Occurrence of a rare 49·66 structural topology, chirality, and weak ferromagnetism in the [NH4][M II(HCOO)3] (M = Mn, Co, Ni) frameworks

Article abstract of DOI:10.1021/ic0610031

We report the synthesis, crystal structures, thermal, IR, UV-vis, and magnetic properties of a series of divalent transition metal formates, [NH ₄][M(HCOO)₃], where M = divalent Mn, Co, or Ni. They crystallize in the hexagonal chiral space group P6₃22. The structure consists of octahedral metal centers connected by the anti-anti formate ligands, and the ammonium cations sit in the channels. The chiral structure is a framework with the rarely observed 4⁹·6⁶ topology, and the chirality is derived from the handedness imposed by the formate ligands around the metals and the presence of units with only one handedness. The thermal properties are characterized by a decomposition at ca. 200°C. The three compounds exhibit an antiferromagnetic ground state at 8.4, 9.8, and 29.5 K for Mn, Co, and Ni, respectively. The last two display a weak spontaneous magnetization due to a small canting of the moments below the critical temperature, and the Co compound shows a further transition at lower temperatures. The isothermal magnetizations at 2 K show spin-flop fields of 600 Oe (Mn), 14 kOe (Co), and above 50 kOe (Ni) and a small hysteresis with a remnant magnetization of 25 cm³ G mol^-1 (Co) and 50 cm³ G mol^-1 (Ni) and coercive field of 400 Oe (Co) and 830 Oe (Ni).

Full text of DOI:10.1021/ic0610031

Inorg. Chem. 2007, 46, 437−445
Occurrence of a Rare 49
‚
6 Structural Topology, Chirality, and Weak
6
II
Ferromagnetism in the [NH ][M (HCOO) ] (M
) Mn, Co, Ni) Frameworks
4
3
Zheming Wang,*,†,‡ Bin Zhang,†,§ Katsuya Inoue, Hideki Fujiwara, Takeo Otsuka,†
|
†
Hayao Kobayashi,*,† and Mohamedally Kurmoo*,⊥
Institute for Molecular Science and CREST, Japan Science and Technology Corporation, Okazaki
444-8585, Japan, College of Chemistry and Molecular Engineering, Peking UniVersity, Beijing
100871, China, Institute of Chemistry, Chinese Academy of Sciences, Beijing 100080, China,
Department of Chemistry, Faculty of Science, Hiroshima UniVersity, 1-3-1 Kagamiyama, Higashi
Hiroshima, Hiroshima 739-8526, Japan, and Laboratoire de Chimie de Coordination Organique,
CNRS-UMR 7140, Institut Le Bel, UniVersit e´ Louis Pasteur, 4 rue Blaise Pascal, F-67000
Strasbourg, France
Received June 6, 2006
We report the synthesis, crystal structures, thermal, IR, UV
transition metal formates, [NH ][M(HCOO) ], where M divalent Mn, Co, or Ni. They crystallize in the hexagonal
chiral space group P6 22. The structure consists of octahedral metal centers connected by the anti anti formate
ligands, and the ammonium cations sit in the channels. The chiral structure is a framework with the rarely observed
49 66 topology, and the chirality is derived from the handedness imposed by the formate ligands around the metals
and the presence of units with only one handedness. The thermal properties are characterized by a decomposition
at ca. 200 C. The three compounds exhibit an antiferromagnetic ground state at 8.4, 9.8, and 29.5 K for Mn, Co,
−vis, and magnetic properties of a series of divalent
4
3
)
3
−
‚
°
and Ni, respectively. The last two display a weak spontaneous magnetization due to a small canting of the moments
below the critical temperature, and the Co compound shows a further transition at lower temperatures. The isothermal
magnetizations at 2 K show spin-flop fields of 600 Oe (Mn), 14 kOe (Co), and above 50 kOe (Ni) and a small
hysteresis with a remnant magnetization of 25 cm3 G mol- (Co) and 50 cm3 G mol- (Ni) and coercive field of
1
1
400 Oe (Co) and 830 Oe (Ni).
Introduction
they provide a good approach to create novel materials with
dual functionalities or multifunctionalities and possible
interplay between different functions. In this context, chiral
Metal-organic materials with two or more functionalities,
1
e.g., conductivity and magnetism, magnetic and optical
2
3
properties, porosity and magnetism, and chirality and
(
2) (a) Sato, O. Acc. Chem. Res. 2003, 36, 692. (b) Sunatsuki, Y.; Ikuta,
Y.; Matsumoto, N.; Ohta, H.; Kojima, M.; Iijima, S.; Hayami, S.;
Maeda, Y.; Kaizaki, S.; Dahan, F.; Tuchagues, J. P. Angew. Chem.,
Int. Ed. 2003, 42, 1614. (c) Lacroix, P. G.; Malfant, I.; B e´ nard, S.;
Yu, P.; Rivi e` re, E.; Nakatani, K. Chem. Mater. 2001, 13, 441. (d)
Evans, J. S. O.; B e´ nard, S.; Yu, P.; Cl e´ ment, R. Chem. Mater. 2001,
13, 3813.
magnetism,4 currently attract considerable attention because
-7
*
To whom correspondence should be addressed. E-mail: hayao@ims.ac.jp
(
H.K.), zmw@pku.edu.cn (Z.W.), kurmoo@chimie.u-strasbg.fr (M.K.).
†
Institute for Molecular Science and CREST, Japan Science and
Technology Corporation. Fax: 81-564-54-2254.
‡
Peking University. Fax: 86-10-62751708.
Chinese Academy of Sciences.
Hiroshima University.
Universit e´ Louis Pasteur.
(3) (a) Maspoch, D.; Ruiz-Molina, D.; Wurst, K.; Domingo, N.; Cavallini,
M.; Biscarini, F.; Tejada, J.; Rovira, C.; Veciana, J. Nat. Mater. 2003,
2, 190. (b) Maspoch, D.; Ruiz-Molina, D.; Veciana, J. J. Mater. Chem.
2004, 2713 and references cited therein. (c) Kurmoo, M.; Kumagai,
H.; Chapman, K. W.; Kepert, C. J. Chem. Commun. 2005, 3012. (d)
Rujiwatra, A.; Kepert, C. J.; Claridge, J. B.; Rosseinsky, M. J.;
Kumagai, H.; Kurmoo, M. J. Am. Chem. Soc. 2001, 123, 10584. (e)
Kurmoo, M.; Kumagai, H.; Hughes, S. M.; Kepert, C. J. Inorg. Chem.
2003, 42, 6709. (f) Halder, G. J.; Kepert, C. J.; Moubaraki, B.; Murray,
K. S.; Cashion, J. D. Science 2002, 298, 1762. (g) Niel, V.; Thompson,
A. L.; Munoz, M. C.; Galet, A.; Goeta, A. E.; Real, J. A., Angew.
Chem., Int. Ed. 2003, 42, 3759. (h) Kepert, C. J. Chem. Commun.
2006, 695.
§
|
⊥
(
1) (a) Coronado, E.; Galan-M a´ scar o´ s, J. R.; G o´ mez-Garc ´ı a, C. J.; Laukhin,
V. Nature 2000, 408, 447. (b) Kurmoo, M.; Graham, A. W.; Day, P.;
Coles, S. J.; Hursthouse, M. B.; Caulfield, J. L.; Singleton, J.; Pratt,
F. L.; Hayes, W.; Ducasse, L.; Guioneeau, P. J. Am. Chem. Soc. 1995,
1
17, 12209. (c) Coronado, E.; Day, P. Chem. ReV. 2004, 104, 5419.
d) Uji, S.; Shinagawa, H.; Terashima, T.; Yakabe, T.; Terai, Y.;
Tokumoto, M.; Kobayashi, A.; Tanaka, H.; Kobayashi, H. Nature
001, 410, 908. (e) Kobayashi, H.; Cui, H.-B.; Kobayashi, A. Chem.
ReV. 2004, 104, 5265.
(
2
1
0.1021/ic0610031 CCC: $37.00
© 2007 American Chemical Society
Inorganic Chemistry, Vol. 46, No. 2, 2007 437
Published on Web 12/14/2006

Wang et al.
4
-
magnets are of special interest. These materials are not only
magnetic properties. The small stereo effect of HCOO is
of academic interests such as asymmetric magnetic anisot-
ropy, magnetic chirality, and magnetochiral dichroism but
also have potential for applications as new devices. For most
reported chiral magnetic coordination compounds, the chiral-
ity of the structure is introduced either by employing enantio-
of benefit for the formation of coordination frameworks, and
the short HCOO bridge, a three- or single-atom connector,
-
is promising for the magnetic coupling between metal sites.
The structure and magnetism of metal formate dihydrate salts,
M(HCOO)
2
‚2H
O (M ) Mn, Fe, Co, Ni, and Cu),12 were
2
4
,5
pure building blocks, in most case the auxiliary ligands,
extensively investigated 30-40 years ago. This isostructural
or by spontaneous resolution upon crystallization or other
mechanism such as coordination induced chirality from
racemic mixture or achiral reaction system.6,7 To mediate
significant magnetic exchange between metal sites short
series possesses a 3D framework consisting of layers of (4,
4) net of M(HCOO) linked by trans-M(H O) (HCOO)
2 2 4 2
units, and they predominantly exhibit long-range canted
antiferromagnetic ordering. In the 1990s other systems of
bridging ligands, for example, cyanide,4 azide, and oxalate,
are suitable. However, the auxiliary ligands acting as chiral
parts are usually so large as to result in both lower framework
dimensionality and weak magnetic coupling. From the point
of view of magnetism, the auxiliary-ligand-induced chirality,
in principle, is not favorable for long-range magnetic ordering
because it dilutes the moment carriers and reduces the
coupling between these moment carriers in the materials.
Therefore, chiral materials with short ligands only are most
,5
6
7
M(HCOO)
L
13
where L is a coligand such as urea and
2
2
,
formamide, were investigated. They consist also of layers
of a (4, 4) net of M(HCOO) linked by hydrogen bonds,
2
and in some cases, spontaneous magnetization was observed
at the N e´ el transition due to canting of the moments.
-
Combining HCOO and other ditopic ligands to build
magnetic coordination polymers has only recently been
realized and has led to the realization that formato ligand
1
4
behaves quite similar to azide in coordination. Transition
metal formates without coligands are very limited, and
several novel binary systems have recently been added to
this list, except some known Ca/Sr-Cu formate salts.15
8
favorable. While the oxalate systems might be the most
promising, new systems need to be explored.
In this work we present a series of chiral, magnetic salts
of divalent transition metal formates, [NH
4
][M(HCOO)
3
],
2
Examples include ferromagnetic R-Cu(HCOO) having a 3D-
where M ) Mn (1Mn), Co (2Co), and Ni (3Ni). After quite
framework and â-Cu(HCOO) having an infinite chain
2
1
6
a long period of silence in the research of molecular
structure, an anhydrous Mn(HCOO)
2
with a structure
2
O, which orders as
-
magnetism, the formato anion, HCOO , as the smallest and
topologically related to Mn(HCOO) ‚2H
2
1
7
simplest carboxylate but with all the functionalities of
carboxylato ligands, has become attractive again very
recently, compared to other popular and small ligands such
an antiferromagnet at 8 K, and the porous [M
3 6
(HCOO) ]
family (M ) Mn, Fe, Co, Ni, and Zn, as well as non-
(
11) (a) Rao, C. N. R.; Natarajan, S.; Vaidhyanathan, R. Angew. Chem.,
Int. Ed. 2004, 43, 1466. (b) Tamaki, H.; Zhong, Z. H.; Matsumoto,
N.; Kida, S.; Koikawa, K.; Achiwa, N.; Okawa, H. J. Am. Chem. Soc.
as cyanide,4 azide,
,5,9
6,10
and oxalate,
7,8,11
having been ex-
tensively employed in creating materials with interesting
1992, 114, 6974. (c) Mathoniere, C.; Nuttall, C. J.; Carling, S. G.;
(
4) Inoue, K.; Ohkoshi, S. I.; Imai, H. In Magnetism: Molecules to
Materials V; Miller, J. S., Drillon, M., Eds.; Wiley-VCH Verlag GmbH
Day, P. Inorg. Chem. 1996, 35, 1201. (d) Decurtins, S.; Schmalle, H.
W.; Schneuwly, O.; Ensling, J.; Gutlich, P. J. Am. Chem. Soc. 1994,
116, 9521.
&
Co. KgaA: Weinheim, Germany, 2005; Chapter 2.
(
5) (a) Imai, H.; Inoue, K.; Kikuchi, K.; Yoshida, Y.; Ito, M.; Sunahara,
T.; Onaka, S. Angew. Chem., Int. Ed. 2004, 43, 5618. (b) Inoue, K.;
Kikuchi, K.; Ohba, M.; Oh kawa, H. Angew. Chem., Int. Ed. 2003, 42,
(12) (a) Osaki, K.; Nakai, Y. J. Phys. Soc. Jpn. 1963, 18, 919. (b) Osaki,
K.; Nakai, Y.; Watanab e´ , T. J. Phys. Soc. Jpn. 1964, 19, 717. (c)
Abe, H.; Morigaki, H.; Matsuura, M.; Torh, K.; Yamagata, K. J. Phys.
Soc. Jpn. 1964, 19, 775. (d) Abe, H.; Torh, K. J. Phys. Soc. Jpn. 1965,
20, 183. (e) Yamagata, K.; Abe, H. J. Phys. Soc. Jpn. 1965, 20, 906.
(f) Yamagata, K. J. Phys. Soc. Jpn. 1967, 22, 582. (g) Pierce, R. D.;
Friedberg, S. A. Phys. ReV. 1968, 165, 680. (h) Skalyo, J., Jr.; Shirane,
G; Friedberg, S. A. Phys. ReV. 1969, 188, 1037. (i) Takeda, K.;
Kawasaki, K. J. Phys. Soc. Jpn. 1971, 31, 1026. (j) Radhakrishna, P.;
Gillon, B.; Chevrier, G. J. Phys.: Condens. Matter 1993, 5, 6447. (k)
Hoy, G. R.; Barros, S. de S.; Barros, F. de S.; Friedberg, S. A. J.
Appl. Phys. 1965, 36, 936. (l) Pierce, R. D.; Friedberg, S. A. Phys.
ReV. 1971, B3, 934. (m) Takeda, K.; Matsukawa, S. i. J. Phys. Soc.
Jpn. 1971, 30, 887. (n) Flippen, R. B.; Friedberg, S. A. J. Chem. Phys.
1963, 38, 2652. (o) Kobayashi, H.; Haseda, T. J. Phys. Soc. Jpn. 1963,
18, 541. (p) Martin, R. L.; Waterman, H. J. Chem. Soc. 1959, 1359.
(13) (a) Ridwan, Jpn. J. Appl. Phys. 1992, 31, 3559 and references cited
therein. (b) Rettig, S. J.; Thompson, R. C.; Trotter, J.; Xia, S. H. Inorg.
Chem. 1999, 38, 1360.
(14) (a) Manson, J. L.; Lecher, J. G.; Gu, J.; Geiser, U.; Schlueter, J. A.;
Hennig, R.; Wang, X.; Schultz, A. J.; Koo, H. J.; Whangbo, M. H.
Dalton Trans. 2003, 2905. (b) Wang, X. Y.; Wei, H. Y.; Wang, Z.
M.; Chen, Z. D.; Gao, S. Inorg. Chem. 2005, 44, 572.
(15) (a) Sanchis, M. J.; G o´ mez-Romero, P.; Folgado, J. V.; Sapi n˜ a, F.;
Ib a´ n˜ ez, R.; Beltr a´ n, A.; Garc ´ı a, J.; Beltr a´ n, D. Inorg. Chem. 1992,
31, 2915. (b) Levya, A. G.; Polla, G.; de Perazzo, P. K.; Lanza, H.;
de Benyacar, M. A. R. J. Solid State Chem. 1996, 123, 291. (c) Polla,
G.; Levya, G.; de Perazzo, P. K.; Lanza, H.; de Benyacar, M. A. R.
J. Solid State Chem. 1995, 117, 145.
4810.
(
6) (a) Coronado, E.; Gal a´ n-Mascar o´ s, J. R.; G o´ mez-Garc ´ı a, C. J.;
Mart ´ı nez-Ferrero, M.; Almeida, M.; Waerenborgh, J. C. Eur. J. Inorg.
Chem. 2005, 2064. (b) Gao, E. Q.; Yue, Y. F.; Bai, S. Q.; He, Z.;
Yan, C.-H. J. Am. Chem. Soc. 2004, 126, 1419.
(7) (a) Gruselle, M.; Thouvenot, R.; Mal e´ zieux, B.; Train, C.; Gredin, P.;
Demeschik, T. V.; Troitskaya, L. L.; Sokolov, V. I. Chem.sEur. J.
2
004, 10, 4763. (b) Coronado, E.; Gal a´ n-Mascar o´ s, J. R.; G o´ mez-
Garc ´ı a, C. J.; Mart ´ı nez-Agudo, J. M. Inorg. Chem. 2001, 40, 113. (c)
Andr e´ s, R.; Brissard, M.; Gruselle, M.; Train, C.; Vaissermann, J.;
Mal e´ zieux, B.; Jamet, J. P.; Verdaguer, M. Inorg. Chem. 2001, 40,
4
633.
8) (a) Cl e´ ment, R.; Decurtins, S.; Gruselle, M.; Train, C. Monatsh. Chem.
003, 134, 117. (b) Coronado, E.; Gal a´ n-Mascar o´ s, J. R.; G o´ mez-
Garc ´ı a, C. J.; Mart ´ı nez-Agudo, J. M. AdV. Mater. 1999, 11, 558.
9) For reviews, see the following: (a) Ohba, M.; Oh kawa, H. Coord. Chem.
ReV. 2000, 198, 313. (b) Miller, J. S.; Manson, J. L. Acc. Chem. Res.
(
(
2
2
001, 34, 563. (c) Lescou e¨ zec, R.; Toma, L. M.; Vaissermann, J.;
Verdaguer, M.; Delgado, F. S.; Ruiz-P e´ rez, C.; Lloret, F.; Julve, M.
Coord. Chem. ReV. 2005, 249, 2691.
(
10) For example, see the following: (a) Ribas, J.; Escuer, A.; Monfort,
M.; Vicente, R.; Cort e´ s, R.; Lezama, L.; Rojo, T. Coord. Chem. ReV.
1
999, 193-195, 1027. (b) Hong, C. S.; Do, Y. Angew. Chem., Int.
Ed. 1999, 38, 193. (c) Han, S.; Manson, J. L.; Kim, J.; Miller, J. S.
Inorg. Chem. 2000, 39, 4182. (d) Liu, T. F.; Fu, D.; Gao, S.; Zhang,
Y. Z.; Sun, H. L.; Su, G.; Liu, Y. J. J. Am. Chem. Soc. 2003, 125,
1
3976. (e) Zhang, Y. Z.; Wei, H. Y.; Pan, F.; Wang, Z. M.; Chen, Z.
(16) Sapi n˜ a, F.; Burgos, M.; Escriv a´ , E.; Folgado, J.-V.; Marcos, D.; Beltr a´ n,
A.; Beltr a´ n, D. Inorg. Chem. 1993, 32, 4337.
(17) Viertelhaus, M.; Henke, H.; Anson, C. E.; Powell, A. K. Eur. J. Inorg.
Chem. 2003, 2283.
D.; Gao, S. Angew. Chem., Int. Ed. 2005, 44, 5841. (f) Zhang, Y. Z.;
Gao, S.; Sun, H. L.; Su, G.; Wang Z. M.; Zhang, S. W. Chem.
Commun. 2004, 1906.
438 Inorganic Chemistry, Vol. 46, No. 2, 2007

II
[
4 3
NH ][M (HCOO) ] (M ) Mn, Co, Ni) Frameworks
transition-metal Mg)18-21 possessing an unusual diamond
open framework and showing a wide spectrum of guest
inclusion. In this family the Mn and Fe members have been
proved to exhibit long-range magnetic ordering and guest
[NH
obtained by the reaction of the metal chloride with [NH
from formic acid neutralized by ammonia in methanol. For 1Mn,
0 mL of methanol solution containing 203 mg of MnCl ‚4H
was mixed with 5.5 mL of methanol solution of 0.80 M [NH
HCOO] (prepared by mixing 2.7 g of 25% aqueous NH ‚H O and
4
][M(HCOO)
3
] (M ) Mn (1Mn), Co (2Co), and Ni (3Ni)) were
4
][HCOO]
1
2
2
O
18
4
]-
modulated Curie temperature. Enlightened by a 3D NaCl-
[
3
2
III
22
3
type framework of Mn (HCOO) , reported in 1999, with
2
.4 g of HCOOH in 50 mL of methanol with pH ∼ 5). The mixed
carbon dioxide and/or formic acid guests in the cavities, the
fact that many known divalent metal formates1 have layers
of a (4, 4) net, and the cation template effect exhibited in
solution was kept undisturbed. Pale pink hexagonal bipyramid
shaped crystals were harvested after 1 day. The crystals were
washed with methanol and dried under vacuum. The yield is 72%
based on Mn. However, 2Co and 3Ni were prepared via a carefully
applied slow diffusion method due to their lower solubilities. For
2,13
2
3
cyanide, azide, and dicyanamide 3D NaCl-type systems,
we and other authors have successfully obtained NaCl-type
II
-
frameworks of [M (HCOO)
3
] in series of a perovskite
2Co, 5 mL of methanol solution containing 0.80 M [NH ][HCOO]
4
+
-
24
compounds of [AmineH ][M(HCOO)
amine cations, AmineH ) CH
3
], when protonated
was placed at the bottom of a glass tube (6 mm inner diameter).
+
+
+
3
NH
3
, (CH
3
)
2
NH
2
, CH
3
-
On the [NH
followed by carefully layering 5 mL of methanol solution of 0.20
M CoCl ‚6H O. The tube was sealed and kept undisturbed. Violet-
4
][HCOO] solution, 4 mL of methanol was gently added,
+
+
CH
2 3 2 3 2
NH , and (CH ) NH , possessing about 3 non-
hydrogen atoms, as well as non-coordinating solvent, were
2
2
employed.2 However, employment of a bulky AmineH
4b
+
red, hexagonal bipyramid-shaped crystals were harvested after 5
days. The yield is 90% based on the starting cobalt salt. The product
was washed with methanol and dried in vacuum. A similar
+
+
3 2
such as (CH CH )
3
3 2
NH (CH CH )
2
NH
2 3 2 2
, or CH CH CH -
+
18,19,20b
NH
3
3
resulted in the porous [M (HCOO)
6
].
The
procedure employing NiCl
0 days of crystallization to produce green crystals of 3Ni in a
yield of 42%, and the crystal shape was found to be similar to that
of 1Mn and 2Co. Anal. Calcd for 1Mn, C NO Mn: C, 17.32;
H, 3.39; N, 6.73. Found: C, 17.11; H, 3.30; N, 6.68. Calcd for
Co, C NO Co: C, 16.99; H, 3.33; N, 6.61. Found: C, 16.84;
H, 3.26; N, 6.49. Calcd for 3Ni, C H NO Ni: C, 17.01; H, 3.33;
2
2
‚6H O instead of the CoCl
2 2
‚6H O took
question is thus opened to what will happen if the smallest
1
+
ammonium NH
4
is used. We here report the outcome, where
][M(HCOO) ] were isolated.
the chiral magnetic salts [NH
4
3
3
H
7
6
It is interesting to see the appearance of chirality from these
simple achiral starting materials. The structure is a framework
2
H
3 7
6
9
6
with rarely observed 4 ‚6 topology, consisting of octahedral
metal centers connected by anti-anti formate ions and the
ammonium cation arrays located in the channels. 1Mn is an
antiferromagnet, exhibiting spin-flop field at very low field,
while both 2Co and 3Ni are weak ferromagnets and 2Co
displays possible spin-reorientation after the antiferromag-
netic ordering. Thermal and spectroscopic properties are also
investigated.
3
7
6
N, 6.61. Found: C, 16.99; H, 3.38; N, 6.37.
X-ray Crystallography. The crystallographic data for the single
crystals of the three compounds were collected at room temperature
on a Rigaku AFC7 Mercury CCD diffractometer with 5.4 kW
rotating anode source using graphite-monochromated Mo KR
radiation of λ ) 0.710 73 Å.25 The structures were solved by direct
2
methods and refined by full-matrix least-squares on F using the
SHELX program.26 The H atoms were located from the difference
Experimental Section
Fourier synthesis, and refined isotropically. The refined C/N-H
distances, bond angles involving H atoms, and isotropic thermal
Synthesis. All starting chemicals were commercially available
reagents of analytical grade and used without further purification.
+
factors of H atoms are all of rational values. The tetrahedral NH
4
cation showed a trigonal disorder but has a well-defined unique H
atom in the structure solution and refinement. The details of data
collection, data reduction, and crystallographic data are summarized
in Table 1. Powder XRD patterns of the three compounds were
obtained on a Rigaku RINT2000 diffractometer at room temperature
with Cu KR radiation in a flat plate geometry.
Physical Measurements. Dc and ac magnetization measurements
were performed on three different Quantum Design SQUID systems,
MPMS7EB, MPMS5S, and MPMS2, for polycrystalline samples
tightly sealed in Al foil. Diamagnetic corrections were estimated
(
18) (a) Wang, Z. M.; Zhang, B.; Fujiwara, H.; Kobayashi, H.; Kurmoo,
M. Chem. Commun. 2004, 416. (b) Zhang, B.; Wang, Z. M.; Kurmoo,
M.; Gao, S.; Inoue, K.; Kobayashi, H. AdV. Funct. Mater. 2007, in
press. (c) Wang, Z. M.; Zhang, Y. J.; Liu, T.; Kurmoo, M.; Gao, S.
AdV. Funct. Mater. 2007, in press.
19) Wang, Z. M.; Zhang, B.; Kurmoo, M.; Green, M. A.; Fujiwara, H.;
Otsuka, T.; Kobayashi, H. Inorg. Chem. 2005, 44, 1230.
20) (a) Viertelhaus, M.; Adler, P.; Cl e´ rac, R.; Anson, C. E.; Powell, A.
K. Eur. J. Inorg. Chem. 2005, 692. (b) Wang, Z. M.; Zhang, Y. J.;
Kurmoo, M.; Liu, T.; Vilminot, S.; Zhao, B.; Gao, S. Aust. J. Chem.
(
(
2006, 59, 617.
(
(
(
21) (a) Dybtsev, D. N.; Chun, H.; Yoon, S. H.; Kim, D.; Kim, K. J. Am.
Chem. Soc. 2004, 126, 32. (b) Rood, J. A.; Noll, B. C.; Henderson,
K. W. Inorg. Chem. 2006, 45, 5521.
22) Cornia, A.; Caneschi, A.; Dapporto, P.; Fabretti, A. C.; Gatteschi, D.;
Malavasi, W.; Sangregorio, C.; Sessoli, R. Angew. Chem., Int. Ed.
2
7
-6
-6
using Pascal constants (-78 × 10 , -76 × 10 , and -74 ×
-
6
3
-1
10 cm mol for 1Mn, 2Co, and 3Ni, respectively) and back-
ground correction by experimental measurement on neat Al foil.
Thermal analyses, TGA and DSC, were performed on a SDT 2960
thermal analyzer and a DSC 2010 differential scanning calorimeter
1999, 38, 1780.
23) (a) Entley, W. R.; Girolami, G. S. Inorg. Chem. 1994, 33, 5165. (b)
Sato, O.; Iyoda, T.; Fujishima, A.; Hashimoto, K. Science 1996, 271,
2
at 5 °C/min under N . FTIR spectra were recorded using pure
49. (c) Ferlay, S.; Mallah, T.; Ouah e` s, R.; Veillet, P.; Verdaguer, M.
-
1
samples in the range of 4000 to 650 cm on a Nicolet Magna 750
FT/IR spectrometer. UV-vis spectra of 1Mn, 2Co, and 3Ni were
recorded on a Shimadzu UV-VIS-3100 spectrophotometer with an
Nature 1995, 378, 701. (d) Ferlay, S.; Mallah, T.; Ouah e` s, R.; Veillet,
P.; Verdaguer, M. Inorg. Chem. 1999, 38, 229. (e) Dong, W.; Zhu, L.
N.; Song, H. B.; Liao, D. Z.; Jiang, Z. H.; Yan, S. P.; Cheng, P.; Gao,
S. Inorg. Chem. 2004, 43, 2465. (f) Mautner, F. A.; Cort e´ s, R.; Lezama,
L.; Rojo, T. Angew. Chem., Int. Ed. 1996, 35, 78. (h) Tong, M. L.;
Ru, J.; Wu, Y. M.; Chen, X. M.; Chang, H. C.; Mochizuki, K.;
Kitagawa, S. New J. Chem. 2003, 27, 779.
(25) CrystalClear software; Rigaku Corp.: Tokyo, Japan, 2000.
(26) Sheldrick, G. M. SHELX-97, Program for Crystal Structure Deter-
mination; University of G o¨ ttingen: G o¨ ttingen, Germany, 1997.
(27) Mulay, L. N.; Boudreaux, E. A. Theory and Applications of Molecular
Diamagnetism; John Wiley & Sons Inc.: New York, 1976.
(
24) (a) Wang, X. Y.; Gan, L.; Zhang, S. W.; Gao, S. Inorg. Chem. 2004,
4
3, 4615. (b) Wang, Z. M.; Zhang, B.; Otsuka, T.; Inoue, K.;
Kobayashi, H.; Kurmoo, M. Dalton Trans. 2004, 2209.
Inorganic Chemistry, Vol. 46, No. 2, 2007 439

Wang et al.
Table 1. Crystallographic Data for 1Mn, 2Co, and 3Ni
1Mn
2Co
3Ni
formula
fw
T, K
C3H7MnNO6
208.04
293
C3H7CoNO6
212.03
293
C3H7NiNO6
211.81
293
crystal system
space group
a, Å
b, Å
c, Å
hexagonal
P6322
7.356(2)
7.356(2)
8.478(2)
90
90
120
397.3(1)
2
1.739
hexagonal
P6322
7.297(2)
7.297(2)
8.179(2)
90
90
120
377.1(2)
2
1.867
hexagonal
P6322
7.286(1)
7.286(1)
8.021(2)
90
90
120
368.8(1)
2
1.908
R, deg
â, deg
γ, deg
3
V, Å
Z
3
Dc, g/cm
-
1
µ(Mo KR), mm
crystal size, mm
Tmin and Tmax
1.648
2.261
2.616
3
0.11 × 0.10 × 0.09
0.882, 1.000
3.20, 27.46
6804
313 (0.0378)
291
0.15 × 0.15 × 0.10
0.884, 1.000
4.99, 27.41
6296
297 (0.0288)
285
0.15 × 0.13 × 0.09
0.879, 1.000
4.11, 27.45
6201
280 (0.0294)
251
θmin, θmax, deg
no. of total reflections
no. of unique reflections (Rint)
no. of observed [I g 2σ(I)]
no. of parameters
26
26
25
R1, wR2 [I g 2σ(I)]
R1,wR2 (all data)
GOF
0.0195, 0.0441
0.0216, 0.0443
1.152
0.0157, 0.0413
0.0166, 0.0415
1.192
0.0168, 0.0418
0.0180, 0.0421
1.172
Flack parameters
0.01(4)
0.153, -0.189
0.000, 0.000
0.02(3)
0.141, -0.194
0.000, 0.000
0.01(4)
0.210, -0.228
0.000, 0.000
a
3
∆F, e/Å
b
max and mean ∆/σ
a
Max and min residual density. b Max and mean shift/sigma.
9
6
28,29
integrated sphere attachment in the range 200-1000 nm on ground
the rare 4 ‚6 one
that is different from the NaCl-like
powder samples referenced to a BaSO
4
background.
one (see structure discussion later). While the smaller
protonated amine cations are found to coexist with the
metal-formate frameworks, the bulky ones are absent in the
final frameworks. This is because the metal-formate frame-
works with the short HCOO ligand are unable to accom-
modate the large protonated amine cations. Therefore, we
can reach the conclusion that the size of protonated amine
cations controls the structures of the final metal-formate
frameworks. In addition, it is worth noting that the use of
noncoordinating solvent such as methanol as the major
solvent is another key requirement to obtain these metal
formates without coligands because it inhibits the formation
of metal-formates with coordinated ligands, as what was
Results and Discussion
Synthesis and the Role of Protonated Amine Cations.
During our systematic investigation of the cation-template
effect1
8,19,24b
on the formation of 3d metal formate frame-
works, we have examined the smallest ammonium cation,
+
NH
4
. In this work the three compounds [NH
4
][M(HCOO)
3
]
(M ) Mn, Co, and Ni) were prepared by the reaction of
divalent metal chlorides with formic acid neutralized by
ammonia in methanol. This work emphasizes the conclusion
drawn in previous reports where we demonstrate the role of
protonated amine cations of different size in controlling the
1
2,13
observed for many known metal formates.
Finally, the
19,24b
type of metal-formate framework.
When large or bulky
PXRD patterns of the three compounds revealed that they
are single phase products, as shown in Figure S1 (Supporting
Information).
amines such as triethylamine, diethylamine, or propylamine
are used, the products are the nanoporous diamond frame-
work compounds [M
3
(HCOO)
6
]‚solvent (M ) divalent Mn,
Crystal Structure. The three compounds are isomorphs
Fe, Co, Ni, and Zn), with open channels occupied by
and belong to the chiral hexagonal space group P6
3
22 (Table
solvents.1
8,19,20b
The solvents are easily removed to leave a
-
1). The structure is an unusual 3D anionic [M(HCOO)
3
]
stable framework with free space which can be refilled with
other guests. The use of amines of middle size with 2-4
non-H atoms (methylamine, dimethylamine, ethylamine, and
framework (Figures 1 and S2) displaying hexagonal chan-
+
nels along the c-axis in which the NH
4
cations are located.
) metal ion is
In the framework, each octahedral (MO
6
connected to six neighboring metal ions via bridging HCOO
groups adopting the anti-anti mode; thus, it is a 6-connected
node (Figure S2a). The framework can be considered as (4,
cyclotrimethyleneamine) results in the perovskite compounds
+
[
AmineH ][M(HCOO)
3
] (M ) divalent Fe, Mn, Co, Ni, Cu,
24b
and Zn)
having a NaCl-like anionic metal-formate
4
) sheets along the a direction linked along the b direction
framework incorporating the ammonium cations within the
cavities. The smallest ammonium used in this work produces
(
28) (a) Wells, A. F. Three-Dimensional Nets and Polyhedra; Wiley-
Interscience: New York, 1977. (b) Wells, A. F. Further Studies of
Three-dimensional Nets; American Crystallographic Association:
Pittsburgh, PA, 1979 (distributed by Polycrystal Book Service).
a hexagonal variety of metal-formate frameworks, [NH
4
]-
+
[
M(HCOO)
3
] (M ) Mn, Co, and Ni), where the NH
4
cations
occupy hexagonal channels and the framework topology is
(29) Batten, S. R.; Robson, R. Angew. Chem., Int. Ed. 1998, 37, 1460.
440 Inorganic Chemistry, Vol. 46, No. 2, 2007

II
[
4 3
NH ][M (HCOO) ] (M ) Mn, Co, Ni) Frameworks
as NaClO
3
, quartz, and urea inclusion compounds.31 The
channels having a diameter of 3.1 Å not including the van
der Waals radii of the surface atoms (Figure S2c) are
+
occupied by NH
4
cations in a linear array (Figure 1, middle,
and Figure S2b). The ammonium shows trigonal disorder
and N-H‚‚‚O hydrogen bonds to the anionic framework
+
(Table 2). It is clear that the NH
4
not only balances the
charge but also plays a template role in the formation of
II
-
this particular [M (HCOO)
the unique M-O distances of 2.186, 2.101, and 2.064 Å
Table 2), for 1Mn, 2Co, and 3Ni, respectively, are in good
agreement with the decrease in the ionic radii in the sequence
3
] framework. The decreases in
(
2
+
2+
2+
32
Mn (0.97 Å), Co (0.89 Å), and Ni (0.83 Å), as well
as to those in other metal-formates.
1
2,13,24a
Consequently, a
systematic contraction of the lattice parameters (Table 1) and
M‚‚‚M distances via bridging HCOO, being 6.000, 5.871,
and 5.812 Å for 1Mn, 2Co, and 3Ni, respectively, is
observed. The bond angles around the metal sites (Table 2)
6
characterize the distortion of the MO octahedra. It is worth
pointing out that there is no center of symmetry between
-
metal sites bridged by HCOO , and each coordination
octahedron of metal ion has a different orientation from its
six neighbors. This provides the possibility of the Dzy-
Figure 1. Structure of chiral salts of [NH4][M(HCOO)3], with 2Co as
the representative: top left, the topological view where spheres are Co atoms
and bonds the anti-anti HCOO linkages; top right, the hexagonal framework
33
aloshinsky-Moriya interaction between magnetic metal
1
2,13,14b,24
+
sites, as for many metal-formates.
of [NH4][Co(HCOO)3] with NH4 cations in channels omitted; middle, one
channel with trigonally disordered NH4+ cation array inside, highlighted
in a space-filling model; bottom, the helical characteristics of the channel,
a triplet helix with a pitch of 3 × c. One helix (with C-H toward inside
the channel) is highlighted by green C and yellow O atoms. The helixes
are further cross-linked by HCOO groups with C-H toward outside the
channel. This linkage creates other groups of triplet helixes but with the
C-H toward the outside of the channel. Colors for coding atoms: H, white;
C, gray and green; O, red and yellow; Co, blue.
IR and UV-Vis Spectra and Thermal Properties. The
IR and UV-vis absorption bands in the spectra and their
assignments for the three compounds are given in Table 3.
The IR spectra of the three compounds are almost the same
(
Table 3 and Figure S3), with characteristic bands for the
+
-
34
NH
4
ion and the HCOO group, reflecting the fact that
the three structures are the same, these bands being coincident
or vise versa, or the same (4, 4) sheets along a + b linked
along a-b, with the intersheet linkage in a zigzag style. In
fact, the framework is the three equivalent sets of the (4, 4)
sheet, parallel to the a, b and a + b directions, merged
together. Since there is one unique 6-connected node in the
framework and there are nine 4-gons and six 6-gons (the
small circuits) around each node, the topology of the 3D
17,24b,35
with those previously reported.
The UV-vis absorp-
tion bands (Table 3 and Figure S4) are typical for octahedral
2+
2+ 36
M
2 6
ions and very similar to that of M(H O) . The strong
absorption in the visible region of the chiral magnetic salts
of 2Co and 3Ni makes them possible candidates for further
magneto-optical study.
The thermal properties of the three compounds were
investigated by TGA/DSC under nitrogen atmosphere (Figure
S5). 1Mn and 2Co show two well-defined weight losses
while 3Ni displayed only one with a percentage correspond-
ing to roughly the sum of the two for 1Mn and 2Co. For
9
6
framework is therefore 4 ‚6 using the Schafli symbol (Figure
1
, top left).2 This is unlike the recently reported perovskite
8,29
+
24
3
or NaCl frameworks, [AmineH ][M(HCOO) ], which has
the 4 ‚6 topology. The 4 ‚6 topology is rarely observed
1
2
3
9
6
in coordination polymers, and probably the only known
example is [Eu(Ag(CN)
2
)
3
(H
2
O)
3
] where the nodes are
(31) (a) McBride, J. M.; Carter, R. L. Angew. Chem., Int. Ed. 1991, 30,
293. (b) Cotton, F. A.; Wilkinson, G. C.; Murillo, A.; Bochmann, M.
trigonal prismatic Eu sites and the connections are Eu-NC-
AdVanced Inorganic Chemistry, 6th ed.; John Wiley & Sons, Inc.:
New York, 1999; p 273. (c) Hollingsworth M. D.; Harris, K. D. M.
In ComprehesiVe Supramolecular Chemistry Vol. 6, Solid-State
Supramolecular Chemistry: Crystal Engineering; MacNical, D. D.,
Toda, F., Bishop, R., Eds.; Pergamon Elsevier Science Ltd.: Oxford,
U.K., 1996; pp 178-182.
Ag-CN-Eu linkages.2
9,30
The sides of each hexagonal
] are composed of zigzag
channel of [NH ][M(HCOO)
4
3
M-O-CH-O-M links (Figure 1, middle). The chirality
of the framework, originating from the presence of only one
enantiomer M(OCO) (Figure S2a), results in the helical
6
channels (Figure 1, bottom). The framework is a bidirec-
(
32) Cotton, F. A.; Wilkinson, G. C.; Murillo, A.; Bochmann, M. AdVanced
Inorganic Chemistry, 6th ed.; John Wiley & Sons, Inc.: New York,
1999; p 1304.
(
33) (a) Dzyaloshinsky, I. J. Phys. Chem. Solid 1958, 4, 241. (b) Moriya,
T. Phys. ReV. 1960, 120, 91. (c) Moriya, T. In Magnetism Vol. 1;
Rado, G. T., Suhl, H., Eds.; Academic Press: New York, 1963; pp
tional, triple helix with a pitch of 3 × c and repeat unit of
6
metal ions. It is interesting to observe the formation of a
+
8
5-124.
chiral network from the simple achiral components (NH
4
,
(
34) Nakamoto, K. Infrared and Raman Spectra of Inorganic and Coor-
dination Compounds; Wiley: New York, 1986.
2
+
-
M , and HCOO ) as that observed in simple systems such
(
35) Stoilova, D.; Koleva, V. J. Mol. Struct. 2000, 553, 131.
(
30) Assefa, Z.; Staples, R. J.; Fackler, J. P., Jr. Acta. Crystallogr., Sect. C
(36) Figgis, B. N.; Hitchman, M. A. Ligand Field Theory and Its
Application; Wiley-VCH: New York, 2000; p 205.
1995, 51, 2527.
Inorganic Chemistry, Vol. 46, No. 2, 2007 441

Wang et al.
Table 2. Unique Bond Distances (Å) and Angles (deg) and N/C-H‚‚‚O Hydrogen Bonds (Å, deg) Observed in 1Mn, 2Co, and 3Ni
1
Mna
2Cob
3Nib
M(1)-O(1)
C(1)-O(1)
2.186(1)
1.235(2)
2.101(1)
1.240(2)
2.064(1)
1.238(2)
#
#
#
1
2
3
O(1)-M(1)-O(1)
O(1)-M(1)-O(1)
O(1)-M(1)-O(1)
82.29(6)
96.94(6)
90.85(4)
169.67(6)
123.3(1)
127.2(3)
82.53(6)
95.28(6)
91.44(4)
171.07(6)
123.3(1)
125.9(2)
82.64(7)
94.56(7)
91.70(5)
171.67(7)
123.6(2)
125.9(3)
#
2-
#3
O(1) M(1)-O(1)
M(1)-O(1)-C(1)
#
4
O(1)-C(1)-O(1)
D-H‚‚‚A
d(D-H)
d(H‚‚‚A)
d(D‚‚‚A)
<(DHA)
1
Mna
Cob
Nic
N(1)-H(2)‚‚‚O(1)
0.97(2)
1.12(5)
0.96(2)
1.07(3)
1.04(4)
0.98(4)
2.03(2)
2.42(2)
2.06(2)
2.39(2)
2.07(5)
2.42(2)
2.972(1)
3.127(3)
2.976(1)
3.039(2)
2.986(1)
3.006(2)
163(2)
119(1)
159(2)
117.3(7)
146(3)
118.1(8)
#
5
5
5
C(1)-H(1)‚‚‚O(1)
N(1)-H(2)‚‚‚O(1)
2
3
#
C(1)-H(1)‚‚‚O(1)
N(1)-H(2)‚‚‚O(1)
#
C(1)-H(1)‚‚‚O(1)
a
Symmetry codes: #1 -y + 1, -x + 1, -z + 1/2; #2 x, x - y + 1, -z + 1/2; #3 -x + y, -x + 1, z; #4 -x, -x + y, -z; #5 -y + 1, x - y + 1, z.
Symmetry codes: #1 -y + 1, -x + 1, -z + 3/2; #2 x, x - y, -z + 3/2; #3 -x + y + 1, -x + 1, z; #4 -x + 2, -x + y + 1, -z + 2; #5 -y + 1, x
b
d
-
y, z. The difference in symmetry codes in this table arose from the different absolute configuration of the chiral crystal structures, where 2Co and 3Ni
are the same while 1Mn is different.
Table 3. IR and UV-Vis Absorption Bands (cm-1) and Their Assignments for 1Mn, 2Co, and 3Nia
IR
assignments
1Mn
2Co
3Ni
+
ν(NH4 ): ν1 + ν5 (ν5, lattice mode)
3330 sh
3167 m
3000 m, br
2929 sh
2870 m
2755 w
1690 sh
1575 s
3335 sh
3171 m
2995 m, br
2933 sh
2887 m
2742 w
1691 sh
1583 s
3333 sh
3182 m
3000 m, br
2938 sh
2894 m
2743 w
1689 sh
1583 s
ν3
ν1 or ν2 + ν4
2ν4
+
νs(C-H) stretch or 2ν4(NH4 )
2ν5
δas(N-H), ν2
ν4(OCO) stretch, asym
+
ν4(NH4 )
1441 m
1389 s
1367 s
1442 m
1379 sh
1372 s
1445 m
ν5(OCO) deformation, asym
ν2(OCO) stretch, sym
1372 s
1072 vw, 1023 vw
ν6 out-of-plane deformation
1074 vw
1070 vw
949 br, vw
ν6 OCO deformation, sym
795 s
807 s
815 s
UV-Vis
1
Mn
2Co
3Ni
13600 s, A2g(F) f E1g(D)
6
4
4
3
1
1
2
2
7900 w, A1g f 4T1g(G)
16000 sh, T1g(F) f A2g(F)
19300 s, T1g(F) f T2g(F)
21400 sh, T1g(F) f T1g(P)
6
4
4
4
3
3
4600 w, A1g f T2g(G)
7400 w, A1g f Eg(D)?
14900 s, A2g(F) f T1g(F)
6
4
4
4
3
21500 sh, A2g(F) f ?
3
3
2
5100 s, A2g(F) f T1g(P)
a
Key: s, strong; m, medium; w, weak; vw, very weak; sh, shoulder; br, broad.
1
Mn and 2Co, the first weight loss occurred at ca. 190 and
energy consumption for the two thermal processes for 1Mn
and 2Co. This indicates that for 3Ni the loss of ammonia
220 °C, respectively. It corresponds to the lost of one
ammonia and one formic acid per formula resulting in the
formation of the binary phase with the stoichiometry of
M(HCOO) . This phase is stable up to ca. 330 and 280 °C,
2
2
and formic acid and the decomposition of Ni(HCOO) are
not separable. The final residue for 3Ni (at 800 °C) is within
1.5% of that calculated on the basis of NiO. The results
suggest that the stability of the ammonium salts decreases
with increasing size of the ionic radii of the metal in the
order Mn < Co ∼ Ni. In comparison with previous results
respectively, where it decomposes into the corresponding
metal oxide, MO. The two processes are endothermic under
nitrogen. From the DSC, an estimation of the energy required
-
1
24
for the two processes is similar, ca. 130 kJ mol . The
experimental (calculated) percentage weight loss for the first
process is 30.4 (30.3) and 28.9 (29.7) for 1Mn and 2Co,
respectively. For the second step, the corresponding weight
losses are within 2% of those calculated on the basis of
residues of MnO and CoO. In contrast, 3Ni shows one step
of weight loss at ca. 240 °C. It is also endothermic, with an
on other salts with larger amines, we note slight changes
in the temperature of the transformation into M(HCOO)
2
.
However, the stability of M(HCOO) has the reverse order.
2
It should be pointed out that the three compounds in the
present work have thermal stability similar to that of the
2
4
perovskite compounds [AmineH][M(HCOO)
3
]
but lower
than that of the more robust nanoporous diamond framework
-
1
18-21
energy requirement of 220 kJ mol , roughly the sum of the
3 6
compounds of [M (HCOO) ].
442 Inorganic Chemistry, Vol. 46, No. 2, 2007

II
[NH
4 3
][M (HCOO) ] (M ) Mn, Co, Ni) Frameworks
Table 4. Summary of Magnetic Properties of 1Mn, 2Co, and 3Ni
1Mn
2Co
3Ni
a
3
-1
C /cm K mol
4.64
-11.2
4.37
8.4
7.8
-0.32
3.92
-57.5
3.21
9.8, 6.0
9.6, 5.8
-3.8
400
25
14
1.29
-61.1
1.08
29.5
29.0
-7.6
830
b
Θ /K
3
-1
øT(300 K)/cm K mol
c
TN /K
d
Tp /K
e
(
J /kB)/K
f
Hc /Oe (at 2 K)
Mr /cm G mol (at 2 K)
HSF /kOe (at 2 K)
g
3
-1
50
>50
h
0.6
a
Curie constants. b Weiss constants. Critical temperatures based on
c
d
ZFC/FC measurements. Temperatures at peak positions in ac measure-
ments at zero dc field. Estimated by J/kB ) 3Θ/[2zS(S + 1)]. Coercive
field. Remnant magnetization. Peak positions in dM/dH.
e
f
g
h
Figure 3. ZFC/FC measurements under 5 Oe field for 1Mn, 2Co, and
Ni. The negative ZFC values of 3Ni were due to the small negative residual
3
field of the zero field setting of the SQUID instrument and easy
magnetization of the sample.
turn in øT around 6 K is observed, followed by a decrease
3
-1
of øT to 0.56 cm K mol at 1.9 K. After a minimum of
3
-1
0
.41 cm K mol at 30 K, the øT value of 3Ni displays a
3
-1
sharp rise to a broad maximum of 7.20 cm K mol at ca.
0 K, and then it decreases again to 1.07 cm K mol at 2
3
-1
2
K. From these data it appears that in the low-temperature
region 1Mn is a simple antiferromagnet while 2Co and 3Ni
are weak ferromagnets, and for 2Co the two magnetic phase
transitions are observed around 9 and 6 K.
Figure 2. Plots of øT vs T for 1Mn, 2Co, and 3Ni in an applied field of
1
00 Oe. The inset shows the low-temperature region.
The magnetism in the low-temperature region for these
compounds was further investigated by measuring the
magnetization in the low field following zero-field (ZFC)
and field-cooled (FC) protocol (Figure 3) and the ac
susceptibility (Figure S6). 1Mn displays a broad maximum
in both ZFC/FC with the in-phase ø′ around 8 K confirming
the antiferromagnetic ground state (Figures 3 and S6a). At
Magnetic Properties. The investigation of the magnetic
properties reveals that 1Mn, 2Co, and 3Ni are antiferro-
magnets with the later two showing weak ferromagnetism
at low temperatures. The basic magnetic parameters are listed
in Table 4. Therefore, we will discuss the properties first in
the paramagnetic region and then in the low-temperature
region.
The temperature dependence of magnetic susceptibility,
measured in an applied field of 100 Oe for 1Mn, 2Co, and
Ni (Figure 2), shows mainly antiferromagnetic character.
3
.6 K, a sudden increase of the dc susceptibility was
observed, and at the same temperature, peaks of both ø′ and
ø′′, though very weak in ø′ (star marked in Figure S6a), were
observed. It is possible that the 3.6 K transition might result
3
At room temperature, the øT values, being 4.37, 3.21 and
from a very small amount of Mn(HCOO)
2
2
‚2H O impurity
3
-1
1
.08 cm K mol for 1Mn, 2Co, and 3Ni, respectively, are
in the samples given that its transition temperature is very
2+
37
close to those expected for the M ions. On lowering of
the temperature from 300 to 50 K, the øT values decrease
slowly and then decrease more rapidly. The susceptibility
data in the high-temperature region (above 20, 50, and 60 K
for 1Mn, 2Co, and 3Ni, respectively) can be fitted to the
12c-h
close to 3.7 K.
For 2Co, the ZFC/FC magnetizations
show clearly two transitions at 9.8 and 6.0 K (Figure 3).
The lower temperature transition is higher than observed for
12i,m
Co(HCOO)
2
‚2H
2
O at 5.1 K,
confirming the absence of
the dihydrate salt. Meanwhile in ac susceptibility data (Figure
S6b) both ø′ and ø′′ display two sharp peaks at 9.6 and 5.8
K that are compatible with ZFC/FC dc susceptibility. The
strength of the lower temperature peak is more significant
than that at higher temperature. In addition to the phase purity
proved by PXRD (Figure S1), the ZFC/FC measurement
3
-1
Curie-Weiss law with C ) 4.64, 3.92, and 1.29 cm K mol
and Θ ) -11.2, -57.5, and -61.1 K, respectively. These
negative Weiss temperatures correspond to antiferromagnetic
exchange interactions between nearest neighbors. In the low-
temperature region, different magnetic behaviors are observed
(
Figure 2, inset). 1Mn shows a discontinuity around 7 K in
(Figure S7) for five carefully selected, randomly oriented,
3
-1
øT followed by a faster decrease to 0.31 cm K mol at 1.9
clean crystals gave the same results as described before on
a polycrystalline sample of 10 mg (Figure 3). Similarly, two
3
K. For 2Co, the øT value goes to a minimum of 0.72 cm K
mol around 10 K and then rises sharply to a maximum of
.88 cm K mol at 8.5 K. After the maximum, a second
-
1
magnetic transitions was reported for the perovskite com-
3
-1
1
24a
pounds of [(CH
3
)
2
NH
2
][Co(HCOO)
3
],
where the two
transition temperatures are 14.9 and 13.1 K. These might
arise from a spin-reorientation and will need further inves-
tigation. For 3Ni, the transition at 29.5 K from the ZFC/FC
(
37) Casey, A. T.; Mitra, S. In Theory and Application of Molecular
Paramagnetism; Mulay, L. N., Boudreaux, E. A., Eds.; John Wiley
&
Sons Inc.: New York, 1976; p 184.
Inorganic Chemistry, Vol. 46, No. 2, 2007 443

Wang et al.
Figure 4. Isothermal magnetizations for (a) 1Mn, (b) 2Co, and (c) 3Ni. The inset shows the low-field region.
measurements (Figure 3) and peak around 29.5 K in ac data
for both ø′ and ø′′ (Figure S6c) confirm the magnetic
transition. Finally, the weak ferromagnetism of 2Co and 3Ni
is confirmed by the spontaneous magnetizations observed
in ZFC/FC under low fields.
linear dependence at high field characterize the weak
ferromagnetism or spin-canting in the two materials. Weak
ferromagnetism has also been observed for the related
+
perovskite compounds of [AmineH ][M(HCOO)
3
] with
2
4a
M ) Co and Ni. The spin-flop transitions in 2Co and 3Ni
occur at much higher fields than that for 1Mn, being 14 kOe
(2Co) and possibly above 50 kOe (3Ni), while the magne-
tizations at the highest applied field, 0.85 and 0.11 Nâ for
2Co and 3Ni, respectively, are also far from the expected
N
The critical temperatures (T ’s) of 1Mn, 2Co (the first
N
T ), and 3Ni (Table 4) are close to and in the same sequence
as the recently reported perovskite formate compounds of
+
[
(
[
AmineH ][M(HCOO)
3
] of the M ) Mn (7.6-8.5 K), Co
][Co(HCOO) ]), and Ni (35.6 K for
]) series, with the same numbers
2
+
2+
14.9 K for [(CH
(CH NH ][Ni(HCOO)
3
)
2
NH
2
3
saturation values for Co and Ni . From the remnant
24
38
3
)
2
2
3
magnetizations the canting angle is estimated to be 0.1°
of anti-anti HCOO links between metal ions and similar
local coordination environment around metal ions, though
the framework topologies are different. It is worth noting
that the Ni compound 3Ni has a considerably high critical
temperature of ca. 30 K; this might be of interest for the
chiral magnet. These critical temperatures are in the same
sequence and two times higher than those of the related metal
for 2Co and 0.2° for 3Ni, respectively.
For this particular framework topology no suitable model
is available for estimating the coupling constant J between
2+
nearest M neighbors bridged by anti-anti formato ligand.
Therefore, the molecular field result J/k ) 3Θ/[2zS(S +
B
3
9
1)] was used. With z ) 6, S ) 5/2, 3/2, and 1 for 1Mn,
2Co, and 3Ni, respectively, and the Weiss temperatures, Θ’s,
formate dihydrates M(HCOO)
2
2
‚2H O which are all 2D
we estimate the J/k
B
values of -0.32, -3.8 and -7.6 K for
antiferromagnets with T ’s of 3.7, 5.1, and 15.5 K for M )
N
1Mn, 2Co, and 3Ni, respectively. These estimations are close
Mn, Co, and Ni, respectively.12 It is as expected that the
to -0.35, -4.3, and -8.6 K of M(HCOO)
‚2H
‚2L, as well as those of the recently reported
O
12
and
2
2
1
3
higher critical temperatures of the perovskite compounds of
M(HCOO)
2
+
+
24
[
AmineH ][M(HCOO)
3
] and the compounds of this work
[AmineH ][M(HCOO)
3
], with M ) Mn (-0.34 to -0.37
are due to the higher dimensionality (3D) of the frameworks
compared to the 2D ones of M(HCOO) ‚2H O, given the
very similar metal-metal linkages and thus similar magni-
tudes of exchange coupling.
K), Co (-3.4 K), and Ni (-7.3 K), both possessing similar
anti-anti HCOO linkages.
It is well-know that spin canting may be a result of
antisymmetric exchange and/or single-ion anisotropy.33 As
mentioned before, the structures satisfy the requirement for
the Dzyaloshinsky-Moriya interaction, i.e., the antisym-
metric exchange between magnetic metal sites, as found for
2
2
In the isothermal magnetization measurement at 2 K
(Figure 4), 1Mn shows no noticeable hysteresis, but a small
kink in the magnetization versus field is observed at ca. 600
Oe (Figure 4a). At higher field the magnetization increases
linearly and reaches ca. 2.5 Nâ at the highest applied field
of 70 kOe being half of the saturation value of 5 Nâ for
1
2,13,14,24
other metal formates.
For 2Co and 3Ni, the single-
ion anisotropy of Co and Ni2+ enhances the Dzyaloshin-
sky-Moriya interaction because the antisymmetric exchange
is proportional to the single-ion anisotropy. Neutron diffrac-
tion experiments, as well as very low-temperature structure
determinations, are needed for understanding the detailed
magnetic structures.
2+
2
+
Mn (S ) 5/2 and g ) 2.00). This indicates a spin-flop
transition for the compound at 600 Oe. The magnetism of
1
Mn is similar to that of the perovskite compounds,
+
24b
3
[AmineH ][Mn(HCOO) ]. However, there is no indication
of weak ferromagnetism at the N e´ el transition as in the
perovskite Mn compounds. For 2Co and 3Ni (Figure 4b,c),
hysteresis is observed in the isothermal magnetization (Figure
Conclusion
In summary, employing the smallest and simplest am-
monium results in the series of chiral magnets [NH ]-
4
4
b,c, inset), with the remnant magnetization and coercive
3
-1
field being 25 cm G mol and 400 Oe for 2Co, and 50
cm G mol and 830 Oe for 3Ni, respectively. Spontaneous
3
-1
(
38) Kahn, O. Molecular Magnetism; John Wiley & Sons Inc.: New York,
993; p 322.
1
magnetization in very low applied field together with the
(
39) Carlin, R. L. Magnetochemistry; Springer-Verlag: Berlin, Heidelberg,
3
-1
low magnetization values of tens of cm G mol and the
Germany, 1986; p 149.
444 Inorganic Chemistry, Vol. 46, No. 2, 2007

II
[NH
4
][M (HCOO)
3
] (M ) Mn, Co, Ni) Frameworks
[
M(HCOO)
3
] (M ) Mn, Co, and Ni). The structure possesses
render them attractive for possible magneto-optical proper-
ties, and this merit further study when homochiral samples
are available. Finally, that many formate compounds are
magnets with interesting and abundant magnetism gives us
more inspiration to use the simple formato ligands in future
studies.
9
6
a rarely observed 4 ‚6 topology and channels occupied by
linear NH
+
4
arrays. This result, together with the previous
reports, demonstrates clearly the template effect of the
protonated amine cations for the formation of different
metal-formate frameworks. It also revealed that chirality
can be produced from such simple achiral starting compo-
nents. The Mn compound is an antiferromagnet (T
K and low spin-flop field of 600 Oe), while both Co and Ni
compounds exhibit weak ferromagnetism (T ) 9.8 K (Co)
and 29.5 K (Ni)) and there is a second transition at 5.8 K
for 2Co probably due to spin-reorientation. The estimated
couplings, J/k
-
Acknowledgment. This work is supported by the CREST,
Japan Science and Technology Corp., Chinese Academy of
Sciences, CMS-CX200510, and NSFC (Grants 20571005,
N
) 8.4
N
20473095, 20490210, and 20221101). We thank Prof. Stuart
R. Batten of the School of Chemistry of Monash University,
Monash, Australia, for his kind help in discussion of the
network topology.
B
, using the molecular field approximation are
0.32 (Mn), -3.8 (Co), and -7.6 K (Ni). The weak
Supporting Information Available: Figure S1-S7 and CIF
files of crystallography data for the structures in this work.
This material is available free of charge via the Internet at
http://pubs.acs.org.
ferromagnetism arises from the antisymmetric exchange via
the noncentrosymmetric HCOO bridges, enhanced by single-
ion anisotropy for the Co and Ni compounds. The compounds
are fairly stable up to ca. 200 °C. The strong absorption bands
of the chiral magnetic salts of Co and Ni in the visible region
IC0610031
Inorganic Chemistry, Vol. 46, No. 2, 2007 445