Syntheses, structures and magnetic properties of μ1,5- dicyanamide bridged di- and polynuclear manganese(II) complexes containing neutral N-donor Schiff bases: Control of coordination number and nuclearity by varying denticity

Article abstract of DOI:10.1016/j.ica.2010.06.021

Two hexacoordinated dinuclear compounds [Mn(L1)(dca)]₂(ClO ₄/PF₆)₂·CH₃OH (1/2) and two heptacoordinated coordination polymers [Mn(L2)(dca)]_n(ClO ₄/PF₆)_n (3/4) [L1 = N,N′-(bis-(pyridin-2- yl)benzylidene)-1,3-propanediamine; L2 = N,N′-(bis-(pyridin-2-yl) benzylidene)diethylenetriamine; dca = dicyanamide] are synthesized and characterized. Structures of 1-3 have been solved by X-ray diffraction measurements. Each manganese(II) center in 1/2 is located in a distorted octahedral environment with an MnN₆ chromophore coordinated by the four N atoms of L1 and two nitrile N atoms of bibridged μ_1,5 dca. Interestingly, the coordination polymer 3 forms a 1D chain through single Mn-(NCNCN)-Mn units in which each manganese(II) center adopts a pentagonal bipyramidal geometry with an MnN₇ chromophore occupied with five N atoms of L2 and two nitrile N atoms of monobridged μ_1,5 dca. Magnetic susceptibility measurements of 1-3 in the 2-300 K temperature range reveal weak antiferromagnetic interactions.

Full text of DOI:10.1016/j.ica.2010.06.021

Inorganica Chimica Acta 363 (2010) 3308–3315
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Inorganica Chimica Acta
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Syntheses, structures and magnetic properties of
l1,5-dicyanamide bridged
di- and polynuclear manganese(II) complexes containing neutral N-donor Schiff
bases: Control of coordination number and nuclearity by varying denticity
Kishalay Bhar a, Sumitava Khan a, Sumitra Das a, Partha Mitra b, Georgina Rosair c, Joan Ribas d,
**
,
*
Barindra Kumar Ghosh a,
a Department of Chemistry, The University of Burdwan, Burdwan 713 104, India
b Department of Inorganic Chemistry, Indian Association for the Cultivation of Science, Kolkata 700 032, India
c Chemistry, School of Engineering and Physical Sciences, Heriot Watt University, Edinburgh EH14 4AS, UK
d Departament de Quimica Inorganica, Universitat de Barcelona, Diagonal 647, 08028 Barcelona, Spain
a r t i c l e i n f o
a b s t r a c t
Article history:
Two hexacoordinated dinuclear compounds [Mn(L1)(dca)]2(ClO4/PF6)2ꢀCH3OH (1/2) and two heptacoordi-
nated coordination polymers [Mn(L2)(dca)]n(ClO4/PF6)n (3/4) [L1 = N,N0-(bis-(pyridin-2-yl)benzylidene)-
1,3-propanediamine; L2 = N,N0-(bis-(pyridin-2-yl)benzylidene)diethylenetriamine; dca = dicyanamide]
are synthesized and characterized. Structures of 1–3 have been solved by X-ray diffraction measure-
ments. Each manganese(II) center in 1/2 is located in a distorted octahedral environment with an MnN6
Received 26 March 2010
Accepted 9 June 2010
Available online 15 June 2010
This paper is dedicated to Professor
Animesh Chakravorty, Kolkata on the eve of
his 75th birth anniversary.
chromophore coordinated by the four N atoms of L1 and two nitrile N atoms of bibridged l1,5 dca. Interest-
ingly, the coordination polymer 3 forms a 1D chain through single Mn–(NCNCN)–Mn units in which each
manganese(II) center adopts a pentagonal bipyramidal geometry with an MnN7 chromophore occupied
with five N atoms of L2 and two nitrile N atoms of monobridged
ments of 1–3 in the 2–300 K temperature range reveal weak antiferromagnetic interactions.
Ó 2010 Elsevier B.V. All rights reserved.
l1,5 dca. Magnetic susceptibility measure-
Keywords:
Di-/polynuclear manganese(II)
Dicyanamide bridging
N-donor Schiff base
X-ray structure
Antiferromagnetism
1. Introduction
anate and cyanate in combination with multidentate N-donor Schiff
bases. To extend such work with dca, we have undertaken a pro-
gram to prepare different mono-, di- and polymeric compounds
of 3d transition series metal ions. In our present endeavour, we
have examined the coordination behaviour of dca in combination
with manganese(II) (S = 5/2) and two different Schiff bases
[30,31] such as tetradentate N,N0-(bis-(pyridin-2-yl)benzylidene)-
1,3-propanediamine (L1) and pentadentate N,N0-(bis-(pyridin-2-
yl)benzylidene)diethylenetriamine (L2) (Scheme 1). Successfully,
we have prepared two hexacoordinated dinuclear compounds
[Mn(L1)(dca)]2(ClO4/PF6)2ꢀCH3OH (1/2) and two heptacoordinated
coordination polymers [Mn(L2)(dca)]n(ClO4/PF6)n (3/4). The details
of syntheses, structures, and magnetic behaviours of these com-
pounds are described here.
Design and synthesis [1,2] of mono-, di- and polynuclear coordi-
nation compounds of manganese(II) continue unabated because of
their interesting synthetic, structural and magnetic features [3–10].
Self-assembly [11] of the metal ion with different organic spacers
and suitable bridging units is an efficient approach to prepare such
coordination molecules. Pseudohalides like azide, thiocyanate and
cyanate [12–17] have been extensively used for the isolation of
such coordination polymers and polymer-based supramolecular
entities. Dicyanamide (dca), a larger pseudohalide molecular ion-
rod is now under active consideration because of its versatile
coordination motifs [18–25] such as
l1,5-, l1,3-, l1,3,5-, l1,1,3,5-
and 1,1,3,5,5, exhibiting rich diversity in magnetic behaviours
l
including ferromagnetism, antiferromagnetism and canted-spin
antiferromagnetism. Recently, we are active [26–29] to isolate
different magnetic materials using pseudohalides like azide, thiocy-
2. Experimental
2.1. General remarks and physical measurements
* Corresponding author. Tel.: +34 93 4039141; fax: +34 934907725.
** Corresponding author. Tel.: +91 342 2533913; fax: +91 342 2530452.
E-mail addresses: joan.ribas@qi.ub.es (J. Ribas), barin_1@yahoo.co.uk (B.K.
Ghosh).
2.1.1. Materials
High purity 1,3-propanediamine (Spectrochem, India), diethyl-
enetriamine (SRL, India), 2-benzoylpyridine (Lancaster, UK), sodium
0020-1693/$ - see front matter Ó 2010 Elsevier B.V. All rights reserved.
doi:10.1016/j.ica.2010.06.021

K. Bhar et al. / Inorganica Chimica Acta 363 (2010) 3308–3315
3309
H
N
N
N
N
N
N
N
N
N
L1
L2
Scheme 1.
dicyanamide (Lancaster, UK), manganese(II) chloride (E. Merck, In-
dia), sodium perchlorate (Lancaster, UK) and ammonium hexafluro-
phosphate (Fluka, Germany) were purchased from respective
concerns and were used as received. All other chemicals and sol-
vents were AR grade and were used as received.
dropwise. The intense yellow solution was left undisturbed in an
open air for slow evaporation. After a few days yellow rectangular
shaped single crystals of 1 that separated, were washed with dehy-
drated alcohol and dried in vacuo over silica gel indicator. Yield:
0.513 g (80%). Compound 2 was prepared similarly using NH4PF6
(0.163 g, 1 mmol) instead of NaClO4 as counter anion. Yield:
0.515 g (75%). Compound 2 was also isolated by metathesis of 1
with NH4PF6 in 1:2 ratio from a methanolic solution with constant
stirring for 45 min at room temperature. The resulting yellow solu-
tion was processed as described above in 1 to get pure 2. The
microanalytical and spectroscopic results of 2 obtained from both
the methods were very similar. Anal. Calc. for C59H52N14O9Cl2Mn2
(1): C, 55.3; H, 4.1; N, 15.4. Found: C, 55.1; H, 4.0; N, 15.2%. IR
2.1.2. Physical measurements
Elemental analyses were performed on a Perkin–Elmer 2400
CHNS/O elemental analyzer. IR spectra (KBr discs, 4000–
300 cmꢁ1) were recorded using a Perkin–Elmer FTIR model RX1
spectrometer. Molar conductances were measured using a Systron-
ics conductivity meter where the cell constant was calibrated with
0.01 M KCl solution and dry MeCN was used as solvent. Thermal
behaviours were examined with a Perkin–Elmer Diamond TG/DT
analyzer heated from 30 to 500 °C under nitrogen. Ground state
absorption (in dry DMF) was made with a Shimadzu model UV-
2450 UV–Vis spectrophotometer. Fluorescence measurements
were done using Hitachi Fluorescence Spectroflurimeter F-4500.
The temperature-dependence magnetic susceptibilities were mea-
sured on polycrystalline samples with a Quantum Design SQUID
MPMS-XL susceptometer operating at a magnetic field 0.1 T over
a temperature range 2–300 K. The diamagnetic corrections were
evaluated from Pascal’s constants.
(KBr, cmꢁ1): mas
as(C–N) 1352, 1322,
+
ms(C„N) 2301,
mas(C„N) 2236, ms(C„N) 2183;
m
ms(C–N) 901;
m
(C@N) +
m(C@C) 1622, 1592;
Table 1
Crystallographic data and structure refinement for 1–3.
Complex
1
2
3
Formula
Formula
weight
Crystal
system
Space group
a (Å)
C
59H52N14O9Cl2Mn2 C59H52N14OF12P2Mn2 C30H27N8O4ClMn
1281.93
1372.97
653.99
triclinic
triclinic
monoclinic
2.2. Preparation of Schiff bases
ꢀ
ꢀ
Cc
P1
P1
10.7608(5)
12.3531(6)
12.6038(8)
60.728(2)
83.956(4)
86.854(3)
1453.34(13)
0.71073
1.465
10.7523(10)
12.5070(12)
12.6306(13)
117.645(5)
94.757(5)
95.718(5)
1481.0(2)
0.71073
10.6664(6)
22.9033(15)
12.3070(6)
90
94.348(2)
90
2997.9(3)
0.71073
1.449
b (Å)
c (Å)
L2 was prepared following the reported method [32] and L1 was
synthesized as described below.
a
(°)
b (°)
2.2.1. N,N0-(bis-(pyridin-2-yl)benzylidene)-1,3-propanediamine (L1)
1,3-Propanediamine (0.074 g, 1 mmol) and 2-benzoylpyridine
(0.366 g, 2 mmol) were mixed together and refluxed in dehydrated
alcohol (25 ml) for 10 h. The yellowish brown solution was concen-
trated on a steam bath and dried in vacuo over CaCl2 to a yellowish
brown semi-solid for subsequent use. Yield: 0.283 g (70%). Anal.
Calc. for C27H24N4 (L1): C, 80.1; H, 6.0; N, 13.9. Found: C, 79.9; H,
c
(°)
V (Å3)
k (Å)
qcalcd (g cmꢁ3
)
1.539
Z
1
1
4
T (K)
l
100(2)
0.597
100(2)
0.574
150(2)
0.580
(mmꢁ1
)
F(0 0 0)
660
700
1348
5.9; N, 13.7%; IR (KBr, cmꢁ1):
m(C=N) + m(C=C) 1624, 1596. UV–
Vis (k, nm): 271.
Crystal size
0.65 ꢂ 0.38 ꢂ 0.30
0.56 ꢂ 0.46 ꢂ 0.28
0.24 ꢂ 0.21 ꢂ 0.15
(mm3)
h ranges (°)
h/k/l
2.54–29.98
ꢁ15,14/ꢁ15,17/
ꢁ17,14
1.84–30.07
ꢁ15,13/ꢁ17,17/
ꢁ16,17
1.78–21.76
ꢁ11,11/ꢁ23,23/
ꢁ12,12
2.3. Preparation of the complexes
Reflections
collected
72 668
25 591
12 773
Compounds 1–4 were obtained from methanolic solutions of
1:1:1 molar ratios of manganese(II) chloride, Schiff bases (L1 for
1 and 2 and L2 for 3 and 4) and dicyanamide with extraneous addi-
tion of NaClO4/NH4PF6 as counter ions. All the reactions were per-
formed at room temperature and were reproducible. The typical
syntheses of 1–4 are described below.
Independent
reflections
Tmax and Tmin
Data/
8394
8015
3203
0.8413 and 0.6977
8394/6/396
0.8559 and 0.7577
8015/0/413
3203/2/397
1.036
restraints/
parameters
Goodness-of-
fit (GOF)
1.027
1.032
on F2
2.3.1. [Mn(L1)(dca)]2(ClO4)2ꢀCH3OH (1) and
Final R indices 0.0371
[I > 2 (I)]
0.0400
0.0328
[Mn(L1)(dca)]2(PF6)2ꢀCH3OH (2)
r
MnCl2ꢀ4H2O (0.197 g, 1 mmol) and L1 (0.404 g, 1 mmol) each in
15 ml methanol were taken in separate containers and mixed to-
gether slowly. To the yellow mixture, a methanolic solution
(15 ml) of NaN(CN)2 (0.089 g, 1 mmol) followed by NaClO4
(0.140 g, 1 mmol) dissolved in the same solvent (15 ml) was added
R indices (all
0.0448
0.0725
0.0385
data)
Largest peak
and hole
1.279 and ꢁ0.871
0.431 and ꢁ0.595
0.323 and ꢁ0.260
(e Åꢁ3
)

3310
K. Bhar et al. / Inorganica Chimica Acta 363 (2010) 3308–3315
m(ClO4) 1094, 623. UV–Vis (k, nm): 280. Anal. Calc. for
refined by full-matrix least-squares methods based on F2 using
C
59H52N14OF12P2Mn2 (2): C, 51.6; H, 3.8; N, 14.3. Found: C, 51.7;
ms (C„N) 2304, as(C„N)
as(C–N) 1358, 1323, s(C–N) 903;
(C@C) 1621, 1589. (PF6) 843, 557. UV–Vis (k, nm): 280.
SHELXS-97 [35] and SHELXL-97 [35]. All non-hydrogen atoms were re-
fined with anisotropic displacement parameters whereas hydrogen
atoms were placed in calculated positions when possible and given
isotropic U values 1.2 times that of the atom to which they are
bonded. In the final difference Fourier maps, the residual maxi-
mum and minimum were 1.279 and ꢁ0.871 e Åꢁ3 for 1, 0.431
and ꢁ0.595 e Åꢁ3 for 2 and 0.356 and ꢁ0.305 e Åꢁ3 for 3. Materials
for publication were prepared using SHELXTL [35], PLATON [36] and OR-
TEP-32 [37] programs. A summary of the crystallographic data and
structure determination parameters are given in Table 1.
H, 3.5; N, 14.2%. IR (KBr, cmꢁ1): mas
+
m
2237,
ms(C„N) 2182,
m
m
m(C@N) +
m
m
2.3.2. [Mn(L2)(dca)]n(ClO4)n (3) and [Mn(L2)(dca)]n(PF6)n (4)
L2 (0.433 g, 1 mmol) in methanol (15 ml) was added dropwise
to a solution of MnCl2ꢀ4H2O (0.197 g, 1 mmol) dissolved in the
same solvent (15 ml). To the resulting light yellow solution, a
methanolic solution (15 ml) of NaN(CN)2 (0.089 g, 1 mmol) was
added slowly followed by NaClO4 (0.140 g, 1 mmol) also in metha-
nol (15 ml). The final yellow solution was processed as in 1 to get
yellow rectangular single crystals of 3. Yield: 0.569 g (80%). Com-
pound 4 was prepared similarly using the same stoichiometry
and reaction condition except that NH4PF6 (0.163 g, 1 mmol) in-
stead of NaClO4 was used. Yield: 0.489 g (70%). It was also isolated
by metathesis of 3 with NH4PF6 in 1:2 ratio from a methanolic
solution with constant stirring for 45 min at room temperature.
The resulting yellow solution was processed as described above
to get pure 4. The microanalytical and spectroscopic results of 4
obtained from both the methods are very similar. Anal. Calc. for
3. Results and discussion
3.1. Synthesis and formulation
One-pot synthesis of 1:1:1:1 molar ratio of manganese(II) chlo-
ride, tetradentate Schiff base, L1, dca and NaClO4/NH4PF6 in meth-
anol afforded hexacoordinated dicationic dinuclear compounds of
type [Mn(L1)(dca)]2(ClO4/PF6)2ꢀCH3OH (1/2). Changing the ligand
denticity from 4 in L1 to 5 in L2, heptacoordinated one-dimen-
sional coordination polymers of the type [Mn(L2)(dca)]n(ClO4/
PF6)n (3/4) were obtained under similar reaction condition. Com-
pound 2/4 was also isolated by metathesis of 1/3 in methanol using
NH4PF6. The typical syntheses of 1–4 are summarized in Scheme 2.
The compounds were characterized using microanalyses, solu-
tion electrical conductivity measurements, spectroscopic and ther-
mal studies. The microanalytical results are in good agreement
with formulations 1–4. The air-stable compounds are soluble in a
wide range of common organic solvents such as methanol, acetoni-
trile, dimethyformamide, dimethylsulfoxide, but are insoluble in
water. In MeCN solutions, 1 and 2 show 2:1 electrolytic behaviours
[38] as reflected in their VM values (1: 230 ꢁ1 cm2 molꢁ1 and 2:
235 ꢁ1 cm2 molꢁ1). However, 3 and 4 exhibit low conductivity val-
ues (ꢃ55 ohmꢁ1 cm2 molꢁ1) in MeCN reflecting association of the
counter ions with the metallated cationic organic frameworks in
solid state and in solution. In IR spectra, the stretching vibrations
C
30H27N8O4ClMn (3): C, 55.1; H, 4.2; N, 17.2. Found: C, 54.9; H,
4.1; N, 17.0%. IR (KBr, cmꢁ1):
(N–H) 3328, 3279; mas s(C„N)
2282; as(C„N) 2225; s(C„N) 2155; as(C–N) 1341, 1320; s(C–
N) 931; (C@N) + (C@C) 1622, 1593; (ClO4) 1092, 624. UV–Vis
(, nm): 281. Anal. Calc. for C30H27N8F6PMn (4): C, 51.5; H, 3.9; N,
16.1. Found: C, 51.4; H, 3.9; N, 16.0%. IR (KBr, cmꢁ1):
(N–H)
3325, 3276; mas s(C„N) 2283; as(C„N) 2224; s(C„N) 2155;
as(C–N) 1344, 1320; s(C–N) 931; (C@N) + (C@C) 1621, 1594;
(PF6) 844, 559. UV–Vis (, nm): 281.
m
+ m
m
m
m
m
m
m
m
m
+
m
m
m
m
m
m
m
m
2.4. X-ray crystallographic analyses
Single crystals of 1–3 suitable for X-ray analyses were selected
from those obtained by open evaporation of methanolic solutions
of the reaction mixtures at 298 K. Crystallographic data were col-
lected on a Bruker APEX-II CCD diffractometer (for 1 and 2 at
100 K) and Bruker SMART APEX-II CCD area detector diffractome-
of dca in 1 and 2 are seen as strong
gion 2170–2190 cmꢁ1 and two weak to medium mas
m
as(C„N) absorptions in the range 2240–2310 cmꢁ1 (vide Section
ms(C„N) absorptions in the re-
+
m
s(C„N) and
ter (for 3 at 150 K) using graphite monochromated Mo K
a
radiation
(k = 0.71073 Å). For unit cell determination, the single crystal was
exposed to X-rays for 10 s in three sets of frames. The detector
frames were integrated by use of the program SAINT [33] and the
empirical absorption corrections were performed using TWINABS
program [34]. The structures were solved by direct methods, and
2); the shift towards higher frequency values as compared to those
of free dca (2179 cmꢁ1, 2232 and 2286 cmꢁ1) [39] is presumably
due to bibridging l1,5 coordination mode of the pseudohalide
[19,25]. However, in 3/4, corresponding dca stretches are shifted
towards lower values [22,23] indicating single l1,5-bridging mode
(ii)
(iv)
[Mn(L2)(dca)]n(PF6)n
[Mn(L1)(dca)]2(PF6)2.MeOH
(4)
(2)
Hexacoordinated
Heptacoordinated
MnCl2.4H2O
(v)
(v)
(i)
(iii)
[Mn(L2)(dca)]n(ClO4)n
[Mn(L1)(dca)]2(ClO4)2.MeOH
(3)
(1)
Heptacoordinated
Hexacoordinated
(i) L1, dca, NaClO4, (ii) L1, dca, NH4PF6, (iii) L2, dca, NaClO4, (iv) L2, dca, NH4PF6
(v) NH4PF6
Scheme 2.

K. Bhar et al. / Inorganica Chimica Acta 363 (2010) 3308–3315
3311
of dca in 1D chain structure. Bands corresponding to
s(C–N) stretching vibrations of dca are found in the range 1370–
1320 cmꢁ1 and 950–900 cmꢁ1, respectively, in all the complexes.
m
as(C–N) and
ꢃ3330 and ꢃ3280 nm. In DMF solutions, L1 and L2 show absorp-
tion maxima at 271 and 273 nm, respectively, and the correspond-
ing manganese(II) compounds 1–4 exhibit bands at kmax values
ꢃ280 nm assignable to ligand-based charge transfer [42]. Upon
photoexcitation at the corresponding absorption bands, free li-
gands exhibit broad fluorescent emissions centered at 383 nm
(for L1) and 382 nm (for L2). However, the corresponding paramag-
netic manganese(II) compounds 1–4 are fluorescence-inactive.
m
m
(C@N) plus m(C@C) stretching frequencies [40] of the Schiff bases
in metal bound states are observable at ꢃ1620 and ꢃ1590 cmꢁ1
.
The presence of perchlorate bands at ꢃ1090 and ꢃ620 cmꢁ1 (in 1
and 3) and hexafluorophosphate stretches at ꢃ840 and ꢃ560
cmꢁ1 (in 2 and 4) are noticed reflecting counter anionic view
[40] with no metal coordination. Additionally, in 3 and 4
m(N–H)
stretching vibrations [41] of –NH– group of L2 are observed at
Fig. 1. Molecular structure of [Mn(L1)(dca)]2(ClO4)2ꢀMeOH (1) (ORTEP, 30% thermal ellipsoids probability).
Fig. 2. Molecular structure of [Mn(L1)(dca)]2(PF6)2ꢀMeOH (2) (ORTEP, 30% thermal ellipsoids prorability).

3312
K. Bhar et al. / Inorganica Chimica Acta 363 (2010) 3308–3315
3.2. Thermal analyses
and bond angles relevant to the metal coordination spheres are set
in Tables 2 and 3.
To examine thermal stabilities of 1–4, thermogravimetric and
differential thermal analyses (TG–DTA) were made between 30
and 500 °C in the static atmosphere of nitrogen. The thermal
decomposition behaviours of 1 and 2 are similar. TG curves (Figs.
S1 and S2) show that both are stable up to ꢃ260 °C and then
decompose gradually with exothermic effects at 319 °C (for 1)
and 263 °C (for 2). The nature of thermal decomposition (Figs. S3
and S4) of 3 and 4 is also similar; both show thermal stability up
to ꢃ250 °C and then decompose gradually with exothermic effects
at 262, 309 °C (for 3) and 252 °C (for 4).
The structures (Figs. 1 and 2) of 1 and 2 are made up of dication-
ꢁ
ꢁ
ic dinuclear unit ½MnðL1ÞðdcaÞꢄ22þ, ClO4 (in 1) and PF6 (in 2)
counter anions and a disordered CH3OH molecule. On application
of symmetry operations CH3OH molecule appears as three atoms
which are equal to one molecule of CH3OH per dimer. The O atom
in 1 and the CH3 moiety in 2 is on the inversion center. Within the
complex cation (in 1 and 2) the two manganese(II) centers are
bridged by two
l1,5-dicyanamide to form a planar 12-membered
Mn–(NCNCN)2–Mn ring. The overall geometry around each manga-
nese(II) in both complexes is best described as a distorted octahe-
dron with an MnN6 chromophore. One imine N atom (N8), one
pyridine N atoms (N19) of the tetradentate Schiff base (L1) and
two cis-coordinated nitrile N atoms (N112, N110 in 1 and N32,
3.3. Crystal structures of [Mn(L1)(dca)]2(ClO4)2ꢀCH3OH (1),
[Mn(L1)(dca)]2(PF6)2ꢀCH3OH (2) and [Mn(L2)(dca)]n(ClO4)n (3)
N34 in 2) of the l1,5-bridging dca units define the equatorial plane;
the remaining imine N atom (N12) and pyridine N atom (N1) of L1
occupy the axial sites. In both the cases, each manganese(II) center
deviates 0.008 Å from the mean plane. Mn–N bond distances are in
the range 2.2128(15)–2.2821(13) Å (for 1) and 2.2012(19)–
The structural analyses reveal that 1 and 2 comprise of dinuclear
units containing double l1,5 dca bridgings, whereas 3 forms a 1D
chain through single
l1,5 dca bridges. ORTEP diagrams of the indi-
vidual units of 1–3 are shown in Figs. 1–3. Selected bond distances
Fig. 3. (a) An ORTEP diagram of the individual unit in 3 with atom numbering scheme and 30% thermal ellipsoid probability. (b) A segment of the 1D chain in the polycation of
3 running along [1 0 1] direction.

K. Bhar et al. / Inorganica Chimica Acta 363 (2010) 3308–3315
3313
Table 2
amine nitrogen (N3) of L2 occupy the equatorial plane; two nitrile
nitrogens (N6 and N8) of two different 1,5-bridged dca complete
Selected bond distances (Å) and bond angles (°) for 1 and 2.
l
the heptacoordination and connect other neighboring manga-
nese(II) centers in a non-ending fashion producing the 1D chain
(Fig. 3b). Distortion from the ideal geometry is due to the asym-
metric nature of the bound Schiff base and the deviations of the re-
fine angles formed at the metal center. The manganese(II) center
deviates 0.033 Å from the mean plane. Among the five equatorial
nitrogens N1 and N4 deviate (N4 0.365 Å and N6 0.271 Å) towards
N8 whereas N2 and N5 show considerable deviation (N2 0.258 Å
and N5 0.369 Å) towards N6 from the mean plane. The remaining
nitrogen N3 is almost on the mean plane compared to other atoms
with maximum deviation 0.009 Å. The intrachain Mnꢀ ꢀ ꢀMn separa-
tion in 3 is 8.086 Å which is much larger than that in 1 and 2 as ex-
pected due to presence of single l1,5 dca bridging in the former.
Dicyanamide coordinates to the metal centers via l1,5 bridge in a
bending fashion as reflected in the bond angles [C29–N6–Mn1
149.0(4)° and C30–N8–Mn1 133.8(4)°]. The skeletal bond angles
of dca are N8–C30–N7 175.6(5)°, C29–N7–C30 118.7(4)° and N6–
C29–N7 175.2(5)° that reflects non-linearity of the larger pseudo-
halide rod.
Bond distances and angles for 1
Bond distances and angles for 2
Mn1–N1
2.2694(14)
Mn1–N1
Mn1–N19
Mn1–N12
Mn1–N8
Mn1–N32
Mn1–N34
N32–C33
N36–C33a
N36–C35
C35–N36
C33–N36a
2.2669(16)
2.2800(17)
2.2668(17)
2.2737(16)
2.2012(19)
2.2234(18)
1.154(3)
1.305(3)
1.153(2)
1.306(2)
1.305(3)
Mn1–N19
Mn1–N12
Mn1–N8
Mn1–N110
Mn1–N112
N112–C112i
N111–C112
N111–C111
C111–N110
C112–N112i
2.2821(13)
2.2614(14)
2.2724(13)
2.2128(15)
2.2306(15)
1.162(2)
1.307(2)
1.310(2)
1.159(2)
1.162(2)
N110–Mn1–N112
N110–Mn1–N12
N112–Mn1–N12
N110–Mn1–N1
N112–Mn1–N1
N12–Mn1–N1
N110–Mn1–N8
N112–Mn1–N8
N110–C111–N111
N112–C112–N111i
C112–N111–C111
N12–Mn1–N8
82.82(5)
97.69(5)
N32–Mn1–N34
N32–Mn1–N1
N34–Mn1–N1
N32–Mn1–N12
N34–Mn1–N12
N1–Mn1–N12
N32–Mn1–N8
N34–Mn1–N8
N1–Mn1–N8
N12–Mn1–N8
N32–Mn1–N19
N34–Mn1–N19
N1–Mn1–N19
N12–Mn1–N19
N8–Mn1–N19
C33–N32–Mn1
C35–N34–Mn1
N32–C33–N36a
N34–C35–N36
C35–N36–C33a
82.48(7)
109.80(6)
90.24(6)
97.84(7)
124.32(6)
138.60(6)
82.76(6)
151.73(6)
72.39(6)
81.57(6)
149.86(6)
81.17(6)
95.43(6)
71.40(6)
121.65(6)
153.08(17)
161.34(18)
174.9(2)
173.8(2)
119.47(17)
123.63(5)
111.28(5)
90.60(5)
138.02(5)
83.88(5)
152.79(5)
175.25(18)
174.80(17)
118.46(14)
81.65(5)
Due to unavailability of X-ray quality single crystals, the struc-
ture of 4 could not be solved using X-ray diffraction measurement.
However, based on spectroscopic, thermal and other physicochem-
ical properties compounds 3 and 4 are assumed to have cognate
structures.
N1–Mn1–N8
72.37(5)
N110–Mn1–N19
N112–Mn1–N19
N12–Mn1–N19
N1–Mn1–N19
149.34(5)
80.30(5)
71.39(5)
94.35(5)
N8–Mn1–N19
121.08(5)
168.54(14)
150.40(14)
3.4. Magnetic properties
C112–N112–Mn1i
C111–N110–Mn1
Variable-temperature magnetic susceptibility measurements
for 1–3 have been performed in the temperature range 2–300 K.
Symmetry transformations used to generate equivalent atoms: (i) 1 ꢁ x, 1 ꢁ y, 1 ꢁ z
(for 1); (a) 2 ꢁ x, ꢁy, 1 ꢁ z (for 2).
The experimental
vMT values at room temperature are ca.
9.0 cm3 molꢁ1 K for 1 and 8.85 cm3 molꢁ1 K for 2, close to spin-
only value (8.76 cm3 molꢁ1 K for g = 2.00) for two isolated high-
spin manganese(II) ions, whereas that of 3 is ca. 4.5 cm3 molꢁ1
K
Table 3
Selected bond distances (Å) and bond angles (°) for 3.
close to the spin-only value (4.38 cm3 molꢁ1 K for g = 2.00) for
Bond distances
Bond angles
one isolated high-spin manganese(II) ion. With decrease in tem-
perature
100 K. From 100 K to 2 K the decrease is more pronounced with
values 2.1 cm3 molꢁ1 (for 1), 4.25 cm3 molꢁ1
(for 2) and
1.2 cm3 molꢁ1 K (for 3) at 2 K. The global feature (Figs. 4–6) is in
vMT values practically remain unchanged down to
Mn1–N6
Mn1–N8
Mn1–N4
Mn1–N3
Mn1–N1
Mn1–N2
Mn1–N5
N6–C29
2.237(5)
2.245(5)
2.304(4)
2.307(3)
2.363(3)
2.373(4)
2.415(4)
1.151(6)
1.305(7)
1.309(7)
1.156(6)
1.309(7)
N6–Mn1–N8
N4–Mn1–N3
N1–Mn1–N2
N3–Mn1–N2
N4–Mn1–N5
N1–Mn1–N5
C30–N8–Mn1
C29–N6–Mn1
N8–C30–N7#1
N6–C29–N7
170.59(15)
72.83(13)
68.19(12)
69.76(12)
68.12(12)
85.86(12)
133.8(4)
149.0(4)
175.6(5)
175.2(5)
118.7(4)
K
K
C29–N7
N7–C30#2
N8–C30
C29–N7–C30#2
C30–N7#1
8
6
4
2
10
8
Symmetry transformations used to generate equivalent atoms: #1 = x ꢁ 1/2, ꢁy +
3/2, z ꢁ 1/2; #2 = x + 1/2, ꢁy + 3/2, z + 1/2.
2.2800(17) Å (for 2). The degrees of distortion from ideal octahe-
dral geometry are reflected in cisoid [71.39(5)–94.35(5)° in 1 and
71.40(6)–95.43(6)° in 2] and transoid [149.34(5)–125.79(5)° in 1
and 149.86(6)–151.73(6)° in 2] bond angles; the N110–Mn1–
N112 (in 1) and N32–Mn1–N34 (in 2) bridging angles are
82.82(5)° and 82.48(7)°, respectively. In Mn–(NCNCN)2–Mn link-
age, the dca units do not coordinate to the metal centers in a per-
fectly linear arrangement, as is reflected in the bond angles of
Mn1–N110–C111 168.54(14)° and Mn1–N112–C112 150.40(14)°
6
4
2
0
0
10
20
30
40
50
H / mT
in
1
and Mn1–N34–C35 161.34(18)° and Mn1–N32–C33
153.08(17)° in 2. The intradinuc
0
50
100
150
T / K
200
250
300
The coordination polyhedron around each manganese(II) center
in polymeric 3 is best described as a distorted pentagonal bipyra-
mid (pbp) with an MnN7 chromophore (Fig. 3a). Two pyridine
nitrogens (N1 and N5), two imine nitrogens (N2 and N4) and one
Fig. 4. Plots of the
vMT vs. T and M/NlD vs. H (inset, 2 K) for 1. Solid line indicates
the best fit obtained with the parameters (see text).

3314
K. Bhar et al. / Inorganica Chimica Acta 363 (2010) 3308–3315
given by Fisher [43,45] for classical S = 5/2 spins. The best fit values
9
8
7
6
5
4
are: J = ꢁ1.2 0.1 cmꢁ1, g = 2.01 0.01 and R = 1.3 ꢂ 10ꢁ5. The plot
of the reduced magnetization (M/NlD) versus H (in G) tends to the
value of ca. 5 NlD corresponding to one manganese(II) ion and does
10
8
not follow the Brillouin function due to small antiferromagnetic
coupling between the two manganese(II) centers. The best fit
parameters obtained for 1–3 are comparable to those reported
for similar manganese(II) systems with single or double bridging
l1,5 dca [24].
6
4
4. Conclusion
2
Using single-pot reactions of the building components in preas-
signed ratios we have prepared two new hexacoordinated dinucle-
ar complexes and two new heptacoordinated coordination
polymers of manganese(II) dicyanamides by varying the denticities
of Schiff base ligands. The interesting feature of this work is the en-
hanced coordination of the 3d ion; the use of the pentacoordinated
ligand and larger-sized bridging unit ensures such unusual coordi-
nation number with this 3d5 ion. The difference in molecular archi-
tectures in 1–3 shows how composition may tailor topology. The
compounds show weak antiferromagnetic coupling regardless
the nuclearities, geometries and number of bridges, which may
0
0
10
20
30
40
50
H / mT
0
50
100
150
T / K
200
250
300
Fig. 5. Plots of the
the best fit obtained with the parameters (see text).
vMT vs. T and M/NlD vs. H (inset, 2 K) for 2. Solid line indicates
be due to the long
l1,5-bridging of dca. We are now active to ex-
tend such work with other paramagnetic 3d ions like cobalt(II)
and iron(III).
5
Acknowledgements
4
5
Financial supports from the DST, CSIR and UGC, New Delhi, In-
dia is gratefully acknowledged. The authors also acknowledge the
use of DST-funded National Single Crystal X-ray Diffraction Facility
at the Department of Inorganic Chemistry, IACS, Kolkata, India for
crystallographic studies. K.B., S.K. and S.D. are grateful to CSIR, New
Delhi, India for fellowship. J.R. thanks Spanish Government (Grant
CTQ2009/07264) for the financial support.
4
3
2
1
3
2
1
0
Appendix A. Supplementary material
CCDC 771060, 771061 and 771062 contain the supplementary
crystallographic data for 1, 2 and 3. These data can be obtained free
of charge from The Cambridge Crystallographic Data Centre via
www.ccdc.cam.ac.uk/data_request/cif. Supplementary data associ-
ated with this article can be found, in the online version, at
doi:10.1016/j.ica.2010.06.021.
0
10000 20000 30000 40000 50000
H / G
0
50
100
150
200
250
300
T / K
Fig. 6. Plots of the
vMT vs. T and M/NlD vs. H (inset, 2 K) for 3. Solid line indicates
the best fit obtained with the parameters (see text).
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