Chemistry Reference
In-Depth Information
Figure 6.21. Chain structure of Co(hfac)
2
(NITPhOMe) along the
c
-direction. Co
and C atoms are represented by large dark grey and small black balls, respectively.
The rest of the atoms are represented by white balls. Crystallographic data from
Caneschi
et al.
, 2001.
Ising-type anisotropy. An estimation of the exchange coupling gives
J
19 meV.
At low temperature the spin of octahedral Co
+
2
centres can be handled as an
effective
S
2 spin with anisotropic
g
values significantly different from 2. The
chains behave as 1D ferrimagnets, because of the non-compensation of the magnetic
moments of the Co
+
2
=
1
/
χ
centre and the radical. In addition, the ac
measured at
0 and with an oscillating field applied along the chain direction is strongly
frequency dependent below 17 K, clearly indicating that the relaxation of
M
in this
temperature range becomes slow on the time scale of the experiment (2
µ
s-1 s).
This frequency dependence rules out any 3D transition.
We next turn our attention to the single-chain magnet formed by the heterometal-
lic chain of Mn
+
3
and Ni
+
2
ions, [Mn
2
(saltmen)
2
Ni(pao)
2
(C
5
H
5
N)
2
](ClO
4
)
2
(Clerac
et al.
, 2002). This compound (
C
2
B
=
/
c
,
a
=
2
.
114 nm,
b
=
1
.
597 nm,
059
◦
) consists of two fragments, the out-of-plane dimer
[Mn
2
(saltmen)
2
]
2
+
as a coordination acceptor building block and the neutral
mononuclear unit [Ni(pao)
2
(C
5
H
5
N)
2
] as a coordination donor building block,
forming an alternating chain having the repeating unit [-Mn-(O)
2
-Mn-ON-Ni-
NO-]
n
. Figure 6.22 shows a detail of the complex chain structure revealing that the
oximato group of the [Ni(pao)
2
(C
5
H
5
N)
2
] monomeric species bridges the Mn
+
3
dimers to form an alternating 1D chain. Each chain is contained in the
ac
-plane
and is separated from the nearest chains with a minimum intermetallic distance
between manganese and nickel of 1.039 nm, thus ensuring good magnetic isolation
of the chains. No significant interchain
c
=
1
.
862 nm and
β
=
98
.
π
stacking is observed between the phenyl
rings of the saltmen ligand.
