Synthesis, crystal structure, and magnetic properties of binuclear Mn III-azido and 1D polymeric MnII-μ1,3- thiocyanato novel species based on a neutral hexadentate Schiff base

Article abstract of DOI:10.1016/j.poly.2004.11.014

A binuclear manganese(III) complex [Mn₂(L¹)(N ₃)₆] (2) and an unprecedented 1D chain of manganese(II) binuclear units bridged by two end-to-end thiocyanato anions {[Mn2II(L1)(NCS)4]·2CH3CN}n (3 ? 2CH₃CN) have been prepared from N-(1-pyridin-2-ylbenzylidene)-N′-[2-({2-[(1-pyridin-2- ylbenzylidene)amino]ethyl}amino)ethyl]ethane-1,2-diamine (L), manganese(II) salts and azide/thiocyanate anions in air. L¹, N-(1-pyridin-2- ylbenzylidene)-N-[2-(4-{2-[(1-pyridin-2-ylbenzylidene)amino]ethyl} piperazin-1-yl)ethyl]amine, results from an alkylating cyclization of the flexible hexadentate Schiff base L occurring along the course of the complexation reactions. Both complexes have been characterized by single crystal X-ray diffraction studies. The Mn centres of complexes 2 and 3 are in distorted octahedral (2: Mn^IIIN₆, 3: Mn^IIN₅S) coordination environments with intramolecular Mn?Mn distance (2: 6.473(2) A?, 3: 6.437(1) A?) consistent with the absence of intramolecular magnetic interactions. Compound 3, exhibits weak intermolecular antiferromagnetic interactions (J = -1.5 cm^-1) between pairs of Mn^II ions bridged via two μ_1,3-NCS.

Full text of DOI:10.1016/j.poly.2004.11.014

Polyhedron 24 (2005) 343–350
www.elsevier.com/locate/poly
Synthesis, crystal structure, and magnetic properties of
binuclear MnIII-azido and 1D polymeric MnII-l1,3-thiocyanato
novel species based on a neutral hexadentate Schiff base
a
Soma Deoghoria , Sujit K. Bera , Brian Moulton , Michael J. Zaworotko ,
a
b
b
c
d
d
Jean-Pierre Tuchagues , Golam Mostafa , Tian-Huey Lu , Swapan K. Chandra
a,
*
a
Department of Chemistry, The University of Burdwan, Burdwan 713104, India
b
Department of Chemistry, University of South Florida, 4202 E. Fowler Avenue, SCA 400, Tampa, FL 33620, USA
c
Laboratoire de Chimie de Coordination du CNRS, UPR 8241, 205 route de Narbonne, 31077 Toulouse Cedex, France
d
Physics Department, National Tsing Hua University, Hsinchu 300, Taiwan, ROC
Received 18 October 2004; accepted 30 November 2004
Available online 29 December 2004
Abstract
A binuclear manganese(III) complex [Mn2(L1)(N3)6] (2) and an unprecedented 1D chain of manganese(II) binuclear units
1
II
bridged by two end-to-end thiocyanato anions f½Mn2 ðL ÞðNCSÞ ꢀ ꢁ 2CH3CNgn (3 Æ 2CH3CN) have been prepared from N-(1-pyri-
4
din-2-ylbenzylidene)-N0-[2-({2-[(1-pyridin-2-ylbenzylidene)amino]ethyl}amino)ethyl]ethane-1,2-diamine (L), manganese(II) salts
and azide/thiocyanate anions in air. L1, N-(1-pyridin-2-ylbenzylidene)-N-[2-(4-{2-[(1-pyridin-2-ylbenzylidene)amino]ethyl}pipera-
zin-1-yl)ethyl]amine, results from an alkylating cyclization of the flexible hexadentate Schiff base L occurring along the course of
the complexation reactions. Both complexes have been characterized by single crystal X-ray diffraction studies. The Mn centres
of complexes 2 and 3 are in distorted octahedral (2: MnIIIN6, 3: MnIIN5S) coordination environments with intramolecular Mnꢁ ꢁ ꢁMn
˚
˚
distance (2: 6.473(2) A, 3: 6.437(1) A) consistent with the absence of intramolecular magnetic interactions. Compound 3, exhibits
weak intermolecular antiferromagnetic interactions (J = ꢂ1.5 cmꢂ1) between pairs of MnII ions bridged via two l1,3-NCS.
ꢀ 2004 Elsevier Ltd. All rights reserved.
Keywords: Schiff bases; Alkylating cyclization; Pseudo-halide bridges; Manganese polynuclear complexes; 1D Chains; Magnetic exchange
interactions
1. Introduction
between
paramagnetic
centres:
pseudo-halides
(N3ꢂ, NCSꢂ, NCOꢂ) have been well documented for
their numerous bonding abilities leading to various
species [5]. End-on (l1,1-N3/NCS/NCO) [6] and end-to-
end (l1,3-N3/NCS/NCO) [7] bridged complexes are
known to mediate ferromagnetic [8] and antiferro-
magnetic [9] exchange interactions, respectively. The
use of polydentate ligands, especially polynucleating
ones, is an efficient way for assembling metal centres
in close proximity, thus ensuring electronic communica-
tion. Coordination compounds including both polyden-
tate ligands and suitable bridging anions such as
Coordination chemistry of manganese compounds is
an area of considerable interest [1]. These complexes are
significant not only for their redox active role in several
biochemical processes, but also for the diversity of their
magnetic properties [2–4]. Bridging ligands play an
important role in the magnetic exchange pathways
*
Corresponding author. Tel.: +91 342 2557814; fax: +91 342
2557938.
E-mail address: dr_swapan@sify.com (S.K. Chandra).
0277-5387/$ - see front matter ꢀ 2004 Elsevier Ltd. All rights reserved.
doi:10.1016/j.poly.2004.11.014

344
S. Deoghoria et al. / Polyhedron 24 (2005) 343–350
pseudo-halide ions capable of propagating magnetic
interactions between paramagnetic centres play an
important role in the area of molecular magnetism
[3–10].
2.2.2. [Mn2III (L1)(N3)6] (2)
To a methanolic solution (5 cm3) of MnCl2 Æ 4H2O
(0.396 g, 2.0 mmol) was added 0.477 g (1.0 mmol) of
the L ligand in methanol (15 cm3) over a period of
15 min. To the resulting deep orange solution, an aque-
ous solution of sodium azide (0.260 g, 6.0 mmol, 8 cm3
H2O) was added slowly. The solution was then filtered
and the filtrate was left to stand. Within 2–3 days of slow
evaporation a black compound was obtained. This
resulting compound was dissolved in dichloromethane
(ꢃ12 cm3) and layered with hexane (ꢃ36 cm3). After
about 5 days black prismatic crystals suitable for X-ray
analysis were obtained. Yield: 0.225 g, ꢃ27%. Anal. Calc.
for C32H34N24Mn2: C, 44.41; H, 3.96; N, 38.88, Mn,
12.70. Found: C, 44.48; H, 3.82; N, 38.76; Mn, 12.62%.
We report here on the unusual behaviour of a flexible
hexadentate ligand, N-(1-pyridin-2-ylbenzylidene)-N0-[2-
({2-[(1-pyridin-2-ylbenzylidene)amino]ethyl}amino)ethyl]
ethane-1,2-diamine, (L, Scheme 1) resulting from the
bis-condensation reaction of 2-benzoylpyridine and tri-
ethylenetetramine. While [MnIIL](ClO4)2 (1) resulted
from the reaction of L with manganese(II) perchlorate,
1
III
the binuclear complex ½Mn2 ðL ÞðN3Þ ꢀ (2) and the
6
1
II
1D polymer f½Mn2 ðL ÞðNCSÞ ꢀ ꢁ 2CH3CNgn (3 Æ 2CH3
4
CN) resulted from the reaction of L and manganese(II)
salts, in the presence of sodium azide (2) or ammonium
thiocyanate (3), respectively. L1, N-(1-pyridin-2-ylben-
zylidene)-N-[2-(4-{2-[(1-pyridin-2-ylbenzylidene)amino]-
ethyl}piperazin-1-yl)ethyl]amine, results from an
alkylating cyclization of L. The synthesis, characteriza-
tion including X-ray structure, and magnetic properties
of the novel compounds 2 and 3 are described in this
report.
2.2.3. {[Mn2II (L1)(NCS)4]ꢁ2CH3CN}n (3 ꢁ 2CH3CN)
Compound 3 was synthesized by slow addition of an
acetonitrile solution (12 cm3) containing the L ligand
(0.239 g, 0.5 mmol) to an acetonitrile solution (16 cm3)
of Mn(ClO4)2 Æ 6H2O (0.362 g, 1.0 mmol) with constant
stirring for 30 min. To the resulting solution, an aqueous
solution of ammonium thiocyanate (0.152 g, 2.0 mmol,
12 cm3 H2O) was added slowly with constant stirring
for 15 min. The resulting solution was left to stand at
room temperature and after several days, orange, pris-
matic, X-ray quality single-crystal were obtained. Due
to solvent loss when the crystals are taken out of the
mother solution, the fully desolvated (under vacuum)
sample subjected to elemental analyses had the formula-
2. Experimental
2.1. Materials
Triethylenetetramine, 2-benzoylpyridine, sodium
azide and ammonium thiocyanate were purchased from
Lancaster and used as received. All other solvents and
chemicals were of analytical grade. The hexadentate li-
gand (L) was prepared as reported previously and gave
satisfactory elemental analysis [11].
1
II
tion ½Mn2 ðL ÞðNCSÞ ꢀ (3). Yield: 0.138 g, ꢃ17%. Anal.
4 n
Calc. for C36H34N10S4Mn2: C, 51.18; H, 4.06; N, 16.58,
Mn, 13.0. Found: C, 51.06; H, 3.92; N, 16.39; Mn,
12.74%.
CAUTION: Perchlorate salts and azido compounds
are potentially explosive especially in the presence of or-
ganic compounds. They must be prepared and handled in
small amounts, and with special care.
2.2. Synthesis of complexes
2.2.1. [MnIIL](ClO4)2 (1)
A methanolic solution (4 cm3) of the L ligand (0.239 g,
0.5 mmol) was added dropwise to a methanolic solution
(4 cm3) of Mn(ClO4)2 Æ 6H2O (0.181 g, 0.5 mmol) with
constant stirring for 1 h at room temperature. The
orange-red compound of composition [MnL](ClO4)2
(1) was filtered off, washed with methanol and dried
under vacuum. Yield: 0.220 g, ꢃ60%. Anal. Calc. for
C30H32N6O8Cl2Mn: C, 49.33; H, 4.42; N, 11.51,
Mn, 7.52. Found : C, 49.28; H, 4.53; N, 11.39; Mn,
7.37%.
2.3. Physical measurements
Elemental analyses for C, H and N were performed
using a Perkin Elmer 2400II elemental analyzer. Manga-
nese contents were determined by titrimetric methods.
IR spectra (4000–400 cmꢂ1) were recorded on KBr pel-
lets at 298 K using a JASCO FT/IR-420 spectrometer.
Magnetic data were obtained with a Quantum Design
MPMS SQUID susceptometer. Magnetic susceptibility
C=N
N
N
N=C
N=C
NH
NH
C=N
N
N
N
N
1
L
L
Scheme 1. The hexadentate Schiff base ligands L and L1.

S. Deoghoria et al. / Polyhedron 24 (2005) 343–350
345
measurements were performed in the 2–300 K tempera-
ture range in a 1 T applied magnetic field, and diamag-
netic corrections were applied by using Pascalꢀs
constants [12]. The magnetic susceptibility has been
computed by exact calculation of the energy levels asso-
ciated to the spin Hamiltonian through diagonalization
of the full matrix with a general program for axial sym-
metry [13]. Least-squares fittings were accomplished
with an adapted version of the function-minimization
program MINUIT [14].
hydrogen atoms were placed in calculated positions
and given isotropic U values 1.2 times that of the atom
to which they are bonded. Acetonitrile hydrogen atoms
were neither located nor placed in calculated positions.
The atomic scattering factors and anomalous dispersion
terms were taken from the standard compilation [17].
All crystallographic calculations were carried out using
SHELX-97 [18] and ORTEP-3 [19] program packages.
The crystal data and data collection details are gathered
in Table 1.
2.4. Crystal structures determination and refinement
3. Results and discussion
Single-crystals suitable for X-ray crystallographic
analysis were selected following examination under a
microscope. X-ray data of 2 were collected at 293 K with
a Siemens SMART CCD diffractometer. Crystals of
3.1. Synthesis
The reaction of L with manganese(II) perchlorate
hexahydrate using a 1:1 molar ratio in methanol/water
or acetonitrile/water mixtures yielded an orange-red
compound (1) formulated [MnIIL](ClO4)2 on the basis
of elemental analyses and IR data. The crystal structure
of the nickel analogue [NiL](ClO4)2, prepared by a sim-
ilar synthetic route evidenced a monomeric NiII com-
pound where the hexadentate N6 ligand is L (no L to
L1 rearrangement) [20].
1
II
f½Mn2 ðL ÞðNCSÞ ꢀ ꢁ 2CH3CNgn (3 Æ 2CH3CN) were
4
quickly coated with an inert oil to prevent solvent loss
and the X-ray data were collected at 200 K on a Bru-
ker-AXS SMART APEX/CCD diffractometer. Both
data collections were carried out using Mo Ka radiation
˚
(k = 0.71073 A) in an x ꢂ 2h scan mode. 11942 reflec-
tions were collected for 2, of which 4434 were indepen-
dent (Rint = 0.056) and 14195 reflections for 3, of
which 5227 were independent (Rint = 0.039). In both
cases, intensity data were corrected for Lorentz and
polarization effects. Empirical absorption corrections
were made based on w-scans for 2 [15] and using the
SADABS program [16] for 3. The structures were solved
by direct methods and the structure solution and refine-
ment was based on |F|2. All non-hydrogen atoms were
refined with anisotropic displacement parameters except
those of the disordered acetonitrile which were refined
isotropically. Even when located in the Fourier map,
On the other hand, a manganese(III) binuclear crys-
1
III
talline complex, ½Mn2 ðL ÞðN3Þ ꢀ (2) has been prepared
6
in methanol/water from manganese(II) salts, L, and so-
dium azide (2:1:6 (or 2:1:4) molar ratio) in air. The same
reactions carried out in acetonitrile/water instead of
methanol/water yielded compound 1, i.e., no L to L1
rearrangement. Reaction of manganese(II) salts, L,
and ammonium thiocyanate (2:1:4 (or 2:1:6) molar ra-
tio) in acetonitrile/water yielded orange crystals of an
unprecedented 1D chain of manganese(II) binuclear
1
II
units bridged by
l
1,3-NCS anions, f½Mn2 ðL Þ
ðNCSÞ ꢀ ꢁ 2CH3CNgn (3 Æ 2CH3CN). The same reactions
4
Table 1
Crystallographic data for 2 and 3 Æ 2CH3CN
carried out in methanol/water instead of acetonitrile/
water yielded compound 1, i.e., no
L
to L1
Compound
2
3 Æ 2CH3CN
rearrangement.
Formula
C
32H34N24Mn2
C40H40N12S4Mn2
926.96
The rearrangement from L to L1 (Scheme 2), consist-
ing in an alkylating cyclization centred on the two sec-
ondary amine functions of L, occurred exclusively
along the course of complexation reactions where a
pseudo-halide was involved in addition to L and a metal
salt in the required solvent (methanol/water for 2, and
acetonitrile/water for 3). L1 could not be identified from
reaction media devoid either of pseudo-halide or of me-
tal salt, or carried out in different solvent mixtures. Sim-
ilar rearrangement reactions also occurred with
nickel(II) salts and pseudo-halides [11]. However,
replacement of pseudo-halides by halides did not yield
rearrangement of L to L1. In addition, the poor yields
of 2 and 3 suggest that the extra –CH2–CH2– fragment
present in L1 compared to L most probably originates
from the L ligand itself. A plausible mechanism for this
Formula weight
Space group
Temperature (K)
864.71
P21/c (no. 14)
293
ꢀ
P1 ðno: 2Þ
200
˚
a (A)
8.8709(19)
9.770(2)
25.036(5)
90
7.8187(12)
12.0249(18)
12.1189(18)
81.291(2)
87.416(2)
86.716(2)
1123.7(3)
1
˚
b (A)
˚
c (A)
a (ꢁ)
b (ꢁ)
c (ꢁ)
109.482(7)
90
3
˚
V (A )
2045.6(7)
2
Z
˚
k (A)
0.71073
1.404
0.675
0.71073
1.361
0.791
qcalc. (g cmꢂ3
)
l (Mo Ka) (mmꢂ1
)
Ra
0.0527
0.0798
0.0413
0.1005
wRb
P
P
a
R = iFo| ꢂ |Fci/ |Fo|.
P
P
Rw = [ w(|Fo|2 ꢂ |Fc|2)2/ w|Fo2|2]1/2
.
b

346
S. Deoghoria et al. / Polyhedron 24 (2005) 343–350
N
3
N
3
Mn2+
C
N
NH
NH
N
C
C
N
NH
NH
N
C
-
N3
N
N
N
N
A
Mn
B
Hydrolysis
O
O
O
H
O
+ Mn2+ + N3- + other C fragments
C
C
N
NH
NH
N
C
C
H
N
N
N
N
Mn
A
C
C
N
N+
HC
N+
N C
Mn
N
N
N
N
CH
Mn
Mn
N3
Mn
N
N3
N
N3
N3
N3
N3
N3
N3
N3
D
N3
N3
N3
[Mn2(L1)(N3)6] (2)
Scheme 2. A plausible mechanism for the alkylating cyclization of L to L1 (case of complex 2).
alkylating cyclization of L to L1 may involve the follow-
ing steps: (a) pseudo-halides in the presence of manga-
nese ions may undergo a nucleophilic attack on the
–CH2–CH2– bridge located between the two secondary
amine functions of L (A), producing a di-azido (-thiocy-
anato) (B) intermediate which on subsequent hydrolysis
would generate an oxamido-like derivative (C) [21]; (b)
this oxamido-like derivative would break down, produc-
ing glyoxal and C fragments; (c) glyoxal would then re-
act, most possibly through a metal assisted concerted
route, with the two secondary amine functions of an-
other L ligand molecule, producing a di-imminium-like
intermediate (D) [22], that would be subsequently re-
duced to L1.
absence of L to L1 rearrangement, indicates that at least
one intermediate in this ligand rearrangement results
from an equilibrium reaction: precipitation of the result-
ing complex (2 or 3) is most probably the driving force
allowing the L to L1 rearrangement.
3.2. IR spectroscopy
The IR spectrum of 2 exhibits a very strong absorp-
tion at 2040 cmꢂ1 corresponding to the azido asymmet-
ric stretching vibrations [6b,6c]. The IR spectrum of 3
exhibits strong absorptions at 2098 and 2053 cmꢂ1 cor-
responding to the N,S-bonded thiocyanate ions
[10a,10f]. The absorptions corresponding to the
m(C@N) stretches of L1 are located at 1639 and 1590
cmꢂ1 and 1633 and 1588 cmꢂ1 for compounds 2 and
3, respectively [10a,10f].
The role of the solvent with regard to the formation
of compounds 2 or 3 is also remarkable. Indeed, while
formation of 3 only requires the L to L1 rearrangement,
formation of 2 requires manganese oxidation from the
+2 to the +3 state, in addition to the L to L1 rearrange-
ment. A possible explanation is that the stronger r do-
nor ability of the azido anion favours oxidation of the
manganese centres in the presence of methanol, allowing
4. X-ray structures
4.1. [Mn2III (L1)(N3)6] (2)
1
III
formation of the ½Mn2 ðL ÞðN3Þ ꢀ ð2Þ species. This oxi-
6
dation may be further assisted by coordination of two
extra azido ligands per binuclear unit, yielding the neu-
tral hexacoordinated complex 2. On the other hand,
while the weaker r donor ability of NCS does not favour
oxidation of manganese centres, the presence of the very
weakly coordinating acetonitrile solvent allows bridging
of manganese(II) binuclear units into the 1D chain of 3
through l1,3-NCS anions. Finally, formation of 1 in the
reaction conditions of 2 or 3, but in the absence of the
required solvent (MeOH for 2 and CH3CN for 3), i.e.
The molecular structure of 2 consists of isolated binu-
clear molecules. The ORTEP drawing of the centrosym-
metric binuclear unit with atom labeling scheme is
shown in Fig. 1 and selected bond distances and angles
are listed in Table 2.
Each manganese atom is located in a distorted octa-
hedral N6 coordination environment, with three nitro-
gen atoms from L1 (N1, N2 and N3) and three
nitrogen donors from terminal azido groups (N4, N7
and N10). The Mn–N(L1) distances are in the

S. Deoghoria et al. / Polyhedron 24 (2005) 343–350
347
Fig. 1. ORTEP plot with atom labeling scheme for [Mn2(L1)(N3)6] (2). For clarity the hydrogen atoms are omitted.
˚
donors from thiocyanate anions (N1 (2.090(2) A) from
˚
an end-to-end NCS bridge and N2 (2.097(2) A) from a
˚
terminal NCS), and one sulfur donor (S2) (3.084(1) A)
Table 2
1
˚
Selected bond lengths (A) and angles (ꢁ) for [Mn2(L )(N3)6] (2)
Bond lengths
from another end-to-end NCS. This end-to-end thiocy-
anato bridging mode has already been observed, with
˚
corresponding M–S distances either in the 2.6–2.9 A
Mn–N1
Mn–N3
Mn–N7
2.249(3)
2.395(3)
1.955(4)
Mn–N2
Mn–N4
Mn–N10
2.094(3)
1.949(3)
1.962(3)
˚
range [23], or in the longer 3.11–3.18 A range [10f], the
Bond angles
N1–Mn–N2
N1–Mn–N4
N1–Mn–N10
N2–Mn–N4
N2–Mn–N10
N3–Mn–N7
N4–Mn–N7
N7–Mn–N10
N7–N8–N9
latter suggesting weak Mꢁ ꢁ ꢁS interactions rather than
73.76(10)
90.74(12)
90.41(13)
91.24(12)
89.01(12)
108.00(11)
89.94(13)
89.94(13)
174.8(5)
N1–Mn–N3
N1–Mn–N7
N2–Mn–N3
N2–Mn–N7
N3–Mn–N4
N3–Mn–N10
N4–Mn–N10
N4–N5–N6
N10–N11–N12
152.01(10)
99.93(12)
78.35(10)
173.59(12)
87.46(11)
91.48(10)
178.84(12)
177.8(5)
the covalent bonding suggested by the former. The inter-
˚
mediate 3.084 A value observed for 3 is close to the
lower limit for weak Mꢁ ꢁ ꢁS interactions preventing us
to qualify this Mnꢁ ꢁ ꢁS interaction as a covalent bonding.
The N5S coordination sphere is severely distorted from
octahedral symmetry, with quite large deviations from
the regular cis and trans angles and large axial distortion
evidenced by the quite long Mn–S distance. The intradi-
177.9(4)
mer MnIIꢁ ꢁ ꢁMnII separation (6.437(1) A), originating
˚
2.094(3)–2.395(3) A range, while the Mn–N(azido) dis-
˚
tances are almost equal (1.949(3)–1.962(3) A range). It
˚
from the presence of the central –N(–CH2–CH2–)2N–
cycle in L1, is understandably quite similar to that in
complex 2, and slightly longer than the interdimer
is worth noting that none of the azido anions behaves
as a bridging ligand: this unusual azido coordination
mode [6,7] may originate from the L to L1 rearrange-
ment. Due to the presence of the central –N(–CH2–
CH2–)2N– cycle in L1, the intramolecular Mnꢁ ꢁ ꢁMn
MnIIꢁ ꢁ ꢁMnII distance (6.203(1) A).
˚
4.3. Magnetic properties
˚
distance in complex 2 is quite large (6.473(2) A).
As expected from the large intramolecular
MnIIIꢁ ꢁ ꢁMnIII separation and nature of the polyatomic
bridge, and absence of intermolecular contacts in com-
pound 2, there are no pathways for intra- and/or inter-
molecular magnetic interactions, as indicated by the
paramagnetic behaviour of this binuclear compound.
Its vMT product of 5.97 cm3 K molꢂ1, close to the
spin-only value for two non-interacting S = 2 ions, is
constant over the whole 300–25 K temperature range
and decreases from 5.78 (25 K) to 2.44 cm3 K molꢂ1
(1.95 K) due to single-ion zero fields splitting (ZFS) of
4.2. {[Mn2II (L1)(NCS)4] ꢁ 2CH3CN}n (3)
The structure of 3 Æ 2CH3CN (Fig. 2) consists of cen-
1
II
trosymmetric binuclear ½Mn2 ðL ÞðNCSÞ ꢀ repeat units
4
doubly l1,3-NCS bridged into 1D chains extending
along a. Selected bond distances and angles are listed
in Table 3.
The octahedral coordination sphere around each
manganese(II) consists of three nitrogen donors from
1
L (N3, N4 and N5, 2.183(2)–2.390(2) A), two nitrogen
˚

348
S. Deoghoria et al. / Polyhedron 24 (2005) 343–350
1
II
Fig. 2. ORTEP plot with atom labelling scheme of the ½Mn2 ðL ÞðNCSÞ ꢀn 1D polymeric chain of (3 Æ 2CH3CN). For clarity the hydrogen atoms and
4
solvent molecules are omitted.
units along the 1D chains [9]. Taking into account the ab-
sence of intramolecular magnetic interaction between the
MnII ions of binuclear constituting units, the overall
magnetic behaviour of 3 can not result from extended
magnetic interactions along 1D chains, but from pair-
wise interactions between MnII bridged by two NCS an-
ions; in other words, the structural constituting units of
complex 3 do not correspond to the magnetically inter-
acting pairs.
The experimental magnetic susceptibility data (vM,
lozenges in Fig. 3) were thus fitted by using the theoretical
magnetic susceptibility calculated by exact diagonaliza-
tion of the effective spin Hamiltonian for a pair of inter-
Table 3
˚
Selected bond lengths (A) and angles (ꢁ) for 3 Æ 2CH3CN
Bond lengths
Mn–N1
Mn–N3
Mn–N5
2.0897(18)
2.3897(18)
2.2436(17)
Mn–N2
Mn–N4
Mnꢁ ꢁ ꢁS2a
2.097(2)
2.1832(18)
3.084(1)
Bond angles
N1–Mn–N2
N1–Mn–N4
N2–Mn–N3
N2–Mn–N5
N3–Mn–N5
N1–Mn–S2a
N3–Mn–S2a
N5–Mn–S2a
N2–C4–S3
99.60(7)
152.62(7)
90.76(7)
97.54(7)
148.56(6)
82.90(6)
89.08(5)
81.30(4)
179.3(2)
N1–Mn–N3
N1–Mn–N5
N2–Mn–N4
N3–Mn–N4
N4–Mn–N5
N2–Mn–S2a
N4–Mn–S2a
N1–C3–S2
108.00(7)
100.46(7)
107.50(7)
76.02(6)
72.55(6)
177.41(7)
69.96(5)
179.2(2)
acting S1 = S2 = 5/2 ions, taking into account single-ion
^ ^
2
^
^
ZFS: H ¼ ꢂ2JS1S2 þ DSZ: The best fit (solid lines in
Symmetry operation a: 1 ꢂ x, 1 ꢂ y, ꢂz.
high-spin MnIII. This result being perfectly consistent
with the severe distortion of the MnN6 octahedron evi-
denced by the crystal structure, we did not attempt to fit
these data.
0.4
0.3
0.2
0.1
8
6
4
2
The experimental vMT product of 3 (desolvated crys-
tals) smoothly decreases from 8.48 cm3 K molꢂ1 at 300 K
(slightly below the spin-only value for two non-interact-
ing S = 5/2 ions) to 7.61 cm3 K molꢂ1 at 80 K, and then
sharply, down to 0.67 cm3 K molꢂ1 at 1.96 K, clearly
indicating operation of antiferromagnetic interactions
in 3. While no intramolecular magnetic interaction is ex-
pected between the MnII centres of 3 (same rationale as
for 2), weak intermolecular interactions are expected to
be mediated by the double end-to-end thiocyanate
0
0
0
100
200
T(K)
300
Fig. 3. vM and vMT vs. T data for complex 3. Solid lines represent the
best fit of the data with the model described in the text.
1
II
bridges between binuclear ½Mn2 ðL Þ ðNCSÞ ꢀ repeat
4

S. Deoghoria et al. / Polyhedron 24 (2005) 343–350
349
Fig. 3) was obtained for the following set of parameters:
J = ꢂ1.5 cmꢂ1, D = ꢂ2 · 10ꢂ4 cmꢂ1, g = 1.996, and 1.4%
of paramagnetic impurity. This result is in good agree-
ment with the presence of a weak antiferromagnetic inter-
sion (under DSA program), New Delhi, for financial
support. S.D. thanks The University of Burdwan for a
fellowship.
1
II
action between the binuclear ½Mn2 ðL ÞðNCSÞ ꢀ repeat
4
units along the 1D chains of 3. The negligible single MnII
ion ZFS value, D, is in agreement with the expectation for
a d5 shell. The fit evidenced as well a low contribution
from temperature independent paramagnetism (TIP =
1.2 · 10ꢂ4). Finally, attempts made to take into account
additional inter-pair interactions (molecular field
approximation according to Ginsberg and Linesꢀ ap-
proach [24]) also yielded a negligible value of the intermo-
lecular interaction parameter zj0, thus confirming that the
magnetic behaviour of 3 does not result from extended
magnetic interactions along 1D chains, but from pairwise
interactions between MnII ions.
Appendix A. Supplementary data
X-ray crystallographic files in CIF format for com-
plexes 2 and 3, CCDC Reference Nos. 172397 and
187481, respectively. This material is available free of
charge via www.ccdc.cam.ac.uk/conts/retrieving.html
(or from the Cambridge Crystallographic Data Centre,
12 Union Road, Cambridge CB2 1EZ, UK; fax: +44
1223 336 033; or deposit@ccdc.ca.ac.uk). Supplemen-
tary data associated with this article can be found, in
the online version, at doi:10.1016/j.poly.2004.11.014.
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