.8;
Mn(CH3OH)2], 1, [L5 Mn4(H2O)2](CH3OH)2, 2, and [L4Mn-
4
1
(CH3OH)]n, 3.
H, 7.3; N, 14.4. Found: C, 61.5; H, 7.1; N, 14.4. H NMR (250
MHz, 20 °C, DMSO-d6): δ 1.15 (d, J ) 6.5 Hz, 3H, CH3), 3.17
(m, 1H, CH3CH), 3.27-3.41 (m, 2H, CH2), 6.83 (t, J ) 8 Hz, 1H,
C(5)H), 6.94 (d, J ) 8 Hz, 1H, C(3)H), 7.39 (td, J ) 1.0 and 8 Hz,
1H, C(4)H), 7.95 (dd, J ) 1.0 and 8 Hz, 1H, C(6)H), 9.55 (l, 1H,
NH). 13C{1H} NMR (62.896 MHz, 20 °C, DMSO-d6): δ 20.3 (s,
CH3), 46.4 (s, CH3C), 46.6 (s, CH2), 116.4 (s, ArC(3)H), 117.1 (s,
ArC(1)), 118.3 (s, ArC(5)H), 129.0 (s, ArC(6)H), 133.0 (s,
ArC(4)H), 162.3 (s, ArC(2)OH), 168.5 (s, OCNH). Characteristic
Experimental Section
Materials. Phenyl salicylate, 1,2-diamino-2-methylpropane, 1,2-
diaminopropane, 1,2-diaminoethane, salicylaldehyde, and Mn-
(OAc)2‚4H2O (Aldrich) were used as purchased. High-grade
(1) See for examples: Boyd, P. D. W.; Li, Q.; Vincent, J. B.; Folting,
K.; Chang, H. R.; Streib, W. E.; Huffman, J. C.; Christou, G.;
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C. P.; Terzis, A.; Bakalbassis, E. G.; Perlepes S. P. Angew. Chem.,
Int. Ed. 1999, 38, 983. Barra, A. L.; Caneschi, A.; Cornia, A.; Fabrizi
de Biani, F.; Gatteschi, D.; Sangregorio, C.; Sessoli, R.; Sorace, L. J.
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Winpenny, R. E. P. Angew. Chem., Int. Ed. 2001, 40, 151.
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Tsai, H.-L.; Wang, S.; Wemple, M. W. Polyhedron 1998, 17, 3005.
Cdiou, C.; Murrie, M.; Paulsen, C.; Villar, V.; Wernsdorfer, W.;
Winpenny, R. E. P. Chem. Commun. 2001, 2666. Wernsdorfer, W.;
Aliaga-Alcalde, N.; Hendrickson, D. N.; Christou, G. Nature 2002,
416, 406. Gatteschi, D.; Sessoli, R. Angew. Chem., Int. Ed. 2003, 42,
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(3) Palopoli, C.; Gonza´lez-Sierra, M.; Robles, G.; Dahan, F.; Tuchagues,
J.-P.; Signorella, S. J. Chem. Soc., Dalton Trans. 2002, 3813 and refs.
therein.
(4) Khangulov, S. V.; Pessiki, P. J.; Barynin, V. V.; Ash, D. E.; Dismukes,
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Jr.; Goldstein, J. I.; Ash, D. E.; Elgren, T. E.; Kurtz, D. M., Jr.; Penner-
Hahn, J. E. Biochemistry 1997, 36, 9847.
(5) Sjoeberg, B.-M. In Structure and Bonding; Hill, H. A. O., Sadler, P.
J., Thomson, A. J., Eds.; Springer-Verlag: Berlin, 1997; Vol. 88, p
139.
(6) Cammack, R.; Chapman, A.; Lu, W.-P.; Karagouni, A.; Kelly, D. P.
FEBS Lett. 1989, 253, 239.
IR absorptions (Nujol mull): 3260,1646, 1594, 1528 cm-1
.
L3H2. A mixture of phenyl salicylate (2.14 g, 1 × 10-2 mol)
and 1,2-diaminoethane (0.60 g, 1 × 10-2 mol) in dichloromethane
(40 mL) was stirred overnight. To the resulting white precipitate
was added diethyl oxide (60 mL) and acetone (2 mL). Stirring for
3 h at room temperature yielded a bulky precipitate that was filtered
off and washed with diethyl ether. Yield: 1.0 g (45%). Anal. Calcd
for C12H16N2O2: C, 65.4; H, 7.3; N, 12.7. Found: C, 65.2; H, 7.1;
1
N, 12.4. H NMR (250 MHz, 20 °C, DMSO-d6): δ 1.90 (s, 3H,
CH3), 2.04 (t, J ) 1.4 Hz, 3H, CH3), 3.44 (m, 2H, CH2N), 3.60 (q,
J ) 5.5 Hz, 2H, CH2NH), 6.98 (td, J ) 1 and 8 Hz, 1H, C(5)H),
7.00 (dd, J ) 1 and 8 Hz, 1H, C(3)H), 7.49 (td, J ) 1.5 and 8 Hz,
(7) Yachandra, V. K.; DeRose, V. J.; Latimer, M. J.; Mukerjee, I.; Sauer,
K.; Klein, M. P. Science 1993, 260, 675. Hoganson, C. W.; Babcock,
G. Science 1997, 277, 1953. Tommos, C.; Babcock, G. Acc. Chem.
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P. J., Jr.; Armstrong, W. H. J. Am. Chem. Soc. 1998, 120, 3704.
Limburg, J.; Vrettos, J. S.; Liable-Sands, L. M.; Rheingold, A. L.;
Crabtree, R. H.; Brudvig, G. W. Science 1999, 283, 1524. Ruettinger,
W. F.; Dismukes, G. C. Inorg. Chem. 2000, 39, 1021. Zouni, A.; Witt,
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2001, 409, 739.
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Chem. 1990, 29, 2193. (e) Theil, S. Ph.D. Thesis, Universite´ de
Toulouse III, 1993. (f) Reddy, K. R.; Rajasekharan, M. V.; Tuchagues,
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Rajasekharan, M. V.; Hureau, C.; Rivie`re, E.; Cano, J.; Girerd, J. J.
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Inorganic Chemistry, Vol. 43, No. 8, 2004 2737

Costes et al.
1H, C(4)H), 7.93 (dd, J ) 1.8 and 8 Hz, 1H, C(6)H), 9.11 (t, J )
5.5 Hz, 1H, OCNH). 13C{1H} NMR (62.896 MHz, 20 °C, DMSO-
d6): δ 19.5 (s, CH3), 29.8 (s, CH3), 41.2 (s, CH2NH), 51.0 (s,
CH2N), 116.8 (s, ArC), 118.5 (s, ArC(3)H), 119.2 (s, ArC(5)H),
129.2 (s, ArC(6)H), 134.4 (s, ArC(4)H), 161.3 (s, ArC(2)OH), 168.7
(s, C)N), 169.6 (s, OCNH). Characteristic IR absorptions (Nujol
ArC(4′)H), 133.7 (s, ArC(4)H), 159.9 (s, ArC(2)OH), 160.6 (s,
ArC(2′)OH), 165.2 (s, CdN), 169.0 (s, OCNH). Characteristic IR
absorptions (Nujol mull): 3364, 1645, 1633, 1593, 1544 cm-1
.
MnIII Complexes. [L6Mn(CH3OH)2] (1). A mixture of L2H2
(0.40 g, 2 × 10-3 mol) and salicylaldehyde (0.24 g, 2 × 10-3 mol)
in methanol (20 mL) was heated for 30 min and then left to cool
under stirring. NaOH (0.24 g, 6 × 10-3 mol) was first added and
then Mn(OAc)2‚4H2O (0.5 g, 2 × 10-3 mol). The solution which
turned darker immediately was stirred for 2 h and set aside; crystals
appeared 2 days later. Yield: 0.42 g (51%). Anal. Calcd for C19H23-
MnN2O5: C, 55.1; H, 5.6; N, 6.8. Found: C, 54.7; H, 5.3; N, 6.8.
mull): 3383, 3350, 1644, 1600, 1577, 1539 cm-1
.
L4H3. A mixture of L3H2 (0.80 g, 3.6 × 10-3 mol) and
salicylaldehyde (0.44 g, 3.6 × 10-3 mol) in ethanol (20 mL) was
refluxed for 10 min with stirring. The solution was left to stand
overnight, yielding yellow crystals that were filtered off and dried.
Yield: 0.6 g (55%). Anal. Calcd for C16H16N2O3: C, 67.6; H, 5.7;
N, 9.8. Found: C, 67.7; H, 5.3; N, 9.8. 1H NMR (250 MHz, 20 °C,
DMSO-d6): δ 3.63 (q, J ) 5.5 Hz, 2H, CH2NH), 3.80 (t, J ) 5.5
Hz, 2H, CH2N), 6.88 (t + t + d, J ) 8 Hz, 3H, C(5)H, C(3′)H and
C(5′)H), 6.91 (d, J ) 8 Hz, 1H, C(3)H), 7.32 (td, J ) 1.5 and 8
Hz, 1H, C(4′)H), 7.39 (td, J ) 1.5 and 8 Hz, 1H, C(4)H),7.42 (dd,
J ) 1.5 and 8 Hz, 1H, C(6′)H), 7.84 (dd, J ) 1.5 and 8 Hz, 1H,
C(6)H), 8.56 (s, 1H, HCdN), 9.00 (t, J ) 5.5 Hz, 1H, OCNH),
12.49 (s, 1H, OH), 13.47 (s, 1H, O′H). 13C{1H} NMR (62.896 MHz,
20 °C, DMSO-d6): δ 40.7 (s, CH2NH), 58.4 (s, CH2N), 116.3 (s,
ArC(1)), 117.3 (s, ArC(3′)H), 118.2 (s, ArC(3)H), 119.4 (s,
ArC(5)H), 119.5 (s, ArC(5′)H), 119.8 (s, ArC(1′)), 128.7 (s,
ArC(6)H), 132.6 (s, ArC(6′)H), 133.2 (s, ArC(4′)H), 134.5 (s,
ArC(4)H), 160.7 (s, ArC(2)OH), 161.4 (s, ArC(2′)OH), 167.8 (s,
CdN), 169.8 (s, OCNH). Characteristic IR absorptions (Nujol
[L5 Mn4(H2O)2](CH3OH)2 (2). A mixture of L1H2 (0.75 g, 3.6
4
× 10-3 mol) and salicylaldehyde (0.44 g, 3.6 × 10-3 mol) in
methanol (20 mL) was heated for 30 min and then left to cool under
stirring. NaOH (0.43 g, 1.08 10-2 mol) was first added and then
Mn(OAc)2‚4H2O (0.95 g, 3.6 × 10-3 mol). The solution which
turned darker immediately was stirred for 2 h and set aside; crystals
appeared 2 days later. Yield: 0.40 g (29%). Anal. Calcd for C74H80-
Mn4N8O16: C, 57.1; H, 5.2; N, 7.2. Found: C, 56.8; H, 5.1; N, 6.9.
[L4Mn(CH3OH)]n (3). To a solution of L4H2 (0.30 g, 1.1 ×
10-3 mol) in methanol (20 mL) was first added NaOH (0.13 g, 3.3
× 10-3 mol) and then Mn(OAc)2‚4H2O (0.27 g, 1.1 × 10-3 mol).
The reaction mixture was heated for 30 min and then left to cool
under stirring. NaOH (0.24 g, 6 × 10-3 mol) was first added and
then Mn(OAc)2‚4H2O (0.5 g, 2 × 10-3 mol). The solution which
turned darker immediately was stirred for 2 h and set aside; crystals
appeared 3 days later. Yield: 0.16 g (40%). Anal. Calcd for C17H17-
MnN2O4: C, 55.4; H, 4.6; N, 7.6. Found: C, 55.1; H, 4.5; N, 7.4.
Crystallographic Data Collection and Structure Determina-
tion for 1, 2, and 3. Crystals suitable for X-ray analyses were
obtained by slow evaporation of the corresponding methanol
solutions. The selected crystal of 1 (red plate, 0.35 × 0.20 × 0.15
mm3) was mounted on an Oxford-Diffraction Xcalibur diffracto-
meter using a graphite-monochromated Mo KR radiation (λ )
0.71073 Å) and equipped with an Oxford Instruments Cryojet cooler
device. Data were collected10 at 190 K with 4 runs (æ ) 0°, 90°,
180°, 270°) and ω scans up to θ ) 30.3° (153 frames with a
maximum time of 50 s). The selected crystal of 2 (dark-red plate,
0.30 × 0.15 × 0.10 mm3) was mounted on a Stoe imaging plate
diffractometer system (IPDS) using a graphite monochromator (λ
) 0.71073 Å), and equipped with an Oxford Cryosystems cooler
device. Data were collected11 at 180 K with a æ oscillation
movement (æ ) 0.0-200.2°, ∆f ) 1.1°), the crystal-to-detector
distance being equal to 80 mm (max θ value 24.2°). The selected
crystal of 3 (red plate, 0.35 × 0.30 × 0.15 mm3) was mounted on
an Oxford-Diffraction Xcalibur diffractometer using a graphite-
monochromated Mo KR radiation (λ ) 0.71073 Å) and equipped
with an Oxford Instruments Cryojet cooler device. Data were
collected10 at 180 K with 4 runs (æ ) 0°, 90°; 180°, 270°) and ω
scans up to θ ) 30.3° (164 frames with a maximum time of 40 s).
There were 8333 reflections collected for 1, of which 5041 were
independent (Rint ) 0.0408). Gaussian absorption corrections12 were
applied (Tmin-max ) 0.5631-0.6758). There were 34187 reflections
collected for 2, of which 5560 were independent (Rint ) 0.0673).
mull): 3379,1634, 1592, 1549 cm-1
.
L5H3. A mixture of L1H2 (0.42 g, 2 × 10-3 mol) and
salicylaldehyde (0.24 g, 2 × 10-3 mol) in propane-2-ol (10 mL)
was refluxed for 10 min with stirring. The solution was set aside,
yielding yellow crystals that were filtered off and dried. Yield: 0.3
g (49%). Anal. Calcd for C18H20N2O3: C, 69.2; H, 6.5; N, 9.0.
Found: C, 68.9; H, 6.3; N, 8.8. 1H NMR (250 MHz, 20 °C, DMSO-
d6): δ 1.43 (s, 6H, CH3), 3.64 (d, J ) 6.2 Hz, 2H, CH2NH), 6.95-
7.03 (m, 4H, C(5)H, C(3)H, C(3′)H, and C(5′)H), 7.43 (td, J ) 1.5
and 8 Hz, 1H, C(4′)H), 7.49 (td, J ) 1.5 and 8 Hz, 1H, C(4)H),
7.60 (dd, J ) 1.5 and 8 Hz, 1H, C(6′)H), 7.99 (dd, J ) 1.5 and 8
Hz, 1H, C(6)H), 8.70 (s, 1H, HCdN), 8.90 (t, J ) 6.2 Hz, 1H,
OCNH), 12.26 (s, 1H, OH), 13.96 (s, 1H, O′H). 13C{1H} NMR
(62.896 MHz, 20 °C, DMSO-d6): δ 26.1 (s, CH3), 50.1 (s, CH2-
NH), 61.6 (s, C(CH3)2N), 117.4 (s, ArC(1)), 117.6 (s, ArC(3′)H),
118.3 (s, ArC(3)H), 119.4 (s, ArC(5)H), 119.8 (s, ArC(5′)H), 120.0
(s, ArC(1′)), 129.8 (s, ArC(6)H), 133.2 (s, ArC(6′)H), 133.3 (s,
ArC(4′)H), 134.5 (s, ArC(4)H), 160.1 (s, ArC(2)OH), 162.0 (s,
ArC(2′)OH), 163.8 (s, CdN), 169.4 (s, OCNH). Characteristic IR
absorptions (Nujol mull): 3380, 1644, 1630, 1597, 1544 cm-1
.
L6H3. A mixture of L2H2 (0.19 g, 1 × 10-3 mol) and
salicylaldehyde (0.12 g, 1 × 10-3 mol) in dichloromethane (10 mL)
was refluxed for 10 min with stirring. The solution was concentrated
and cooled. Addition of pentane yielded a yellow sticky product
that was washed with pentane and dried. Yield: 0.1 g (36%). Anal.
Calcd for C17H18N2O3: C, 68.4; H, 6.1; N, 9.4. Found: C, 68.0; H,
1
5.8; N, 9.3. H NMR (250 MHz, 20 °C, DMSO-d6): δ 1.39 (d, J
) 6.5 Hz, 3H, CH3), 3.54 and 3.67 (m, 2H, CH2NH), 3.80 (m, 1H,
CH3CHN), 6.97-7.00 (m, 4H, C(5)H, C(3)H, C(3′)H, and C(5′)-
H), 7.43 (td, J ) 1.5 and 8 Hz, 1H, C(4′)H), 7.50 (t, J ) 8 Hz, 1H,
C(4)H), 7.52 (dd, J ) 1.5 and 8 Hz, 1H, C(6′)H), 7.93 (dd, J )
1.5 and 8 Hz, 1H, C(6)H), 8.65 (s, 1H, HCdN), 9.01 (t, J ) 6.5
Hz, 1H, OCNH), 12.45 (s, 1H, OH), 13.41 (s, 1H, O′H). 13C{1H}
NMR (62.896 MHz, 20 °C, DMSO-d6): δ 20.0 (s, CH3), 45.4 (s,
CH2NH), 63.0 (s, CH3CHN), 115.6 (s, ArC(1)), 116.5 (s, ArC(3′)H),
117.4 (s, ArC(3)H), 118.7 (s, ArC(5)H), 118.7 (s, ArC(5′)H), 118.8
(s, ArC(1′)), 128.1 (s, ArC(6)H), 131.8 (s, ArC(6′)H), 132.4 (s,
Numerical absorption corrections13 were applied (Tmin-max
)
0.4555-0.5826). There were 12206 reflections collected for 3, of
(10) CRYSALIS, version 169; Oxford-Diffraction, Poland, 2001.
(11) STOE, IPDS Manual, version 2.93; Stoe & Cie: Darmstadt, Germany,
1997.
(12) Spek, A. L. PLATON. An Integrated Tool for the Analysis of the
Results of a Single-Crystal Structure Determination. Acta Crystallogr.
1990, A46, C34.
(13) X-SHAPE. Crystal Optimisation for Numerical Absorption Corrections,
revision 1.01; Stoe & Cie: Darmstadt, Germany, 1996.
2738 Inorganic Chemistry, Vol. 43, No. 8, 2004

MnIII Complexes with Asymmetric Trianionic Ligands
Table 1. Crystallographic Data for Complexes 1, 2, and 3
decoupling with selective proton irradiation were obtained with a
Bruker WM250 facility working at 62.89 MHz. 2D 1H COSY
experiments using standard programs and 2D pulse-field gradient
HMQC 1H-13C correlation using a PFG-HMQC standard program
were performed on a Bruker AMX400 spectrometer. Chemical shifts
are given in ppm versus TMS (1H and 13C) using (CD3)2SO as
solvent. Magnetic data were obtained with a Quantum Design
MPMS SQUID susceptometer. All samples were 3 mm diameter
pellets molded from ground crystalline samples. Magnetic suscep-
tibility measurements were performed in the 2-300 K temperature
range in a 0.5 T applied magnetic field, and diamagnetic corrections
were applied by using Pascal’s constants.18 Isothermal magnetization
measurements were performed up to 5 T at 2 K. The magnetic
susceptibility has been computed by exact calculation of the energy
levels associated to the spin Hamiltonian through diagonalization
of the full matrix with a general program for axial symmetry,19
and with the MAGPACK program package20 in the case of
magnetization. Least-squares fittings were accomplished with an
adapted version of the function-minimization program MINUIT.21
1
2
3
chem formula
fw
C19H23MnN2O5 C37H40Mn2N4O8 C17H17MnN2O4
414.33
778.61
368.27
space group
a, Å
b, Å
P1h
Pbcn (No. 60)
23.8283(15)
11.1605(7)
26.152(2)
P21/c
7.8582(14)
10.9225(16)
12.4882(18)
67.231(14)
72.134(14)
82.589(13)
940.6(3)
2
11.7443(14)
7.5996(10)
18.029(2)
c, Å
R, deg
â, deg
γ, deg
V, Å-3
Z
100.604(10)
6954.8(8)
8
1.487
0.71073
180
1581.6(3)
4
1.547
0.71073
180
8.59
F
calcd, g cm-3
λ, Å
1.463
0.71073
190
T, K
µ(Mo KR), cm-1 7.35
7.86
Ra obsd, all
0.0371, 0.0597 0.0453, 0.0593
0.0606, 0.0704 0.0960, 0.1014
0.0296, 0.0351
0.0559, 0.0585
Rwb obsd, all
a R ) ∑||Fo| - |Fc||/∑|Fo|. b Rw ) [∑w(|Fo | - |Fc |)2/∑w|Fo | ]1/2
.
2
2
2 2
Table 2. Selected Bond Lengths and Angles for Complexes 1, 2, and 3
2 Mn six- 2 Mn five-
coordinate coordinate
Results and Discussion
1
3
Syntheses. The ligands L4H3, L5H3, and L6H3 used in this
study for manganese complexation have been prepared
according to an experimental procedure adapted from an
earlier described method.9 Owing to the involvement of one
amide and one imine linkages, these ligands include an
uncommon asymmetrical trianionic tetradentate N2O2 coor-
dination site with one amide, one imine, and two phenol
functions. Accordingly, their synthesis requires a stepwise
process: the amide part of the ligands has been synthesized
by the method described earlier by Daidone.22 Reaction of
phenyl salicylate with 1,2-diamino-2-methylpropane or 1,2-
diaminopropane in propane-2-ol is straightforward and
produces the pure half-unit ligands L1H2 and L2H2 in good
yields (Scheme 1). “Half-unit” is meant to indicate that only
one function of the diamine reactant has been involved in
the reaction process.23 When similar reaction conditions are
used with 1,2-diaminoethane, a mixture of the half-unit and
of the symmetrical ligands is obtained (see Scheme 2). Use
of dichloromethane as solvent without heating produces the
half-unit in higher yield. After 12 h and after dichloromethane
removal, diethyl ether including a small amount of acetone
was added to the resulting pasty product. Stirring induces
formation of a bulky white precipitate which is easily isolated
by filtration. Spectroscopic analyses (NMR, IR) confirm the
presence of an L3H2 derivative in which a Schiff base
condensation has occurred between the unreacted amine
function of the half-unit and acetone (Scheme 2). Further
Mn-Ophenol(amide) 1.857(1)
1.852(3)
1.879(3)
1.937(3)
1.990(3)
2.255(2)
1.839(3)
1.878(2)
1.905(3)
1.983(3)
2.074(3)
1.856(1)
1.918(1)
1.955(1)
1.990(1)
2.219(1)
2.316(1)
Mn-Ophenol(imine) 1.897(1)
Mn-N(amide)
Mn-N(imine)
Mn-O(amide)
Mn-OHCH3
Mn-OH2
1.960(2)
2.005(2)
2.264(2) 2.290(1)
2.352(3)
1.267(4)
OdC(amide)
1.276(2)
6.8800(6)
1.266(4)
1.272(2)
Mn‚‚‚Mnshortest
5.9712(7) 5.9712(7) 5.1733(4)
which 4438 were independent (Rint ) 0.0471). Gaussian absorption
corrections12 were applied (Tmin-max ) 0.55373-0.6820).
The structures were solved using SHELXS-9714 and refined on
F2 by full-matrix least-squares using SHELXL-9715 with anisotropic
displacement parameters for all non-hydrogen atoms. H atoms were
introduced in calculations using the riding model, except those
bonded to the O(3) and O(4) atoms in 1 and to the O(7) atom in 2
that were allowed to vary. Isotropic UH values were 1.1 times higher
than those of the atom to which they are bonded. The atomic
scattering factors and anomalous dispersion terms were taken from
the standard compilation.16 The maximum and minimum peaks on
the final difference Fourier map were 0.271 and -0.284 e Å-3 for
1, 0.323 and -0.319 e Å-3 for 2, and 0.306 and -0.308 e Å-3 for
3. Drawings of the molecules were performed with the program
ZORTEP.17 Crystal data collection and refinement parameters are
given in Table 1, and selected bond distances and angles are
gathered in Table 2.
Physical Measurements. Elemental analyses were carried out
at the Laboratoire de Chimie de Coordination Microanalytical
Laboratory in Toulouse, France, for C, H, and N. IR spectra were
recorded on a GX system 2000 Perkin-Elmer spectrophotometer.
Samples were run as KBr pellets. 1D 1H NMR spectra were
acquired at 250.13 MHz on a Bruker WM250 spectrometer. 1D
13C spectra using 1H broadband decoupling {1H}13C and gated 1H
(18) Pascal, P. Ann. Chim. Phys. 1910, 19, 5.
(19) Clemente-Juan, J. M.; Mackiewicz, C.; Verelst, M.; Dahan, F.;
Bousseksou, A.; Sanakis, Y.; Tuchagues, J.-P. Inorg. Chem. 2002,
41, 1478.
(14) Sheldrick, G. M. SHELXS-97. Program for Crystal Structure Solution;
University of Go¨ttingen: Go¨ttingen, Germany, 1990.
(15) Sheldrick, G. M. SHELXL-97. Program for the refinement of crystal
structures from diffraction data; University of Go¨ttingen: Go¨ttingen,
Germany, 1997.
(16) International Tables for Crystallography; Kluwer Academic Publish-
ers: Dordrecht, The Netherlands, 1992; Vol. C.
(20) (a) Borra´s-Almenar, J. J.; Clemente-Juan, J. M.; Coronado, E.;
Tsukerblat, B. S. Inorg. Chem. 1999, 38, 6081. (b) Borra´s-Almenar,
J. J.; Clemente-Juan, J. M.; Coronado, E.; Tsukerblat, B. S. J. Comput.
Chem. 2001, 22, 985-991.
(21) James, F.; Roos, M. MINUIT Program, a System for Function
Minimization and Analysis of the Parameters Errors and Correlations.
Comput. Phys. Commun. 1975, 10, 345.
(17) Zsolnai, L.; Pritzkow, H.; Huttner, G. ZORTEP. Ortep for PC, Program
for Molecular Graphics; University of Heidelberg: Heidelberg,
Germany, 1996.
(22) Daidone, G.; Raffa, D.; Maggio, B.; Plescia, S.; Matera, M.; Caruso,
A. Farmaco, Ed. Sci. 1990, 45, 285.
(23) Costes, J. P.; Fenton, D. E. J. Chem. Soc., Dalton Trans. 1983, 2235.
Inorganic Chemistry, Vol. 43, No. 8, 2004 2739

Costes et al.
Scheme 1
Scheme 3
Scheme 2
process, their spectroscopic parameters have been investi-
gated. Surprisingly, the characteristic sharp NH stretching
of the amide function is broadened and lowered in the
infrared spectra (Nujol mulls) of L1H2 and L2H2, implying
that the NH group is involved in a strong hydrogen bond.24
On the contrary, two sharp absorptions are present in the IR
spectra of L3H2 at 3383 and 3350 cm-1. As a consequence,
the CdO stretch is also lowered in the L1H2 ligand (1617
cm-1) while it appears at 1644 cm-1 for L3H2 and L4H3.
NMR results, obtained in DMSO solutions, confirm this
behavior, with a sharp triplet for the amide HN proton at
9.11 ppm resulting from its coupling with the neighboring
methylene group in the case of L3H2, L4H3, and L5H3, while
broad signals are observed at 9.55 ppm for L1H2 and L2H2.
Unique NH stretching bands are also present in the infrared
spectra of L4H3 and L5H3 (3380 cm-1). Amide II bands are
not easily assigned, due to presence of CdC and imine Cd
N bands in the same spectral zone.
In order to complete the characterization of the complexes,
we have performed a detailed study of the 1H and 13C NMR
spectra of the L5H3 ligand. 1H-13C HMQC-GS, HMQC-LR,
1
and H-1H COSY experiments allowed us to assign the
1
whole sets of H and 13C signals. Eventually, IR and NMR
data do confirm the structure of these asymmetrical poly-
dentate ligands.
Molecular Structure of [L6Mn(CH3OH)2], 1, [L5 Mn4-
4
(H2O)2](CH3OH)2, 2, and [L4Mn(CH3OH)]n, 3. ZORTEP
views of the molecular structure of the manganese(III)
complexes 1-3 are sketched in Figures 1-3, respectively.
Relevant bond distances and angles are gathered in Table 2.
The racemic 1,2-diaminopropane used to prepare L2H2
may yield both geometrical and optical isomers. The NMR
study of L2H2 clearly demonstrates that the geometrical
isomer where the methyl substituent is remote from the amide
function is the only one obtained. Furthermore, the achiral
P1h space group of complex 1 requires the presence of both
reaction of the L1H2, L2H2, and L3H2 half-unit ligands with
salicylaldehyde yields L5H3, L6H3, and L4H3, respectively.
These new asymmetrical ligands possess an inner tetradentate
N2O2 coordination site and an outer amido oxygen donor
atom (Scheme 3). The complexes are readily obtained by
aerobic reaction of the preformed polyfunctional ligand or
the ligand prepared in situ with manganese(II) acetate in
methanol in the presence of sodium hydroxide. Within 2-3
days, the desired complexes were obtained as crystals from
the resulting reaction media with satisfying yields.
IR and NMR Data. Considering that the original half-
unit ligands L1H2, L2H2, and L3H2 are the cornerstone of the
(24) Silverstein, R. M.; Webster, F. W. Spectrometric Identification of
Organic Compounds, 6th Ed.; John Wiley: New York, 1975.
2740 Inorganic Chemistry, Vol. 43, No. 8, 2004

MnIII Complexes with Asymmetric Trianionic Ligands
Figure 1. Molecular plot for 1 with ellipsoids drawn at the 50% probability
level.
Figure 3. Structure of the tetranuclear unit of complex 2. Symmetry
1
operation: ′, 1 - x, y, /2 - z.
hydrogen-bonded to two different MeOH molecules coor-
dinated to the previous and next manganese centers. This
arrangement creates an infinite ribbon with two slightly
different Mn‚‚‚Mn distances (6.8880(6) and 6.9615(6) Å).
Furthermore, π-π stackings involving the phenyl rings of
the salicylaldimine part of the ligand operate between the
ribbons. Alternation of these stacked cycles yields a two-
dimensional arrangement of the neutral complex molecules
running parallel to the c axis, with a Mn‚‚‚Mn separation of
7.3790(6) Å (Figure S1).
The structures of complexes 2 and 3 are significantly
different from that of complex 1: their amido oxygen atoms
are involved in the coordination process as well as the related
nitrogen atom, allowing the amido function to actually bridge
adjacent manganese(III) ions, thus leading to polynuclear
structures. In both cases, the bridge is constituted by an
equatorial Namido donor and its related Oamido as axial donor
to the adjacent MnIII ion.
The actual structure of [L4Mn(CH3OH)]n, 3, is an infinite
zigzag chain of six-coordinated MnIII ions (Figure 2). As in
the previous complex 1, the N2O2 donor set of the asym-
metrical ligand constitutes the equatorial coordination plane
while the apical positions of the octahedron are occupied
by oxygen atoms from a solvent molecule (methanol) and
from the amido function of a neighboring complex molecule.
The MnIII ion is slightly displaced from the mean equatorial
plane (0.05 Å) toward the methanol molecule although the
Mn-Oamido bond is shorter (2.219(1) Å) than the Mn-
Omethanol one (2.316(1) Å). The central Mn-N-C-C-N
five-membered ring is not planar and has a λ gauche
conformation. As a whole, the ligand is less distorted than
in 1, with only one phenyl ring deviating from the N2O2
equatorial coordination plane. The L4Mn constituting units
are organized into infinite zigzag chains with a head to tail
arrangement allowing coordination of the amido oxygen of
each unit to the metal ion of the next unit in the chain. In a
zigzag chain, two arrays of parallel molecules may be
Figure 2. Molecular plot for 3 with ellipso¨ıds drawn at the 50% probability
level. Symmetry operations: i, 1 - x, 1/2 + y, 1/2 - z; ii, 1 - x, -1/2 + y,
1/2 - z.
enantiomers in the unit cell. The MnIII ion of complex 1 is
coordinated to the amido and imine nitrogen and the two
phenoxo oxygen atoms while the amide oxygen atom is not
involved in coordination (Figure 1). The four donor atoms
of the ligand form the equatorial plane of a distorted
octahedron around manganese, while the apical positions are
occupied by the oxygen atom of two methanol molecules.
The axial Mn-O bonds (2.264(2) and 2.290(1) Å) are longer
than the basal ones: 1.857(1) and 1.897(1) Å for Mn-O,
and 1.960(2) and 2.005(2) Å for Mn-N. The central Mn-
N-C-C-N five-membered ring is not planar and has a δ
conformation for the S enantiomer; by symmetry, the R
enantiomer has a λ conformation: the methyl substituent of
both enantiomers is thus in an equatorial position. The
equatorial N2O2 donor atoms are not strictly coplanar, but
alternately displaced by 0.05 Å from the mean Mn, O1, N1,
N2, O2 plane. Both phenyl rings deviate from this mean
plane in such a way that the complex molecule displays a
boat-shaped conformation. The neutral molecules of 1 are
linked together by two hydrogen bonds involving the axial
MeOH molecules and the amide oxygen atoms. Due to their
head to tail arrangement, the amido oxygen atoms are
Inorganic Chemistry, Vol. 43, No. 8, 2004 2741

Costes et al.
ø
Figure 5. Thermal dependence of MT for 1 at 0.1 T. The full line (s)
corresponds to the best data fit.
of the amido moiety) < Mn-O(phenoxo of the imine
moiety) < Mn-Namido < Mn-Nimine < Mn-Oamido < Mn-
O(MeOH) < Mn-O(H2O).
Figure 4. ZORTEP plot of the asymmetric unit for 2 with ellipsoids drawn
at the 50% probability level.
distinguished: starting from a molecule ranked number n,
the molecules ranked n, n + 2, n + 4, and so forth, are
parallel to each other while the molecules n + 1, n + 3, and
so forth, form a second array of parallel molecules. The angle
between the two arrays is equal to 38.2°.
Magnetic Properties. The magnetic susceptibility of
complexes 1, 2, and 3 has been measured in the 2-300 K
temperature range in a 0.5 T applied magnetic field. The
magnetic behavior of complex 1 is shown in Figure 5 as the
thermal variation of the øMT versus T plot. øM is the molar
magnetic susceptibility corrected for the diamagnetism of
the ligands.18 The øMT product is practically constant in the
300-50 K range with an observed value (3.05 ( 0.03 cm3
K mol-1) corresponding to an isolated high-spin MnIII ion.
On further lowering the temperature, øMT decreases down
to 1.66 cm3 K mol-1 at 2 K. The molecular structure of 1
shows that the metal centers are linked by hydrogen bonds
and π-π stacking, and it is known that such interactions
are able to transmit magnetic interactions.25 As the π-π
stackings are located in the equatorial plane of the Mn
centers, their effect may be anticipated to be predominant.
From a magnetic point of view, the two-dimensional ar-
rangement of complex 1 may then be reduced to a dinuclear
one. The experimental magnetic data may then be analyzed
In complex 2, [L5 Mn4(H2O)2](CH3OH)2, four MnIII ions
4
are linked together by four amido groups to form a
parallelogram shaped tetranuclear species (Figure 3) com-
posed of two asymmetric units, each one including one L5-
Mn and one L5Mn(H2O) constituting units as shown in Figure
4. As a result, the coordination of the two metal ions is
different: Mn1 is six-coordinate while Mn2 is five-
coordinate. The apical positions of the Mn1 coordination
octahedron are occupied by the amido oxygen and a water
molecule while the N2O2 equatorial donor set from L5 is
strictly planar, the MnIII deviation from this plane being
negligible (0.0100(5) Å). The apical position of the Mn2
square-pyramidal coordination is occupied by an amido
oxygen atom. The four basal N2O2 donor atoms deviate from
the mean coordination plane by less than 0.06 Å while Mn2
and the amido oxygen atom are displaced in the same
direction by 0.1921(4) and 2.554(3) Å, respectively. The
Mn2-O4 apical bond length (2.074(3) Å) is slightly larger
than the equatorial Mn-O bonds (Mn2-O5 ) 1.878(2) and
Mn2-O6 ) 1.839(3) Å). A larger difference (ca. 0.44 Å) is
observed for the Mn1-O bonds. Furthermore, the Mn1-
on the basis of the spin Hamiltonian H ) -2JSMn1SMn2
+
DSz2Mn, where D is the axial single-ion zero field splitting
(ZFS). The best fit yields an interaction parameter equal to
- 0.2 cm-1 with g ) 2.03, D ) - 0.01 cm-1, and an
agreement factor R ()∑[(øT)obsd - (øT)calcd]2/∑[(øT)obsd]2)
of 3 × 10-5. However, almost equally good fits may be
obtained for D values ranging from 3 to -3 cm-1. This
indetermination of the axial single-ion ZFS of MnIII was
confirmed by an error-surface plot showing that while the
value of J is well determined by the fitting procedure, the
value of D is not.
Oamido bond is significantly longer than the related Mn2-O
bond. The dimethyl group of the diamino chain is remote
from the amido function. The central Mn-N-C-C-N five-
membered ring is not planar with a λ gauche conformation
for the five-coordinate Mn2, and a δ conformation for the
six-coordinate Mn1. The edges of the parallelogram shaped
tetranuclear species equal 5.971(2) and 6.149(2) Å while its
diagonals equal 7.529(3) and 8.638(3) Å. The shortest
metal-metal intercluster contact of 6.747(1) Å precludes
significant intermolecular magnetic interactions. A methanol
molecule, not involved in coordination, is hydrogen bonded
to the water molecule coordinated to the octahedral MnIII
ion and to the phenoxo oxygen atom linked to the five-
coordinate MnIII ion.
The magnetic data obtained for complex 3 are shown in
Figure 6. At 300 K, the øMT product, 3.07 cm3 K mol-1,
corresponds to the value expected for an isolated high-spin
MnIII ion. It decreases very smoothly down to 2.93 cm3 K
mol-1 at 150 K and then more steeply, reaching 1.27 cm3 K
mol-1 at 10 K. Further temperature decrease results in a sharp
øMT increase with a maximum of 2.08 cm3 K mol-1at 5 K,
(25) Colacio, E.; Costes J.-P.; Kivekas, R.; Laurent, J.-P.; Ruiz, J.;
Sundberg, M. Inorg. Chem. 2002, 41, 1478. Vazquez, M.; Taglietti,
A.; Gatteschi, D.; Sorace, L.; Sangregorio, C.; Gonzalez, A. M.;
Maneiro, M.; Pedrido, R. M.; Bermejo, M. R. Chem. Commun. 2003,
1840.
It is worth noticing that in the three complexes the bond
lengths are in the same increasing order: Mn-O(phenoxo
2742 Inorganic Chemistry, Vol. 43, No. 8, 2004

MnIII Complexes with Asymmetric Trianionic Ligands
seeming unreasonable in view of the quality of the micro-
crystalline sample, we then considered a model involving
one J parameter and two D terms. Indeed, considering their
ligand environment, the four Mn centers of the tetranuclear
complex 2 cannot have the same axial single-ion ZFS
parameter: in the following, D1 is related to the six-
coordinate Mn centers and D2 to the five-coordinate Mn
centers. The best fit (R ) 1 × 10-4) was obtained for the
following parameter values: J ) -1.1 cm-1, D1 ) 2.2 cm-1,
D2 ) -2.8 cm-1, g ) 1.97. Extensive calculations were then
carried out in order to draw several error-surface plots: the
D versus J error-surfaces showed that the value of J is unique
and well determined by the fitting procedure; the D2 versus
D1 error-surfaces showed two symmetry-related minima
corresponding, as expected, to the D1 T D2 permutation.
The D1 ) 2.2 cm-1, D2 ) -2.8 cm-1 couple may be
considered as having more physical meaning than its D1 )
-2.8 cm-1, D2 ) 2.2 cm-1 counterpart: the square pyramidal
ligand environment of Mn2 (Mn2′) may be considered as
yielding larger axial elongation than the axially elongated
octahedral ligand environment of Mn1 (Mn1′). The obtained
D values are in the range of those previously reported.8e,27
Positive D parameters are usually associated with either
tetragonal compression or trigonal bipyramidal five-coor-
dination.27a,28 However, by considering the interaction be-
tween the ground state and LMCT states with the valence
bond configuration interaction (VBCI) model, it has been
recently shown that D can be positive for tetragonally
elongated MnIII complexes.29
ø
Figure 6. Thermal dependence of MT for 3 at 0.1 T. The full line (s)
corresponds to the best data fit.
ø
Figure 7. Thermal dependence of MT for 2 at 0.1 T. The full line (s)
corresponds to the best data fit.
followed by a steep decrease down to 0.99 cm3 K mol-1 at
2 K. For an infinite chain of /2 local spins, the simpler
analytical expression that may be used to fit the experimental
data derives from Fisher’s expression:26
4
øT ) [Ng2â2S(S + 1)/3k][(1 + u)/(1 - u)] with
u ) coth[-2JS(S + 1)/kT] - [kT/-2JS(S + 1)]
The best agreement between experimental and calculated data
from 300 to 20 K corresponds to J ) -1.1 cm-1 and g )
2.05 with an agreement factor R ()∑[(øT)obsd - (øT)calcd]2/
∑[(øT)obsd]2) of 3.6 × 10-4. It is not possible to fit the
experimental data in the low-temperature range (20-2 K).
Indeed, the sharp increase is reminiscent of a magnetic phase
transition triggered by a 3D ordering, or a spin canting
phenomenon. In complex 3, the 38.2° angle between the two
arrays of parallel spins (see molecular structure section)
clearly indicates that spin canting is most probably respon-
sible for the magnetic phase transition at low temperature.
Magnetization studies at 2 K show the presence of an
hysteresis loop with a small coercive field (260 G) and a
remnant magnetization of 0.24 Nâ (Figure S2 in Supporting
Information). As expected for spin canting, the saturation
magnetization (1.84 Nâ) does not reach the 4Nâ value of
high-spin MnIII.
The magnetic data obtained for complex 2 are shown in
Figure 7. The øMT product decreases smoothly from 11.02
cm3 K mol-1 at 300 K, down to 9.20 cm3 K mol-1 at 50 K,
and then more abruptly down to 1.41 cm3 K mol-1 at 2 K.
An initial fit (not shown) was performed by considering the
simplifying assumption that the four magnetically interacting
MnIII ions are at the vertices of a square (unique J parameter).
A good agreement (R ) 2 × 10-4) with the experimental
data was obtained for the following parameter values: J )
-1.2 cm-1, g ) 1.93, par (paramagnetic impurity) ) 5.6%
(D fixed to 0 cm-1). With the high value obtained for par
Conclusion
Trianionic asymmetrical ligands with amide and imine
functions have been first used to prepare Cu-Gd complexes,
with the aim to promote self-assembly of dinuclear units in
order to obtain new polynuclear systems with a large ground
spin-state.9,30 Our preparative conditions differ from the
synthetic process recently described, where the so-called
“intermediate product” (corresponding to the half-unit) was
not characterized.30 From a synthetic point of view, the most
striking result originates from the presence or absence of
one or two methyl substituents at the remote position of the
diamino fragment in these asymmetrical polydentate ligands,
which allows an impressive variation in the nuclearity of
the manganese complexes. Indeed, it is possible to isolate a
mononuclear complex (1), a tetranuclear one (2), or a 1D
chain (3) when one (L6H3), two (L5H3), or no (L4H3) methyl
substituents are located away from the N2O2 coordination
site, respectively. Another interesting property of these MnIII
(27) (a) Kennedy, B. J.; Murray, K. S. Inorg. Chem. 1985, 24, 1557. (b)
Wieghardt, K. Angew. Chem., Int. Ed. Engl. 1989, 28, 1153. (c) Thorp,
H. H.; Brudvig, G. W. New J. Chem. 1991, 15, 479. (d) Zhang, Z.;
Brouca-Cabarrecq, C.; Hemmert, C.; Dahan, F.; Tuchagues, J. P. J.
Chem. Soc., Dalton Trans. 1995, 1453.
(28) Whittaker, J. W.; Whittaker, M. M. J. Am. Chem. Soc. 1991, 113,
5528.
(29) Mossin, S.; Weihe, H.; Barra, A. L. J. Am. Chem. Soc. 2002, 124,
8764.
(30) (a) Kido, T.; Nagasato, S.; Sunatsuki, Y.; Matsumoto, N. Chem.
Commun. 2000, 2113. Kido, T.; Ikuta, Y.; Sunatsuki, Y.; Ogawa, Y.;
Matsumoto, N. Inorg. Chem. 2003, 42, 398.
(26) Fisher, M. E. Am. J. Phys. 1964, 32, 343.
Inorganic Chemistry, Vol. 43, No. 8, 2004 2743

Costes et al.
complexes originates from the neutrality of the LiMn building
unit. Previously, neutral MnIII complexes have essentially
been obtained by association of a dianionic Schiff base with
a pseudohalide ion in the metal coordination sphere.8 In
addition to this difference, the bridging atom in the present
series is included into the ligand, aside from the coordination
site, thus allowing self-assembling. The almost identical
values of the J interaction parameter in the polynuclear
systems 2 and 3 originate from the fact that an NCO amido
function similarly bridges an equatorial position of one Mn
center (through N) to one axial position of the next Mn center
(through O) in both complexes. This antiferromagnetic
interaction is quite weak in agreement with our previous
result showing that coupling of copper and gadolinium ions
through the same type of NCO bridge is also weak, 0.6 cm-1,
although ferromagnetic.9
Acknowledgment. We thank Dr. A. Mari for his con-
tribution to the magnetic measurements. M.-J.R.D. and M.-
I.F.G. acknowledge the Ministerio de Ciencia y Tecnologia
(MCYT BQU2003-00167) for financial support.
Supporting Information Available: X-ray crystallographic files
including the structural data for in CIF format. Additional figures.
This material is available free of charge via the Internet at
http://pubs.acs.org.
IC0348796
2744 Inorganic Chemistry, Vol. 43, No. 8, 2004