B
S. Chi et al.
N
N
Nd(NO ) ·6H O, NdCl ·6H O
3
3
2
3
2
Nd(salen) (NO ) Cl(1)
2
3 2
OH HO
CH Cl , MeOH
2 2
H salen
2
Scheme 1. Synthesis of complex 1
CH Cl /MeOH produced a 3D structure in ,54.9 % overall
2
2
yield (Scheme 1). Dichloromethane was employed to increase
the solubility of the ligand. The immediate colour change of the
solution upon addition of LnCl ꢀ6H O and Ln(NO ) ꢀ6H O
1
2
3
2
3 3
2
indicates instant occurrence of the coordination reaction.
Yellow crystals suitable for X-ray analysis were obtained by
slow diffusion of diethyl ether into the solution for one week.
Complexes 1–4 are stable in air and moderately soluble in polar
organic solvents such as methanol, ethanol, and DMF.
3
4
IR Spectra
The IR absorption spectra of the ligand and complexes 1–4 are
shown in Fig. S1 (Supplementary Material). There are con-
spicuous differences between the complex 1 and the free ligand
in the IR spectra. For complex 1, the C¼N stretching vibration
Simulation
40
10
20
30
50
2
q [deg.]
ꢁ
1
ꢁ1
shifts to higher wavenumber (by 10 cm to ,1641 cm ) which
[34]
is identical to the Salen-type lanthanide complexes. Four bands
Fig. 1. PXRD patterns for 1–4.
ꢁ1
near 1481 (n ), 1270 (n ), 1162 (n ), and 817 (n ) cm in the IR
4
1
2
6
spectrum of complex 1 can be assigned to the vibrations of the
coordinated nitrate group (Fig. S2, Supplementary Material). The
ꢁ
1
difference between the n and the n peak positions is ,200 cm
,
which is typical for a bidentate nitrate group. This is identical to
supramolecular structure is assembled which seems typical of
MOFs formed by Salen ligands. It is worth noting that all the
tails of the mechanical spring model are right-handed in com-
plex 1. First of all, in a head-to-tail ligation mode, mechanical
spring models link each other and form two of the same 1D right-
handed helical chains, which only occupy different directions in
the crystal. Furthermore, these two helixes interweave each
4
1
the lanthanide Schiff base complexes [Pr(H salen)
2
[36]
NO ) (CH OH) ] and [Ln(H salen) (NO ) ] .
(
3 3 3 2 n 2 1.5 3 3 n
Structural Description of Nd(salen) (NO ) Cl (1)
2
3 2
X-Ray crystallographic analysis has revealed that complexes
–4 are isomorphic, as revealed by comparison of their powder
3þ
other by sharing the Nd ion, thus resulting in the formation of
D MOFs (Fig. 3). It is easily observed that there are several
holes in the 3D MOF. The structure was simplified parallel
1
3
X-ray diffraction (PXRD) patterns (Fig. 1). The PXRD patterns
of complexes 1–4 are in agreement with the simulated ones from
the respective single-crystal X-ray data. The differences in
intensity are due to the preferred orientation of the powder
samples. Taking 1 as an example, X-ray crystallographic anal-
ysis reveals that complex 1 crystallising in a tetragonal space
group P43212 possesses a 3D structure. The unit cell contains
one monomeric unit of the coordination complex Nd(salen)2
to the c-axis resulting in a novel 3D coordination polymer
(
Fig. 4). In this 3D network, each ligand can be seen to adopt a
3þ
2
(
-connecting node as well as each Nd ion, thus an unusual
2,2)-connected net is obtained. Further analysis suggests that
complex 1 shows a rutile-type framework with a Schlafli symbol
of {6^6} [6(2).6(2).6(2).6(2).6(2).6(2)] and a 1D channel along
the a-axis (Fig. 5).
(
NO ) Cl without solvent molecule (Fig. 2a). The unique
3
2
3þ
Nd ion is nine-coordinated by four phenol oxygen atoms, two
bidentate nitrate oxygen atoms, and one chlorine atom, exhi-
I
biting a tri-capped trigonal prism geometry. The O1, O1 , and Cl
Photophysical Properties
The UV-vis absorption data of complexes 1–4 and H salen are
2
atoms are at the vertices of each square pyramid (Fig. 2b).
Selected bond lengths and angles within the inner coordination
sphere of complex 1 are summarised in Table 1. The bond dis-
presented in Fig. S3 (Supplementary Material). In CH OH,
3
H salen presents three main absorptions at ,220, 265, and
2
298 nm, which are assigned to the p–p* transitions of Ar–OH
chromophores and the imine group. As for 1, there are three sets
of absorption bands at ,230, 270, and 300 nm, which are due to
the intraligand transitions of the ligand. The NIR emissions of
complex 1 were measured in the solid state at room temperature.
˚
tances of Nd–O are in the range of 2.415(7)–2.652(8)A
˚
av. 2.510 A). Notably, the Nd–O bond distances for phenolic
(
oxygen atomsO4andO5ofthe ligands(2.415 (7) and 2.426 (7) A)
˚
are significantly shorter than those oxygen atoms of nitrate
˚
3þ
(
2.547(5)–2.652(7) A).
The structure of complex 1 is only made up of one building
Excited at 415 nm, it resulted in Nd ion NIR emission bands
4
4
which are assigned to the F - I ( j ¼ 9, 11, 13) transitions
3
/2
j/2
3þ
ꢁ
4
4
unit, a [NdL ] metal–organic subunit (MOS), Cl , and two
2
in complex1. The emission near 890 nm is assigned to F - I ,
near 1061 nm to F - I , and near 1316 nm to F - I
3/2 11/2 3/2 13/2
3/2 9/2
ꢁ
3þ
4
4
4
4
NO . Interestingly, the Nd ion acts as the head and the
3
H salen molecule acts as the tail, connecting from end to
2
transitions (Fig. 6). The free H salen ligand does not exhibit NIR
2
end. Through intermolecular bonding interactions (C–OꢀꢀꢀNd,
luminescence under similar conditions. The H salen provides
2
3
av. 2.510 A) between a phenolic oxygen and a Nd ion, a 3D
þ
3þ
˚
efficient energy transfer for the sensitisation of the Ln ion.
Chi, Shushen
