Enneanuclear [Ni
6
Ln
3
] Cages: [Ln
III
3
] Triangles Capping [Ni
II
6
] Trigonal
Prisms Including a [Ni
6
Dy
3
] Single-Molecule Magnet
Angelos B. Canaj,
†
Demetrios I. Tzimopoulos,
‡
Milosz Siczek,
§
Tadeusz Lis,
§
Ross Inglis,*
,∥
and Constantinos J. Milios*
,†
†
Department of Chemistry, The University of Crete, Voutes, 71003, Herakleion, Greece
‡
Department of Chemistry, Aristotle University of Thessaloniki, 54124 Thessaloniki, Greece
§
Faculty of Chemistry, University of Wroclaw, Joliot-Curie 14, 50-383, Wroclaw, Poland
∥
School of Chemistry, The University of Edinburgh, David Brewster Road, EH9 3FJ Edinburgh, U.K.
* S Supporting Information
ABSTRACT: The use of (2-(β-naphthalideneamino)-2-hydroxymethyl-1-propanol)
ligand, H
3
L, in Ni/Ln chemistry has led to the isolation of three new isostructural
[Ni
II
6
Ln
III
3
] metallic cages. More specifically, the reaction of Ni(ClO
4
)
2
·6H
2
O, the
corresponding lanthanide nitrate salt, and H
3
L in MeCN, under solvothermal
conditions in the presence of NEt
3
, led to the isolation of three complexes with the
formulas [Ni
6
Gd
3
(OH)
6
(HL)
6
(NO
3
)
3
]·5.75MeCN·2Et
2
O·1.5H
2
O (1·5.75MeCN·
2Et
2
O·1.5H
2
O), [Ni
6
Dy
3
(OH)
6
(HL)
6
(NO
3
)
3
]·2MeCN·2.7Et
2
O·2.4H
2
O (2·2MeCN·
2.7Et
2
O·2.4H
2
O), and [Ni
6
Er
3
(OH)
6
(HL)
6
(NO
3
)
3
]·5.75MeCN·2Et
2
O·1.5H
2
O (3·
5.75MeCN·2Et
2
O·1.5H
2
O). The structure of all three clusters describes a [Ln
III
3
]
triangle capping a [Ni
II
6
] trigonal prism. Direct current magnetic susceptibility studies in
the 5−300 K range for complexes 1−3 reveal the different nature of the magnetic
interactions within the clusters: dominant antiferromagnetic exchange interactions for
the Dy
III
and Er
III
analogues and dominant ferromagnetic interactions for the Gd
III
example. Alternating current magnetic susceptibility measurements under zero external dc field displayed fully formed
temperature- and frequency-dependent out-of-phase peaks for the [Ni
II
6
Dy
III
3
] analogue, establishing its single molecule
magnetism behavior with U
eff
= 24 K.
■
INTRODUCTION
One of the most active areas in the field of molecular magnetism
is the search for single molecule magnets (SMMs), i.e., molecules
that retain their magnetization once magnetized in the absence of
magnetic field.
1
The number of such species has grown
exponentially over the last 2 decades, with the phenomenon
initially observed for transition-metal centers such as Mn, Fe, Co,
and Ni, with the [Mn
12
OAc] and the [Fe
8
/tacn] molecules being
the very first examples.
2
In addition, in 2003 the mononuclear
complex (NBu
2
)[Pc
2
Ln] (Ln = Tb, Dy) was also found to
display SMM behavior, thus opening the way for 4f SMMs.
3
Nowadays, the introduction of 4f centers in the field of SMMs is
mainly due to the two fundamental properties of lantha-
nides(1) their large magnetic moment, since they can host
up to seven unpaired electrons in the 4f orbitals, and (2) their
large magnetic anisotropy, due to the large spin−orbit coupling
present (with the exceptions of La
III
, Gd
III
, and Lu
III
)both of
which are the main prerequisites for the appearance of SMM
behavior. Today, molecules with impressive SMM properties
have been reported with examples including 4f centers, while the
3d SMMs seem to have reached their peak. These new 4f-
containing species, either 3d−4f or purely 4f, display extremely
large energy barriers for the reorientation of the magnetization,
assuming, of course, that an Arrhenius analysis is valid for such
systems.
4
We recently reported the use of the naphthalene-based triol
ligand H
3
L [L = 2-(β-naphthalideneamino)-2-hydroxymethyl-1-
propanol, Scheme 1] for the synthesis of polynuclear 3d
complexes
5
and Mn-4f complexes.
6
Herein, we report the use
Received: May 21, 2015
Scheme 1. Structure of the Ligand Discussed in the Text and
Its Coordination Modes in 1−3
Article
pubs.acs.org/IC
© XXXX American Chemical Society A DOI: 10.1021/acs.inorgchem.5b01149
Inorg. Chem. XXXX, XXX, XXX−XXX