Synthesis, Structural Characterization, and Chiroptical Studies of Bidentate Salen-Type Lanthanide (III) Complexes

Article abstract of DOI:10.1002/chir.22499

The salen-type ligand prepared with (R,R) diphenylethan-1,2-diamine and salicylaldehyde provides stable and inert complexes KLnL₂ upon simple reaction with lanthanide halides or pseudohalides LnX₃ (Ln = Tb³⁺-Lu³⁺

Full text of DOI:10.1002/chir.22499

CHIRALITY 27:857–863 (2015)
Special Issue Article
Synthesis, Structural Characterization, and Chiroptical Studies of
Bidentate Salen-Type Lanthanide (III) Complexes
1
1
1,2
1,3
4
ROBERTO BERARDOZZI, GENNARO PESCITELLI, SEBASTIANO DI PIETRO, CLAUDIO RESTA, FRANCESCO P. BALLISTRERI,
4
4
1
ANDREA PAPPALARDO, GAETANO A. TOMASELLI, AND LORENZO DI BARI *
1
Dipartimento di Chimica, Università di Pisa, Pisa, Italy
2
École Noramle Supérieure de Lyon, Lyon, France
3
CSGI-Dipartimento di Chimica “Ugo Schiff”, Università di Firenze, Sesto Fiorentino (FI), Italy
4
Dipartimento di Scienze Chimiche, Università di Catania, Catania, Italy
ABSTRACT
The salen-type ligand prepared with (R,R) diphenylethan-1,2-diamine and
salicylaldehyde provides stable and inert complexes KLnL upon simple reaction with lantha-
2
3+
3+
ꢀ
ꢀ
nide halides or pseudohalides LnX (Ln = Tb -Lu ; X = Cl or TfO ) of its potassium salt. All
3
the complexes were completely characterized through nuclear magnetic resonance (NMR),
3+
3+
3+
electronic circular dichroism (ECD) in the UV and some (Er , Tm , Yb ) also with Near-IR
3+
3+
ECD (NIR-ECD) and luminescence (Tb , Tm ). Careful analysis of the NMR shifts demon-
strated that the complexes are isostructural in solution and afforded an accurate geometry. This
3+
was further confirmed by means of Density Functional Theory (DFT) optimization of the Lu
complex, and by comparing the ligand-centered experimental and time-dependent TD-DFT
computed UV-ECD spectra. As final validation, we used the NIR-ECD spectrum of the Yb3+ de-
rivative calculated by means of Richardson’s equations. The excellent match between calculated
and experimental ECD spectra confirm the quality of the NMR structure. Chirality 27:857–863,
2
015. © 2015 Wiley Periodicals, Inc.
KEY WORDS: salen-type ligand; electronic circular dichroism; near-IR circular dichroism;
TD-DFT calculation; paramagnetic NMR
Chiral lanthanide complexes are interesting for their appli-
In the following, we discuss Ln3+ complexes with a bis
(salicylaldimine)-type ligand, derived from enantiopure
1
–3
cations including enantioselective catalysis,
detection of
bio-analytes,4 circularly polarized light emitting devices,
–6
7,8
(1R,2R)-1,2-diphenylethylene-1,2-diamine (H L), prepared ac-
2
9
and metal organic frameworks. The organic ligands define
cording to Scheme 1.
the Ln3+ coordination sphere, modulating the access of fur-
ther chemical species to the ion and making it soluble, sta-
ble, and persistent in various environments. Furthermore,
the ligand may provide the necessary conditions to sensitize
Complexes with the general formula KLnL (Ln = Tb3+,
2
3+
3+
3+
3+
3+
3+
Dy , Ho , Er , Tm , Yb and Lu ) were readily obtained
following Scheme 2, and fully characterized in chloroform
solution by means of (paramagnetic) NMR, as well as of chi-
roptical and emission spectroscopies.
1
0
the ion’s photo- (or electro-) luminescence. In this context,
salen-type ligands (N,N’-bis(salicylidine)diamine) have shown
promising properties especially in binding late lanthanides and
MATERIALS AND METHODS
3+
11–15
promoting Near-IR luminescence of Yb complexes.
General
3+
3+
3+
With the exception of La and Lu , all Ln ions induce charac-
teristic paramagnetic NMR shifts, which can be used to determine
Unless otherwise indicated, all materials were purchased from Sigma-
Aldrich (St. Louis, MO) and were used without further purification. All
the lanthanide salts were stored in a dessicator with P O .
16–19
3+
accurate solution structures.
Gd may induce a relevant con-
2
5
tact shift, which is, however, hardly detectable owing to the severe
line broadening brought about by this ion. The introduction of chi-
rality elements into Ln3 complexes’ architecture opens the possi-
bility to investigate their structure with electronic circular
dichroism (ECD) in an extended range of energies (Near-IR,
UV-vis). Additionally, ECD spectra may be simulated by various
approaches. For example, ligand-centered ECD may be evaluated
by means of time-dependent Density Functional Theory (TD-
NMR measurements were performed on a Varian (Palo Alto, CA)
INOVA 600 spectrometer operating at 600 MHz for H. The temperature
1
+
was controlled to ±0.1 °C. CDCl was used as the solvent and the (residual)
3
1
13
solvent signal (7.26 ppm for H and 77.16 ppm for C) was used to reference
the spectra.
[
This article is part of the Thematic Issue: “Chirality in Separation Science and
Molecular Recognition Honoring Prof. F. Gasparrini.” See the first articles for
this special issue previously published in Volumes 27:9, 27:10, and 27:11.
More special articles will be found in this issue as well as in those to come.]
20
DFT), while a simple approach based on Richardson’s
equations2
1,22
provides an estimate of the metal-centered Near-IR
*
Correspondence to: L. Di Bari, Dipartimento di Chimica, Università di Pisa,
3+
ECD of Yb . The predicted spectra may then be compared with
the experimental data, validating the solution geometry obtained
from paramagnetic nuclear magnetic resonance (NMR)
analysis.2
Via G. Moruzzi 13 I-56124 Pisa, Italy. E-mail: lorenzo.dibari@unipi.it
Received for publication 15 June 2015; Accepted 20 July 2015
DOI: 10.1002/chir.22499
Published online 30 September 2015 in Wiley Online Library
(wileyonlinelibrary.com).
3–25
©
2015 Wiley Periodicals, Inc.

8
58
BERARDOZZI ET AL.
Preparation of KLnL Lanthanide Complexes
2
The synthesis of lanthanide complexes (KLnL
2
) has been optimized for
Yb starting from an already reported procedure for M[Ln(Salen) ] com-
plexes and then extended to the preparation of all the other terms of the
3
+
2
2
8
3
+
3+
3+
3+
3+
3+
series (Tb , Dy , Ho , Er , Tm and Lu ). See the Supporting Infor-
mation for the isolated yields of the various KLnL
2
.
Synthesis of KYbL
2
and General Method for KLnL
2
2
Scheme 1. Preparation of ligand H L.
In a 10 mL two-neck flask, 0.01 g (0.50 mmol) of (H
2
L) were dissolved
in 1 mL of anhydrous diethylether under nitrogen atmosphere. Then
.17 g of Yb(TfO ·6H O (0.25 mmol) was added at once, which resulted
in a turbid suspension. Finally, 1.20 mL of KOH solution (1.10 mmol in
mL of MeOH) was added: an immediate change of color (from off-white
0
3
)
3
2
2
to bright yellow) was appreciated, followed by the precipitation of the
metal chelate. The solution was stirred for 2 h at 80 °C, then it was cooled,
filtered, and the precipitate washed several times with diethyl ether to re-
move traces of unreacted ligand. Then the pale yellow solid was dried
1
(
0.01 g, yield 90%) and characterized through H NMR (see Supporting
Information).
Scheme 2. Preparation of lanthanide complexes with salen-type ligand
KLnL and atom-labeling (see Supporting Information for details and yields).
Computational Section
2
DFT and TD-DFT calculations were run with Gaussian ’0929 with de-
30
fault grids and convergence criteria, using the functionals M06 and
UV-vis spectra were recorded using a Varian Cary 4E UV-vis spectro-
photometer at room temperature and using a cylindrical quartz cell with
an optical path of 0.01 cm.
UV-vis ECD spectra were recorded with a Jasco (Tokyo, Japan) J710 spec-
tropolarimeter at room temperature using the following settings: 0.01 cm op-
tical path; bandwidth 1.0 nm; response 4 s; speed 20 nm/min. All spectra
31
32
CAM-B3LYP. Ahlrichs TZVP basis set was employed for geometry op-
timization and TD-DFT calculations for all atoms except Lu, for which the
33
SDD basis set and MWB60 effective core potential (ECP) were used.
The input structure for DFT geometry optimizations was obtained by
34
the routine PERSEUS by means of NMR data analysis. The number of
excited states considered was 150 for single-molecule calculations. UV
and CD spectra were generated using the program SpecDis by applying
a Gaussian band shape with σ = 0.24 eV exponential half-width.
were recorded in commercial CHCl
The emission spectra were collected only for Tm and Tb , which
3
at concentrations around 2.5 mM.
35
3+
3+
3+
show emission bands respectively in the region of blue (Tm ) and green
3
+
(
Tb ). The spectra were recorded using a Horiba Fluorolog-3 Fluorime-
RESULTS AND DISCUSSION
3+
ter at room temperature and at a concentration of 0.695 mM (Tm ) and
NMR Characterization
3
+
0
3
.496 mM (Tb ) in CHCl as the solvent, using a 1 cm cell. The following
An NMR titration of the deprotonated ligand L in CDCl3
parameters were employed: excitation wavelength 348 nm, integration
time 0.3 s, slits opening 1 nm, 5 accumulations.
with the Ln salt reveals the full disappearance of the free li-
3+
Near-IR ECD spectra were recorded at room temperature on a Jasco
J200D spectropolarimeter, operating between 750 and 1350 nm, modified
by a tandem detector Si/InGaAs with dual photomultiplier amplifier and
using a “semimicro” square cell with optical path of 1 cm. The following
gand resonances at L:Ln = 2:1 stoichiometry. At this point,
1
13
the H and C-NMR spectra (CDCl ) show a unique set of
3
eight (relatively) narrow resonances, which confirms KLnL2
as the main species in solution, characterized by an effective
3+
3+
set of parameters was employed: sensitivity 1 m°/cm (Yb , Er ) and
D -symmetry.
2
3
+
sensitivity 20 m°/cm (Tm ); scan speed 2 cm/min; time constant 1 sec;
bandwidth 3.2 nm. A 1 cm quartz cell was used and for each sample 20 ac-
cumulations were collected (averaged by means of a Jasco DP-500 N data
Except for La , Gd , and Lu ions, all other Ln3+ ions
3+
3+
3+
possess unpaired electrons and this paramagnetism induces
remarkable shifts of nuclear resonances (Lanthanide In-
duced Shift or LIS effect) with respect to the diamagnetic
terms (lutetium derivative in this study). In the principal sys-
tem of Ln magnetic susceptibility tensor (χ ), under the
assumption that the unpaired electron(s) cloud can be effec-
tively described as a point (i.e., that the 4f-electron radial dis-
tribution is small compared to the Ln-H or Ln-C distances),
3
processor). Solutions (1.3 mM) were prepared in reagent-grade CHCl .
Synthesis of H
2
L
3+
Ln
2
The salen-type ligand H L was prepared by condensation of the di-
amine with the salicaldehyde in ethanol heated at reflux (Scheme 1),
following a reported literature procedure.2
6,27
A 100 mL three-neck flask
equipped with a mechanical stirrer, a reflux condenser, and a dropping
funnel was loaded with 0.35 g of 2-hydroxybenzaldehyde (1, 2.90 mmol),
16,18
one can write well-established relationships
0
.83 g of K
was stirred until complete dissolution of the solids, then ethanol
15 mL) was added. The resulting turbid mixture was stirred at reflux
2
CO
3
(6.00 mmol) and deionized water (4 mL). The mixture
exp
dia
para
dia
FC
PCS
δ
δ
δ
¼ δi þ δij ¼ δi þ δij þ δij
(1)
(2)
ij
(
for 2 h, and then a solution of 1.23 g of (1R, 2R)-1,2-diphenylethane-1,2-
diamine (2, 5.80 mmol) in 7 mL of EtOH was added dropwise over
Α hSZ i
FC
ij
i
j
¼ ꢀ
¼ F hS i
i
Z
j
ℏ γ B
I
0
3
0 min. The obtained yellow slurry was stirred at reflux for 2 h and then
2
2
2
cooled at room temperature. Subsequently, water (150 mL) was added
and the solution was cooled at 0–5 °C: this allowed the crude product
to precipitate within 2 h. The product was then collected by filtration and
washed with ethanol. The crude solid was redissolved in CH
washed with water (2 × 7.5 mL) and brine (2.5 mL), and the solvent
was evaporated affording 2.17 g of 2,2′-(((1R, 2R)-1,2-diphenylethane-1,2-
diyl)-bis(azanylylidene))-bis(metanylylidene))-diphenol (H
solid (isolated yield = 89%) which was used without further purification
3
cos θ ꢀ 1
sin θ sin Ω ꢀ 1
PCS
ij
i
i
i
¼ DI;j
þ DII;j
3
r
3
r
i
i
¼
DI;jG þ DII;jH
(3)
2 2
Cl
(12 mL),
i
i
in which the index i-th refers to the considered resonant nu-
cleus and the j-th index to the lanthanide; δ
dia
is the chemical
2
L) as a yellow
ij
3+
3+
shift in a reference diamagnetic compound ( j = La or Lu );
1
FC
PCS
(for the H-NMR see Supporting Information).
δ ij is the Fermi contact shift and δ ij is the pseudocontact
Chirality DOI 10.1002/chir

SOLUTION STRUCTURE OF SALEN-TYPE LANTHANIDE COMPLEXES
859
shift; A /ħ is the hyperfine coupling constant; γ is the gyro-
1H-NMR spectrum of a complex with strongly shifted
i
1
magnetic ratio of the observed nucleus and B is the applied
resonances: taking the distances r from a roughly optimized
0
i
magnetic field; hS i is the expectation value of S operator
(by molecular mechanics, MM) structure, one can seek the
best linear trend in a ρ1,ij vs. ri plot. In this specific case,
z j
z
para
ꢀ6
for the specific lanthanide; G and H are geometrical factors
i
i
of the i-th nucleus, dependent on (r , θ , Ω ), its spherical co-
because of the effective D symmetry, this preliminary opera-
tion can be performed on a model structure including only ½
i
i
i
2
ordinates in a polar system centered on the metal ion; D
I,j
Ln
and DII, j are respectively the axial and rhombic term of χ
.
of the salen ligand. The result for KYbL starting with an MM
2
Paramagnetism enhances longitudinal, ρ , and transverse,
ρ2, relaxation rates according to
model of the complex is shown in Figure 1.
With the aid of H relaxation rates, of homo- and
1
1
8
1
heteronuclear correlation spectra, and following a protocol
exp
ð1;2Þ;ij
dia
para
ð1;2Þ;ij
16,19,36,37
ρ
¼ ρ
þ ρ
(4)
ð1;2Þ;ij
based on eqs. (1–5) described elsewhere,
we ob-
tained the complete assignment of the NMR spectrum of
where the superscripts dia and para refer to diamagnetic and
paramagnetic contributions, similarly to what we said above
for the shift equations. Grossly estimating the term
KYbL2.
Linearity of δi
tween the Yb and the Ln-compounds, which is indeed
the case for all systems from Tb to Tm . This condition en-
sures that separation of Fermi contact and pseudocontact
shifts can be obtained through the method described in previ-
para,Yb
vs. δipara,Ln reveals isostructurality be-
3+
37
dia
1
ꢀ1
ρ
= 1 s , we can write
3+
3+
K
para
exp
1;j
6
i
ρ
¼ ρ1;ij ꢀ 1 ¼
(5)
1
;ij
r
37
ous work, with the results displayed in Tables 1 and 2.
in which K is constant for all nuclei of the j-th lanthanide
1
complex. Equation 5 is particularly helpful for assigning the
From PCSs to PERSEUS Structure
Once isostructurality in solution has been demonstrated
and pseudocontact shifts are available, one can use our rou-
tine PERSEUS19 to determine the accurate solution geome-
try of KLnL . To this end, in a first run we used only the
2
1
H data obtaining an agreement factor (see the caption to
Figure 2) A.F. = 1%, which is completely satisfactory. Second,
we introduced also the 13C paramagnetic shifts for KYbL , on
2
the assumption that the contact contribution for this ion is
negligible, as indeed witnessed by the 1H data shown in
Table 1. The resulting A.F. = 7% is extremely good. The
3
+
principal values of magnetic anisotropy for Yb , D and D ,
I
II
3
are respectively –3980.19 and –1602.05 ppm · Å (see eq. 3
para
iꢀ6
Fig. 1. Longitudinal relaxation rate ρ1,ij
vs. r
for KYbL
2
complex.
in the above section).
para
PCS
FC
TABLE 1. Experimental paramagnetic shifts δi,Ln
, pseudocontact δi,Ln , and Fermi Contact δi,Ln contributions for KLnL
2
series (in ppm)
3
+
3+
3+
(
a)
Tb
Dy
Ho
1
para
PCS
FC
para
PCS
FC
para
PCS
FC
H
δ
δ
δ
δ
δ
δ
δ
δ
δ
3
5
6
i
bz
o
27.76
38.54
8.22
43.38
50.46
32.69
85.83
ꢀ11.48
ꢀ10.38
ꢀ17.55
ꢀ12.24
ꢀ17.67
4.50
44.19
53.89
26.24
89.43
54.10
62.93
40.77
ꢀ10.30
ꢀ9.31
ꢀ15.74
ꢀ10.98
ꢀ15.85
4.03
21.66
26.00
12.54
27.94
32.50
21.05
ꢀ8.16
ꢀ7.38
ꢀ12.48
ꢀ8.71
ꢀ12.57
3.20
81.58
107.04
ꢀ161.19
ꢀ121.94
ꢀ43.82
ꢀ36.00
45.95
55.27
ꢀ159.90
ꢀ79.27
ꢀ28.74
ꢀ23.86
ꢀ129.25
ꢀ97.78
ꢀ35.13
ꢀ28.87
ꢀ168.58
ꢀ128.13
ꢀ45.49
ꢀ36.65
ꢀ93.11
ꢀ61.84
ꢀ22.01
ꢀ17.77
ꢀ83.24
ꢀ62.97
ꢀ22.63
ꢀ18.59
m
p
1.86
1.87
1.66
1.67
1.32
1.33
3
+
3+
3+
3+
(
b)
Er
Tm
Yb
Lu
1
para
PCS
FC
para
PCS
FC
para
PCS
FC
dia
H
δ
δ
δ
δ
δ
δ
δ
δ
δ
δ
3
5
6
i
bz
o
ꢀ13.28
(*)
(*)
ꢀ22.17
16.47
24.25
8.83
ꢀ8.93
(*)
(*)
ꢀ17.66
26.60
20.12
7.23
ꢀ5.55
(*)
(*)
ꢀ5.91
ꢀ8.54
2.17
0.90
0.90
ꢀ21.75
ꢀ16.67
(*)
ꢀ40.29
51.12
41.73
15.00
12.50
ꢀ18.42
ꢀ21.43
(*)
ꢀ36.45
54.90
41.53
14.92
12.26
ꢀ2.96
ꢀ2.68
(*)
ꢀ3.16
ꢀ4.56
1.16
ꢀ8.36
ꢀ8.40
ꢀ3.40
ꢀ15.71
23.46
21.09
7.55
ꢀ8.44
ꢀ9.82
ꢀ6.36
ꢀ16.70
25.15
19.03
6.84
ꢀ0.93
ꢀ0.85
ꢀ1.43
ꢀ1.00
ꢀ1.44
0.37
6.47
6.94
6.51
7.52
6.04
7.4
m
p
0.48
0.48
0.15
0.15
7.29
7.18
7.37
5.94
6.14
5.62
dia
3+
In the last column the diamagnetic shifts δi,Ln for Lu are also reported. *Values are not experimentally available.
Chirality DOI 10.1002/chir

8
60
BERARDOZZI ET AL.
1
3
3+
3+
TABLE 2. Total observed C shifts for Lu and Yb
are allied with the electronic transitions centered on the
ligand moieties, each containing two salicylidiimine moieties
and two phenyl rings. Since ECD spectra are very sensitive
to the structure, the consistent profile observed for all com-
plexes further confirms the isostructurality for all the Ln3+
species considered, at least in terms of relative orientation
between the various chromophores.
1
3
obs, Lu
obs, Yb
C
δ
δ
3
5
6
i
121.02
101.69
86.07
106.79
100.42
(*)
139.63
125.69
122.37
132.74
134.79
162.49
74.8
130.08
128.65
127.05
bz
o
m
p
Ligand-Centered ECD Calculations
TD-DFT is currently recognized as one of the methods with
the best cost/efficiency compromise to simulate the UV-vis
and CD spectra of medium-size transition metal com-
*
Values are not experimentally available.
20,41–43
plexes.
The isostructurality we observed along the se-
ries allows us to extrapolate the geometry and to extend it
to the Lu3+ derivative, which is a closed-shell system, amena-
ble to a TD-DFT/DFT protocol to calculate the ligand-
In this structure the salen ligand is twisted (NCCN dihedral
angle) by –54°, which is close to the value found on a
heteroleptic Dy complex containing the same ligand.
3+
15
44
centered ECD spectrum .
Starting from the PERSEUS structure, this latter was
reoptimized with DFT using the M06 functional and TZVP ba-
sis set for all atoms except Lu, for which the SDD basis set
and MWB60 effective core potential (ECP) were used (see
UV-vis and ECD Spectra
The UV–vis spectrum of the free ligand H L (see
Supporting Information) exhibits two absorption peaks at
2
33
Supporting Information). The final structure possesses D2-
2
48 nm and 312 nm, due to the transitions of conjugated
symmetry (in agreement with NMR data) and Lu-O e Lu-N
distances equal respectively to 2.445 e 2.700 Å (in keeping
38–40
cromophores.
UV-vis absorption and CD spectra for the salen-type com-
plexes are shown in Figures 3 and 4. Compared with the ab-
sorption peak of the ligand, one can note a bathochromic
shift by 20 nm, indicating the deprotonation of the ligand
45
with the literature for similar cases). No axial coordination
or solvent effects were considered in the geometry optimiza-
tion and in the following ECD calculations. The DFT-
optimized geometry is reported in Figure 5 and appears very
similar to the NMR one, confirming our structural determina-
tion (R.M.S. deviation = 0.21 Å; see distance comparison in the
Supporting Information).
ECD calculations were run on the DFT-optimized structure
with the TD-DFT method using the CAM-B3LYP functional
and the same set of basis and ECP discussed above, and
the result is shown in Figure 6. The nice agreement with
the experimental ECD spectrum confirms the quality of the
NMR-derived and DFT-optimized structures, in terms of
interchromophoric arrangement.
3
+
and its coordination to Ln ions.
Comparing the different Ln-adducts along the series, the
absorption spectra show consistent similarities in the
2
00–330 nm range, while some differences can be found in
3+
3+
the 330–450 nm region for Er and Tb . In the UV region there
are two strong bands at 260 nm and 220 nm. Above 300 nm, two
weaker and broader absorptions are observed around 400 nm
3+
3+
3+
3+
3+
and 320 nm for Dy , Ho , Lu , Tm , and Yb . In this region,
the behavior of Er3+ and Tb derivatives appears different, as
the longer-wavelength band is red-shifted by 50 nm in compari-
son with the other terms of the series.
3+
The ligand-centered UV-vis ECD spectra show no varia-
tion along the series and several consistent features may
be observed (approximate wavelength in nm, sign and
strength are indicated): 400 (+, weak); 370 (ꢀ, medium);
Near-IR Electronic CD
Finally, we took advantage of the Near-IR ECD spec-
trum associated with the monoelectronic Yb transitions
F7/2 → F5/2. The Near-IR ECD spectrum of the Yb
complex, displayed in Fig. 7 (dashed blue line), consists
3+
2
2
17
3+
3
50 (+, medium ); 330 (ꢀ,weak ); 270 (ꢀ, medium); 260
(
+, strong); 230 (ꢀ, strong); 210 (+, strong). These bands
pcs,calc
Fig. 2. Solution structure of KYbL
2
, as determined through the analysis of paramagnetic NMR data. The agreement factor is defined as A.F. = [(Σ
i
(‹δ
i
›
pcs,exp 2
pcs,exp 2 1/2
ꢀ
δ
i
) /Σ
i
(δ
i
) )]
.
Chirality DOI 10.1002/chir

SOLUTION STRUCTURE OF SALEN-TYPE LANTHANIDE COMPLEXES
861
2 3
Fig. 3. Ligand-centered UV-vis spectra of KLnL complexes (CHCl solution).
Fig. 6. TD-DFT calculated (continuous red line; red shift = +30 nm;
σ = 0.024 eV) and experimental (dashed blue line) ECD spectra of KLuL
complex.
2
Fig. 4. Ligand-centered ECD spectra of KLnL
2
3
complexes (CHCl solution).
Fig. 7. Comparison between calculated (continuous red line) and experi-
mental (dashed blue line) Near-IR CD spectra of KYbL complex.
2
Lorentzian function with Δν = 50 cm 1. For details on the pro-
cedure, see Ref. 20. The result, shown in Figure 7, is very sat-
isfactory: with the exception of a small red-shift for the
highest-energy band, the calculated spectrum matches very
well the experimental one, which further validates our struc-
ture, this time in terms of crystal field geometry around the
lanthanide ion.
ꢀ
2ꢀ
Currently, we are not able to compute other lanthanide-
centered ECD spectra and consequently we only report the
experimental NIR-ECD data of Er3+ and Tm (see Supporting
Information).
Fig. 5. Comparison between DFT-refined structure of LuL (hue in blue)
2
and PERSEUS output for KYbL (hue in pink).
3+
of an intense and broad positive band at 970 nm and a weak
one at 960 nm.
Emission Spectra
To simulate the same spectrum, we used Richardson’s
equations, a simplified electrostatic model based on charge
and polarizability of atoms and groups of an organic ligand
Upon irradiation at 348 nm, Tm3+ and Tb3+ derivatives dis-
play blue and red luminescence, respectively. Their emission
spectra are shown in Figures 8 and 9. We can recognize a
broad band in the range 400–480 nm, due to the ligand fluo-
rescence. In addition, we can distinguish the typical narrow
2
2
around a lanthanide ion. Charge and polarizability were
evaluated respectively by standard natural bond orbital
4
6
3+
(
NBO) analysis (from DFT calculations) and the atom-
bands associated to f-f Ln transitions, which are clearly sen-
4
7
3+
based method by Miller. The CD spectrum was simulated
weighting each transition by the Boltzmann population of
the starting crystal-field sublevel and applying to each line a
sitized by the ligand. The Tm compound displays blue lumi-
nescence when irradiated at 365 nm and its emission
spectrum shows only two narrow bands centered respectively
Chirality DOI 10.1002/chir

8
62
BERARDOZZI ET AL.
UV-vis one to the (relative) orientation of the aromatic
ligands, while the NIR one to the crystal field geometry
around the lanthanide ion. Therefore, a combined approach
based on both methods allows a safer structural assignment
3+
than any single method alone. Emission spectra of Tb and
3+
Tm derivatives display the expected sharp lines typical for
these two metal ions, which emerge over a broad background
of ligand-centered emissions.
ACKNOWLEDGMENTS
We thank Dr. A. Pucci for help in the measurements of the
emission spectra and Dr. D. Padula for helpful discussions.
SUPPORTING INFORMATION
Additional supporting information may be found in the
online version of this article at the publisher’s web-site.
3+
Fig. 8. Photoluminescence of Tb ion in KTbL
2
complex.
LITERATURE CITED
1
2
. Shibasaki M, Kanai M, Matsunaga S, Kumagai N. Recent progress in
asymmetric bifunctional catalysis using multimetallic systems. Acc Chem
Res 2009;42:1117–1127.
. Robinson JR, Fan X, Yadav J, Carroll PJ, Wooten AJ, Pericàs MA, Schelter
EJ, Walsh PJ. Air- and water-tolerant rare earth guanidinium BINOLate
complexes as practical precatalysts in multifunctional asymmetric cataly-
sis. J Am Chem Soc 2014;136:8034–8041.
3
4
5
. Di Bari L, Di Pietro S, Pescitelli G, Tur F, Mansilla J, Saá JM. [Ln
(
binolam)3](OTf)3, a new class of propeller-shaped lanthanide(III) salt
complexes as enantioselective catalysts: structure, dynamics and mecha-
nistic insight. Chem Eur J 2010;16:14190–14201.
. Carr R, Di Bari L, Lo Piano S, Parker D, Peacock RD, Sanderson JM. A
chiral probe for the acute phase proteins alpha-1-acid glycoprotein and
alpha-1-antitrypsin based on europium luminescence. Dalton Trans
2012;41:13154–13158.
. Montgomery CP, Murray BS, New EJ, Pal R, Parker D. Cell-penetrating
metal complex optical probes: targeted and responsive systems based
on lanthanide luminescence. Acc Chem Res 2009;42:925–937.
3
+
6. Dickins RS, Aime S, Batsanov AS, Beeby A, Botta M, Bruce JI, Howard
JAK, Love CS, Parker D, Peacock RD, Puschmann H. Structural, lumines-
cence, and NMR studies of the reversible binding of acetate, lactate, cit-
rate, and selected amino acids to chiral diaqua ytterbium, gadolinium,
and europium complexes. J Am Chem Soc 2002;124:12697–12705.
2
Fig. 9. Photoluminescence of Tm ion in KTmL complex.
1
3
1
3
3+
at 380 nm ( D → H ) and 390 nm ( D → H ). The Tb
compound shows green luminescence and we can recognize
at least five distinct transitions: (a) D → F (380 nm, weak);
2
4
2
5
7
. Zinna F, Giovanella U, Di Bari L. Highly circularly polarized electrolu-
minescence from chiral europium complex. Adv Mater 2015;27:
791–1795.
5
7
3
6
a
5
7
5
7
1
(
b) D → F (490 nm, strong); (c) D → F (540 nm,
4 6 4 5
5
7
5
7
8
. Zinna F, Di Bari L. Lanthanide circularly polarized luminescence: bases
and applications. Chirality 2015;27:1–13.
strong); (d) D → F (575 nm, weak); (e) D → F
4
4
4
3
(
610 nm, weak).
9
. Fordham S, Wang X, Bosch M, Zhou H-C. Lanthanide metal-organic
frameworks: syntheses, properties, and potential applications. In:
Cheng P editor, Structure and bondings. Springer International Pub-
lishing: Switzerland; 2015.p1–27.
CONCLUSION
The salen-type ligand H L is very well suited to promptly
2
10. Buenzli J-CG, Eliseeva SV. Intriguing aspects of lanthanide luminescence.
obtain stable and inert complexes with late lanthanides.
Their structure in solution was determined by means of
Chem Sci 2013;4:1939–1949.
11. Sun L, Qiu Y, Liu T, Feng J, Deng W, Shi L. Visible-near-infrared lumines-
cent lanthanide ternary complexes based on beta-diketonate using visible-
light excitation. Luminescence 2015. DOI:10.1002/bio.2860.
3+
paramagnetic NMR and remains conserved from Tb to
3
+
Yb . We used two widely different computational ap-
proaches to account for the ECD spectra in the UV, which
is due to ligand-centered electronic transitions, and—for
the Yb3+ compound—in the Near-IR, around 1000 nm, allied
to the magnetically allowed transition of this ion. In the for-
mer case, we used TD-DFT; in the latter we employed
Richardson’s equations, based on a simplified electrostatic
1
2. Dong B, Cao B, He Y, Liu Z, Li Z, Feng Z. Temperature sensing and
in vivo imaging by molybdenum sensitized visible upconversion lumines-
cence of rare-earth oxides. Adv Mater 2012;24:1987–1993.
1
3. Ballistreri FP, Gentile S, Pappalardo A, Tomaselli GA, Pradhan S, Di Bari
L. Reversible mutarotation in a macrocyclic ytterbium complex. Chem
Eur J 2011;17:322–328.
14. Maudoux N, Roisnel T, Dorcet V, Carpentier J, Sarazin Y. Chiral (1,2)-
diphenylethylene-salen complexes of triel metals: coordination patterns
and mechanistic considerations in the isoselective ROP of ;actide. Chem
Eur J 2014;20:6131–6147.
3+
model describing the interaction between the ligand and Ln .
The match between computed and experimental spectra
demonstrates that the quality of our structure is completely
satisfactory. It is interesting to observe that the two spectral
windows are sensitive to different structural portions, the
Chirality DOI 10.1002/chir
1
5. Yao M, Zheng Q, Gao F, Li Y, Song Y, Zuo J. Field-induced slow magnetic
relaxation in chiral seven-coordinated mononuclear lanthanide com-
plexes. Dalton Trans 2012;41:13682–13690.

SOLUTION STRUCTURE OF SALEN-TYPE LANTHANIDE COMPLEXES
863
1
6. Berardozzi R, Di Bari L. A simple and general method to determine reli-
able pseudocontact shifts in lanthanide complexes. Inorg Chem
2
30. Zhao Y, Truhlar D. The M06 suite of density functionals for main group
thermochemistry, thermochemical kinetics, noncovalent interactions, ex-
cited states, and transition elements: two new functionals and systematic
testing of four M06 functionals and 12 other functional. Theor Chem
Acc 2008;119:525–545.
013;52:11514–11518.
7. Buenzli J-CG, Eliseeva SV. Basics of lanthanide photophysics. Lan Lum
011;7:1–45.
1
1
1
2
2
3
1. Yanai T, Tew DP, Handy NC. A new hybrid exchange-correlation func-
tional using the Coulomb-attenuating method (CAM-B3LYP). Chem Phys
Lett 2004;393:51–57.
8. Bertini I, Luchinat C. NMR of paramagnetic substances, Chapters I-III.
Coord Chem Rev 1996;150:1–296.
9. Di Bari L, Salvadori P. Solution structure of chiral lanthanide complexes.
Coord Chem Rev 2005;249:2854–2879.
0. Autschbach J. Computing chiroptical properties with first-principles theo-
retical methods: Background and illustrative examples. Chirality 2009;21:
E116–E152.
1. Richardson FS, Faulkner TR. Optical activity of the f–f transitions in trigo-
nal dihedral (D3) lanthanide(III) complexes. I Theory J Chem Phys
32. Schäfer A, Huber C, Ahlrichs R. Fully optimized contracted Gaussian ba-
sis sets of triple zeta valence quality for atoms Li to Kr. J Chem Phys
1994;100:5829–5835.
3
3. Krauss M, Stevens WJ. Effective potentials in molecular quantum chemis-
try. Annu Rev Phys Chem 1984;35:357–385.
2
2
2
3
4. Di Bari L, Pintacuda G, Ripoli S, Salvadori P. Structure of metal adducts of
anthracyclines probed by absorption, circular dichroism and paramag-
netic NMR. Magn Reson Chem 2002;40:396–405.
1
982;76:1595–1607.
2. Berardozzi R, Di Bari L. Optical activity in the near IR: the λ=980 nm mul-
3
+
3
3
3
5. Bruhn T, Schaumlöffel A, Hemberger Y, Bringmann G. SpecDis: Quanti-
fying the comparison of calculated and experimental electronic circular
dichroism spectra. Chirality 2013;25:243–249.
6. Di Bari L, Pescitelli G, Sherry AD, Woods M. Structural and chiroptical
properties of the two coordination isomers of YbDOTA-type complexes.
Inorg Chem 2005;44:8391–8398.
tiplet of chiral Yb complexes. ChemPhysChem 2015. DOI:10.1002/
cphc.201500355.
3. Krohn K, Kock I, Elsasser B, Florke U, Schulz B, Draeger S, Pescitelli
G, Antus S, Kurtan T. New natural products from the endophytic fun-
gus Ascochyta sp. from Meliotus dentatus. Eur
007;45:1123–1129.
J Org Chem
2
7. Di Pietro S, Lo Piano S, Di Bari L. Pseudocontact shifts in lanthanide com-
plexes with variable crystal field parameters. Coord Chem Rev 2011;255:
2
2
2
2
4. Hussain H, Krohn K, Florke U, Schulz B, Draeger S, Pescitelli G, Antus S,
Kurtan T. Absolute configuration of globosuxanthone A and secondary
metabolites from Microdiplodia sp. —A novel solid-state CD/TDDFT ap-
proach. Eur J Org Chem 2007;12:292–295.
5. Krick A, Kehraus S, Gerhauser C, Klimo K, Nieger M, Maier A, Fiebig HH,
Atodiresei I, Raabe G, Fleischhauer J, Konig GM. Potential cancer chemo-
preventive in vitro activities of monomeric xanthone derivatives from the ma-
rine algicolous fungus Monodictys putredinis. J Nat Prod 2007;70:353–360.
6. Krohn K, Farooq U, Florke U, Schulz B, Draeger S, Pescitelli G, Salvadori
P, Antus S, Kurtan T. Secondary metabolites isolated from an endophytic
Phoma sp. Absolute configuration of tetrahydropyrenophorol using the
solid-state TDDFT CD methodology. Eur J Org Chem 2007;13:3206–3211.
7. Larrow J, Jacobsen E, Gao Y, Hong Y, Nie X, Zepp C. A practical method for
the large-scale preparation of [N,N’-Bis(3,5-di-tertbutylsalicylidene)-1,2-
cyclohexanediaminato(2-)]manganese(II) chloride, a highly enantiose-
lective epoxidation catalyst. J Org Chem 1994;59:1939–1942.
2810–2820.
38. Ghosh T, Mondal B, Sutradhar M, Mukherjee G, Drew MGB. Synthesis,
structure, solution chemistry and the electronic effect of para substituents
on the vanadium center in a family of mixed-ligand [VVO (ONO)(ON)]
complexes. Inorg Chim Acta 2007;360:1753–1761.
39. Dong W, He X, Yan H, Lv Z, Chen X, Zhao C, Tang X. Synthesis, structural
characterization and solvent effect of copper(II) complexes with a varia-
tional multidentate salen-type ligand with bisoxime groups. Polyhedron
2009;28:1419–1428.
40. Dong W, Duan J, Guan Y, Shi J, Zhao C. Synthesis, crystal structure and
spectroscopic behaviors of Co(II) and Cu(II) complexes with salen-type
bisoxime ligands. Inorg Chim Acta 2009;362:1129–1134.
41. Berova N, Woody R, Polavarapu P, Nakanishi K. Comprehensive chiropti-
cal spectroscopy. Wiley: New York; 2012.p593–642.
2
2
8. Dutt N, Nag K. Chemistry of Lanthanos-XVII: Bis-salicylaldehyde
ethylenediamine and bis-salicylaldehyde o-phenylenediamine complexes
of rare-earths. J Inorg Nucl Chem 1968;30:2493–2499.
42. Cox H, Stace A. Recent advances in the visible and UV spectroscopy of
metal dication complexes. Int Rev Phys Chem 2010;29:555–588.
4
3. Dragna J, Pescitelli G, Tran L, Lynch V, Anslyn E, Di Bari L. In situ assem-
bly of octahedral Fe(II) complexes for the enantiomeric excess determina-
tion of chiral amines using CD spectroscopy. J Am Chem Soc 2012;134:
4398–4407.
9. Frisch MJ, Trucks GW, Schlegel HB, Scuseria GE, Robb MA, Cheeseman
JR, Scalmani G, Barone V, Mennucci B, Petersson GA, Nakatsuji H,
Caricato M, Li X, Hratchian HP, Izmaylov AF, Bloino J, Zheng G,
Sonnenberg JL, Hada M, Ehara M, Toyota K, Fukuda R, Hasegawa J,
Ishida M, Nakajima T, Honda Y, Kitao O, Nakai H, Vreven T, Montgomery
JA, Peralta JE, Ogliaro F, Bearpark M, Heyd JJ, Brothers E, Kudin KN,
Staroverov VN, Kobayashi R, Nomand J, Raghavachari K, Rendell A,
Burant JC, Iyengar SS, Tomasi J, Cossi M, Rega N, Millam JM, Klene
M, Knox JE, Cross JB, Bakken V, Adamo C, Jaramillo J, Gomperts R,
Stratmann RE, Yazyef O, Austin AJ, Cammi R, Pomelli C, Ochterski JW,
Martin RL, Morokuma K, Zakrzewski VG, Voth GA, Salvador P,
Dannenberg JJ, Dapprich S, Daniels AD, Farkas O, Foresman JB, Ortiz
JV, Cioslowski J, Dox DJ. Gaussian 09, Revision C.01. Gaussian, Inc.:
Wallingford. CT; 2009.
4
4. You L, Pescitelli G, Anslyn E, Di Bari L. An exciton-coupled circular di-
chroism protocol for the determination of identity, chirality, and enantio-
meric excess of chiral secondary alcohols. J Am Chem Soc 2012;134:
7117–7125.
4
5. Huang C. Rare earths coordination chemistry: fundamental and applica-
tions. Wiley (Asia): Peking; 2010.p137–193.
4
6. Foster J, Weinhold F. Natural hybrid orbitals. J Am Chem Soc 1980;102:
7211–7215.31.
47. Miller K. Additivity methods in molecular polarizability. J Am Chem Soc
1990;112:8533–8547.
Chirality DOI 10.1002/chir