Journal of the American Chemical Society
Communication
6
the two Pcs rings are rotated 45° with respect to each other,
using the coupling of 1,3,3-trichloroisoindolenine with 5,6-
bis(hexylthio)-1,3-diiminoisoindoline (Scheme SI-1 in the
Supporting Information). The ABAB phthalocyanine was
giving a non-centrosymmetric structure of approximately D4d
symmetry. If one imagines lanthanide complexes with crosswise
ABAB macrocycles featuring alternating electron-donor and
electron-acceptor groups, an almost exact representation of the
octupolar cube could be obtained (Figure 1), even if the
9
obtained as the major product, but significant amounts of
2,3,9,10,16,17-hexa(hexylthio)phthalocyanine (AB ) and traces
3
of the symmetric derivative 2,3,9,10,16,17,23,24-octa-
symmetry is lowered to D , an unusual apolar chiral group.
(hexylthio)phthalocyanine (B ) were nevertheless produced,
2
4
Because of their extended π-electron systems, phthalocyanines
and their transition-metal complexes have been used to build
up interesting nonlinear compounds, including various
requiring thorough purification by chromatography. Finally, the
bis(phthalocyaninato)lutetium complex 2 was obtained in good
yield from the ABAB phthalocyanine and lutetium(III) acetate
in refluxing 1-chloronaphthalene using DBU as a base (Scheme
7
octupolar structures. Surprisingly, intervalent bis-
10
(
phthalocyaninato)lanthanide sandwich complexes have sel-
1).
dom been studied. Only their third-order nonlinear properties
have been reported. The most detailed study was reported by
Shirk et al., who investigated the cubic hyperpolarizabilities γ
2 was crystallized from a concentrated chloroform solution
8
by slow diffusion of methanol, and the crystal structure was
8
a
11
resolved by X-ray diffraction. The molecular central core has a
of a series of homoleptic simple [Pc Ln] complexes by
structure very similar to that of the previously reported
2
6b
12
degenerate four-wave mixing at 1064 nm. The measured
hyperpolarizabilities γ were among the highest reported at this
wavelength. The authors showed that the intervalence
transition, which involves considerable charge transfer, does
not have a dominant influence when it is not in resonance with
the incident wavelength.
unsubstituted and octasubstituted bis(phthalocyaninato)-
lutetium(III) complexes. Two phthalocyanine rings flank the
central Lu3+ ion. As expected, there is a staggering angle (α) of
45° between the two cycles that creates a chiral non-
3
+
centrosymmetric molecule (Figure 2a). The Lu ion is
octacoordinated by the eight nitrogen atoms of the isoindoles
In this communication, we report on our first step toward the
construction of a true octupolar cube using lanthanide
complexes with crosswise ABAB macrocycles. A bis-
(N2 and N6, denoted as N ) in a slightly distorted square-
iso
antiprism geometry (Figure 2b). In Figure 2b, the N2 atoms
(the Niso atoms of the isoindole rings bearing the electron-
accepting groups) and the N6 atoms (which bear the electron-
donating groups) are pictured in different colors to show the
parallel between the coordination polyhedron and the
(phthalocyaninato)lutetium sandwich complex with a crosswise
ABAB phthalocyanine bearing electron-donor (thioalkyl)
groups on two opposite rings was synthesized and its first
molecular hyperpolarizability β measured. Although there are
no real electron-acceptor groups, the required ABAB-type
alternation for one face of the cube is present, as thioalkyl
groups and hydrogen atoms do not have the same electronic
effect.
A large number of homoleptic and even heteroleptic lutetium
sandwich complexes have been prepared with symmetrical A4
phthalocyanines, usually by cyclic tetramerization of the
octupolar cube in Figure 1. The Lu−N distances (2.356
iso
and 2.366 Å) are slightly shorter than those reported for similar
complexes [2.377−2.394 Å for the octa(hexylthio) analogue
and 2.380 Å for Pc Lu]. The interplane distance between the
2
two macrocycles, defined as the distance between the mean
planes formed by the two sets of four Niso atoms, is 2.656 Å,
which is also shorter than the reported values (2.67−2.70
6b,12
Å).
In 2, the two phthalocyanine rings are only slightly
corresponding phthalodinitriles in the presence of a lanthanide
salt and 1,8-diazabicyclo[5.4.0]undec-7-ene (DBU). This
method could not be envisaged in our case, as a specific
ABAB geometry is required for the two macrocycles. Therefore,
the regioselective synthesis of the crosswise free base 2,3,16,17-
tetra(hexylthio)phthalocyanine (1) (Scheme 1) was achieved
distorted from planarity, with a maximum of only 8.7° for the
dihedral angle between the mean plane of the four Niso atoms
and the isoindole ring bearing the two thioalkyl chains. This
small angle, combined with the short interplanar distance, gives
hope for good electronic delocalization and good optical
properties.
Figure 3 shows the absorption spectra of 1 and 2 in
chloroform solution. 1 presents the classical spectrum of a low-
symmetry phthalocyanine with a B band at 340 nm and an
intense Q band split in two with maxima at 682 and 719 nm.
Upon complexation, small hypsochromic shifts are observed for
both the B and Q bands, with disappearance of the splitting.
The substitution of the Pc ring with the four electron-donating
thio(hexyl) groups provokes a red shift of all maxima relative to
Scheme 1. Synthesis of Complex 2
4
the unsubstitued analogues. The main features of the
electronic spectrum of 2 (Figure 3 inset) are a broad, intense
absorption in the near-IR appearing between 1200 and 1600
nm and a sharp but weak band at 933 nm. This is characteristic
of the intervalence band and corresponds to the b → a
1
2
excitation between the delocalized b bonding molecular orbital
1
1
3
(
MO) and the a antibonding MO.
2
Nonpolarized harmonic light scattering (HLS; also named
14
hyper-Rayleigh scattering) experiments in chloroform were
used to measure the dynamic molecular first hyperpolarizability,
2
⟨β
⟩
of 2. The incident wavelength of 1907 nm is
HLS
1907
higher than the absorption cutoff and is therefore off-resonance
3
656
dx.doi.org/10.1021/ja211064a | J. Am. Chem. Soc. 2012, 134, 3655−3658
Ayhan, Mehmet Menaf
