Synthesis and magnetic study of μ1,1-azido-bridged dinuclear manganese(II) complexes based on tripyridyl ligands

Article abstract of DOI:10.1002/ejic.200700680

Three azido-bridged Mn^II complexes of formulas [Mn ₂(N₃)₄-(ttp)₂] (1), [Mn ₂(N₃)₄(ttp-N₃)₂] (2) and [Mn₂(N₃)₄(ttp-N₃)₂] ₃-[Mn^III(ttp-N₃)(N₃) ₃]₂ (3), where ttp and ttp-N₃ represent 4′-p-tolyl-2,2′:6′,2″-terpyridine and 4′-p-azidomethylphenyl-2,2′:6′,2″-terpyridine, were synthesized and characterized by single-crystal X-ray diffraction analysis and magnetic studies. The Mn ions in complexes 1 and 2 are coordinated by three N atoms of the ttp or ttp-N₃ ligands, and they are connected by double end-on (EO) azide ligands; this forms a dinuclear Mn^II system with Mn-N-Mn bridging angles of 103.5 and 103.1°. The Br atoms of the -CH ₂Br ligands were replaced by azido groups during the formation of complexes 2 and 3. The structure of complex 3 comprises two structurally similar Mn^II dimers with double end-on bridging azide groups and one mononuclear Mn^III structure. The bridging Mn-N-Mn angles in 3 are 104.2, 105.1, and 106.73°. Magnetic studies indicate the presence of intramolecular ferromagnetic superexchange. The strength of ferromagnetic coupling within the Mn₂ cores in 1-3 is dependent on the Mn-N-Mn bridging angles. The magnetic coupling constants for intermolecular exchange are 2.46(4), 2.25(2), and 1.92(4) cm^-1 for 1, 2, and 3, respectively, on the basis of Hamiltonian H = -2JS₁S₂. Wiley-VCH Verlag GmbH & Co. KGaA, 2007.

Full text of DOI:10.1002/ejic.200700680

FULL PAPER
DOI: 10.1002/ejic.200700680
Synthesis and Magnetic Study of µ1,1-Azido-Bridged Dinuclear Manganese(II)
Complexes Based on Tripyridyl Ligands
Ming-Ming Yu,[a] Zhong-Hai Ni,[a] Chong-Chao Zhao,[a] Ai-Li Cui,[a] and
Hui-Zhong Kou*[a]
Keywords: Manganese / Dinuclear complexes / Crystal structures / Magnetic properties / Azido bridge
Three azido-bridged MnII complexes of formulas [Mn2(N3)4-
(ttp)2] (1), [Mn2(N3)4(ttp-N3)2] (2) and [Mn2(N3)4(ttp-N3)2]3-
[MnIII(ttp-N3)(N3)3]2 (3), where ttp and ttp-N3 represent 4Ј-
p-tolyl-2,2Ј:6Ј,2ЈЈ-terpyridine and 4Ј-p-azidomethylphenyl-
2,2Ј:6Ј,2ЈЈ-terpyridine, were synthesized and characterized
by single-crystal X-ray diffraction analysis and magnetic
studies. The Mn ions in complexes 1 and 2 are coordinated
by three N atoms of the ttp or ttp-N3 ligands, and they are
connected by double end-on (EO) azide ligands; this forms a
dinuclear MnII system with Mn–N–Mn bridging angles of
103.5 and 103.1°. The Br atoms of the –CH2Br ligands were
replaced by azido groups during the formation of complexes
2 and 3. The structure of complex 3 comprises two structur-
ally similar MnII dimers with double end-on bridging azide
groups and one mononuclear MnIII structure. The bridging
Mn–N–Mn angles in 3 are 104.2, 105.1, and 106.73°. Mag-
netic studies indicate the presence of intramolecular ferro-
magnetic superexchange. The strength of ferromagnetic
coupling within the Mn2 cores in 1–3 is dependent on the
Mn–N–Mn bridging angles. The magnetic coupling con-
stants for intermolecular exchange are 2.46(4), 2.25(2), and
1.92(4) cm–1 for 1, 2, and 3, respectively, on the basis of
ˆ
ˆ ˆ
Hamiltonian H = –2JS1S2.
(© Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim,
Germany, 2007)
tween the exchange coupling constant (J) and the Mn–N–
Mn bridging angle (θ) on the basis of results obtained for
only four complexes.[15a] We then prepared a series of end-
on azido-bridged MnII complexes with the [Mn2(phen)4-
(N3)2]2+ core and improved the J–θ relationship.[15b] Appar-
ently, more effort should be exerted to make the assumption
of the relation of J and θ more clear. Herein, we describe
the syntheses, structures, and magnetic properties of three
dinuclear MnII compounds with tridentate 4Ј-p-tolyl-
2,2Ј:6Ј,2ЈЈ-terpyridine (ttp) and 4Ј-p-bromomethylphenyl-
2,2Ј:6Ј,2ЈЈ-terpyridine (ttp-Br) ligands. Interestingly, the Br
atoms in the ttp-Br ligands were replaced by azido groups
to give the new 4Ј-p-azidomethylphenyl-2,2Ј:6Ј,2ЈЈ-terpyrid-
ine (ttp-N3) ligand, which then goes on to form complexes
[Mn2(N3)4(ttp-N3)2] (2) and [Mn2(N3)4(ttp-N3)2]3[Mn(ttp-
N3)(N3)3]2 (3). The bridging Mn–N–Mn angle of complex
3 is the largest hitherto found in double EO azido-bridged
dimeric MnII complexes.
Introduction
During the last two decades chemists have been inter-
ested in the azido ligand for its versatile coordination
modes and remarkable ability to transmit ferro- or antifer-
romagnetic interactions.[1] The azido ligand is able to bridge
metal ions in several forms, including the usual µ-1,1 (end-
on, EO) or µ-1,3 (end-to-end, EE) mode[2] and the unusual
µ-1,1,3, µ-1,1,1, µ-1,1,1,1, µ-1,1,3,3 or µ-1,1,1,3,3,3
modes.[3–6] EE bridging usually transmits antiferromagnetic
interactions between the metallic centers, whereas EO
bridging is known to transmit ferromagnetic interactions
irrespective of what metal ions are involved.[7] The theory
of spin polarization developed by Kahn et al.[8] has been
used to interpret the magnetic interaction through the azido
group in CuII, NiII, and MnII systems.[9] Many studies con-
cerning the ferromagnetic interactions in CuII and NiII end-
on azido systems have been carried out extensively, and
structure parameters, especially bridging angle, were found
to be the main factors controlling the strength of the ferro-
magnetic interaction.[10–13] For MnII systems with only end-
on azido bridges, examples are limited.[14,15] Recently,
Aromí et al. found that there is a linear relationship be-
Results and Discussion
Synthesis and General Characterization
Tridentate ttp-type ligands are analogous to the com-
monly used 2,2Ј:6Ј,2ЈЈ-terpyridine (terpy) ligand. Pre-
viously, Rojo et al. reported an end-on azide-bridged MnII
dimer [Mn2(terpy)2(µ1,1-N3)2(N3)2]·2H2O.[14a] This complex
has a bridging Mn–N–Mn angle of 104.6°, which is the
[a] Department of Chemistry, Tsinghua University,
Beijing 100084, People’s Republic of China
Fax: +86-10-62771748
E-mail: kouhz@mail.tsinghua.edu.cn
Supporting information for this article is available on the
WWW under http://www.eurjic.org/ or from the author.
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µ1,1-Azido-Bridged Dinuclear MnII Complexes Based on Tripyridyl Ligands
largest among the reported EO azido-bridged dimeric MnII shoulder band at 400–450 nm is apparent; this shoulder is
complexes. In this work, we used ttp-type ligands in the responsible for the color of the compounds. The spectrum
hope of obtaining similar dimeric complexes. Complexes 1– of 1 in MeCN shows no apparent absorption in the visible
3 were prepared and characterized. They have EO azido- region, which is consistent with the light color of the com-
bridged dimeric structures that are similar to [Mn2(terpy)2- plex. Relative to the spectra of the ttp and ttp-Br ligands,
(µ1,1-N3)2(N3)2]·2H2O.[14a] Interestingly, a 1D polymeric the UV absorptions related to the n–π* or π–π* transitions
[16]
MnII complex, [Mn(tptz)(µ1,1-N3)2]n
[tptz = 2,4,6-tris(2- within the ligands show an obvious redshift, which is due
pyridyl)-1,3,5-triazine], was synthesized with the tptz ligand to better planarity of the tripyridyl group accompanied by
that is similar to ttp. During the preparation of complexes chelation to MnII ions (see the Supporting Information).
2 and 3, ttp-N3 formed in situ by substitution of the bromo
group by an azido group (Scheme 1). In organic synthesis,
sodium azide is often used as a reactant to substitute bro-
moalkyl groups.[17] However, the substitution reaction of an
azido group accompanied by crystallization of metallic
complexes is rare. It is known that azide can stabilize di-
valent transition-metal ions when neutral pyridyl reagents
are used as auxiliary ligands. We found that tripyridyl MnII
can be slowly oxidized by oxygen dissolved in the solvent.
The exposure to light accelerates the oxidation process. The
formed neutral [Mn(ttp-N3)(N3)3] monomer cocrystallized
with the MnII dimer in 3.
Crystal Structure of Complexes 1, 2, and 3
Crystal data are summarized in Table 1. Selected bond
lengths and angles of complexes 1, 2, and 3 are included
in Table 2. ORTEP representations of the crystallographic
molecular structure of complexes 1, 2, and 3 are shown in
Figures 1, 2, and 3.
Table 1. Crystallographic data for complexes 1, 2, and 3.
1
2
3
Chemical formula
Fw
T / K
C44H34N18Mn2 C44H32N24Mn2 C176H128N102Mn8
924.77
293
1006.82
293
4111.32
293
Crystal system
Space group
a / Å
b / Å
c / Å
monoclinic
P21/c
8.608(2)
10.371(2)
23.806(5)
90
92.74(3)
90
2122.8(7)
2
monoclinic
P21/c
14.725(3)
13.230(3)
11.751(2)
90
97.01(3)
90
2272.2(8)
2
monoclinic
P21/c
14.757(3)
14.883(3)
22.828(5)
78.40(3)
78.78(3)
69.47(3)
4557.1(16)
1
α / °
β / °
γ / °
V / Å3
Z
ρcalcd / gcm–3
F(000)
1.447
948
1.472
1028
1.498
2098
GOF (S)
1.054
1.050
1.044
Data/restraints/paras 4824/0/290
9769/0/281
0.0559
0.1093
15905/15/1288
0.0507
0.1472
R1 [IϾ2σ(I)]
wR2 (all data)
0.0322
0.0930
Scheme 1. Possible formation mechanism of ttp-N3 and complex 2.
Complexes 1 and 2 exhibit centrosymmetric dimers
The IR spectra of three complexes show a strong peak [Mn(N3)2(ttp)]2 or [Mn(N3)2(ttp-N3)]2, respectively. The
at ca. 1600 cm–1, which is assigned to the C=N stretching MnII ions in complexes 1 and 2 are linked by double end-
–
vibration in the pyridine rings of the ligands. The νasym(N3 ) on bridging azide groups. The other two azide moieties act
mode of complexes 1–3 appear at ca. 2000–2100 cm–1. The as terminal ligands. In complex 1, each Mn ion exhibits a
splitting of the signals indicates the presence of both bridg- slightly distorted octahedral coordination sphere and the
ing and terminal azide ligands. The peaks at 2093 cm–1 for three nitrogen atoms of the terpy ligand [Mn1–N1:
complex 2 and 2086 cm–1 for complex 3 should be assigned 2.269(1) Å, Mn1–N2: 2.224(1) Å, Mn1–N3: 2.279(2) Å] and
to the alkyl azido asymmetric stretching vibration.[17] The the nitrogen atom of one bridging azide group [Mn1–N4A:
peak at 2037 cm–1 for complex 3 may be due to the 2.127(1) Å (A: 2 –x, – y, 1 – z)] form the equatorial plane.
–
νasym(N3 ) mode of the [MnIII(ttp-N3)(N3)3] moiety by con- The nitrogen atom of one terminal azido group [Mn1–N7:
sidering that the [MnIII(terpy)(N3)3] analog exhibits a 2.153(2) Å] and the nitrogen atom of the second bridging
strong band at 2035 cm–1.[18] In addition, azido complexes group [Mn1–N4: 2.363(2) Å] are situated in the axial posi-
–
are expected to show νsym(N3 ) and deformation mode tions. The existence of an inversion center causes the Mn–
–
δ(N3 ) at ca. 1300–1350 and ca. 620 cm–1, respectively.[18] N4–Mn1A–N4A bridging unit to form a plane. In this di-
For complexes 1–3, only the symmetric azide stretching vi- meric unit, the Mn cations are separated from each other
bration was observed as a medium signal.
by 3.528(4) Å. The bridging Mn–N4–Mn1A angle is 103.5°.
Complexes 1, 2, and 3 are slightly soluble in MeCN, but The bridging and terminal azido ligands are quasilinear and
they are not soluble in alcohol solvents. The electronic spec- the N4–N5–N6 and N7–N8–N9 angles measure 177.03 and
tra of compounds 2 and 3 in MeCN are similar and a 178.22°, respectively.
Eur. J. Inorg. Chem. 2007, 5670–5676
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FULL PAPER
Table 2. Selected bond lengths [Å] and angles [°] for complexes 1,
2, and 3.
1
Mn1–N1
Mn1–N3
Mn1–N4A
2.2689(14)
2.2786(15)
2.1270(14)
Mn1–N2
Mn1–N4
Mn1–N7
2.2238(14)
2.3634(16)
2.1530(17)
Mn1A–N4–Mn1 103.45(6)
2
Mn1–N4
Mn1–N4B
N1–Mn1
2.378(3)
2.126(3)
2.272(3)
N3–Mn1
N2–Mn1
N7–Mn1
2.274(3)
2.213(3)
2.180(4)
Mn1B–N4–Mn1 103.13(12)
3
Mn1–N1
Mn1–N7
Mn1–N14
Mn2–N1
2.331(3)
2.135(3)
2.223(2)
2.191(3)
2.147(5)
2.239(2)
2.244(3)
2.248(3)
1.951(3)
2.279(3)
2.296(3)
2.143(3)
106.72(12)
Mn1–N4
2.168(3)
2.290(3)
2.294(3)
2.279(3)
2.287(3)
2.291(3)
2.107(3)
1.982(3)
1.977(3)
2.209(3)
2.341(3)
2.138(4)
104.20(11)
Mn1–N13
Mn1–N15
Mn2–N4
Mn2–N10
Mn2–N17
Mn3–N28
Mn3–N30
Mn3–N34
Mn4–N19
Mn4–N21
Mn4–N22C
Mn1–N4–Mn2
Mn2–N16
Mn2–N18
Mn3–N29
Mn3–N31
Mn3–N37
Mn4–N20
Mn4–N22
Mn4–N25
Mn2–N1–Mn1
Mn4C–N22–Mn4 105.11(13)
Figure 1. Crystal structure of complex 1.
Figure 3. Crystal structure of complex 3 showing three cocrys-
tallized moieties.
In complex 2, each Mn cation exhibits a distorted octa-
hedral coordination sphere and the Mn–N bond lengths
range from 2.126(3) Å [Mn1–N4A (A: 1 –x, 1 – y, 1 – z)]
to 2.378(2) Å (Mn1–N4). In this dimeric unit, the Mn cat-
ions are separated from each other by 3.532(4) Å with a
bridging Mn–N4–Mn1A angle of 103.1°. The bridging and
terminal azido ligands are quasilinear [177.29 and 179.90°].
The structure of complex 3 comprises three doubly end-
on azide-bridged MnII dimers and two MnIII monomers.
One dimer exhibits a centrosymmetric structure and the
Figure 2. Crystal structure of complex 2.
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Eur. J. Inorg. Chem. 2007, 5670–5676

µ1,1-Azido-Bridged Dinuclear MnII Complexes Based on Tripyridyl Ligands
other is asymmetric. The dimeric structure is very similar
to that of complexes 1 and 2. In the asymmetric dimer com-
prised of Mn1 and Mn2, the nitrogen atoms of one terminal
azido group [Mn1–N7: 2.135(3) Å] and one bridging group
[Mn1–N1: 2.331(3) Å] are situated in the axial positions.
The intradimer Mn1···Mn2 distance is 3.569(6) Å, and the
bridging Mn1–N1–Mn2 and Mn1–N4–Mn2 bond angles
are 104.2 and 106.73°, respectively. In the inversion center
related unit, the Mn–N distances are in the range 2.138(4)
(Mn4–N25) to 2.341(3) Å (Mn4–N22). In this dimeric unit,
the Mn cations are separated from each other by
3.562(3) Å. The bridging azides slightly deviate (up and
down) from that plane and the bridging Mn–N4–Mn1A an-
Figure 4. χmT vs. T plot for complex 1. The solid line represents
the best fit.
gle is 105.1°. In the neutral MnIII monomer Mn(ttp-
N3)(N3)3, the Mn–N bond lengths range from 1.951(3) to
2.248(3) Å, which is consistent with a MnIII ion with a
Jahn–Teller effect for the d4 electronic configuration. The
bond lengths and coordination geometry are very similar to
those of [Mn(terpy)(N3)3].[18]
Magnetic Behavior of Complexes 1, 2, and 3
The χmT vs. T plots (2–300 K) of complexes 1, 2, and 3
are shown in Figures 4, 5, and 6, respectively. At 300 K, the
χmT values per dimer are 8.762 and 8.904 emuKmol–1 for
1 and 2, respectively, which are both close to the expected
value (8.75 emuKmol–1) for two uncoupled spin SMn = 5/2
systems. With decreasing temperature, χmT increases
sharply to reach a maximum value of 6.43 emuKmol–1 at
8 K for complex 1 and 14.34 emuKmol–1 at 9 K for com-
plex 2; it then decreases because of weak intermolecular
antiferromagnetic interaction and/or zero-field splitting of
the ground spin state of S = 5. Magnetic susceptibility
could be fit to a Curie–Weiss law with Curie constant C =
8.96 emuKmol–1 and a positive Weiss constant θ = 8.68 K
for complex 1 and C = 4.08 emuKmol–1 and θ = 7.89 K for
complex 2. These results indicate that the overall magnetic
behavior of 1 and 2 is ferromagnetic, which should be at-
tributed to the dinuclear superexchange mediated through
the µ1,1-azido bridges. The expression for the magnetic
susceptibility (χd) of a MnII dimer derived from Van Vleck’s
Figure 5. χmT vs. T plot for complex 2. The solid line represents
the best fit.
ˆ
ˆ
ˆ
equation (the spin Hamiltonian H = –2JSMn1SMn2) is ex-
pressed in Equation (1), in which A = 55 + 30exp(–10J/kT)
+ 14exp(–18J/kT) + 5exp(–24J/kT) + exp(–28J/kT) and B=
11 + 9exp(–10J/kT) + 7exp(–18J/kT) + 5exp(–24J/kT) +
3exp(–28J/kT) + exp(–30J/kT).
Figure 6. χmT vs. T plot for complex 3. The solid line represents
the best fit.
The best-fit parameters obtained are J = 2.46(4) cm–1, g
= 1.99(1), and zJЈ = –0.0078 cm–1 with an agreement factor
of R = ∑(χobsdT – χcaldT)2/∑(χobsdT)2 = 4.24ϫ10–5 for com-
(1)
plex
1 and J = g = 1.98(1), zJЈ =
2.25(2) cm–1,
Considering weak intermolecular antiferromagnetic
coupling, the final molar magnetic susceptibility takes the
form of Equation (2), where zJЈ is the interaction between
molecules, and the N, g, β, and θ parameters have their
usual meaning.
–0.0072(3) cm–1 and R = 2.03ϫ10–5 for complex 2.
The decrease in χmT at low temperature could be alterna-
tively interpreted by the presence of zero-field splitting
(ZFS) of the spin ground state ST = 5. The data were fit to
a model that includes the energy splitting of the ground
spin state. By using a modified term of the Heisenberg spin
(2)
ˆ
ˆ ˆ
ˆ
Hamiltonian of a dinuclear system (H = –2JS1S2) as HZFS
Eur. J. Inorg. Chem. 2007, 5670–5676
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M.-M. Yu, Z.-H. Ni, C.-C. Zhao, A.-L. Cui, H.-Z. Kou
FULL PAPER
2
ˆ
= D[STz – ST(ST+1)/3], the expression for the magnetic
Taking the contributions of intermolecular interaction
susceptibility of ferromagnetically coupled MnII dimer is and the MnIII monomers into account and using one J
depicted in Equation (3),[15c] where A = 6exp(9D/kT) + value for simplicity, the final molar magnetic susceptibility
24exp(6D/kT)+54exp(D/kT) + 96exp(–6D/kT) + 150exp- is in the form of Equation (4), where χdimer is the expression
(–15D/kT) + 180exp(–10J/kT) + 84exp(–18J/kT) + 30exp- including both J and zJЈ for complexes 1 and 2.
(–24J/kT) + 6exp(–28J/kT), B = exp(10D/kT) + 2exp(9D/kT)
(4)
+ 2exp(6D/kT) +2exp(D/kT) + exp(–6D/kT) + 2exp(–15D/
kT) + 9exp(–10J/kT) + 7exp(–18J/kT) + 5exp(–24J/kT) +
3exp(–28J/kT) +exp(–30J/kT).
The least-square fit of the experimental data gives the
following parameters: J = 1.92(4) cm–1, g = 1.98(1), zJЈ =
–0.0019(4) cm–1, and R = 5.47ϫ10–5 for complex 3.
Field dependence of the magnetization at 2 K of com-
plexes 1, 2, and 3 are shown in the Supporting Information.
(3)
The least-square fit of the experimental data to the above Experimental data fit well to the Brillouin function value
expression gives the following parameters: J = 2.46(2) cm–1, for S = 5, and are well above that for two noncoupling S =
g = 1.99(1), D = 0.019(1) cm–1, and R = 4.10ϫ10–5 for 5/2 MnII ions, which indicates the existence of ferromag-
complex 1 and J = 2.26(2) cm–1, g = 1.98(1), D = netic interactions between double EO azido-bridged MnII
III
0.017(1) cm–1, and R = 2.02ϫ10–5 for complex 2.
ions. For complex 3, the MnIII monomers (SMn = 2)
The best-fit results including intermolecular interaction should be included when calculating the Brillouin curve,
or zero-field splitting are very similar. Both effects are likely that is, S = 5ϫ3 + 2ϫ2 and noninteracting S = 6ϫ5/2 +
operative with similar strength, and it is impossible to dis- 2ϫ2, respectively. The experimental data for 3 are above
tinguish between them.[15c]
the Brillouin curve for S = 6ϫ5/2 + 2ϫ2 at low magnetic
At 300 K, the χmT value of complex
3
is ca. field (Ͻ20 kOe), and they are below that for S = 5ϫ3 +
33.0 emuKmol–1, which is close to that (32.25 emuKmol–1) 2ϫ2. The discrepancy in 3 compared with complexes 1 and
expected for an uncoupled system (6MnII + 2MnIII). With 2 is assigned to the presence of MnIII ions, and it is usually
a decrease in the temperature, the χmT values increase difficult to reach magnetic saturation because of magnetic
sharply to reach a maximum value of 47.66 emuKmol–1 at anisotropy.[19]
7 K, and then they decreases to 42.62 emuKmol–1 at 2 K
The above results could be interpreted by the theoretical
due to weak antiferromagnetic interaction and/or zero-field point of view for dinuclear complexes by using the spin-
splitting. These results indicate that the overall behavior of polarization model and hybrid density functional theory
3 corresponds to a ferromagnetic interaction, which should (DFT). Kahn et al. first explained the ferromagnetic inter-
be attributed to the dinuclear superexchange mediated actions between EO azido-bridged dinuclear complexes on
through the µ1,1-azido bridges. Magnetic susceptibility the basis of the spin-polarization effect. This model con-
could be fit to a Curie–Weiss law with Curie constant C = siders that the electron of a bridging nitrogen atom (α spin)
32.57 emuKmol–1 and a positive Weiss constant θ = of the in-plane πg orbital (HOMO) is partially delocalized
6.25 K. The positive θ value and the shape of the χmT toward the two metal orbitals; the unpaired electrons occu-
curves for 3 indicate the existence of ferromagnetic interac- pying the orbitals are likely to have β spins, which favors
tions between double EO azido-bridged MnII ions.
ferromagnetic interactions. The interaction through the
Table 3. Comparison of structural parameters and magnetic data for end-on azido-bridged complexes.[a]
Complex
Mn–Nazido / Å
∆d / Å
θ / °
J / cm–1
Mn2(N3)4(ttp)2
Mn2(N3)4(ttp-N3)2
2.245(2)
2.252(3)
2.242(3)
2.227(3)
2.249(3)
2.240(3)
2.248(5)
0.236
0.252
0.150
0.090
0.030
0.072
0.053
0.002
0.003
0.006
0.059
0.0017
0
103.45(6)
103.13(12)
105.29(12)
104.6(1)
102.12
104.29
103.58
102.6(4)
102.55(12)
101.4(3)
103.11(10)
106.16(4)
98.8(5)
2.46(4)
2.25(2)
1.92(4)
2.43
0.77(1)
2.04(3)
1.75(2)
1.27
1.10
1.20
1.12
2.03
[Mn2(N3)4(ttp-N3)2]2[Mn(ttp-N3)(N3)3]
[Mn(terpy)(N3)2]2·2H2O[14a]
[Mn2(L1)2(µ1,1-N3)2](ClO4)2[15a]
[15a]
[Mn2(L2)2(µ1,1-N3)2](ClO4)2[15a]
[Mn2(L3)2(µ1,1-N3)2](ClO4)2
[Mn2(phen)4(µ1,1-N3)2][Co(bpb)(CN)2]2·H2O[15b] 2.229(6)
[Mn2(phen)4(µ1,1-N3)2][Cr(bpb)(CN)2]2·H2O[15b] 2.226(2)
[Mn2(phen)4(µ1,1-N3)2][Fe(bpb)(CN)2]2·H2O[15b] 2.288(5)
[Mn2(2,2Ј-dpa)2(N3)2(µ1,1-N3)2][14b]
2.237(3)
2.273(1)
2.234(2)
2.197(4)
[16]
[Mn(tptz)(µ1,1-N3)2]n
[Mn(pyz)(µ1,1-N3)2][20a]
0.61
0.40
[20b]
[Mn(2-bzpy)(µ1,1-N3)2]n
0.032
100.5(2)
[a] Average values. ∆d = d(Mn–Nazido) – d(Mn–NЈazido). L1 = [N,N-bis(pyridine-2-yl)benzylidene]ethane-1,2-diamine, L2 = [N,N-bis(pyrid-
ine-2-yl)-benzylidene]propane-1,3-diamine, L3 = [N,N-bis(pyridine-2-yl)benzylidene]butane-1,4-diamine, bpb2– = 1,2-bis(pyridine-2-car-
boxamido)benzenate, 2,2Ј-dpa = 2,2Ј-dipicolylamine, tptz = 2,4,6-tris(2-pyridyl)-1,3,5-triazine, pyz = pyrazine, 2-bzpy = 2-benzoylpyr-
idine.
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Eur. J. Inorg. Chem. 2007, 5670–5676

µ1,1-Azido-Bridged Dinuclear MnII Complexes Based on Tripyridyl Ligands
previously reported.[21] All other reagents were commercial grade
materials and used as received.
azido bridge does not depend on the surroundings of the
metal ions but only on the fashion of azido bridges.[9] DFT
calculations show that the value of J is mainly dependent
on the energy gap between the molecular orbitals associated
with the unpaired electrons (SOMOs). Aromí et al. recently
gave a rough relationship between the exchange coupling
constant (J) and the Mn–N–Mn bridging angle (θ), which
was afterwards improved to J = 0.614θ – 61.9 on the basis
of eight complexes.[15a,15b] The magnet data of this work
and available EO azido-bridged dinuclear complexes are in
good agreement with the fact that the exchange coupling
constant increase with the Mn–N–Mn bridging angle
(Table 3), which is consistent with theoretical predictions.[9a]
Measurements: Elemental analyses were determined with an Ele-
mentar Vario EL elemental analyzer. IR spectra were measured as
KBr pellets with a Magna-IR 750 spectrophotometer in the 4000–
400 cm–1 region. Variable-temperature magnetic susceptibility was
measured with a SQUID magnetometer with an applied magnetic
field of 2000 Oe for 1, 2, and 3.
Caution! Perchlorate and azide salts are potentially explosive and
should be handled carefully in small amounts.
4Ј-p-Tolyl-2,2Ј:6Ј,2ЈЈ-terpyridine (ttp): Yield: 8%. 1H NMR
(400 MHz, CDCl3): δ = 8.73 (s, 2 H), 8.69–8.60 (m, 4 H), 7.89–
7.80 (m, 4 H), 7.51 (d, J = 6.3 Hz, 2 H), 7.32 (ddd, J = 7.2, 4.6,
The J–θ relationship can be now improved on the basis of 1.2 Hz, 2 H), 2.45 (s, 3 H) ppm. C22H17N3 (323.40): calcd. C 81.71,
H 5.30, N 12.99; found C 81.53, H 5.47, N 12.50.
15 data sets listed in Table 3 to give the equation J =
0.276θ – 26.9, as shown in Figure 7. In addition, an increase
in the asymmetry of the azido bridging (∆d in Table 3) was
shown to bring about a decrease in antiferromagnetic inter-
actions (JAF), and consequently an increase in the global
magnetic exchange constant (J = JAF + JF).[14a] Careful ex-
amination of the data in Table 3 shows that the J values for
the dimeric complexes generally increase with an increase
in ∆d, which is in agreement with the above prediction.
4Ј-(p-Bromomethylphenyl)-2,2Ј:6Ј,2ЈЈ-terpyridine (ttp-Br): Yield
85%. 1H NMR (400 MHz, CDCl3): δ = 8.79 (s, 2 H), 8.76–8.69
(m, 4 H), 7.98–7.89 (m, 4 H), 7.61 (d, J = 6.5 Hz, 2 H), 7.41 (ddd,
J = 7.5, 4.8, 1.3 Hz, 2 H) ppm. C23H16BrN3 (414.30): calcd. C
65.68, H 4.01, N 10.44; found C 65.42, H 3.91, N 10.49.
[Mn2(N3)4(ttp)2] (1): An aqueous solution (5 mL) of sodium azide
(1.5 mmol) was placed in a tube to which was added a buffer layer
of water/methanol (10 mL). A methanol solution (10 mL) of
Mn(ClO4)2·6H2O (0.5 mmol) and ttp (0.5 mmol) was added to
form a third layer. Orange crystals were formed on interdiffusion
of the reactants in about 1 week. One suitable crystal was chosen
for single-crystal X-ray diffraction. Yield: 80.9 mg (35% based on
manganese). IR (KBr): ν = 2046 (vs) N=N=N, 1607 (vs), 1546 (s),
˜
1546 (s), 1474 (s), 1329 (m), 1015 (m), 821 (m), 790 (m), 733 (w),
686 (w), 660 (w) cm–1. C44H34Mn2N18 (924.77): calcd. C 57.15, H
3.71, N 27.26; found C 57.07, H 3.90, N 27.37.
[Mn2(N3)4(ttp-N3)2] (2): A solution of Mn(ClO4)2·6H2O (0.5 mmol)
and ttp-Br (0.5 mmol) in methanol (10 mL) was slowly diffused
into an aqueous solution (5 mL) of sodium azide (1.5 mmol) in the
dark. After 1 week, well-formed orange single crystals were ob-
tained. Yield: 75.5 mg (30% based on manganese). IR (KBr): ν =
˜
2093 (vs), 2056 (vs), 1603 (vs), 1569 (s), 1546 (s), 1404 (s), 1347
(m), 1326 (m), 1246 (s), 1199 (w), 1165 (m), 1014 (s), 883 (w), 856
(w), 829 (w), 786 (s), 740 (w), 686 (w), 659 (w) cm–1. C44H32Mn2N24
(1006.82): calcd. C 52.49, H 3.20, N 33.39; found C 52.11, H 3.29,
N 33.85.
Figure 7. Plot of J vs. Mn–N–Mn bond angle (θ) for EO azido-
bridged MnII compounds (᭹ this work, ᭡ 1D complexes). The
straight line represents the best fit.
[Mn2(N3)4(ttp-N3)2]3[Mn(ttp-N3)(N3)3]2 (3): The synthetic method
is slightly different from that of 2. A solution of Mn(ClO4)2·6H2O
(0.2 mmol) and ttp-Br (0.2 mmol) in methanol (10 mL) was dif-
fused into a solution of sodium azide (1.5 mmol) in water (5 mL).
After 4 weeks of exposure to light, red-brown crystals were formed.
Conclusions
We successfully prepared three doubly EO azido-bridged
dinuclear MnII complexes. The ferromagnetic properties of
dinuclear superexchange mediated through the µ1,1-azido
bridges were confirmed in all complexes. Consideration of
the intermolecular antiferromagnetic coupling of MnII or
the presence of zero-field splitting (ZFS) of the molecular
spin ground state allows the magnetic coupling constants
to be evaluated. On the basis of the results of this work and
the available µ1,1-azido-bridged MnII complexes, a clearer
magnetostructural correlation was reached.
Yield: 25.7 mg (25% based on manganese). IR (KBr): ν = 2086
˜
(sh), 2063 (vs), 2037 (vs), 1608 (vs), 1573 (s), 1547 (s), 1477 (s),
1431 (s), 1400 (s), 1326 (m), 1276 (m), 1246 (m), 1164 (m), 1013
(s), 891 (w), 829 (w), 790 (s), 733 (w), 690 (w), 659 (w) cm–1.
C176H128Mn8N102 (4111.32): calcd. C 51.42, H 3.14, N 34.75; found
C 51.40, H 3.25, N 34.48.
X-ray Structure Determination: Diffraction data were collected with
a Bruker Smart CCD area detector with graphite-monochromated
Mo-Kα (λ = 0.71073 Å) at room temperature. All calculations were
performed by using the SHELXS-97 and SHELXL-97 pro-
grams.[22] All structures were solved by direct method and refined
by the full-matrix least-squares method on F2 with anisotropic ther-
Experimental Section
Materials: 4Ј-p-Tolyl-2,2Ј:6Ј,2ЈЈ-terpyridine (ttp) and 4Ј-(p-bro- mal parameters for all non-hydrogen atoms. The hydrogen atoms
momethylphenyl)-2,2Ј:6Ј,2ЈЈ-terpyridine (ttp-Br) were prepared as were located geometrically and refined by using a riding model.
Eur. J. Inorg. Chem. 2007, 5670–5676
© 2007 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
www.eurjic.org
5675

M.-M. Yu, Z.-H. Ni, C.-C. Zhao, A.-L. Cui, H.-Z. Kou
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Received: June 29, 2007
Published Online: October 29, 2007
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