Magnetic susceptibility and ground-state zero-field splitting in high-spin mononuclear manganese(III) of inverted N-methylated porphyrin complexes: Mn(2-NCH3NCTPP)Br

Article abstract of DOI:10.1021/ic800490t

The crystal structures of diamagnetic dichloro(2-aza-2-methyl-5,10,15,20- tetraphenyl-21-carbaporphyrinato-N,N′,N″)-tin(IV) methanol solvate [Sn(2-NCH₃NCTPP)Cl₂·2(0.2MeOH); 6·2(0.2MeOH)] and paramagnetic bromo(2-aza-2-methyl-5,10,15,20- tetraphenyl-21-carbaporphyrinato-N,N′,N″)-manganese(III) [Mn(2-NCH₃NCTPP)Br; 5] were determined. The coordination sphere around Sn⁴⁺ in 6·2(0.2MeOH) is described as six-coordinate octahedron (OC-6) in which the apical site is occupied by two transoid Cl ^- ligands, whereas for the Mn³⁺ ion in 5, it is a five-coordinate square pyramid (SPY-5) in which the unidentate Br^- ligand occupies the axial site. The g value of 9.19 (or 10.4) measured from the parallel polarization (or perpendicular polarization) of X-band EPR spectra at 4 K is consistent with a high spin mononuclear manganese(III) (S = 2) in 5. The magnitude of axial (D) and rhombic (E) zero-field splitting (ZFS) for the mononuclear Mn(III) in 5 were determined approximately as -2.4 cm^-1 and -0.0013 cm^-1, respectively, by paramagnetic susceptibility measurements and conventional EPR spectroscopy. Owing to weak C(45)-H(45A)...Br(1) hydrogen bonds, the mononuclear Mn(III) neutral molecules of 5 are arranged in a one-dimensional network. A weak Mn(III)...Mn(III) ferromagnetic interaction (J = 0.56 cm^-1) operates via a [Mn(1)-C(2)-C(1)-N(4)-C(45)-H(45A)...Br(1)-Mn(1)] superexchange pathway in complex 5.

Full text of DOI:10.1021/ic800490t

Inorg. Chem. 2008, 47, 7202-7206
Magnetic Susceptibility and Ground-State Zero-Field Splitting in
High-Spin Mononuclear Manganese(III) of Inverted N-Methylated
Porphyrin Complexes: Mn(2-NCH3NCTPP)Br#
Sheng-Wei Hung,† Fuh-An Yang,† Jyh-Horung Chen,*,† Shin-Shin Wang,‡ and Jo-Yu Tung*,§
Department of Chemistry, National Chung-Hsing UniVersity, Taichung 40227, Taiwan, Material
Chemical Laboratories, Hsin-Chu 300, Taiwan, and Department of Occupational Safety and
Health, Chung Hwai UniVersity of Medical Technology, Tainan 717, Taiwan
Received March 20, 2008
The crystal structures of diamagnetic dichloro(2-aza-2-methyl-5,10,15,20-tetraphenyl-21-carbaporphyrinato-N,N′,N′′)-
tin(IV) methanol solvate [Sn(2-NCH3NCTPP)Cl2 · 2(0.2MeOH); 6· 2(0.2MeOH)] and paramagnetic bromo(2-aza-2-
methyl-5,10,15,20-tetraphenyl-21-carbaporphyrinato-N,N′,N′′)-manganese(III) [Mn(2-NCH3NCTPP)Br; 5] were de-
termined. The coordination sphere around Sn4+ in 6· 2(0.2MeOH) is described as six-coordinate octahedron (OC-
6) in which the apical site is occupied by two transoid Cl- ligands, whereas for the Mn3+ ion in 5, it is a five-
coordinate square pyramid (SPY-5) in which the unidentate Br- ligand occupies the axial site. The g value of 9.19
(or 10.4) measured from the parallel polarization (or perpendicular polarization) of X-band EPR spectra at 4 K is
consistent with a high spin mononuclear manganese(III) (S ) 2) in 5. The magnitude of axial (D) and rhombic (E)
zero-field splitting (ZFS) for the mononuclear Mn(III) in 5 were determined approximately as -2.4 cm-1 and -0.0013
cm-1, respectively, by paramagnetic susceptibility measurements and conventional EPR spectroscopy. Owing to
weak C(45)-H(45A) · · · Br(1) hydrogen bonds, the mononuclear Mn(III) neutral molecules of 5 are arranged in a
one-dimensional network. A weak Mn(III) · · · Mn(III) ferromagnetic interaction (J ) 0.56 cm-1) operates via a
[Mn(1)-C(2)-C(1)-N(4)-C(45)-H(45A) · · · Br(1)-Mn(1)] superexchange pathway in complex 5.
Introduction
(NCP is also known as inverted porphyrin or 2-aza-21-
carbaporphyrin). Recently, essential progress has been observed
in the literature concerning the synthesis and characterization
of NCP and its derivatives. Hung et al.4 reported the X-ray
structure of a five-coordinate manganese(III) complex of
N-confused 5,10,15,20-tetraphenylporphyrin Mn(NCTPP)Br (1)
(NCTPP, dianion of 5,10,15,20-tetraphenyl-N-confused por-
phyrin) and Harvey and Ziegler5 described the structural
characterization of a six-coordinate Mn(III) complex of Mn(NCT-
PP)(py)2 (2). Krzystek and co-workers6 reported the high-
frequency and -field electron paramagnetic resonance (HFEPR)
study of complex 2. It turned out that the inversion of a single
pyrrole ring of 2 greatly changes the equatorial ligand field
exerted and leads to large magnitudes of both the axial and
rhombic ZFS (respectively, D ) -3.08 cm-1, E ) -0.61
cm-1), which are unprecedented in other Mn(III) porphyrinoids.6
In general, Electron Paramagnetic Resonance (EPR) spec-
troscopy at conventional microwave frequencies [X-band, ∼9
GHz (0.3 cm-1); Q-band, ∼35 GHz (1.2 cm-1)] is not
applicable to “EPR-silent” systems with integral-spin ground
states where the zero-field splitting (ZFS) is larger than the
microwave quantum, in particular, where the ZFS interaction
approaches axial symmetry.1–3 Thus, conventional EPR studies
of high-spin manganese(III) (d4, S ) 2) compounds are rather
limited especially for the N-confused porphyrin (NCP) complex
* To whom correspondence should be addressed. E-mail: jyhhchen@
dragon.nchu.edu.tw (J.H.C.), joyuting@mail.hwai.edu.tw (J.Y.T.).
# Dedicated to Prof. Rob Dunbar (Case Western Reserve University) on
the occasion of his 65th birthday.
†
National Chung-Hsing University.
Material Chemical Laboratories.
Chung Hwai University of Medical Technology.
‡
§
(1) Dexheimer, S. L.; Gohdes, J. W.; Chan, M. K.; Hagen, K. S.;
Armstreng, W. H.; Klein, M. P. J. Am. Chem. Soc. 1989, 111, 8923.
(2) Talsi, E. P; Bryliakov, K. P. MendeleeV Commun. 2004, 111.
(3) Bryliakov, K. P.; Bahushkin, D. E.; Talsi, E. P. MendeleeV Commun.
1999, 29.
(4) Bohle, D. S.; Chen, W. C.; Hung, C. H. Inorg. Chem. 2002, 41, 3334.
(5) Harvey, J. D.; Ziegler, C. J. Chem. Commun. 2003, 2890.
(6) Harvey, J. D.; Ziegler, C. J.; Telser, J.; Ozarowski, A.; Krzystek, J.
Inorg. Chem. 2005, 44, 4451.
7202 Inorganic Chemistry, Vol. 47, No. 16, 2008
10.1021/ic800490t CCC: $40.75  2008 American Chemical Society
Published on Web 07/23/2008

InWerted N-Methylated Porphyrin Complexes
Recently, Ziegler et al.7 reported an improved methodol-
ogy for the synthesis of 2-N-methyl-5,10,15,20-tetraphenyl-
21-carbaporphyrin, 2-NCH3NCTPPH (3). Compound 3 in
this work was prepared in the way described by the Ziegler
group using CH3I and p-xylene in 48.6% yield. Unlike the
NH tautomerism that exists in NCTPPH2 (4),8 the free base
3 has only one stable form. Thus, a placement of a Mn(III)
ion (I ) 5/2) with a paramagnetism and a Sn(IV) ion (I )
1/2) with a diamagnetism in a core of N-methylated
carbaporphyrin provides a promising route to synthesize a
paramagnetic complex, bromo(2-aza-2-methyl-5,10,15,20-
tetraphenyl-21-carbaporphyrinato-N,N′,N′′)-manganese(I-
II) [Mn(2-NCH3NCTPP)Br; 5] and a diamagnetic complex,
dichloro(2-aza-2-methyl-5,10,15,20-tetraphenyl-21-carbap-
orphyrinato-N,N′,N′′)-tin(IV) [Sn(2-NCH3NCTPP)Cl2; 6].
This new diamagnetic compound 6 is used as a diamagnetic
correction for 5 in the solid-state magnetic susceptibility
measurements.9 In this paper we focus on details of the
manganese(III) electronic structure. Studies of temperature
dependence of the magnetic susceptibility and of the effective
moment show that S ) 2 is the ground state for high-spin
mononuclear Mn3+ in 5 at 20 °C. Application of the
Bleaney-Bowers10 equation permits evaluation of D, |2J|,
and an average g value for powder samples. Measurement
of the ESR spectrum arising from 5 with the S ) 2 state
and application of the spin Hamiltonian (eq 1) permits
derivation of the rhombic ZFS parameter E.
3
3J(H-H) ) 7.2 Hz, o-H] and 7.61 [d, J(H-H) ) 7.2 Hz, o-H];
7.47-7.78 [m, meta and para protons]; 3.30 (s, N-CH3). FAB-MS
m/z (assignment. rel intensity): 154 ([NBA + H]+, 56.82), 761
([Sn(4-NCH3NCTPP)]+, 48.11), 796 ([Sn(4-NCH3NCTPP)Cl]+,
100). UV-vis spectrum, λ (nm) [ε × 10-3, M-1 cm-1] in CH2Cl2:
458 (126.1), 565 (29.8), 606 (31.4), 722 (23.3), 884 (32.2).
Mn(2-NCH3NCTPP)Br (5). A mixture of 2-NCH3NCTPPH (3)
(50 mg, 0.08 mmol) in CH2Cl2 (20 mL) and MnBr2 (52 mg, 0.24
mmol) in MeOH (1 mL) was refluxed for 3 h. After concentrating
it, the residue was dissolved in CH2Cl2 and filtered. The filtrate
was concentrated and the residue was purified by a silica gel column
using CH2Cl2/EA [20% EA (ethyl acetate)] as the eluent to yield
impure 5, which upon further recrystallization from CH2Cl2/EA
afforded 5 (37 mg, 0.049 mmol, 61%) as a pure green solid.
Compound 5 was redissolved in CH2Cl2 and layered with EA to
afford green crystals for single-crystal X-ray analysis. FAB-MS
m/z (assignment. rel intensity): 629 ([4-NCH3NCTPP]+, 27.35), 681
([Mn(4-NCH3NCTPP)]+, 100), 762 ([Mn(4-NCH3NCTPP)Br +
H]+, 4.67). UV-vis spectrum, λ (nm) [ε × 10-3, M-1cm-1] in
CH2Cl2: 396 (35.9), 416 (34.1), 459 (24.6), 508 (59.3), 582 (10.7),
752 (10.1), 815 (12.7), 884 (12.3). Anal. Calcd. for C45H30BrMnN4:
C, 70.90; H, 3.90; N, 7.30. Found: C, 70.49; H, 4.17; N, 7.22.
Magnetic Susceptibility Measurements. The solid-state mag-
netic susceptibilities were measured under helium on a Quantum
Design MPMS5 SQUID susceptometer from 2 to 300 K at a field
of 5 kG. The sample was held in a Kel-F bucket. The bucket had
been calibrated independently at the same field and temperature.
The raw data for 5 were corrected for the molecular diamagnetism.
The diamagnetic contribution of the complex 5 was measured from
an analogous diamagnetic metal complex, that is, 6. The details of
the diamagnetic corrections made can be found in ref 9.
Experimental Section
Spectroscopy. ESR spectra were measured on an X-band Bruker
EMX-10 spectrometer equipped with an Oxford Instruments liquid
helium cryostat. Magnetic field values were measured with a digital
counter. The X-band resonator was a dual-mode cavity (Bruker
ER 4116 DM). 1H NMR spectra were recorded at 599.95 MHz on
a Varian Unity Inova-600 spectrometer using the solvent CDCl3
and δ ) 7.24 as the reference peak. Element analyses were carried
out on an Elementar Vario EL III analyzer.
The positive-ion fast atom bombardment mass spectrum (FABMS)
was obtained in a nitro benzyl alcohol (NBA) matrix using a JEOL
JMS-SX/SX 102A mass spectrometer. UV-vis spectra were
recorded at 20 °C on a Hitachi U-3210 spectrophotometer.
Crystallography. Table 1 presents the crystal data as well as
other informations for 5 and 6·2(0.2MeOH). Measurements were
taken on a Bruker AXS SMART-1000 diffractometer using
monochromatized Mo KR radiation (λ ) 0.71073 Å). Empirical
absorption corrections were made for both complexes. The struc-
tures were solved by direct methods (SHELXTL-97)11 and refined
by the full-matrix least-squares method. All non-hydrogen atoms
were refined with anisotropic thermal parameters, whereas all
hydrogen atoms were placed in calculated positions and refined
with a riding model. The Br coordination to Mn(1) within 5 is
disordered with an occupancy factor of 0.6 for Br(1) and 0.4 for
Br(1′). These Br(1) and Br(1′) atoms were also refined with
anisotropic thermal parameters. Table 2 lists selected bond distances
and angles for both complexes.
Preparation of Complex 2-NCH3NCTPP (3). A solution of
NCTPPH2 (4) (0.5 g, 0.81 mmol) and CH3I (0.3 mL, 2.1 mmol) in
dry p-xylene (10 mL) in the presence of dry Cs2CO3 (0.5 g, 1.5
mmol) was heated for 2 h. After cooling down to room temperature
(rt), the mixture was filtered and purified by column chromato-
graphic separation with EtOAc-CH2Cl2 [1:4 (v/v)] as a green band
on silica gel (70-230 mesh, 60 g). Further recrystallization from
CH2Cl2-MeOH [1:2 (v/v)] afforded 3 (0.3 g, 0.47 mmol, 48.6%)
as a blue solid.
Sn(2-NCH3NCTPP)Cl2 (6). A mixture of 2-NCH3NCTPPH (3)
(50 mg, 0.08 mmol) and SnCl2 (300 mg, 1.6 mmol) was refluxed
in pyridine (10 mL) for 30 min, poured into hexane (50 mL), and
filtered, and the solid was dissolved in CH2Cl2. The resulting CH2Cl2
solution was rotary evaporated to dryness, and the residue was
purified by a silica gel column using CH2Cl2/MeOH (2% MeOH)
as the eluent, which on further recrystallization from CH2Cl2/MeOH
afforded 6 (40 mg, 0.053 mmol, 66%) as a blue solid. Compound
6 was redissolved in CH2Cl2 and layered with MeOH to afford
1
blue crystals for single-crystal X-ray analysis. H NMR (599.95
MHz, CDCl3, 20 °C): δ 8.98 [d, Hꢀ, 3J(H-H) ) 5.4 Hz]; 8.95 [d,
Hꢀ, 3J(H-H) ) 4.8 Hz]; 8.86 [d, Hꢀ, 3J(H-H) ) 4.8 Hz]; 8.82 [d,
Hꢀ, 3J(H-H) ) 4.2 Hz]; 8.81 [d, Hꢀ, 3J(H-H) ) 4.2 Hz]; 8.76 [d,
3
3
Hꢀ, J(H-H) ) 4.2 Hz]; 8.22 [d, J(H-H) ) 4.2 Hz, o-H (ortho
3
3
proton)] and 8.10 [d, J(H-H) ) 4.2 Hz, o-H]; 8.13 [d, J(H-H)
) 7.2 Hz, o-H] and 8.00 [d, J(H-H) ) 7.2 Hz, o-H]; 7.97 [d,
3
(7) Ou, W.; Ding, T.; Cetin, A.; Harvey, J. D.; Taschner, M. J.; Ziegler,
C. J. J. Org. Chem. 2006, 71, 811.
(8) Chmielewski, P. J.; Latos-Grazynski, L. J. Chem. Soc., Perkin Trans.
2 1995, 503.
(11) Sheldrick, G. M. SHELXL-97. Program for Refinement of Crystal
Structure from Diffraction Data; University of Gottingen: Gottingen,
Germany, 1997.
(12) Xie, Y.; Morimoto, T.; Furuta, H. Angew. Chem., Int. Ed. 2006, 45,
6907.
(9) Drago, R. S. Physical Methods for Chemists, 2nd ed.; Saunders College
Publishing: New York, 1992; pp 473-475, 591-593.
(10) Bleaney, B.; Bowers, K. D. Proc. R. Soc. London. 1952, A214, 451.
Inorganic Chemistry, Vol. 47, No. 16, 2008 7203

Hung et al.
Table 1. Crystal Data for 5 and 6·2(0.2MeOH)
45.4H30Cl2N4O0.4
C
formula
Sn〈6·2(0.2MeOH)〉
C45H30N4MnBr (5)
761.58
P21/n
monoclinic
10.1225(18)
16.506(3)
21.104(4)
90
90.989(3)
90
3525.6(10)
4
fw
827.52
P21/n
space group
cryst syst
a, Å
monoclinic
10.0782(10)
8.3363(7)
23.747(2)
90
95.061(2)
90
1987.3(3)
2
b, Å
c, Å
R, deg
ꢀ, deg
γ, deg
V, Å3
Z
F000
835
1.383
0.815
1.106
0.31 × 0.22 × 0.20
2.13 to 26.08
293(2)
3944
3186
1552
1.435
1.547
1.075
Dcalcd, g cm-3
µ(Mo KR), mm-1
S
cryst size, mm3
θ, deg
T, K
no. of reflcns measd
no. of reflcns obsd
R1a (%)
wR2b (%)
0.158 × 0.143 × 0.125
1.93 to 26.17
293(2)
6976
4555
7.09
21.53
6.67
23.12
a R1 ) [∑||Fo| - |Fc||/∑|Fo|]. b wR2 ) {∑[w(Fo2 - Fc2)2]/∑[w(Fo ) ]}1/2
.
2 2
Table 2. Selected Bond Distances (Å) and Angles (deg) for
Compounds 5 and 6·2(0.2MeOH)
5
Br(1)-Mn(1)
Mn(1)-C(2)
Mn(1)-N(2)
H(45A)sBr(1)
2.570(4)
2.008(5)
2.047(4)
2.982(4)
Br(1′)-Mn(1)
Mn(1)-N(1)
Mn(1)-N(3)
C(45)sBr(1)
2.458(7)
2.051(4)
2.022(4)
3.907(4)
C(2)-Mn(1)-N(3)
C(2)-Mn(1)-N(1)
N(3)-Mn(1)-N(2)
C(2)-Mn(1)-Br(1′)
N(1)-Mn(1)-Br(1′)
C(2)-Mn(1)-Br(1)
N(1)-Mn(1)-Br(1)
87.95(18)
88.07(17)
89.42(16)
97.0(2)
N(3)-Mn(1)-N(1)
C(2)-Mn(1)-N(2)
N(1)-Mn(1)-N(2)
160.98(18)
161.79(19)
88.58(16)
N(3)-Mn(1)-Br(1′) 96.20(17)
102.75(17) N(2)-Mn(1)-Br(1′) 101.18(19)
101.99(17) N(3)-Mn(1)-Br(1) 103.72(14)
95.31(14)
N(2)-Mn(1)-Br(1) 96.14(15)
Figure 1. (a) Molecular structure of Mn(2-NCH3NCTPP)Br (5) and (b)
Sn(2-NCH3NCTPP)Cl2 ·2(0.2MeOH); 6·2(0.2MeOH)], with 30% thermal
ellipsoids. Hydrogen atoms and solvent MeOH for 6·2(0.2MeOH)] are
omitted for clarity.
C(45)-H(45A)sBr(1) 162.17(14)
6·2(0.2MeOH)
2.063(19)
2.123(5)
Sn-C(7)
Sn-N(1)
Sn-Cl(1)
Sn-N(3A)
2.5116(17)
2.084(14)
Scheme 1
Cl(1)-Sn-Cl(1A)
Cl(1)-Sn-C(7)
C(7)-Sn-N(3A)
180.00(8)
88.6(5)
172.9(7)
C(7)-Sn-N(1)
Cl(1)-Sn-N(1)
91.5(5)
90.55(16)
Results and Discussion
Molecular Structures of 5 and 6 · 2(0.2MeOH). Mn(2-
NCH3NCTPP)Br (5) was produced in 61% yield by heating
a 2-NCH3NCTPPH (3) solution in CH2Cl2/MeOH under
aerobic conditions with an excess of MnBr2 (Scheme 1).
The complex Sn(2-NCH3NCTPP)Cl2 (6) was synthesized
in 66% yield by reacting 2-NCH3NCTPPH (3) with excess
SnCl2 in pyridine under aerobic conditions (Scheme 1). X-ray
structures are depicted in Figure 1a for complex 5 and Figure
1b for 6 · 2(0.2MeOH).
The geometry of the coordination around Mn(III) in 5 is
closely related to a square-base pyramid, giving a trigonal
distortion parameter (τ) value of 0.01, with Mn(III) having
coordination of five, MnN3CBr, with normal bonds to the
N(1), N(2), N(3), C(2), and Br(1) atoms. The bond lengths
of Mn(1)-C(2), Mn(1)-N(1), Mn(1)-N(2), Mn(1)-N(3),
and Mn(1)-Br(1) in 5 are 2.008(5), 2.051(4), 2.047(4),
2.022(4), and 2.570(4) Å, respectively (Table 2).
In 6 · 2(0.2MeOH), the geometry about Sn is a slightly
distorted octahedron and has six-coordination with two axial
7204 Inorganic Chemistry, Vol. 47, No. 16, 2008

InWerted N-Methylated Porphyrin Complexes
Figure 3. Temperature variation of the molar magnetic susceptibility (ꢁm)
and effective magnetic moment (µeff) for the powder sample of 5 in the
range 2-300 K. Points represent the experimental data; solid lines represent
the least-squares fit of the data to eq 2.
|1-〉], and a singlet corresponding to the ms ) |0〉 state,that
is, |0′〉.16 The forbidden EPR transitions may be observed
between the levels of the |2+〉, |2-〉 non-Kramer’s doublet.1,16
Magnetic Properties. Magnetic data for complex 5 are
reported in Figure 3 in the forms of ꢁm and µeff versus T.
As can be seen in Figure 3, the µeff for 5 remains constant
at 4.83 µB from 300 K down to 30 K, below which it rises
slowly to 5.25 µB at 3 K before decreasing again. This kind
of behavior is expected for a high-spin mononuclear Mn(III)
(S ) 2) complex for 5 in which there is appreciable zero-
field splitting of the ground state and/or weak ferromagnetic
magnetic coupling. Low-symmetry S ) 5/2 Mn(II) species,
which may be present as impurities in Mn(III) compounds,
can also give rise to downfield EPR signals near g ) 2. The
molecular structure of 5 shows that the metal (Mn) centers
are linked by weak C(45)-H(45) · · · Br(1) hydrogen bonds
(Figure 2), and it is known that such interactions are able to
transmit interactions. From a magnetic point of view, the
weak one-dimensional arrangement of 5 may then be reduced
to a dinuclear one.17 The possibility of weak magnetic
Figure 2. View of the one-dimensional network of 5 linked through weak
hydrogen bonds in the unit cell.
chloride ligands; the bond distances are as follows: Sn-Cl(1)
) 2.5116(17), Sn-C(7) ) 2.063(19), Sn-N(1) ) 2.123(5),
and Sn-N(3A) ) 2.084(14) Å (Table 2). The tin atom in
6 · 2(0.2MeOH) is directly in the plane of the four internal
core atoms, and the manganese in 5 lies 0.33 Å above the
plane of the core atoms. The structure of 6 · 2(0.2MeOH) is
similar to that of the Sn4+ complex of N-confused tetraphe-
nylporphyrin Sn(NCTPP)Cl2.12
The crystal packing of complex 5 along the b axis is shown
in Figure 2 in which weak hydrogen bonds link the
mononuclear Mn(2-NCH3NCTPP)Br units into an extended
one-dimensional chain.
The C(45)-H(45A)· · · Br(1) hydrogen bond is formed
mainly between C(45) and Br(1) with a C(45) · · · Br(1)
distance of 3.907(4) Å and a corresponding angle of
162.17(14)° (Table 2). The short interatomic contacts of
H(45A) · · · Br(1) ) 2.982(4) Å provide the most likely
exchange pathway (Table 2).
Spin Hamiltonian. The quintet energy levels of the high-
spin mononuclear Mn3+ (S ) 2) are parametrized in terms
of the spin Hamiltonian13–15
ˆ
b b
exchange in 5 with the spin Hamiltonian (Hs)2 ) -2JS1 · S2
+ ꢀHgs · St for Mn3+ · · · Mn3+ dimer (with S1 ) S2 ) 2) is
b
included in fitting the magnetic susceptibility data.18 Here
b
St is the total spin operator, that is, St ) 0, 1, 2, 3, 4 and gs
)(g1 +g2)/2.18 ThedatawereinsertedintotheBleaney-Bowers
equation (eq 2) and the term p (or q) which is the fraction
of Mn3+(or Mn3+ · · · Mn3+ dimer), respectively,19,20 where y
) 1.44D (cm-1)/T and x ) 1.44J (cm-1)/T. Here g is the
average g value, TIP is the temperature independent para-
magnetism, p (or q) is the fraction of Mn3+(or Mn3+ · · ·Mn3+
dimer), and other symbols have their standard meanings. The
best fits as represented in Figure 3 gave the values of g )
1.67, D ) -2.4 cm-1, 2J ) 1.12 cm-1, p ) 0.56, q ) 0.29,
and a temperature independent paramagnetism value TIP
1
3
2
2
2
ˆ
(Hs)1 ) D Sz - S(S + 1) + E(Sx - Sy ) + ꢀHgS (1)
[
]
where H is the applied magnetic field, g is the g tensor, S is
the electronic spin, and D and E are the parameters which
describe the effects of the axial and rhombic ligand field,
respectively. The zero-field interaction splits the levels of
system with S ) 2 spin into two doublets, one of them is a
linear combination of the ms ) |(2〉 states, that is, [|2+〉,
|2-〉], and the other one of the ms ) |(1〉 states, that is, [|1+〉,
(17) Costes, J. P.; Dahan, F.; Donnadieu, B.; Douton, M. J. R.; Garcia,
M. I. F.; Bousseksou, A.; Tuchaguess, J. P. Inorg. Chem. 2004, 43,
2736.
(13) Gerritsen, H. J.; Sabisky, E. S. Phys. ReV. 1963, 132, 1507.
(14) Baranowski, J.; Cukierda, T.; Jezowska-Trzebiatowska, B.; Kozlowski,
H. J. Magn. Reson. 1979, 33, 585.
(18) Yang, F. A.; Guo, C. W.; Chen, Y. J.; Chen, J. H.; Wang, S. S.; Tung,
J. Y.; Hwang, L. P.; Elango, S. Inorg. Chem. 2007, 46, 578.
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(16) The formula for Non-Kramer’s doublets are shown in the Supporting
Information.
(20) Yates, M. L.; Arif, A. M.; Manson, J. L.; Kalm, B. A.; Barkhart, B. M.;
Miller, J. S. Inorg. Chem. 1998, 37, 840.
Inorganic Chemistry, Vol. 47, No. 16, 2008 7205

Hung et al.
)1.4 × 10-4 cm3/mol. The negative value of -2J indicates
a weak ferromagnetic nature of the spin coupling in
Mn3+ · · ·Mn3+(dimer). The intrachain Mn · · ·Mn separations
of 9.558(4) Å in 5 precludes direct metal-metal bonding,
so superexchange via the C(45)-H(45A)· · · Br(1) hydrogen
bonding in Mn3+ · · ·Mn3+(dimer) must be responsible for this
ferromagnetic interaction (Figure 2). The shortest interchain
Mn · · · Mn distance of 11.508(4) Å indicates that the inter-
chain interactions are expected to be negligible. This
ferromagnetic interaction is quite weak, that is, similar to
the previous result showing that coupling of Mn(III) ions
with J ) -0.2 cm-1 in the complex (N-(2-hydroxybenzoyl)-
N′-(2-hydroxybenzylidene)propane-1,2-diamine)-bis(metha-
nol-O)-manganese(III), L6Mn(CH3OH)2, through π-π stack-
ing, although antiferromagnetic.17
ESR Studies. The X-band EPR spectra of a frozen solution
of 5 in CHCl3 at 4 K is shown in Figure 4.
The field position and shape of the observed peak signal
at g ) 9.19 (or 10.4) in parallel mode (or perpendicular
mode) are close to those observed for tris(acetylacetonato)-
manganese(III), Mn(acac)3, and are attributed to a forbidden
transition within the |2+〉 and |2-〉 non-Kramer’s doublet
(Figure 4).1,16 The resonance field for the transition between
the ε|2+〉 and ε|2-〉 levels at a given hν quantum is calculated
either from eq 313,15
Figure 4. X-band ESR spectra for 5 in CHCl3 at 4 K: (a) parallel
polarization, (b) perpendicular polarization. ESR conditions: microwave
frequency of 9.398 GHz (parallel polarization), 9.650 GHz (perpendicular
polarization); microwave power of 3.994 mW, magnetic field modulation
amplitude of 1.60 G, and modulation frequency of 100.00 KHz.
φ
+
-
|ε|2 〉 - ε|2 〉| ) 2 3r sin + 120o ) hν
(3)
√
(
)
3
where r ) [(4g2ꢀ2H2)/3 + (16D2)/9 + 4E2]1/2, cos φ) (-q1H2
- q2)/(2r3), q1 ) (-32Dg2ꢀ2)/3, and q2 ) (128D3)/27 +
16DE2, or from eq 414,16
diamagnetic 6, and their X-ray structures are established. A
technique is also reported by combining the conventional
ESR spectroscopy and magnetic susceptibility measurements
to evaluate the ZFS parameters (D and E) for the high-spin
mononuclear Mn(III) (S ) 2) of 5. The complex 5 is a
mononuclear complex linked through H(45A) · · · Br(1) hy-
drogen bonds into a one-dimensional chain and displays
simple weak ferromagnetism between the Mn(III) ions.
F1H6 + F2H4 + F3H2 + F4 ) 0
(4)
where F1 ) 4p1 , F2 ) 12p1 p2 + 9 p1 (hν)2 + 27q1 , F3 )
3
2
2
2
12p1p2 + 18p1p2(hν)2 + 6p1(hν)4 + 54q1q2, F4 ) 4p2
+
2
3
9p2 (hν)2 + 6p2(hν)4 + (hν)6 + 27q2 , p1 ) -4g2ꢀ2, and p2
2
2
) (-16D2)/3 - 12E2.
The rhombic zero field parameter E ) -1.3 × 10-3 cm-1
is obtained by substitution of D ) -2.4 cm-1 and the field
position of g ) 9.19 (H ) 730.5 G) into either eq 3 or eq 4.
Despite the lack of a C4 rotation axis, compound 5, which
is five-coordinate, shows relatively little rhombic ZFS. This
ZFS is different from that of Mn(NCTPP)(py)2 (2), which
is six-coordinate and has a relatively large magnitude, highly
rhombic ZFS: D ) -3.08 cm-1, E ) -0.61 cm-1.
Acknowledgment. The financial support from the National
Science Council of the ROC under Grant NSC 95-2113-M-
005-014-MY3 is gratefully acknowledged. We thank Dr. S.
Elango for helpful discussions.
Supporting Information Available: The formula for non-
Kramer’s doublets, ORTEP drawings with the atom-labeling
schemes for complexes 5 and 6·2(0.2MeOH) (30% probability
ellipsoids), and SQUID magnetic susceptibility for 5 in the
temperature range of 2-100 K. This material is available free of
charge via the Internet at http://pubs.acs.org.
Conclusions
We have investigated two new inverted N-methyl por-
phyrin metal complex, namely, one paramagnetic 5 and one
IC800490T
7206 Inorganic Chemistry, Vol. 47, No. 16, 2008