Synthesis and characterization of mononuclear and dinuclear Mn complexes with N,N′-disubstituted octaaza macrocycle

Article abstract of DOI:10.1016/j.poly.2008.03.021

A new 24-membered octaaza macrocyclic ligand (L) containing two methoxybenzyl pendant arms has been synthesized. While its complexation with MnCl₂ in the presence of perchlorate anion yielded a mononuclear complex, [MnL](ClO₄)₂, a similar reaction in the absence of perchlorate anion led to an endocyclic dinuclear complex, [Mn₂LCl₄]. In [MnL](ClO₄)₂, the Mn(II) ion was tightly surrounded by the N8-macrocyclic ligand to form a distorted bicapped octahedral geometry. In [Mn₂LCl₄], the endomacrocyclic bound two manganese ions are bridged via two chloro ligands to form a bis-(μ-chloro) Mn₂Cl₂ diamond core. Each Mn(II) ion in the dinuclear complex is additionally ligated with a diaminomethyl pyridinyl nitrogen donor atom of the ligand and a terminal chloride, which leads to a distorted octahedral geometry of the N₃Cl₃ donor set. An EPR study of [MnL](ClO₄)₂ in DMSO or DMF showed an unprecedented Mn(II) EPR signal spreading from ～100 G over ～7000 G with ⁵⁵Mn nuclear hyperfine structures at 600-1800 G. For [Mn₂LCl₄], a typical high-spin Mn(II) signal was observed near g = ～2 with an average ⁵⁵Mn nuclear hyperfine coupling constant of 91 G and small ZFS.

Full text of DOI:10.1016/j.poly.2008.03.021

Polyhedron 27 (2008) 2043–2048
Contents lists available at ScienceDirect
Polyhedron
journal homepage: www.elsevier.com/locate/poly
Synthesis and characterization of mononuclear and dinuclear Mn complexes
with N,N0-disubstituted octaaza macrocycle
Wonchoul Park a, Jang-Hoon Cho b, Hong-In Lee b, Mira Park c, Myoung Soo Lah c, Dongyeol Lim a,
*
a Department of Chemistry, Sejong University, Seoul 143-747, South Korea
b Department of Chemistry, Kyungpook National University, Daegu 702-701, South Korea
c Department of Chemistry and Applied Chemistry, Hanyang University, Ansan, Kyunggi-do 426-791, South Korea
a r t i c l e i n f o
a b s t r a c t
Article history:
A new 24-membered octaaza macrocyclic ligand (L) containing two methoxybenzyl pendant arms has
been synthesized. While its complexation with MnCl2 in the presence of perchlorate anion yielded a
mononuclear complex, [MnL](ClO4)2, a similar reaction in the absence of perchlorate anion led to an
endocyclic dinuclear complex, [Mn2LCl4]. In [MnL](ClO4)2, the Mn(II) ion was tightly surrounded by
the N8-macrocyclic ligand to form a distorted bicapped octahedral geometry. In [Mn2LCl4], the endomac-
rocyclic bound two manganese ions are bridged via two chloro ligands to form a bis-(l-chloro) Mn2Cl2
diamond core. Each Mn(II) ion in the dinuclear complex is additionally ligated with a diaminomethyl
pyridinyl nitrogen donor atom of the ligand and a terminal chloride, which leads to a distorted octahedral
geometry of the N3Cl3 donor set. An EPR study of [MnL](ClO4)2 in DMSO or DMF showed an unprece-
dented Mn(II) EPR signal spreading from ꢀ100 G over ꢀ7000 G with 55Mn nuclear hyperfine structures
at 600–1800 G. For [Mn2LCl4], a typical high-spin Mn(II) signal was observed near g = ꢀ2 with an average
55Mn nuclear hyperfine coupling constant of 91 G and small ZFS.
Received 5 November 2007
Accepted 20 March 2008
Available online 12 May 2008
Keywords:
Manganese(II) complexes
Octaaza macrocycle
Crystal structures
Ó 2008 Elsevier Ltd. All rights reserved.
1. Introduction
nitrogen atoms of the macrocycle. We have prepared a new 24-
membered octaaza macrocycle that contains two methoxybenzyl
The synthesis and coordination chemistry of polyaza macrocy-
clic ligands bearing pendant arms has attracted much interest in
the last few decades [1,2]. The incorporation of pendant arms on
polyaza macrocyclic ligands can change the complexation capabil-
ity of the ligands, and can increase the stability of their complexes
with multiple metal ions. Among the transition metals that form
complexes with polyaza macrocycles, manganese is well known
to have an important role in many biological reactions [3], such
as water oxidation (photosystem II) [4], decomposition of hydro-
gen peroxide (catalase), and dismutation of the superoxide anion
radical (superoxide dismutase). Therefore, studies on manganese
complexes with various geometries would expand our understand-
ing of the coordination geometries and the mechanisms of manga-
nese enzymes.
substituents as pendant arms (Fig. 1). When a Mn(II) ion was com-
plexed with the ligand, two different species were obtained,
depending on conditions, one is the mononuclear Mn(II) complex
in the presence of perchlorate anion and the other is a dinuclear
Mn(II) endomacrocyclic complex with a bis-l-chloro bridge in
the absence of perchlorate anion. The latter structure is an attrac-
tive model for the study of the role of chloride anions in the man-
ganese assembly found in photosynthetic water oxidation systems
[9]. Here, we present the synthesis of a new ligand and its manga-
nese complexes (Scheme 1), the solid-state characterizations of the
complexes using single-crystal structure analysis, and studies on
the solution characteristics using EPR spectroscopy.
The octaaza macrocycle containing two pyridyl groups, specifi-
cally 3,6,9,17,20,23,29,30-octaazatricyclo[23,3,1,1]triaconta-1(29),-
11,13,15,25,27-hexaene (BPBD) shown in Scheme 1, has been
studied as a host for phosphate and transition metal ions [5,6].
Its Cu(II), Ni(II) and Zn(II) complexes have been prepared and the
structure determined [6–8]; all of them were dinuclear and each
metal ion in the complexes was coordinated to the equatorial four
2. Experimental
2.1. General procedures and methods
All reagents were obtained from commercial suppliers and used
without purification unless specified otherwise. 1H and 13C NMR
spectra were collected on a Bruker AVANCE II 500 spectrometer
at resonance frequencies of 500.1 MHz and 125.7 MHz, respec-
tively. The solvents used were CDCl3 and D2O. The chemical shifts
(in ppm) are reported from tetramethylsilane or referenced to
* Corresponding author. Tel.: +82 2 3408 3218; fax: +82 2 462 9954.
E-mail address: dylim@sejong.ac.kr (D. Lim).
0277-5387/$ - see front matter Ó 2008 Elsevier Ltd. All rights reserved.
doi:10.1016/j.poly.2008.03.021

2044
W. Park et al. / Polyhedron 27 (2008) 2043–2048
NsHN
H2N
H2N
NsHN
OHC
PhSH,
K2CO3, DMF
OMe
N
N
NH
NaBH3CN, MeOH
91%
MeO
MeO
85%
NsHN
NsHN
3
2
1
Mn(OAc)2,
MeOH, NaClO4
[MnL](ClO4)
N
N
H
O
H
N
NH
N
HN
84%
O
MeO
N
OMe
NH
HN
BaCl2 H2O,
Mn2LCl4
MnCl2, MeOH
92%
NaBH4, MeOH
75%
L
Scheme 1. Synthesis of macrocyclic ligand L and its two manganese complexes.
2.2.2. N1-(2-amino-ethyl)-N1-(2-methoxy-benzyl)-ethane-1,2-
diamine (3)
Thiophenol (0.46 g, 4.2 mmol) was added to a stirred solution of
N
N
N
NH
NH
HN
HN
NH
NH
HN
HN
compound 2 (1.0 g, 1.68 mmol) and anhydrous potassium carbon-
ate (0.70 g, 5.05 mmol) in dimethyl formamide (DMF). The result-
ing mixture was stirred for 4 h at room temperature and then the
solvent was removed in vacuo. The residue was dissolved in a mix-
ture of EtOAc (50 mL) and 1 N-HCl (20 mL). The aqueous layer was
washed with EtOAc until the by-product was removed, and then
basified with 2 N-KOH. The aqueous solution was extracted with
CH2Cl2, dried over Na2SO4 and concentrated in vacuo to give a col-
orless viscous oil. Yield, 0.38 g (85%). 1H NMR (500 MHz, D2O) as a
HCl salt; d 7.35 (t, 1H, J = 7.9 Hz), 7.25 (m, 1H, J = 7.4 Hz), 7.06 (d,
1H, J = 8.3 Hz), 6.98 (t, 1H, J = 7.4 Hz), 3.81 (s, 3H), 3.59 (s, 2H),
3.07 (t, 4H, J = 5.7 Hz), 2.75 (t, 4H, J = 5.8 Hz); 13C NMR
(125.76 MHz, D2O); d 157.70, 131.91, 129.82, 125.10, 120.92,
111.82, 55.55, 51.50, 50.37, 36.90. ESI-MS [M+H]+: 224.3.
MeO
NH
HN
N
N
OMe
N
L
BPBD
Fig. 1. Structure of N,N0-disubstituted octaaza macrocycle.
solvent on the d scale. LRMS (ESI) spectra were recorded on an Agi-
lent 1100 LC/MSD instrument. The ATR-FTIR spectra of the manga-
nese complexes were measured from 4000 cmꢁ1 to 650 cmꢁ1 with
a Spectrum 100 spectrometer (Perkin–Elmer).
2.2.3. 6,20-Bis-(2-methoxy-benzyl)-3,6,9,17,20,23,29,30-octaaza-
tricyclo[23.3.1.111,15]triaconta-1(29),11,13,15(30),25,27-hexaene (4)
A solution of compound 3 (0.30 g, 1.34 mmol) in MeOH was
added dropwise over 15 min to 2,6-diformylpyridine (0.18 g,
1.34 mmol) and BaCl2 ꢂ 2H2O (0.16 g, 0.67 mmol) in MeOH. The
resulting mixture was refluxed for 4 h. After the yellow solution
was allowed to cool to room temperature, solid NaBH4 (0.25 g,
6.7 mmol) was added slowly and stirred for 30 min, and then the
solvent was removed in vacuo. The residue was dissolved in a mix-
ture of CH2Cl2 (50 mL) and 1 N-HCl (20 mL). The aqueous layer was
washed with CH2Cl2 until the by-product was removed, and then
basified with 2 N-KOH. The aqueous solution was extracted with
CH2Cl2 and the organic layer was dried over Na2SO4 and concen-
trated. The crude product was purified by chromatography on a sil-
ica gel column (10:1 MeOH/NH4OH) to give a light yellow viscous
oil. Yield, 0.66 g (75%). 1H NMR (500 MHz, D2O) as a HCl salt: 7.88
(dt, 2H, J = 1.5 and 7.8 Hz), 7.45 (dt, 1H, J = 1.4 and 8.1 Hz), 7.39 (d,
4H, J = 7.9 Hz), 7.36 (dd, 2H, J = 1.4H and 7.4 Hz), 7.04-6.99 (m, 4H),
4.42 (s, 6H), 4.39 (s, 4H), 3.74 (s, 4H), 3.72 (m, 8H), 3.64 (m, 8H);
13C NMR (125.76 MHz, D2O): 157.95, 149.95, 139.66, 132.70,
132.62, 123.16, 121.30, 116.90, 111.75, 55.61, 53.93, 50.75, 50.04,
42.15. ESI-MS [M+H]+: 653.6.
2.2. Synthesis of the macrocycle L
2.2.1. 4-(2-Methoxy-benzyl)-1,7-bis(2-nitrophenylsulfonyl)-1,4,7-
triazaheptane (2)
Compound 1 (in Scheme 1) [10] (1.0 g, 2.11 mmol) and a 2-
methoxybenzaldehyde (0.35 g, 2.53 mmol) were mixed in MeOH
(30 mL) at room temperature. Sodium cyanoborohydride (0.20 g,
3.17 mmol) and glacial acetic acid (0.13 g, 2.11 mmol) were added,
and the mixture was stirred for 6 h at room temperature. The reac-
tion mixture was quenched with saturated aqueous NaHCO3 solu-
tion, and the product was extracted with CH2Cl2. The solvent was
removed in vacuo, and the crude product was purified by chroma-
tography on a silica gel column (1:2 hexane/EtOAc) to give a light
yellow solid. Yield, 1.14 g (91%). 1H NMR (500 MHz, CDCl3); d 7.99–
7.98 (m, 2H), 7.70–7.75 (m, 2H), 7.69–7.66 (m, 4H), 7.20 (t, 1H,
J = 7.8 Hz), 7.04 (d, 1H, J = 7.3 Hz), 6.88 (d, 1H, J = 8.2 Hz), 6.79 (t,
1H, J = 7.4 Hz), 3.89 (s, 4H), 3.54 (s, 2H), 3.01 (t, 4H, J = 5.7 Hz),
2.56 (t, 4H, J = 4.7 Hz); 13C NMR (125.76 MHz, CDCl3); d 158.05,
148.08, 133.49, 133.43, 132.58, 131.17, 130.69, 129.25, 125.46,
125.39, 120.28, 110.93, 55.53, 54.27, 53.82, 41.43. ESI-MS
[M+H]+: 594.3.

W. Park et al. / Polyhedron 27 (2008) 2043–2048
2045
Table 1
2.2.4. [MnL](ClO4)2
Crystal data and structure refinement for [MnL](ClO4)2 and [Mn2LCl4] ꢂ CH3OH
[MnL](ClO4)2
[Mn2LCl4] ꢂ CH3OH
38H52Cl2MnN8O10 C39H56Cl4Mn2N8O3
Mn(OAc)2 ꢂ 4H2O (28 mg, 0.16 mmol) was added to a stirred
solution of macrocyclic ligand L (50 mg, 0.08 mmol) in MeOH
(5 mL) and the resulting mixture was stirred at room temperature
for 2 h. Sodium perchlorate (20 mg, 0.16 mmol) was added and the
mixture was stirred for another 30 min. The crude product was dis-
solved in H2O (10 mL), extracted with CH2Cl2, and dried over
Na2SO4. The solvent was removed in vacuo to give a light yellow
solid. Yield, 61 mg (84%). Colorless single-crystals suitable for X-
ray diffraction studies were obtained by slow evaporation of
CH2Cl2 solution of Mn complex. IR (powder, cmꢁ1): 3319 (w),
2856 (w), 1601 (m), 1583 (m), 1492 (m), 1466 (m), 1451 (m),
1248 (m), 1165 (m), 1081 (s). ESI-MS [MnLClO4]+: 806.5.
Empirical formula
Formula weight
Temperature (K)
Wavelength (Å)
Crystal system
Space group
C
906.72
173(2)
0.71073
monoclinic
P21/n
936.60
173(2)
0.71073
orthorhombic
Pccn
Unit cell dimensions
a (Å)
b (Å)
c (Å)
a (°)
10.4164(10)
21.403(2)
18.6642(18)
90
14.3503(11)
17.0012(12)
17.6197(13)
90
b (°)
99.285(2)
90
4106.5(7)
4
1.467
0.519
90
90
4298.7(5)
4
1.447
c (°)
2.2.5. [Mn2LCl4] ꢂ CH3OH
V (Å3)
Anhydrous MnCl2 (38 mg, 0.3 mmol) was added to a stirred
solution of macrocyclic ligand L (100 mg, 0.15 mmol) in MeOH
(10 mL) and the resulting mixture was stirred for 1 h at room tem-
perature. The white precipitate was collected by filtration and
washed with cooled MeOH and ether, and dried in vacuo. Yield,
0.12 g (92%). Colorless single crystals suitable for X-ray diffraction
studies were obtained by vapor diffusion of diethyl ether into a
solution of the Mn complex in methanol. IR (powder, cmꢁ1):
3243 (w), 3221 (w), 2801 (w), 1601 (m), 1582 (m), 1494 (m),
1467 (m), 1434 (m), 1244 (m), 1152 (m). ESI-MS [Mn2LCl4–
MnCl3]+: 742.5.
Z
Dcalc (Mg/m3)
Absorption coefficient (mmꢁ1
F(000)
)
0.883
1952
1900
Crystal size (mm)
h Range for data collection (°)
Reflections collected
0.45 ꢃ 0.20 ꢃ 0.13
1.90–28.29
25579
0.50 ꢃ 0.13 ꢃ 0.13
1.86–28.30
25691
Independent reflections [Rint
]
9683 [0.0311]
94.9
0.9356 and 0.8000 0.8938 and 0.6665
9683/0/740
1.017
R1 = 0.0459
wR2 = 0.1080
R1 = 0.0790
wR2 = 0.1252
0.616 and ꢁ0.440
5256 [0.0646]
98.3
Completeness to h = 28.29° (%)
Maximum and minimum transmission
Data/restraints/parameters
Goodness-of-fit (GOF) on F2
Final R [I > 2r(I)]
5256/0/267
1.011
R1 = 0.0413
wR2 = 0.0941
R1 = 0.0827
wR2 = 0.1127
0.533 and ꢁ0.340
R (all data)
2.3. Crystallography
Largest differences in peak and hole
(e Åꢁ3
)
Crystals were coated with paratone oil to prevent loss of crys-
tallinity on exposure to air. Data were collected at ꢁ100 °C using
Mo-Ka radiation (k = 0.71073 Å) employing a Bruker SMART CCD
equipped with a graphite crystal, incident-beam monochromator.
The SMART and SAINT software packages [11] were used for data col-
lection and integration, respectively. The data were corrected for
absorbance using SADABS [12] based upon Laue symmetry using
equivalent reflections. Structures were solved by direct methods,
and refined using full-matrix, least-squares calculations employing
2,6-diformylpyridine under reducing conditions in a 2 + 2 manner,
yielding the disubstituted octaaza macrocycle L. The ligand was
complexed with Mn(II) ion under different conditions (see Section
2) to afford the two complexes [MnL](ClO4)2 and [Mn2LCl4],
respectively.
the SHELXTL-PLUS software package [13]. All non-hydrogen atoms
3.2. Description of the crystal structures
were refined anisotropically. Hydrogen atoms in the crystal of
[MnL](ClO4)2 were found by difference Fourier peaks, and refined
isotropically, but hydrogen atoms in the crystal of [Mn2LCl4] ꢂ
CH3OH were assigned isotropic displacement coefficients
U(H) = 1.2U (C, N) or 1.5U (Cmethyl, O), and their coordinates were
allowed to ride on their respective atoms. Crystal and intensity
data are given in Table 1.
The molecular structure of [MnL](ClO4)2 is shown in Fig. 2. In
the crystal structure of the complex, the Mn(II) ion is encapsulated
by the N8-macrocyclic ligand, resulting in an overall distorted bi-
capped octahedral geometry. The planes of a typical meridional tri-
dentate, two 2,6-diaminomethyl pyridine moiety of the ligand
[N(2), N(1), and N(8) and N(6), N(5), and N(7) with Mn ion] are
2.4. EPR spectroscopy
X-band (9 GHz) EPR spectra were recorded on a Jeol JES-TE300
ESR spectrometer using 100 kHz field modulation. Low-tempera-
ture spectra were obtained using a Jeol ES-DVT3 variable temper-
ature controller for liquid nitrogen temperature and an Oxford
continuous-flow cryostat ESR900 for liquid helium temperature.
3. Results and discussion
3.1. Synthesis
The synthesis of ligand L is described in Scheme 1. Bis-nosylated
diethylenetriamine 1 was prepared as described [10], and the sec-
ondary amine was reductively alkylated with 2-methoxybenzalde-
hyde to give compound 2 with 91% yield in the presence of sodium
cyanoborohydride. Two nosyl groups of compound 2 were re-
moved under basic conditions in 85% yield, and then cyclized with
Fig. 2. ORTEP view of the cation of [MnL](ClO4)2 complex with 30% probability.
Hydrogen atoms are omitted for clarity.

2046
W. Park et al. / Polyhedron 27 (2008) 2043–2048
Table 2
The crystal structure of [Mn2LCl4] is displayed in Fig. 3. The
Selective bond distances (Å) and angles (°) for [MnL](ClO4)2
complex consists of two endo-encapsulated Mn(II) centers bridged
by two chloro ligands, which leads to a bis-l-chloro Mn2Cl2 dia-
mond core. Each Mn(II) atom is coordinated additionally with a
diaminomethyl pyridine and a terminal chloride, giving a six-coor-
dinated N3Cl3 ligand donor set with distorted octahedral geometry.
This type of dinuclear chloro-bridged Mn(II) compound with N/O
ligands is relatively rare [17–27] and, as far as we know, this is
the first example of a structurally defined Mn(II) endomacrocyclic
complex with a bis-l-chloro bridge.
Mn(1)–N(1)
Mn(1)–N(5)
Mn(1)–N(4)
2.261(2)
2.263(2)
2.336(2)
144.61(7)
140.55(7)
71.79(7)
71.78(8)
136.46(7)
87.50(8)
72.22(8)
83.71(7)
Mn(1)–N(8)
Mn(1)–N(2)
Mn(1)–N(6)
N(4)–Mn(1)–N(2)
N(8)–Mn(1)–N(2)
N(1)–Mn(1)–N(6)
N(5)–Mn(1)–N(6)
N(4)–Mn(1)–N(6)
N(8)–Mn(1)–N(6)
N(2)–Mn(1)–N(6)
2.340(2)
2.381(2)
2.411(2)
109.97(8)
139.83(8)
82.05(7)
71.63(7)
136.38(8)
103.33(8)
88.71(7)
N(1)–Mn(1)–N(5)
N(1)–Mn(1)–N(4)
N(5)–Mn(1)–N(4)
N(1)–Mn(1)–N(8)
N(5)–Mn(1)–N(8)
N(4)–Mn(1)–N(8)
N(1)–Mn(1)–N(2)
N(5)–Mn(1)–N(2)
The selected bond lengths and bond angles for [Mn2LCl4] are gi-
ven in Table 3. As in the mononuclear manganese complex above,
the bond distances to the Mn(II) ion are shorter for the pyridyl
nitrogen atoms N(2) (2.230 Å) than for the secondary nitrogen
atoms N(1) (2.343 Å) and N(3) (2.296 Å). The two Mn–Cl bond dis-
tances in the Mn2Cl2 diamond core are slightly different (2.5261 Å
and 2.6608 Å), and are longer than the terminal Mn–Cl bond dis-
tances (2.4135 Å), as expected for the chloride in bridging mode.
The Mn–Mn distance is 3.886 Å, which is comparable to that found
in other bis-l-chloro-bridged Mn(II) complexes [17–27]. The bond
angles in the diamond core are 82.80° [Cl(3)–Mn(1)–Cl(2)], 82.81°
[Cl(3)–Mn(1)#1–Cl(2), #1: ꢁx + 3/2, ꢁy + 1/2, z], 93.82° [Mn(1)–
Cl(2)–Mn(1)#1], and 100.57° [Mn(1)#1–Cl(3)–Mn(1)]. The signifi-
cant difference between the two chloride-centered bridging angles
(93.82° and 100.57°) may arise from the different bridging chloride
environments caused by the conformational restriction on the li-
gand in a 2-fold symmetric environment. The structural feature
of our bis-l-chloro-bridged Mn(II) complex, in comparison to other
dinuclear BPBD complexes on which no significant interaction be-
tween two metal ions is found [7,8], seems to arise from the attrac-
tive hydrophobic interaction between the pendant arm and the
pyridine moiety of the ligand.
slightly bent [i.e. the torsional angles of N(2), Mn(1), N(1), and N(8)
and N(6), Mn(1), N(5), and N(7) are ꢁ161.89° and 155.80°, respec-
tively]. The two pyridine planes are twisted about ꢁ71° and wrap
round the Mn ion, and the remaining ‘‘open” spaces are capped
with two weakly coordinated tertiary nitrogen atoms. The dis-
tances of Mn–N(3) and Mn–N(7) are 2.838 Å and 2.989 Å,
respectively.
Selected bond distances and angles are given in Table 2. The
average distance between Mn and pyridyl nitrogen atoms [N(1)
and N(5)] is 2.262 Å, while that of Mn secondary amines is
2.367 Å, reflecting the stronger coordination ability of the pyridyl
nitrogen. These average distances are similar to those found in
other manganese complexes of acyclic ligands [14–16].
3.3. EPR spectra
Fig. 4 displays frozen-solution EPR spectra obtained from
[MnL](ClO4)2 and [Mn2LCl4] dissolved in DMSO and DMF at
110 K. The overall shape of each spectrum is unchanged at helium
temperature, but the signal intensities are increased. [MnL](ClO4)2
exhibits an unprecedented Mn(II) EPR spectrum. The EPR signal ob-
tained from the sample in DMSO spreads from ꢀ100 G over
ꢀ7000 G, while that in DMF shows almost the same feature as in
DMSO, with 55Mn nuclear hyperfine structures at 600–1800 G.
EPR of the high-spin Mn(II) (d5, S = 5/2) complex can be de-
scribed by the Hamiltonian [28]:
ꢀ
ꢁ
1
3
H ¼ D S2z ꢁ SðS þ 1Þ þ EðSx2 ꢁ S2y Þ þ bB ꢂ g ꢂ S þ S ꢂ A ꢂ I
Table 3
Selective bond distances (Å) and angles (°) for [Mn2LCl4] ꢂ CH3OHa
Mn(1)–N(2)
Mn(1)–N(3)
Mn(1)–N(1)
Mn(1)–Cl(1)
N(2)–Mn(1)–N(3)
N(2)–Mn(1)–N(1)
N(3)–Mn(1)–N(1)
N(2)–Mn(1)–Cl(1)
N(3)–Mn(1)–Cl(1)
N(1)–Mn(1)–Cl(1)
N(2)–Mn(1)–Cl(3)
N(3)–Mn(1)–Cl(3)
N(1)–Mn(1)–Cl(3)
2.230(2)
2.296(2)
2.343(2)
2.4135(8)
73.76(8)
74.94(8)
146.56(8)
95.64(6)
97.46(6)
97.02(6)
161.35(6)
93.49(6)
113.53(6)
Mn(1)–Cl(3)
Mn(1)–Cl(2)
Cl(2)–Mn(1)#1
Cl(3)–Mn(1)#1
Cl(1)–Mn(1)–Cl(3)
N(2)–Mn(1)–Cl(2)
N(3)–Mn(1)–Cl(2)
N(1)–Mn(1)–Cl(2)
Cl(1)–Mn(1)–Cl(2)
Cl(3)–Mn(1)–Cl(2)
Mn(1)–Cl(2)–Mn(1)#1
Mn(1)#1–Cl(3)–Mn(1)
2.5261(7)
2.6608(7)
2.6608(7)
2.5261(7)
99.56(3)
81.73(6)
80.67(6)
83.50(6)
177.10(3)
82.80(2)
93.82(3)
100.57(4)
a
Due to the C2 symmetric nature of the complex, only half of the data is dis-
played. #1: ꢁx + 3/2, ꢁy + 1/2, z.
Fig. 3. ORTEP view (top and side) of [Mn2LCl4] with 30% probability. The complex is
on the crystallographic 2-fold axis. Hydrogen atoms are omitted for clarity.

W. Park et al. / Polyhedron 27 (2008) 2043–2048
2047
gand pocket along the molecular C2 axis toward the face consisting
of terminal chloride ions and one of the bridging chloride ions,
whereas the Mn site of [MnL](ClO4)2 is buried inside the chelating
ligand. The structural characteristics of [Mn2LCl4] make the Mn2
center vulnerable to attack by basic solvents, and changes the
dinuclear complex to
a more stable mononuclear species,
[MnL]2+. But the signal from [MnL]2+ is not fully responsible for
the observed intensity of [Mn2LCl4] in both DMSO and DMF. The
hyperfine structure near g ꢀ 2 indicates that a solvated mononu-
clear Mn(II) species also exists in the solution. The remaining
intensities may arise from the dinuclear Mn2 center of [Mn2LCl4].
Hence, the observed EPR spectra suggest that [Mn2LCl4] in the sol-
vent is in an equilibrium in the forms of [Mn2LCl4], [MnL]2+, and
solvated mononuclear Mn(II).
4. Conclusions
The complexation of new ligand L, a 24-membered octaaza
macrocyclic ligand containing two non-coordinating pendant
arms, with Mn(II) gave a mononuclear [MnL](ClO4)2 in the pres-
ence of perchlorate ion, but an endocyclic dinuclear [Mn2LCl4] in
the absence of perchlorate ion. The crystal structure analysis of
[MnL](ClO4)2 revealed that a Mn(II) ion is encapsulated with the
N8-macrocyclic ligand, resulting in an overall distorted bicapped
octahedral geometry. In the crystal structure of [Mn2LCl4], an
endomacrocyclic dinuclear bis-l-Cl-bridged center was observed,
where two Mn(II) ions formed a Mn2Cl2 diamond core with two
bridging chloro ligands. Each Mn(II) ion is coordinated additionally
with a diaminomethyl pyridine of the ligand and terminal chloride,
giving a six-coordinated N3Cl3 ligand donor set with distorted octa-
hedral geometry. An EPR study of [MnL](ClO4)2 exhibited an
unprecedented Mn(II) EPR signal in DMSO and DMF, spreading
from ꢀ100 G over ꢀ7000 G with 55Mn nuclear hyperfine structures
at 600–1800 G. For the [Mn2LCl4] complex, a typical high-spin
Mn(II) signal appeared near g ꢀ 2 with an average 55Mn nuclear
hyperfine coupling constant of 91 G and small ZFS, and weak sig-
nals were found at g = 4.91 (1343 G) and g = 3.60 (1830 G).
Fig. 4. EPR spectra of the complexes [MnL](ClO4)2 and [Mn2LCl4] dissolved in DMSO
and DMF. Numerically reduced [MnL](ClO4)2 EPR spectra (broken line) are inserted
for comparison. Experimental conditions: microwave frequency, 9.221 GHz; micro-
wave power, 1.2 mW; modulation width, 10 G for [MnL](ClO4)2 and 5 G for [Mn-
L](ClO4)2; time constant, 0.3 s; scan time, 4 min; temperature, 110 K.
where D and E are the axial and rhombic zero-field splitting (ZFS)
parameters, BꢂgꢂS represents the electron Zeeman interaction, and
SꢂAꢂI is the nuclear hyperfine coupling term. High-spin Mn(II) in
the octahedral field of the 6A1g state generally has small ZFS param-
eters (D and E) and its X-band EPR signal is readily interpretable.
However, as revealed by the single-crystal study of the complex,
where Mn–N bond lengths are in the range of 2.26–2.41 Å and N–
Mn–N bond angles are 71.6–144.6°, the Mn–N coordination struc-
ture is severely distorted from the octahedral geometry, which
would give rise to strong ZFS and hamper the quantitative analysis
of the spectra at the X-band. The previous multifrequency EPR
experiment on a high-spin Mn(II) complex with an N6 donor set
consisting of two tridentate 1,4,7-triazacyclononane ligands
showed that the D value of the complex is 0.090 cmꢁ1 and E/D is
0.1 [29]. The X-band spectrum of [MnL](ClO4)2 is similar to but
not identical with that reported. We performed numerical simula-
tions to fit the observed spectra using the parameters reported pre-
viously for four to six-coordinated high-spin Mn(II) complexes
[30,31]. None provides a good explanation of the X-band EPR of
[MnL](ClO4)2. Further investigation using high-field high-frequency
EPR to elucidate the details of the electronic structure of this highly
distorted Mn(II)N6 compound exhibiting an unprecedented X-band
EPR spectra is needed and is being planned [30].
The EPR of [Mn2LCl4] in DMF (Fig. 4) shows a typical high-spin
Mn(II) feature near g ꢀ 2 with an average 55Mn nuclear hyperfine
coupling constant of 91 G and small ZFS, and shows weak signals
at g = 4.91 (1343 G) and g = 3.60 (1830 G). The EPR in DMF displays
a richer signal from low field up to ꢀ6000 G with some 55Mn nu-
clear hyperfine structures. Though the crystal structure tells us
that [Mn2LCl4] has a bis-l-Cl bridged Mn(II)Mn(II) dinuclear cen-
ter, the spectra do not resemble previously reported EPR of spin-
coupled Mn(II)Mn(II) complexes [32–34]. Closer examination of
the spectra reveals some signal intensity that resembles the EPR
features of [MnL](ClO4)2, represented by a broken line (EPR of
[MnL](ClO4)2 ꢃ 0.15), implying that the [Mn2LCl4] solution con-
tains the mononuclear species, [MnL]2+. A plausible explanation
can be derived from the crystal structure of [Mn2LCl4]. The Mn2
dinuclear center of [Mn2LCl4] is exposed to the outside of the li-
Acknowledgements
This work was supported by a Grant from the MarineBio21,
Ministry of Maritime Affairs and Fisheries, Korea. M.S.L. acknowl-
edges the financial support of KOSEF (R01-2005-000-10490-0).
HRMS(FAB) data were obtained from the facilities of the Korea Ba-
sic Science Institute.
Appendix A. Supplementary data
CCDC 658518 and 658519 contain the supplementary crystallo-
graphic data for [MnL](ClO4)2 and [Mn2LCl4]. These data can be ob-
tained free of charge via http://www.ccdc.cam.ac.uk/conts/
retrieving.html, or from the Cambridge Crystallographic Data Cen-
tre, 12 Union Road, Cambridge CB2 1EZ, UK; fax: (+44) 1223-336-
033; or e-mail: deposit@ccdc.cam.ac.uk. Supplementary data asso-
ciated with this article can be found, in the online version, at
doi:10.1016/j.poly.2008.03.021.
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