Lanthanide complexes of DOTA monoamide derivatives bearing an isophthalate pendent arm

Article abstract of DOI:10.1039/c1dt11029b

An isophthalate-bearing DOTA monoamide derivative has been synthesised and used to prepare a family of lanthanide complexes. Luminescence and NMR studies in solution show that the predominant form of the complexes in solution is a mono-capped square antiprism about the lanthanide centre, in which a solvent molecule occupies the ninth coordination site. The crystal structure of the terbium complex is presented and is in close agreement with the solution state data.

Full text of DOI:10.1039/c1dt11029b

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PAPER
Lanthanide complexes of DOTA monoamide derivatives bearing an
isophthalate pendent arm†
Emma J Shiells,a Louise S. Natrajan,a Daniel Sykes,a,b Manuel Tropiano,b Paul Cooper,a Alan M. Kenwrightc
and Stephen Faulkner*a,b
Received 1st June 2011, Accepted 18th August 2011
DOI: 10.1039/c1dt11029b
An isophthalate-bearing DOTA monoamide derivative has been synthesised and used to prepare a
family of lanthanide complexes. Luminescence and NMR studies in solution show that the
predominant form of the complexes in solution is a mono-capped square antiprism about the
lanthanide centre, in which a solvent molecule occupies the ninth coordination site. The crystal
structure of the terbium complex is presented and is in close agreement with the solution state data.
Introduction
Results and discussion
Kinetically stable lanthanide complexes are already being widely
used as imaging agents in both whole body MRI and luminescence
microscopy.1,2 In recent years, the use of gadolinium complexes
as MRI contrast agents has become almost ubiquitous in MRI
blood pool imaging,3 and the strategy has been extended using
complexes that respond to changes in their environment,4 and
to bioconjugates with peptides that are internalised by specific
cell types.5 Luminescent lanthanide complexes have become a
keystone of bioassay,6 and are beginning to be exploited as tags7
and responsive probes8 for time-gated luminescence microscopy,
where the long luminescence lifetimes associated with lanthanide
centred transitions lend themselves to such applications.
Over the last few years, we and others have devoted considerable
effort to developing strategies that can be used to link lanthanide
complexes together through carrying out chemical modifications
to stable complexes, using Ugi9 and click10 reactions, and develop-
ing orthogonal protection strategies that can be used to control the
position of lanthanide complexation.11 Related strategies have also
been used to incorporate aromatic and transition metal complexes
into lanthanide containing systems.12,13
Our synthetic strategy is shown in Scheme 1. Reaction of
dimethyl 3-aminoisophthalate (1) with chloroacetyl chloride in the
presence of sodium hydrogencarbonate yielded 2-chloro-N-(3,5-
di(methoxycarbonyl)phenyl)acetamide (2). Reaction of the well-
known triester14 (3) with compound 2 yielded the orthogonally
protected DOTA-monoamide derivative (4). Cleavage of the tert-
butyl ester groups using trifluoroacetic acid yielded H3·5, which
was used to form the Ln·5 complexes. Base hydrolysis of H3·5
and subsequent work up and complexation with the appropriate
lanthanide triflate yielded H5·6 and Ln·6 respectively. We elected
to use this approach in the light of previous experience of lability
of lanthanide coordinated amide bonds:11 indeed, attempts at base
hydrolysis of Ln·5 proved capricious, with evidence of Ln·DOTA
contaminants being observed in NMR spectra of the crude
mixtures that were obtained. This lends further weight to the
supposition that treatment of aqueous solutions of such complexes
with strong base should be avoided wherever possible.
Structures of the complexes in solution
Initially, NMR spectroscopy was used to probe the structures of
the complexes in solution. The NMR spectra of the complexes
are shown in Fig. 1 and 2. All bear a clear resemblance to the
NMR spectra of other DOTA-monoamide complexes,9,11 and the
chemical shifts observed are similar to the analogous complexes
of DOTA itself,15 with the obvious difference that the broken
symmetry in these structures gives rise to a much greater number
of peaks in the spectra of the monoamide complexes (since
all the protons in the structure are now inequivalent). For the
neodymium complexes, this inequivalence is much less obvious
than it is in the other complexes, since exchange broadening
gives rise to broad and relatively featureless spectra. The other
complexes all give rise to clearly defined spectra, and in all cases
comparison of the chemical shifts observed for the most shifted
protons with those corresponding to the same protons in literature
We now report the synthesis of a family of DOTA-monoamide
complexes bearing an isophthalate group which is suitable for
further functionalisation with a pair of targeting vectors.
aSchool of Chemistry, University of Manchester, Oxford Road, Manchester,
UK, M13 9PL
bUniversity of Oxford, Chemistry Research Laboratory, Mansfield Road,
Oxford, UK, OX1 3TA. E-mail: Stephen.Faulkner@chem.ox.ac.uk; Tel: +44
1865 285148
cUniversity of Durham, Department of Chemistry, South Road, Durham,
UK, DH1 3LE. E-mail: A.M.Kenwright@dur.ac.uk; Tel: +44 191 334 2095
† Electronic supplementary information (ESI) available: Crystallographic
Information File (CIF) of Tb·5. CCDC reference number 828726. See
DOI: 10.1039/c1dt11029b
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Scheme 1
Fig. 1 1H NMR spectra (500 MHz, D2O, 295 K) of the lanthanide
complexes of 5.
reports9,11,15,16 suggest that the dominant isomer in solution is a
hydrated square antiprismatic structure. Tb·5, Tb·6, Yb·5 and
Yb·6 are all dominated by a single set of resonances, with only
traces of the diastereomeric twisted square antiprismatic form
being observed in solution at 295 K (e.g. around 80 ppm in the
case of Yb·6). In the case of the europium complexes, there is much
clearer evidence for a minor isomer in which the metal adopts a
twisted square antiprismatic geometry.
Furthermore, it is clear that the spectra of the complexes of 5
and 6 with the same lanthanide are very similar to one another,
implying that remote substituents have little effect on the local
environment close to the lanthanide.
Luminescence spectroscopy was used to probe the structures
further. All the complexes were found to be luminescent, though
facile quenching by O–H oscillators ensured that only weak
emission was observed from the erbium complexes. Key aspects
of their properties are shown in Table 1.
Time-resolved data was used to assess the inner sphere hydration
of the complexes. The lifetimes of lanthanide-centred emission in
water and deuterium oxide can be used to calculate qLn, the number
of inner-sphere water molecules bound to the lanthanide ion, using
the equation
qLn = A(1/tH - 1/tD - B)
(1)
O
O
2
2
11452 | Dalton Trans., 2011, 40, 11451–11457
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Table 1 Photophysical properties of the complexesa
Complex
lex/nm
l
em/nm
tH O/ms
tD O/ms
qcalc
2
2
Nd·5
337
260
260
337
337
260
260
337
337
337
1055
617
545
1530
980
617
545
1530
980
0.14
550
1630
—
0.78
570
1690
—
0.38
1850
2730
0.81
5.21
2180
3030
0.94
7.74
0.34
Eu·5
1.1
0.9
Tb·5
Er·5
Yb·5
0.9
1.0
1.0
[Eu·6]2-
[Tb·6]2-
[Er·6]2-
[Yb·6]2-
[Nd·6]2-
0.79
0.11
1.0
1055
a qLn was calculated using eqn (1), and the A and B parameters in ref. 17.
Crystal structure of Tb·5
Suitable colourless needles of Tb·5 for structural analysis were
obtained by slow evaporation of a saturated aqueous solution at
room temperature. To the best of our knowledge, there is only one
previous structural report of a DOTA monoamide complex and
one group 3 derivative; these are Gd·719 and Y·8.20
The complex crystallises as a racemate and both K(dddd)
and D(llll) configurations are observed in the asymmetric
unit cell. Average cyclen N–C–C–N and N–C–C–O torsion
angles are respectively measured as +58.7◦ and -28.6◦ for the
K(dddd) diastereomer and -58.9◦ and +28.2◦ for the D(llll)
configuration.
The solid state structure of Tb·5 (Fig. 3) shows that the
terbium(III) ion is 9 coordinate and the resultant coordination
geometry is best described as a distorted mono capped square
antiprism (SAP). The basal plane is described by the four cyclen
N atoms (N(1)–N(4)) and the orthogonal plane occupied by the
three acetate O atoms (O(2), O(4), O(6)) and the amide O atom
(O(8)). The displacements of these atoms from their respective
˚
mean planes are 0.006 and 0.019 A respectively. The two planes
Fig. 2 1H NMR spectra (500 MHz, D2O, 295 K) of the lanthanide
complexes of 6.
lie almost parallel to one another; the angle between them being
1.8◦ and the Tb3+ ion lies 1.611 A from the centre of the N4
˚
˚
plane and 0.709 A from the O4 plane. The dihedral or twist angle
between the cyclen N4 donor set and that of the acetate/amide
donor set is 39◦ ( 1◦) and is characteristic of distorted SAP
coordination polyhedra observed in mono, bis, tri and tetraamide
DOTA derivatives.21
where A and B are constants for a given lanthanide ion. For
europium AEu = 1.2 ms and BEu = (0.25 - 0.075x) ms-1, where
x is the number of exchangeable N–H oscillators (i.e. x = 1, in this
case). Effective calculations of q are also possible for terbium and
ytterbium complexes (ATb = 5 ms, BTb = 0.06 ms-1, AYb = 1 ms and
BYb = 0.1 ms-1), but the facility of C–H quenching in neodymium
and erbium complexes means that this approach cannot be applied
to calculate qNd and qEr.18 In the cases for which q can be calculated
effectively, it is clear that the data from luminescence spectroscopy
bears out the NMR study. In all cases, calculated values of q are
close to 1, implying that a hydrated square antiprismatic structure
dominates in solution.
˚
The average Ncyclen–Tb distance is 2.641(4) A, the mean Oacetate
–
˚
Tb distance is 2.341(3) A and the Oamide–Tb distance is longer at
˚
2.409(3) A. These values are again consistent with those reported
for mid-lanthanide DOTA and amide derivatives.21 The axial
position is occupied by a water molecule; the interatomic distance
˚
between the oxygen atom and the terbium ion is 2.415(4) A.
This value is comparable to that measured for the Gd·7 (2.429(5)
-
3+
˚
˚
A), and to [Gd·DOTA(OH2)] (2.463 A), [Gd·DOTAM(OH2)]
22
˚
(2.395 A) and related terbium triamide complexes.
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the Aldrich Chemical Company. All chemicals were used as
supplied.
Mass spectra were obtained using positive electrospray in
acetonitrile or methanol solutions on a Micromass Platform II
spectrometer, or by MALDI using methanol solutions with an
ALPHA matrix on a Micromass TOF Spec 2E spectrometer.
Elemental analyses were performed using a Carlo ERBA
Instruments CHNS-O EA1108 elemental analyzer (C, H, N and
S analysis) and a Fisons Horizon Elemental Analysis ICP-OED
spectrometer for metals and halogens.
Absorption spectra were recorded in H2O on a T60U spectrom-
eter (PG Instruments Ltd.) using fused silica cells with a path
length of 1 cm.
NMR spectra of the complexes were recorded at 500 MHz and
295 K unless otherwise stated, using millimolar solutions of the
complex and referencing spectra to the water peak at 4.7 ppm.
Spectra were acquired over 5000 repetitions using an acquisition
time of 0.1 s, relaxation delay of 0.1 s, and appropriate spectral
widths of up to 500 kHz.
Preparation of ligands and complexes
1,3-Dimethyl-5-aminoisophthalate
acetylchloride,
(2).
Dimethyl-5-aminoisophthalate (1.02 g, 4.79 mmol) was dissolved
in dichloromethane (50 cm3), and then NaHCO3 (5.08 g, 47.9
mmol) was added to the stirring mixture. Chloroacetyl chloride
(0.53 g, 0.37 cm3, 4.79 mmol) was added drop-wise to the solution,
and then the mixture was stirred at room temperature for 24 h.
Dichloromethane (200 cm3) was added to the mixture, which was
then filtered. The filtrate was evaporated under reduced pressure,
to produce a creamy beige/white solid. The crude product was
then recrystallised using minimum hot DCM (~75 cm3) to leave
the product as a white solid, (1.29 g, 93%). ES- MS (MeCN):
Fig. 3 Thermal ellipsoid drawings of Tb·5 at the 50% probabil-
ity level, H atoms and lattice water molecules removed for clar-
ity. Top: perspective above the plane of the aza macrocycle. Bot-
tom: perspective in the mean p◦lane of the isophthalate ring. Se-
˚
lected distances (A) and angles ( ): Tb(1)–O(1) 2.415(4), Tb(1)–O(2)
2.364(3), Tb(1)–O(4) 2.295(3), Tb(1)–O(6) 2.365(3), Tb(1)–O(8)
2.409(3), Tb(1)–N(1) 2.612(4), Tb(1)–N(2) 2.659(4), Tb(1)–N(4)
2.654(4); O(4)–Tb(1)–O(2) 87.57(12), O(2)–Tb(1)–O(6) 146.11(13),
O(6)–Tb(1)–O(8) 83.67(11), O(8)–Tb(1)–O(1) 69.56(12), O(6)–Tb(1)–N(1)
140.41(12), N(1)–Tb(1)–N(3) 104.00(13), N(1)–Tb(1)–N(4) 69.08(13),
N(4)–Tb(1)–N(2) 105.65(12), N(1)–Tb(1)–N(2) 67.81(12).
+
+
1
m/z 284 {M - H} ; ES+ MS (MeCN): m/z 308 {M + Na} ; H
The solid state structure clearly correlates closely with the
structure in solution in this case. Though attempts to crystallise
Ln·6 complexes proved unsuccessful, the similarities between
solution state data for Ln·5 and Ln·6 suggest that this structural
motif persists in the fully deprotected form.
NMR (400 MHz, CDCl3, 300 K) dH (ppm) 3.8 (6H, s, 2CH3),
1
4.2 (2H, s, CH2-Cl), 8.4 (3H, s, Ar-H), 8.5 (1H, s, NH); 13C{ H}
NMR (400 MHz, MeOD, 300 K) dC (ppm) 42.8 (CO2CH3), 52.6
(COCH2Cl), 125.1, 127.3, 131.7, 137.2 (Ar-C), 164.1 (CONH),
165.7 (Ar-CO2CH3); IR(ATR): n (C O) 1716 cm-1, (C O)
1683 cm-1, (N–H) 1547 cm-1; CHN expected for C12H12NO5Cl: C,
50.45; H, 4.23; N, 4.90; found: C, 50.21; H, 4.15; N, 4.86.
Conclusions
Isophthalate appended DOTA-monoamide derivatives form sta-
ble and well-defined complexes in solution and in the solid phase.
The dominant form is a nine-coordinate square antiprismatic
diastereoisomer with a single water molecule bound to the metal
ion. This structural motif is well suited to applications in lumines-
cence spectroscopy and contrast imaging. Furthermore, the two
carboxylic acidgroups lend themselves to further functionalisation
with chromophores or targeting vectors. In the latter case, this
complex offers the potential for functionalisation with more
than one vector, raising the possibility of chelating interactions
that can enhance specificity. We are currently investigating these
possibilities.
Tris-tert-butyl 1,4,7,10-tetraazacyclododecane-1,4,7-triacetate
hydrobromide salt (3). Prepared as described in ref. 14.
1,4,7-Tris-(tert-butoxycarbonylmethyl)-10-acetyldimethyl-5-
aminoisophthalate-1,4,7,10-tetraazacyclododecane, (4). Triester
3 (1.02 g, 1.98 mmol) was dissolved in acetonitrile (30 cm3), then
caesium carbonate (3.18 g, 9.78 mmol) was added to the stirring
solution. Dimethyl-5-aminoisophthalate acetylchloride 2 (0.55 g,
1.98 mmol) was dissolved in acetonitrile (10 cm3), and added
drop-wise to the triester mixture. The mixture was stirred at room
temperature for 5 d, and was monitored by TLC. The solution was
filtered and the filtrate was evaporated under reduced pressure to
yield a yellow solid. The yellow solid was dissolved in minimum hot
methanol (~10 cm3), from which the product crystallised out as a
Experimental
*
white powder overnight in the fridge (0.51 g, 34%). lmax (p→p ) =
General methods
263 nm (e 11 588 M-1 cm-1); ES+ MS (MeCN): m/z 764 {M +
+
+
1
Cyclen was purchased from Strem Chemicals, and other
reagents, solvents and starting materials were obtained from
H} , 785 {M + Na} ; H NMR (400 MHz, CDCl3, 300 K) dH
1.3 (81H, m, CCH3), 2.6, 2.8, 2.9, 3.0, 3.1, 3.2, 3.3, 3.4 (24H, m,
11454 | Dalton Trans., 2011, 40, 11451–11457
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1
N-CH2 and NCH2CO), 8.3 (1H, s, ArH), 8.5 (2H, s, ArH); 13C{ H}
filtered, and the filtrate was evaporated under reduced pressure to
yield a colourless oil. To the residue minimum ethanol (3 cm3) was
added, followed by the addition of diethyl ether until precipitate
formed. The white precipitate was filtered, washed with diethyl
ether and dried under vacuum to give the product.
NMR (400 MHz, CDCl3, 300 K) dC 28.2 (CCH3), 50.8, 51.9, 52.3,
52.9, 55.2, 56.0, 56.9, 59.0 (CO2CH3, N-CH2CONH, N-CH2 and
N-CH2COO), 80.8, 81.1 (CCH3), 124.7, 125.8, 131.1, 139.2 (Ar-
C), 166.2 (CONH), 170.5, 170.7, 171.2 (CO2CH3 and CO2CCH3);
IR(ATR): n (C O) 1720 cm-1, (C O) 1682 cm-1; CHN expected
for C38H61N5O11: C, 59.75; H, 8.05; N, 9.17. Found: C, 59.46; H,
8.21; N, 8.99.
*
Nd·5 (0.09 g, 88%). lmax (p→p ) = 260 nm (e 2102 M-1 cm-1);
+
+
Maldi MS (a-MeOH) m/z: 596 {M-Nd + H} , 737 {M + 3H} ;
NMR (500 MHz, D2O, 295 K) dH -20.0, -7.7, -6.1, 10.2, 16.9,
Only major resolved peaks outside the range +10 to -5 ppm
reported; IR (ATR): n (C O) 1722 cm-1, (C O) 1581 cm-1;
10-Acetyldimethyl-5-aminoisophthalate-1,4,7,10-tetraazacyclo-
dodecane-1,4,7-triacetate (H3·5). 1,4,7-Tris-(tert-butoxycarbon-
ylmethyl)-10-acetyldimethyl-5-aminoisophthalate-1,4,7,10-tetra-
azacyclododecane 4 (0.6 g, 7.9 ¥ 10-4 mol) was dissolved in
dichloromethane (10 cm3) and trifluoroacetic acid (10 cm3) was
added drop-wise to the stirring solution. The reaction mixture
was stirred at room temperature for 24 h. The solvents were then
removed in vacuo and the residue was washed repeatedly with
dichloromethane (3 ¥ 10 cm3) and methanol (5 ¥ 10 cm3). This
Luminescence: lem = 1055 nm, lex = 337 nm, t(H O) = 144 ns, t(D
=
O)
2
2
376 ns.
*
Eu·5 (0.10 g, 96%). lmax (p→p ) = 260 nm (e 1547 M-1 cm-1);
+
+
Maldi MS (a-MeOH) m/z: 598 {M-Eu + 3H} , 748 {M+3H} ,
+
+
768 {M+Na+2H} , 1492 {Mx2+2H} ; NMR (500 MHz, D2O,
295 K) dH -17.3, -15.9, -14.5, -13.4, -10.1, -7.8, -7.6, -4.7, -3.4,
-2.8, -0.01, 1.5, 7.5, 8.5, 9.1, 9.2, 30.1, 30.5, 31.4, 34.4 (only major
resolved peaks outside the range +2 to +6 ppm reported); IR
(ATR): n (C O) 1721 cm-1, (C O) 1582 cm-1; Luminescence:
lem = 617 nm, lex = 260 nm, t(H = 0.55 ms, t(D = 1.83 ms, q =
*
yielded a hygroscopic yellow solid (0.43 g, 91%). lmax (p→p ) =
261 nm (e 79 250 M-1 cm-1); Maldi MS (a-MeOH): m/z 596
O)
O)
2
2
+
1
{M+H} ; H NMR (400 MHz, D2O, 300 K) dH 3.0–3.6 (24H,
1.1.
broad signal, N-CH2 and NCH2CO), 3.9 (6H, s, CO2CH3), 8.15
*
Gd·5 (0.05 g, 45%). lmax (p→p ) = 260 nm (e 33 100 M-1 cm-1);
(2H, s, arH), 8.25 (1H, s, ArH); 13C{ H} NMR (400 MHz, D2O,
1
+
+
Maldi MS (a-MeOH) m/z: 595 {M-Gd} , 751 {M+H} , 1500
300 K) dC 50.9, 54.9 (broad signal, CO2CH3, N-CH2CONH, N-
CH2 and N-CH2COO), 114.9, 117.6, 125.2, 126.2, 130.9 (Ar-C),
162.3, 163.4, 167.5 (CONH, CO2CH3 and COOH); IR(ATR): n
(C O) 1718 cm-1, (C O) 1664 cm-1, (N–H) 1574 cm-1; CHN
expected for C26H37N5O11(CF3COOH)(H2O)2: C, 45.10; H, 5.68;
N, 9.39. Found: C, 45.69; H, 5.95; N, 9.19.
{Mx2} ; IR (ATR): n (C O) 1718 cm-1, (C O) 1583 cm-1; CHN
+
expected for C26H34N5O11(H2O)4: C, 38.00; H, 5.15; N, 8.52; Gd,
19.13. Found: C, 38.00; H, 4.69; N, 8.48; 19.37.
Tb·5 (0.10 g, 90%). lmax (p→p ) = 260 nm (e 2832 M-1 cm-1);
*
+
+
Maldi MS (a-MeOH) m/z: 596 {M-Tb + H} , 752 {M+H} ;
NMR (500 MHz, D2O, 295 K) dH -411.6, -370.8, -359.1,
-147.8, -142.4, -126.6, -114.4, -100.7, -95.9, -88.9, -79.4,
-63.9, -52.9, 84.2, 125.8, 131,9, 181.0, 189.1, 230.8, 246.7 (only
major peaks outside the range +60 to - 45 ppm reported); IR
(ATR): n (C O) 1721 cm-1, (C O) 1582 cm-1; CHN expected
for C26H34N5O11Tb·(CF3COOH)3(H2O)3: C,33.49; H, 3.78; N,
6.10; Tb, 13.84. Found: C, 29.39; H, 3.61; N, 6.02; Tb, 14.32.
10-Acetyldicarboxylic
acid-5-aminoisophthalate-1,4,7,10-tet-
raazacyclododecane-1,4,7-triacetate sodium salt, (Na5·6). H3·5
(0.2 g, 3.36 ¥ 10-4 mol) was dissolved in distilled water (2 cm3),
then 5 molar equivalents of NaOH (1.67 cm3, 1 M) were added
drop-wise to the stirring solution. The solution was stirred at
room temperature for 5 h. Any precipitate was filtered off, before
adding an excess of acetone to the filtrate, until the solution
went cloudy. The solution was kept in the fridge overnight,
where an orange oil formed at the bottom of the flask. The
solution was carefully decanted off, to leave behind the orange oil
product, which was dried overnight under vacuum, to yield the
Luminescence: lem = 545 nm, lex = 260 nm, t(H O) = 1.63 ms, t(D
=
O)
2
2
2.73 ms, q = 0.9.
*
Er·5 (0.07 g, 66%). lmax (p→p ) = 260 nm (e 1984 M-1 cm-1);
+
+
Maldi MS (a-MeOH) m/z: 597 {M-Er + H} , 760 {M} , 1520
+
{Mx2} ; NMR (500 MHz, D2O, 295 K) dH -84.4, -77.9, -70.7,
+
-67.6, -59.0, -55.2, -37.9, -33.5, -30.0, 14.9, 21.4, 22.7, 25.5, 33.9,
130.2, 133.4, 144.6, 152.7 (only major peaks outside the range +10
to -20 ppm reported); IR (ATR): n (C O) 1722 cm-1, (C O)
product (0.13 g, 68%). Maldi MS (a-MeOH): m/z 568 {M+H} ,
+
+
+
590 {M+Na} , 612 {M-H+2Na} , 634 {M-2H+3Na} , 656
+
1
{M-3H+4Na} ; H NMR (400 MHz, D2O, 300 K) dH 2.2, 2.4,
1582 cm-1; Luminescence: lem = 1530 nm, lex = 337 nm, t(D
=
O)
2
2.6, 2.9, 3.2, 3.3 (24H, br m, N-CH2 and N-CH2CO), 7.8 (2H, s,
Ar-H), 7.9 (1H, s, Ar-H); 13C { H} NMR (400 MHz, D2O, 300
1
805 ns.
*
Yb·5 (0.09 g, 84%). lmax (p→p ) = 260 nm (e 967 M-1 cm-1);
K) dC 56.9, 58.6, 58.7, 59.3 (broad signal, N-CH2CONH, N-CH2
and N-CH2COO), 123.9, 124.1, 125.6, 136.9, 137.4 (Ar-C),
172.2, 173.5, 174.3, 180.2, 180.3, 180.4 (CONH, Ar-CO2H and
COOH); IR(ATR): n (O–H) 3319 cm-1, (C O) 1695 cm-1, (N–H)
1590 cm-1; CHN expected for C24H27N5O11Na6(NaOH)6·6H2O:
C, 27.52; H, 4.33; N, 6.69; Na, 26.34. Found: C, 27.91; H, 4.24;
N, 6.57; Na, 26.78.
+
+
Maldi MS (a-MeOH) m/z: 596 {M-Yb + H} , 767 {M+H} ,
+
1534 {Mx2 + 2H} ; NMR (500 MHz, D2O, 295 K) dH -73.5,
-72.9, -72.1, -70.5, -61.4, -60.4, -45.6, -42.7, -24.6, -23.8, -18.9,
-10.7, 10.8, 12.5, 14.1, 16.2, 16.5, 17.0, 23.1, 28.3, 35.9, 112.0,
114.2, 118.5, 129.5 (only major peaks outside the range +10 to -4
ppm reported); IR (ATR): n (C O) 1719 cm-1, (C O) 1584 cm-1;
Luminescence: lem = 980 nm, lex = 337 nm, t(H O) = 0.78 ms, t(D
=
O)
2
2
5.21 ms, q = 0.9.
General procedure for the preparation of Ln·5
5 (0.13 g, 1.4 ¥ 10-4 mol) was dissolved in the minimum volume
of methanol (3 cm3), and mixed with a solution of the lanthanide
triflate salt (1.0 eq, 1.4 ¥ 10-4 mol) in methanol (3 cm3). The
solution was stirred at room temperature for 7 d. The solution was
General procedure for the preparation of [Ln·6]2-
Na5·6 (0.05 g, 4.8 ¥ 10-5 mol) was dissolved in distilled water
(1 cm3), and the pH was adjusted from pH 11 to pH 5 by
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adding dilute HCl (~3 cm3, 1 M) to the solution. A solution of
the lanthanide triflate salt dissolved distilled water (1 cm3) was
then added drop-wise to the mixture. The solution was heated at
Elmer LS55 fluorimeter operating in phosphorescence mode
counting. In the case of the erbium, ytterbium and neodymium
complexes, the sample was excited using a pulsed nitrogen laser
(337 nm) operating at 10 Hz. Light emitted at right angles to the
excitation beam was focused onto the slits of a monochromator,
which was used to select the appropriate wavelength. The growth
and decay of the luminescence at selected wavelengths was detected
using a germanium photodiode (Edinburgh Instruments, EI-P)
and recorded using a digital oscilloscope (Tektronix TDS220) be-
fore being transferred to a PC for analysis. Luminescence lifetimes
were obtained by iterative reconvolution of the detector response
(obtained by using a scatterer) with exponential components
for growth and decay of the metal centred luminescence, using
a spreadsheet running in Microsoft Excel. The details of this
approach have been discussed elsewhere.23 Unless otherwise stated,
fitting to a double exponential decay yielded no improvement in
fit as judged by minimisation of residual squared and reduced chi
squared.
◦
60 C for 18 h. The solvent was then evaporated under reduced
pressure to yield a white solid. Minimum ethanol (3 cm3) was
added to dissolve the white residue, followed by the addition of
excess diethyl ether until the white product precipitated out. The
solution was filtered using a filter stick under vacuum, and the
hygroscopic white product was then washed with diethyl ether and
dried under vacuum to give the product.
[Nd·6]2- (0.02 g, 67%). Maldi MS (a-MeOH) m/z: 710
+
{M+4H} , 1418 {Mx2 + 6H}; IR (KBr): n (O–H) 3449 cm-1,
(C O) 1702 cm-1, (N–H) 1614 cm-1. Luminescence: lem = 1055
nm, lex = 337 nm, t(H = 110 ns, t(D = 340 ns.
O)
O)
2
2
[Eu·6]2- (0.03 g, 81%). lmax (p→p ) = 260 nm (e 4700 M-1 cm-1);
*
+
1
Maldi MS (no matrix) m/z: 718 {M+H} ; H NMR (500 MHz,
D2O, 300 K) dH (ppm) -17.5, -16.5, -16.2, -14.9, -14.6, -13.6,
-13.2, -12.6, -12.2, -11.7, -10.5, -8.3, -7.9, -7.3, -6.9, -5.1, -3.9,
-3.2, -1.2, -0.7, -0.1, +1.0, +1.2, +8.9, +11, +12, +13.5, +29.3,
+29.8, +30.7, +34.1 (only major resolved peaks outside the range
+3 to +5 ppm reported); IR (ATR): n (O–H) 3427 cm-1, (C O)
X-Ray crystallography
1708 cm-1, (N–H) 1582 cm-1; Luminescence: lem = 617 nm, lex
260 nm, t(H = 0.57 ms, t(D = 2.18 ms, q = 1.2.
=
X-Ray diffraction data for Tb·5 were collected at 150 K using
a Bruker APEX II CCD diffractometer on station 9.8 of the
Synchrotron Radiation Source at CCLRC Daresbury Laboratory,
O)
O)
2
2
[Tb·6]2- (0.03 g, 87%). lmax (p→p ) = 260 nm (e 3840 M-1 cm-1);
*
+
+
˚
Maldi MS (a-MeOH) m/z: 746 {M+Na} , 768 {M+2Na - H} ,
at 0.69040 A, from a silicon 111 monochromator using w scans.
+
+
The structure was solved by direct methods using SHELXS-97.24
The structure was completed by iterative cycles of DF-syntheses
and a full matrix least squares refinement. All non-H atoms
were refined anisotropically and difference Fourier syntheses
were employed in positioning idealised hydrogen atoms and were
allowed to ride on their parent C or N-atoms. All refinements were
against F2 and used SHEL-XL-97.25
790 {M+3Na - 2H} , 1447 {Mx2 + H} , 1470 {Mx2+Na +
+
+
+
H} , 1491 {Mx2 + 2Na - H} , 1513 {Mx2 + 3Na - 2H} ,
+
+
1535 {Mx2 + 4Na - 3H} , 1557 {Mx2 + 5Na - 4H} , 1578
+
{Mx2 + 6Na - 6H} ; 1H NMR (500 MHz, D2O, 300 K) dH
(ppm) -405.4, -364.6, -352.4, -144.7, -127.3, -121.3, -111.9,
-100.6, -96.8, -77.9, -73.7, -66.3, -63.9, -54.2, +83.9, +117.4,
+125.2, +138.0, +169.5, +224.2, +234.3, +238.7, +247.8, +262.7
(only major resolved peaks outside the range -40 to +100 ppm
reported); IR (KBr): n (O–H) 3446 cm-1, (C O) 1700 cm-1, (N–
H) 1617 cm-1; Luminescence: lem = 545 nm, lex = 260 nm, t(H
=
Notes and references
O)
2
1.69 ms, t(D = 3.03 ms, q = 1.0.
O)
2
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[Er·6]2- (0.03 g, 81%). lmax (p→p ) = 260 nm (e 4660 M-1 cm-1);
*
+
+
Maldi MS (a-MeOH) m/z: 755 {M+Na} , 778 {M+2Na} , 800
+
+
+
{M+3Na - 1H} , 1468 {Mx2 - 4H} , 1486 {Mx2+Na - 1H} ,
+
+
1508 {Mx2 + 2Na - 2H} , 1530 {Mx2 + 3Na - 3H} , 1551 {Mx2 +
+
+
4Na - 5H} , 1572 {Mx2 + 5Na - 7H} ; 1H NMR (500 MHz, D2O,
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-37.9, -37.4, -33.4, -29.9, +21.0, +21.9, +34.0, +129.4, +132.2,
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[Yb·6]2- (0.03 g, 89%). lmax (p→p ) = 260 nm (e 6120 M-1 cm-1);
*
+
+
Maldi MS (a-MeOH) m/z: 761 {M+Na} , 783 {(M+6H + K} ,
+
1498 {Mx2 - H + Na} ; 1H NMR (500 MHz, D2O, 300 K)
dH (ppm) -81.6, -72.9, -72.0, -70.8, -69.2, -61.6, -57.9, -45.2,
-44.1, -41.9, -37.5, -26.2, -24.4, -18.5, -9.9, +19.8, +22.1, +24.1,
+29.4, +37.4, +110.9, +115.5, +119.0, +132.1, +132.8 (only major
resolved peaks outside the range -5 to +19 ppm reported); IR
(KBr): n (O–H) 3488 cm-1, (C O) 1694 cm-1, (N–H) 1633, 1614
and 1588 cm-1.
Photophysical measurements
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11456 | Dalton Trans., 2011, 40, 11451–11457
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Dalton Trans., 2011, 40, 11451–11457 | 11457
©