'Facial' and 'meridional' coordination geometries and luminescence properties of tris(N-[(imidazol-4-yl)methylidene]-dl-alaninato)europium(III) and tris(N-[(imidazol-4-yl)methylidene]-dl-phenylalaninato)europium(III)

Article abstract of DOI:10.1016/j.poly.2012.10.003

Two racemic tridentate ligands, N-[(imidazol-4-yl)methylidene]-dl-alanine (H₂L^dl-ala) and N-[(imidazol-4-yl)methylidene]-dl- phenylalanine (H₂L^dl-phe), were synthesized by the 1:1 condensation reaction of 4-formylimidazole and either of dl-alanine and dl-phenylalanine, respectively. The Eu^III complexes 'fac'-[Eu ^III(HL^dl-ala)₃]·8H₂O (1) and 'mer'-[Eu^III(HL^dl-phe)₃]·7.75H ₂O (2) were synthesized by mixing the ligand and Eu ^III(acetate)₃ n-hydrate with 3:1 M ratio in methanol and the crystal structures were determined. Compounds 1 and 2 with three tridentate ligands have 'facial' and 'meridional' geometries, respectively, while they have a tricapped trigonal prismatic (TTP) and a capped square antiprismatic (CSAP) coordination geometry, respectively. In the crystal lattice, 1 consists of enantiomers 'fac'-[Eu^III(HL^d-ala)₃] and 'fac'-[Eu^III(HL^l-ala)₃], while 2 consists of 'mer'-[Eu^III(HL^d-phe)₂(HL^l-phe)] and 'mer'-[Eu^III(HL^d-phe)(HL^l-phe)₂]. Compounds 1 and 2 displayed sharp emission bands based on the f-f transitions by excitation and showed a different emission pattern due to their 'fac'- and 'mer'-coordination geometries. The luminescence quantum yields and life times of 1 and 2 were estimated to be (Φ = 0.25 and 1.40 ms) and (Φ = 0.30 and 1.23 ms), respectively.

Full text of DOI:10.1016/j.poly.2012.10.003

Polyhedron 49 (2013) 105–112
Contents lists available at SciVerse ScienceDirect
Polyhedron
journal homepage: www.elsevier.com/locate/poly
‘‘Facial’ and ‘meridional’ coordination geometries and luminescence properties
of tris(N-[(imidazol-4-yl)methylidene]-DL-alaninato)europium(III) and
tris(N-[(imidazol-4-yl)methylidene]-DL-phenylalaninato)europium(III)
Suguru Yamauchi a, Tomotaka Hashibe a, Mami Murase a, Hiroaki Hagiwara a, Naohide Matsumoto a,
,
⇑
Masanobu Tsuchimoto b
a Department of Chemistry, Faculty of Science, Kumamoto University, Kurokami 2-39-1, Kumamoto 860-8555, Japan
b Department of Chemistry, Chiba Institute of Technology, Shibazono 2-1-1, Narashino, Chiba 275-0023, Japan
a r t i c l e i n f o
a b s t r a c t
Two racemic tridentate ligands, N-[(imidazol-4-yl)methylidene]-DL-alanine (H2L -ala) and N-[(imidazol-4-yl)
DL
Article history:
methylidene]-DL-phenylalanine (H2L -phe), were synthesized by the 1:1 condensation reaction of 4-formylim-
DL
Received 6 June 2012
Accepted 3 October 2012
Available online 12 October 2012
III
idazole and either of DL-alanine and DL-phenylalanine, respectively. The EuIII complexes ‘fac’-[Eu (HL -ala)3]-
DL
III
ꢀ8H O (1) and ‘mer’-[Eu (HL -phe)3]ꢀ7.75H2O (2) were synthesized by mixing the ligand and EuIII(acetate)3
n-hydrate with 3:1 M ratio in methanol and the crystal structures were determined. Compounds 1 and 2 with
three tridentate ligands have ‘facial’ and ‘meridional’ geometries, respectively, while they have a tricapped tri-
gonal prismatic (TTP) and a capped square antiprismatic (CSAP) coordination geometry, respectively. In the
2
DL
Keywords:
Europium(III) complex
Tridentate ligand
Imidazole group
DL-Phenylalanine
DL-Alanine
D-ala
III
crystal lattice, 1 consists of enantiomers ‘fac’-[EuIII(HL
)3] and ‘fac’-[Eu (HL -ala)3], while 2 consists of ‘mer’-
L
D-phe
[EuIII(HLD-phe)2(HLL-phe)] and ‘mer’-[EuIII(HL
)(HL -phe)2]. Compounds 1 and 2 displayed sharp emission
L
bands based on the fꢁf transitions by excitation and showed a different emission pattern due to their
‘fac’- and ‘mer’-coordination geometries. The luminescence quantum yields and life times of 1 and 2 were
Luminescence
Stereochemistry
estimated to be (
U
= 0.25 and 1.40 ms) and (
U
= 0.30 and 1.23 ms), respectively.
Ó 2012 Elsevier Ltd. All rights reserved.
1. Introduction
complexes with b-diketonates, such as their ionic character and
unsaturated coordination number, can be improved by new alter-
native ligand. It is anticipated that an electronic mono-negative tri-
dentate ligand reacts with EuIII ion at the 3:1 M ratio to form an
electro-neutral homoleptic EuIII complex with the saturated coor-
dination number of nine. Such mono-negative tridentate ligands
were used for the syntheses of neutral EuIII complexes and some
of the complexes give high quantum yields around ca. 60% for
tris(4-phenyl-6-(20-pyridyl)pyridine-2-carboxylate)-europium(III)
[10–12] and tris(benzimidazole-substituted-pyridine-2-carboxy-
lato)europium(III) [13].
We have reported that the metal complexes with multidentate
ligand involving imidazole groups have a high-probability for
enantioselective interaction. (1) Copper(II) complex [CuII(H2L1)]
(ClO4)2 with an achiral pentadentate strand-type ligand involving
two imidazole groups, (H2L1 = bis{3-[(2-methylimidazol-4-yl)
Since EuIII complexes have specific luminescence properties
such as large Stokes shifts, sharp emission profiles corresponding
to the 5D0 ? 7Fj (j = 0,1,2,3,4) transitions and long luminescence
lifetimes, recently luminescent EuIII complexes have attracted con-
siderable attention aimed to the practical applications from elec-
troluminescent devices to bio-probes for immunoassays or for
imaging live cells [1–4]. Many luminescent EuIII complexes have
been synthesized and their physical properties have been reported
[5,6]. Despite extensive attempts aimed at producing highly lumi-
nescent molecules, quantum yields above 40% are rare [7]. EuIII
complexes with b-diketonate have been extensively studied and
high quantum yield reaching 85% is observed for [tris(thenoyltri-
fluoroacetonate)bis(dibenzylsulfoxide)europium(III)] [8]. On the
other hand, b-diketonate is mono-anionic bidentate ligand and
cannot provide neutral homoleptic lanthanide complexes with a
saturated coordination sphere [9]. Optimization of the intrinsic
quantum yield is achieved by the design of a tight, rigid, and fully
coordinative environment. The disadvantages for the EuIII
methylideneamino]propyl}methylamine), gives either
D (clock-
wise) or (anticlockwise) enantiomers, due to the spiral coordina-
K
tion arrangement of achiral ligand. The mono-deprotonated
complex [CuII(HL1)]ClO4 has one imidazole and one imidazolate
moiety per molecule, which functions as a chiral self-complemen-
tary building component, and aggregates into homochiral (ꢀDDDD
ꢀ
⇑
Corresponding author. Tel./fax: +81 96 342 3390.
E-mail address: naohide@aster.sci.kumamoto-u.ac.jp (N. Matsumoto).
and
ꢀKKKKꢀ) 1D zigzag chains due to the intermolecular
0277-5387/$ - see front matter Ó 2012 Elsevier Ltd. All rights reserved.
http://dx.doi.org/10.1016/j.poly.2012.10.003

106
S. Yamauchi et al. / Polyhedron 49 (2013) 105–112
(a)
3
Eu
N
HO
H N
2
HN
N
O
OH
O
HN
N
HN
N
III
Eu (OAc) nH O
3
2
∗
H
+
O
O
N
∗
∗
O
R
H
H
R
R
R = Me, Benzyl
R
(b)
∗
H
O
H
HN
∗
R
N
N
O
N
O
O
O
R
O
R
O
∗
N
NH
NH
O
∗
NH
N
Eu
N
H
Eu
N
H
N
O
O
N
N
N
N
H
N
H
H
∗
∗
O
N
H
O
R
R
'facial'
'meridional'
Scheme 1. (a) Synthetic scheme of unsymmetric tridentate ligand H2LR and the EuIII complex. Tridentate ligand H2LR is synthesized by the 1:1 condensation reactions of
4-formylimidazole and DL-alanine or DL-phenylalanine. The 3:1 reaction of the ligand and EuIII(acetate)3 n-hydrate gives [EuIII(HLR)3]ꢀxH2O. (b) ‘Facial’ and ‘meridional’
geometrical isomers of [EuIII(HLR)3] with N6O3 nine-coordinate. As strictly speaking (IUPAC) fac and mer only apply to six-coordinated octahedral complexes, ‘fac’ and ‘mer’ are
used in this text.
imidazoleꢀ ꢀ ꢀimidazolate hydrogen bond [14,15]. (2) Cobalt(III) com-
plex with achiral tripod-type ligands involving three imidazole
groups, [CoIII(H3L2)](ClO4)3 (H3L2 = tris{2-[(imidazol-4-yl)methy-
plexes with ‘facial’ and ‘meridional’ coordination geometries. The
crystal structures showed diastereoselective assembly manner.
Here, we report the syntheses, crystal structures, and luminescent
properties in the solid state of these two complexes.
lideneamino]ethyl}amine) induces the chirality of the
D- and
K
-enantiomers due to the screw coordination arrangement. The
formally hemi-deprotonated complex [CoIII(H1.5L2)](ClO4)1.5 func-
tions as a self-complementary chiral building block to form an
extended 2D homochiral layer structure due to the intermolecular
imidazoleꢀ ꢀ ꢀimidazolate hydrogen bonds leading to a spontaneous
resolution [16–21]. (3) Copper(II) and zinc(II) complexes of triden-
tate ligands involving imidazole and amino acid [MIIX(HL)] (MII =
CuII, ZnII; X = Clꢁ, Brꢁ) showed another enantioselective interaction
[22–24]. In addition to the coordination by the imidazolate group
to the adjacent molecule, the amino acid moiety is also a functional
group for assembly process, in which the amino acid can coordinate
and/or make hydrogen-bond to the adjacent molecule.
2. Experimental
2.1. Materials
All reagents and solvents used in this study are commercially
available from Tokyo Kasei Co. Ltd. and Wako Pure Chemical Indus-
tries Ltd. These were used without further purification.
2.2. Preparations of materials
DL-ala
DL-phe
2.2.1. Preparations of ligands HL
and HL
In this study, two racemic tridentate ligands involving imidazole
A tridentate ligand N-[(imidazol-4-yl)methylidene]-DL-alanine,
which is abbreviated as HL -ala, was prepared by the 1:1 condensa-
DL
and amino acid moieties, N-[(imidazol-4-yl)-methylidene]-DL
-
alanine (H2L -ala) and N-[(imidazol-4-yl)methylidene]-DL-phenylala-
DL
tion reaction of 4-formylimidazole and DL-alanine according to the
method reported in the literature [22,23]. To a solution of 4-formy-
limidazole (1.5 mmol, 0.144 g) in 10 mL of methanol was added a
solution of DL-alanine (1.5 mmol, 0.134 g) in 5 mL of water, and
the mixture was stirred on a hot plate at 50 °C for 1 h and then
cooled to room temperature. The resultant ligand solution was
nine (H2L -phe), were used for the syntheses of EuIII complexes.
DL
Firstly, such mono-negative tridentate ligands H2LR can be useful
for the synthesis of electronically neutral EuIII complex with the
saturated coordination number and high quantum yield. Secondly,
the EuIII complexes of such tridentate ligands can form enantiose-
lective interaction, because the amino acid moiety is a functional
group for assembly process and the chirality of the amino acid
can give a diastereoselective effect for assembly process. The
ligand (H2LR) was synthesized by the 1:1 condensation reactions
of 4-formylimidazole derivative and various amino acids according
to Scheme 1(a). As shown in Scheme 1(b) and confirmed by the
not isolated and used for the synthesis of EuIII complex. HL
DL-phe
was prepared by a similar way of HL -ala, using DL-phenylalanine
DL
instead of DL-alanine.
2.2.2. Preparation of ‘fac’-[Eu (HL -ala)3]ꢀ8H2O (1)
III
DL
DL-ala
To the resultant ligand solution of HL
thus obtained
X-ray analyses described later, the resulting EuIII complexes with
(1.5 mmol) was added a solution of europium(III)acetate n-hydrate
(0.5 mmol, 0.165 g) in 5 mL of water at room temperature. The
mixture was stirred for 10 min at room temperature and then
III
three mono-negative tridentate ligands, ‘fac’-[Eu (HL -ala)3]ꢀ8H2O
DL
III
(1) and ‘mer’-[Eu (HL -phe)3]ꢀ7.75H2O (2), are homoleptic com-
DL

S. Yamauchi et al. / Polyhedron 49 (2013) 105–112
107
Table 1
filtered. For the crystallization, a diffusion method was applied. A
vessel of the filtrate was left to stand for several days in an
X-ray crystallographic data for ‘fac’-[EuIII(HL -ala)3]ꢀ8H2O (1) at 103 K and ‘mer’-
DL
[EuIII(HL -phe)3]ꢀ7.75H2O (2) at 296 K.
DL
atmosphere saturated by vapor of acetone, precipitating colorless
DL-ala
Complex
‘fac’-[EuIII(HL
(1)
3]ꢀ8H2O
‘mer’-[EuIII(HL -phe)3]ꢀ7.75H2O
III
block shape crystals. Yield 64%. Anal. Calc. for [Eu (HL -ala)3]ꢀ8H2O
DL
DL
(2)
21
= C H24N9O6Euꢀ8H2O: C, 31.74; H, 5.07; N, 15.87. Found: C, 31.99;
Formula
Formula
weight
Space group
a (Å)
C
21H40N9O14Eu
C39H51.5N9O13.75Eu
1018.35
H, 5.02; N, 15.83%. TGA; 18% weight loss was observed in the heat-
ing mode. In the cooling mode, the sample absorps the vapor to
increase the weight from ꢁ18% to ꢁ2%.
794.56
ꢀ
I41/a (No. 88)
23.1450(6)
23.1450(6)
34.8469(9)
18667.1(9)
16
R3 (No. 148)
13.6136(7)
13.6136(7)
29.051(2)
4662.8(4)
6
2.2.3. Preparation of ‘mer’-[Eu (HL -phe)3]ꢀ7.75H2O (2)
III
DL
b (Å)
DL-phe
c (Å)
To the resultant ligand solution of HL
(1.5 mmol) was
V (Å3)
added
a solution of europium(III)acetate hydrate (0.5 mmol,
Z
Dcalc (g cmꢁ3
)
1.698
1.449
0.165 g) in 5 mL of water at room temperature. The mixture was
filtered and the filtrate was left to stand for several days in an
l
(cmꢁ1
)
20.927
0.0562, 0.1580
14.116
0.0852, 0.2030
Ra, Rw
b
atmosphere saturated by vapor of acetone to precipitate colorless
III
block shape crystals. Yield 55%. Anal. Calc. for [Eu (HL -phe)3]-
P
P
DL
a
R = ||Fo| ꢁ |Fc||/ |Fo|.
P
P
2
2
1=2
Rw ¼ ½ wðjF2oj ꢁ jFc2jÞ = wjF2oj ꢂ
.
b
2
ꢀ7.5H O = C39H36N9O6Euꢀ7.5H2O: C, 46.20; H, 5.07; N, 12.43. Found:
C, 46.51; H, 5.15; N, 12.19%.
2.3. Physical measurements
Table 2
Relevant coordination bond distances, angles, and hydrogen bond distances for ‘fac’-
[EuIII(HL -ala)3]ꢀ8H2O (1) and ‘mer’-[EuIII(HL -phe)3]ꢀ7.75H2O (2).
DL
DL
Elemental C, H, and N analyses were carried out at the Center for
Instrumental Analysis of Kumamoto University. Thermogravimetric
analyses (TGA) were performed on a TG/DTA6200 (Seiko Instrument
Inc.). The samples of ca. 3 mg were heated from room temperature to
130 °C in the heating mode at the heating rate of 5 °C minꢁ1, kept the
temperature for 1 h, and then cooled to room temperature. UV–Vis
electronic spectra were measured on a Shimadzu UV-2450 UV–Vis
spectrophotometer. Excitation and emission spectra were measured
on a HITACHI F-7000 fluorescence spectrophotometer. The quantum
yields in the solid state were obtained by an absolute method using a
Hitachi F-7000 fluorescence spectrometer equipped with an inte-
grating sphere by excitation at 302 nm.1 The lifetimes were obtained
on a HITACHI F-7000 fluorescence spectrophotometer by using the
attachment program of time-domain phosphorescence lifetime mea-
surement with optical chopping of excitation light.
Complex (1)
Complex (2)
EuꢁO(1)
EuꢁN(2)
EuꢁN(3)
2.395(4)
2.582(6)
2.553(7)
EuꢁO(1)
EuꢁN(2)
EuꢁN(3)
EuꢁO(3)
EuꢁN(5)
EuꢁN(6)
EuꢁO(5)
EuꢁN(8)
EuꢁN(9)
2.397(9)
2.569(9)
2.548(9)
2.430(8)
2.589(9)
2.596(9)
2.448(8)
2.571(11)
2.577(12)
O(1)ꢁEuꢁN(2)
O(1)ꢁEuꢁN(3)
N(2)ꢁEuꢁN(3)
127.44(19)
63.64(18)
63.86(16)
O(1)ꢁEuꢁN(2)
O(1)ꢁEuꢁN(3)
N(2)ꢁEuꢁN(3)
O(3)ꢁEuꢁN(5)
O(3)ꢁEuꢁN(6)
N(5)ꢁEuꢁN(6)
O(5)ꢁEuꢁN(8)
O(5)ꢁEuꢁN(9)
N(8)ꢁEuꢁN(9)
126.1(3)
64.2(3)
64.1(3)
124.1(3)
62.2(3)
63.8(3)
121.6(3)
62.5(3)
64.1(4)
2.4. X-ray crystal structure analyses
O(1)ꢁEuꢁO(1)⁄1
N(2)ꢁEuꢁN(2)⁄1
N(3)ꢁEuꢁN(3)⁄1
77.35(17)
80.37(16)
120.00(15)
O(1)ꢁEuꢁN(5)
N(2)ꢁEuꢁO(3)
N(3)ꢁEuꢁN(6)
O(1)ꢁEuꢁO(5)
N(2)ꢁEuꢁN(8)
N(3)ꢁEuꢁN(9)
O(5)ꢁEuꢁN(5)
O(3)ꢁEuꢁN(8)
N(6)ꢁEuꢁN(9)
90.0(3)
68.5(3)
123.2(3)
72.0(3)
75.6(3)
104.4(4)
74.3(3)
83.7(3)
132.4(3)
The X-ray diffraction data were collected by a Rigaku RAXIS
RAPID imaging plate diffractometer using graphite monochromat-
III
radiation (k = 0.71073 Å) for ‘fac’-[Eu (HL -ala)3]ꢀ8H2O
DL
ed Mo K
a
III
(1) at 103 K and ‘mer’-[Eu (HL -phe)3]ꢀ7.75H2O (2) at 296 K. The
temperature of the crystal was maintained at the selected value
by means of a Rigaku cooling device to within an accuracy of
2 K. The structures were solved by direct methods and expanded
using the Fourier technique [25,26]. Hydrogen atoms were fixed at
the calculated positions and refined using a riding model. All calcu-
lations were performed using the Crystal Structure crystallo-
graphic software package [27].
DL
Hydrogen bond (Å)
N(1)ꢀ ꢀ ꢀO(4)⁄2
O(2)ꢀ ꢀ ꢀO(4)
2.780(8)
2.690(10)
2.762(6)
2.735(17)
2.703(18)
N(1)ꢀ ꢀ ꢀO(5)⁄4
N(4)ꢀ ꢀ ꢀO(4)⁄5
N(7)ꢀ ꢀ ꢀO(10)
O(2)ꢀ ꢀ ꢀO(10)
2.837(12)
2.694(14)
2.744(16)
2.637(16)
O(3)ꢀ ꢀ ꢀO(4)
O(4)ꢀ ꢀ ꢀO(5)
O(5)ꢀ ꢀ ꢀO(2)⁄3
3. Results and discussion
Symmetry operations: (⁄1), ꢁy + 1, x ꢁ y, z; (⁄2), x + 1/3 ꢁ 1, y + 2/3 ꢁ 1, z + 2/3 ꢁ 1;
(⁄3), ꢁx + 2/3 + 1, ꢁy + 1/3 + 1, z + 1/3 + 1; (⁄4), y + 3/4 ꢁ 1, ꢁx + 3/4, z + 3/4 ꢁ 1;
(⁄5), ꢁy + 3/4, x + 1/4, z + 1/4.
3.1. Synthesis and characterization
Two racemic tridentate ligands, N-[(imidazol-4-yl) methylidene]-
DL-alanine (H2L -ala) and N-[(imidazol-4-yl)methylidene]-DL-phenyl-
DL
alanine(H2L -phe),weresynthesizedbythe1:1condensationreaction
of 4-formylimidazole and either of DL-alanine and DL-phenylalanine,
respectively in a mixed solution of methanol and water. The ligands
were not isolated and the ligand solutions were used for the synthesis
DL
III
of the EuIII complexes. The EuIII complexes ‘fac’-[Eu (HL -ala)3]ꢀ8H2O
DL
(1) and ‘mer’-[Eu (HL -phe)3]ꢀ7.75H2O (2) were crystallized from
III
DL
the mixed solution of the ligand and EuIII(acetate)3 n-hydrate with
3:1 M ratio. The C, H, and N elemental analyses suggested the exis-
tence of the crystal water. The TGA analyses revealed the number of
the crystal water. In the heating mode from room temperature to
130 °C, 18% weight loss corresponding to 8H2O was observed for 1.
1
Measurements of the amounts of fluorescence were carried out with a Hitachi F-
7000 fluorescence spectrometer equipped with an integrating sphere by excitation at
302 nm.

108
S. Yamauchi et al. / Polyhedron 49 (2013) 105–112
In the cooling mode, the sample absorps the atmospheric moisture
amount of 7H2O to increase the 16% weight. For 2, theweight loss cor-
respondingto 7–8watermoleculeswasobservedintheheatingmode
and the 4% weight increase corresponding to 2 water molecules was
observed in the cooling mode.
C3 axis (c-axis) and viewed perpendicular to the C3 axis. The com-
plex has a C3 symmetry and three unsymmetrical ONN tridentate
ligands are oriented parallel to each other, showing ‘facial’ config-
uration. Three methyl groups at the alanine moieties related by C3
III
symmetry operations are well-packed in ‘fac’-[Eu (HL -ala)3], dem-
D
D-ala
III
onstrating that ‘fac’-[EuIII(HL
)3] and ‘fac’-[Eu (HL -ala)3] are
L
III
3.2. Crystal structure of ‘fac’-[Eu (HL -ala)3]ꢀ8H2O (1) and ‘mer’-
DL
preferable molecular geometry. The space filling representation
III
of ‘fac’-[Eu (HL -ala)3] also suggests that the species involving
D
III
[Eu (HL -phe)3]ꢀ7.75H2O (2)
DL
D-ala
D-ala
L
HL
and HLL-ala, that is, ‘fac’-[EuIII(HL
)2(HL -ala)] and ‘fac’-
[EuIII(HLL-ala)2(HL -ala)] are un-preferable due to the steric hin-
drance on the basis of the space filling consideration.
D
III
The crystal structures of ‘fac’-[Eu (HL -ala)3]ꢀ8H2O (1) and
DL
III
‘mer’-[Eu (HL -phe)3]ꢀ7.75H2O (2) were determined by the single-
DL
The EuIII ion on threefold rotation axis is coordinated by N6O3
crystal X-ray diffraction method at 103 and 296 K, respectively.
The crystallographic data and the relevant coordination bond dis-
tances with the hydrogen bond distances are given in Tables 1
and 2, respectively.
donor atoms of three unsymmetrical NNO tridentate ligands
D-ala
HL
or HLL-ala and the EuIII complex has saturated coordination
number of nine, where one imidazole and one imine nitrogen
atoms, and one carboxylate oxygen atom per ligand coordinate
to a EuIII ion to give adjacent two five-membered chelate rings.
The coordination bond distances are EuꢁN(2) (imidazole) =
2.582(6) Å, EuꢁN(3) (imine) = 2.553(7), and EuꢁO(1) (carboxylate
oxygen) = 2.395(4) Å. The coordination geometry is described as a
tricapped trigonal prism (TTP) [29,30], whose geometry is
observed for GdIII complex of three linear tridentate ligands
([Gd(oda)3]odaꢀH2O; oda = oxydiacetate dianion) [31]. Three imid-
azole nitrogen atoms generated by C3 symmetry operations to N(2)
and three carboxylate oxygen atoms generated by C3 symmetry
operations to O(1) form the two outer triangular faces, and the
capping positions are occupied by three imine nitrogen atoms
generated by C3 symmetry operations to N(3).
III
3.2.1. Crystal structure of ‘fac’-[Eu (HL -ala)3]ꢀ8H2O (1)
DL
III
The complex with the formula of [Eu (HL -ala)3]ꢀ8H2O crystal-
DL
ꢀ
lized into a centrosymmetric trigonal space group R3 (No. 148)
with Z = 6. The crystallographic unique unit is one third of ‘fac’-
III
[Eu (HL -ala)3]ꢀ8H2O, consisting of one EuIII ion at the special posi-
DL
DL-ala
tion on threefold rotation axis, one tridentate ligand HL
and
two water molecules at the general positions, and two water mol-
ecules at the special positions. As the complex crystallized into a
centrosymmetric space group and has C3 symmetry, the crystal
III
structure consists of two enantiomers of ‘fac’-[Eu (HL -ala)3] and
D
III
‘fac’-[Eu (HL -ala)3]. The complex takes ‘facial’ geometrical configu-
L
ration of two possible ‘facial’ and ‘meridional’ isomers [28].
Fig. 2(a) and (b) show the manner of the hydrogen bonds
Fig. 1(a), (a0), (b), and (b0) show the molecular structures and the
III
around ‘fac’-[Eu (HL -ala)3]. The carboxylate oxygen atom O(2) is
D
III
space filling representations of ‘fac’-[Eu (HL -ala)3] viewed along a
D
Fig. 1. (a) Molecular structure of ‘fac’-[EuIII(HL -ala)3] viewed along the C3 axis with the selected atom numbering scheme, showing ‘facial’ configuration and coordination
geometry of tricapped trigonal prism (TTP). Three imidazole nitrogen atoms N2 and three carboxylate oxygen atoms O1 form the two outer triangular faces, and the capping
positions are occupied by three imine nitrogen atoms N3. Hydrogen atoms except for those bound for the asymmetric carbon atoms are omitted for clarity. (a0) Space filling
representation. (b) Side view of ‘fac’-[EuIII(HLD-ala)3]. (b0) Space filling representation.
D

S. Yamauchi et al. / Polyhedron 49 (2013) 105–112
109
Fig. 2. (a) Hydrogen bonding manner around ‘fac’-[EuIII(HL -ala)3] viewed along the C3 axis. (b) Side view of the hydrogen bonding manner, showing the carboxylate side of the
molecule is covered by the hydrogen bonds consisting of two water molecules O(3) and O(4) and the imidazole side is hydrogen bonded to the symmetry related water
molecule O(4)⁄.
D
Fig. 3. (a) Homochiral 3D network structure constructed by the hydrogen bonds of O(2)ꢀ ꢀ ꢀO(4) and O(4)ꢀ ꢀ ꢀN(1)⁄ viewed projected on the bc-plane, showing all the
constituting molecules with the same chirality are arrayed in the same direction (c-axis). (b) Packing diagram of two 3D networks with opposite chiralities (red and green) in
the crystal lattice, showing the different directions of the two 3D networks. (Color online.)
III
‘fac’-[Eu (HL -ala)3] species (green color) are arrayed in the opposite
direction. Two 3D networks with opposite chiralities are weakly
linked by a water molecule O(5) through the two hydrogen bonds
of O(4)ꢀ ꢀ ꢀO(5) = 2.735(17) Å and O(5)ꢀ ꢀ ꢀO(2)⁄⁄ = 2.703(18) Å to com-
plete the crystal structure. The thermal parameters of O(5), which
plays a role of linker between two 3D networks, are extremely large
compared to those of O(3) and O(4), suggesting that the interaction
between two 3D networks with the opposite chiralities is week.
The D-Fourier synthesis located another peak at the special po-
sition assignable to the water molecule O(6), whose thermal
parameters are even larger than those of O(5). The TGA analysis de-
tected 8 crystal waters, which were found by the X-ray analysis
(O3 ꢃ 1, O4 ꢃ 3, O5 ꢃ 3, O6 ꢃ 1). In the heating mode from room
temperature to 130 °C, the weight loss of 8H2O was observed,
but the sample absorps the amount of 7H2O from the atmospheric
moisture in the cooling mode to room temperature. The TGA data
as well as the X-ray structural analysis demonstrate that these
water molecules are essential for the formation of the crystal struc-
ture. The lost one water must be O(6).
L
hydrogen bonded to a water molecule O(4) with O(2)ꢀ ꢀ ꢀO(4) =
2.690(10) Å. Three O(4) oxygen atoms generated by C3 symmetry
operations are hydrogen bonded to a water molecule O(3) on C3
rotation axis with O(3)ꢀ ꢀ ꢀO(4) = 2.762(6) Å. As shown in Fig. 2(a)
and (b), three O(3)ꢀ ꢀ ꢀO(4) and three O(4)ꢀ ꢀ ꢀO(2) hydrogen bonds
cover or cap the carboxylate side of the complex. Three imidazole
III
nitrogen atom N(1) of a ‘fac’-[Eu (HL -ala)3] at the imidazole side
D
are hydrogen bonded to O(4)⁄ generated by the symmetry opera-
tion with N(1)ꢀ ꢀ ꢀO(4)⁄ = 2.780(8) Å. In turn, the water oxygen atom
O(4) is hydrogen bonded to the imidazole nitrogen atom N(1)⁄ of
III
the adjacent ‘fac’-[Eu (HL -ala)3], in addition to the hydrogen bonds
D
of O(4)ꢀ ꢀ ꢀO(2) and O(4)ꢀ ꢀ ꢀO(3). Thus the water molecule O(4) plays
a linker between adjacent complexes, where the species with same
chirality are linked by the hydrogen bonds through O(4) to form a
homo-chiral 3D network structure. Fig. 3(a) shows the homo-chiral
3D network structure viewed perpendicular to the b-axis, in which
the 3D network with the opposite chirality is omitted in Fig. 3(a).
III
In the crystal lattice, all the ‘fac’-[Eu (HL -ala)3] species (red color)
D
of the 3D network are arrayed in the same direction and all the

110
S. Yamauchi et al. / Polyhedron 49 (2013) 105–112
D-phe
Fig. 4. (a) Molecular structure of ‘mer’-[EuIII(HL
)2(HL -phe)] with the selected atom numbering scheme, showing ‘meridional’ configuration and coordination geometry of
L
capped square antiprism (CSAP). Two imidazole nitrogen atoms of two tridentate ligands and one carboxylate oxygen atom of one ligand (N2, N8, O3) form the one outer
triangular face, two carboxylate oxygen atoms and one imidazole nitrogen atom (O1, O5, N5) form the another outer triangular face, and the capping positions are occupied
by three imine nitrogen atoms (N3, N6, N9). Hydrogen atoms except for those bound for the asymmetric carbon atoms are omitted for clarity. (a0) Space filling representation
D-phe
of ‘mer’-[EuIII(HL
)2(HL -phe)]. (b) Side view of ‘mer’-[EuIII(HLD-phe)2(HLL-phe)]. (b0) Space filling representation.
L
III
3.2.2. Crystal structure of ‘mer’-[Eu (HL -phe)3]ꢀ7.75H2O (2)
DL
The complex 2 crystallized into a centrosymmetric tetragonal
space group I41/a (No. 88) with Z = 16. The crystallographic unique
III
unit consists of one ‘mer’-[Eu (HL -phe)3] and several water mole-
DL
cules as the crystal solvents. In the crystal lattice two enantiomers
D-phe
related by an inversion center, ‘mer’-[EuIII(HL
)2(HL -phe)] and
L
‘mer’-[EuIII(HL
)(HL -phe)2], exist. Fig. 4 shows the molecular
D-phe
L
structure of ‘mer’-[EuIII(HLD-phe)2(HLL-phe)] involving two HL
D-phe
and one HL -phe, in which two of three ligands with NNO donor
L
set array in the same direction and one ligand arrays in the oppo-
site direction forming ‘meridional’ configuration. The EuIII ion is
coordinated by N6O3 donor atoms of three tridentate ligands and
the coordination geometry is approximately described as a capped
square antiprism (CSAP). In the CSAP geometry with the ‘meridio-
nal’ configuration, two imidazole nitrogen atoms of two tridentate
ligands and one carboxylate oxygen atom of one ligand (N2, N8,
O3) form the one outer triangular face, two carboxylate oxygen
atoms and one imidazole nitrogen atom (O1, O5, N5) form the an-
other outer triangular face, and the capping positions are occupied
by three imine nitrogen atoms (N3, N6, N9). Three EuꢁO distances
are 2.397(9)ꢁ2.448(8) Å, and three EuꢁN(imine) distances are
2.548(9)ꢁ2.596(9) Å, and three EuꢁN(imidazole) distances are
2.569(9)ꢁ2.589(9) Å.
Two intermolecular imidazoleꢀ ꢀ ꢀcarboxylate hydrogen bonds of
N(1)ꢀ ꢀ ꢀO(5)⁄ = 2.837(12) Å and O(4)ꢀ ꢀ ꢀN(4)⁄ = 2.694(14) Å are re-
peated to gives a one-dimensional chain structure, where the chain
consists of two enantiomers (DDL)11 (above) or (DLL)11 (below). The
chain structure of (DDL is shown in Fig. 5(a). As shown in
)
11
Fig. 5(b), the adjacent chains with (DDL
)
and (DLL)11 were hydro-
11
Fig. 5. (a) One-dimensional structure of ‘mer’-[EuIII(HLL-phe)2(HL -phe)] running
D
gen-bonded through a crystal water O(10) (gray) with N(7)ꢀ ꢀ ꢀO(10)
= 2.744(16) Å and O(2)ꢀ ꢀ ꢀO(10) = 2.637(16) Å. Another two crystal
waters O(7) and O(4) are hydrogen bonded to the carboxylate
along the c-axis constructed by intermolecular imidazoleꢀ ꢀ ꢀcarboxylate hydrogen
bonds. (b) The adjacent chains with (DDL
through a crystal water O(10).
)11 and (DLL)11 are lined by hydrogen-bonds

S. Yamauchi et al. / Polyhedron 49 (2013) 105–112
111
Fig. 6. Excitation and emission spectra of ‘fac’-[EuIII(HL -ala)3]ꢀ8H2O (1) in the solid state at room temperature. The emission spectrum was measured by excitation at 296 nm.
DL
Fig. 7. Excitation and emission spectra of ‘mer’-[EuIII(HL -phe)3]ꢀ7.75H2O (2) in the solid state at room temperature. The emission spectrum was measured by excitation at
DL
309 nm.
oxygen atoms of ‘mer’-[EuIII(HLL-phe)2(HL -phe)] with O(7)ꢀ ꢀ ꢀO(4) =
2.67(4) Å and O(14)ꢀ ꢀ ꢀO(6) = 2.99(4) Å. The several other peaks
assignable to the crystal waters were located on the D-Fourier
but the thermal parameters were extremely large. Three crystal
waters of O(7), O(10), and O(14) are bound by the hydrogen bonds,
but the other crystal waters can easily eliminate, being consistent
with the TGA result.
larger than those of 1. The 5D0 ? 7F1 transition is magnetic-dipolar
in character, and the emission intensity of the transition is rela-
tively independent of the coordination environment around the
europium(III) ion. On the other hand, the 5D0 ? 7F2 transition is
predominantly electric-dipolar in character, and the emission
intensity of the transition is very sensitive to the coordination
environment around the europium(III) ion [33–35]. These different
emission spectra of 1 and 2 may be caused by the different coordi-
nation environment around the europium ion: the ‘fac’-coordina-
tion environment for 1, and the ‘mer’-coordination environment
for 2 with lower symmetry.
The luminescence quantum yields in the solid state obtained
by an absolute method at room temperature (kex = 302 nm) is
0.25 for 1, and 0.30 for 2, respectively. The luminescence life times
in the solid state obtained at room temperature (kex = 302 nm) is
1.40 ms for 1, and 1.23 ms for 2, respectively.
D
3.3. Luminescence properties
Bright red luminescence based on the fꢁf transitions is visibly
DL-ala
III
observed for ‘fac’-[EuIII(HL
)3]ꢀ8H2O (1) and ‘mer’-[Eu (HL -phe)3]ꢀ
DL
2
7.75H O (2) when the samples in the solid state were irradiated by
UV light. The excitation and emission spectra of 1 and 2 in the solid
state are shown in Figs. 6 and 7. Broad bands in the range of
200–350 nm at the maximum around 300 nm were observed in
the excitation spectra of both 1 and 2. On the other hand, the emis-
sion spectra of 1 and 2 show a different pattern. The emission spec-
trum of 1 displays emission bands at 582 nm (5D0 ? 7F0), 595 nm
(5D0 ? 7F1), 618 nm (5D0 ? 7F2), 651 nm (5D0 ? 7F3), and 690,
695, 704, 710 nm (5D0 ? 7F4). The emission spectrum of 2 displays
emission bands at 581 nm (5D0 ? 7F0), 592, 595 nm (5D0 ? 7F1),
617, 620 nm (5D0 ? 7F2), 653 nm (5D0 ? 7F3), and 687, 692,
698 nm (5D0 ? 7F4). A single peak is observed for the 5D0 ? 7F1
transition of 1, whereas splitting two peaks are observed for that
of 2, although the amounts of fluorescence (total area of the emis-
sion bands) of the emission bands for the 5D0 ? 7F1 transition are
almost the same [32]. Moreover, the amount of fluorescence of
the emission bands for the 5D0 ? 7F2 transition of 2 is 1.7 times
Acknowledgements
H. Hagiwara was supported by the Research Fellowship for
young scientists of the Japan Society for the Promotion of Science.
Appendix A. Supplementary data
CCDC 885087 and 885088 contain the supplementary crystallo-
DL-ala
III
graphic data for [EuIII(HL
)3]ꢀ8H2O (1) and [Eu (HL -phe)3]-
DL
2
ꢀ7.75H O (2). These data can be obtained free of charge via http://
www.ccdc.cam.ac.uk/conts/retrieving.html, or from the Cambridge

112
S. Yamauchi et al. / Polyhedron 49 (2013) 105–112
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