New topology in azide-bridged cobalt(11) complexes: The weak ferromagnet [Co2(N3)4(HexamethylenetetramineKH 2O)]n

Article abstract of DOI:10.1021/ic9005373

A new polynuclear azido-bridged Co(11) compound with formula [Co ₂(N₃)₄(HMTA)(H₂O)]_n (1) (HMTA = hexamethyl-enetetramine) has been structurally and magnetically characterized. The compound 1 crystalli

Full text of DOI:10.1021/ic9005373

6
280 Inorg. Chem. 2009, 48, 6280–6286
DOI: 10.1021/ic9005373
New Topology in Azide-Bridged Cobalt(II) Complexes: the Weak Ferromagnet
Co (N ) (Hexamethylenetetramine)(H O)]
[
2
3 4
2
n
:
:
::
†
‡
†
,§
Franz A. Mautner, Lars Ohrstrom, Beate Sodin, and Ramon Vicente*
†
::
::
Institut fur Physikalische und Theoretische Chemie, Technische Universitat Graz, Rechbauerstrasse 12,
::
A-8010, Graz, Austria, Department of Chemical and Biological Engineering, Chalmers Tekniska Hogskola,
‡
::
§
SE-412 96 Goteborg, Sweden, and Departament de Quı ´m ica Inorg aꢀ nica, Universitat de Barcelona, Martı´ i
Franqu eꢀ s 1-11, 08028 Barcelona, Spain
Received March 19, 2009
A new polynuclear azido-bridged Co(II) compound with formula [Co (N ) (HMTA)(H O)] (1) (HMTA = hexamethyl-
n
2
3 4
2
enetetramine) has been structurally and magnetically characterized. The compound 1 crystallizes in the monoclinic
system C2/m space group, and consist of a complex three-dimensional system in which end-to-end and end-on azido
bridging ligands between the Co(II) atoms coexist. The HMTA ligand is also linking three different Co(II) atoms. The
network analysis shows for 1 a three- and six-connected network topology not previously reported. The magnetic
properties of 1 are also reported, and it was found that the magnetic interactions define another new three- and four-
2
4
2
connected net assigned as a (6.8 )(6 .10 )-tfo net. In the high temperature region the χ versus T plot can be fitted by
M
using the Curie-Weiss law, and the best fit theta value is -26.6 K. For 1 magnetic ordering and spontaneous
magnetization is achieved below T = 15.6 K.
c
4
Introduction
The number of one-dimensional (1D) to three-dimensional
(N ) ]. Another SCM azido-bridged Co(II) compound
3
2
14
has been reported recently, and, on the other hand, the
combination of the anisotropic Co(II) cation with the co-
ordination versatility and the consequent different super-
exchange coupling ways of the azido bridging ligand has
produced several compounds having unusual properties in
their combinations of magnetism and structure as multi-
layer systems with complex long-range magnetic order-
ing behavior, the compound [Co(bpg)(N ) ] (DMF)
4/3
(bpg = meso-R,β-bi(4-pyridiyl)glycol) showing a Kagomeꢁ
layer or the weak ferromagnet [Co(μ -N ) (4-acpy) ]
1-16
(3D) azido bridged Co(II) compounds
is quickly increas-
ing mainly after the report of the double end-on (EO) azide
0
bridged single-chain magnet (SCM) [Co(2,2 -bithiazoline)-
*
To whom correspondence should be addressed. E-mail: ramon.vicente@
qi.ub.es. Fax: +34 934907725.
1) Viau, G.; Lombardi, M. G.; De Munno, G.; Julve, M.; Lloret, F.;
Faus, J.; Caneschi, A.; Clemente-Juan, J. M. Chem. Commun. 1997, 1195.
2) Hong, C. S.; Koo, J.-e.; Son, S.-K.; Lee, Y. S.; Kim, Y.-S.; Do, Y.
Chem. Eur. J. 2001, 7, 4243.
16
(
3 2
3
5
(
1,3 3 2
2 n
10,11
(
4-acpy=4-acetylpyridine).
(
3) Doi, Y.; Ishida, T.; Nogami, T. Bull. Chem. Soc. Jpn. 2002, 75, 2455.
(
4) Liu, T.-F.; Fu, D.; Gao, S.; Zhang, Y.-Z.; Sun, H.-L.; Su, G.; Liu,
In this paper, we report the synthesis and magnetic
properties of a new Co(II) azido compound forming a 3D
Y.-J. J. Am. Chem. Soc. 2003, 125, 13976.
5) Wang, X.-Y.; Wang, L.; Wang, Z.-M.; Gao, S. J. Am: Chem. Soc.
006, 128, 674.
6) Liu, F.-C.; Zeng, Y.-F.; Jiao, J.; Bu, X.-H.; Ribas, J.; Batten, S. R.
Inorg. Chem. 2006, 45, 2776.
(
coordination network: [Co (N ) (HMTA)(H O)] (1) (HM-
2
3 4
2
n
2
(
TA=hexamethylenetetramine). 1 shows a complex structure
in which coexist Co(II) atoms linked by end-to-end azido
bridging ligands, by end-on azido bridging ligands, and by
the HTMA ligand acting as tridentate bridging ligand. From
the point of view of the magnetic properties, 1 is a bulk
antiferromagnetically coupled system in which spontaneous
(
7) Liu, T.; Zhang, Y.; Wang, Z.; Gao, S. Inorg. Chem. 2006, 45, 2782.
(
8) Yoo, H. S.; Kim, J. I.; Yang, N.; Koh, E. K.; Park, J.-G.; Hong, C. S.
Inorg. Chem. 2007, 46, 9054.
(
(
9) Wang, X.-T.; Wang, Z.-M.; Gao, S. Inorg. Chem. 2007, 46, 10452.
10) Abu-Youssef, M. A. M.; Mautner, F. A.; Vicente, R. Inorg. Chem.
2
007, 46, 4654.
(
(
magnetization is achieved below T =15.6 K. The canting
11) Wang, X.-Y.; Wang, Z.-M.; Gao, S. Inorg. Chem. 2008, 47, 5720.
12) Mondal, K. C.; Sengupta, O.; Nethaji, M.; Mukherjee, P. S. Dalton
c
11
angle, γ, has been roughly calculated from the powder
direct current (dc) magnetic measurements to be 7.2°. Taking
into account the complex structure of 1 and the fact that the
coupling through EE and EO azido bridging ligands is
usually antiferromagnetic (AF) or ferromagnetic (F) respec-
tively (no magnetic coupling is expected through the HMTA
bridging ligand), we have performed a network analysis for 1
Trans. 2008, 767.
13) Li, R.-Y.; Wang, X.-Y.; Liu, T.; Xu, H,-B; Zhao, F.; Wang, Z.-M.;
Gao, S. Inorg. Chem. 2008, 47, 8134.
(
(
(
14) Sun, H.-L.; Wang, Z.-M.; Gao, S. Chem. Eur. J. 2009, 15, 1757.
15) Wang, X.-T.; Wang, X.-H.; Wang, Z.-M.; Gao, S. Inorg. Chem. 48,
2
009, 1301.
16) Gao, E.-Q.; Liu, P.-P.; Wang, Y.-Q.; Yue, Q.; Wang, Q.-L. Chem.
(
Eur. J. 2009, 15, 1217.
pubs.acs.org/IC
Published on Web 06/09/2009
r 2009 American Chemical Society

Article
Inorganic Chemistry, Vol. 48, No. 13, 2009 6281
as bulk compound to best understand the structure and also
an analysis of the magnetic network for 1, to try to justify the
magnetic properties. The 3D-nets formed in 1 are of some
importance, as they show topologies not previously reported.
Especially the magnetic net, as this is a highly symmetric
network built from nodes with geometries easily obtainable
from various “secondary building units” and molecular
building blocks. The present case seems to be the first
assigned example of this net in chemistry.
Table 1. Relevant Crystal Data for 1
empirical formula
formula weight
cryst system
C
444.19
monoclinic
C2/m
11.708(2)
12.641(3)
9.482(2)
90
90.03(3)
90
1403.3(5)
4
2.102
896
5579
1486
0.0448, 0.0944
0.0520, 0.0973
1.114
6
H
14Co
2 16
N O
space group
˚
a (A)
˚
b (A)
˚
c (A)
R (deg)
β (deg)
γ (deg)
3
˚
V (A )
Z
Experimental Section
-1
Fcalcd(g.cm
F(000)
)
Starting Materials. Co(II) chloride hexahydrate, HMTA, and
sodium azide (Aldrich) were used as obtained. Aqueous hydra-
zoic acid is obtained with a modified Kipp’s generator
no. reflections coll.
no. reflections unique
R
R
1
, wR
, wR
2
(obs. refls)
(all data)
by decomposition of NaN
sequent transfer of HN into H O with aid of an inert-gas
3 2 4 2
in H SO /H O (1:3, v:v) and sub-
1
2
3
2
GOF
17,18
stream.
Caution! Hydrazoic acid and Azide compounds are potentially
explosive. Only a small amount of material should be prepared,
and it should be handled with care.
a
˚
Table 2. Selected Bond Lengths (A) and Bond Angles (deg) for 1
Co1-N11A
Co1-O1
Co2-N23D
Co2-N2G
N11-N12
N21-N22
N32-N31E
2.093(3)
2.159(4)
2.059(3)
2.370(3)
1.206(6)
1.172(4)
1.188(3)
Co1-N21C
Co1-N1
Co2-N31D
Co2-N2F
N12-N13
N22-N23
N2-Co2B
2.123(3)
2.201(4)
2.148(3)
2.370(3)
1.130(7)
1.187(4)
2.370(3)
Spectral and Magnetic Measurements. Infrared spectra (4000-
-1
4
3
00 cm ) were recorded from KBr pellets on a Perkin-Elmer
80-B spectrophotometer. Magnetic susceptibility measurements
under several magnetic fields in the temperature range 2-300 K
and magnetization measurements in the field range of 0-5 T
were performed with a Quantum Design MPMS-XL SQUID
magnetometer at the Magnetochemistry Service of the University
of Barcelona. All measurements were performed on powdered
polycrystalline samples. Pascal’s constants were used to estimate
the diamagnetic corrections, which were subtracted from the
experimental susceptibilities to give the corrected molar magnetic
susceptibilities.
N11A-Co1-N11
N11-Co1-N21
N11A-Co1-O1
N11-Co1-N1
O1-Co1-N1
N23-Co2-N2G
N12-N11-Co1
N13-N12-N11
N21-N22-N23
N32-N31-Co2
77.0(2)
N11A-Co1-N21
N21-Co1-N21C
N21-Co1-O1
167.47(12)
98.3(2)
91.97(13)
87.82(9)
100.83(9)
168.9(2)
91.59(11)
128.50(9)
180.0
85.80(11)
86.94(11)
90.46(12)
92.08(11)
103.0(2)
134.1(3)
123.4(3)
178.1(5)
N21-Co1-N1
N23D-Co2-N31D
N31-Co2-N2G
Co1A-N11-Co1
N22-N21-Co1
N22-N23-Co2
N31-N32-N31E
2 3 4 2 n
Synthesis. [Co (N ) (HMTA)(H O)] (1). Sodium azide (0.293 g,
4
.5 mmol) CoCl 6H O (0.480 g, 2.02 mmol) and HMTA (0.280 g,
2
177.9(4)
129.2(2)
3
2
2
.00 mmol) were dissolved in minimum amount of aqueous hydra-
zoic acid (21 mL) to obtain a clear red solution upon heating to
0 °C. Transparent red crystals of 1 were separated by slow cooling
of the solution to 4 °C within 2 days. (yield approximately 0.375 g,
3.7%) Anal., Found: C, 16.0; H, 3.0; Co, 26.4; N, 50.7. Calcd for
C H Co N O (444.19): C, 16.2; H, 3.2; Co, 26.5; N, 50.5. IR
a
Symmetry codes: (A) -x + 1, -y + 1, -z; (B) x, y, z - 1; (C) x,
y + 1, z; (D) -x + 3/2, -y + 3/2, -z + 1; (E) -x + 1, y, -z + 1;
7
-
(
F) x, y, z + 1; (G) -x + 3/2, -y + 3/2, -z.
8
6
14
2
16
atoms of the HMTA ligand were inserted in calculated positions.
Full-matrix least-squares refinement on F with anisotropic
thermal motion parameters for all the non-hydrogen atoms and
-
1
2
(
1
9
(
KBr, cm ): 3408 vw, 3351 vw, 3007 vw, 2961 vw, 2084 vs (νas
451 w, 1359 w, 1297 w, 1233 m, 1228 w, 1061 w, 1005 m, 973 m,
15 w, 844 w, 797 m, 774 w, 692 m, 662 w, 614 w, 511 w, 425 w
v=very, s=strong, m=medium, w=weak).
3
N ),
2
0
isotropic for the remaining atoms were employed. Selected
bond parameters are summarized in Table 2.
From the synthetic point of view, it should be emphasized that a
compound of formula [Co(N ) (HMTA)(H O) ] has been ob-
Network Analysis. Abbreviations (three-letter codes) for 3D
nets were taken from the web-based Reticular Chemistry Struc-
ture Resource, where crystallographic coordinates and other
3
2
2
2 n
9
1
tained under controlled hydrothermal synthesis. This compound
is a 1D infinite polymeric chain in which the HMTA acts as
bidentate bridging ligand, and the azido is only a terminal ligand.
Structure Determination. A suitable single crystal of 1 (ap-
proximately size: 0.26ꢀ0.18ꢀ0.12 mm) was selected for X-ray
diffraction. Intensity data were collected with a Bruker AXS
KAPPA APEX II diffractometer using graphite monochromated
Mo-KR radiation. Data were collected at 100 K using ω-scans.
Cell parameters were retrieved and refined using Bruker SMART
and SAINT software programs. Absorption correction was
applied using SADABS. The structure was solved by direct
methods by using the SHELXS-86 program and was refined with
SHELXL-93 incorporated in the SHELXTL/PC sofware pack-
age. Relevant structural data are given in Table 1. Hydrogen
2
1
useful details for 3D-nets can be obtained. More unusual and
exotic nets with confirmed occurrence in known structures are
listed in the TTO collection obtainable with the TOPOS pro-
2
2,23
gram, also used to established the topologies of the nets in 1.
The six- and three-connected net in 1 has been given the loh1
symbol in the TTO collection. Mathematically derived nets can
(20) (a) Blessing, R. H. Acta Crystallogr. 1995, A51, 33. SADABS; Bruker
AXS: Madison, WI, 1998. (b) Sheldrick, G. M. SHELXS-86, Program for the
Solution of Crystal Structure; University of Goettingen: Goettingen, Germany,
1
986. (c) Sheldrick, G. M. SHELXL-93, Program for the Refinement of Crystal
Structure; University of Goettingen: Goettingen, Germany, 1993. (d) SHELXTL
5.03 (PC-Version), Program library for the Solution and Molecular Graphics;
Siemens Analytical Instruments Division: Madison, WI, 1995.
(21) O’Keeffe, M.; Yaghi, O. M.; Ramsden, S. Reticular Chemistry
(
17) Bitschnau, B.; Egger, A.; Escuer, A.; Mautner, F. A.; Sodin, B.;
Vicente, R. Inorg. Chem. 2006, 45, 868, and references therein.
18) Energetic Materials; Fair, H. D., Walker, R. F., Eds.; Plenum Press:
New York, 1977; Vol. I, pp 25-31.
19) Chakraborty, J.; Samanta, B.; Rosair, G.; Gramlich, V.; Salah El
Fallah, M.; Ribas, J.; Mitra, S. Polyhedron 2006, 25, 3006.
Structure Resource; Australian National University Supercomputer Facil-
ity: http://rcsr.anu.edu.au/, February 2009
(22) Blatov, V. A.; Shevchenko, A. P.; Serezhkin, V. N. J. Appl. Crystal-
logr. 2000, 33, 1193.
(23) TOPOS website: http://www.topos.ssu.samara.ru/, Ac. Pavlov St. 1,
(
(
443011 Samara, Russia, February 2009.

6
282 Inorganic Chemistry, Vol. 48, No. 13, 2009
Mautner et al.
be searched in the EPINET database. For the less common
nets the short (Schlafli) symbol before the three-letter code was
2
4
::
25
4
2
included for clarity as in 6 .8 -nbo. This notation reveals the
number of smallest rings found in the net, and, for nets with
more than two nodes, also identifies the stoichiometry of the
nodes, and the type of network in question. The ideal geometry
2
6
of the new nets was obtained using SYSTRE.
Results and Discussion
Synthesis. The reaction of Co(II) salt, with HMTA and
NaN in aqueous hydrazoic medium afforded the forma-
3
tion of the title complex 1, whereas the previously re-
ported [Co(N ) (HMTA)(H O) ] , has been obtained
1
9
3
2
2
2 n
under controlled hydrothermal conditions. The use
of diluted hydrazoic acid allows formation of an
acidic medium with pH value <5.5 without introducing
a foreign ion and prevents the quick precipitation of 1 in
microcrystalline form.
Structure of 1. A perspective view together with the
atom numbering scheme of complex 1 is shown in
Figure 1a, a packing plot in Figure 1b, and the packing
plot of Co-azido-sublattice in Figure 1c. Selected bond
distances and bond angles are listed in Table 2. In the
structure there exist two cobalt(II) centers: Co1 with
(
z-coordinate (0.056) and Co2 (z-coordinate = 1/2) on
inversion center of space group C2/m and Z=4. Co1 is
six-coordinated by N1 of the HMTA and by O1 of the
aqua ligand, further by N11 and N11A of two EO azide
bridges, and in addition by N21 and N21C of the two EE-
azide bridges. Co2 is six-coordinated by N23, N31,
N23D, N31D of 4 EE-azide bridges and trans coordi-
nated HMTA nitrogen atoms N2G, N2F. The HMTA
molecule acts as tridentate bridge between Co1, Co2B,
and Co2H. The aqua ligand forms hydrogen bonds of
type O-H N to N31 and N31C, respectively.
3
3 3
The 3D network of the structure is defined by the
HMTA nodes connecting two Co2 atoms and one
Co1-Co1 dimer, the Co2 atoms connecting two HMTA
and four Co1-Co1 dimers, and the Co1-Co1 dimers
connecting two HMTA ligands and four Co2 atoms. This
gives a three- and six-connected 3D net, and the nodes
and link definitions are shown in Scheme 1.
The resulting network is shown in Figure 2 left. This 3D
net was found to have vertex symbols 4 4 4 for the
trigonal nodes and 4 4 4 4 4 4 6 6 6 6 6 6 8
3
3
3
3 3 3 3 3 3
2
3
2
3
2
3
2
3
4
3
4
3
8
828
828 for the octahedral nodes. Although the structure
3
contains two chemically different six-connected nodes,
these two are equivalent from the topology point of view.
The highest possible symmetry of this net can be calcu-
lated, and this indeed results in a 3D-net with space group
R3m and only two different nodes, one three-connected
and one six-connected, see Figure 2 right.
Magnetic Network. As the exchange interaction
through the HTMA ligand can be considered as negligi-
1
9
ble, the magnetic net is reduced in complexity as this
node can be deleted. On the other hand, from the mag-
netic point of view it is necessary to consider the Co1-
Co1 dimer as two separate nodes. Thus, we build the net
Figure 1. (a) ORTEP view of 1 (50% thermal ellipsoids) with atom num-
bering scheme. (A) -x + 1, -y + 1, -z; (B) x, y, z-1; (C) x, -y + 1, z; (D)
-
x + 3/2, -y + 3/2, -z + 1; (E) -x + 1, y, -z + 1; (F) x, y, z + 1; (G) -x
3/2, -y+3/2, -z;(H)-x+3/2, y-1/2, -z;(I)-x+1, y, -z;(K)x-1/2,
y + 3/2, z + 1; (L) x-1/2, -y + 3/2, z. Hydrogen bonds are indicated
by broken bonds. (b) Packing plot of 1 viewed along the a-axis of the unit cell.
c) The Co(ii)-azide-sublattice of 1 viewed along the b-axis of the unit cell.
(24) Hyde, S. T. epinet.anu.edu.au (accessed Sept. 16, 2008).
+
-
(25) O’Keeffe, M.; Eddaoudi, M.; Li, H. L.; Reineke, T.; Yaghi, O. M. J.
Solid State Chem. 2000, 152, 3–20.
(26) SYSTRE; Delgado Friedrichs, O., 2007; http://gavrog.sourceforge.
net/.
(

Article
Inorganic Chemistry, Vol. 48, No. 13, 2009 6283
Figure 2. (Left) Net in 1, black spheres, six-connected Co1-Co1 dimers; white spheres, six-connected Co2; crossed spheres, three-connected HMTA
ligands. (Right) Ideal net contains only two types of nodes, black spheres, six-connected; crossed spheres, three-connected.
a
a
Scheme 1. Structural Network in 1
Scheme 2. Magnetic Network in 1
a
The gray lines define the links between the network nodes: a four-
connected at Co2 and a three-connected at Co1. There is no magnetic
coupling transmitted through the HMTA ligand, thus this link is not
part of the magnetic net.
3
1
theoretical nets serve as blue prints, and the ultimate
goal, from a synthetic point of view, is to be able to chose a
particular 3D net, find out the geometrical requirements
of the nodes and links, and then go into the laboratory
and mix the molecular building blocks corresponding to
these requirements.
a
The gray lines define the links between the network nodes: a six-
connected at Co2 and at the Co1 dimer, and a three-connected at the
HMTA ligand.
from links (couplings) between Co1-Co1 and Co2 via the
end-to-end azides and the Co1-Co1 coupling trans-
mitted by the end-on azides. This results in the nodes
and links definition shown in Scheme 2 below.
In this latter respect, the use of binodal nets combing
high and low connectivity has recently been suggested
3
2
This results in a three- and four-connected net with
vertex symbols 6 8 8 for the trigonal nodes and
as a way of obtaining porous materials. One possible
class of this type is the three- and six-connected nets.
Batten and co-workers have recently reported a number
of these and discussed the possibilities with this node
2
3
2
3
2
6
6 6 6 10 10 for the square planar nodes (Figure 3,
2 2
3
3 3 3
3
2
1
left) with topology symbol tfo. This 3D-net in its highest
possible symmetry has space group Fmmm and almost
ideal trigonal planar and square planar nodes (the trigo-
nal angles deviate somewhat: 126.4°, 126.4° and 107.2°),
see Figure 3 right.
3
3
combination, and other recent examples have been
reported by Cordes and Hanton and by Miller and co-
3
4
3
5
workers. The present compound is not porous and
cannot be classified as a MOF; however, the net-
work formed in 1 is of some interest, as it is of a topology
not previously reported. The stoichiometry of this net is
Discussion of the Networks. Originally proposed by
2
7
A. F. Wells in the 1950s, network analysis is emerging
as an important tool in understanding crystal structures
with strong intermolecular interactions such as coordina-
(3-connected) (6-connected) and is thus different from
the most common of these nets that have equal numbers
2 3
2
8-30
tion polymers. In the deliberate synthesis of metal-
organic framework compounds, so-called MOFs, the
(31) Yaghi, O. M.; Ockwig, N. W.; Chae, H. K.; Eddaoudi, M.; Kim, J.
Nature 2003, 423, 705–714.
::
ꢁ
::
(32) Borel, C.; Hakansson, M.; Ohrstrom, L. CrystEngComm 2006, 8,
(
(
(
27) Wells, A. F. Acta Crystallogr. 1954, 7, 535–44.
28) O’Keeffe, M.; Yaghi, O. M. J. Solid State Chem. 2005, 178, V–VI.
29) Ockwig, N. W.; Delgado-Friedrichs, O.; O’Keeffe, M.; Yaghi, O. M.
666–669.
(33) Du, M.; Zhang, Z. H.; Tang, L. F.; Wang, X. G.; Zhao, X. J.; Batten,
S. R. Chem. Eur. J. 2007, 13, 2578–2586.
Acc. Chem. Res. 2005, 38, 176–182.
(34) Cordes, D. B.; Hanton, L. R. Inorg. Chem. 2007, 46, 1634–1644.
(35) Zhu, Q.; Arif, A. M.; Ohrstrom, L.; Miller, J. S. J. Mol. Struct. 2008,
890, 41–47.
::
::
::
::
(
30) Ohrstrom, L.; Larsson, K. Molecule-Based Materials: The Structural
Network Approach; Elsevier: Amsterdam, 2005.

6
284 Inorganic Chemistry, Vol. 48, No. 13, 2009
Mautner et al.
Figure 3. (Left) Magnetic net in 1, black spheres, three-connected Co1; white spheres, four-connected Co2. (Right) Ideal net, black spheres, three-
connected; white spheres, six-connected.
4
2
Figure 4. Reduced magnetic net in 1, isofthe niobiumoxide or6 .8 -nbo
topology. Black spheres are Co1-Co1 dimers and white spheres are Co2
atoms.
Figure 5. Plot of χ
Co (N (HMTA)(H
of 1000 G. Inset: Plot of χ
M
T νs T in the 300-2 K range of temperatures for
[
2
)
3 4
2
O)] (1) measured under an external magnetic field
n
M
T νs T in the 25-2 K range of temperatures for
2
of nodes, namely, the (4.6 )(4 .6 .8 )-rtl (or rutile) net
2
10
3
1 measured under external magnetic fields of 30, 100, and 1000 G.
3
12
3
and the (6 )(6 .8 )-pyr (or pyrite) net. This stoichiometry
means that every six-connected node links to four other
six-connected nodes and two three-connected nodes,
while the three-connected nodes only link to six-con-
nected nodes. Of the 17 reported six-connected and
three-connected nets in the Reticular Chemistry Structure
of the applied magnetic field of 1000 G (Figure 5). The
3
-1
room temperature χ T value of 3.24 cm mol K is
M
3
smaller than the spin only value of 3.750 cm mol K for
-1
two uncoupled S=3/2 Co(II) ions. Upon lowering the
temperature, χ T decreases slowly, attains a minimum
M
3
6
3
-1
Resource (RCSR) database, none exists with this parti-
cular relation between the nodes.
We note that HMTA has been observed as a three-
at 20 K (χ T=1.61 cm mol K) and shows an abrupt
M
3
increase to a maximum value of 13.43 cm mol K at
12 K before decreasing in the lowest temperature region.
-1
3
7
3
-1
connected node before.
At the same temperature, the χ T value is 287 cm mol
M
The magnetic net is possibly of more importance, as
this is a highly symmetric net built from nodes with
geometries easily obtainable from various “secondary
building units” (SBUs) and molecular building blocks.
The present case seems to be the first assigned example of
this net in chemistry, although six earlier examples have
been found in the database searches of Blatov and co-
K at the applied field of 30 G. The magnetic susceptibi-
lity in the 25-300 K range obeys the Curie-Weiss law.
-
1
The Curie-Weiss fitting of χ
data above 25 K pro-
M
3
-1
vides C=3.53 cm mol K and θ=-26.62 K, Figure 6.
The continuous decrease in χ T from room temperature
M
to 20 K can be attributed to both the spin-orbit coupling
4
of the octahedral Co(II) ions with a T ground term and
1
g
3
8-40
workers,
dicted.
and it has also been mathematically pre-
the moderate antiferromagnetic coupling between the
Co(II) centers through the μ1,3-azido bridging ligands.
2
4
A further reduction in complexity can be achieved if we
consider the Co1-Co1 dimer as a one high spin entity.
This unites the two three-connected nodes into one four
connected node, and the resulting network is of the
niobium oxide or 6 .8 -nbo topology, see Figure 4.
Magnetic Properties. The magnetic properties of 1, in
Below 20 K, where an abrupt increase in χ T νersus T is
M
observed, the susceptibility becomes field dependent,
thus suggesting a ferromagnetic phase transition. Both
0
00
the in-phase (χM ) and out-of-phase (χM ) alternating
current (ac) susceptibility signals, Figure 7, which are
4
2
frequency independent, show a sharp peak at T =15.6 K
c
the form of χ T versus T, are represented for the value
M
(T =Curie temperature), confirming the presence of net
c
magnetization. At 2 K, 1 exhibits a magnetic hysteresis
loop (Figure 8) with a large coercitive field of 4700 G
and a remnant magnetization of 0.27 Nβ. The magnetiza-
tion at 2 K increases slowly with the increasing of the
magnetic field, Figure 9, attaining a highest value at 5 T of
0.70 Nβ, which is significantly below the theoretical
saturation magnetization of 3 Nβ for an isotropic high
spin Co(II). Zero-field-cooled and field cooled magneti-
zation (ZFCM/FCM) of 1 have been measured at 10 Oe
(
36) O’Keeffe, M.; Peskov, M. A.; Ramsden, S.; Yaghi, O. M. Acc. Chem.
Res. 2009, 41, 1782.
37) Carlucci, L.; Ciani, G.; Proserpio, D. M.; Sironi, A. Inorg. Chem.
997, 36, 1736.
38) Blatov, V. A.; Carlucci, L.; Ciani, G.; Proserpio, D. M. CrystEng-
Comm 2004, 6, 377–395.
39) Baburin, I. A.; Blatov, V. A.; Carlucci, L.; Ciani, G.; Proserpio,
D. M. Cryst. Growth Des. 2008, 8, 519–539.
40) Baburin, I. A.; Blatov, V. A. Acta Crystallogr., Sect. B: Struct. Sci.
007, 63, 791–802.
(
1
(
(
(
2

Article
Inorganic Chemistry, Vol. 48, No. 13, 2009 6285
-
1
Figure 6. Plot of χ
M
νs T in the 300-2 K range of temperatures for
O)] (1) measured under external magnetic field of
000 G. The solid line shows the best fit in the high-temperature region as
Curie-Weiss law (see text).
[
2 3 4
Co (N ) (HMTA)(H
2
n
Figure 9. Field dependent magnetization at 2 K for 1.
1
Figure 10. FC and ZFC magnetization νs T plots of compound 1 in an
applied field of 10 Oe.
Figure 7. Temperature dependence of real and imaginary components
ofthe acsusceptibilityin zeroapplied staticfield withan oscillatingfield of
4
Oe at a frequencies of 122 and 997 Hz. The lines are guides.
characteristic of spin canted antiferromagnetism, leading
In the description of the
4
1,42
to weak ferromagnetism.
structure, the magnetic network is a 3D structure of
parallel sheets built from decanuclear Co(II) rings (see
Figure 3, right). In a plane, the spin distribution is shown
in Figure 11 and, in the ground state in the idealized
structure, S for the sheet should be zero. It should be
stressed that the azido bridged sheet described in Fig-
ure 11 is also a new 2D topology in the polynuclear azido-
1
-17,43
bridged Co(II) and Mn(II) compounds.
The planes
in 1 are AF coupled by EE azido bridges and, for the
idealized structure, S in the ground state for the 3D
compound should be also zero.
The observed high values of the magnetization below
the critical temperature may be attributed to the single
ion magnetic anisotropy of the octahedral Co(II) ions
and to the alternation of the relative orientation of
Figure 8. M-H curve of 1 measured at 2 K.
4
2
adjacent metal chromophores in the planes: the local
spins in the ordered magnetic state are not parallel, but
are canted (spin canting). In the structure of 1, the Co1/
and are plotted in Figure 10. The ZFCM curve increases
as the temperature rises from 2 K, reaches the maximum
at 15.2 K, and then decreases quickly, which reveals the
antiferromagnetic intrinsic state. As the sample cools,
the FCM curve increases rapidly and diverges with the
ZFCM curve around 16 K, which indicates the existence
of spontaneous ferromagnetic ordering.
The reported magnetic properties (negative Weiss
constant, hysteresis loop at 2K, abrupt increase in
χMT versus T below 20 K and no saturation limit) are
44
Co1A (basal azide plane of the dimeric di-EO-azide
bridged Co octahedra) forms an interplanar angle of
1
8.6° with the a/b plane. The interplanar angle of Co1/
Co1A (basal azide plane of the dimeric di-EO-azide
bridged Co octahedra) with the basal Co-azide plane of
Co2 octahedron is 120.9°, Figure 1a. The angle of basal
::
(
(
42) Rodrı
´
guez, A.; Kivekas, R.; Colacio, E. Chem. Commun. 2005, 5228.
43) Ribas, J.; Escuer, A.; Monfort, M.; Vicente, R.; Cort ꢁe s, R.; Lezama,
L.; Rojo, T. Coord. Chem. Rev. 1999, 193-195, 1027.
(44) Kahn, O. Molecular Magnetism; VCH Publishers, Inc: New York,
1993; pp 321-325.
(
41) Retting, S. J.; Thompson, R. C.; Trotter, J.; Xia, S. Inorg. Chem.
1
999, 38, 1360.

6
286 Inorganic Chemistry, Vol. 48, No. 13, 2009
Mautner et al.
p
p
11
MR , through the equation sin(γ) = M /gSNβ. For
R
2+
octahedral Co at 2 K, the effective spin of 1/2 is used
with a common value of g=4.3. Taking into account the
complex 3D structure of 1, the canting angle of 7.2° serves
only for comparative purposes.
Conclusion
In this paper we have described the synthesis and structural
characterization of a new azido bridged 3D compound
derived from the anisotropic Co(II) cation by using also the
polydentate HMTA ligand. The formula of the compound is
[
Co (N ) (HMTA)(H O)] (1) and shows a complex 3D
2 3 4 2 n
structure in which Co(II) atoms linked by end-to-end azido
bridging ligands coexist with end-on azido bridging ligands
and with the HTMA ligand acting as tridentate bridging
ligand. The coordination network formed in 1 is of a new
three-and six connected topology (loh1), and the magnetic
three- and four-connected 3D-net is of the highly symmetric
tfo topology, not previously reported, that could serve as a
blue print for other coordination polymers and MOFs
through readily available square planar and trigonal SBUs.
From the magnetic point of view, in the high temperature
region 1 obeys the Curie-Weiss law but shows magnetic
ordering at low temperature because of the Co(II) anisotropy
and the canting effect.
Figure 11. Co(II)-azido sublattice of 1: View onto sheets of decanuclear
rings oriented along [010] and [102] directions (compare with Figure 1c
and Figure 3). Spin pattern within sheetsof decanuclear rings. Along [100]
(i.e.: a-axis of the unit cell) the Co2 centers of these sheets are antiferro-
magnetically coupled by single EE azide brigdes to form the 3D network.
As a consequence adjacent sheets have opposite spin orientations. (See
also Figure 1c).
Acknowledgment. This research was partially sup-
ported by CICYT (Grant CTQ2006-01759) and the
Swedish Research Council (VR Grant 2007-4412). F.A.M.
thanks Dr. J. Baumgartner (TU Graz), for assistance.
plane of Co2 octahedron with that of the Co2C or Co2E
octahedron is 76.9°. The torsion angles are Co1-
N21 N23-Co 2= -83.9°; Co2-N31 N31E-Co2E =
3
3 3
3 3 3
Supporting Information Available: Tables of X-ray crystal-
lographic data in CIF format for the structure reported in this
paper. This material is available free of charge via the Internet at
http://pubs.acs.org.
1
18.4°, and N2F-Co2 Co2E-N2K = 110.0°. The
3 3 3
canting angle γ at 2 K can be roughly estimated as 7.2°
from the remnant magnetization of the powder sample,