Five new pseudohalide bridged Mn(II) complexes of pyrimidine derived Schiff base ligands: Synthesis, crystal structures and magnetic properties

Article abstract of DOI:10.1016/j.poly.2013.10.021

Four new azide bridged dinuclear Mn(II) complexes [Mn(L₁) (μ_1,1-N₃)(N₃)]₂ (1), [Mn(L ₂)(μ_1,1-N₃)(N₃)]₂ (3), [Mn(L₃)(μ_1,1-N₃)(N₃)] ₂[(N₃)Mn(L₃)(μ_1,1-N ₃)(N₃)]₂ (4) and [Mn(L₄)(μ _1,1-N₃)(N₃)]₂[Mn(L ₄)(μ_1,1-N₃)(N₃)]₂ (5) and one new dicynamide bridged binuclear Mn(II) complex {[Mn₂(L ₁)₂(dca)₂(H₂O)₂(μ _1,5-dca)](ClO₄)} (2) have been synthesized using the pyrimidine derived primary Schiff base ligands L_n (n = 1-4), with azide and dicynamide as bridging ligands. All the five complexes were characterized by elemental analyses, IR spectroscopy and single crystal X-ray crystallography, together with magnetic measurements of 1-4. The tridentate Schiff base ligands are the [1 + 1] condensation products of 2-hydrazino-4,6-dimethyl pyrimidine with 2-acetyl pyridine, pyridine-2- carbaldehyde, 2-benzoyl pyridine and di(2-pyridyl) ketone for L_n (n = 1-4), respectively. All the complexes except 2 contain Mn(II)-azido links in which the Mn(II) centres are bridged by a di-μ_1,1-azido (double EO) group. The double EO bridging fragments in the complexes are similar with bridging angles (Mn-N-Mn) ranging from 102.59 to 104.81. Magnetic property studies reveal that in 1, 3 and 4 intramolecular ferromagnetic interactions are mediated through the EO azido bridges with J parameters in the range 4.3-5.12 cm^-1, while a weak antiferromagnetic interaction prevails in 2 (J = -0.12 cm^-1) via μ_1,5-dicynamide bridges. In addition, complexes 1, 3 and 4 show weak intermolecular antiferromagnetic interactions (J = -0.025 to -0.027 cm^-1).

Full text of DOI:10.1016/j.poly.2013.10.021

Polyhedron 68 (2014) 212–221
Contents lists available at ScienceDirect
Polyhedron
journal homepage: www.elsevier.com/locate/poly
Five new pseudohalide bridged Mn(II) complexes of pyrimidine derived
Schiff base ligands: Synthesis, crystal structures and magnetic properties
Sangita Ray a, Saugata Konar b, Atanu Jana a, Anamika Dhara a, Kinsuk Das c, Sudipta Chatterjee d,
Mohamed Salah El Fallah e, , Joan Ribas e, Susanta Kumar Kar a,
⇑
⇑
a Department of Chemistry, University College of Science, University of Calcutta, 92, A.P.C. Road, Kolkata 700009, India
b Department of Chemistry, Jadavpur University, Jadavpur, Kolkata 700032, India
c Department of Chemistry, Darjeeling Govt. College, Darjeeling 734101, India
d Department of Chemistry, Serampore College, Serampore, Hooghly 712201, India
e Departament de Química Inorgànica, Universitat de Barcelona Martí i Franquès, 1-11, 08028 Barcelona, Spain
a r t i c l e i n f o
a b s t r a c t
Article history:
Four new azide bridged dinuclear Mn(II) complexes [Mn(L1)(
l
1,1-N3)(N3)]2 (1), [Mn(L2)(
1,1-N3)(N3)]2[Mn(L4)(
and one new dicynamide bridged binuclear Mn(II) complex {[Mn2(L1)2(dca)2(H2O)2( 1,5-dca)](ClO4)} (2)
l
1,1-N3)(N3)]2 (3),
Received 30 April 2013
Accepted 9 October 2013
Available online 30 October 2013
[Mn(L3)(
l
1,1-N3)(N3)]2[(N3)Mn(L3)(l1,1-N3)(N3)]2 (4) and [Mn(L4)(
l
l1,1-N3)(N3)]2 (5)
l
have been synthesized using the pyrimidine derived primary Schiff base ligands Ln (n = 1–4), with azide
and dicynamide as bridging ligands. All the five complexes were characterized by elemental analyses, IR
spectroscopy and single crystal X-ray crystallography, together with magnetic measurements of 1–4. The
tridentate Schiff base ligands are the [1 + 1] condensation products of 2-hydrazino-4,6-dimethyl pyrim-
idine with 2-acetyl pyridine, pyridine-2-carbaldehyde, 2-benzoyl pyridine and di(2-pyridyl) ketone for Ln
(n = 1–4), respectively. All the complexes except 2 contain Mn(II)-azido links in which the Mn(II) centres
Keywords:
Manganese(II)
Double end-on azide
Dicyanamide
Dinuclear complexes
Magnetic properties
are bridged by a di-l1,1-azido (double EO) group. The double EO bridging fragments in the complexes are
similar with bridging angles (Mn–N–Mn) ranging from 102.59° to 104.81°. Magnetic property studies
reveal that in 1, 3 and 4 intramolecular ferromagnetic interactions are mediated through the EO azido
bridges with J parameters in the range 4.3–5.12 cmꢀ1, while a weak antiferromagnetic interaction pre-
vails in 2 (J = ꢀ0.12 cmꢀ1) via
l1,5-dicynamide bridges. In addition, complexes 1, 3 and 4 show weak
intermolecular antiferromagnetic interactions (J = ꢀ0.025 to ꢀ0.027 cmꢀ1).
Ó 2013 Elsevier Ltd. All rights reserved.
1. Introduction
(1-1,1 or EO) and antiferromagnetic for the end-to-end mode
(1-1,3 or EE) [8,9]. On the other hand, the appropriate choice of
metal ions along with the bridging ligands is also an important fac-
tor for such works. Among the first-row transition metal ions,
high-spin Mn(II) centers are quite desirable because they contain
the highest possible number of unpaired electrons [10]. To date,
the reported Mn(II)-azido coordination compounds include one-
dimensional (1D) chain complexes [11], two-dimensional (2D)
layer complexes [12,13], three-dimensional (3D) framework
complexes [14,15] and polynuclear complexes [16,17]. Dicyanam-
ide (dca) has been shown to be a versatile ligand which may
coordinate to metal ions as a terminal ligand through the nitrile
The construction of transition-metal supramolecular arrays
based on covalent or hydrogen bonding interactions are an area
of great research activity in inorganic chemistry. From a magnetic
point of view, covalent systems are particularly interesting as they
can provide high magnetic ordering. A rational design of these ar-
rays implies that the selection and employment of appropriate
bridging ligands which can mediate magnetic coupling between lo-
cal spin carriers has allowed us to access a variety of high nuclear-
ity products with interesting structural and magnetic properties.
Our strategy is to use potential bridging ligands, such as azide [1]
or dicyanamide [2,3], having versatile binding modes and confor-
mational flexibility in the synthesis of new Mn(II) complexes
[4,5]. The coordination modes of the azide ligand greatly affect
the nature and magnitude of the magnetic exchange interactions
in dinuclear complexes. Magnetic coupling mediated through an
azide bridge is normally ferromagnetic [6,7] for the end-on mode
nitrogen [2,18] or amide nitrogen [2,18], a
the amide nitrogen and one nitrile nitrogen [2,18], and an
end-to-end 2-1,5 bridge through two nitrile nitrogen atoms
with weak antiferromagnetic coupling [2,18], and also a 3-1,3,5
l2-1,3-bridge through
l
l
bridge through all of the nitrogen atoms, showing weak or
strong ferromagnetic coupling [2,18]. As a matter of fact, dca can
be utilized as a useful connector between metal centers to form
higher-dimensional molecular frameworks having interesting
structures and molecular properties. In continuation, using
⇑
Corresponding authors. Tel.: +91 9831077929; fax: +9103323508386.
E-mail address: skkar_cu@yahoo.co.in (S.K. Kar).
0277-5387/$ - see front matter Ó 2013 Elsevier Ltd. All rights reserved.
http://dx.doi.org/10.1016/j.poly.2013.10.021

S. Ray et al. / Polyhedron 68 (2014) 212–221
213
manganese(II) perchlorate as the metal precursor, four new azide
bridged dinuclear manganese(II) complexes, [Mn(L1)( 1,1-N3)(N3)]2
(1), [Mn(L2)( 1,1-N3)(N3)]2 (3) [Mn(L3)( 1,1-N3)(N3)]2[Mn(L3)
1,1-N3)(N3)]2 (4) and [Mn(L4)( 1,1-N3)(N3)]2[Mn(L4)( 1,1-N3)
(N3)]2 (5), and one new dca bridged binuclear manganese(II)
complex, {[Mn2(L1)2(dca)2(H2O)2( 1,5-dca)](ClO4)} (2), have been
Caution! Although we have not encountered any problems, it
should be kept in mind that perchlorate compounds of metal ions
are potentially explosive in the presence of organic ligands. Only a
small amount of the material should be prepared and it should be
handled with care.
l
l
l
(
l
l
l
l
synthesized (Scheme 1). We report here the synthetic details, spec-
tral characterizations and X-ray crystal structures of 1, 2, 3, 4 and 5,
and the magnetic properties of 1–4, where the pseudohalides
(azide, dca) act as terminal ligands as well as bridges (l1,1; l1,5)
in the presence of the primary ligands.
2.2. Physical measurements
The infrared spectra of the complexes were recorded on a Per-
kin–Elmer RX I FT-IR spectrophotometer with KBr discs (4000–
400 cmꢀ1). Elemental analyses (C, H and N) were carried out using
a Perkin–Emer 2400 II elemental analyzer.1H NMR spectra were re-
corded on a Bruker 300 MHz FT-NMR spectrometer using trimeth-
ylsilane as an internal standard in d6-DMSO for ligands L3 and L4.
The electronic spectra of 1, 2, 3, 4 and 5 in purified methanol solu-
tion were recorded on a Hitachi model U-3501 spectrophotometer.
The magnetic studies of 1–4 were carried out on polycrystalline
samples using a Quantum Design MPMS-XL SQUID magnetometer
operating in the 300–2 K temperature range and 0.05–0.7 T. Pas-
cal’s constants were utilized to estimate the diamagnetic correc-
tions, the value in each case being subtracted from the
experimental susceptibility data to give the molar magnetic sus-
ceptibility (øM).
2. Experimental
2.1. Materials
All chemicals were of reagent grade, purchased from commer-
cial sources and used without further purification. Pyridine-2-carb-
aldehyde, 2-acetyl pyridine, 2-benzoyl pyridine and di(2-pyridyl)
ketone were purchased from Aldrich. The other commercially
available chemicals and solvents were used and purified by stan-
dard procedures.
e
M
N
R
+
N
NH2
N
N
H
e
M
O
:
mo ar rat o
1 1
l
,
i
,
e
re ux
fl
M
H
O
e
M
N
N
N
N
N
H
e
M
R
Scheme 1. Schematic representation of the ligands (L1, L2, L3 and L4) and their complexes (1–5).

214
S. Ray et al. / Polyhedron 68 (2014) 212–221
2.3. Syntheses of the ligands (L1, L2, L3 and L4)
filtered. The light yellow solution was kept in a refrigerator at
15 °C, which produced orange yellow hexagonal crystals suitable
for X-ray diffraction after 10 days. The crystals were isolated by fil-
tration and air-dried. Yield: (0.556 g, 61.5%). Anal. Calc. for C32H34-
Mn2N19O6Cl: C, 41.50; H, 3.70; N, 28.74. Found: C, 41.45; H, 3.66;
The ligands L1 and L2 were synthesized following the literature
method [19].
The ligand L3 was synthesized by refluxing a methanolic solu-
tion (30 ml) of 2-hydrazino-4,6-dimethyl pyrimidine (1.38 g,
10 mmol) with 2-benzoyl pyridine (1.83 g, 10 mmol) taken in the
same solvent (10 ml). Refluxing was continued for 1 h at water
bath temperature. The resulting light yellow solution was filtered
and kept at RT for slow evaporation. A light yellow microcrystalline
compound separated out after a week. It was filtered off, washed
several times with cold methanol and dried in vacuo over fused
CaCl2.
N, 28.79%. IR (KBr; m mas), 2176 (ms C„N),
/cmꢀ1): 2285 (ms C„N +
1085 (ClO4 ion) UV–Vis (MeOH; kmax/nm): 376.
2.4.3. Preparation of complexes 3, 4 and 5
Complexes 3, 4 and 5 were prepared by the same procedure as
1, using Mn(ClO4)2ꢁ6H2O as the metal precursor and with the
ligands L2, L3 and L4, respectively.
For 3: Yield: (0.450 g, 61.5%). Anal. Calc. for C24H26Mn2N22: C,
39.35; H, 3.58; N, 42.07. Found: C, 39.29; H, 3.52; N, 42.11%. IR
L3: Yield: 3.13 g (85%); M.p.:95 °C; Anal. Calc. for C18H17N5: C,
71.27; H, 5.65; N, 23.09. Found: C, 71.21; H, 5.61; N, 23.11%. 1H
´
(KBr;
(MeOH; kmax/nm): 377.
m m C@Npym). UV–Vis
/cmꢀ1): 2070 (vs) (mas N3), 1605 (s) (
NMR, (d6-DMSO, d): 2.34 (6H, s, 400-CH3 and 600–CH3), 6.78 (1H, s,
500-H), 7.46 (1H, ddd, J = 8.0, 5.0, 1.5 Hz, H-5), 7.47 (1H, ddd,
J = 8.0, 1.0, 1.0 Hz, H-3), 7.53 (1H, ddd, J = 8.0, 5.0, 1.5 Hz, H-50),
7.94 (1H, ddd, J = 8.0, 1.5, 1.0 Hz, H-30), 7.96 (1H, ddd, J = 8.0, 8.0,
1.5 Hz, H-40), 7.97 (1H, ddd, J = 8.0, 7.5, 1.5 Hz, H-4), 8.57 (1H,
ddd, J = 5.0, 1.5, 1.0 Hz, H-6), 8.84 (1H, ddd, J = 5.0, 1.5, 1.0 Hz, H-
For 4: Yield: (0.500 g, 61.5%). Anal. Calc. for: C36H34Mn2N22: C,
48.87; H, 3.87; N, 34.83. Found: C, 48.80; H, 3.82; N, 34.89%. IR
(KBr;
(MeOH; kmax/nm): 378.
m m C@Npym). UV–Vis
/cmꢀ1): 2071 (vs) (mas N3), 1615 (s) (
For 5: Yield: (0.550 g, 61.5%). Anal. Calc. for C34H34Mn2N24O: C,
60). IR (KBr;
C–H), 1215 (ms), (
m
/cmꢀ1): 3412 (
C@C), 1065 (m) (pym).
m N–H), 1528 (m C@N), 2920 (w) (m
44.31; H, 3.83; N, 36.47. Found: C, 40.24; H, 3.80; N, 36.53%. IR
(KBr; m m C@Npym). UV–Vis
/cmꢀ1): 2080 (vs) (mas N3), 1594 (s) (
m
The ligand L4 was synthesized by refluxing a methanolic solu-
tion (30 ml) of 2-hydrazino-4,6-dimethyl pyrimidine (1.38 g,
10 mmol), with di(2-pyridyl) ketone (1.84 g, 10 mmol) taken in
the same solvent (10 ml). Refluxing was continued for 1 h at water
bath temperature. The resulting light yellow solution was filtered
and kept at RT for slow evaporation. A light yellow microcrystalline
compound separated out after a week. It was filtered off, washed
several times with cold methanol and dried in vacuo over fused
CaCl2.
(MeOH; kmax/nm): 377.
3. Single crystal X-ray crystallography
Selected crystal data for 1, 2, 3, 4 and 5 are given in Table 1 and
selected metrical parameters of the complexes are given in
Table S1. For complexes 1, 2, 4 and 5, data collections were made
using a Bruker SMART APEX II CCD area detector equipped with a
graphite monochromated Mo K
in the scan mode at 150(2) K. For complex 3, data collection
was made using a Bruker SMART APEX CCD area detector area detec-
tor equipped with a graphite monochromated Mo K radiation
(k = 0.71073 Å) source in the and scan modes at 296(2) K. Cell
a radiation (k = 0.71073 Å) source
L4: Yield: 3.13 g (85%); M.p.: 84 °C; Anal. Calc. for C17H16N6: C,
67.09; H, 5.30; N, 27.61. Found: C, 67.02; H, 5.25; N, 27.65%. 1H
NMR, (CDCl3, d): 2.41 (6H, s, 400-CH3 and 600-CH3), 6.56 (1H, s, 500-
H), 7.39 (3H, ddd, J = 8.0, 5.0, 1.5 Hz, H-5), 7.47 (1H, ddd, J = 8.0,
1.0, 1.0 Hz, H-3), 7.53 (1H, ddd, J = 8.0, 5.0, 1.5 Hz, H-50), 7.97
(1H, ddd, J = 8.0, 7.5, 1.5 Hz, H-4), 7.64–7.69 (1H, m), 8.87 (1H,
x
a
u
x
parameter refinement and data reduction were carried out using
Bruker SMART [20] and Bruker SAINT software for all the five com-
plexes. The structures were solved by direct and Fourier methods
and refined by full-matrix least-squares based on F2 using the SHEL-
XS-97 and SHELXL-97 programs [21] For 5, one water molecule was
present as a solvent molecule, which was removed using SQUEEZE.
Thus two hydrogen atoms and one oxygen atom of a water mole-
cule were added to the chemical formula to adjust the density,
molecular mass and F000 value. For 1, 2, 4 and 5, the non-hydrogen
atoms were refined anisotropically until the convergence was
attained.
´
dd, J = 5.0, 1.5, Hz, H-6), 8.62 (1H, ddd, J = 5.0, 1.5, 1.0 Hz, H-6).IR
(KBr; N–H), 1528 ( C@N), 2920 (w) ( C–H),
/cmꢀ1): 3412 (
1215 (ms), ( C@C), 1065 (m) (pym).
m
m
m
m
m
2.4. Preparation of the complexes
2.4.1. Preparation of complex 1
To a methanol solution (30 ml) of Mn(ClO4)2.6H2O (0.18 g,
2 mmol), a solution of the Schiff base L1 in the same solvent
(20 ml) (0.482 g, 2 mmol) was slowly added with stirring at RT, fol-
lowed by drop-by-drop addition of a 4 ml aqueous solution of
NaN3 (0.260 g, 4 mmol). The stirring was continued for an addi-
tional 2 h and then the reaction mixture was filtered. The orange
yellow filtrate was left at room temperature. Orange yellow crys-
tals suitable for X-ray diffraction were obtained by slow evapora-
tion of the filtrate after several days in a refrigerator at 15 °C.
The crystals were isolated by filtration and air-dried. Yield:
(0.395 g, 61%). Anal. Calc. for C26H30Mn2N22: C, 41.06; H, 3.98; N,
4. Result and discussion
4.1. Syntheses
The ligands L1, L2, L3 and L4 were synthesized by the direct con-
densation reaction of 2-hydrazino-4,6-dimethyl pyrimidine with
2-acetyl pyridine, pyridine-2-carbaldehyde, 2-benzoyl pyridine
and di(2-pyridyl) ketone, respectively, taken in methanol in a
1:1 M proportion. The complexation behavior of L1, L2, L3 and L4
toward Mn(II) salts was investigated. The complexes 1, 3, 4 and 5
were obtained by mixing the ligands with Mn(ClO4)2ꢁ6H2O salt
and sodium azide, taken in a 1:1:2 M ratio in methanol, whereas
complex 2 was obtained by mixing the ligand L1 with the
Mn(ClO4)2ꢁ6H2O) salt and sodium dicynamide, taken in a 1:1:2 M
ratio in methanol. X-ray quality crystals of 1, 2, 3, 4 and 5 were
obtained upon slow evaporation of the filtered reaction mixtures
at 10 °C in a refrigerator.
40.52. Found: C, 41.01; H, 3.91; N, 40.60%. IR (KBr;
(vs) ( as N3), 1618 (s) ( C@Npym). UV–Vis (MeOH; kmax/nm): 378.
m
/cmꢀ1): 2064
m
m
2.4.2. Preparation of complex 2
To a methanol solution (30 ml) of Mn(ClO4)2ꢁ6H2O (0.18 g,
2 mmol), a solution of the Schiff base L1 in the same solvent
(20 ml) (0.482 g, 2 mmol) was slowly added, followed by a solution
of sodium dicyanamide (0.356 g, 4 mmol) in a minimum volume
(5 ml) of aqueous methanol with constant stirring. The stirring
was continued for another 2 h and then the reaction mixture was

S. Ray et al. / Polyhedron 68 (2014) 212–221
215
Table 1
Experimental data for crystallographic analysis of 1, 2, 3, 4 and 5.
Compound
1
2
3
4
5
Empirical formula
Formula weight
T (K)
C
26H30Mn2N22
C32H34Mn2N19O2,ClO4
926.11
150
C24H26Mn2N22
732.55
296
C36H34Mn2N22
884.73
150
C34H32Mn2N24, H2O
904.72
150
760.60
150
Wavelength (Å)
Crystal system
Space group
Unit cell dimensions
a (Å)
0.71073
monoclinic
C2/c
0.71073
monoclinic
C2/c
0.71073
orthorhombic
Pca21
0.71073
triclinic
P1
0.71073
triclinic
ꢀ
ꢀ
P1
16.789(5)
14.647(4)
14.447(4)
90.00
106.25(2)
90.00
3410.7(17)
4
1.481
10.1357(3)
15.8739(5)
25.6927(8)
90.00
92.519(1)
90.00
4129.8(2)
4
1.490
17.326(2)
11.4451(14)
16.430(2)
90.00
90.00
90.00
3258.0(7)
4
1.493
10.761(3)
11.404(3)
18.429(5)
87.50(3)
85.64(4)
80.37(3)
2222.2(11)
2
10.8317(9)
11.3594(9)
18.3187(15)
88.760(2)
84.470(2)
80.168(2)
2210.5(3)
2
b (Å)
c (Å)
a
(°)
b (°)
c
(°)
V (Å3)
Z
Dcal (Mg mꢀ3
)
1.322
1.332
Absorption coefficient
0.796
0.743
0.829
0.622
0.741
(mmꢀ1
)
F(000)
1560
1.9–27.0
1896
1.6–35.4
1496.0
1.8–23.5
908
1.8–24.7
908
1.1, 26.5
h Range (o) for data
collection
Index ranges
ꢀ20 6 h 6 20,
ꢀ17 6 k 6 17,
ꢀ17 6 l 6 18
ꢀ16 6 h 6 16,
ꢀ25 6 k 6 25,
ꢀ41 6 l 6 40
1.034
ꢀ14 6 h 6 19,
ꢀ12 6 k 6 12,
ꢀ18 6 l 6 18
0.962
ꢀ12 6 h 6 12,
ꢀ13 6 k 6 13,
ꢀ21 6 l 6 19
1.029
ꢀ12 6 h 6 13,
ꢀ14 6 k 6 14,
ꢀ22 6 l 6 22
1.091
Goodness-of-fit (GOF) on 0.995
F2
Completeness to
98.6
98.0
100
97.9
91.7
h = 25.00° (%)
Independent reflections 3697 (0.111)
9199 (0.026)
4794 (0.027)
7427 (0.034)
8445 (0.030)
(Rint
)
Absorption correction
Refinement method
multi-scan
multi-scan
multi-scan
multi-scan
multi-scan
full-matrix least squares
full-matrix least squares
full-matrix least squares
full-matrix least squares
full-matrix least squares
on F2
on F2
on F2
on F2
on F2
Data/restraints/
parameters
3697, 0, 228
9199, 0, 287
4794, 1, 437
7427, 0, 533
8445, 2, 553
Reflections collected
8251
34436
19099
7427
8445
Final R indices [I > 2r(I)] R1 = 0.0643, WR2 = 0.1831 R1 = 0.0501, WR2 = 0.1610 R1 = 0.0330, WR2 = 0.0956 R1 = 0.0635, WR2 = 0.1996 R1 = 0.0471, WR2 = 0.1551
Largest difference peak
ꢀ0.41, 0.63
ꢀ0.56, 0.56
ꢀ0.14, 0.31
ꢀ0.55, 0.57
ꢀ0.28, 0.41
and hole (e Åꢀ3
Max and min
)
0.8899 and 0.8700
0.9163 and 0.8952
0.905 and 0.861
0.9348 and 0.9180
0.9163 and 0.8969
Transmission
4.2. Structural description
4.2.1. Structural description of complexes 1 and 3
Perspective views of complexes 1 and 3 with the atom number-
ing schemes are shown in Figs. 1 and 5, respectively. Complexes 1
and 3 crystallize in the space groups C2/c and Pca21 respectively.
The structure of 1 is a centrosymmetric [Mn(L1)(
mer, while the structure of 3 is a non-centrosymmetric [Mn(L2)(-
1,1-N3)(N3)]2 dimer, and each structure is formed by the union
l1,1-N3)(N3)]2 di-
l
of two MnL1(N3)2 and MnL2(N3)2 fragments, respectively. The unit
cells of 1 and 3 are comprised of four molecules. Each Mn(II) cation
shows a distorted octahedral geometry. In 1, the equatorial plane is
formed by the nitrogen atoms N1 from pyrimidine, N4 from azo-
methine, N5 from pyridine and N6 from a bridging azide group.
In case of 3, four nitrogen atoms, N15 from pyrimidine, N13 from
azomethine, N12 from pyridine and N6 from a bridging azide
group form the equatorial plane for Mn1, and N4 from pyrimidine,
N2 from azomethine, N1 from pyridine and N9 from another
bridging azide group form the equatorial plane for Mn2. In both
complexes the axial positions are occupied by an N atom from a
bridging azide (N6 for 1, N9 for 3) and another nitrogen atom from
a dangling azide (N9 for 1 and N17 for 3). The Mn atoms in
complex 1 are shifted by a distance of 0.215 Å downward from
the basal plane, but in the case of complex 3 the same atoms are
shifted by distances of 0.207 and 0.220 Å downward from the basal
plane towards the dangling azide unit in both cases. The N1,
Fig. 1. Structural representation and atom numbering scheme of 1 (H-atoms are
omitted for clarity).

216
S. Ray et al. / Polyhedron 68 (2014) 212–221
Fig. 2. Hydrogen bonding interactions in complex 1.
Fig. 3. Structural representation and atom numbering scheme of 2 (H-atoms are omitted for clarity).
Fig. 4. Hydrogen bonding interactions in complex 2.
1-azide–Mn–N1,1-azide bond angle of 77.41° is greater than the
N(9)1,1-azide–Mn1–N(6)1,1-azide bond angle of 76.26° and the
N(9)1,1-azide–Mn2–N(6)1,1-azide bond angle of 76.61°. The exis-
tence of an inversion center causes the Mn1–N6–Mn1A–N6A unit
in 1 to form a parallelogram (sides and angles are a = 2.175 Å,
b = 2.339 Å, 77.41 and 102.59°). In dimeric unit of 1 the Mnꢁ ꢁ ꢁMn
distance is 3.524 Å, which is greater than the Mnꢁ ꢁ ꢁMn distance
of 3.493 Å in 3. The bridging Mn1–N9–Mn1A angle of 102.59° in
complex 1 is slightly smaller than the bridging Mn1–N6–Mn2 an-
gle of 103.96° and Mn1–N9–Mn2 angle of 103.17° in complex 3.
The crystal structures of compounds 1 and 3 can be described as
1D and a 2D layer due to intermolecular hydrogen bonding (Figs. 2
and 6). The complexes are stabilized by a network of intermolecu-
lar hydrogen bonding between H3N of N3 and N9 of the dangling
azide for 1, H20 of N14 and N22 of the dangling azide, H4 of N3
and N19 of the dangling azide for 3. Details of the hydrogen bond-
ing are given in Table 2.
4.2.2. Structural description of complex 2
A perspective view of complex 2 with the atom numbering
scheme is shown in Fig. 3. Complex 2 crystallizes in the space group
C2/c. The structure of 2 consists of two Mn(L1)(H2O)(dca) fragments

S. Ray et al. / Polyhedron 68 (2014) 212–221
217
Table 2
Details of hydrogen bond distances (Å) and angles (°) for 1, 2, 3 and 5.
D–Hꢁ ꢁ ꢁA
d(D–H)
d(Hꢁ ꢁ ꢁA)
d(Dꢁ ꢁ ꢁA)
\(DHA)
Complex 1
N3–H3Nꢁ ꢁ ꢁN9
0.8600
0.76(3)
2.2800
2.05(3)
2.956(7)
2.797(3)
136.00
168(3)
Complex 2
O1–H1Bꢁ ꢁ ꢁN8
Complex 3
N3–H4ꢁ ꢁ ꢁN19
N14–H20ꢁ ꢁ ꢁN22
Complex 5
0.8600
0.8600
2.1000
2.0400
2.891(8)
2.882(7)
153.00
165.00
N15–H15Nꢁ ꢁ ꢁN2
0.88(2)
0.88(2)
2.22(2)
2.52(3)
3.081(3)
2.989(3)
167.00
114.00
N3–H3Nꢁ ꢁ ꢁN6
non-identical units of centrosymmetric [Mn(L3)(
l
1,1-N3)(N3)]2,[-
Mn(L3)( 1,1-N3)(N3)]2 and [Mn(L4)(l1,1-N3)(N3)]2,[Mn(L4)(l1,1-
l
N3)(N3)]2 dimers, formed by the union of two separate MnL3(N3)2
fragments and MnL4(N3)2 respectively. Complexes 4 and 5 crystal-
ꢀ
lize in the space group P1. The unit cells of 4 and 5 comprise of two
molecules. Each manganese(II) cation sits at the centre of a dis-
torted octahedral geometry in each unit of the two complexes. In
4, the equatorial plane of one unit is formed by the atoms N5 from
pyrimidine, N2 from azomethine, N1 from pyridine and N9 from a
bridging azide group and another unit by the atoms N16 from
pyrimidine, N13 from azomethine, N12 from pyridine and N20
from a bridging azide group. In 5, the equatorial plane of one unit
is formed by the atoms N9 from pyrimidine, N12 from azomethine,
N7 from pyridine and N4 from a bridging azide group and another
unit by the atoms N24 from pyrimidine, N21 from azomethine,
N19 from pyridine and N13 from a bridging azide group. In both
complexes the axial positions are occupied by a nitrogen atom
from a bridging azide (N9 for Mn1 in one unit and N20 for Mn2
in other unit for complex 4, N4 for Mn1 in one unit and N13 for
Mn2 in other unit for complex 5) and another nitrogen atom from
a dangling azide (N6 for Mn1 in one unit and N17 for Mn2 in other
unit for complex 4 and N1 for Mn1 in one unit and N16 for Mn2 in
other unit for complex 5). The Mn1 and Mn2 atoms are shifted by
distances of 0.276 and 0.242 Å upward from the equatorial plane
towards the dangling azide unit respectively for complex 4, and
0.244 and 0.212 Å upward from the equatorial plane towards the
dangling azide unit for complex 5. The existence of an inversion
center causes the Mn1–N4–Mn1A–N4A and Mn2–N13–Mn2A–
N13A units to form parallelograms in complex 4 and the Mn1–
N9–Mn1A–N9A and Mn2–N20–Mn2A–N20 units in complex 5
(sides and angles for Mn1 and Mn2 are a1 = 2.171, b1 = 2.338,
a2 = 2.153, b2 = 2.323 Å, 75.19° and 76.54° for 4, and sides and
Fig. 5. Structural representation and atom numbering scheme of 3 (H-atoms are
omitted for clarity).
bridged by one end-on bridging dicynamide group. The unit cell
comprises of four molecules. A dangling dicynamide is attached
to each Mn(II) centre. Here the ligand L1 acts as a neutral tridentate
NNN donor. Each Mn atom has a distorted octahedral geometry
with a N(CN)2 bridge. Three nitrogen atoms, N5 from pyrimidine,
N2 from azomethine and N1 from pyridine, and one oxygen atom,
O1 from H2O, form the equatorial plane for Mn01. In both the metal
centers the axial positions are occupied by N9 from a bridging
dicynamide and N6 from a dangling dicynamide. Both the Mn
atoms are shifted downward slightly towards the dangling dicyna-
mide by 0.060 Å from the equatorial plane. The axial Mn1–N9 bond
(2.182 Å) is larger than the other axial Mn1–N6 bond (2.150 Å). In
this species, the Mnꢁ ꢁ ꢁMn separation is 8.563 Å. The complex is sta-
bilized by a network of intermolecular hydrogen bonding involving
H1B of H2O and N8 of a dangling dicynamide (Fig. 4). Details of the
hydrogen bonding are given in Table 2.
4.2.3. Structural description of complexes 4 and 5
Perspective views with atom numbering schemes of 4 and 5 are
shown in Figs. 7 and 8. The structures of 4 and 5 consist of two
Fig. 6. Hydrogen bonding interactions in complex 3.

218
S. Ray et al. / Polyhedron 68 (2014) 212–221
Fig. 7. Structural representation and atom numbering scheme of 4 (H-atoms are omitted for clarity).
Fig. 8. Structural representation and atom numbering scheme of 5 (H-atoms are omitted for clarity).
angles for Mn1 and Mn2 are a1 = 2.169, b1 = 2.327, a2 = 2.161,
b2 = 2.298 Å, 75.91° and 76.26° for 5). In complex 4, the Mnꢁ ꢁ ꢁMn
separation distances are 3.574 and 3.516 Å in the two units. In
complex 5, the Mnꢁ ꢁ ꢁMn separation distances are 3.547 and
3.509 Å in the two units. The crystal structure of complex 5 can
be described as a 1D layer due to intermolecular hydrogen bonding
(Fig. 9).
5. Characterization of the ligand and the complex species
5.1. Infrared spectroscopy
The infrared spectra of the complexes are consistent with the
structural data given in this paper. The coordination mode of azide
is usually detected by an intense IR band due to mas(N3), which
Fig. 9. Hydrogen bonding interactions in complex 5.

S. Ray et al. / Polyhedron 68 (2014) 212–221
219
15
14
13
12
15
14
13
12
11
10
9
10
8
10
8
6
6
μ
μ
4
4
2
2
0
11
0
0
10000
20000
30000
40000
50000
χ
H / G
0
10000 20000
30000 40000
50000
χ
10
9
H / G
0
50
100
150
T / K
200
250
300
0
50
100
150
200
250
300
T / K
Fig. 12. Experimental and calculated temperature dependence of
complex 3.
vMT for
Fig. 10. Experimental and calculated temperature dependence of
complex 1.
vMT for
at 25 K for 1, 14.4 cm3 molꢀ1 K at 25 K for 3 and 14.577 cm3 -
molꢀ1 K for 4 at 10 K, and finally decreased to 12.7 cm3 molꢀ1
K
K
occurs above 2000 cmꢀ1 The strong sharp bands at 2064, 2070,
.
at 2 K for 1, 12.6 cm3 molꢀ1 K at 2 K for 3 and 12.76 cm3 molꢀ1
2071 and 2080 cmꢀ1 in the IR spectra of 1, 3, 4 and 5 are attributed
to the presence of the l1,1 bridging azide group in their structures
at 2 K for 4. The shapes of these curves are characteristic for the
occurrence of ferromagnetic interactions between the Mn(II) cen-
ters and the existence of antiferromagnetic intermolecular interac-
tions. Taking into account the dinuclear nature of complexes 1, 3
and 4, the susceptibility data were fitted by the formula given by
Kahn [24] based on the exchange Hamiltonian H = ꢀJSiSj including
the J0 parameter (intermolecular interactions) using of the mean
field approach. The best fit is given by the exchange parameters
J = 5.12 0.09 cmꢀ1, J0 = ꢀ0.026 cmꢀ1; g = 2.00 0.002 (typical va-
[22]. The strong
m(C@N) azomethine bands occurring at 1618,
1605, 1615 and 1594 cmꢀ1 for 1, 3, 4 and 5 respectively are
shifted considerably towards lower frequencies compared to that
of the free Schiff base ligands (1635 cmꢀ1), indicating coordination
of the imino nitrogen atom [23]. Complex 2 exhibit strong charac-
teristic absorption bands in the region 2300–2170 cmꢀ1 which are
attributed to massym
+ m
sym (C„N) combination modes (2285 cmꢀ1),
m
assym(C„N) (2230 cmꢀ1) and msym (C„N) (2176 cmꢀ1).
lue for a Mn(II) ion) and R = 3.1 ꢂ 10ꢀ4 for 1, J = 4.30 0.1 cmꢀ1
,
J0 = ꢀ0.025 cmꢀ1; g = 1.99 0.003 (typical value for a Mn(II) ion)
and R = 3.3 ꢂ 10ꢀ4 for 3 and J = 4.43 0.06 cmꢀ1, J0 = ꢀ0.027 cmꢀ1
;
6. Magnetic properties
g = 2.02 0.01 and R = 7.6 ꢂ 10ꢀ5 for 4. The plot of the reduced
6.1. Magnetic behavior of complexes 1, 3 and 4
magnetization (M/lB) vs H at 2 K achieves a value of ca 10 NlB
(corresponding to 2 Mn2+ ions) for 1 and 3 and 10.04 NlB for 4
(again corresponding to 2 Mn2+ ions), but it does not follow per-
fectly the Brillouin function, due undoubtedly to the ferromagnetic
coupling between the two manganese centers. The ferromagnetic
behavior of these Mn(II) complexes can be explained taking into
account the two azido bridging ligands in a 1,1 (end-on) coordina-
tion mode. This coordination mode generally gives a ferromagnetic
The variable temperature magnetic susceptibility data for com-
plexes 1, 3 and 4 were recorded between 300 and 2 K. The plots of
v
MT vs. T, Figs. 10, 12 and 13, give vM T values of 9.2 cm3 molꢀ1
K
for 1, 9.1 cm3 molꢀ1 K for 3 and 9.449 cm3 molꢀ1 K for 4 at 300 K,
which are the values expected for two Mn ions. On decreasing
the temperature, the values of
v K
MT increased to 14.6 cm3 molꢀ1
8.5
10
8.0
8
6
7.5
μ
4
7.0
2
χ
0
0
10000
20000
30000
40000
50000
6.5
H / G
0
50
100
150
200
250
300
T / K
Fig. 11. Experimental and calculated temperature dependence of
complex 2.
v
MT for
Fig. 13. Experimental and calculated temperature dependence of
complex 4.
vMT for

220
S. Ray et al. / Polyhedron 68 (2014) 212–221
interaction for any metal (with a few exceptions, due to crystallo-
graphic peculiarities). This ferromagnetic behavior may be attrib-
uted to the principal factors that influence the sign of the
bridged dicynamide ions (l1,5) in 2. In all the former four isostruc-
tural complexes each metal centre has a distorted octahedral
geometry. In complex 2, one Mn(II) centre is coordinated by three
nitrogen donors of the Schiff base ligand (L1) and the remaining
three donor atoms are supplied by two nitrogen atoms of the
exchange interaction in [{l
1,1-N3}2MII] systems [24–26]. Mag-
neto-structural correlation studies have shown a dependence of
the ferromagnetic exchange coupling constant (J) on the M–
N(azide)–M angle. For Mn, the ferromagnetic exchange appears
to increase with an increase of the bridging angle (starting from
100°) involved in the exchange pathway [27]. Some authors [28]
have tried to deduce from only four dinuclear MnII compounds a
linear relationship between the exchange integral (J) and the azide
bridging angle (h), which is not well accomplished in complexes 1,
3 and 4. More examples of cluster complexes and their J values
with this kind of azido bridging ligand have been reported in liter-
ature [29].
(l1,5) dangling dca anion and an oxygen atom of a water molecule.
Complexes 1, 3, 4 and 5 show similar magnetic properties, charac-
teristic of a ferromagnetic interaction between the Mn centres with
a certain amount of antiferromagnetic intermolecular interactions.
Compound 2 shows a weak antiferromagnetic interaction between
the Mn centres.
Acknowledgements
Sangita Ray acknowledges the University Grants Commission
(UGC), New Delhi, India for financial assistance. Financial support
[Sanc. No. F.5-1/2007(BSR)/5-16/2007(BSR), dated 12.02.2006]
from the Department of Science and Technology (DST), New Delhi,
India, is also gratefully acknowledged. S.K. thanks CSIR for the
award of an SRF. X-ray crystallography was performed at the DST
funded National Single Crystal Diffractometer facility at the
Department of Chemistry, University of Calcutta. Mohamed Salah
El Fallah and Joan Ribas acknowledge the financial support given
by the Spanish and Catalan Governments (grant BQU2009-07264
and grant 2009 SGR 1454).
6.2. Magnetic behavior of complex 2
The temperature dependence of
susceptibility for two MnII ions) for complex 2 is shown in
Fig. 11 (from 300 to 2 K). The
MT value is 8.7 cm3 molꢀ1 K at
300 K, a value which is as expected for an ‘‘isolated’’ Mn(II) ion
(with g ꢃ 2.00). Decreasing the temperature, the values of MT
vMT (vM being the magnetic
v
v
are practically constant to 50 K. From 50 to 2 K the decrease is
more pronounced, reaching a value of 6.5 cm3 molꢀ1 K at 2 K. The
shape of this curve is characteristic of the occurrence of weak anti-
ferromagnetic interactions between the Mn(II) center. Taking into
account the dinuclear nature of 2, the susceptibility data were fit-
ted by the formula given by Kahn [24], based on the exchange
Hamiltonian H = ꢀJSiSj. The best fit is given by the exchange
parameters J = ꢀ0.12 0.006 cmꢀ1, g = 1.99 0.01 (the standard
value for Mn(II) ions) and R = 3.1 ꢂ 10ꢀ5. The plot of the reduced
Appendix A. Supplementary data
CCDC 928831, 928832, 928833, 928829 and 928830 contains
the supplementary crystallographic data for 1–5. These data can
be obtained 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
http://dx.doi.org/10.1016/j.poly.2013.10.021.
magnetization (M/NlB) versus H achieves a value of ca 10 NlB
(corresponding to 2 Mn2+ ions) and its shape follows the Brillouin
function, due undoubtedly to the small antiferromagnetic coupling
between the two manganese centers. In a recent review, a compre-
hensive study of the structural and magnetic data of coordination
compounds containing a dicyanamide bridging ligand has been re-
ported [3]. From this review and the references given in it, a clas-
sification of these compounds is given. For example, the most
important series (from a magnetic point of view) is the called ‘ru-
tile-like’ complexes of the formula [M(dca)2] (M = VII, CrII, MnII, FeII,
CoII, NiII), which show magnetic ordering [3]. They are ferromag-
nets for M = CoII and NiII below 9 and 21 K, respectively, and weak
(canted) ferromagnets for M = CrII, MnII and FeII below 47, 16 and
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7. Conclusion
The pyrimidine derived NNN donor Schiff base ligands L1, L2, L3
and L4 form five dinuclear Mn(II) complexes, where the Mn centers
are bridged by l1,1 bridged azide ions in 1, 3, 4 and 5 and end-on

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