Two new 1-D dicyanamide bridged polymeric complexes [Mn(μ1,5- dca)2(salicyh)2]n and {[Ni(μ1,5- dca)(TTA)](ClO4)}n (dca = dicyanamide, N(CN) 2-; salicyh = salicylic hydrazide; TTA = triethylenetetramine): Synthesis, structures and magnetic studies

Article abstract of DOI:10.1016/j.ica.2005.08.006

Two new dicyanamide bridged complexes [Mn(μ_1,5-dca) ₂(salicyh)₂]_n (1) and {[Ni(μ_1,5- dca)(TTA)](ClO₄)}_n (2) (dca = dicyanamide, N(CN) ₂^-; salicyh = salicylic hydrazide; TTA = triethylenetetramine) have been synthesised and structurally characterised. Both the compounds 1 and 2 consist in 1-D coordination polymers. In 1 the manganese atoms are doubly bridged by μ_1,5-dca ligands, whereas in 2 the nickel atoms are bridged by a single μ_1,5-dca ligand. The magnetic measurements indicate that whereas intrachain interactions take place between the metal ions for compound 1 (J = -0.26 cm^-1), no evidence for any exchange coupling is found for compound 2.

Full text of DOI:10.1016/j.ica.2005.08.006

Inorganica Chimica Acta 358 (2005) 4534–4540
www.elsevier.com/locate/ica
Two new 1-D dicyanamide bridged polymeric complexes
[Mn(l1,5-dca)2(salicyh)2]n and {[Ni(l1,5-dca)(TTA)](ClO4)}n
ꢀ
(dca = dicyanamide, NðCNÞ2 ; salicyh = salicylic hydrazide;
TTA = triethylenetetramine): Synthesis, structures and magnetic studies
a
a
a,
b
Soma Sen , Pritha Talukder , Samiran Mitra *, Georgina Rosair ,
c
d
e
f
Glenn Yap , Volker Gramlich , Jinkwon Kim , T. Matsushita ,
g
,g,h
*
´
Cedric Desplanches , Jean-Pascal Sutter
a
Department of Chemistry, Jadavpur University, Kolkata 700 032, India
Department of Chemistry, Heriot-Watt University, Edinburgh EH14 4AS, UK
Department of Chemistry and Biochemistry, University of Delaware, Newark, DE 19716, USA
b
c
d
Laboratorium fu¨r Kristallographie ETH, Eidgeno¨ssische Technische Hochschule Zu¨rich, CH-8092 Zu¨rich, Switzerland
e
Department of Chemistry, Kongju National University, Kongju, Chungnam 314-701, Korea
f
Department of Material Chemistry, Ryukoku University, Seta, Otsu 520-2194, Japan
g
`
Institut de Chimie de la Matiere Condensee de Bordeaux – CNRS, Universite Bordeaux 1, Avenue du Dr. Schweitzer, F-33608 Pessac, France
h
´
´
Laboratoire de Chimie de Coordination du CNRS, Universite´ Toulouse 3, 205, route de Narbonne, F-31077 Toulouse, France
Received 28 April 2005; received in revised form 23 July 2005; accepted 3 August 2005
Available online 21 September 2005
Abstract
Two new dicyanamide bridged complexes [Mn(l1,5-dca)2(salicyh)2]n (1) and {[Ni(l1,5-dca)(TTA)](ClO4)}n (2) (dca = dicyanamide,
NðCNÞ2ꢀ; salicyh = salicylic hydrazide; TTA = triethylenetetramine) have been synthesised and structurally characterised. Both the
compounds 1 and 2 consist in 1-D coordination polymers. In 1 the manganese atoms are doubly bridged by l1,5-dca ligands, whereas
in 2 the nickel atoms are bridged by a single l1,5-dca ligand. The magnetic measurements indicate that whereas intrachain interactions
take place between the metal ions for compound 1 (J = ꢀ0.26 cmꢀ1), no evidence for any exchange coupling is found for compound 2.
ꢀ 2005 Elsevier B.V. All rights reserved.
Keywords: Manganese(II), Nickel(II) complexes; Dicyanamide; Structural studies; Magnetic studies
1. Introduction
monodentate coordination through nitrile nitrogen atom
(1a), bis-monodentate bridging through one nitrile and
one amide nitrogen atoms (1b), end-to-end bridging
through two nitrile nitrogen atoms (1c), tris-monodentate
bridging of three metal atoms (1d) [8] and rarer l4 coordi-
nation where one of the two nitrile nitrogen atoms is coor-
dinated to two metal ions (1e).
Modification of structures and the magnetic properties
of the coordination polymers of dca ligand is possible by
incorporation of coligands into the structures. As for
example, Escure et al. [9] reported two one dimensional
dicyanamide bridged derivatives with formula [Mn(ac)-
(terpy)(l1,5-dca)]n and [Mn(pdz)2(l1,5-dca)2]n {ac = acetate;
Dicyanamide [N(CN)2]ꢀ, bridged polynuclear systems
are a fast growing research field due to the large variety
of topologies and magnetic properties that may be ob-
tained from this ligand. The versatility of the dicyanamide
as a ligand is well illustrated by its five structurally charac-
terised coordination modes shown in Scheme 1 [1–8],
*
Corresponding author. Tel.: +91 33 2668 4193/2017; fax: +91 33 2414
6266.
E-mail addresses: smitra_2002@yahoo.com (S. Mitra), sutter@
lcc-toulouse.fr (J.-P. Sutter).
0020-1693/$ - see front matter ꢀ 2005 Elsevier B.V. All rights reserved.
doi:10.1016/j.ica.2005.08.006

S. Sen et al. / Inorganica Chimica Acta 358 (2005) 4534–4540
4535
a
c
b
d
N
To the best of our knowledge, complex 2 is the first re-
ported dca bridged polymeric Ni(II) complex containing
tetramine as coligand (according to CSD version 5.26 +1
update, November 2004 released).
N
N
N
µ1
N
N
µ1,3
2. Experimental
N
2.1. Materials
N
N
N
µ1,5
Manganese nitrate tetrahydrate, nickel perchlorate
hexahydrate, salicylichydrazide, triethylenetetramine, and
sodium dicyanamide (Fluka) were used as received. The
solvents used were of reagent grade.
N
N
µ1,3,5
e
Caution. Perchlorate salts are potentially explosive and
should be used in small quantity with much care.
N
N
N
2.2. Physical measurements
µ1,1,3,5
The infrared spectra were recorded on a Perkin–Elmer
FT-IR spectrophotometer with a KBr disc. The electronic
spectrum was recorded on a Perkin–Elmer Lambda 40
(UV–Vis) spectrophotometer in acetonitrile. Elemental
analyses were carried out using a Perkin–Elmer 2400 II ele-
mental analyser.
Magnetic susceptibility measurement of 1 was carried
out with a Quantum Design MPMS-5S SQUID magne-
tometer under an applied magnetic field of 5000 Oe
whereas the magnetic susceptibility measurement of 2 was
carried out with a Nichaim SQUID magnetometer under
an applied magnetic field of 5000 Oe. The temperature
dependence of the molar magnetic susceptibility, vM, for
complexes 1 and 2 was measured on polycrystalline sam-
ples in the temperature range 2–300 K. Diamagnetic cor-
rections were estimated from Pascal tables and magnetic
data were corrected for diamagnetic contributions of the
sample holder.
Scheme 1. Different bridging modes of dicyanamide ligand.
terpy = 2,20:60200-terpyridine; pdz = pyridazine} having sin-
gle and double dca bridges respectively. The first complex
contains hepta coordinated manganese(II) central atom
with MnN5O2 petangonal bipyramid environment, whereas
in the second complex manganese atom is hexacoordinated
and both the complexes show weak antiferromagnetic cou-
pling. Similarly, there are several reports of dca complexes
of nickel where the geometry and magnetic properties of
complexes depend on the nature of the coligand used [10–
12]. Among all possible coordination modes of dca, the
l
1,5-dca bridged complexes are very common [13–15] and
are generally characterised by antiferromagnetic interac-
tions among the so-linked metal ions [9,13,16,17].
These interesting properties of dca complexes prompted
us to prepare two new dca bridged polymeric complexes
[Mn(l1,5-dca)2(salicyh)2]n (1) and {[Ni(l1,5-dca)(TTA)]-
(ClO4)}n (2). Here, in case of manganese, we chose a differ-
ent type of ligand, salicylichydrazide (salicyh), to examine
the variation in geometry and magnetic property of the
complex with this ligand. But for nickel we used triethyl-
enetetramine as coligand. Brˇezina et al. [18] reported some
new mononuclear dca complexes of Ni(II) using triethyl-
enetetramine and some other tetramines as coligands. They
measured the temperature dependence magnetic suscepti-
bility of one complex {[Ni(TTA){N(CN)2}](ClO4); TTA =
triethylenetetramine} and no antiferromagnetic interaction
was detected. Here, our aim was to prepare a polymeric
Ni(II) complex using this tetramine by changing the reac-
tion condition and monitor the magnetic behaviour of
the polymeric complex.
2.3. Synthesis of complexes
2.3.1. Synthesis of [Mn(salicyh)2(dca)2]n (1)
To the solution of Mn(NO3)2 Æ 4H2O (0. 251 g., 1 mmol)
in 20 ml methanol, added methanolic solution (5 ml) of sal-
icylichydrazide (0.152 g, 1 mmol) followed by the addition
of a solution of sodium dicyanamide (0.178 g, 2 mmol) in
minimum volume of water into the mixture with continu-
ous stirring. The resulting solution was filtered and the fil-
trate was kept at room temperature. After 10 days, very
light pink hexagonal crystals suitable for X-ray analysis
were formed. Yield 54%. Anal. Calc. for C18H16N10O4Mn:
C, 43.96; H, 3.25; N, 28.49. Found: C, 43.61; H, 2.98; N,
28.41%.
The present report describes the synthesis, spectral char-
acterisation, crystal structure and magnetic behaviour of
two new one dimensional dca bridged polymeric complexes
[Mn(salicyh)2(dca)2] (1) and {[Ni(l1,5-dca)(TTA)](ClO4)}n
(2). The coordination modes of the dca in both the com-
plexes is end-to-end, by means of nitrile nitrogen atoms.
2.3.2. Synthesis of {[Ni(l1,5-dca)(TTA)](ClO4)}n (2)
Methanolic solution of the ligand TTA (1 mmol) was
added to the solution of Ni(ClO4)2 Æ 6H2O (0.365 g.,
1 mmol) in 25 ml methanol followed by the dropwise addi-
tion of a solution of sodium dicyanamide (0.089 g, 1 mmol)

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S. Sen et al. / Inorganica Chimica Acta 358 (2005) 4534–4540
in minimum volume of water into the mixture with con-
stant stirring at a temperature of 313 K; stirring was con-
tinued further for 30 min. The resulting solution was
filtered and the filtrate was kept at room temperature. After
several days, purple coloured hexagonal crystals suitable
for X-ray analysis were formed. Yield 62%. Anal. Calc.
for C8H16N7Ni Æ ClO4: C, 26.05; H, 4.34; N, 26.59. Found :
C, 25.89; H, 4.32; N, 26.50%.
ion was disordered and the Cl atom with three of the O
atoms are situated on a mirror plane. The fourth O atom
lies off the mirror plane and was assigned an occupancy
of 0.75. Crystallographic computing was performed using
SHELXTL [19] programs. Further details are given in Table 1.
3. Results and discussion
3.1. Description of crystal structures
2.4. X-ray data collection and structure refinement
3.1.1. Crystal structure of 1
The determination of unit cell and the data collection
for 1 was performed on an Bruker AXS APEX diffractom-
eter equipped with a graphite crystal monochromated Mo
Ka radiation source. The structure was solved by direct
methods followed by successive different Fourier syntheses.
Hydrogen atoms were not included in the calculations. The
structure was refined in full-matrix least-squares. All non-
hydrogen atoms were refined with anisotropic thermal
parameters in the final cycles. The details of data collection
and refinement for 1 are given in Table 1.
The determination of the unit cell and the data collec-
tion for purple coloured crystal of 2 was performed on a
Rigaku AFC7 four circle serial diffractometer. Data were
corrected for absorption empirically by means of multi-
scans (SADABS). The structure was solved by direct and
difference Fourier methods and refined by full-matrix
least-squares on F2. All non-hydrogen atoms were refined
with anisotropic displacement parameters. The perchlorate
A labelled ORTEP plot of the molecular structure of 1 is
shown in Fig. 1. Selected bond lengths and angles are given
in Table 2. The crystal structure of 1 consists of chains of
manganese atoms bridged by means of double end-to-end
l1,5-dca bridge, two salicyh ligands are additionally coordi-
nated at the manganese centre giving octahedral metal
sites. The manganese atoms are octahedrally coordinated
by means of two nitrogen atoms from two molecules of sal-
icyh ligand in trans arrangement and four nitrile nitrogen
atoms of the four dca ligands. Two of the dca ligands act
as end-to-end bridging ligands with one neighbouring man-
ganese atom and the other two act as end-to-end bridging
ligands to other neighbouring manganese atom, giving a
Table 1
Crystallographic data for complexes 1 and 2
1
2
Chemical formula
Formula weight
Temperature (K)
Radiation
C
491.35
120
Mo Ka
18H16MnN10O4
C8H16N7O4ClNi
368.44
293
Mo Ka
0.71073
˚
Wave length (A)
0.71073
Crystal system
Space group
Z
monoclinic
C2/c
4
21.978(3)
7.5837(12)
13.064(2)
90.00
115.347(2)
90.00
1967.9(5)
10378
2230 [0.0266]
1.658
0.727
1004
0.12 · 0.10 · 0.02
2.05–28.07
R1 = 0.0447
wR2 = 0.1132
R1 = 0.0413
wR2 = 0.1094
0.444, ꢀ0.274
orthorhombic
Pbcm
Fig. 1. ORTEP diagram of complex 1 with atom numbering scheme
(thermal ellipsoids are drawn at 30% probability level).
4
˚
a (A)
11.178(2)
8.542(2)
15.015(3)
90.00
90.00
90.00
1433.7(5)
1714
1714 [0.0000]
1.707
1.567
760
0.10 · 0.10 · 0.20
2.7–27.5
R1 = 0.0823
wR2 = 0.1454
R1 = 0.0450
wR2 = 0.1277
0.828, ꢀ0.783
˚
b (A)
Table 2
˚
c (A)
˚
Selected bond distances (A) and bond angles (ꢁ) for complexes 1 and 2
a (ꢁ)
b (ꢁ)
c (ꢁ)
Complex 1
Complex 2
Mn–N3
Mn–N1
Mn–N4
2.2118(19)
2.226(2)
2.281(2)
Ni–N1
Ni1–N4
Ni1–N7
2.116(3)
2.119(4)
2.114(3)
3
˚
V (A )
Reflections collected
Independent reflections [Rint
]
Density (calculated) (Mg/m3)
Absorption coefficient (mmꢀ1
F(000)
N3–Mn–N3A
N3–Mn–N1
N3–Mn–N1A
N1–Mn–N1A
N3–Mn–N4A
N4–Mn–N4A
N1–Mn–N4A
N3–Mn–N4
N1–Mn–N4
87.43(10)
178.32(7)
92.69(7)
87.24(10)
87.88(7)
178.19(10)
90.43(7)
93.43(7)
88.25(7)
N1–Ni1–N4
N1–Ni1–N7
N1–Ni1–N1A
N1–Ni1–N4A
N1–Ni1–N7A
N4–Ni1–N7
N4–Ni1–N4A
N4–Ni1–N7A
N7–Ni1–N7A
92.01(15)
91.44(14)
94.61(18)
89.65(15)
170.19(14)
82.40(13)
177.55(19)
95.76(14)
83.67(19)
)
Crystal size (mm)
h Range for data collection (ꢁ)
R indices (all data)
Final R indices [I > 2r(I)]
Largest differential peak
Symmetry code for 1: A, 1 ꢀ x, y, 1/2 ꢀ z.
Symmetry code for 2: A, x, 1/2 ꢀ y, 1 ꢀ z.
ꢀ3
˚
and hole [e A
]

S. Sen et al. / Inorganica Chimica Acta 358 (2005) 4534–4540
4537
Fig. 2. Side view of adjacent infinite 1-D chains of complex 1 showing H-
bonding interactions.
uniform one dimensional system (Fig. 2). The distorted
octahedral metal site is located on an inversion centre,
where the donor nitrogen atoms from four bridging dca li-
gands [N1, N1A, N3, N3A] form the equatorial plane with
angle subtended by the Mn(II) ion varying from 87.24(10)
to 92.69(7)ꢁ (Table 2). Two nitrogen atoms from the two
molecules of the salicyh ligand occupy the axial position
with N4–Mn–N4A angle being 178.19(10)ꢁ. The equatorial
Fig. 3. Side view of adjacent infinite 1-D chains of complex 1 showing six
membered ring stacking.
˚
Mn–N bond distances [Mn–N3 = 2.2118(19) A, Mn-
Table 3
˚
˚
˚
N3A = 2.212(2) A, Mn–N1 = Mn–N1A = 2.226(2) A] are
comparable to similar systems [9]. The axial Mn–N dis-
Hydrogen bonding interactions (A, ꢁ) of complex 1
D–H. . .A
D–H
H. . .A
D. . .A
\D–H. . .A
˚
tance [2.282(2) A] is slightly longer than the equatorial
N1–H2. . .O1
O1–H1. . .O2_$1
N2–H3. . .N4_$2
0.86(3)
0.835(19)
0.82(4)
1.94(3)
1.81(2)
2.51(4)
2.607(3)
2.643(3)
3.168(4)
133(3)
173(4)
137(4)
distances. As depicted in Fig. 1, the bridging array Mn–
NCNCN–Mn adopts a ‘‘V’’-type conformation because
of the sp2 hybridisation of the middle nitrogen atom of
the dca, where C–N–C angle [C1–N2–C2] is 120.2(2)ꢁ
[20]. ½NðCNÞ2ꢀꢁ has pseudo C2v symmetry with average
Symmetry code: $1, X, 1 ꢀ Y, 0.5 + Z; $2, 1 ꢀ X, 1 ꢀ Y, ꢀZ.
˚
C–N and C@N bond lengths of 1.302(3) and 1.160(3) A,
means of single end-to-end l1,5-dca bridge (Fig. 4). Each
nickel(II) atom is octahedrally surrounded by four nitrogen
atoms from TTA ligand and two nitrile nitrogen atoms
from two dicyanamide ligands. Two nitrogen atoms of
the TTA ligand and two nitrogen atoms of the dca ligand
form the equatorial plane, the deviations of these two types
of nitrogen atoms from this equatorial plane are ꢀ0.1419,
respectively, as commonly observed in ½NðCNÞ2ꢀꢁ anions
[21–33]. The carbon atoms of the dca ligand are sp hybri-
dised, with N–C–N angles (173.5(2) and 175.(2)ꢁ) are al-
most linear [16], while the C–N–Mn angle 159.56(18)ꢁ is
deviated from linearity. Intramolecular H-bonding is pres-
ent in the complex between N1–H, O1 of the salicyh moiety
(Fig. 2). In the crystal, the chains are packed by O–H. . .O
and N–H. . .N hydrogen bonds (Fig. 2) in one direction and
by a six membered ring stacking in the other (Fig. 3). The
infinite chain propagates along b-axis. The distance be-
tween two adjacent manganese centres within the same
˚
0.1419, 0.1567, and ꢀ0.1567 A for N1, N1A, N7 and N7A,
respectively. The central nickel(II) ion (Ni1) lies on the
equatorial plane. The other two nitrogen atoms N4 and
N4A of TTA ligand occupy the axial position with trans
axial angle N4–Ni–N4A = 177.55(19)ꢁ. The equatorial an-
gles range from 82.40(13) to 95.76(14)ꢁ. The equatorial
˚
chain is 7.57(2) A. The minimum distance between two
˚
˚
˚
manganese centres in the successive chains is 7.34 A (see
bond distances [2.114(14)–2.116(3) A] are nearly equal to
Table 3).
the axial bond distances [2.119(3) A]. Similar to 1 in this
complex also, the bridging array Ni–NCNCN–Ni adopts
a V-type conformation because of sp2 hybridisation of mid-
dle nitrogen atom of the dca ligand, where C–N–C angle
[C2–N2–C2B] is 122.1(5)ꢁ [20]. ½NðCNÞ2ꢀꢁ has pseudo C2v
symmetry with average C–N and C@N bond lengths of
3.1.2. Crystal structure of complex 2
A labelled ORTEP plot of the structure of 2 is shown in
Fig. 4. The relevant bond angles are given in Table 2. The
structure consists of chains of nickel(II) atoms bridged by

4538
S. Sen et al. / Inorganica Chimica Acta 358 (2005) 4534–4540
Fig. 4. ORTEP diagram of complex 2 with atom numbering scheme (thermal ellipsoids are drawn at 30% probability level).
˚
1.302(5) and 1.146(5) A, respectively, as commonly ob-
served in ½NðCNÞ2ꢀꢁ anions [21–33]. The carbon atoms of
the dca ligand are sp hybridised, with N–C–N angles
173.5(5)ꢁ are almost linear [16], while the C–N–Ni angle
151.8(3)ꢁ is deviated from linearity. The distance between
two nickel centres bridged by single l1,5-dca ligand is
2 K, suggesting the occurrence of antiferromagnetic inter-
actions between the Mn(II) ions. This experimental behav-
iour has been analysed with a model appropriate for a
chain derived from the spin Hamiltonian
nꢀ1
X
H ¼ ꢀJ
SA ꢂ SA
;
i
iþ1
˚
i¼1
7.508 A. One perchlorate ion for each asymmetric unit is
where the summation runs over the n sites of the chain. For
large values of the spin, S = 5/2 in our case, it is possible to
treat the spin as a classical vector resulting in the following
expression for vMT [42,43]:
present in the lattice.
3.2. Infrared spectra
The IR spectra of complexes 1 and 2 show the character-
istic stretching vibration bands of dicyanamide ligand. The
solid state of complexes depict several mCN bands at 2303,
2240, 2172 cmꢀ1 for 1 and 2306, 2229, 2160 cmꢀ1 for 2
which are attributed to msym + masym (CN), masym(CN) and
Ng2b2SðS þ 1Þ 1 þ u
vMT ¼
with
3k
1 ꢀ u
ꢀ
ꢁ
ꢀ
ꢁ
JSðS þ 1Þ
kT
u ¼ coth
ꢀ
.
kT
JSðS þ 1Þ
m
sym(CN) modes. All data are in good agreement with the
The best fit of this expression to the experimental data
leads to an intrachain exchange parameter of J =
ꢀ0.26 cmꢀ1 with g = 2.02 (Fig. 5). These values are in good
agreement with some previously reported Mn(II)-dicya-
namido complexes. With one exception (J = +1.6 cmꢀ1),
in all other cases the exchange interaction is very weak anti-
ferromagnetic [17].
The magnetic behaviour for compound 2 is shown in
Fig. 6. For this compound, vMT is invariant over the whole
temperature range except a sharp decrease observed below
literature [23,34–39]. Relative to m(N(CN)2) values of the
free ligand (2287, 2229 and 2181 cmꢀ1), those of complex
1 and complex 2 show higher frequency shifts, due to the
bridging coordination mode of dca in the complexes. For
complex 1 compared with the free salicylic hydrazide li-
gand, the bands at 3177–3279 cmꢀ1 attributed to PhO-H
group remain nearly unchanged after complexation indi-
cates the presence of uncoordinated phenolic-OH group
in the complex [40].
4.5
4
3.3. Electronic spectrum
As the solution of complex 1 is almost colourless, elec-
tronic spectrum was not recorded for this complex. The
peaks in the electronic spectrum of complex 2 in acetoni-
trile exhibit the d–d maxima of octahedral NiII. The bands
at 245, 382 and 640 nm are assigned to the spin allowed
3.5
3
3
3
3
3
3
3
transitions A2g ! T2g, A2g ! T1g, A2g ! T1g(P),
respectively. The last transition appeared as shoulder [41].
2.5
2
3.4. Magnetic studies
The magnetic behaviour for compound 1 is shown in the
form of vMT versus T plot (Fig. 5). At 300 K, the vMT
value is 4.4 cm3molꢀ1 K in good agreement with that ex-
pected for an isolated spin S = 5/2 (4.37 cm3 molꢀ1 K).
The vMT values remain constant from 300 K down to
ca. 50 K, then decrease rapidly to 1.6 cm3 molꢀ1 K at
1.5
0
50
100
150
200
250
300
T (K)
Fig. 5. Experimental (h) and calculated (—) temperature dependence of
MT for complex 1.
v

S. Sen et al. / Inorganica Chimica Acta 358 (2005) 4534–4540
4539
5 K. The vMT value between 10 and 300 K is
1.16 cm3 K molꢀ1, which is consistent with a S = 1 spin
for a d8 electronic configuration in an octahedral geometry.
The observed magnetic behaviour in the low temperature
domain might be ascribed either to very weak antiferro-
magnetic interactions between the metal ions within a
chain as found for 1, or to the effect of zero-field splitting
on the Ni ions in the absence of any exchange interaction
mediated by the dca ligand. In order to evaluate the two
hypotheses, the magnetic behaviour was first analysed by
considering exchange interaction among the Ni ions. The
spin Hamiltonian that applies is the same as that for 1
but the Fisher solution relevant only for larger spins was
replaced by the Weng equation [44]. The expression for
vMT appropriate to compound 2 is given below
g = 2.17. The obtained D parameter is in the range of those
usually found for Ni(II) ions. For instance, for six-coordi-
nated Ni(II) ions linked by oxalate-bridges into a chain
organisation, a D value of 1.87 cmꢀ1 has been deduced
using high-field/high-frequency EPR spectroscopy [45].
The calculated behaviour considering a D parameter clo-
sely follows the experimental data, especially in the low
temperature domain (Fig. 5). Consequently, the decrease
of vMT observed below 10 K for 2 can be attributed to
the single-ion anisotropy rather than to exchange among
the Ni(II) ions.
4. Concluding remarks
In case of compound 1, using a different coligand we
do not get any remarkable variation in the geometry com-
pared to that of previously reported dca bridged Mn(II)
polymers whereas compound 2 is the first reported dca
bridged polynuclear Ni(II) complex having tetramine as
coligand. On the magnetic point of view, the weak antifer-
romagnetic interaction found for compound 1 is perfectly
in line with the behaviour usually found for l1,5-dca
bridged Mn(II) ions. When Ni(II) ions are involved in-
stead of Mn(II), it is rather surprising that no exchange
interaction is detected. In the reported compound 2, the
experimental behaviour was best analysed by considering
only the contribution of the zero-field splitting on the
Ni(II) ion, confirming the very poor ability of the dca
linker to mediate the magnetic interaction for this ion.
For such S = 1 chain compounds with antiferromagnetic
interactions, a peculiar behaviour known as Haldane
gap [46] is anticipated, however for compound 2 the
weakness of the exchange interaction precludes the obser-
vation of this gap.
Ng2b2
k
2 þ Ad þ Bd2
vMT ¼
with
3 þ Cd þ Dd2 þ Ed3
A ¼ 0:019; B ¼ 0:777; C ¼ 4:346; D ¼ 3:232; E ¼ 5:834 and
d ¼ jJj=kT.
The fit of this expression to the experimental data yielded
an intrachain exchange parameter of J = ꢀ0.14 cmꢀ1 with
g = 2.16 but agreement between the experimental and cal-
culated behaviour is poor (Fig. 6), suggesting that the ob-
served behaviour does not result from antiferromagnetic
interactions.
We have then neglected the exchange contribution be-
tween the Ni ions and introduced axial zero-field splitting
using the Hamiltonian H ¼ D½S2z ꢀ SðS þ 1Þ=3ꢁ, the result-
ing expression for the susceptibility is given by [44]
vMT ¼ ðvM;z þ 2vM;xÞT=3
2Ng2b2 expðꢀyÞ þ 2½1 ꢀ expðꢀyÞꢁ=y
¼
with y ¼ D=kT .
3k
1 þ 2expðꢀyÞ
5. Supplementary material
Best fit to the experimental data yielded a zero-field split-
ting parameter |D| = 2.16 cmꢀ1 and a Lande factor
´
CCDC – 266438 (1) and 266439 (2) – contains the sup-
plementary crystallographic data for this paper. These data
can be obtained free of charge at www.ccdc.cam.ac.uk [or
from Cambridge Crystallographic Data Center, 12, Union
Road. Cambridge CB2 1EZ, UK; e-mail: deposit@ccdc.
cam.ac.uk].
1.2
1.15
1.1
Acknowledgements
1.05
1
We acknowledge the financial assistance to S. Sen from
the CSIR (New Delhi, India). The magnetic measurement
of complex 1 is supported by the Centre Franco-Indien
´
pour la promotion de la Recherche Avancee/Indo-French
Centre for the Promotion of Advanced research, Project
(Project 3108-3). Magnetic measurement of complex 2
was financially supported by the MOST(NRL), Korea.
0.95
0
20
40
60
80 100 120 140
T (K)
References
Fig. 6. Experimental (h) and calculated temperature dependence of vMT
for complex 2: (---) when considering exchange coupling between the Ni
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