A mixed-valence diacetate-bridged MnII-MnIII complex incorporating a bridging phenolate ligand

Article abstract of DOI:10.1107/S0108270105039910

The synthesis and characterization of a new unsymmetrical dinucleating N,O-donor ligand, 2-[N,N-bis(2-pyridylmethyl)aminomethyl]-6-[N-(3,5-di-tert- butyl-2-oxidobenzyl)-N-(2-pyridylamino)aminomethyl]-4-methylphenol (H ₂Ldtb), as well as the X-r

Full text of DOI:10.1107/S0108270105039910

metal-organic compounds
Acta Crystallographica Section C
Crystal Structure
Communications
We report here the synthesis and X-ray structure of the title
novel mixed-valence MnII±MnIII complex, (I), containing the
unsymmetrical dinucleating ligand Ldtb2 {H2Ldtb is 2-
[N,N-bis(2-pyridylmethyl)aminomethyl]-6-[N-(3,5-di-tert-butyl-
2-oxidobenzyl)-N-(2-pyridylmethylamino)amino]-4-methyl-
phenol} and acetate bridges, as a further interesting structural
model for mixed-valence MnII±MnIII catalase.
ISSN 0108-2701
A mixed-valence diacetate-bridged
MnII±MnIII complex incorporating a
bridging phenolate ligand
The asymmetric unit of (I) consists of a discrete [MnII-
MnIII(Ldtb)(ꢀ-OAc)2]+ cation complex and a tetraphenyl-
borate counter-ion. In the crystal structure, the packing
arrangement is governed by electrostatic forces between ion
pairs. The molecular structure of (I) (Fig. 1) shows that, in the
dinuclear [MnIIIMnII(Ldtb)(ꢀ-OAc)2]+ unit, the MnIII and
MnII ions are bridged by phenolate atom O1 of the Ldtb2
ligand and by two carboxylate groups of the acetate ligands.
The charge distribution is the major contributor to the
enhanced stability of the mixed-valence species, as observed
by Dubois et al. (2003). Atoms N1, N22 and N32, from the
tertiary amine and two pyridine groups (soft side), complete
the octahedral coordination sphere of Mn1, typical of high-
Adailton J. Bortoluzzi, Ademir Neves,* Ricardo A. A.
Couto and Rosely A. Peralta
Â
Â
Departamento de Quõmica ± UFSC, 88040-900 Florianopolis, SC, Brazil
Correspondence e-mail: adajb@qmc.ufsc.br
Received 26 July 2005
Accepted 30 November 2005
Online 14 January 2006
spin MnII (Karsten, Neves, Bortoluzzi, Stahle & Maichle-
È
Mossmer, 2002). A comparison of the bond lengths around the
The synthesis and characterization of a new unsymmetrical
dinucleating N,O-donor ligand, 2-[N,N-bis(2-pyridylmethyl)-
aminomethyl]-6-[N-(3,5-di-tert-butyl-2-oxidobenzyl)-N-(2-pyri-
dylamino)aminomethyl]-4-methylphenol (H2Ldtb), as well as
the X-ray crystal structure of its corresponding mixed-valence
diacetate-bridged manganese complex, di-ꢀ-acetato-ꢀ-{2-[N,-
N-bis(2-pyridylmethyl)aminomethyl]-6-[N-(3,5-di-tert-butyl-
2-oxidobenzyl)-N-(2-pyridylamino)aminomethyl]-4-methyl-
phenolato}dimanganese(II,III) tetraphenylborate, [MnII-
MnIII(C42H49N5O2)(C2H3O2)2](C24H20B), are reported. The
complex may be regarded as an interesting structural
model for the mixed-valence MnII±MnIII state of manganese
catalase.
È
six-coordinated Mn ion (Table 1; mean 2.201 A) are in good
agreement with those reported by Karsten, Neves, Bortoluzzi,
II
Ê
II
È
È
Strahle & Maichle-Mossmer (2002) for the compound [Mn -
MnIII(bpbpmp)(OAc)2]BF4, (II), where H2bpbpmp is the
ligand {2-[N,N-bis(2-pyridylmethyl)aminomethyl]-6-[(2-hy-
droxybenzyl)(2-pyridylmethyl)]aminomethyl}-4-methylphenol,
and by Karsten, Neves, Bortoluzzi, Lanznaster & Drago,
(2002) in the compound [MnIIFeIII(bpbpmp)(OAc)2](ClO4),
(III).
Comment
Catalases are enzymes responsible for hydrogen peroxide
dismutation, according to the reaction 2H2O2 ! O2 + 2H2O.
The dimanganese catalase extracted from Thermus thermo-
philus was recently characterized by X-ray diffraction analysis,
which con®rmed the existence of a dinuclear manganese
centre in the active site situated in a cavity rich in hydrophobic
residues (see scheme) (Barynin et al., 1997; Antonyuk et al.,
Ê
2000). The MnÁ Á ÁMn distance is 3.18 A in the reduced form
II
III
Ê
(Mn2 ) and 3.14 A in the oxidized form (Mn2 ). On the other
hand, the mixed-valence MnII±MnIII oxidation state is the
least well characterized, and the Lactobacillus plantarum
enzyme has not been shown to form a stable MnII±MnIII form
(Waldo et al., 1995; Khangulov et al., 1990). In fact, the design
of biomimetic systems aiming to help in the understanding of
The distances around MnII average 2.210 A in (II) and
Ê
Ê
2.206 A in (III), with the same N3O3 environment as (I). The
distances from the pyridine N atom to Mn1 in (I) are quite
Ê
similar [2.237 (3) and 2.262 (4) A], while the distance of the N
atom trans to the oxygen bridge is slightly longer, re¯ecting
the mechanism of H2O2 disproportionation by manganese
catalases has attracted many research groups (Wu et al., 2004).
Acta Cryst. (2006). C62, m27±m29
DOI: 10.1107/S0108270105039910
# 2006 International Union of Crystallography m27

metal-organic compounds
Figure 1
The molecular structure of (I), with the atom-labelling scheme. Displacement ellipsoids are drawn at the 40% probability level. C atoms are shown as
small circles of arbitrary size and H atoms have been omitted for clarity.
the weak trans effect of the phenolate group. The longest bond
on the N3O3 side is that to tertiary amine atom N1
Ê
[2.335 (3) A]. This value is rather similar to those found in (II)
complexes (I) and (II), the E1/2 value of the redox couple
[MnIIMnIII]/[MnIIMnII] is cathodically shifted by 55 mV, a
result which is consistent with the electron-donating effect of
the tert-butyl groups and the slightly shorter MnIIIÐOphenolate
bond length in complex (I), as described above. As reported
by Miyasaka et al. (2003), the redox potentials can exhibit a
linear correlation with the Hammett substituent constant ꢁp.
In summary, a new unsymmetrical mixed-valence MnII±
MnIII complex has been structurally characterized and
provides the possibility of studies of peroxide dispropor-
tionation and of correlating the redox potential and ligand
®eld contribution to the rate and ef®ciency of this catalytic
process.
Ê
and (III) [2.313 (2) and 2.279 (3) A, respectively].
The coordination sphere of Mn2 is complemented by atoms
N4 and N42 from the tertiary amine and pyridine group, and
atom O50 from the terminal phenolate (hard side). The bond
lengths around MnIII (mean 2.041 A) are quite similar to those
Ê
Ê
found in (II) (mean 2.052 A), and the longer axial bond
Ê
2.278 (3) A and Mn2ÐO62
lengths [Mn2ÐN42
Ê
=
2.129 (3) A] are consistent with a Jahn±Teller distortion of this
=
high-spin d4 ion. The terminal MnIIIÐOphenolate bond
Ê
Ê
[1.825 (3) A] and MnÁ Á ÁMn distance [3.466 (1) A] are slightly
Ê
shorter than those found in (II) [1.852 (2) and 3.497 A,
respectively], as expected, due to the effect caused by the tert-
Experimental
butyl substituents.
The ligand H2Ldtb was prepared as follows. To a solution of 2-[bis-
(2-pyridylmethyl)aminomethyl]-6-[(2-pyridylmethyl)aminomethyl]-
4-methylphenol (Greatti et al., 2004) (3.4 g, 8 mmol) in dichloro-
methane, triethylamine (1.21 g, 12 mmol) and 4,6-di-tert-butyl-2-
(chloromethyl)phenol (Sokolowski et al., 1997) (3.02 g, 12 mmol)
were added. The resulting mixture was allowed to react for 24 h while
being stirred at room temperature. The product was extracted with
aqueous NaHCO3 solution (8 Â 50 ml). The organic layers were dried
over Na2SO4, the solvent was removed under reduced pressure and a
pale-yellow solid was obtained (4.65 g, 7.2 mmol, yield 90%).
1H NMR (CDCl3): ꢂ 8.54, 7.61, 7.53, 7.15, 6.97, 6.84 (16H, aromatic
H), 3.92, 3.85, 3.84, 3.80 (s, 12H, CH2), 2.23 (s, CH3), 1.42, 1.25 (s, tert-
butyl). Complex (I) was prepared by adding Mn(OAc)2Á4H2O
(1.0 mmol) and NaOAc (1.0 mmol) to a methanolic solution of the
ligand H2Ldtb (0.5 mmol) with stirring at 313 K for 20 min. The
solution immediately turned dark red and then NaBPh4 (0.5 mmol)
was added. After slow evaporation of the solvent, dark-red crystals of
(I) suitable for X-ray analysis were isolated (yield 82%).
The Mn1ÐO1ÐMn2 bridging angle of 116.8 (1)ꢀ falls
within the range found for similarly coordinated mixed-
valence manganese dimers with the structural [MnIIIMnII(ꢀ-
phenoxo)(ꢀ-OAc)2] unit. In (II), this angle is 116.6ꢀ, in
[Mn2(L-Im)(ꢀ-OAc)2]+ it is 116.8ꢀ [HL-Im is 2,6-bis({bis[(1-
methylimidazol-2-yl)methyl]amino}methyl)-4-methylphenol;
Buchanan et al., 1988], in [Mn2(bpmp)(ꢀ-OAc)2]+ it is 114.4ꢀ
{Hbpmp
is
2,6-bis[bis(2-pyridylmethyl)aminomethyl]-4-
methylphenol; Diril et al., 1989} and in [Mn2(ꢀ-L)(ꢀ-OAc)2-
(H2O)]2+ it is 115.59ꢀ {HL is 2-[N-bis(2-pyridylmethyl)-
aminomethyl]-6-[N-(benzyl)(2-pyridylmethyl)aminomethyl]-
4-methylphenol; Dubois et al., 2003}.
Redox potentials are strongly dependent on the electronic
character of the ligand substituent and on the asymmetry of
the ligand. It is interesting to note that, despite the similarities
of the averaged bond lengths and angles in the isostructural
ꢁ
m28 Bortoluzzi et al.
[Mn2(C42H49N5O2)(C2H3O2)2](C24H20B)
Acta Cryst. (2006). C62, m27±m29

metal-organic compounds
Crystal data
factors of 0.7 and 0.3. Some non-H atoms show abnormally high
displacement parameters, but all these atoms were re®ned with
anisotropic displacement parameters, with a positive de®nite thermal
tensor. This gives high Ueq(max):Ueq(min) ratios for C and H atoms.
H atoms were added in their calculated positions and included in the
Ê
structure-factor calculations, with CÐH distances of 0.93±0.96 A and
Uiso(H) = 1.2Ueq(C), or 1.5Ueq(C) for methyl atoms.
3
[Mn2(C42H49N5O2)(C2H3O2)2]-
(C24H20B)
Mr = 1203.04
Monoclinic, P21=n
a = 16.492 (3) A
Dx = 1.244 Mg m
Mo Kꢄ radiation
Cell parameters from 25
re¯ections
ꢅ = 9.9±13.2ꢀ
ꢀ = 0.45 mm
T = 293 (2) K
Ê
Ê
1
b = 16.804 (3) A
Ê
c = 24.519 (5) A
ꢃ = 109.07 (3)ꢀ
Irregular block, dark red
0.47 Â 0.40 Â 0.13 mm
Data collection: CAD-4 EXPRESS (Enraf±Nonius, 1994); cell
re®nement: SET4 in CAD-4 EXPRESS; data reduction: HELENA
(Spek, 1996); program(s) used to solve structure: SIR97 (Altomare et
al., 1999); program(s) used to re®ne structure: SHELXL97 (Shel-
drick, 1997); molecular graphics: ORTEP-3 (Farrugia, 1997); software
used to prepare material for publication: SHELXL97.
3
Ê
V = 6422 (2) A
Z = 4
Data collection
Enraf±Nonius CAD-4
diffractometer
!/2ꢅ scans
4980 re¯ections with I > 2ꢁ(I)
Rint = 0.052
ꢅmax = 25.0ꢀ
Absorption correction: scan
[(North et al., 1968) and
PLATON (Spek, 2003)]
Tmin = 0.829, Tmax = 0.937
11638 measured re¯ections
11223 independent re¯ections
h = 0 ! 19
This work was supported by FINEP and CNPq.
k = 19 ! 0
l = 29 ! 27
3 standard re¯ections
every 200 re¯ections
intensity decay: 1%
Supplementary data for this paper are available from the IUCr electronic
archives (Reference: TA1508). Services for accessing these data are
described at the back of the journal.
Re®nement
Re®nement on F2
R[F2 > 2ꢁ(F2)] = 0.052
wR(F2) = 0.127
S = 0.86
11223 re¯ections
784 parameters
H-atom parameters constrained
w = 1/[ꢁ2(Fo2) + (0.058P)2]
where P = (Fo2 + 2Fc2)/3
(Á/ꢁ)max < 0.001
References
Altomare, A., Burla, M. C., Camalli, M., Cascarano, G., Giacovazzo, C.,
Guagliardi, A., Moliterni, A. G. G., Polidori, G. & Spagna, R. (1999). J.
Appl. Cryst. 32, 115±119.
Antonyuk, S. V., Melik-Adamyan, W. R., Popov, A. N., Lamzin, V. S.,
Hempstead, P. D., Harrison, P. M., Artymiuk, P. J. & Barynin, V. V. (2000).
Crystallogr. Rep. 45, 111±122.
Barynin, V. V., Hempstead, P. D., Vagin, A. A., Antonyuk, S. V., Melik-
Adamyan, W. R., Lamzin, V. S., Harrison, P. M. & Artymiuk, P. J. (1997). J.
Inorg. Biochem. 67, 196.
Buchanan, R. M., Oberhausen, K. J. & Richardson, J. F. (1988). Inorg. Chem.
27, 971±973.
Diril, H., Chang, H.-R., Nilges, M. J., Zhang, X., Potenza, J. A., Schugar, H. J.,
Isied, S. S. & Hendrickson, D. N. (1989). J. Am. Chem. Soc. 111, 5102±5114.
Dubois, L., Xiang, D.-F., Tan, X.-S., Pecaut, J., Jones, P., Baudron, S., Le Pape,
L., Latour, J.-M., Baffert, C., Chardon-Noblat, S., Collomb, M.-N. &
Deronzier, A. (2003). Inorg. Chem. 42, 750±760.
3
Ê
Áꢆmax = 0.24 e A
3
Ê
0.31 e A
Áꢆmin
=
Table 1
Selected geometric parameters (A, ).
ꢀ
Ê
Mn1ÐO61
Mn1ÐO71
Mn1ÐO1
Mn1ÐN32
Mn1ÐN22
Mn1ÐN1
2.067 (3)
2.139 (3)
2.161 (2)
2.237 (3)
2.262 (4)
2.335 (3)
Mn2ÐO50
Mn2ÐO1
Mn2ÐO72
Mn2ÐN4
Mn2ÐO62
Mn2ÐN42
1.823 (2)
1.905 (2)
1.984 (3)
2.118 (3)
2.129 (3)
2.278 (3)
O61ÐMn1ÐO71
O61ÐMn1ÐO1
O71ÐMn1ÐO1
O61ÐMn1ÐN32
O71ÐMn1ÐN32
O1ÐMn1ÐN32
O61ÐMn1ÐN22
O71ÐMn1ÐN22
O1ÐMn1ÐN22
N32ÐMn1ÐN22
O61ÐMn1ÐN1
O71ÐMn1ÐN1
O1ÐMn1ÐN1
97.80 (13)
100.42 (11)
88.22 (10)
101.59 (13)
87.95 (11)
157.97 (11)
96.88 (14)
164.95 (13)
85.85 (10)
92.38 (12)
169.30 (13)
91.08 (11)
85.76 (10)
72.64 (12)
74.71 (13)
177.69 (12)
O50ÐMn2ÐO72
O1ÐMn2ÐO72
O50ÐMn2ÐN4
O1ÐMn2ÐN4
86.59 (11)
92.36 (10)
88.71 (11)
91.88 (11)
167.14 (12)
92.03 (12)
90.15 (11)
97.88 (12)
94.24 (11)
91.52 (12)
86.42 (11)
89.94 (12)
78.22 (12)
171.59 (12)
116.74 (11)
Enraf±Nonius (1994). CAD-4 EXPRESS. Version 5.1/1.2. Enraf±Nonius,
Delft, The Netherlands.
Farrugia, L. J. (1997). J. Appl. Cryst. 30, 565.
Greatti, A., de Brito, M. A., Bortoluzzi, A. D. & Ceccato, A. S. (2004). J. Mol.
Struct. 688, 185±190.
O72ÐMn2ÐN4
O50ÐMn2ÐO62
O1ÐMn2ÐO62
O72ÐMn2ÐO62
N4ÐMn2ÐO62
O50ÐMn2ÐN42
O1ÐMn2ÐN42
O72ÐMn2ÐN42
N4ÐMn2ÐN42
O62ÐMn2ÐN42
Mn2ÐO1ÐMn1
Karsten, P., Neves A., Bortoluzzi, A. J., Lanznaster, M. & Drago, V. (2002).
Inorg. Chem. 41, 4624±4626.
È
È
Karsten P., Neves A., Bortoluzzi, A. J., Strahle, J. & Maichle-Mossmer, C.
(2002). Inorg. Chem. Commun. 5, 434±438.
Khangulov, S. V., Barynin, V. V., Voevodskaya, N. V. & Grebenko, A. I. (1990).
Biochim. Biophys. Acta Bioenergetics, 1020, 305±310.
Miyasaka, H., Izawa, T., Sugiura, K. I. & Yamashita, M. (2003). Inorg. Chem.
42, 7683±7690.
North, A. C. T., Phillips, D. C. & Mathews, F. S. (1968). Acta Cryst. A24, 351±
359.
N32ÐMn1ÐN1
N22ÐMn1ÐN1
O50ÐMn2ÐO1
È
Sheldrick, G. M. (1997). SHELXL97. University of Gottingen, Germany.
Sokolowski, A., Jochen, M., Weyhermuller, T., Schnepf, R., Hildebrandt, P.,
Hildebrandt, K., Bothe, E. & Wieghardt, K. (1997). J. Am. Chem. Soc. 119,
8889±8900.
Spek, A. L. (1996). HELENA. University of Utrecht, The Netherlands.
Spek, A. L. (2003). J. Appl. Cryst. 36, 7±13.
Waldo, G. S. & Penner-Hahn, J. E. (1995). Biochemistry, 34, 1507±1512.
Wu, A. J., Penner-Hahn, J. E. & Pecoraro, V. L. (2004). Chem. Rev. 104, 903±
938.
The crystals of (I) grew from the mother solution as large prisms,
but these diffracted poorly. Thus, the number of observed re¯ections
in the hkl ®le is small (44%), giving rise to the consistency values
Rint = 0.0518 and Rꢁ = 0.1572. One tert-butyl group is disordered and
its terminal C atoms have two alternative positions, with occupancy
ꢁ
Acta Cryst. (2006). C62, m27±m29
Bortoluzzi et al.
[Mn2(C42H49N5O2)(C2H3O2)2](C24H20B) m29