Polyhedron 20 (2001) 1365 – 1369
Synthesis, characterization and magnetic properties of
[Mn
30
O
24
(OH)
8
(O
2
CCH
2
C(CH
3
)
3
)
32
(H
2
O)
2
(CH
3
NO
2
)
4
]:
the largest manganese carboxylate cluster
Mo ` nica Soler
a
, Evan Rumberger
b
, Kirsten Folting
a
, David N. Hendrickson*
b,1
,
George Christou*
a,2
a
Department of Chemistry, Indiana Uniersity, Bloomington, IN 47405 -4001, USA
b
Department of Chemistry, Uniersity of California at San Diego, La Jolla, CA 92093 -0358, USA
Received 17 September 2000; accepted 28 October 2000
Abstract
We report the synthesis, structure and magnetic properties of a new member of the family of high nuclearity Mn clusters. The
complex [Mn
30
O
24
(OH)
8
(O
2
CCH
2
C(CH
3
)
3
)
32
(H
2
O)
2
(CH
3
NO
2
)
4
](1), is the highest nuclearity manganese cluster to date. Complex
1 was obtained from the comproportionation reaction between Mn(OAc)
2
·4H
2
O and KMnO
4
, followed by ligand substitution
with Me
3
CCH
2
CO
2
H. It is mixed-valent with a trapped-valence 3Mn
II
, 26Mn
III
, Mn
IV
oxidation state description. Dc magnetic
susceptibility studies indicate an S =7 ground state, and ac susceptibility studies show an out-of-phase susceptibility signal below
3 K, indicating complex 1 to display the slow magnetization relaxation diagnostic of a single-molecule magnet. © 2001 Elsevier
Science Ltd. All rights reserved.
Keywords: Manganese; Crystal structure; High nuclearity cluster; Single-molecule magnets
www.elsevier.nl/locate/poly
1. Introduction
Over the last decade, a strong interest has developed
in our group in 3d metal carboxylate clusters because
they represent a large family of high-nuclearity prod-
ucts with interesting structural, spectroscopic and mag-
netic properties. The majority of our efforts has been
concentrated in polynuclear manganese complexes and
has led to a large variety of clusters, such as Mn
4
[1–3],
Mn
6
[4,5], Mn
7
[6,7], Mn
8
[8–11], Mn
9
[9,12,13], Mn
10
[14–17], Mn
11
[18,19], Mn
12
[20,21], Mn
13
[22], Mn
18
[23 – 26] species. Magnetic studies have shown that they
often possess a large number of unpaired electrons. In
combination with a sufficiently large magnetic an-
isotropy, this has led some of them to display the new
magnetic phenomenon of single-molecule magnetism
(SMM).
The largest manganese clusters studied to date are
the Mn
18
complexes [23 – 26], possessing three different
types of structure and different kinds of magnetic be-
havior. We have now been able to synthesize an even
larger Mn cluster, [Mn
30
O
24
(OH)
8
(O
2
CCH
2
C-
(CH
3
)
3
)
32
(H
2
O)
2
(CH
3
NO
2
)
4
](1) from a multistep reac-
tion employing Mn(O
2
CCH
3
)
2
·4H
2
O and KMnO
4
, fol-
lowed by addition of tert -butylacetic acid [27]. This
compound has been characterized using IR, EA, mag-
netic studies and crystallography. In this paper we
describe the crystal structure and magnetic properties of
this new compound, showing that it is a new example
of a single-molecule magnet.
2. X-ray crystallography
[Mn
30
O
24
(OH)
8
(O
2
CCH
2
C(CH
3
)
3
)
32
(H
2
O)
2
(CH
3
-
NO
2
)
4
]·solvent (1) crystallizes in the monoclinic space
group C 2/c. The asymmetric unit contains half of a
Mn
30
complex located on a twofold axis, which passes
through four manganese ions (Mn1, Mn2, Mn6 and
Mn7). In addition to the main molecule of interest, the
asymmetric unit contains some unidentified solvent.
1
*Corresponding author. E-mail: dhendrickson@ucsd.edu
2
*Corresponding author. E-mail: christou@indiana.edu
0277-5387/01/$ - see front matter © 2001 Elsevier Science Ltd. All rights reserved.
PII:S0277-5387(01)00620-9