Structural and photophysical behavior of lanthanide complexes with a tetraazacyclododecane featuring carbamoyl pendant arms

Article abstract of DOI:10.1039/a809459d

The crystal and molecular structure of 1,4,7,10-tetrakis(N-benzylcarbamoylmethyl)-1,4,7,10-tetraazacyclododecane, L¹, revealed an S₂-symmetric molecule. One pair of pendant arms is involved in intramolecular hydrogen bonding while th

Full text of DOI:10.1039/a809459d

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Structural and photophysical behaviour of lanthanide complexes
with a tetraazacyclododecane featuring carbamoyl pendant arms†
Gaël Zucchi,a Rosario Scopelliti,a Pierre-André Pittet,a Jean-Claude G. Bünzli*a and
Robin D. Rogersb
a Institute of Inorganic and Analytical Chemistry, University of Lausanne, CH-1015 Lausanne,
Switzerland. E-mail: Jean-claude.Bunzli@icma.unil.ch
b Department of Chemistry, The University of Alabama, Tuscaloosa, Alabama, 35487-0336,
USA
Received 3rd December 1998, Accepted 21st January 1999
The crystal and molecular structure of 1,4,7,10-tetrakis(N-benzylcarbamoylmethyl)-1,4,7,10-tetraazacyclododecane,
L1, revealed an S2-symmetric molecule. One pair of pendant arms is involved in intramolecular hydrogen bonding
while the other interacts with two other ligand molecules through strong intermolecular hydrogen bonds. In solution,
the ligand adopts a similar geometrical arrangement at low temperature but complexes with EuIII and LuIII display an
averaged C4-symmetry on the NMR timescale. One isomer only was detected, as reported for similar complexes, and
the arrangement around EuIII and LuIII appears to be rigid while it is more fluxional around LaIII. Rotation of the
benzyl group around the amide function was observed for EuIII and a dynamic NMR study in the range 253–333 K
yielded ∆H‡ = 43.0 0.1 kJ molϪ1, ∆S‡ = Ϫ49.3 0.4 J KϪ1 molϪ1 and k298 = 47.7 1.1 sϪ1. In the solid state,
anhydrous eight-co-ordinate complexes were isolated and high resolution luminescence spectroscopy of EuIII in the
europium and Eu-doped compounds of La, Gd and Lu confirmed a site symmetry close to C4 along the lanthanide-
series. Energy transfer from the L1 3ππ* state to the Tb(5D4) excited state is sizable leading to an absolute quantum
yield of 6.4% in MeCN, while the EuIII luminescence is only poorly sensitized, possibly because of photoinduced
electron transfer processes. The Tb(5D4) and Eu(5D0) lifetimes for both solid state samples and solutions in MeCN
are consistent with no water molecule in the inner co-ordination sphere but addition of water results in the ninth
co-ordination site being bound to H2O: number of bound waters, q = 0.96 (Eu) and 0.71 (Tb) in MeCN ϩ 2 M H2O
and 1.19 (Eu) and 1.30 (Tb) in water. The relaxivity r1 of the gadolinium() complex is pH dependent and varies
between 4.08 (pH 0.8), 1.88 (6.7) and 6.14 (11.1) mϪ1 sϪ1
.
labelling of biomolecules. Since lanthanide() ions have
extremely weak molar absorption coefficients, we have chosen a
ligand with phenyl moieties to provide chromophoric groups
favouring light harvesting and energy transfer onto the metal
ion. Ligand L1 [1,4,7,10-tetrakis(N-benzylcarbamoylmethyl)-
1,4,7,10-tetraazacyclododecane] features eight co-ordinating
donor atoms, satisfying the large co-ordination number
requirement of lanthanide() ions, while leaving an extra
position free for water co-ordination and exchange, a manda-
tory condition for contrast agents. We expect that the
lanthanide ions will be tightly encapsulated between the
macrocyclic ring and the pendant arms, as was recently shown
for [Eu(L2)][trif]3 {L2 is 1,4,7,10-tetrakis[N-(1-phenylethyl)-
carbamoylmethyl]-1,4,7,10-tetraazacyclododecane, trif = O3-
SCF3}.10 In this paper we present a solid state and solution
study of ligand L1 and its complexes with Ln(trif)3 (Ln = La,
Nd, Eu, Gd or Tb) with particular reference to structural and
photophysical properties.
Introduction
Lanthanide macrocyclic edifices with ligands derived from
cyclen (1,4,7,10-tetraazacyclododecane) are being intensively
studied in view of their potential applications in biomedical
research. These complexes are thermodynamically stable and
kinetically inert to the release of lanthanide() ions in water.
Some of them are used as contrast agents in magnetic reson-
ance imaging (MRI),1,2 as diagnostic and therapeutic radio-
pharmaceuticals,3 as catalysts for the hydrolysis of phosphate
diester bonds,4 or as responsive luminescent lanthanide()
chelates for the analysis of bioactive ions and molecules.5,6
Furthermore, the paramagnetism of the lanthanide(III) ions,
particularly EuIII, can be taken advantage of to determine
the solution structure of their complexes by analysing the lan-
thanide induced shifts in the NMR spectra.7
In addition, complexes of EuIII and TbIII often display useful
luminescent properties since the metal ions have easily recog-
nizable narrow emission spectra and long excited state lifetimes,
in the millisecond range, provided that the metal ion is effi-
ciently protected from non-radiative deactivation processes.8 In
view of the effectiveness of cyclen derivatives with carbamoyl
pendant arms to complex lanthanide ions and to display sizable
luminescence,9 we have launched a research programme with
the aim of detecting whether ligands for potential contrast
agents could simultaneously yield edifices for the luminescent
† Supplementary data available: least-squares planes, relaxation times,
NMR and electronic spectra. For direct electronic access see http://
www.rsc.org/suppdata/dt/1999/931/, otherwise available from BLDSC
(No. SUP 57491, 12 pp.) or the RSC Library. See Instructions for
Authors, 1999, Issue 1 (http://www.rsc.org/dalton).
J. Chem. Soc., Dalton Trans., 1999, 931–938
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Table 1 Selected bond lengths (Å) and angles (Њ) in L1
O(1)–C(6)
1.232(4)
1.457(4)
1.473(4)
1.474(4)
1.339(4)
1.344(5)
1.526(5)
1.508(5)
1.395(5)
1.375(5)
1.387(5)
1.496(5)
1.388(5)
1.369(6)
1.389(6)
O(2)–C(15)
N(1)–C(4)a
N(2)–C(14)
N(2)–C(2)
N(3)–C(7)
N(4)–C(16)
C(3)–C(4)
1.237(4)
1.466(4)
1.459(4)
1.480(4)
1.448(4)
1.467(4)
1.522(5)
1.524(5)
1.381(5)
1.385(5)
1.375(5)
1.512(5)
1.382(5)
1.380(5)
1.377(6)
N(1)–C(5)
N(1)–C(1)
N(2)–C(3)
N(3)–C(6)
N(4)–C(15)
C(1)–C(2)
C(7)–C(8)
C(5)–C(6)
C(8)–C(9)
C(8)–C(13)
C(10)–C(11)
C(12)–C(13)
C(16)–C(17)
C(17)–C(18)
C(19)–C(20)
C(21)–C(22)
C(9)–C(10)
C(11)–C(12)
C(14)–C(15)
C(17)–C(22)
C(18)–C(19)
C(20)–C(21)
C(5)–N(1)–C(4)a
C(4)a–N(1)–C(1)
C(14)–N(2)–C(2)
C(6)–N(3)–C(7)
N(1)–C(1)–C(2)
N(2)–C(3)–C(4)
N(1)–C(5)–C(6)
O(1)–C(6)–C(5)
N(3)–C(7)–C(8)
O(2)–C(15)–N(4)
N(4)–C(15)–C(14)
113.5(3)
114.3(3)
113.0(3)
121.4(3)
111.9(3)
114.6(3)
116.7(3)
121.2(4)
114.5(3)
123.7(4)
115.9(4)
C(5)–N(1)–C(1)
C(14)–N(2)–C(3)
C(3)–N(2)–C(2)
111.5(3)
110.8(3)
111.4(3)
C(15)–N(4)–C(16)
N(2)–C(2)–C(1)
N(1)a–C(4)–C(3)
O(1)–C(6)–N(3)
N(3)–C(6)–C(5)
N(2)–C(14)–C(15)
O(2)–C(15)–C(14)
N(4)–C(16)–C(17)
122.4(3)
111.1(3)
112.7(3)
123.2(3)
115.6(3)
115.9(3)
120.4(4)
113.5(3)
a Symmetry code: Ϫx ϩ 1, Ϫy, Ϫz ϩ 1.
rings at a C ؒ ؒ ؒ C stacking distance of about 3.5 Å, while the
C17–C22 aromatic rings participate in weaker, edge-to-face
interactions with neighbouring chains (closest C ؒ ؒ ؒ C distance:
4 Å).
Analysis of the 12-membered ring confirms a double-chair
conformation with nitrogen atoms N1, N2 in the upper part
while the N atoms generated by the crystallographic inversion
centre (N1A, N2A) lie in the lower part (deviations from
the mean plane: N1 Ϫ0.411, N2 Ϫ0.629, C2 ϩ0.023 and C4
ϩ0.025 Å).
Fig. 1 Molecular structure of L1 showing the atom-numbering scheme
and the intramolecular (a) and interstrand intramolecular (b) hydrogen
bonds.
At room temperature a solution of L1 in CD3OD exhibits 1H
and 13C NMR spectra characteristic of a fluxional species, with
respect to arm rotation and ring inversion processes. For
instance, the 13C spectrum displays one broad signal for the
amide carbon atoms (δ 169.0), four signals for the aromatic
carbon atoms (δ 140.3, 130.5, 129.4 and 129.2), one for
NCH2CO (δ 57.3), one broad signal for the ring CH2 (δ 52.5)
and one for CH2Ph (δ 45.2), pointing to a time-averaged C4
symmetry. Upon cooling, however, most of the signals become
narrow and several split. At 212 K the 13C spectrum is consist-
ent with a diagonal symmetry. More specifically, two sharp
signals are observed for the amide carbon atoms, eight for
the aromatic carbon atoms, two for each of the methylenic
NCH2CO and CH2Ph groups, while one broad signal only is
observed at δ 52.9 for the ring methylene carbon atoms (Fig. 2).
This points to a solution structure close to the one observed in
the solid state as far as the pendant arms are concerned, while
the ring inversion process is still fast on the NMR timescale at
this temperature.
Results and discussion
Solid state and solution structure of L1
Colourless single crystals of L1 suitable for X-ray analysis were
obtained from acetonitrile. The molecular structure (Fig. 1)
is, to the best of our knowledge, the first reported for such a lig-
and in its free form and confirms the 1,7-trans arrangement
predicted for similar molecules on the basis of photophysical
data.9b Selected bond lengths and distances are in Table 1. The
molecule lies on a crystallographic inversion centre and displays
S2 symmetry with two sets of equivalent opposite pendant
arms. The four-bladed propeller shape of the molecule, with
maximum expansion of the pendant arms, results from a
network of hydrogen bonds (Table 2) and stacking interactions:
(i) one pair of arms are further connected to the 12-membered
ring through two intramolecular hydrogen bonds involving the
H4 atom of the amide function and N1, N2. The presence of
the intramolecular interaction explains why all the atoms
belonging to this pair of arms (phenyl ring not included) lie on
the same plane: the maximum and minimum deviations from
the mean plane are Ϫ0.016 (C14) and ϩ0.001 Å (C16) and the
interplanar angle with the phenyl ring amounts to 81.3Њ. (ii) The
two other arms are involved in strong intermolecular hydrogen
bonding through the H3 atoms of their amide groups and the
N3 atoms of two other ligand molecules. The amide functions
of these arms are planar, the deviations from the least-squares
planes being Ϫ0.003 (O1), Ϫ0.003 (N3), Ϫ0.002 (C5) and 0.008
Å (C6), while the interplanar angle with the least-squares plane
of the C8–C13 aromatic ring is 79.8Њ. (iii) In addition, the
C8–C13 aromatic rings face-to-face interact with similar phenyl
Solution structure of the [Ln(L1)][trif]3 complexes
Ligand L1 reacts with lanthanide triflates to yield 1:1 com-
plexes the formulation of which, after drying under vacuum at
333 K, is consistent with anhydrous [Ln(L1)][trif]3. We note that
C4-symmetric monohydrated complexes of Eu and Dy with L2
have been evidenced by X-ray crystallography.10 Complexation
is evidenced in the vibrational spectra which show a red shift of
the ν(C᎐O) mode. The presence of a single ν(C᎐O) stretching
᎐
᎐
band ascertains that the ions are bound by all of the amide
groups. Despite numerous attempts, involving different solvent
mixtures and counter anions, the isolated crystals were all
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J. Chem. Soc., Dalton Trans., 1999, 931–938

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twinned and not suitable for X-ray analysis. We have therefore
investigated the solution structure of the complexes in CD3OD
by 13C (Table 3) and 1H (Table 4) NMR spectroscopy.
co-ordination environment appears to be quite rigid, including
the macrocyclic ring, since two sharp signals are observed for
the ring carbon atoms while the amide carbon atoms appear
as one signal. The 1H NMR spectrum is also temperature
independent and shows nine resonances (Fig. 3) as reported
for other lanthanide complexes with amide7 or phosphin-
ate 11 substituted tetraazacyclododecanes. A dynamic process
involving the macrocyclic carbon atoms takes place at higher
temperature, the corresponding signals becoming broader and
closer at 333 K, a too high temperature, however, given the
solvent used, to study the corresponding exchange mechanism.
Proton assignments have been achieved with the help of
a COSY spectrum (Fig. F1, SUP 57491) and by considering the
Newman representation shown in Fig. 3. They are consistent
with the above discussion. The resonances of the aromatic
protons appear as a broad signal between δ 7.31 and 7.22 and
the methylenic protons CH2Ph give rise to two doublets shifted
[Lu(L1)][trif]3. The 13C NMR spectrum of this compound
displays nine resonances in the range 212 to 333 K, character-
istic of a complex with time-averaged C4 symmetry (Fig. 2). The
Fig. 2 13C-{1H} NMR Spectra of L1 (212 K, bottom trace) and
[Lu(L1)][trif]3 (295 K, ≈10Ϫ2 , top trace) in CD3OD. The assignment
refers to the numbering illustrated.
Fig. 3 The 1H NMR (360.16 MHz) spectrum of [Lu(L1)][trif]3 ≈10Ϫ2 
in CD3OD at 295 K. Asterisks point to the signals of the solvent
(δ 3.21) and water (δ 4.80).
Table 2 Hydrogen bonding geometry in the crystal structure of L1
Donor–hydrogen ؒ ؒ ؒ acceptor
D–H/Å
H ؒ ؒ ؒ A/Å
D ؒ ؒ ؒ A/Å
D–H ؒ ؒ ؒ A/Њ
N(3)–H(3A) ؒ ؒ ؒ O(1)a
N4–H(4A) ؒ ؒ ؒ N(1)
N4–(H4A) ؒ ؒ ؒ N(2)
1.032
1.034
1.844
2.032
2.281
2.869(4)
2.973(4)
2.739(4)
171.7
150.1
105.1
a Symmetry code: Ϫx ϩ 1, Ϫy, Ϫz ϩ 1.
Table 3 13C-{1H} NMR Chemical shifts (δ, Irel) of [LnL1][CF3SO3]3 (Ln = Lu or Eu) ≈ 10Ϫ2 M in CD3OD (90.6 MHz, 295 K)a
Ln
Lu
Eu
CO
C6H5
NCH2CO
64.0 (1)
ring CH2
PhCH2
45.8 (1)
39.9 (1)
177.6
190.5
138.8 (q, 1), 130.5 (2),
129.7 (1), 129.2 (2)
137.5 (q, 1), 129.1 (2),
128.4 (1), 127.4 (2)
57.1 (1), 56.4 (1)
107.2 (1), 90.8 (1)
75.7 (br, 1)
a Key: q = quaternary, br = broad; all other peaks are singlets.
Table 4 1H NMR Chemical shifts (δ, Irel, J/Hz) of [LnL1][CF3SO3]3 (Ln = Lu or Eu) 10Ϫ2 M in CD3OD (360.16 MHz, 295 K)a
ring CH2
Ln
Lu
Eu
C6H5
C6H5CH2
NCH2CO
equatorial
axial
7.31–7.22 (5)
4.42 (d, 1), 4.35 (d, 1)
2J = 14.8
2.98 (d, 1), 2.35 (d, 1)
2J = 16.8
Ϫ13.76 (br, 1), Ϫ14.29
(br, 1)
2.51 (dd, 1), 2.26 (dd, 1)
3.24 (td, 1), 2.01 (td, 1)
25.61 (1), Ϫ7.94 (1)b
2Jgem(ax-eq) = 3Jax-ax = 14.5, 3Jax-eq = 2.1
Ϫ2.37 (1), Ϫ6.63 (1)
6.35 (2), 6.24 (1),
6.17 (2)
2.59 (d, 1), 2.14 (d, 1)
2J = 11.9
a Key: d = doublet, dd = doublet of doublets, td = triplet of doublets, br = broad; other peaks are singlets; CONH protons exchange with the solvent.
b Broad bands; assignment eq/ax impossible (see text).
J. Chem. Soc., Dalton Trans., 1999, 931–938
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Fig. 4 Eyring plot for the benzyl rotation in [Eu(L1)][trif]3 (2.3 × 10Ϫ2
 in CD3OD).
to lower field due to the proximity of the phenyl groups. The
axial protons of the ring CH2 groups (Hb and Hc) reveal vicinal
coupling in addition to geminal coupling and appear as two
triplets of doublets, while the equatorial protons (Ha, Hd) show
up as two broad doublets.
[Eu(L1)][trif]3. At room temperature the 13C NMR spectrum
displays nine resonances, as for the lutetium(III) complex, which
were assigned on the basis of a simultaneous analysis of the 1H
NMR and 13C–1H HSQC (Heteronuclear Single Quantum
Coherence) spectra (Fig. F2, SUP 57491) and which again
point to a time-averaged C4 symmetry. By increasing the tem-
perature the same phenomenon observed for the lutetium com-
plex and involving the macrocyclic carbon atoms takes place.
Fig. 5 Top: fluorescence (λexc = 259 nm, bandpath = 8 nm, 295 K) and
phosphorescence (λexc = 270 nm, bandpath = 10 nm, delay time = 50 µs,
77 K) spectra of solid L1. Middle: phosphorescence of [Eu(L1)][trif]3
(λexc = 240 nm, bandpath = 6 nm, delay time = 20 µs). Bottom: phos-
phorescence of [Tb(L1)][trif]3 (left, λexc = 258 nm, bandpath = 6 nm,
delay time = 20 µs); ligand-centred emission of [Tb(L1)][trif]3 (lower
trace right, λexc = 258 nm, bandpath = 2.5 nm); solid state, 77 K. Vertical
scale: arbitrary units.
1
However, eleven resonances appear in the H NMR spectrum
complex, even at low temperature, which prevented us perform-
ing a detailed analysis of its NMR spectrum.
since the aromatic protons display three signals in the range δ
6.00–6.55. The methylenic protons CH2Ph generate two doub-
lets, two broad signals of same intensity are observed for the
NCH2CO protons and the macrocyclic protons give rise to four
broad resonances. The too short values of the transverse relax-
ation times of the latter (Table S2, SUP 57491) did not allow us
to detect all the cross-peaks in the 2-D homonuclear COSY
experiment at the frequency used (360.16 MHz) as we have
done above with the lutetium complex, but comparison with
similar complexes11,12 and 1-D NOE difference experiments
allowed us to assign the ring CH2 and the NCH2CO protons. A
line shape broadening occurs upon lowering the temperature to
213 K, in line with the presence of a paramagnetic europium()
species, but no new sets of signals are detected. This is consist-
ent with the presence of only one isomer (>95%) in solution.
The line shape of the signals does not change either upon
increasing the temperature, except for the two doublets corre-
sponding to the resonances of the CH2Ph which undergo an
exchange process with coalescence occurring at 333 K (Fig. F3,
SUP 57491). This dynamic process is due to the rotation of the
benzyl group around the amide N–C bond and the activation
parameters determined using Eyring eqn. (1) (Fig. 4) are
Relaxivity measurements on [Gd(L1)][trif]3
We have measured relaxivity versus pH and it parallels the
behaviour described for the gadolinium complex with DTMA
[tetrakis(methylamide) of 1,4,7,10-tetraazacyclododecane-
1,4,7,10-tetraacetate].13a,b At 10 MHz and 298 K the gado-
linium complex displays the following relaxivities at pH 0.8, 1.0,
6.7 and 11.1: 4.08, 2.08, 1.88 and 6.14 mϪ1 Ϫ1, respectively.
s
The enhancement of the relaxivity at basic pH can be explained
by a prototropic exchange catalysed by OHϪ. For acidic pH the
measurements were started 3 h after preparing the solutions.
Taking this into account, the increase in relaxivity can be
explained by the protonation of the complex which results in
a weakening of the N–Gd bond as recently reported for
[Gd(DTMA)]3ϩ 13b
and allows an easy diffusion of water mol-
,
ecules around the gadolinium() ion.
Photophysical properties
The absorption spectrum of L1 in MeCN displays the charac-
teristic π → π* transitions of the C᎐O groups at 52 630 cmϪ1
᎐
(ε ≈ 190 000 Ϫ1 cmϪ1; shoulder at 47 620 cmϪ1, ε ≈ 45 000 Ϫ1
cmϪ1) and phenyl groups at 38 760 cmϪ1 (ε ≈ 800 Ϫ1 cmϪ1).
Absorption and reflectance spectra of the complexes show the
same bands, with small shifts only (Fig. F4, SUP 57491). The
luminescence spectrum of L1 in the solid state (77 K, Fig. 5) is
k = (kBT/h) exp[Ϫ(∆H‡/RT) ϩ (∆S‡/R)]
(1)
∆G‡ = 57.5 0.5 kJ molϪ1, ∆H‡ = 43.0 0.1 kJ molϪ1, ∆S‡ =
Ϫ49.3 0.4 J KϪ1 molϪ1, with k298 = 47.7 1.1 sϪ1. To our
knowledge, no similar kinetic process has been described for
this class of macrocyclic complexes. The benzyl rotation points
to a tendency of the complexes to lose their structural rigidity
as the ionic radius increases: the europium() ion seems to be
less tightly encapsulated by the pendant arms than LuIII and the
loss of rigidity of the co-ordinating environment is certainly the
cause of the very broad 1H NMR signals observed for the ring
and NringCH2CO methylenic protons of the lanthanum()
1
comprised of two transitions, assigned to the lowest ππ* and
3ππ* states: the former lies at 31 250 cmϪ1 while the latter occurs
at 23 250 cmϪ1 (maxima of the band envelopes). The emission
band corresponding to the 3ππ* state displays a vibrational
progression of about 1400 cmϪ1, probably corresponding to a
ring breathing mode, and the 0-phonon transition could be
located at 26 300 cmϪ1. In frozen solution in acetonitrile (77 K,
10Ϫ4 ), the emission maximum of the singlet state is found at
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Table 5 Observed radiative rate constants of the Eu(5D0) and Tb(5D4)
excited levels in [Ln(L1)][trif]3 under various experimental conditions
Ln Conditions
T/K Excitation
k/msϪ1
Eu Solid
Solid
10
295
295
295
295
295
77
5D0 ← 7F0 0.81 0.02
5D0 ← 7F0 0.85 0.02
Ligand 1ππ* 0.78 0.01
Ligand 1ππ* 1.69 0.03
Ligand 1ππ* 1.54 0.01
Ligand 1ππ* 0.41 0.02
Ligand 1ππ* 0.53 0.01
Ligand 1ππ* 0.53 0.02
Ligand 1ππ* 0.51 0.04
Ligand 1ππ* 0.68 0.06
Ligand 1ππ* 0.66 0.04
Ligand 1ππ* 0.35 0.02
9 × 10Ϫ4 /MeCN
9 × 10Ϫ4 /MeCN–watera
6.6 × 10Ϫ4 /water
5.9 × 10Ϫ4 /D2O
Tb Solid
Solid
295
295
1.1 × 10Ϫ3 /MeCN
1.1 × 10Ϫ3 /MeCN–watera 295
6.1 × 10Ϫ4 /water
6.8 × 10Ϫ4 /D2O
295
295
a [H2O]t/[LnIII]t = 2000.
34 840 cmϪ1 and the band corresponding to the emission of the
3ππ* state is structureless with a maximum at 23 250 cmϪ1. No
emission arising from an excimer could be detected in the fluor-
escence spectra, contrary to what was found for a similar ligand
bearing naphthalene moieties,14 meaning that the interaction
between the phenyl groups observed in the crystal structure is
not very strong. The lifetime of the triplet state amounts to
0.62 0.01 s in the solid state and 1.03 0.01 s in MeCN at
77 K. In frozen solutions of the complexes of LaIII and LuIII,
10Ϫ4  in MeCN, the maximum of the triplet state is blue
shifted at 23 100 (La) and 22 700 cmϪ1 (Lu) and the lifetime
becomes shorter: 0.93 0.01 (La) and 0.86 0.02 s (Lu).
When luminescent ions such as EuIII and TbIII are introduced
into the macrocyclic edifices the luminescence spectra display
a mixture of ligand-centred band emission and metal-centred
line emission (Fig. 5). For [Tb(L1)[trif]3 the ligand-to-metal
energy transfer is fairly efficient and the low-temperature
spectrum is dominated by strong 5D4 → 7FJ transitions while
Fig. 6 Corrected emission spectra of the 5D0 → 7F1 (top), 5D0 →
7F2 (middle) and 5D0 → 7F4 (bottom) transitions of [Eu(L1)][trif]3
at 10 K under selective laser excitation (17 234 cmϪ1, bandpath =
0.3 Å).
been observed for other tetraazamacrocyclic compounds with
pendant arms bearing amide18 or phosphinate17 functions and
for triple helical complexes with bis(benzimidazole)pyridines.19
The quantum yield of the europium() complex relative to
[Eu(terpy)][ClO4]3 is very small (≈5 × 10Ϫ2), which corresponds
to an absolute quantum yield of about 0.06%. These observ-
ations are opposite to those reported for complexes with an
octadentate tetraazamacrocyclic ligand bearing naphthyl
chromophores, where the differences between the triplet and the
excited metal ion states are respectively 750 (TbIII) and 3900
cmϪ1 (EuIII): transfer onto the europium() ion is efficient while
a back transfer process takes place for TbIII.14
1
a sizable emission from the ππ* state is still observed, but the
3ππ* state emits very weakly. The lifetime of the Tb(5D4) excited
state is relatively long and temperature independent (Table 5),
pointing to an absence of back transfer, a process commonly
observed for TbIII containing edifices.15 Furthermore, the quan-
tum yield of a 10Ϫ3  solution in degassed MeCN has been
measured relatively to [Tb(terpy)][ClO4]3 (terpy = 2,2Ј:6Ј,2Љ-
terpyridine; absolute quantum yield 4.8%15) and found to be
1.36 (absolute quantum yield: 6.4%). Although the inter-
Structural properties of [Eu(L1)][trif]3 as probed by lumin-
escence measurements. High resolution excitation and emission
spectra have been recorded at 10, 77 and 295 K to probe the
site symmetry of the europium() environment. Broad band
excitation at 397 nm (5L6 ← 7F0,1 transitions) yields an emis-
sion spectrum in which the corrected relative intensities for
1
3
system crossing between ππ* and ππ* states is not complete
[cf. the ligand-centred emission band in the spectrum of the
terbium() complex], L1 is a fairly efficient ligand to sensitize
the TbIII-centred luminescence. This was expected from the
correlation between the lowest triplet state energy of the ligand
and the terbium() quantum yield recently published by Latva
et al.16 for several polyaminocarboxylate chelates, in which the
authors show triplet states with energy between ca. 22 000 and
27 000 cmϪ1 being the most efficient sensitizers of TbIII. Benzyl
substituted cyclenes have also been described as good sensi-
tizers of TbIII when the systems lack the presence of closely
diffusing OH and CO oscillators.11,17
5
the D0 → 7FJ transitions to J = 0, 1, 2, 3 and 4 are 0.19,
1.00, 1.36, 0.04 and 1.64, respectively. Selective excitation at
580.24 nm (5D0 ← 7F0 transition) yields the spectrum in
Fig. 6, which is almost temperature independent, so that only
the 10 K data are discussed below. The laser excited excitation
spectrum of the 0–0 transition recorded upon monitoring the
5
high energy component of the D0 → 7F1 transition displays
On the other hand, energy transfer from the 3ππ* state to the
europium() excited states is quite poor and the luminescence
one symmetrical band at 17 234 cmϪ1 with a full width at half
height (fwhh) of 12 cmϪ1 (Fig. F5, SUP 57491). When the
europium() ion lies in a rigid and well defined site the fwhh
5
spectrum of [Eu(L1)][trif]3 displays weak D0 → 7FJ transi-
tions besides sizable 3ππ* and 1ππ* state emission. This is
somewhat surprising because for polyaminocarboxylate che-
lates a triplet state with an energy of about 27 000 cmϪ1 was
shown to transfer reasonably well its energy onto the 5LJ mani-
fold.16 The effectiveness of the ligand for energy transfer to LnIII
and the quantum yield of the metal-centred luminescence also
depend on many other factors. In particular, the europium()
ion is easily reduced to EuII, with the intermediate formation of
a radical cation, by photoinduced electron transfer (PET) from
the singlet state of the ligand directly to the metal, as has
of this transition is usually only a few cmϪ1 20
. The moderately
large fwhh observed here probably arises from slightly different
metal environments, as often observed for microcrystalline
materials.21 In fact, when the observation wavelength is set onto
the various emission bands of the spectrum displayed in Fig. 6,
the 0–0 transition spans an energy range between 17 225 and
17 245 cmϪ1, consistent with the above interpretation. More-
over, laser excitation between these wavenumbers yielded essen-
tially similar spectra, the transitions displaying a shift varying
linearly with the excitation energy.
J. Chem. Soc., Dalton Trans., 1999, 931–938
935

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Table 6 Identified electronic and vibronic transitions in the lumi-
nescence spectrum of [Eu(L1)][trif]3 (solid state, 10 K, excitation:
5D0 ← 7F0 transition)
E/cmϪ1
Intensitya
E*/cmϪ1
Transitionb
17 234
16 971
16 814
16 797
16 779
16 267
16 257
16 252
16 238
16 221
16 211
16 189
15 274
14 490
14 437
14 381
14 243
m
m
w
w
w
sh
m
m
vs
w
sh
vw
vw
m
vw
w
0
263
420
437
455
967
977
982
996
1013
1023
1045
1960
2744
2797
2853
2991
5D0 → 7F0
5D0 → 7F1
5D0 → 7F1
Vibronic (420)b
5D0 → 7F1
Vibronic (970)b
5D0 → 7F2
5D0 → 7F2
5D0 → 7F2
Vibronic (1022)b
Vibronic (1031)b
Vibronic (1038)b
5D0 → 7F3
5D0 → 7F4
5D0 → 7F4
5D0 → 7F4
5D0 → 7F4
Fig. 7 Energy migration scheme for [Ln(L1)][trif]3 complexes (Ln = Eu
or Tb).
amine (Ϫ12.1) and have deduced from our work on nine-
co-ordinate triple-helical complexes with the benzimidazole-
containing ligands a δHN parameter equal to Ϫ15.3.24 Taking
the latter value into account, as well as δamide = Ϫ15.7 and
CCN = 1.06,23 we find 17 243 cmϪ1 for [Eu(L1)]3ϩ, while the
experimental value at 295 K is 17 246 cmϪ1. This result is there-
fore consistent with no bound water molecule in the first
co-ordination sphere, which can be explained by the vigorous
drying performed after isolation of the complexes (60 ЊC, 1
mbar, 12 h). That no water is co-ordinated to EuIII is corrob-
orated by the small radiative rate constant observed for the 5D0
excited state between 10 and 295 K in the solid state (0.81 and
0.85 msϪ1 respectively, Table 5). A similar value holds for
a solution 10Ϫ3  in dry MeCN; however, when water is
added ([H2O]t/[EuIII]t = 2000) the rate constant increases in a
proportion corresponding to a number of bound water
molecules q = 0.96, as calculated by Horrocks’ equation,25
which increases to q = 1.19 in water. Under these experimental
conditions, the ninth co-ordination position is occupied by a
water molecule. For the terbium() complex q increases from
0.71 in aqueous MeCN to 1.30 in pure water. Taking into
account the corrections proposed by Dickins et al.5 for closely
diffusing OH [∆kЈ(Eu) = Ϫ0.25, ∆kЈ(Tb) = Ϫ0.06 msϪ1] and
NH [∆kЈ(Eu) = Ϫ0.08 msϪ1], and their new formulation of
Horrock’s equation, qЈ = AЈ(∆k ϩ ∆kЈ) with AЈ(Eu) = 1.25 and
AЈ(Tb) = 4.9, we find the following data: qЈ(Eu) = 0.43 (aqueous
MeCN) and 0.70 (H2O), qЈ(Tb) = 0.54 (aqueous MeCN) and
1.23 (H2O).
m
a s = Strong, m = medium, w = weak, vw = very weak, sh = shoulder.
b The IR data are given in parentheses.
The symmetry of the europium() ion has been determined
as follows. First, the intensity of the D0 → 7F0 transition is
5
particularly large, pointing to a Cn (or Cnv) point group of
symmetry. Given the formulation of the complex, the only
feasible point groups are C4 and C4v. Group theoretical con-
siderations predict the same number of transitions from the 5D0
7
excited state to the FJ manifold for J = 0, 1 and 2 (subscripts
refer to C4v):20 1 (A(1)), 2 (A(2) ϩ E), 2 (A(1) ϩ E), so that a dis-
tinction can only be made by analysing the transition to J = 4
for which C4 allows 5 transitions (3A ϩ 2E) and C4v 4 transi-
tions (2A1 ϩ 2E). Selectively excited spectra (5D0 ← 7F0) have
been recorded to determine the number of components for
each 5D0 → 7FJ transition (J = 1, 2 and 4, Fig. 6). The
5D0 → 7F1 transition displays 3 components, two of them
appearing as a doublet with a splitting of 35 cmϪ1; addition-
ally, the transition contains a vibronic component at 437 cmϪ1
(Table 6). Analysis of the hypersensitive transition to J = 2 is
more difficult since it is essentially comprised of one intense
and sharp transition and of six weak components, several of
which can be assigned to vibronic transitions (Table 6); we
assign tentatively the more intense band to an A-type transition
and the doublet (spacing 5 cmϪ1) on its high energy side to an
E-type transition. Finally, the D0 → 7F4 transition displays
5
Conclusion
three sizable components and two very weak ones. Globally,
therefore, the emission spectra are consistent with a slightly
distorted C4 symmetry, which splits the E components of the
transitions to J = 1, 2 into two components. The distortion may
occur in the ground or in the excited state, but we note that
a distorted square antiprismatic co-ordination geometry has
been found by X-ray analysis for the lanthanum() com-
plex with 1,4,7,10-tetrakis(2-carbamoylethyl)-1,4,7,10-tetraaza-
cyclododecane.22 Finally, no changes are observed in the
emission spectra of the europium() ion for [Ln0.98Eu0.02(L1)]-
[trif]3 (Ln = La, Eu, Gd or Lu) compounds in the solid state,
pointing to an isotypical series of edifices, with pseudo-C4
symmetry.
We have shown that ligand L1 adopts a twofold symmetry both
in the solid state and in solution, in which rapid movements of
the macrocyclic ring and the pendant arms occur. The ligand
provides a tight co-ordination cage for the heavier lanthan-
ide() ions, as demonstrated by a detailed NMR analysis of the
diamagnetic lutetium() complex. For both complexes of LuIII
and EuIII only one C4-symmetric isomer is present in solution
and no exchange process is evidenced in the temperature range
studied (212–323 K), as observed for similar europium()
compounds. In addition, the rotation of the benzyl groups in
[Eu(L1)][trif]3, quantified by a dynamic NMR analysis, and the
broad NMR signals generated by the lanthanum() complex
lead to the conclusion that the structure becomes somewhat
fluxional for larger lanthanum() ions. Luminescence data
demonstrate that L1 is a suitable ligand for sensitizing TbIII, but
not EuIII, because the energy of its lowest triplet state (26 300
cmϪ1 for the 0-phonon transition in the solid state) is about
Frey and Horrocks23 recently proposed a correlation between
the energy of the 0–0 transition, that is the position of the D0
5
level, and parameters describing the ability δ of co-ordinating
atoms to produce a nephelauxetic effect: ν Ϫ ν0 = CCNΣiniδi
where CCN is a coefficient depending upon the europium()
co-ordination number (1.06 for CN = 8, 1.0 for CN = 9), ni the
number of atoms of type i, and ν0 = 17 374 cmϪ1 at 295 K; the
parameters δ are tabulated for several functional groups. We
have recently demonstrated that a heterocyclic N atom (HN)
tends to produce a larger nephelauxetic effect than a primary
5
5000 cmϪ1 higher than the D4 level and so no back transfer
is observed in [Tb(L1)][trif]3 (Fig. 7). On another hand, the
internal conversion from the singlet to the triplet state appears
to be insufficient to ensure large quantum yields. However,
a comparison with literature data on similar compounds
936
J. Chem. Soc., Dalton Trans., 1999, 931–938

View Article Online
shows that the physical properties of the lanthanide edifices
with [12]aneN4 ligands may be easily tuned by changing the
nature of the pendant arm properties, which offers interesting
perspectives for the development of efficient luminescent
stains.
nitrile (yield 60%) (Found: C, 69.62; H, 7.21; N, 14.48. C11H14-
N2O requires C, 69.45; H, 7.42; N, 14.72%). ES-MS (10Ϫ4
mol dmϪ3 in MeCN ϩ CF3SO3H): two peaks at m/z = 762.0
(L1Hϩ) and 381.2 (L1H22ϩ). δC{1H} (90.6 MHz, CD3OD ϩ
CF3SO3H, 212 K) 173.0 (1C, CO), 166.0 (1C, CO), 140.0 (1C,
aryl), 139.4 (1C, aryl), 130.0 (2C, aryl), 129.6 (2C, aryl),
129.0 (2C, aryl), 128.9 (1C aryl), 128.1 (2C ϩ 1C, aryl), 57.0
(1C, NCH2CO), 55.9 (1C, NCH2CO), 52.9 (4C, br, ring
CH2), 44.3 (1C, CH2Ph) and 43.8 (1C, CH2Ph). IR: νmax 3304
Experimental
Starting materials, procedures and spectroscopic measurements
(N–H), 1651 and 1662 cmϪ1 (C᎐O).
᎐
Solvents and chemicals were purchased from Fluka AG (Buchs,
Switzerland). Acetonitrile was treated by CaH2 and P2O5.26
Dichloromethane and tetrahydrofuran were distilled from
CaH2. Lanthanide trifluoromethanesulfonates (triflates) were
prepared from the oxides (Rhône-Poulenc, 99.99%) and triflic
acid.27 Elemental analyses were performed by Dr H. Eder of
the Microchemical Laboratory of the University of Geneva.
Electrospray mass spectra (ES-MS) were measured on a
Finnigan SSQ-710C spectrometer driven by a Digital Personal
DEC station 5000/25. Geometry calculations have been
performed by PLATON 98.28
Complexes. The complexes [Ln(L1)][trif]3 were prepared by
heating under reflux 1 equivalent of the lanthanide salt and 1
equivalent of L1 in dry MeCN. After cooling, the solution was
filtered on sintered glass and concentrated, CH2Cl2 was added
and the resulting solution kept for 10 h at 277 K. The deposited
solid was recovered by filtration, washed with CH2Cl2 and dried
(2 h, 1 mbar, 313 K). The complexes were recrystallized from
MeCN (yield ≈ 70%).
[La(L1)][trif]3 (Found: C, 41.78; H, 4.13; N, 8.19. Calc. for
C47H56F9LaN8O13S3: C, 41.91; H, 4.19; N, 8.35%). δC{1H}
(CD3OD, 295 K) 177.1 (1C, CO), 138.6 (1C, aryl), 130.3 (2C,
aryl), 129.5 (1C, aryl), 129.4 (2C, aryl), 61.9 (1C, NCH2CO),
56.0 (br, 1C, ring CH2), 53.2 (br, 1C, ring CH2) and 45.8 (1C,
The 1- and 2-D NMR spectra were recorded on a Bruker
AM-360 (360.16 and 90.6 MHz respectively) or on a Bruker
Avance DRX-400 spectrometer (400.03 and 100.04 MHz).
Proton chemical shifts are reported in parts per million (ppm)
with respect to TMS, and 13C chemical shifts are related to
CD3OD (δ 49.3). We have chosen CD3OD as NMR solvent
because in CD3CN signals became broader, pointing to an
interaction between the complexes and the solvent as described
previously.29 Activation parameters have been obtained by
fitting spectra using the program NMRICMA.30 All the ligand
solution studies have been achieved with added protons
(CF3SO3H ≈ 1–5 µM). Relaxivity measurements have been per-
formed at 10 MHz with a Stelar fast field cycling Spinmaster
relaxometer equipped with a Stelar VTC-91 air flow heating
unit. For both NMR and relaxivities measurements the tem-
perature was measured by a substitution technique.31 Electronic
UV-VIS-NIR spectra were recorded at 295 K on a Perkin-
Elmer Lambda 900 spectrometer, infrared spectra on a FT-IR
Mattson Alpha Centauri spectrometer (4000–400 cmϪ1, KBr
pellets) and on a Bruker IFS-113v FT-IR interferometer (700–
100 cmϪ1, polyethylene pellets). Low-resolution luminescence
measurements (spectra and lifetimes) were recorded on a
Perkin-Elmer LS-50B spectrofluorimeter. High-resolution
spectra and lifetimes of the europium complexes in the solid
state were measured on a previously described instrumental
set-up;32 lifetimes were averages of at least four determinations.
Quantum yields of [Tb(L1)][trif]3 and [Eu(L1)][trif]3 were
determined in anhydrous and degassed MeCN relative to
[Tb(terpy)3][ClO4]3 and [Eu(terpy)3][ClO4]3 respectively,33 with
the help of a Perkin-Elmer LS-50B spectrofluorimeter.
CH2Ph). IR: νmax 3264 (N–H) and 1627 cmϪ1 (C᎐O).
᎐
[Nd(L1)][trif]3 (Found: C, 41.69; H, 4.23; N, 8.20. Calc. for
C47H56F9N8NdO13S3: C, 41.74; H, 4.17; N, 8.29%). IR: νmax
3265 (N–H) and 1629 cmϪ1 (C᎐O).
᎐
[Eu(L1)][trif]3 (Found: C, 41.49; H, 4.09; N, 8.20. Calc. for
C47H56EuF9N8O13S3: C, 41.50; H, 4.15; N, 8.24%). νmax 3268
(N–H) and 1632 cmϪ1 (C᎐O).
᎐
[Gd(L1)][trif]3 (Found: C, 41.27; H, 4.20; N, 8.17. Calc. for
C47H56F9GdN8O13S3: C, 41.34; H, 4.13; N, 8.21%).
[Tb(L1)][trif]3 (Found: C, 41.12; H, 4.11; N, 8.15. Calc. for
C47H56F9N8O13S3Tb: C, 41.28; H, 4.13; N, 8.20%). IR: νmax 3270
(N–H) and 1634 cmϪ1 (C᎐O).
᎐
[Lu(L1)][trif]3 (Found: C, 40.57; H, 4.04; N, 8.05. Calc. for
C47H56F9LuN8O13S3: C, 40.82; H, 4.08; N, 8.10%). νmax 3273
(N–H) and 1639 cmϪ1 (C᎐O).
᎐
Crystal structure of L1
A transparent single crystal of L1 was mounted on a pin and
transferred to the goniometer. The crystal was cooled to
Ϫ100 ЊC during data collection by using a stream of cold
nitrogen gas. The monoclinic space group P21/c was uniquely
determined by the systematic absences. A summary of data
collection and refinement parameters is given in Table 7. The
geometrically constrained hydrogen atoms were placed in cal-
culated positions and allowed to ride on their attached atoms
with B = 1.2Ueq(C). The two unique NH hydrogen atoms were
located from a Fourier difference map and allowed to ride on
the bonded atom with B = 1.2Ueq(N). Refinement of non-
hydrogen atoms was carried out with anisotropic thermal
parameters. Drawings were made using the ORTEP 3 program
package.37
Syntheses and characterization
1,4,7,10-Tetraazacyclododecane was synthesized as previously
described.29 N-Benzylbromoacetamide was prepared using the
method of Hamada et al.34 with bromoacetyl chloride instead
of chloroacetyl chloride. The yield is 70%. TLC: 1 spot, Rf = 0.8
(5% MeOH in CHCl3). δH (CDCl3) 3.92 (s, 2 H, BrCH2), 4.43
and 4.50 (dd, 2J = 16.6 Hz, 2 H, NCH2Ph), 6.74 (s, br, 1 H, NH)
and 7.30 (m, 5 H, aryl). mp 110 ЊC.
CCDC reference number 186/1326.
See http://www.rsc.org/suppdata/dt/1999/931/ for crystallo-
graphic files in .cif format.
Acknowledgements
1,4,7,10-Tetrakis(N-benzylcarbamoylmethyl)-1,4,7,10-tetra-
azacyclododecane (L1). A mixture of 1 equivalent of 1,4,7,10-
tetraazacyclododecane (113.2 mg, 0.66 mmol), 4 equivalents
of N-benzylbromoacetamide (599.5 mg, 2.64 mmol) and 4 equiv-
alents of triethylamine (0.37 ml, 2.64 mmol) in dry THF was
refluxed under nitrogen during 7 h. The deposited solid was
recovered by filtration and washed with 500 ml water portions
until negative reaction of the filtrate with AgNO3, and with
100 ml EtOH. It was purified by recrystallization from aceto-
This research is supported by grants from the Swiss National
Science Foundation and the Swiss Federal Office for Science
and Education (COST project D8). We thank the Fondation
Herbette (Lausanne) for spectroscopic equipment, F. Monlien
for her assistance in using the NMRICMA program, F. Dunan
for relaxivity measurements, D. Baumann for recording far-IR
spectra and V. Foiret for her help in the acquisition of some
luminescence data.
J. Chem. Soc., Dalton Trans., 1999, 931–938
937

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Table 7 Summary of crystal data, data collection, structure solution
and refinements details for L1 a
10 R. S. Dickins, J. A. K. Howard, C. W. Lehmann, J. Moloney,
D. Parker and R. D. Peacock, Angew. Chem., Int. Ed. Engl., 1997,
38, 521.
11 S. Aime, A. S. Batsanov, M. Botta, J. A. K. Howard, D. Parker,
K. Senanayake and J. A. G. Williams, Inorg. Chem., 1994, 33, 4696.
12 S. Aime, M. Botta, D. Parker and J. A. G. Williams, J. Chem. Soc.,
Dalton Trans., 1995, 2259.
13 (a) S. Aime, A. Barge, M. Botta, D. Parker and A. S. de Sousa,
J. Am. Chem. Soc., 1997, 119, 4767; (b) L. Alderighi, A. Bianchi,
L. Calabi, P. Dapporto, C. Giorgi, P. Losi, L. Paleari, P. Paoli,
P. Rossi, B. Valtancoli and M. Virtuani, Eur. J. Inorg. Chem., 1998,
1581.
14 D. Parker and J. A. G. Williams, J. Chem. Soc., Perkin Trans. 2,
1995, 1305.
15 L. J. Charbonnière, C. Balsiger, K. J. Schenk and J.-C. G. Bünzli,
J. Chem. Soc., Dalton Trans., 1998, 505.
16 M. Latva, H. Takalo, V. M. Mukkala, C. Matachescu, J.-C.
Rodriguez-Ubis and J. Kankare, J. Lumin., 1997, 75, 149.
17 S. Aime, A. S. Batsanov, M. Botta, R. S. Dickins, S. Faulkner, C. E.
Foster, A. Harrison, J. A. K. Howard, J. M. Moloney, T. J. Norman,
D. Parker, L. Royle and J. A. G. Williams, J. Chem. Soc., Dalton
Trans., 1997, 3623.
18 D. Parker and J. A. G. Williams, J. Chem. Soc., Dalton Trans., 1996,
3613.
19 S. Petoud, T. Glanzmann, J.-C. G. Bünzli, C. Piguet, Qin Xiang and
R. P. Thummel, J. Lumin., 1999, in the press.
20 J.-C. G. Bünzli, Lanthanide Probes in Life, Chemical and Earth
Sciences. Theory and Practice, eds. J.-C. G. Bünzli and G. R.
Choppin, Elsevier, Amsterdam, 1989, ch. 7, pp. 219–293.
21 F. Nicolo, D. Plancherel, G. Chapuis and J.-C. G. Bünzli, Inorg.
Chem., 1988, 27, 3518.
22 J. R. Morrow, S. Amin, C. H. Lake and M. R. Churchill, Inorg.
Chem., 1993, 32, 4566.
23 S. T. Frey and W. d. J. Horrocks, Inorg. Chim. Acta, 1995, 229, 383.
24 N. Martin, J.-C. G. Bünzli, V. McKee, C. Piguet and G. Hopf-
gartner, Inorg. Chem., 1998, 37, 577.
25 W. DeW. Horrocks, Jr. and D. R. Sudnik, Acc. Chem. Res., 1981, 14,
384.
Formula
M
Colour, habit
Crystal size/mm
Crystal system
Space group
a/Å
C44H56N8O4
760.97
Colourless, plate
0.06 × 0.18 × 0.22
Monoclinic
P21/c
13.0360(11)
16.1964(14)
9.7490(9)
97.117(3)
2042.5(3)
2
816
b/Å
c/Å
β/Њ
U/Å3
Z
F(000)
Dc/g cmϪ3
1.237
0.081
µ/mmϪ1
Unit-cell reflections (θ range/Њ)
hkl Ranges
1610 (1.57 to 24.68)
Ϫ13 to 15, Ϫ18 to 19, Ϫ7 to 11
10 230
Reflections measured
Unique reflections
Reflections with I > 2σ
Absorption correction
Extinction coefficient
Refinement method
3461 (Rint = 0.1091)
1716
SADABS35
0.013(2)
Full-matrix least squares on F2,
no restraints
Direct methods
254
Solution method
No. variables
Goodness of fit on F2
Final R1, wR2 indices (I ≥ 2σ)
(all data)
1.027
0.0733, 0.1174
0.1815, 0.1732
0.213 and Ϫ0.208
Density range in final map/e ÅϪ3
a Data collection on a Siemens SMART instrument with CCD area
detector and graphite monochromatized Mo-Kα radiation (λ = 0.71073
Å). Computing was done with SHELXTL.36
26 D. D. Perrin and W. L. F. Armarego, Purification of Laboratory
Chemicals, Pergamon, Oxford, 1988.
27 J.-C. G. Bünzli and F. Pilloud, Inorg. Chem., 1989, 28, 2638.
28 L. J. Farrugia and T. Spek, PLATON 98 for Windows, 1998.
29 P. A. Pittet, D. Früh, V. Tissières and J.-C. G. Bünzli, J. Chem. Soc.,
Dalton Trans., 1997, 895.
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