Luminescent lanthanide complexes with phosphoramide and arylphosphonic diamide ligands

Article abstract of DOI:10.1007/s11696-019-00799-6

The sensitization of Eu(III) luminescence by the phosphoramide and arylphosphonic diamide ligands OP(NMe₂)₂Ind, OP(NMe₂)₂Cbz, OP(NMe₂)₂Ph, OP(NMe₂)₂(1-Naph) and OP(NMe

Full text of DOI:10.1007/s11696-019-00799-6

Chemical Papers
https://doi.org/10.1007/s11696-019-00799-6
ORIGINAL PAPER
Luminescent lanthanide complexes with phosphoramide
and arylphosphonic diamide ligands
Marco Bortoluzzi1,2 · Alberto Gobbo1 · Alberto Palù1 · Francesco Enrichi1,3 · Alberto Vomiero1,3
Received: 12 February 2019 / Accepted: 23 April 2019
© Institute of Chemistry, Slovak Academy of Sciences 2019
Abstract
The sensitization of Eu(III) luminescence by the phosphoramide and arylphosphonic diamide ligands OP(NMe2)2Ind,
OP(NMe2)2Cbz, OP(NMe2)2Ph, OP(NMe2)2(1-Naph) and OP(NMe2)2(2-Naph) (Ind=indol-1-yl; Ph=phenyl; Cbz=carba-
zol-9-yl; 1-Naph=naphtalen-1-yl; 2-Naph=naphtalen-2-yl) was verifed by coordination to the [Eu(NO3)3] metal fragment.
The emission spectra of the corresponding complexes showed only the 5D0 →7FJ transitions of the metal centre, with the
exception of the carbazolyl derivative. Some of the ligands were also able to sensitize Tb(III) luminescence, in agreement
with the triplet state energies estimated from the phosphorescence spectra of the analogous Gd(III) nitrates. On the basis
of the photoluminescence results achieved using nitrate as ancillary ligand, heptacoordinate Eu(III) complexes having gen-
eral formula [Eu(β-dike)3L] (β-dike=dibenzoylmethanate, tenoyltrifuoroacetonate; L=phosphoramide or arylphosphomic
diamide ligand) were prepared and characterized. All the complexes exhibited bright red emission upon excitation with
near-UV and violet-blue light, with intrinsic quantum yields ranging between 18 and 36%.
Keywords Europium(III) · Gadolinium(III) · Terbium(III) · Photoluminescence · Phosphoramide · Arylphosphonic diamide
Introduction
and lanthanide ketyl radicals (Hou and Wakatsuki 1997).
Moreover, hmpa plays a crucial role also in other lanthanide-
mediated organic transformations, such as aldimines dimeri-
zation (Jin et al. 2001).
Hexamethylphosphoramide (hmpa) has been widely used
as ligand in the chemistry of lanthanide elements. Organic
reactions mediated by Ln(II) can be carried out in the pres-
ence of hmpa to enhance the reactivity (Inanaga et al. 1987;
Molander 1994). The sterically demanding hmpa ligand is
able to stabilize divalent lanthanide complexes (Bao et al.
2006; Hou and Wakatsuki 1994, 1995; Hou et al. 1996; Hou
et al. 1997; Mashima et al. 1996; Yoshimura et al. 1995)
Because of the hard Lewis character of trivalent lan-
thanide ions (Cotton 2006), hmpa has been considered as
O-donor ligand towards these metal centers. The behavior
of Ln(III) cations in hmpa solution has been investigated
(Ishiguro 1997), and halide, trifate and perchlorate hmpa
complexes have been isolated and characterized (Donoghue
and Peters 1969; Donoghue et al. 1969; Petriček et al. 2000;
Petriček 2005a, b; Scholer and Merbach 1975; Tsuruta et al.
2003). The ligand hmpa is present in the coordination sphere
of carboxylate and picrate derivatives (Bombieri et al. 2001;
Kuzmina et al. 1993; Silva et al. 1995; Silva Oliveira et al.
2000) and in some Ln(III) organometallic derivatives (Cend-
rowski-Guillaume et al. 2001, 2003; Sun et al. 2009). The
X-ray structure of the β-diketonate Eu(III) heptacoordinate
compound [Eu(dbm)3(hmpa)] (dbm = dibenoylmethanate)
has been reported (Panin et al. 1992). Nitrato complexes
of Eu(III) with hmpa exhibit triboluminescence (Bukvet-
skii and Kalinovskaya 2017; Bukvetskii et al. 2017; Bün-
zli and Wong 2018) and the luminescence of Tb(III) and
Gd(III) nitrato complexes with hmpa and dbm has been
This work was presented at the International Conference on
Coordination and Bioinorganic Chemistry held in Smolenice on
June 2–7, 2019.
* Alberto Gobbo
alberto.gobbo93@gmail.com
1
Dipartimento di Scienze Molecolari e Nanosistemi,
Università Ca’ Foscari Venezia, Via Torino 155,
30170 Mestre, VE, Italy
2
Consorzio Interuniversitario Reattività Chimica e Catalisi
(CIRCC), via Celso Ulpiani 27, 70126 Bari, Italy
3
Division of Materials Science, Department of Engineering
Science and Mathematics, Luleå University of Technology,
971 87 Luleå, Sweden
Vol.:(0123456789)
1 3

Chemical Papers
studied (Silva et al. 2013). The complexes [Ln(depma)
(NO3)3(hmpa)2] (depma = 9-diethylphosphono-methylan-
thracene; Ln = Dy, Gd) are recent examples of magneto-
optic materials (Huang et al. 2018).
was heated to 80 °C until complete dissolution of the oxide.
Water was then evaporated at reduced pressure and the resi-
due was dissolved in ethanol (30 mL). The solution was fl-
tered and taken to dryness under high vacuum. The resulting
solid was further dried overnight under vacuum at 110 °C in
the presence of P4O10.
Luminescent lanthanide(III) complexes fnd widespread
use in advanced technologies (Binnemans 2009; Bünzli and
Piguet 2005; Carlos et al. 2011; Bünzli and Eliseeva 2013;
Bünzli 2015). Among the most intriguing applications have
to be cited: electronic devices (Kuriki and Koike 2002;
Rocha et al. 2011), electroluminescent materials (Kido and
Okamoto 2002; Xu et al. 2015), photovoltaics (Zhang et al.
2017), biological probes and multifunctional sensors (Allen-
dorf et al. 2009; Bünzli 2010; Eliseeva and Bünzli 2010;
Li and Li 2018; Zheng et al. 2018). Recent developments
include multifunctional compounds, such as luminescent
single-molecule magnets based on lanthanides (Guo et al.
2013, 2014; Jia et al. 2019).
All the ligand syntheses were carried out under inert
atmosphere (nitrogen) using standard Schlenk techniques.
The preparations of the lanthanide complexes were car-
ried out under inert atmosphere, working in a glove-box
(MBraun Labstar with MB 10 G gas purifer) flled with N2
and equipped for inorganic syntheses.
N,N,N’,N’-tetramethyl-P-indol-1-ylphosphonic diamide,
OP(NMe2)2Ind, and N,N,N’,N’-tetramethyl-P-carbazol-
9-ylphosphonic diamide, OP(NMe2)2Cbz, were synthesized
on the basis of the methods proposed by Van den Bos et al.
(1961) and Katritzky et al. (1988). Indole and carbazole
were deprotonated in THF with potassium tert-butoxide and
then reacted with a stoichiometric amount of OP(NMe2)2Cl
at room temperature in THF. The ligand N,N,N’,N’-tetra-
methyl-P-phenylphosphonic diamide, OP(NMe2)2Ph, was
obtained by reacting OPCl2Ph with an excess of NHMe2, as
previously described by Keat and Shaw (1965). The reac-
tion was carried out in CH2Cl2 at room temperature. The
ligands N,N,N’,N’-tetramethyl-P-naphtalen-1-ylphosphonic
diamide, OP(NMe2)2 (1-Naph), and N,N,N’,N’-tetramethyl-
P-naphtalen-2-ylphosphonic diamide, OP(NMe2)2 (2-Naph),
were prepared by reacting in THF (30 mL) at -40 °C the
proper bromonaphtalene precursor (2.795 g, 13.5 mmol)
with 8.5 mL of 1.6 M butyllithium solution in hexanes. The
reaction mixture was then slowly added to a THF solution
(20 mL) containing 13.5 mmol (2 mL) of OP(NMe2)2Cl,
cooled at − 40 °C. The resulting solution was allowed
to react overnight at room temperature, then cold water
(20 mL) was added. Most of the THF was removed by
evaporation under reduced pressure and the product was
extracted with diethylether (3×10 mL). Anhydrous sodium
sulfate was added to the organic fraction, which was then
fltered. The crude products were obtained as oils by evapo-
ration of the solvent and were purifed from diethylether/
cyclohexane. Analytical and spectroscopic data for the new
ligands are collected in Tables 1 and 2. The ligands are
sketched in Scheme 1 for clarity.
Ligands based on the hmpa skeleton, where one [NMe2]
fragment is replaced by a light-harvesting group, appear
promising candidates for the sensitization of lanthanide
luminescence. As a part of our research on new luminescent
metal complexes with phosphoramide and arylphosphonic
diamide ligands (Bortoluzzi et al. 2018; Bortoluzzi and Cas-
tro 2019), in this paper we report the synthesis and pho-
tophysical characterization of new Ln(III) complexes with
the ligands N,N,N’,N’-tetramethyl-P-indol-1-ylphosphonic
diamide, N,N,N’,N’-tetramethyl-P-carbazol-9-ylphospho-
nic diamide, N,N,N’,N’-tetramethyl-P-phenylphosphonic
diamide, N,N,N’,N’-tetramethyl-P-naphtalen-1-ylphos-
phonic diamide and N,N,N’,N’-tetramethyl-P-naphtalen-
2-ylphosphonic diamide.
Experimental
Commercial solvents (Aldrich) were purifed as described
in the literature (Armarego and Perrin, 1996). Lanthanide
oxides and chlorides were purchased from Chempur. All the
other reagents (Aldrich, Alfa Aesar) were used as received.
[Ln(NO3)3(H2O)3] (Ln = Eu, Gd, Tb) nitrato complexes
were obtained in almost quantitative yield by reacting 2.0 g
of the proper Ln2O3 oxide, suspended in 3.0 mL of water,
with 6 equivalents of concentrated aq. HNO3. The mixture
Table 1 Characterization data
Compound
Formula
Mr
ωi (calc.)/ %
ωi (found)/ %
Yield
of newly prepared ligands
C
H
N
%
OP(NMe2)2(1-Naph)
OP(NMe2)2(2-Naph)
C14H19N2OP
C14H19N2OP
262.29
262.29
64.11
63.85
7.30
7.33
10.68
10.63
80
64.11
7.30
10.68
82
63.95
7.34
10.65
1 3

Chemical Papers
Table 2 Absorption, IR and NMR data of newly prepared ligands
(25 mL) at room temperature under inert atmosphere (glove
box). Stirring was continued overnight, then the solvent was
evaporated at reduced pressure and the resulting solid was
triturated with diethylether (10 mL), fltered and dried under
vacuum. The products thus isolated are indicated as LnR
(Ln=Eu, Gd, Tb; R=Ind, Cbz, Ph, 1-Naph, 2-Naph) in the
“Results and discussion” for brevity.
Compound
Spectroscopic data(a)
OP(NMe2)2(1-Naph) UV–VIS (CH2Cl2, 25 °C), nm: 355, 318, 287
max,<252. IR (KBr), cm−1: 1188 s (νPO),
982 s (νPN). 1H NMR (CDCl3, 25 °C), δ:
8.80 (d, 1H, JHH =8.5 Hz, Naph-H), 7.98
(d, 1H, JHH =8.3 Hz, Naph-H(4)), 7.88 (dt,
1H, JHH =8.1 Hz,, JHH =1.4 Hz, Naph-H),
7.70 (ddd, 1H, JPH =16.0 Hz, JHH =7.0 Hz,
JHH =1.3 Hz, Naph-H(2)), 7.60 (ddd, 1H,
JHH =8.5 Hz, JHH =6.8 Hz, JHH =1.4 Hz,
Naph-H), 7.53 (ddd, 1H,, JHH =8.1 Hz,
JHH =6.8 Hz, JHH =1.3 Hz, Naph-H), 7.49
(ddd, 1H, JHH =8.3 Hz, JHH =7.0 Hz,
The complexes [Eu(β-dike)3L] (β-dike = diben-
zoylmethanate (dbm), tenoyltrifluoroacetonate (tta);
L = OP(NMe2)2Ind, OP(NMe2)2Ph, OP(NMe2)2(1-Naph),
OP(NMe2)2(2-Naph)) were prepared on the basis of the fol-
lowing method. 1.5 mmol of dibenzoylmethane (0.336 g)
or tenoyltrifuoroacetone (0.333 g) were dissolved in THF
(20 mL) and reacted with potassium tert-butoxide (0.168 g,
1.5 mmol). After 2 h, the solution was slowly added to anhy-
drous EuCl3 (0.129 g, 0.5 mmol) in 20 mL of THF and the
reaction mixture was left under stirring at room temperature
for 4 h. A THF solution (5 mL) containing 0.5 mmol of the
proper ligand L (OP(NMe2)2Ind, 0.126 g; OP(NMe2)2Ph,
0.106 g; OP(NMe2)2(1-Naph), OP(NMe2)2(2-Naph),
0.131 g) was then added and the mixture was left overnight
under stirring at room temperature. After fltration, the sol-
vent was removed under reduced pressure and dichlorometh-
ane (25 mL) was added. The solution was purifed by cen-
trifugation, then the solvent was evaporated and diethylether
(5 mL) was added. The product was collected by fltration
and dried under vacuum. The Eu(III) β-diketonate complexes
are indicated as 1R (β-dike=dbm) and 2R (β-dike=tta) in
the Results and Discussion section for brevity (R=Ind, Ph,
1-Naph, 2-Naph).
JPH =2.7 Hz, Naph-H(3)), 2.75 (d, 12H,
JPH =9.3 Hz, N–Me). 31P{1H} NMR
(CDCl3, 25 °C), δ: 30.71 (FWHM=2 Hz).
13C{1H} NMR (CDCl3, 25 °C), δ: 134.02
(Naph-Cipso, JCP =9.9 Hz), 133.97
(Naph-Cipso, JCP =10.8 Hz), 132.58
(Naph-CH(4), JCP =3.1 Hz), 131.75(Naph-
CH(2), JCP =9.4 Hz), 128.57 (Naph-CH,
JCP =1.6 Hz), 128.05 (Naph-Cipso(1)
JCP =152.2 Hz), 127.37 (Naph-CH,
JCP =4.4 Hz), 127.33 (Naph-CH),
,
126.28 (Naph-CH), 124.47 (Naph-CH(3)
,
JCP =15.2 Hz), 36.73 (N–Me, JCP =4.5 Hz)
OP(NMe2)2(2-Naph) UV–VIS (CH2Cl2, 25 °C), nm: 324, 315,
309, 290, 279 max,<266. IR (KBr),
cm−1: 1192 s (νPO), 976 s (νPN). 1H NMR
(acetone-d6, 25 °C), δ: 8.41 (d, 1H,
JPH =13.6 Hz, Naph-H(1)), 8.06 (dd, 1H,
JHH =7.8 Hz, 1.5 Hz, Naph-H), 8.01 (dd,
1H, JHH =8.4 Hz, JPH =3.1 Hz, Naph-
H
(4)), 7.98 (d, 1H, JHH =7.8 Hz, Naph-
H), 7.78 (ddd, 1H, JHH =8.4 Hz, 1.5 Hz,
JPH =9.7 Hz, Naph-H(3)), 7.64 (td, 1H,
JHH =7.0, 1.5, Naph-H), 7.60 (td, 1H,
JHH =7.0, 1.5, Naph-H), 2.64 (d, 12H,
JPH =10.1 Hz, N-Me). 31P{1H} NMR (ace-
tone-d6, 25 °C), δ: 28.49 (FWHM=3 Hz).
13C{1H} NMR (acetone-d6, 25 °C), δ:
134.57 (Naph-Cipso, JCP =2.4 Hz), 133.69
(Naph-CH(1), JCP =8.5 Hz), 132.87 (Naph-
Elemental analyses (C, H, N) were carried out at the
University of Padua using a Fison EA1108 microanalyzer.
Magnetic susceptibilities were measured on solid samples
at 298 K with a MK1 magnetic susceptibility balance (Sher-
wood Scientifc Ltd.) and corrected for diamagnetic contri-
bution by means of tabulated Pascal’s constants (Bain and
Berry 2008). Melting point measurements were carried out
with a Büchi B 535 instrument. IR spectra were collected in
the range 4000–400 cm−1 using a Perkin-Elmer Spectrum
One spectrophotometer. The air-sensitive samples were pre-
pared in glove-box, using an air-tight sample holder with
C
ipso, JCP =14.2 Hz), 128.78 (Naph-CH),
128.77 (Naph-Cipso(2), JCP =151.6 Hz),
127.83 (Naph-CH, JCP =12.3 Hz), 127.72
(Naph-CH), 127.66 (Naph-CH), 127.57
(Naph-CH, JCP =8.7 Hz), 126.59 (Naph-
CH), 35.62 (N–Me, JCP =3.3 Hz)
1
KBr windows. H, 13C{1H}, 31P{1H} and 19F NMR spec-
aNumbering of the naphthalene ring is the same of the reactants
1-bromonapthalene and 2-bromonaphtalene
tra were recorded on a Bruker AVANCE 400 spectrometer,
using CDCl3, acetone-d6 and DMSO-d6 as solvent. The
partially deuterated fraction of the solvent was quoted with
respect to tetramethylsilane and used as internal reference
for 1H and 13C spectra. 31P{1H} chemical shifts are reported
with respect to 85% H3PO4, with downfeld shifts considered
positive. 19F chemical shifts are referred to CFCl3.
The reaction between the [Ln(NO3)3(H2O)3] precur-
sors (1.0 mmol; Ln = Eu, 0.392 g; Ln = Gd, 0.397 g;
Ln = Tb, 0.399 g) and two equivalents of the proper
ligand L (OP(NMe2)2Ind, 0.502 g; OP(NMe2)2Cbz,
0.603 g; OP(NMe2)2Ph, 0.424 g; OP(NMe2)2(1-Naph),
OP(NMe2)2(2-Naph), 0.525 g) were carried out in THF
Absorption spectra in solution were collected using a
Perkin-Elmer Lambda 35 spectrophotometer. Emission
(PL) spectra of air-sensitive samples were recorded under
1 3

Chemical Papers
Scheme 1 [OP]-donor ligands
inert atmosphere (glove box) in the range 400–1035 nm
with an OceanOptics Flame-T spectrometer coupled with an
optical fber, a collimating lens and a longpass flter, using
UV led (280–375 nm) excitation sources. When necessary,
samples were cooled at −80 °C with cold N2 gas coming
from a liquid nitrogen evaporator. Photoluminescence emis-
sion (PL) and excitation (PLE) measurements of air-stable
compounds were carried out at room temperature on solid
samples by a Horiba Jobin–Yvon Fluorolog-3 spectrofuo-
rometer or an Edinburgh Instruments FLS980 Photolumi-
nescence Spectrometer. A continuous-wave xenon arc lamp
was used as source selecting the excitation wavelength by
a double Czerny–Turner monochromator. A single grating
monochromator coupled to a photomultiplier tube was used
as detection system for optical emission measurements. Exci-
tation and emission spectra were corrected for the instru-
mental functions. Time-resolved analyses were performed
in Multi Channel Scaling modality (MCS) using a pulsed
UV led source (λemission =377 nm) or a microsecond xenon
fashlamp coupled to a double-grating monochromator. The
intrinsic quantum yield (QEu) was estimated from the τ val-
ues on the basis of Eq. (1)E, uwhere n indicates the refractive
index of the sample. The value of 1.5 is assumed for solid
state samples in this work for comparative purposes, even if
it worth noting that refractive index may difer depending on
the nature of the compound. I(5D0 →7FJ)/I(5D0 →7F1) is the
ratio between the total integrated emission from the Eu(5D0)
level to the 7FJ manifold and the integrated intensity of the
transition 5D0 →7F1 (Bünzli et al. 2010).
Results and discussion
The phosphoramide and arylphosphonic diamide ligands
sketched in Scheme 1 were prepared on the basis of two
synthetic strategies. The phenyl-substituted species were
obtained by reacting the precursor OPCl2Ph with an excess
of NHMe2. The other ligands were synthesized by displac-
ing the chloride from OPCl(NMe2)2 with the proper nucleo-
phile. This last approach allowed the isolation of two new
arylphosphonic diamide ligands containing naphtyl substit-
uents, N,N,N’,N’-tetramethyl-P-naphtalen-1-ylphosphonic
diamide, OP(NMe2)2(1-Naph), and N,N,N’,N’-tetramethyl-
P-naphtalen-2-ylphosphonic diamide, OP(NMe2)2(2-Naph).
Characterization data are collected in Tables 1 and 2.
The sensitization of Eu(III) luminescence by the phos-
phoramide and arylphosphonic diamide ligands was pre-
liminarily verified by coordination to the [Eu(NO3)3]
metal fragment. The compounds (EuR) isolated from the
1:2 reaction between [Eu(NO3)3(H2O)3] and proper ligand
rapidly decompose in the presence of moisture and their
complete characterization is beyond the scopes of this
work. As reported in Table 3, IR data agree with the pres-
ence of nitrato ligands k2-coordinated to Eu(III) (Wang
et al. 1993). Moreover, the coordination of the ligands
is highlighted by the stretchings relative to the PO and
PN bonds (Sinha et al. 1982). The emission (PL) spec-
tra obtained by excitation with near-UV light, reported
in Fig. 1, show in most of the cases predominantly bands
5
associated to the D0 → 7FJ transitions of the metal cen-
tre, the most intense corresponding to the hypersensitive
5D0 →7F2 centered around 617 nm. The 5D0 →7FJ intensity
ratios are scarcely afected by the choice of the substituent
I(5D0 → FJ)
7
QEu = 14.65n3
ꢀ(s)
(1)
Eu
I(5D0 →7 F1)
1 3

Chemical Papers
Table 3 IR and PL data of the nitrato-complexes
Compound Data
EuInd
IR (solid), cm−1: 1473 s (νNO), 1288 s (ꢀ
), 1138 s (νPO), 996 s (νPN). PL (solid, λexcitation =375 nm, r.t.), nm: 581 (5D0 →7F0,
as
ONO
1.4%), 593 (5D0 →7F1, 10.2%), 617 (5D0 →7F2, 75.2%), 653 (5D0 →7F3, 2.9%), 690, 698 (5D0 →7F4, 10.3%). CIE 1931: x=0.640,
y=0.343
GdInd
TbInd
IR (solid), cm−1: 1477 s (νNO), 1292 s (ꢀ
), 1143 s (νPO), 998 s (νPN). PL (solid, λexcitation =375 nm, −80 °C), nm: 498 sh, 514
as
ONO
max, 546 sh. FWHM: 3800 cm−1. Triplet state: 21,800 cm−1
IR (solid), cm−1: 1469 s (νNO), 1293 s (ꢀ
), 1141 s (νPO), 996 s (νPN). PL (solid, λexcitation =375 nm, r.t.), nm: 491 (5D4 →7F6,
as
ONO
15.9%), 545 (5D4 →7F5, 65.1%), 586 (5D4 →7F4, 10.5%), 622 (5D4 →7F3, 6.4%), 649 (5D4 →7F2, 2.1%). CIE 1931: x=0.333,
y=0.595
EuCbz
EuPh
IR (solid), cm−1: 1486 s (νNO), 1294 s (ꢀ
), 1138 s (νPO), 993 s (νPN). PL (solid, λexcitation =375 nm, r.t.), nm: 400-600 (ligands
as
ONO
luminescence); 580 (5D0 →7F0), 593 (5D0 →7F1), 616 (5D0 →7F2), 651 (5D0 →7F3), 691, 697, 702 (5D0 →7F4)
IR (solid), cm−1: 1452 s, 1435 s (νNO), 1281 s (ꢀ
), 1136 s (νPO), 1105 s (νPO), 980 s (νPN). PL (solid, λexcitation =375 nm, r.t.), nm:
as
ONO
580 (5D0 →7F0, 2.8%), 593 (5D0 →7F1, 11.4%). 616 (5D0 →7F2, 72.0%), 651 (5D0 →7F3, 4.9%), 691, 697, 702 (5D0 →7F4, 8.9%).
CIE 1931: x=0.654, y=0.346
GdPh
TbPh
IR (solid), cm−1: 1457 s (νNO), 1283 s (ꢀ
), 1139 s (νPO), 1108 s (νPO), 981 s (νPN). PL (solid, λexcitation =375 nm, −80 °C), nm:
as
ONO
510 max, 529 sh. FWHM: 3100 cm−1. Triplet state: 21,600 cm−1
IR (solid), cm−1: 1448 s (νNO), 1281 s (ꢀ
), 1138 s (νPO), 1108 s (νPO), 980 s (νPN). PL (solid, λexcitation =375 nm, r.t.), nm: 490
as
ONO
(5D4 →7F6, 15.4%), 545 (5D4 →7F5, 63.2%), 586 (5D4 →7F4, 11.0%), 622 (5D4 →7F3, 7.5%), 651 (5D4 →7F2, 2.9%). CIE 1931:
x=0.343, y=0.587
Eu1-Naph
IR (solid), cm−1: 1481 s (νNO), 1298 s (ꢀ
), 1129 s (νPO), 1002 (νPN), 990 s (νPN). PL (solid, λexcitation =375 nm, r.t.), nm: 580
as
ONO
(5D0 →7F0, 0.7%), 592, 596 (5D0 →7F1, 11.1%), 617, 619 (5D0 →7F2, 74.8%), 653 (5D0 →7F3, 3.1%), 691, 698, 702 (5D0 →7F4,
10.3%). CIE 1931: x=0.647, y=0.338
Gd1-Naph
Eu2-Naph
IR (solid), cm−1: 1477 s (νNO), 1298 s (ꢀ
), 1130 s (νPO), 1002 (νPN), 991 s (νPN). PL (solid, λexcitation =375 nm, -80 °C), nm: 445
as
ONO
sh, 495 max, 543 max. PL (solid, λexcitation =375 nm, r.t), nm: 445 sh, 495 max. Triplet state:≈19,500 cm−1
IR (solid), cm−1: 1466 s (νNO), 1293 s (ꢀ
), 1124 s (νPO), 987 s (νPN). PL (solid, λexcitation =375 nm, r.t.), nm: 580 (5D0 →7F0,
as
ONO
1.0%), 593 (5D0 →7F1, 11.6%), 617 (5D0 →7F2, 73.5%), 652 (5D0 →7F3, 3.3%), 691, 697, 702 (5D0 →7F4, 10.6%). CIE 1931:
x=0.657, y=0.343
Gd2-Naph
IR (solid), cm−1: 1461 s (νNO), 1289 s (ꢀ
), 1124 s (νPO), 984 s (νPN). PL (solid, λexcitation =375 nm, −80 °C), nm: 441, 493, 548
as
ONO
max. PL (solid, λexcitation =375 nm, r.t), nm: 441, 493 max. Triplet state:≈19,400 cm−1
Fig. 1 PL spectra of the
Eu(III) nitrato complexes with
phosphoramide and arylphos-
phonic diamide ligands. Solid
samples, r.t., inert atmosphere,
λexcitation =375 nm
1 3

Chemical Papers
Fig. 2 PL spectra of the LnPh derivatives (Ln=Gd, Tb). Inset: LnInd (Ln=Gd, Tb) derivatives. Tb(III), green line; Gd(III), dark cyan line. Solid
samples, inert atmosphere, λexcitation =375 nm. Tb(III), r.t. Gd(III), −80 °C
in the OP(NMe2)2R ligands (see Table 3). As observable
from the normalized PL spectra, the behavior of the EuCbz
derivative is diferent with respect to the other compounds,
because the Eu(III) transitions are superimposed to lumi-
nescence bands probably attributable to the carbazolyl
moiety. This result suggests that the excited states of the
OP(NMe2)2Cbz was no longer considered in the present
study.
The triplet state (T) energies of the other ligands were
estimated on the basis of the phosphorescence spectra of
the corresponding Gd(III) derivatives GdR, collected at
low temperature. As reported in Table 3, the triplet states
of the phenyl- and indolyl-substituted ligands are in the
range 21,600–21,800 cm−1, well above the Eu(III) 5D0 level,
5
ligand are too close to the D0 resonance level to allow
an efcient energy transfer to Eu(III) and for this reason
Table 4 Characterization data
of the β-diketonate Eu(III)
complexes
Compound
Formula
Mr
ωi (calc.)/%
ωi (found)/%
χcMorr
M.p.
Yield
C
H
N
c.g.s.u.
°C
69
%
1Ind
C57H51EuN3O7P
1072.97
1066.76
1033.93
1027.72
1083.99
1077.78
1083.99
1077.78
63.81
63.55
4.79
4.81
3.92
3.90
4.6∙10−3
80
2Ind
C36H30EuF9N3O7PS3
C55H50EuN2O7P
40.53
2.83
3.94
4.2∙10−3
4.5∙10−3
4.1∙10−3
4.5∙10−3
4.5∙10−3
4.8∙10−3
4.8∙10−3
78
95
74
74
70
70
65
74
88
92
75
74
77
81
40.49
2.86
3.89
1Ph
63.89
63.63
4.87
4.89
2.71
2.70
2Ph
C34H29EuF9N2O7PS3
C59H52EuN2O7P
39.73
2.84
2.73
39.70
2.85
2.75
11-Naph
21-Naph
12-Naph
22-Naph
65.37
65.20
4.84
4.81
2.58
2.60
C38H31EuF9N2O7PS3
C59H52EuN2O7P
42.35
2.90
2.60
42.30
2.92
2.58
65.37
65.17
4.84
4.84
2.58
2.55
C38H31EuF9N2O7PS3
42.35
2.90
2.60
42.18
2.92
2.59
1 3

Chemical Papers
Table 5 IR and NMR data of the β-diketonate Eu(III) complexes
Compound Data
1Ind
IR (KBr), cm−1: 1595–1386 (νdbm), 1168 (νPO). 1H NMR (DMSO-d6, 25 °C), δ: 8.22–7.10 (m, 6H, Ind-H), 7.20 (s, 2H, β-dike-CH),
7.19 (s, 1H, β-dike-CH), 6.82 (t, 6H, JHH =7.3 Hz, β-dike-Ph), 6.67 (t, 1H, JHH =7.3 Hz, β-dike-Ph), 5.73 (d, 12H, JHH =7.3 Hz,
β-dike-Ph), 2.61 (d, 12H, JPH =10.1 Hz, N-Me). 31P{1H} NMR (DMSO-d6, 25 °C), δ: 13.5 (FWHM=30 Hz)
2Ind
IR (KBr), cm−1: 1605–1289 (νtta), 1141 (νPO). 1H NMR (DMSO-d6, 25 °C), δ: 7.87 (d, 1H, JHH =8.3 Hz, Ind-H), 7.59 (d, 1H,
JHH =8.2 Hz, Ind-H), 7.44 (s, 3H, β-dike-thioph), 7.35 (dd, 1H, JHH =3.4 Hz, JPH =2.7 Hz, Ind-H), 7.20 (ddd, 1H, JHH =8.3 Hz,
7.2 Hz, 1.3 Hz, Ind-H), 7.14 (ddd, 1H, JHH =8.2 Hz, 7.2 Hz, 1.1 Hz, Ind-H), 6.68 (ddd, 1H, JHH =3.4 Hz, 0.9 Hz, JPH =2.5 Hz,
Ind-H), 6.51 (s, 3H, β-dike-thioph), 6.35 (s, 3H, β-dike-thioph), 3.79 (s, 3H, β-dike-CH), 2.61 (d, 12H, JPH =10.1 Hz, N-Me).
31P{1H} NMR (DMSO-d6, 25 °C), δ: 13.6 (FWHM=90 Hz). 19F NMR (DMSO-d6, 25 °C), δ: −78.3
1Ph
IR (KBr), cm−1: 1595–1384 (νdbm), 1156 (νPO). 1H NMR (DMSO-d6, 25 °C), δ: 7.85–7.40 (m, 5H, P–Ph), 7.20 (s, 2H, β-dike-CH),
7.19 (s, 1H, β-dike-CH), 6.81 (t, 6H, JHH =7.3 Hz, β-dike-Ph), 6.66 (dd, 12H, JHH =6.3 Hz, JHH =7.3 Hz, β-dike-Ph), 5.71 (d,
12H, JHH =6.3 Hz, β-dike-Ph), 2.56 (d, 12H, JPH =9.7 Hz, N-Me). 31P{1H} NMR (DMSO-d6, 25 °C), δ: 27.5 (FWHM=300 Hz)
2Ph
IR (KBr), cm−1: 1613–1302 (νtta), 1144 (νPO). 1H NMR (DMSO-d6, 25 °C), δ: 7.73 (s, br, 2H, P–Ph), 7.60–7.47 (m, 3H, P-Ph),
7.44 (s, 3H, β-dike-thioph), 6.51 (s, 3H, β-dike-thioph), 6.35 (s, 3H, β-dike-thioph), 3.81 (s, 3H, β-dike-CH), 2.56 (d, 12H,
JPH =8.9 Hz, N-Me). 31P{1H} NMR (DMSO-d6, 25 °C), δ: 28.3 (FWHM=230 Hz). 19F NMR (DMSO-d6, 25 °C), δ: −78.3
11−Naph
IR (KBr), cm−1: 1595–1383 (νdbm), 1157 (νPO). 1H NMR (DMSO-d6, 25 °C), δ: 8.80–7.54 (m, 7H, Naph-H), 7.21 (s, 2H,
β-dike-CH), 7.20 (s, 1H, β-dike-CH), 6.82 (t, 6H, JHH =7.5 Hz, β-dike-Ph), 6.67 (dd, 12H, JHH =7.5 Hz, 7.0 Hz, β-dike-Ph),
5.73 (d, 12H, JHH =7.0 Hz, β-dike-Ph), 2.62 (d, 12H, JPH =9.2 Hz, N-Me). 31P{1H} NMR (DMSO-d6, 25 °C), δ: 28.6
(FWHM=60 Hz)
21−Naph
12−Naph
IR (KBr), cm−1: 1605–1305 (νtta), 1141 (νPO). 8.90–7.53 (m, 7H, Naph-H), 7.44 (s, 3H, β-dike-thioph), 6.51 (s, 3H, β-dike-thioph),
6.35 (s, 3H, β-dike-thioph), 3.80 (s, 3H, β-dike-CH), 2.63 (d, 12H, JPH =9.2 Hz, N-Me). 31P{1H} NMR (DMSO-d6, 25 °C), δ:
28.7 (FWHM=70 Hz). 19F NMR (DMSO-d6, 25 °C), δ: −78.3
IR (KBr), cm−1: 1595–1386 (νdbm), 1158 (νPO). 1H NMR (DMSO-d6, 25 °C), δ: 8.42 (d, br, 1H, JPH =14.1 Hz, Naph-H(1)), 8.18
(d, 1H, JHH =8.1 Hz, Naph-H), 8.09–7.95 (m, 2H, Naph-H), 7.70–7.53 (m, 3H, Naph-H), 7.20 (s, 2H, β-dike-CH), 7.19 (s, 1H,
β-dike-CH), 6.80 (t, 6H, JHH =7.4 Hz, β-dike-Ph), 6.65 (t, 12H, JHH =7.4 Hz, β-dike-Ph), 5.71 (d, 12H, JHH =7.4 Hz, β-dike-Ph),
2.62 (d, 12H, JPH =10.1 Hz, N-Me). 31P{1H} NMR (DMSO-d6, 25 °C), δ: 27.7 (FWHM=280 Hz)
22−Naph
IR (KBr), cm−1: 1608–1305 (νtta), 1140 (νPO). 1H NMR (DMSO-d6, 25 °C), δ: 8.48 (s, br, 1H, Naph-H), 8.05 (d, 1H, JHH =8.1 Hz,
Naph-H), 8.02 (dd, 1H, JHH =8.5 Hz, JPH =3.3 Hz, Naph-H), 7.98 (d, 1H, JHH =8.1 Hz, Naph-H), 7.81 (s, br, 1H, Naph-H), 7.63
(ddd, 1H, JHH =8.1 Hz, 7.0 Hz, 1.4 Hz, Naph-H), 7.58 (ddd, 1H, JHH =8.1 Hz, 7.0 Hz, 1.4 Hz, Naph-H), 7.43 (s, 3H, β-dike-
thioph), 6.51 (s, 3H, β-dike-thioph), 6.34 (s, 3H, β-dike-thioph), 3.81 (s, 3H, β-dike-CH), 2.63 (d, 12H, JPH =10.1 Hz, N-Me).
31P{1H} NMR (DMSO-d6, 25 °C), δ: 28.2 (FWHM=380 Hz). 19F NMR (DMSO-d6, 25 °C), δ: −78.3
17,250 cm−1, and also higher than the Tb(III) 5D4 resonance
level, 20,430 cm−1 (Binnemans 2009). Despite the fact that
(tta). The compounds were obtained by reacting EuCl3 with
the β-diketone, previously deprotonated with potassium
tert-butoxide, and then with the proper phosphoramide or
arylphosphonic diamide ligand. The complexes thus isolated
are stable in air at room temperature. Despite the fact that
we were unable to obtain crystals suitable for X-ray dif-
fraction, the characterization data support the formation of
the desired products (see Table 4). In particular, elemental
analyses agree with the proposed formulations and the molar
magnetic susceptivities are in line with the expected value
for Eu(III) derivatives at room temperature (Cotton 2006).
The IR spectra show, besides the typical vibrations of
the β-diketonate ligands, the νPO stretching in the range
5
the T – D4 energy gap is below the value suggested by
Latva et al. (1997) for an efcient energy transfer, the coor-
dination of OP(NMe2)2Ind and OP(NMe2)2Ph to Tb(III)
nitrate aforded green-emitting TbInd and TbPh complexes
upon excitation with near-UV data, and the PL spectra are
constituted by the 5D4 →7FJ transitions of the metal centre,
the most intense centered at 545 nm and corresponding to
J=5 (Table 3). The emission spectra of LnR (Ln=Gd, Tb;
R = Ind, Ph) are shown in Fig. 2. On the other hand, the
introduction of a naphtyl substituent in the arylphosphonic
diamide ligands causes the lowering of the T state around
19,500 cm−1 (Table 3). As a confrmation, attempts to obtain
luminescent Tb(III) derivatives with OP(NMe2)2(1-Naph) or
OP(NMe2)2(2-Naph) were unsuccessful.
1
1168–1140 cm−1. The H NMR spectra in DMSO-d6 of
the 1R complexes exhibit the resonances of the phenyl
substituents at about 6.8, 6.7 and 5.7 ppm, replaced by
three signals at about 7.4, 6.5 and 6.3 ppm in the case of
2R derivatives. The β-dike CH resonances fall at about 7.2
and 3.8 ppm, respectively, for the dbm and tta complexes.
The presence of the –CF3 substituent in the 2R complexes
is confrmed by the 19F NMR singlet at -78.3 ppm. The
phosphoramide and arylphosphonic diamide ligands can be
The sensitization of Eu(III) luminescence by the ligands
OP(NMe2)2Ind, OP(NMe2)2Ph, OP(NMe2)2(1-Naph) and
OP(NMe2)2(2-Naph) was subsequently applied for the
preparation of photoluminescent β-diketonate complexes 1R
and 2R having general formula [Eu(β-dike)3L], where β-dike
is dibenzoylmethanate (dbm) or tenoyltrifuoroacetonate
1 3

Chemical Papers
Fig. 3 1H, 31P{1H} and 19F NMR spectra of 2Ind in DMSO-d6 at 25 °C
1
detected in the H NMR spectra by the N–Me resonance,
of 12-Naph and 22-Naph reported in Fig. 4). As observable in
Fig. 4, the excitation of the coordinated ligands with wave-
lengths below about 480 nm causes the emission from the
Eu(III) centre. The direct excitation of Eu(III) is also present
in the PLE spectra, corresponding to the 5D2 ←7F0 transi-
tion centered at 464 nm (Binnemans 2015). The PL spectra
display only the typical 5D0 →7FJ bands, the most intense
occurring for J=2. The 5D0 →7F2/5D0 →7F1 intensity ratio
ranges from 13 to 19 and the 5D0 →7F1 transition is sepa-
rated in three peaks because of the Stark efect. These data
suggest low symmetry of the frst coordination sphere, being
two the maximum possible rotational symmetry order. The
3
in the range 2.63–2.56 ppm, with JPH coupling constant
around 9–10 Hz. Integration data support the formation of
heptacoordinate complexes with three β-diketonate and one
ligand containing the [OP] donor fragment, in agreement
with the structure of the hmpa complex [Eu(dbm)3(hmpa)]
determined by means of X-ray difraction (Panin et al. 1992).
The aromatic substituents are associated to a series of sig-
nals in the high frequency region of the 1H NMR spectra,
poorly resolved when the steric bulk makes difcult the free
rotation of the substituents, as occurs for 1Ind, 11-Naph and
2
1-Naph. Finally, in all the cases only one singlet is present in
the 31P{1H} NMR spectra, broadened with respect to the free
ligands, indicating that the phosphoramide and arylphos-
phonic diamide ligands interact with the Eu(III) centre in
DMSO-d6 solution. NMR and IR data are summarized in
Table 5. The 1H, 31P{1H} and 19F NMR spectra of 2Ind are
reported as examples in Fig. 3.
occurrence of only one D0 → 7F0 transition supports the
5
presence of only one Eu(III) emitting centre, even if such
information is not conclusive (Binnemans 2015). The emis-
sions of all the compounds fall in the reddish orange region
of the CIE 1931 chromaticity diagram (Schubert 2006).
The lifetimes (τ) were determined from the mono-expo-
nential interpolation of the luminescence decay curves,
reported in Fig. 4. As observable, the complexes can be
divided in two groups depending upon the choice of the
β-diketonate. In the case of dbm as ancillary ligand (1R
Absorption and photoluminescence data of the
β-diketonate complexes are summarized in Table 6. All
the compounds are characterized by strong absorptions in
the near-UV range (see for instance the absorption spectra
1 3

Chemical Papers
Table 6 Absorption and photoluminescence data of the β-diketonate Eu(III) complexes
Compound Data
1Ind
UV–VIS (CH2Cl2, r.t.), nm: 393 max, 346. PL (solid, λexcitation =400 nm, r.t.), nm: 580 (5D0 →7F0, 1.5%), 589, 595, 597 (5D0 →7F1,
4.6%), 614, 626 (5D0 →7F2, 86%), 652, 656 (5D0 →7F3, 4.1%), 692, 702, 706 (5D0 →7F4, 3.8%). PLE (solid, λemission =612 nm,
Eu
r.t.), nm:<480 (423 max, ligands excitation), 464 (5D2 ←7F0). τ (solid, λexcitation =377 nm, λemission =612 nm), μs: 274. QEu =29%.
CIE 1931: x=0.661, y=0.336
2Ind
UV–VIS (CH2Cl2, r.t.), nm: 344 max. PL (solid, λexcitation =375 nm, r.t.), nm: 580 (5D0 →7F0, 1.2%), 589, 593, 596 589, 595, 597
(5D0 →7F1, 5.6%), 614 (5D0 →7F2, 84.3%), 652, 656 (5D0 →7F3, 2.9%), 692, 702 (5D0 →7F4, 6.0%). PLE (solid, λemission =612 nm,
Eu
r.t.), nm:<480 (398 max, ligands excitation), 464 (5D2 ←7F0). τ (solid, λexcitation =377 nm, λemission =612 nm), μs: 376. QEu =33%.
CIE 1931: x=0.663, y=0.335
1Ph
UV–VIS (CH2Cl2, r.t.), nm: 392, 347 max, 298, 260, 254, 246. PL (solid, λexcitation =380 nm, r.t.), nm: 579 (5D0 →7F0, 1.1%), 589,
592, 596 (5D0 →7F1, 5.9%), 614, 617 (5D0 →7F2, 78.7%), 652 (5D0 →7F3, 3.2%), 693, 699, 702 (5D0 →7F4, 11.1%). PLE (solid,
λemission =613 nm, r.t.), nm:<480 (368 max, ligands excitation), 464 (5D2 ←7F0). τ (solid, λexcitation =380 nm, λemission =613 nm),
μs: 214. QEu =18%. CIE 1931: x=0.662, y=0.337
Eu
UV–VIS (CH2Cl2, r.t.), nm: 343 max, 272. PL (solid, λexcitation =375 nm, r.t.), nm: 580 (5D0 →7F0, 1.2%), 590, 594, 596 (5D0 →7F1,
2Ph
5.5%), 614 (5D0 →7F2, 84.1%), 654 (5D0 →7F3, 3.5%), 692, 702 (5D0 →7F4, 5.7%). PLE (solid, λemission =612 nm, r.t.), nm:<480
Eu
(376 max, ligands excitation), 464 (5D2 ←7F0). τ (solid, λexcitation =377 nm, λemission =613 nm), μs: 380. QEu =30%. CIE 1931:
x=0.664, y=0.335
11-Naph
21-Naph
12-Naph
22-Naph
UV–VIS (CH2Cl2, r.t.), nm: 346 max, 294, 253. PL (solid, λexcitation =375 nm, r.t.), nm: 580 (5D0 →7F0, 1.4%), 589, 594,
597 (5D0 →7F1, 4.5%), 613, 626 (5D0 →7F2, 85.4%), 651, 655 (5D0 →7F3, 4.9%), 702, 706 (5D0 →7F4, 3.8%). PLE (solid,
λemission =613 nm, r.t.), nm:<480 (396 max, ligands excitation), 464 (5D2 ←7F0). τ (solid, λexcitation =380 nm, λemission =613 nm),
μs: 215. QEu =24%. CIE 1931: x=0.632, y=0.326
Eu
UV–VIS (CH2Cl2, r.t.), nm: 342 max, 292, 277. PL (solid, λexcitation =375 nm, r.t.), nm: 580 (5D0 →7F0, 1.0%), 590, 594, 596
(5D0 →7F1, 5.0%), 614 (5D0 →7F2, 83.4%), 652, 655 (5D0 →7F3, 4.6%), 691, 702 (5D0 →7F4, 6.0%). PLE (solid, λemission =613 nm,
Eu
r.t.), nm:<480 (350 max, ligands excitation), 464 (5D2 ←7F0). τ (solid, λexcitation =380 nm, λemission =613 nm), μs: 346. QEu =34%.
CIE 1931: x=0.612, y=0.331
UV–VIS (CH2Cl2, r.t.), nm: 391, 346 max, 291, 251. PL (solid, λexcitation =375 nm, r.t.), nm: 580 (5D0 →7F0, 1.4%), 589, 594,
598 (5D0 →7F1, 4.4%), 613, 626 (5D0 →7F2, 85.7%), 651, 656 (5D0 →7F3, 5.0%), 702, 706 (5D0 →7F4, 3.5%). PLE (solid,
λemission =613 nm, r.t.), nm:<480 (392 max, ligands excitation), 464 (5D2 ←7F0). τ (solid, λexcitation =380 nm, λemission =612 nm),
μs: 240. QEu =27%. CIE 1931: x=0.654, y=0.337
Eu
UV–VIS (CH2Cl2, r.t.), nm: 343 max, 275. PL (solid, λexcitation =375 nm, r.t.), nm: 580 (5D0 →7F0, 1.1%), 589-596 (5D0 →7F1,
4.9%), 614 (5D0 →7F2, 83.6%), 652, 654 (5D0 →7F3, 4.1%), 692, 702 (5D0 →7F4, 6.3%). PLE (solid, λemission =613 nm, r.t.),
Eu
nm:<480 (381 max, ligands excitation), 464 (5D2 ←7F0). τ (solid, λexcitation =380 nm, λemission =612 nm), μs: 360. QEu =36%. CIE
1931: x=0.652, y=0.334
compounds) the τ values are comprised between 214 and
274 μs, while longer lifetimes were measured for the cor-
responding tta complexes 2R, in the range 337–376 μs. For
comparison, a very close τ value (337 μs) was measured at
room temperature for a dinuclear Eu(III) complex having the
conjugate base of 2,8-bis(4′,4′,4′-trifuoro-1′,3′-dioxobutyl)-
dibenzothiophene (Liu et al. 2010a) in the coordination
sphere. Lifetimes of 329 and 351 μs were measured for
chemically bonded hybrid materials based on silica net-
works, with 2,2′-bipyridine acting as antenna-ligand for
Eu(III) sensitization (Liu et al. 2010b). As described in the
Experimental section, the intrinsic quantum yields (QEu)
were calculated from the τ values on the basis of Eq. (E1u).
vibrational modes in the coordination spheres, or because
the metal centre is more protected from the interaction with
moisture (Bünzli and Eliseeva 2010; Bünzli 2015).
Conclusions
In this paper, we reported some results concerning the sensi-
tization of visible-emitting lanthanide(III) ions by phospho-
ramide and arylphosphonic diamide ligands. The electronic
features of the substituent in the OP(NMe2)2R skeleton
deeply infuence the possibility of energy transfer towards
Eu(III) and Tb(III), and ligands with too high delocalization
are unable to sensitize Tb(III). In the case of R=carbazol-
9-yl also the energy transfer towards Eu(III) is not efcient.
On the other hand, photoluminescence measurements on
new Eu(III) β-diketonates revealed that the coordination of
bulkier ligands aforded slightly higher intrinsic quantum
yields because of the reduction of non-radiative decays.
The QEu values are between 18% and 36% and highlight that
Eu
a great amount of the energy accumulated in the Eu(III) res-
onance level is not converted in radiative emission. The data
summarized in Table 6, however, indicate that the replace-
ment of the phenyl ring with the naphtyl and indolyl sub-
stituents slightly increases the QEu values, perhaps because
Eu
the increase of steric bulk reduces the possibility of some
1 3

Chemical Papers
Fig. 4 PL spectra (red) and PLE spectra (violet) of the Eu(III)
β-diketonate complexes with phosphoramide and arylphosphonic
diamide ligands. Inset 1: semi-log plot of the luminescence decay
curves of the Eu(III) β-diketonate complexes (solid samples, r.t.).
Inset 2: absorption spectra (CH2Cl2 solution) of 12-Naph and 22-Naph
Acknowledgements Ca’ Foscari University of Venice is gratefully
acknowledged for fnancial support (Bando Progetti di Ateneo 2014,
D.R. 553/2014 prot. 31352; Bando Spin 2018, D.R. 1065/2018 prot.
67416).
Binnemans K (2009) Lanthanide-based luminescent hybrid materials.
Chem Rev 109:4283–4374. https://doi.org/10.1021/cr8003983
Binnemans K (2015) Interpretation of europium(III) spectra. Coord
Chem Rev 295:1–45. https://doi.org/10.1016/j.ccr.2015.02.015
Bombieri G, Benetollo F, Del Pra A, da Silva Oliveira V, Araujo
Melo DM, Zinner LB, Vicentini G (2001) Structural characteri-
zation of [Ln(TFA)3(HMPA)3] (Ln = La, Nd, Er) complexes. J
Alloy Compd 323–324:181–184. https://doi.org/10.1016/S0925
-8388(01)01130-6
Compliance with ethical standards
Conflict of interest There are no conficts to declare.
Bortoluzzi M, Castro J (2019) Dibromomanganese(II) complexes with
hexamethylphosphoramide and phenylphosphonic bis(diamide)
ligands. J Coord Chem. https://doi.org/10.1080/00958
972.2018.1560430
References
Bortoluzzi M, Castro J, Enrichi F, Vomiero A, Busato M, Huang W
(2018) Green-emitting manganese (II) complexes with phospho-
ramide and phenylphosphonic diamide ligands. Inorg Chem Com-
mun 92:145–150. https://doi.org/10.1016/j.inoche.2018.04.023
Bukvetskii BV, Kalinovskaya V (2017) Crystal structure, lumines-
cence and triboluminescence of the complex [Eu(NO3)23hmpa]
NO3·HQuin. J Fluoresc 27:773–779. https://doi.org/10.1007/
s10895-016-2009-7
Allendorf MD, Bauer CA, Bhakta RK, Houk RJT (2009) Luminescent
metal-organic frameworks. Chem Soc Rev 38:1330–1352. https://
doi.org/10.1039/B802352M
Armarego WLF, Perrin DD (1996) Purifcation of laboratory chemi-
cals, 4th edn. Butterworth-Heinemann, Oxford
Bain GA, Berry JF (2008) Diamagnetic corrections and Pascal’s con-
stants. J Chem Ed 85:532–536. https://doi.org/10.1021/ed085p532
Bao L, Yingming Y, Mingyu D, Yong Z, Qi S (2006) Synthesis and
characterization of the frst dinuclear europium (ii) complex
supported by carbon-bridged biphenolate ligand. J Rare Earths
24:264–267. https://doi.org/10.1016/S1002-0721(06)60106-3
Bukvetskii BV, Mirochnik AG, Zhikhareva PA (2017) Tribolumines-
cence and crystal structure of the complex [Eu(NO3)3(HMPA)3]:
role of cleavage planes. Luminescence 32:341–347. https://doi.
org/10.1002/bio.3184
1 3

Chemical Papers
Bünzli JCG (2010) Lanthanide luminescence for biomedical analyses
and imaging. Chem Rev 110:2729–2755. https://doi.org/10.1021/
cr900362e
samarium and ytterbium complexes. J Syn Org Chem Jpn 53:906–
916. https://doi.org/10.5059/yukigoseikyokaishi.53.906
Hou Z, Wakatsuki Y (1997) Trapping of radicals in the coordina-
tion spheres of metals. Chem Eur J 3:1005–1008. https://doi.
org/10.1002/chem.19970030704
Bünzli JCG (2015) On the design of highly luminescent lantha-
nide complexes. Coord Chem Rev 293–294:19–47. https://doi.
org/10.1016/j.ccr.2014.10.013
Hou Z, Fujita A, Yoshimura T, Jesorka A, Zhang Y, Yamazaki H,
Wakatsuki Y (1996) Heteroleptic lanthanide complexes with
aryloxide ligands. synthesis and structural characterization of
divalent and trivalent samarium aryloxide/halide and aryloxide/
cyclopentadienide complexes. Inorg Chem 35:7190–7195. https
://doi.org/10.1021/ic960683c
Bünzli JCG, Eliseeva SV (2010) Basics of Lanthanide Photophysics.
In: Hänninen P, Härmä H (eds) Lanthanide luminescence: pho-
tophysical, analytical and biological aspects. Springer-Verlag,
Berlin. https://doi.org/10.1007/4243_2010_3
Bünzli JCG, Eliseeva SV (2013) Intriguing aspects of lanthanide
luminescence. Chem Sci 4:1939–1949. https://doi.org/10.1039/
C3SC22126A
Hou Z, Zhang Y, Wakatsuki Y (1997) Molecular structures of HMPA-
coordinated samarium(II) and ytterbium(II) iodide complexes.
a structural basis for the HMPA efects in SmI2-promoted reac-
tions. Bull Chem Soc Jpn 70:149–153. https://doi.org/10.1246/
bcsj.70.149
Bünzli JCG, Piguet C (2005) Taking advantage of luminescent
lanthanide ions. Chem Soc Rev 34:1048–1077. https://doi.
org/10.1039/B406082M
Bünzli JCG, Wong K (2018) Lanthanide mechanoluminescence. J
Rare Earths 36:1–41. https://doi.org/10.1016/j.jre.2017.09.005
Bünzli JCG, Chauvin A-S, Kim HK, Deiters E, Eliseeva SV (2010)
Lanthanide luminescence efciency in eight- and nine-coor-
dinate complexes: role of the radiative lifetime. Coord Chem
Rev 254:2623–2633. https://doi.org/10.1016/j.ccr.2010.04.002
Carlos LD, Ferreira RAS, de Zea Bermudez V, Julián-López B,
Escribano P (2011) Progress on lanthanide-based organic-
inorganic hybrid phosphors. Chem Soc Rev 40:536–549. https
://doi.org/10.1039/C0CS00069H
Huang X, Xu Y, Fan K, Bao S, Kurmoo M, Zheng L (2018) Revers-
ible SC-SC transformation involving [4 + 4] cycloaddition of
anthracene: a single-ion to single-molecule magnet and Yellow–
green to blue–white emission. Angew Chem Int Ed 57:8577–
8581. https://doi.org/10.1002/anie.201804102
Inanaga J, Ishikawa M, Yamaguchi M (1987) A mild and conveni-
ent method for the reduction of organic halides by using a
SmI2-THF solution in the presence of hexamethylphosphoric
triamide (HMPA). Chem Lett 16:1485–1486. https://doi.
org/10.1246/cl.1987.1485
Cendrowski-Guillaume SM, Nierlich M, Ephritikhine M (2001)
Synthesis and X-ray crystal structure of [U(η-C8H8)
(HMPA)3][BPh4], the frst cationic monocyclooctatetraenyl
compound of uranium (III), and its neodymium homologue.
Eur J Inorg Chem. https://doi.org/10.1002/1099-0682(20010
6)2001:6%3c1495:aid-ejic1495%3e3.0.co;2-j
Ishiguro S (1997) Thermodynamic and structural aspects on solva-
tion steric efect in nonaqueous solution. Bull Chem Soc Jpn
70:1465–14977. https://doi.org/10.1246/bcsj.70.1465
Jia J-H, Li Q-W, Chen Y-C, Liu J-L, Tong M-L (2019) Lumines-
cent single-molecule magnets based on lanthanides: design
strategies, recent advances and magneto-luminescent stud-
ies. Coord Chem Rev 378:365–381. https://doi.org/10.1016/j.
ccr.2017.11.012
Cendrowski-Guillaume SM, Le Gland G, Nierlich M, Ephritikhine
M (2003) A comparison of analogous 4f- and 5f-element com-
pounds: syntheses and X-ray crystal structures of the mixed
sandwich complexes [M(η-C8H8)(L){OP(NMe2)3}] (M = Nd
or U; L = η-C5Me5 or η-C4Me4P). Eur J Inorg Chem. https://
doi.org/10.1002/ejic.200390180
Jin W, Makioka Y, Kitamura T, Fujiwara Y (2001) A novel reduc-
tive dimerization/oxidative dehydrogenation of aldimines medi-
ated by lanthanoid metals. J Org Chem 66:514–520. https://doi.
org/10.1021/jo001328d
Cotton S (2006) Lanthanide and actinide chemistry. Wiley, Chichester
Donoghue JT, Peters DA (1969) Coordination chemistry of phos-
phoryl compounds—I: lanthanide complexes of hexamethyl
phosphoramide. J Inorg Nucl Chem 31:467–470. https://doi.
org/10.1016/0022-1902(69)80490-2
Katritzky AR, Rewcastle GW, Vazquez de Miguel LM (1988) Improved
syntheses of substituted carbazoles and benzocarbazoles via lithia-
tion of the (dialkylamino)methyl (aminal) derivatives. J Org Chem
53:794–799. https://doi.org/10.1021/jo00239a020
Keat R, Shaw RA (1965) Phosphorus–nitrogen compounds. Part XV.
Donoghue JT, Fernandez E, McMillan JA, Peters DA (1969) Coordi-
nation chemistry of phosphoryl compounds—II: cationic lantha-
nide complexes of hexamethyl phosphoramide. J Inorg Nucl Chem
31:1431–1433. https://doi.org/10.1016/0022-1902(69)80257-5
Eliseeva SV, Bünzli JCG (2010) Lanthanide luminescence for func-
tional materials and bio-sciences. Chem Soc Rev 39:189–227.
https://doi.org/10.1039/B905604C
The 1
H nuclear magnetic resonance and infrared spectra of some
mononuclear phosphorus(V) compounds containing the P-NMe2
grouping. J Chem Soc. https://doi.org/10.1039/jr9650004802
Kido J, Okamoto Y (2002) Organo lanthanide metal complexes for
electroluminescent materials. Chem Rev 102:2357–2368. https
://doi.org/10.1021/cr010309g
Kuriki K, Koike Y (2002) Plastic optical fber lasers and amplifers
containing lanthanide complexes. Chem Rev 102:2347–2356.
https://doi.org/10.1021/cr010309g
Guo P-H, Liu J-L, Jia J-H, Wang J, Guo F-S, Chen Y-C, Lin W-Q, Leng
J-D, Bao D-H, Zhang X-D, Luo J-H, Tong M-L (2013) Multi-
functional DyIII4 cluster exhibiting white-emitting, ferroelectric
and single-molecule magnet behavior. Chem Eur J 19:8769–8773.
https://doi.org/10.1002/chem.201300299
Kuzmina NP, Martynenko LI, Tu ZA, Kaul AR, Girichev GV, Giricheva
NI, Rykov AN, Koronev YM (1993) Rare earth β-diketonate and
carboxylate metal complexes as precursors for MOCVD of oxide
flms. J Phys IV C3:385–390. https://doi.org/10.1051/jp4:1993353
Latva M, Takalo H, Mukkala V, Matachescu C, Rodriguez-Ubis JC,
Kankare J (1997) Correlation between the lowest triplet state
energy level of the ligand and lanthanide(III) luminescence quan-
tum yield. J Lumin 75:149–169. https://doi.org/10.1016/S0022
-2313(97)00113-0
Guo P-H, Meng Y, Chen Y-C, Li Q-W, Wang B-Y, Leng J-D, Bao
D-H, Jia J-H, Tong M-L (2014) A zigzag DyIII4 cluster exhibit-
ing single-molecule magnet, ferroelectric and white-light emitting
properties. J Mater Chem C 2:8858–8864. https://doi.org/10.1039/
C4TC01275E
Hou Z, Wakatsuki Y (1994) Isolation and X-ray structures of the hexa-
methylphosphoramide (hmpa)-coordinated lanthanide(II) diiodide
Li H, Li P (2018) Luminescent materials of lanthanoid complexes
hosted in zeolites. Chem Commun 54:13884–13893. https://doi.
org/10.1039/C8CC07440B
complexes [SmI
2(hmpa)4] and [Yb(hmpa)4(thf)2]I2. J Chem Soc
Chem Commun. https://doi.org/10.1039/c39940001205
Hou Z, Wakatsuki Y (1995) Low valent lanthanides in organic synthe-
sis. ligand efects on the reactivity of some divalent and trivalent
Liu S, He P, Wang H, Shi J, Gong M (2010a) A lumi-
nescent dinuclear Eu(III) complex based on
1 3

Chemical Papers
2,8-bis(4′,4′,4′,-trifluoro-1′,3′-dioxobutyl)-dibenzothiophene
for light-emitting diodes. J Lumin 130:855–858. https://doi.
org/10.1016/j.jlumin.2009.12.013
Silva FA, Nascimento HA, Pereira DKS, Teotonio EES, Brito HF,
Felinto MCFC, Espínola JGP, Sá GF, Faustino WM (2013) Energy
transfer processes in Tb(III)-dibenzoylmethanate complexes with
phosphine oxide ligands. J Braz Chem Soc 24:601–608. https://
doi.org/10.5935/0103-5053.20130073
Liu J-L, Yan B, Guo L (2010b) Photoactive ternary lanthanide-centered
hybrids with schif-base functionalized polysilsesquioxane bridges
and N-heterocyclic ligands. Eur J Inorg Chem 2010:2290–2296.
https://doi.org/10.1002/ejic.201000029
Sinha SP, Pallanen TT, Pakkanen TA, Niinistö L (1982) Prepara-
tion, spectral properties and the crystal structure of the penta-
coordinated trichlorobis(hexamethylphosphoramide)-indium(III)
complex. Polyhedron 1:355–359. https://doi.org/10.1016/S0277
-5387(00)80819-0
Mashima K, Nakayama Y, Shibahara T, Fukumoto H, Nakamura
A (1996) Synthesis of arenethiolate complexes of divalent
and trivalent lanthanides from metallic lanthanides and diaryl
disulfdes: crystal structures of [{Yb(hmpa)3}2(μ-SPh)3][SPh]
and Ln(SPh)3(hmpa)3 (Ln= Sm, Yb; hmpa= hexamethylphos-
phoric triamide). Inorg Chem 35:93–99. https://doi.org/10.1021/
ic950050i
Sun Y, Zhang Z, Wang X, Li X, Weng L, Zhou X (2009) Lanthanide-
induced diinsertion of isocyanates into the N–H bond: synthesis,
structure, and reactivity of organolanthanides containing diureido
ligands. Organometallics 28:6320–6330. https://doi.org/10.1021/
om900631j
Molander GA (1994) Reductions with samarium(II) iodide. In:
Paquette LA (ed) Organic reactions, vol 46. Wiley, New York,
pp 211–367
Tsuruta H, Yamaguchi K, Imamoto T (2003) Tandem mass spectromet-
ric analysis of rare earth(III) complexes: evaluation of the rela-
tive strength of their Lewis acidity. Tetrahedron 59:10419–10437.
https://doi.org/10.1016/j.tet.2003.06.006
Panin ES, Ivanov SB, Kavun VY, Botova IN (1992) Crystal structure of
tris-(1,3-diphenyl-1,3-propanediono)hexamethylphosphotriamide
europium(3) [Eu(C6H5COCHCOC6H5)3OP(N(CH3)2)3]. Koord
Khim 18:663–671
Van den Bos BG, Schoot CJ, Koopmans MJ, Meltzer J (1961)
Investigations on pesticidal phosphorus compounds IV:
N-bis(dimethylamido)phosphoryl heterocyclic. Recl Trav Chim
Pay-B 80:1040–1047. https://doi.org/10.1002/recl.19610800913
Wang S, Lou Q, Zhou X, Zeng Z (1993) Synthesis, characterization
and luminescence properties of lanthanide(III) complexes with
2,6-bis(benzimidazol-2′-yl)pyridine. Polyhedron 12:1939–1945.
https://doi.org/10.1016/S0277-5387(00)81434-5
Petriček S (2005a) Synthesis of lanthanide bromide complexes
from oxides. The crystal structures of [LnBr 2(diglyme)2]
[LnBr4(diglyme)] (Ln = Sm, Eu) and [LnBr2(HMPA)4]
Br·0.5H2O (Ln=La, Sm). Z Anorg Allg Chem 631:1947–1952.
https://doi.org/10.1002/zaac.200500172
Petriček S (2005b) Syntheses and crystal structures of anionic lantha-
nide chloride complexes [(CH3)2NH2][LnCl4(HMPA)2] (Ln=La,
Nd) and [(CH3)2NH2]4[LnCl6]Cl (Ln=Nd, Sm, Eu). Acta Chim
Slov 52:398–403
Xu H, Sun Q, An Z, Wei Y, Liu X (2015) Electroluminescence from
europium(III) complexes. Coord Chem Rev 293–294:228–249.
https://doi.org/10.1016/j.ccr.2015.02.018
Yoshimura T, Hou Z, Wakatsuki Y (1995) Protonation at the aromatic
ring vs. at the carbonyl group of lanthanide-diaryl ketone dianion
species by aryl alcohols. formation, structural characterization,
and reactivity of lanthanide aryloxide, mixed aryloxide/alkoxide,
and aryloxide/enolate complexes. Organometallics 14:5382–5392.
https://doi.org/10.1021/om00011a065
Petriček S, Demšar A, Golič L, Košmrlj J (2000) New com-
plexes of lanthanide chlorides.: reversible isomerization
in octahedral [LaCl3(HMPA)3] and the crystal structure of
fac-[SmCl3(HMPA)3]. Polyhedron 19:199–204. https://doi.
org/10.1016/S0277-5387(99)00345-9
Rocha J, Carlos LD, Almeida Paz FA, Ananias D (2011) Luminescent
multifunctional lanthanides-based metal-organic frameworks.
Chem Soc Rev 40:926–940. https://doi.org/10.1039/C0CS00130A
Scholer RP, Merbach AE (1975) Raman and infrared study of hexa-
methylphosphoramide complexes of lanthanide perchlorates.
Inorg Chim Acta 15:15–20. https://doi.org/10.1016/S0020
-1693(00)93904-5
Zhang X, Wang T, Qin X, Zhang Z, Sun Y, Liang H, Li H (2017)
Large-area fexible, transparent, and highly luminescent flms con-
taining lanthanide (III) complex-doped ionic liquids for efciency
enhancement of silicon-based heterojunction solar cell. Prog Pho-
tovolt Res Appl 25:1015–1021. https://doi.org/10.1002/pip.2915
Zheng K, Liu Z, Jiang Y, Guo P, Li H, Zeng C, Weng Ng S, Zhong S
(2018) Ultrahigh luminescence quantum yield coordination poly-
mer as a multifunctional sensor. Dalton Trans 47:17432–17440.
https://doi.org/10.1039/C8DT03832E
Schubert EF (2006) Light-emitting diodes, 2nd edn. Cambridge Uni-
versity Press, Cambridge, pp 292–303
Silva Oliveira V, Araújo Melo DM, Rocha da Silva Z, Zinner LB,
Zinner K (2000) Preparation and properties of complexes
between rare earth trifuoroacetates and hexamethylphospho-
ramide (HMPA). J Alloy Compd 303–304:157–161. https://doi.
org/10.1016/S0925-8388(00)00658-7
Publisher’s Note Springer Nature remains neutral with regard to
jurisdictional claims in published maps and institutional afliations.
Silva AG, Vicentini G, Zukerman-Schpector J, Castellano EE (1995)
Hexamethylphosphoramide complexes of neodymium and
europium picrates. J Alloy Compd 225:354–356. https://doi.
org/10.1016/0925-8388(94)07039-3
1 3