The SmA A N phase transition is characterized by the collapse
of the hkl = 001 and 002 reflections (Fig. S5, see ESI{), while a
birefringent texture is maintained (Fig. S6, see ESI{). The stronger
intermolecular cohesion observed in the SmA phase of
2
1
[
Eu(Me
nematic phase, while [Lu(Me
possibilities for intermolecular interactions in its SmA phase,
4
L)(NO
3
)
3
] requires DH = 2.4 kJ mol
to enter the
4
L)(NO ], which displays less
3 3
)
21
requires only DH = 0.8 kJ mol
.
In conclusion we have succeeded in demonstrating that the
simple thermodynamics of dimerization of molecules in non-
coordinating solvents can be used as an efficient tool for
programming and rationalizing the formation of smectic and
nematic mesophases in lanthanidomesogens
We thank K.-L. Buchwalder for recording DSC and Drs L.
Gu e´ n e´ e and B. Heinrich for assistance with SAXS analysis.
Financial support from the Swiss National Science Foundation is
gratefully acknowledged.
21
Fig. 1 DSC trace of [Eu(Me L)(NO
4
3
)
3
2
] (5 uC min under N ).
Notes and references
1
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2
3
(a) B. Donnio and D. W. Bruce, Struct. Bonding, 1999, 95, 194–247; (b)
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6, 1495–1513.
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4
5
1
Fig. 2 Proposed organization in the SmA phases obtained by SAXS for
a) [Eu(Me L)(NO ] and (b) [Lu(Me L)(NO ]. Red: coordinating
(
4
3
)
3
4
3 3
)
2
007, 119, 4764–4767); (b) I. Aprahamian, T. Yasuda, T. Ikeda, S. Saha,
benzimidazole–pyridine–benzimidazole unit; green: other aromatic groups;
violet: aliphatic chains.
W. R. Dichtel, K. Isoda, T. Kato and J. F. Stoddart, Angew. Chem., Int.
Ed., 2007, 46, 4675–4679, (Angew. Chem., 2007, 119, 4759–4763).
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6
7
In order to rationalize the thermodynamics of the SmA A N
phase transition, we must first consider the organization of the
molecules in the layered smectic
A phase (SmA). For
[
Eu(Me L)(NO ) ] at 120 uC, the SAXS profile shows the hkl =
4
3 3
˚
01 reflection (= interlayer distance) occurring at 110 A, a length
0
9
corresponding to the fully stretched complex molecule (Fig. 2(a)).
In sharp contrast, the hkl = 001 reflection for [Lu(Me L)(NO
recorded at the same temperature indicates an interlayer separation
8
9
4
3 3
) ]
˚
of only 60 A, which implies the alternative intertwined organiza-
1
tion (Fig. 2(b)). This behaviour agrees with the trend of the larger
central lanthanides (Ln = Eu) to form additional stabilizing nitrate
bridges with adjacent neighbours (Fig. 2(a)), while the smaller
lanthanides (Ln = Lu) cannot participate to this mode of
intermolecular interactions (Fig. 2(b)).
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1
This journal is ß The Royal Society of Chemistry 2008
Chem. Commun., 2008, 181–183 | 183