Copper(II) and lanthanoid(III) complexes of a new β-diketonate ligand with an appended non-coordinating phenol group

Article abstract of DOI:10.1016/j.poly.2008.11.025

New mononuclear compounds of the ligand 1-(2-hydroxyphenyl)-3-phenylpropane-1,3-dione (H₂L) with Cu(II) and several lanthanoid(III) ions, where Ln(III) = Pr, Nd, Eu, Gd, have been synthesized and characterized by spectroscopic methods and X-ray

Full text of DOI:10.1016/j.poly.2008.11.025

Polyhedron 28 (2009) 457–460
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Polyhedron
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Copper(II) and lanthanoid(III) complexes of a new b-diketonate ligand
with an appended non-coordinating phenol group
a
b
b
a
Stefania Tanase a, , Marta Viciano-Chumillas , Jan M.M. Smits , René de Gelder , Jan Reedijk
*
a Leiden Institute of Chemistry, Gorlaeus Laboratories, Leiden University, P.O. Box 9502, 2300 RA, Leiden, The Netherlands
b Radboud University Nijmegen, Institute for Molecules and Materials, Heyendaalseweg 135, 6525 AJ, Nijmegen, The Netherlands
a r t i c l e i n f o
a b s t r a c t
Article history:
New mononuclear compounds of the ligand 1-(2-hydroxyphenyl)-3-phenylpropane-1,3-dione (H2L) with
Cu(II) and several lanthanoid(III) ions, where Ln(III) = Pr, Nd, Eu, Gd, have been synthesized and charac-
terized by spectroscopic methods and X-ray crystal structure determinations. In all compounds, the
ligand coordinates in a bidentate chelating manner, using the diketone function. In the [Cu(HL)2], the
coordination geometry of Cu(II) ion is slightly distorted square-planar; two strong intramolecular
(OHꢀ ꢀ ꢀO) hydrogen-bonding interactions are established between the phenolate group and the neighbor-
ing ketone function. The lanthanoid(III) compounds have the general formula [Ln(HL)3(CH3OH)2] ꢀ
CH3OH ꢀ 2H2O; the lanthanoid(III) ion (Ln) is eight-coordinated and the coordination geometry is based
on a distorted square-antiprism. In addition to the intramolecular hydrogen bonding (OHꢀ ꢀ ꢀO), intermo-
lecular hydrogen-bonding interactions are also present between the coordinated methanol molecule and
the non-coordinated methanol molecule giving rise to a three-dimensional network.
Received 10 October 2008
Accepted 16 November 2008
Available online 26 December 2008
Keywords:
Copper(II)
Lanthanoid(III)
b-Diketone
Crystal structure
Ó 2008 Elsevier Ltd. All rights reserved.
1. Introduction
2. Experimental
The construction of molecular assemblies through the coordina-
tion of a metal ion with polydentate organic ligands has become a
fascinating area of interest in inorganic chemistry. Particularly,
coordination compounds of b-diketone ligands have attracted con-
siderable attention due to their often supramolecular architectures
and their peculiar optical or magnetic properties [1]. Transition-
metal complexes based on various analogues of acetylacetone have
been largely studied and most of the examples reported so far be-
long to the category of cluster compounds [1]. Considerably fewer
examples of compounds with extended networks have been iso-
lated [1–5]. The coordination ability of b-diketone ligands towards
lanthanoid(III) ions has been studied and representative examples
of the formation of highly coordinated complexes are the lantha-
noid(III) tris-(b-diketonates) containing several nitrogen ligands
such as 2,20-bipyridine, and 1,10-phenanthroline or their deriva-
tives [6–8]. In this work, we report the synthesis, spectroscopic
characterization and X-ray crystal structure determination of
new Cu(II) and lanthanoid(III) complexes with the ligand 1-(2-
hydroxyphenyl)-3-phenylpropane-1,3-dione (H2L). The ligand
was selected because of its potential dual binding modes, namely
coordination and hydrogen-bond donor, or bridging coordination.
2.1. General remarks
Starting materials were purchased from Aldrich and all
manipulations were performed using materials as received. The li-
gand 1-(2-hydroxyphenyl)-3-phenylpropane-1,3-dione (H2L) was
synthesized according to the procedure reported previously for
similar ligands [9].
2.2. Synthesis
[Cu(HL)2] (1). A solution of Cu(NO3)3 ꢀ 3H2O (0.3 mmol) in 10 ml
methanol was added to a solution of the ligand H2L (0.6 mmol) and
triethylamine (0.6 mmol) in 10 ml methanol. Slow evaporation of
the resulting solution afforded green single crystals within one
day. After filtration, the crystalline material was washed with
diethyl ether and dried in air. C30H22CuO6, 1 (M = 542.04 g/mol).
Yield: 52% (85 mg). El. Anal. (%): calc. 66.48 C, 4.45 H; exp. 66.98
C, 4.41 H. IR (m
max/cmꢁ1): 2992 (w), 1616 (m), 1584 (m), 1536
(s), 1517 (s), 1481 (s), 1455 (s), 1430 (m), 1389 (s), 1343 (m),
1309 (s), 1243 (m), 1201 (m), 1160 (w), 1137 (m), 1104 (w),
1056 (m), 1020 (m), 941 (m), 845 (m), 806 (w), 787(m), 764 (m),
749 (m), 728 (s), 702 (s), 686 (s), 580 (m), 563 (s), 526 (m) UV–Vis
(k/nm): 270, 365, 415, 620.
2.2.1. Synthesis of the compounds [Ln(HL)3(CH3OH)2] ꢀ CH3OH ꢀ 2H2O
A solution of Ln(NO3)3 ꢀ 6H2O (0.24 mmol) in 10 ml methanol
was added to a solution of the ligand H2L (0.72 mmol) and trieth-
* Corresponding author.
E-mail address: s.grecea@chem.leidenuniv.nl (S. Tanase).
0277-5387/$ - see front matter Ó 2008 Elsevier Ltd. All rights reserved.
doi:10.1016/j.poly.2008.11.025

458
S. Tanase et al. / Polyhedron 28 (2009) 457–460
ylamine (0.72 mmol) in 10 ml methanol. Slow evaporation of the
resulting solution afforded yellow crystalline material in a few
hours. After filtration, the crystalline material was washed with
diethyl ether and dried in air.
ratio) using methanol as solvent. The infrared spectrum of 1 shows
the vibration characteristic of the organic ligand; the most impor-
tant feature that indicates the coordination of the b-diketone li-
gand to the Cu(II) ion, is the shift of the mC
@ stretching vibration
O
C48H49O12Pr, 2 (M = 990.81 g/mol). Yield: 60% (137 mg). El.
of the carbonyl group to lower energy, ca. 1616 cmꢁ1 as compared
with the free ligand (at 1657 cmꢁ1). The ligand field spectrum,
measured as a solid with the diffuse reflectance technique, shows
a broad band at 620 nm which is ascribed to the d-d transitions
of the Cu(II) ion and a Cu–O charge transfer band at 415 nm.
The molecular structure of 1 consists of a centrosymmetric
mononuclear unit in which the Cu(II) ion is coordinated by two
bidentate chelating HLꢁ ligands that use the diketonate function
for coordination to the metal center (Fig. 1). Schematic geometric
information is given in Table 2. The coordination geometry of Cu(II)
ion is slightly distorted square–planar. The Cu–O bond lengths of
1.889(3) Å and 1.896(4) Å, respectively are normal and comparable
with the similar distances in other Cu(II) complexes with b-diketo-
nate ligands [14–18]. The in-plane O–Cu–O angle differs slightly
from 90°, being 87.03(15)°. As shown in Fig. 1, the molecular struc-
ture is stabilized by two strong intramolecular hydrogen-bonding
interactions established between the phenol group and the
neighboring coordinating ketonate function (O5ꢀ ꢀ ꢀO1 = 2.5038 Å;
O5–H5ꢀ ꢀ ꢀO1 = 144°). A view of the crystal packing of 1 is shown
in Fig. 2; the shortest intermolecular Cuꢀ ꢀ ꢀCu distance is 5.838 Å.
The X-band spectrum of the complex 1 as a powder, recorded at
room temperature (Fig. 3), is slightly anisotropic with a g value of
2.05 and a g|| value of 2.25. No hyperfine splitting is resolved. This
might be due to some exchange interactions leading to exchange
narrowing, in view of the rather short intermolecular CuꢀꢀꢀCu dis-
tance indicated by the X-ray crystal structure.
Anal. (%): calc. 58.19 C, 4.98 H; exp. 58.71 C, 4.57 H. IR (mmax
/
cmꢁ1): 3344 (br), 2988 (m), 2858 (m), 1590 (m), 1544 (m), 1509
(s), 1461 (m), 1394 (m), 1343 (m), 1291 (s), 1199 (m), 1138 (m),
1069 (m), 1023 (m), 937 (m), 842 (m), 755 (m), 711 (m), 676
(w), 622 (s), 516 (m). UV–Vis (k/nm): 270, 345, 410, 485, 608.
C48H49O12Nd, 3 (M = 994.32 g/mol). Yield: 61% (145 mg). El.
Anal. (%): calc. 57.98 C, 4.97 H; exp. 58.06 C, 4.57 H. IR (mmax
/
cmꢁ1): 3346 (br), 2988 (m), 2858 (m), 1590 (m), 1544 (m), 1506
(s), 1462 (m), 1397 (m), 1343 (m), 1291 (s), 1199 (m), 1138 (m),
1066 (m), 1023 (m), 937 (m), 842 (m), 754 (m), 711 (m), 676
(w), 623 (s), 516 (m). UV–Vis (k/nm): 270, 346, 409, 520, 537,
586, 752, 810, 900.
C48H49O12Eu, 4 (M = 1001.86 g/mol). Yield: 85% (210 mg). El.
Anal. (%): calc. 57.55 C, 4.93 H; exp. 57.25 C, 4.17 H. IR (mmax
/
cmꢁ1): 3360 (br), 2988 (m), 2858 (m), 1589 (m), 1542 (m), 1508
(s), 1457 (m), 1394 (m), 1339 (m), 1286 (s), 1198 (m), 1137 (m),
1066 (m), 1023 (m), 937 (m), 841 (m), 753 (m), 710 (m), 676
(w), 622 (s), 516 (m). UV–Vis (k/nm): 270, 348, 408.
C48H49O12Gd, 5 (M = 1007.15 g/mol). Yield: 72% (175 mg). El.
Anal. (%): calc. 57.24 C, 4.90 H; exp. 57.07 C, 4.51 H. IR (mmax
/
cmꢁ1): 3360 (br), 2988 (m), 2858 (m), 1590 (m), 1547 (m), 1510
(s), 1461 (m), 1398 (m), 1334 (m), 1286 (s), 1198 (m), 1137 (m),
1066 (m), 1023 (m), 937 (m), 842 (m), 753 (m), 711 (m), 677
(w), 623 (s), 514 (m). UV–Vis (k/nm): 270, 350, 405.
2.3. Physical measurements
3.2. Synthesis and characterization of the compounds of formula
C, H, and N analyses were performed with a Perkin–Elmer 2400
series II analyzer. Infrared spectra (4000–300 cmꢁ1, resol. 4 cmꢁ1
)
3.2.1. [Ln(HL)3(CH3OH)2] ꢀ CH3OH ꢀ 2H2O
were recorded on a Perkin–Elmer Paragon 1000 FTIR spectrometer
equipped with a Golden Gate ATR device, using the reflectance
technique. Diffuse reflectance spectra were obtained on a Perkin–
Elmer Lambda 900 spectrophotometer using MgO as a reference.
X-band powder EPR spectra were obtained on a Bruker-EMXplus
electron spin resonance spectrometer (Field calibrated with DPPH
(g = 2.0036)).
The reaction of the hydrated lanthanoid(III) nitrates with the
ligand H2L in the presence of triethylamine as base (1:3:3 molar
ratio) and using methanol as solvent afforded yellow crystalline
materials. The analytical studies have shown that these com-
pounds have the general formula [Ln(HL)3(CH3OH)2] ꢀ CH3OH. An
X-ray crystallographic study has been performed for the complex
[Ln(HL)3(CH3OH)2] ꢀ CH3OH (4a) and its crystal structure is
described below. The crystallinity of the complexes
2.4. X-ray crystallography
Intensity data for a single crystal of 1 and 4a were collected
using Mo Ka radiation (k = 0.71073 Å) on a Nonius Kappa CCD dif-
fractometer. Crystal data for 1 and 4a are collected in Table 1. The
intensity data were corrected for Lorentz and polarization effects,
for absorption (multiscan absorption correction) and extinction.
The structures were solved by Patterson methods. The programs
SABABS [10], DIRDIF96 [11] and SHELXL-97 [12] were used for data reduc-
tion, structure solution and structure refinement, respectively.
Refinement of F2 was done against all reflections. The weighted R
factor, wR, and goodness of fit S are based on F2. Conventional R fac-
tors are based on F, with F set to zero for negative F2. All non-hydro-
gen atoms were refined with anisotropic displacement parameters.
All hydrogen atoms were placed at calculated positions and were
refined riding on the parent atoms. Geometric calculations and
molecular graphics were performed with the PLATON package [13].
3. Results and discussions
3.1. Synthesis and characterization of the complex [Cu(HL)2]
Complex 1 is easily obtained by the reaction of hydrated Cu(II)
nitrate with triethylamine and the b-diketone ligand H2L (1:2:2
Fig. 1. View of the molecular structure of 1 showing the intramolecular hydrogen
bonds. Hydrogen atoms not involved in hydrogen bonding were omitted for clarity.

S. Tanase et al. / Polyhedron 28 (2009) 457–460
459
Table 2
Selected bond lengths (Å) and angles (°) for compounds 1 and 4a.
Complex 1
Cu1–O1
Cu1–O3
Cuꢀ ꢀ ꢀCu
1.889(3)
1.896(4)
5.838
O1–Cu1–O3
92.97(15)
Complex 4a
Eu1–O1a
Eu1–O1b
Eu1–O1c
Eu1–O3a
Eu1–O3b
Eu1–O3c
Eu1–O21
Eu1–O23
2.334(3)
2.335(3)
2.319(3)
2.396(3)
2.359(3)
2.347(3)
2.477(3)
2.447(3)
O1a–Eu1–O1b
O1a–Eu1–O1c
O1a–Eu1–O3a
O1a–Eu1–O3b
O1a–Eu1–O3c
O1a-Eu1-O21
O1a–Eu1–O23
O1c–Eu1–O1c
O1b–Eu1–O3a
O1b–Eu1–O3b
O1b–Eu1–O3c
O1b–Eu1–O21
76.17(10)
139.98(10)
71.90(9)
106.77(10)
146.77(10)
76.15(11)
81.96(12)
143.49(10)
138.49(10)
70.76(9)
76.80(10)
121.30(9)
[Ln(HL)3(CH3OH)2] ꢀ CH3OH is partly lost upon removing the crys-
tals from the mother liquid and the elemental analysis and spec-
troscopic studies suggest that these compounds all have the
general formula [Ln(HL)3(CH3OH)2] ꢀ CH3OH ꢀ 2H2O (Ln = Pr 2, Nd
3, Eu 4, Gd 5).
Fig. 2. View of the crystal packing of 1 in the ac plane. Hydrogen atoms were
omitted for clarity. Cuꢀ ꢀ ꢀCu contacts are 5.838 Å.
The IR spectra of compounds 2–5 are nearly identical, in agree-
ment with the fact that these compounds are isostructural. The
binding of the b-diketone ligand to the lanthanoid(III) ions is indi-
Table 1
Crystallographic data for compounds 1 and 4a.
cated by the shift of the mC
@ stretching vibration of the carbonyl
O
group to lower energy, ca. 1590 cmꢁ1 as compared with the free li-
gand at 1657 cmꢁ1. The broad band in the range 3200–3400 cmꢁ1
is characteristic to the mO–H stretching vibrations of the lattice
water molecules.
1
4a
Formula
C30H22CuO6
542.02
Monoclinic
C2/c
26.511(3)
5.8379(3)
16.475(2)
90
114.997(10)
90
2311.1(4)
4
1.564
0.992
208
15011
2006
C48H45O12Eu
965.80
Formula weight
Crystal system
Space group
a (Å)
b (Å)
c (Å)
Triclinic
ꢀ
P1
The UV–Vis absorption spectrum of the ligand shows character-
istic bands at 267, 345 and 425 nm. In the UV range, the spectral
features observed for compounds 2–5 are similar to those observed
for the corresponding ligand. In the visible range, compounds 2 and
3 display the characteristic bands due to the f–f transitions. Room-
12.5036(19)
13.9203(15)
14.406(2)
67.418(12)
85.335(16)
67.022(9)
2124.5(6)
2
1.510
1.541
208
46359
9667
0.0424
0.0450
0.0934
1.120
ꢁ0.53, 1.76
a
(°)
b (°)
c
(°)
p ?
p* and
V (Å3)
temperature excitation in the UV absorption bands (
n ?
p
*) of the free ligand does not result in lanthanoid emission
Z
Dcalc (mg mꢁ3
)
in these complexes. This result points to the presence of efficient
non-radiative deactivation pathways in all compounds, which is
due to the presence of lattice water molecules. Nevertheless, a
l
(Mo-a
) (mmꢁ1
)
T (K)
Data collected
Unique data
Rint
R(F) [I > 2
Rw(F2)
S
weak ligand emission was observed at kem = 545 nm (kexc
=
0.0317
0.0686
0.1877
1.101
275 nm).
r
(I)]
The crystal structure of 4a consists of a mononuclear Eu(III)-
containing molecule, [Eu(HL)3(CH3OH)2] and a lattice methanol
molecule. As shown in Fig. 4, the Eu(III) ion is eight-coordinated
by three monodeprotonated ligands (HLꢁ) and two methanol mol-
ecules. The coordination geometry of Eu(III) is based on distorted
square-antiprism; the two bases are identical and they are formed
by two oxygen atoms of the same bidentate ligand, an oxygen
atom of a second HL- ligand and an oxygen atom from a methanol
molecule. Selected bond lengths and angles are listed in Table 2.
The Eu–O bond lengths are in the range 2.320(4)–2.479(3) Å, with
the Eu–O bond lengths involving the methanol molecules being the
longest. The average of the C–O bond length of the b-diketone
group is ca. 1.269 Å, much shorter than the corresponding bond
in other lanthanoid(III) complexes with b-diketone ligands. This
D
qmin
,
D
qmax (e Åꢁ3
)
ꢁ0.43; 2.33
gII = 2.25
g⊥ = 2.05
short distance suggests a lower
p-electron delocalization of the
C@O bond [19].
The molecular structure is stabilized by multiple intra- and
intermolecular O–Hꢀ ꢀ ꢀO hydrogen-bonding interactions (Fig. 5,
Table 3). Three intramolecular hydrogen bonds are established
between the phenolic group and the neighboring oxygen of the
diketonate function. Additionally, the phenolic group of the ligand
is also involved in a hydrogen bond with one of the coordinated
2800
3200
3600
4000
Magnetic Field / Gauss
Fig. 3. Room temperature EPR spectrum of complex 1.

460
S. Tanase et al. / Polyhedron 28 (2009) 457–460
methanol molecule of a neighboring mononuclear unit. The second
coordinated methanol molecule establishes a hydrogen bonding
interaction with the non-coordinated methanol molecule. All these
interactions give rise to a complicated three-dimensional crystal
structure. The shortest intermolecular Euꢀ ꢀ ꢀEu distance is
13.920 Å along the b-axis.
4. Conclusions
The reaction of a new b-diketonate ligand, 1-(2-hydroxy-
phenyl)-3-phenylpropane-1,3-dione, with Cu(II) and Ln(III) ions
does result in the formation of mononuclear complexes. In all com-
pounds, the ligand is coordinated in a bidentate chelating manner,
using the diketone function for coordination to the metal center,
and stabilization of the chromophore by strong intramolecular
hydrogen bonding (OHꢀ ꢀ ꢀO). The preparation of the compounds re-
ported in this paper offers promising prospects in the direction of
heterobimetallic polynuclear compounds. We are currently explor-
ing the coordination chemistry of the 1-(2-hydroxyphenyl)-3-phe-
nylpropane-1,3-dione ligand with other metals.
Supplementary data
CCDC 705139 - 705140 contains the supplementary crystallo-
graphic data for the compounds 1 and 4a. These data can be ob-
tained free of charge via http://www.ccdc.cam.ac.uk/conts/
retrieving.html, or from the Cambridge Crystallographic Data Cen-
tre, 12 Union Road, Cambridge CB2 1EZ, UK; fax: (+44) 1223-336-
033; or e-mail: deposit@ccdc.cam.ac.uk.
Fig. 4. View of the molecular structure of 2. The non-coordinated methanol
molecule and hydrogen atoms were omitted for clarity.
Acknowledgments
This research was financially supported by a Veni grant from
the Netherlands Organization for Scientific Research (NWO) to S.
T. and the ECNetwork of Excellence ‘‘MAGMANet’’ (No. 515767-2).
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Fig. 5. View of the hydrogen bonding interactions in 2.
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Table 3
Details of the hydrogen bonding interactions in 4a.
D–H
Hꢀ ꢀ ꢀA
Dꢀ ꢀ ꢀA
D–Hꢀ ꢀ ꢀA
O5a–H5aꢀ ꢀ ꢀO3a
O5b–H5bꢀ ꢀ ꢀO3b
O5c–H5cꢀ ꢀ ꢀO3c
O21–H21ꢀ ꢀ ꢀO5b
O23–H21ꢀ ꢀ ꢀO25
O25–H25ꢀ ꢀ ꢀO5a
0.83
0.83
0.83
0.94
0.94
0.83
1.76
1.75
1.76
1.89
1.83
1.98
2.489(5)
2.489(4)
2.495(4)
2.711(4)
2.673(6)
2.789(6)
146.1
146.9
146.5
144.4
147.3
163.3
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