Monitoring helical twists and effective molarities in dinuclear triple-stranded lanthanide helicates

Article abstract of DOI:10.1039/c3dt50941a

The replacement of terminal benzimidazole-pyridine binding units in the neutral di-tridentate segmental ligand L1 with phenanthroline in L10 reduces the number of torsional degrees of freedom by two units. Reactions of these ligands with trivalent europium or lutetium cations yield structurally similar self-assembled dinuclear triple-stranded [Ln₂(Lk)₃] ⁶⁺ complexes, thus demonstrating that the increased rigidity of the strand in L10 is compatible with its helical twist. With the larger lanthanum cations, the metallic coordination spheres are completed with two terminal axial triflate counter-anions to give [La₂(L10)₃(CF ₃SO₃)₂]⁴⁺. Thermodynamic investigations in acetonitrile confirm the minor constraints produced by the planar phenanthroline unit in L10 leading to comparable effective molarities EM^Eu,L1 ≈ EM^Eu,L10 = 10 ^-3.9(4) M with mid-range Eu^III cations. The striking minute effective molarities EM^Ln,Ln-2H ≈ 10^-6-10^-9 M obtained upon the replacement of terminal phenanthrolines with structurally analogous fused hydroxyquinolines in L9 can be thus unambiguously assigned to solvation effects, a new tool for controlling complexity in metal-induced self-assembly processes.

Full text of DOI:10.1039/c3dt50941a

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Transactions
An international journal of inorganic chemistry
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Volume 42 | Number 31 | 21 August 2013 | Pages 11023–11328
ISSN 1477-9226
COVER ARTICLE
Piguet et al.
Monitoring helical twists and effective molarities in dinuclear triple-stranded
lanthanide helicates
1477-9226(2013)42:31;1-M

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PAPER
Monitoring helical twists and effective molarities in
dinuclear triple-stranded lanthanide helicates†
Cite this: Dalton Trans., 2013, 42, 11047
a
b
a
Patrick E. Ryan, Laure Guénée and Claude Piguet*
The replacement of terminal benzimidazole–pyridine binding units in the neutral di-tridentate segmental
ligand L1 with phenanthroline in L10 reduces the number of torsional degrees of freedom by two units.
Reactions of these ligands with trivalent europium or lutetium cations yield structurally similar self-
6
+
assembled dinuclear triple-stranded [Ln
2
(Lk)
3
]
complexes, thus demonstrating that the increased rigid-
ity of the strand in L10 is compatible with its helical twist. With the larger lanthanum cations, the metallic
coordination spheres are completed with two terminal axial triflate counter-anions to give
4
+
[
La
2
(L10)
3
(CF
3
SO
3
)
2
]
. Thermodynamic investigations in acetonitrile confirm the minor constraints pro-
Eu,L1
duced by the planar phenanthroline unit in L10 leading to comparable effective molarities EM
≈
≈
Received 9th April 2013,
Accepted 29th April 2013
Eu,L10
= 10−3.9(4) M with mid-range Eu cations. The striking minute effective molarities EM
III
Ln,Ln-2H
EM
1
0−6–10−9 M obtained upon the replacement of terminal phenanthrolines with structurally analogous
DOI: 10.1039/c3dt50941a
fused hydroxyquinolines in L9 can be thus unambiguously assigned to solvation effects, a new tool for
www.rsc.org/dalton
controlling complexity in metal-induced self-assembly processes.
Whereas kinetic studies rapidly delivered pertinent models
for the time evolution of the assembly processes leading to
The extension of the principle of maximum occupancy, origi- dinuclear lanthanide helicates, the rationalization of the
nally set for the design of polynuclear helicates with 4-co- thermodynamic driving forces responsible for the apparent
ordinated and 6-coordinated d-block cations in metallo- selective formation of a single species was delayed until Erco-
Introduction
1
13
2
supramolecular chemistry, led to the isolation of the first lani used the concept of effective molarity (EM) for satisfyingly
triple-stranded dinuclear lanthanide helicates by reacting modelling the intramolecular metal–ligand binding events
nine-coordinated 4f-block cations with the di-tridentate ligand responsible for the formation of metallosupramolecular edi-
3
14
L1. Since then, the helical twist induced by diphenylmethane fices (eqn (1) and Fig. 1).
4
5
spacers was systematically exploited in homotopic (L2, L3
and L4 ) and heterotopic (L5 and L6 ) segmental di-tridentate
ligands for producing lanthanide helicates working as lumi-
nescent bioprobes with unprecedented thermodynamic selec-
ΔG
ꢀΔGintra
inter
6
7
8
Kintra
Kinter
ð
RT
Þ
EM ¼
¼ e
ð1Þ
9
θ
Taking the well-accepted concentration of c = 1 M for the
Structural analyses suggested that the successive reference state, the van’t Hoff isotherm transforms EM into
3
d,7
15
tivities.
θ
non-negligible inter-aromatic torsions observed along the the free energy contribution ΔGintra − ΔGinter = −RT ln(EM/c ),
ligand strands were a pre-requisite for a successful helication which estimates the advantage (EM > 1 M) or drawback (EM <
(
see Scheme 1), and related segmental ligands with an increas- 1 M) produced by the replacement of an intermolecular con-
1
0
16
ing number of torsional degrees of freedom such as L7 (and nection by its intramolecular counterpart.
derivatives of it) or L8 indeed provided stable triple-
1
1
12
The average effective molarity, which controls the intra-
stranded lanthanide helicates.
molecular macrocyclization processes along the assembly of the
6
+
dinuclear lanthanide triple-stranded helicates [Eu
2
(Lk)
3
]
(Lk
L1–L2), amounts to EM = 10− M in acetonitrile. Conse-
4.1
17
=
quently, any intramolecular binding event is penalized by
ΔGintra − ΔGinter = 23.4 kJ mol− (eqn (1)), a trend drastically
amplified upon reduction of the total number of torsional
degrees of freedom along the strands as found in [Eu (L9-2H) ]
1
a
Department of Inorganic and Analytical Chemistry, University of Geneva, 30 quai
E. Ansermet, CH-1211 Geneva 4, Switzerland. E-mail: Claude.Piguet@unige.ch
b
Laboratory of X-ray Crystallography, University of Geneva, 24 quai E. Ansermet,
2
−1
3
CH-1211 Geneva 4, Switzerland
†
−5.8
(
EM = 10
Lu (L9-2H)
Given that ΔGinter = −30 kJ mol (ref. 17) and ΔGinter
M, ΔGi n− tra − ΔGinter = 33.1 kJ mol ) and in
Electronic supplementary information (ESI) available. CCDC 933010 and
33011. For ESI and crystallographic data in CIF or other electronic format see
9 −1 18
[
2
3
] (EM = 10 M, ΔGintra − ΔGinter = 51.3 kJ mol ).
9
Eu,L1
−1
Ln,L9-2H
DOI: 10.1039/c3dt50941a
≈
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Scheme 1 Chemical structures of the segmental di-tridentate ligands L1–L10. The curved arrows highlight the torsional degrees of freedom.
40 kJ mol− (ref. 18), the energetic contribution induced by substitution. Reduction yielded 2 whose hydrolysis eventually
1
−
1
9
the effective molarity represents a crucial parameter for tuning gave 1,10-phenanthroline-2-carboxylic acid 3. Activation of
the driving force controlling the overall stability of the final the carboxylic group into its acyl chloride followed by coupling
2
0
helicates. However, the pertinence of any comparison between with
3,3′-dinitro-4,4′di(N-ethyl)amino-diphenylmethane
ligands L1 or L2 (six torsional degrees of freedom, Scheme 1) resulted in the di-orthonitroamido compound 4, which was
2
1
and L9 (four torsional degrees of freedom, Scheme 1) is finally converted into L10 by reductive cyclization. The nine
1
limited by (i) the use of different tridendate donor groups aromatic signals detected by H NMR combined with the exist-
−
(
neutral N
3
or N
2
O in L1 and L2 and negatively charged N
2
O
ence of three enantiotopic methylene groups were diagnostic
in L9) and (ii) the consideration of different solvents for of L10 adopting a dynamically average C2v symmetry in solu-
2
2
imperative solubility reasons (acetonitrile for L1 and L2 and tion (Fig. 2a). The lack of Nuclear Overhauser Enhancement
dichloromethane–methanol (1 : 1) for L9). In order to decipher effect between H5 and H7 indicated that the transoid confor-
the real impact of the total number of torsional degrees of mation depicted in Scheme 2 was adopted by the benzimid-
freedom on the effective molarity, we report here on the struc- azole–phenanthroline units.
tural and thermodynamic behaviour of the triple-stranded heli-
Reaction of L10 (3 equiv.) with Ln(CF
3 3 3 2
O ) ·xH O (Ln = La,
6
+
cates [Ln
expected to be as rigid as [L9-2H] , but as neutral and soluble of the dinuclear complexes [Ln (L10) ](CF SO ) ·xH O·yCHCl
3
2 3
(L10) ] , in which the di-tridentate ligand L10 is Eu, Lu; x = 1–3) in acetonitrile–chloroform (2 : 3) gave 62–93%
2
−
2
3
3
3 6
2
in acetonitrile as L1.
(Ln = La, x = 3, y = 3; Ln = Eu, x = 7, y = 0; Ln = Lu, x = 5, y = 0).
Slow diffusion of benzene or butyl-methylether into concen-
t
trated acetonitrile solutions of these complexes yielded pale
yellow X-ray quality prisms for [La
CH CN) (C (5) and [Lu (L10)
Both crystal structures contained dinuclear triple helical
2
(L10)
3
(CF
3
SO
3
)
2
](CF
3
SO
3 4
) -
Results and discussion
Synthesis and characterization of ligand and complexes
(
3
6
H )
6 6 6
2
3
](CF
3
SO
3
6
) (CH
3
CN)
4
(6).
The di-tridentate ligand L10 was obtained in five steps from cations, non-coordinated counter-anions and interstitial solvent
commercially available 1,10-phenanthroline (global yield = molecules (Fig. 3 and S1; Tables S1–S5†).
6+
6+
1
2%, Scheme 2). After oxidation into its N-oxide form 1, a
The molecular structures of [Lu
2
(L10)
3
]
and [Eu (L1) ]
2 3
cyano group was introduced via
a
nucleophilic aryl are almost superimposable and globally display one helical
1
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Scheme 2 Synthesis of the ligand L10 with the numbering scheme used for
1
H NMR.
Fig. 1 Illustration of intermolecular (black arrow, top) and intramolecular (pink intermetallic distance (Appendix 1) and (iv) the area of the tri-
arrow, bottom) metal–ligand binding processes operating during the self-assem-
angle defined by the three terminal nitrogen atoms increases
6+
bly of [Eu
2
(L1)
3
]
. Peripheral ligand substituents are omitted for clarity.
2
6+
2
from 4.71 Å in [Lu
2
(L10)
3
]
2 3
to 8.19 Å in [La (L10) -
4
+
(
CF SO ) ] (Fig. 4b). In the absence of related molecular
3
3 2
structures reported for La(III) interacting with L1, the consider-
able changes induced by the coordination of large lanthanum
cations in the triple-stranded architecture cannot be unam-
biguously assigned to the presence of rigid terminal phenan-
throline units in L10.
turn of the strands for an intermetallic distance of 8.8 Å
Fig. 4a). The 0.09 Å contraction of the Ln–N distances
(
III
observed in going from nine-coordinated Eu (average Eu–N =
III
2
.59(3) Å) to nine-coordinated Lu (average Lu–N = 2.50(2) Å)
2
3
exactly fits the expected contraction of the ionic radii, which
logically results in identical bond valences νEu,N = νLu,N = 0.32(2)
within experimental errors (Tables S6–S8†).
A thorough analysis of the successive helical pitches charac-
2
4,25
Speciation and thermodynamics for helicate self-assemblies in
solution
terizing the overall helication of the ligand strands in ESI-MS titrations of L10 with Ln(CF SO ) ·xH O in acetonitrile
3
3 3
6+
2
6
+
6+
6+
[
Eu (L1) ] and [Lu (L10) ] indicates that the rigidification show the formation of [Ln (L10) ] , [Ln (L10) ]
of the ligand in L10 has negligible structural consequences [Ln (L10)] for Ln = La, Eu in the gas-phase, together with an
Appendix 1). However, the use of larger La cations results in additional complex [Ln (L10) ] for Ln = Lu (Tables S9–S11†).
the fixation of two additional axial triflate anions to give In solution, H NMR titrations confirm the formation of intri-
and
2
3
2
3
2
3
2
2
6
+
2
III
9+
(
3 2
1
4
+
[La
2
(L10)
3
(CF
3
SO
3
)
2
]
where (i) each metal is ten-coordinated, cate mixtures of complexes in the intermediate exchange rate
(
ii) the bonding affinities of the heterocyclic nitrogen atoms on the NMR time scale with the emergence of the threefold-
6
+
are reduced (average bond valence νLa,N = 0.27(2), Tables S6 symmetrical [Ln (L10) ] complexes as the only species for
2
3
and S7†), (iii) the helical pitches are reduced by more than 1 Å |Ln|tot/|L10|tot = 0.67 at millimolar concentrations (10 aro-
within the terminal sections without affecting the matic signals, Fig. 2b). The unusual downfield shift monitored
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Fig. 3 Perspective views of the molecular structures of (a) [La
2
(L10)
observed in the crystal structures of
(C (5) and [Lu (L10) ](CF SO
3
-
4
+
6+
(
[
(
CF
La
CH
3
SO
(L10)
CN)
3
)
2
]
and (b) [Lu
SO ](CF SO
2
(L10)
3
]
2
3
(CF
3
3
)
2
3
3
)
4
(CH
3
CN)
6
6
H
6
)
6
2
3
3
3 6
) -
3
4
(6). Color code: grey = C, blue = N, red = O, yellow = S, light blue = F,
green = Lu, pink = La. Hydrogen atoms are omitted for clarity.
1
Fig. 2 Part of the H NMR spectra recorded for (a) L10 in CDCl
3
and (b)
CN at 298 K (|L10|tot = 0.5 mM). The transformation of the
enantiotopic methylene protons H5,5’ (quartet) into their diastereotopic form
two pseudo-sextets) is highlighted.
6+
[Lu
2
(L10)
3
]
in CD
3
(
for the signal of the aromatic proton H2 in the diamagnetic
complexes (Δδ = δcomplex − δligand = −1.90 ppm for Ln = La and
−2.57 for Ln = Lu) is diagnostic of the helication of the
strands, which puts this proton into the shielding domain of
the benzimidazole ring of an adjacent strand (Fig. 2). The
6+
6+
Fig. 4 Superimposition of (a) [Lu
2
(L10)
3
]
(red) and [Eu
2
(L1)
3
]
(blue) and (b)
2
6
6+
4+
[Lu
2
(L10)
3
]
(red) and [La
2
(L10)
3
3
(CF SO
3
)
2
]
(green). Peripheral substituents
observation of diastereotopic H5,5′ methylene protons further connected to the ligand strands and terminal triflate anions are omitted for
clarity.
confirms the non-planar arrangement of the strands, while the
enantiotopic H1,1′ protons indicate the existence of three
twofold axes perpendicular to the threefold axis (Fig. 2b), in
9+
3+
[Ln
3
(L10)
2
]
complex for Ln = Lu , in complete agreement
line with the standard D -symmetry point group adopted by
3
with the speciation detected by ESI-MS in the gas-phase. The
global spectrophotometric data can be fitted with non-linear
least-squares techniques to three macroscopic equilibria for
Ln = La, Eu (eqn (2)–(4)) and to four macroscopic equilibria for
6
+
the relaxed triple-helical [Ln
2
(L10)
3
]
complexes in solution.
3
+
Interestingly, complexation of L10 with Ln is accompanied
by trans to cis conformational changes about the phenanthro-
line–benzimidazole interaromatic bonds, which alters the
envelope of the electronic absorption spectrum produced by
ligand-centred n→π* and π→π* transitions (Fig. 5).
28
Ln = Lu (eqn (2)–(5); Table 1).
2Ln3 þ 3L10 Ð ½Ln ðL10Þ ꢁ
þ
6þ Ln;L10
β
ð2Þ
ð3Þ
ð4Þ
2
3
2;3
2
7
Factor analysis applied to the spectrophotometric titra-
2Ln3 þ 2L10 Ð ½Ln2ðL10Þ2ꢁ6þ
þ
β
2;2
Ln;L10
tions of L10 with Ln(CF SO ) ·xH O suggests the formation of
3
3 3
2
6
+
6+
three absorbing complexes [Ln (L10) ] , [Ln (L10) ] and
Ln (L10)] for Ln = La, Eu together with an additional
2
2
3
2
2
þ
Ln;L10
β
2;1
6
+
2
Ln3 þ L10 Ð ½Ln2ðL10Þꢁ6þ
[
1
1050 | Dalton Trans., 2013, 42, 11047–11055
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À
Á
Ln;L10
Ln;L10
free energy change ΔGN3
¼ ꢀRT ln f
includes the
N3
necessary solvent reorganization. Among the six Ln–N3
binding events occurring in [Ln
cular and characterized with fN3
6
+
2
(L10)
3
] , four are intermole-
Ln;L10
, but two are intramolecular
(
= macrocyclization) and their affinities must be corrected by
Ln;L10
Ln;L10
Ln;L10
using the effective molarity f
u
mann factors correcting the free energy of connection for
intramolecular ligand–ligand (i.e. L10⋯L10), respectively
metal–metal (i.e. Ln⋯Ln) interactions resulting from the
close location of two ligands, respectively two cations in
¼ f
ꢂ EM
. Finally,
are the Boltz-
N3;intra
Ln;Ln
N3
L10;L10
Ln
Ln;Ln
L10
L10;L10
Ln
ꢀðΔE
=RTÞ
ꢀðΔE
=RTÞ
¼ e
and uL10 ¼ e
6
+ 16,31
[
[
Ln
Ln
2
(L10)
3
] .
Obviously, the same model applies for
6
+
2
(L1)
3
]
(eqn (7)) and the extreme similarity of the
6
+
crystal structures of the triple-helical cores in [Eu (L1) ]
and [Ln
affinity of the tridentate binding units (f
interligand interactions (u
2
3
6
+
2
(L10)
3
]
lead us assume that (i) the intermolecular
Ln;L1
Ln;L10
ꢃ f
), (ii) the
N3
N3
L1,L1
L10,L10
Ln
≈ u
) and (iii) the interme-
Ln
Fig. 5 Variation of absorption spectra (left) and corresponding variation of
observed molar extinctions at 5 different wavelengths (right) observed for the
Ln,Ln
Ln,Ln
tallic interactions (uL1 ≈ uL10 ) are identical for L1 and L10.
The simple ratio of the incriminated stability constants thus
spectrophotometric titrations of L10 with (a) La(CF
3
SO
3
)
3
·2H
2
O and (b) Lu-
O (total ligand concentration: 5 × 10− M in acetonitrile–chloroform reduces to the square of the ratio of their effective molarities
4
(CF
3
SO
3
)
3
·H
2
(9 : 1); 298 K).
(eqn (8)).
À
Á À
Á À
Á
Ln;L1
Ln;L1
Ln;L1
6
EMLn;L1
2
L1;L1
6
Ln;Ln
β
¼ ω2;3
f
u
u
ð7Þ
2
;3
N3
Ln
L1
Ln,Lk
Table 1 Cumulative thermodynamic formation constants log(β2,n ) obtained
6+
À
Á À
6
Á À
Á
6
for [Ln
2
(Lk)
n
]
(Lk = L1, L2, L10; Ln = La, Eu, Lu; 298 K)
Ln;L10
Ln;L10 Ln;L10
EMLn;L10
2
L10;L10
Ln;Ln
L10
β
ω
f
u
u
2
;3
2;3
N3
Ln
¼
ꢃ
À
Á À
Á À
Á
Ln;L1
Ln;L1 Ln;L1
6
2
L1;L1
Ln
6
Ln;Ln
L1
ω
f
EMLn;L1
u
u
Metal
Solvent
La
Eu
Lu
Reference
β
2
;3
2;3
N3
ꢀ
ꢁ
Ln;L10
2
Ln,L1
a
a
EM
log(β2,3
)
)
)
)
CH
CH
CH
CH
3
3
3
3
3
3
3
3
CN
CN
CN
CN
CN–CHCl
CN–CHCl
CN–CHCl
CN–CHCl
20–22 24.3(4)
18.1(3)
29
29
Ln,L1
ð8Þ
EMLn;L1
log(β2,2
—
Ln,L2
log(β2,3
25.1(2) 26.0(2) 25.4(5) 30
19.2(5) 19.6(2) 19.3(4) 30
b
Ln,L2
log(β2,2
Introducing the experimental values of the formation con-
stants found for Ln = Eu (Table 1), together with EM
Ln,L10
log(β2,3 ) CH
3
3
3
3
(9 : 1)b 24.8(5) 24.8(5) 24.7(2) This work
Eu,L1
Ln,L10
=
log(β2,2 ) CH
(9 : 1) 16.9(9) 16.9(9) 17.2(6) This work
Ln,L10
b
−4.1
17
Eu,L10
−3.9(4)
log(β3,2 ) CH
(9 : 1)b
—
—
23.4(2) This work 10
M, eventually provides EM
= 10
M.
Ln,L10
log(β2,1 ) CH
(9 : 1) 10.9(8) 10.9(8) 12.2(2) This work
a
4 3
A partial fit of the spectrophotometric titration of L1 with Lu(ClO )
Lu,L1
suggested log(β2,3 ) = 17.5(4) in the absence of a satisfying model of
Lu/L1 > 0.67.
Conclusion
2
9 b
n
+0.01 m Bu
4 4
NClO .
The removal of two torsional degrees of freedom in going from
L1 to L10 has a minor structural and thermodynamic influ-
ence on the formation of the target triple-stranded lanthanide
þ
Ln;L10
3;2
3
Ln3 þ 2L10 Ð ½Ln3ðL10Þ2ꢁ9þ
β
ð5Þ
6
+
Ln,L10
2 3
helicates [Ln (Lk) ] . The solid state structures display a
The stability constants log(β2,3 ) ≈ 24.8 found for the
6
+
similar helical wrapping of the strands leading to comparable
triple-helical complexes [Ln (L10) ]
compare well with
2
3
1
6
+
intermetallic separation (≈ 0.9 nm), while closely related H
related values previously collected for [Ln (L1) ]
and
Within the
2
3
6
+
29,30
NMR characteristics point to identical relaxed D -symmetrical
3
[Ln
2
(L2)
3
]
under similar conditions (Table 1).
structures in solution. The isolation of the unsaturated dinuc-
frame of the site-binding approach, the cumulative formation
macroconstant given in eqn (2) can be modeled with eqn (6).
4
+
1
6,31
2 3 3 3 2
lear triple-stranded [La (L10) (CF SO ) ] helicate with the
largest lanthanide is the only innovative point reported here
for this class of compounds. However, the similitude of the
Eu-complexes with L1 and L10 allowed for a detailed thermo-
À
Á À
Á À
Á
Ln;L10
Ln;L10
Ln;L10
6
EMLn;L10
2
L10;L10
Ln
6
Ln;Ln
L10
β
¼ ω2;3
f
u
u
ð6Þ
2
;3
N3
Ln,L10
In this equation, ω2,3
= 96 is the statistical factor of the dynamic analysis, which led us to conclude that the effective
assembly process, which takes into account the pure entropic molarity (EM ≈ 10− M) is not significantly affected by the
4
contribution due to a change in molecular rotational entropies increased rigidity found in L10. This result contrasts with the
3
2
Ln;L10
occurring upon complexation (Fig. S2†), and fN3
corre- decrease of EM by three to five orders of magnitude observed
sponds to the absolute intermolecular affinities of the triden- for [Ln (L9-2H) ] despite the topological (four degrees of tor-
2
3
3
+
3
tate heterocyclic N binding unit for the entering Ln cation. sional freedom) and structural similitudes between L9 and L10
Each tridentate unit is considered to be bound to the lantha- (Scheme 1). We therefore deduce that the increased rigidity in
nide cation via a single point connector, and the associated L9 is not the origin of its reluctance for macrocyclization in
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the dinuclear triple-stranded helicate. We should however Benzoyl chloride (5.6 g) was dropwise added under stirring for
2
−
stress here that L9 indeed reacts as its dianion [L9-2H] in the 1 h at RT. The resulting precipitate was filtered, washed with
self-assembly of [Ln (L9-2H) ], a molecular form prone to water and crystallized from hot ethanol to give 2-cyano-1,10-
strongly interacting with the hydroxylic co-solvent required for phenanthroline (2, 4.3 g, 20.9 mmol, yield: 73%) as a cream
2
3
1
3
4
solubility reasons. We then suspect that a particular confor- solid. H NMR (CDCl ) δ/ppm: 9.28 (dd, 1H, J = 4.3 Hz, J =
3
3
3
4
mation of the deprotonated ligand in its half-complexed form 1.7 Hz), 8.40 (d, 1H, J = 8.2 Hz), 8.31 (dd, 1H, J = 8.1 Hz, J =
prior to macrocyclization (see Fig. 1, middle) combined with 1.7 Hz), 7.97 (d, 1H, J = 8.2 Hz), 7.96 (d, 1H, J = 8.8 Hz), 7.85
some reluctance to produce neutral [Ln (L9-2H) ] helicates in (d, 1H, J = 8.8 Hz), 7.74 (dd, 1H, J = 8.1 Hz, J = 4.3 Hz).
3
3
3
3
3
2
3
polar acetonitrile–methanol is responsible for the extremely
Preparation of 1,10-phenanthroline-2-carboxylic acid (3).
1
8
small effective molarity reported for these complexes. After 2-Cyano-1,10-phenanthroline (2, 1.0 g, 4.9 mmol) and sodium
3
3
relying on purely entropic (Gaussian exploration of space) or hydroxide (0.85 g, 21 mmol) were refluxed in ethanol–water
3
4
enthalpic (freely joined chains) contributions for rationally (10 mL : 10 mL) until emission of a basic gas (starch paper).
tuning the effective molarity in metal-induced helicate self- The cooled solution was acidified to pH = 3.8 with concen-
1
6
assemblies, we highlight here a third tool based on solvation trated hydrochloric acid, ethanol evaporated and the resulting
effects, in which both enthalpy and entropy aspects may cream precipitate was filtered, washed with water and dried
contribute.
under vacuum to give 1,10-phenanthroline-2-carboxylic acid (3,
1
6
0
.84 g, 3.7 mmol, yield = 77%). H NMR (d -DMSO) δ/ppm:
3
3
3
δ 9.15 (dd, 1H, J = 1.6 Hz, J = 4.3 Hz), 8.66 (d, 1H, J =
3
4
3
8
8
4
.3 Hz), 8.54 (dd, 1H, J = 8.1 Hz, J = 1.6 Hz), 8.35 (d, 1H, J =
Experimental
Solvents and starting materials
3
3
3
.3 Hz), 8.09 (q, 2H, J = 8.8 Hz), 7.83 (dd, 1H, J = 8.1 Hz, J =
−
.3 Hz); ESI-MS (CH
Preparation of N,N′-(methylenebis(2-nitro-4,1-phenylene))bis-
(4). 1,10-Phe-
Dinitro-4,4′di(N-ethyl)amino-diphenylmethane was prepared nanthroline-2-carboxylic acid (3, 4. 0 g, 18 mmol) was refluxed
3 2 3
CN–H O–NEt ): m/z 223.1 [M − H] .
These were purchased from Fluka AG or Aldrich and used
without further purification unless otherwise stated. 3,3′- (N-ethyl-1,10-phenanthroline-2-carboxamide)
2
0
according to a literature procedure. Acetonitrile and dichloro- in thionyl chloride (160 mL) for 30 minutes and evaporated to
methane were distilled over calcium hydride, and tetrahydro- dryness. 3,3′-Dinitro-4,4′-di(N-ethylamino)diphenylmethane
furan was distilled over sodium. The triflate salts Ln- (1.0 g, 3.0 mmol) and dry potassium carbonate (60 g) in
CF SO ·xH O (Ln = La, Eu, Lu; x = 2–4) were prepared from dichloromethane–tetrahydrofuran (200 mL : 60 mL) were
the corresponding oxides (99.99%) and dried according to slowly added, and the resulting mixture was refluxed for 72 h.
(
3
3
)
3
2
3
5
published procedures. The Ln content of solid salts was Water (150 mL) was slowly added to the cooled solution and
determined by complexometric titrations with Titriplex III the org. layer was separated, washed with half sat. aq. NH Cl
(150 mL), water (150 mL) and brine (150 mL), dried with
Preparation of 1,10-phenanthroline-N-oxide (1). 1,10-Phe- sodium sulfate and evaporated to dryness. The crude product
nanthroline (4.7 g, 26 mmol), concentrated acetic acid was purified by column chromatography (silica; MeOH–
30 mL), water (2 mL) and 30% hydrogen peroxide (3.2 mL) CH Cl 2 : 98) to give N,N′-(methylenebis(2-nitro-4,1-pheny-
4
3
6
(Merck) in the presence of urotropine and xylene orange.
(
2
2
were stirred at 70 °C for 3 h. A second crop of 30% hydrogen lene))bis(N-ethyl-1,10-phenanthroline-2-carboxamide) (4, 1.7 g,
peroxide (3.2 mL) was added and stirring was maintained at 2.3 mmol, yield = 77%). ESI-MS (CH CN–MeOH): m/z 756.8
3
+
7
3
0 °C for three more hours. After cooling to RT, a last batch of [M + H] .
0% hydrogen peroxide (2 mL) was added and the resulting Preparation of bis(1-ethyl-2-(1,10-phenanthrolin-2-yl)-1H-
mixture was stirred for 12 h. Evaporation under vacuum benzo[d]imidazol-5-yl)methane (L10). N,N′-(Methylenebis(2-
reduced the volume to 10 mL, fresh water (35 mL) was added nitro-4,1-phenylene))bis(N-ethyl-1,10-phenanthroline-2-carbox-
and the mixture was concentrated to 10 mL, cooled to 0 °C amide) (4, 0.41 g, 0.54 mmol), activated powdered iron (0.91 g,
and neutralized with potassium carbonate (50 g). The resulting 16 mmol) and concentrated hydrochloric acid (25 mL) were
yellow-brown solid was isolated and extracted with hot chloro- dissolved in ethanol–water (70 mL : 25 mL) and refluxed for
form under reflux for 12 h (soxhlet). The org. layer was dried 48 h. Excess iron was separated and ethanol was evaporated
over magnesium sulfate and charcoal, filtered and evaporated under vacuum. Dichloromethane (300 mL) and Na
2 2
H EDTA
to dryness to give 1,10-phenanthroline-N-oxide (1, 3.75 g, (11.1 g, 30.0 mmol) in water (200 mL) were added under stir-
1
1
9.1 mmol, yield = 73.5%) as a pale yellow solid. H NMR ring. Conc. aq. ammonia (24.5%) was dropwise added until
3
4
(
CDCl
3
) δ/ppm: 9.32 (dd, J = 4.3 Hz, J = 1.6 Hz, 1H), 8.76 (dd, pH = 7, followed by conc. H
J = 6.3 Hz, J = 1.0 Hz, 1H), 8.24 (dd, J = 8.2 Hz, J = 1.6 Hz, finally raised to 8.5. The org. layer was separated and the aq.
H), 7.81 (dd, J = 8.8 Hz, 1H), 7.75 (d, J = 8.8 Hz, 1H), 7.75 (d, phase was extracted with dichloromethane (3 × 100 mL). The
J = 8.0 Hz, 1H), 7.67 (dd, J = 8.0 Hz, J = 4.3 Hz, 1H), 7.46 (dd, combined org. phase was washed with water (300 mL), brine
2
O
2
(30%, 3 mL). The pH was
3
4
3
4
3
3
1
3
3
3
3
3
+
J = 8.0 Hz, J = 6.3 Hz, 1H). ESI-MS (CH Cl ): m/z 197.1 [M + H] . (300 mL), dried over Na SO and evaporated to dryness. The
2
2
2
4
Preparation of 2-cyano-1,10-phenanthroline (2). 1,10-Phe- crude product was purified by column chromatography (silica;
nanthroline-N-oxide (1, 5.6 g, 28.5 mmol) and potassium MeOH–CH Cl 2 : 98→3 : 97) to give bis(1-ethyl-2-(1,10-phenan-
cyanide (5.6 g) were stirred for 15 min in water (50 mL). throlin-2-yl)-1H-benzo[d]imidazol-5-yl)methane (L10, 0.15 g,
2
2
1
1052 | Dalton Trans., 2013, 42, 11047–11055
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Dalton Transactions
.23 mmol, yield = 42%) as a white solid. H NMR (CDCl
Paper
1
0
3
)
each addition of 0.20 mL, the absorbance was recorded using
3
3
δ/ppm 9.73 (d, J = 4.4 Hz, 2H), 8.69 (d, J = 8.4 Hz, 2H), 8.28 (d, Hellma optrodes (optical path length 0.1 cm) immersed in the
3
3
J = 8.5 Hz, 2H), 8.15 (d, J = 8.1 Hz, 2H), 7.82 (s, 2H), 7.71 (s, thermostated titration vessel and connected to the spectro-
3
3
3
4
2
2
1
1
4
H), 7.55 (dd, J = 8.5 Hz, J = 4.4 Hz, 2H), 7.44 (d, J = 8.3 Hz, meter. Mathematical treatment of the spectrophotometric
H), 7.31 (d, J = 8.4 Hz, 2H), 5.30 (q, J = 7.0 Hz, 4H), 4.34 (s, titrations was performed with factor analysis and with the
H), 1.56 (t, J = 7.0 Hz, 6H). C NMR (CDCl ) δ/ppm 150.4, SPECFIT program. H and C NMR spectra were recorded at
3
50.2, 149.9, 146.4, 145.4, 143.3, 136.5, 136.4, 135.8, 135.2, 25 °C on Bruker Avance 400 MHz and Bruker DRX-500 MHz
3
3
3
13
28 1
13
28.9, 128.1, 127.1, 126.2, 125.1, 123.5, 123.0, 120.1, 110.2, spectrometers. Chemical shifts were given in ppm with respect
+
2.4, 41.1 ESI-MS (CH
2
Cl
2
): m/z 661.3 [M + H] , 1321.7 [2M + to TMS. Pneumatically-assisted electrospray (ESI-MS) mass
+
−4
−3
H] . Anal. Cald for C43
6.22. Found C, 76.62; H, 4.92; N, 16.09.
Preparation of the complexes [Ln
xH O·yCHCl
Lu, x = 5, y = 0). A solution of L10 (50 mg, 76 μmol) in chloro-
form (3 mL) was added to Ln(CF SO ·xH
O (Ln = La, Eu, Lu; X-ray crystallography
.67 equivalent) in acetonitrile (3 mL). After stirring for 12 h,
32 8 3
H N ·CH OH: C, 76.50; H, 4.96; N, spectra were recorded from 10 mol dm solutions on Finni-
1
gan SSQ7000 and MDS Aciex API III instruments. Elemental
analyses were performed by K.-L. Buchwalder from the Micro-
2
3 3 3 6
(L10) ](CF SO ) ·
2
3
(Ln = La, x = 3, y = 3; Ln = Eu, x = 7, y = 0; Ln = chemical Laboratory of the University of Geneva.
3
3
)
3
2
0
A summary of crystal data, intensity measurements and struc-
the mixture was evaporated to dryness, dissolved in fresh
acetonitrile and diethyl ether was slowly diffused to give micro-
ture refinements for [La (L10) (CF SO ) ](CF SO ) (CH CN) -
2
3
3
3 2
3
3 4
3
6
(
C
6
H
6
)
6
(5) and [Lu
2
(L10)
3
](CF
3
SO
3
)
6
(CH
3
CN)
4
(6) is collected
crystals, which were filtered and dried under vacuum.
in Table S1 (ESI†). The crystals were mounted on quartz fibers
with a protection oil. Cell dimensions and intensities were
measured at 160 K on an Agilent Supernova diffractometer
with mirror-monochromated Cu[Kα] radiation (λ = 1.54184 Å).
Data were corrected for Lorentz and polarization effects and
1
[
La (L10) ](CF SO ) (H O) (CHCl ) . Yield = 93%. H NMR
2
3
3
3 6
2
3
3 3
3
(
CDCN
3
–CDCl
3
2 : 3) δ/ppm 8.70 (d, J = 8 Hz, 2H), 8.52 (dd,
3
4
3
3
J = 8 Hz, J = 4 Hz, 2H), 8.21 (d, J = 4 Hz, 2H), 8.19 (d, J = 8 Hz,
H), 8.00 (d, J = 8 Hz, 2H), 7.90 (d, J = 8 Hz, 2H), 7.30 (q, J =
3
3
3
2
8
2
6
3
3
Hz, J = 4 Hz, 2H), 7.15 (s, 2H), 7.05 ( J = 8 Hz, 2H), 5.91 (s,
for absorption. The structures were solved by direct methods
SIR97), and all other calculations were performed with
3
H), 4.04 (m, 4H), 4.18 (m, 2H), 3.60 (s, 2H), 0.78 (t, J = 8 Hz,
37
(
H). Anal. Cald for La (C H N ) (CF SO ) (H O) (CHCl )
38
39
2
43 32 8 3
3
3 6
2
3
3 3 ShelX97 systems and ORTEP3 programs. CCDC 933010 and
MM = 3566.7): C, 46.47; H, 2.97; N, 9.42. Found C, 46.78; H,
(
CCDC 933011 contain the supplementary crystallographic
3
.02; N, 9.40.
data.
1
[
Eu (L10) ](CF SO ) (H O) . Yield = 62%. H NMR (CDCN –
2
3
3
3 6
2
7
3
3
3
CDCl 2 : 3) δ/ppm 14.75 (s, 2H), 7.82 (d, J = 8 Hz, 2H), 7.45 (d,
3
3
3
J = 8 Hz, 2H), 6.58 (d, J = 8 Hz, 2H), 5.88 (d, J = 8 Hz, 2H),
Acknowledgements
3
3
3
5
2
1
.65 (d, J = 8 Hz, 2H), 5.58 (d, J = 8 Hz, 2H), 4.99 (d, J = 8 Hz,
3
3
H), 4.36 (s, 2H), 3.50 (d, J = 8 Hz, 2H), 2.65 (q, J = 8 Hz, 4H), Financial support from the Swiss National Science Foundation
.40 (s, 2H; H1), −1.23 (t, J = 8 Hz, 6H). Anal. Cald for is gratefully acknowledged.
3
Eu (C H N ) (CF SO ) (H O) (MM = 3306.8): C, 49.03; H,
2
43 32 8 3
3
3 6
2
7
3
.35; N, 10.17. Found C, 49.04; H, 3.18; N, 10.23.
1
[
Lu
2 3 3 3 6 2 5 3
(L10) ](CF SO ) (H O) . Yield = 93%. H NMR (CDCN –
Notes and references
3
3
CDCl 2 : 3) δ/ppm 8.57 (d, J = 8 Hz, 2H), 8.53 (dd, J = 8 Hz,
3
4
3
3
J = 4 Hz, 2H), 8.26 (d, J = 8 Hz, 2H), 8.06 (d, J = 8 Hz, 2H), 7.89
1 (a) C.-A. Palma, M. Cecchini and P. Samori, Chem. Soc. Rev.,
2012, 41, 3713; (b) J.-M. Lehn, Angew. Chem., Int. Ed., 2013,
52, 2836.
3
3
3
3
(d, J = 8 Hz, 2H), 7.80 (d, J = 4 Hz, 2H), 7.22 (q, J = 8 Hz, J =
4
3
Hz, 2H), 7.13 (s, 2H), 5.25 (s, 2H), 4.32 (m, 2H), 4.18 (m, 2H),
.60 (s, 2H), 0.67 (t, J = 8 Hz, 6H). Anal. Cald for
3
2 (a) J.-M. Lehn, Supramolecular Chemistry, VCH, Weinheim,
Lu
2
(C43
H
32
N
8
)
3
(CF
3
SO
3
)
6
(H
2
O)
5
(MM = 3316.8): C, 48.89; H,
New
York,
Basel,
Cambridge,
Tokyo,
1995;
3
.22; N, 10.14. Found C, 48.91; H, 3.18; N, 10.40.
Slow diffusion of benzene into concentrated acetonitrile
(b) E. C. Constable, in Comprehensive Supramolecular Chem-
istry, ed. J. L. Atwood, J. E. D. Davies, D. D. MacNicol and
F. Vögtle, Pergamon, Oxford, 1996, ch. 6; (c) C. Piguet,
G. Bernardinelli and G. Hopfgartner, Chem. Rev., 1997, 97,
2005; (d) M. Albrecht, Chem. Rev., 2001, 101, 3457;
solutions of these complexes yielded pale yellow X-ray quality
prisms for [La (L10) (CF SO ) ](CF SO ) (CH CN) (C H ) (5)
and [Lu
2
3
3
3 2
3
3 4
3
6
6
6 6
2
(L10)
3
](CF
3
SO
3
)
6
(CH
3
CN)
4
(6).
(
1
e) M. J. Hannon and L. J. Childs, Supramol. Chem., 2004,
6, 7.
Spectroscopic and analytical measurements
Spectrophotometric titrations were performed with a J&M
diode array spectrometer (Tidas series) connected to an exter-
3 (a) C. Piguet, G. Bernardinelli and A. F. Williams, Angew.
Chem., Int. Ed. Engl., 1992, 31, 1624. For comprehensive
reviews, see: (b) M. Albrecht, M. Fiege and O. Osetska,
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3
−4
nal computer. In a typical experiment, 50 cm of a 10 mol
−3
dm solution of ligand in acetonitrile–chloroform (9 : 1) were
−
3
−3
3 3 3
titrated at 298 K with a 10 mol dm solution of Ln(CF SO )
in acetonitrile–chloroform (9 : 1) in an inert atmosphere. After
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Paper
Dalton Transactions
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