Synthesis of new phenanthroline-based heteroditopic ligands - Highly efficient and selective fluorescence sensors for copper(II) ions

Article abstract of DOI:10.1002/ejic.200600469

The heteroditopic phenanthroline derivatives 5,6-bis(2-pyridylcarboxamido)- 1,10-phenanthroline (H₂L¹) and 5,6-bis[(4-methoxy-2- pyridyl)carboxamido]-1,10-phenanthroline (H₂L²) have been prepared and characterized, together with their luminescent ruthenium(II) complexes [Ru(bpy)₂(H₂L^1,2)]-(PF ₆)₂ and [Ru(H₂L¹) ₃](PF₆)₂ and the corresponding iron(II) complex [Fe(H₂L¹)₃](PF₆)₂. In these complexes, the metal ion is coordinated by the bidentate phen site of H₂L. The luminescence of the ruthenium complexes (λ _ex = 450 nm, λ_emca. 620 nm) is completely quenched by Cu²⁺ ions in the micromolar concentration range and, to a lesser extent, by other metal ions. At pH 5, the response of the luminescent sensors is highly Cu²⁺-selective. Heterodinuclear complexes [Ru(bpy) ₂(LM)](PF₆)₂, [Ru(LM)₃](PF ₆)₂, and [Fe(LM)₃](PF₆)₂ have been isolated for M = Cu²⁺, Ni²⁺, Co²⁺, and Pd²⁺. It is suggested that M is coordinated to the tetradentate N4 site of L by two deprotonated amide N atoms and two pyridyl groups. This coordination type is confirmed by the EPR spectrum of the compound [Ru ^II(bpy)₂(L¹Cu^II)](PF ₆)₂. Wiley-VCH Verlag GmbH & Co. KGaA, 2006.

Full text of DOI:10.1002/ejic.200600469

FULL PAPER
DOI: 10.1002/ejic.200600469
Synthesis of New Phenanthroline-Based Heteroditopic Ligands – Highly
Efficient and Selective Fluorescence Sensors for Copper(II) Ions
Peter Comba,*[a] Roland Krämer,[a] Andriy Mokhir,[a] Kyaw Naing,[a] and Erik Schatz[a]
Keywords: Sensor / Fluorescence / Copper(II) / Selectivity / Ruthenium
The heteroditopic phenanthroline derivatives 5,6-bis(2-pyr-
idylcarboxamido)-1,10-phenanthroline (H2L1) and 5,6-bis[(4-
metal ions. At pH 5, the response of the luminescent sensors
is highly Cu2+-selective. Heterodinuclear complexes
methoxy-2-pyridyl)carboxamido]-1,10-phenanthroline (H2L2) [Ru(bpy)2(LM)](PF6)2, [Ru(LM)3](PF6)2, and [Fe(LM)3](PF6)2
have been prepared and characterized, together with their
luminescent ruthenium(II) complexes [Ru(bpy)2(H2L1,2)]-
(PF6)2 and [Ru(H2L1)3](PF6)2 and the corresponding iron(II)
complex [Fe(H2L1)3](PF6)2. In these complexes, the metal ion
is coordinated by the bidentate phen site of H2L. The lumi-
nescence of the ruthenium complexes (λex = 450 nm, λem ca.
620 nm) is completely quenched by Cu2+ ions in the micro-
molar concentration range and, to a lesser extent, by other
have been isolated for M = Cu2+, Ni2+, Co2+, and Pd2+. It is
suggested that M is coordinated to the tetradentate N4 site
of L by two deprotonated amide N atoms and two pyridyl
groups. This coordination type is confirmed by the EPR spec-
trum of the compound [RuII(bpy)2(L1CuII)](PF6)2.
(© Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim,
Germany, 2006)
Introduction
tion site covalently to a ligand, which selectively coordinates
another metal ion or has a second coordination center that
selectively binds anions or activates substrates. Tris(bipyrid-
ine)ruthenium(II)-derived systems have been used fre-
quently in this area,[9,10] and metal-ion- and anion-selective
sensors,[10–16] photocatalysts,[12–14] and photoactive phar-
maceuticals[15,16] have been reported.
For many good reasons di- and oligonuclear transition-
metal complexes are attracting much interest. Cooperativity
in general and, more specifically, electron and energy trans-
fer as well as magnetic interactions have been recognized as
important and rather general features in biological sys-
tems,[1,2] and there is an increasing range of applications in
Generally, the synthesis of this type of system relies on a
areas such as catalysis,[3,4] analytical chemistry (metal-ion- suitable ditopic ligand with a multidentate or macrocyclic
and anion-selective sensors),[5,6] and information technol- donor set, coupled to 1,10-phenanthroline (phen) or 2,2Ј-
ogy (switches).[7] Most of these applications imply that the bipyridine (bpy). We report here on the synthesis of the two
two metal centers in a dinuclear complex have different heteroditopic ligands H2L1 and H2L2 (Scheme 1) based on
functions and, therefore, different properties. Synthetically, 5,6-diamino-1,10-phenanthroline and the synthesis of
the required ligand asymmetry is often a demanding task.[8] the corresponding ruthenium(II) complexes ([Ru(bpy)2-
An attractive approach is to couple a photoactive coordina- (H2L1,2)]2+ and [Ru(H2L1)3]2+) and their hetero-oligonu-
Scheme 1.
clear transition-metal complexes ([Ru(bpy)2{(L1,2)M}]2+
and [Ru{(L1)M}3]2+, M = divalent transition-metal ion, e.g.
[a] Universität Heidelberg, Anorganisch-Chemisches Institut,
Im Neuenheimer Feld 270, 69120 Heidelberg, Germany
Cu2+). Of specific interest are the strong and selective coor-
dination of first-row transition-metal ions to the coordina-
Fax: +49-6221-54-66-17
E-mail: peter.comba@aci.uni-heidelberg.de
4442
© 2006 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
Eur. J. Inorg. Chem. 2006, 4442–4448

Synthesis of New Phenanthroline-Based Heteroditopic Ligands
FULL PAPER
tion site offered by L1 and L2 and the quenching of the
fluorescence of the tris(bipyridine-type)ruthenium(II) site
by this selective coordination event.
Results and Discussion
Syntheses and Characterization
The heteroditopic ligands H2L1 and H2L2 are prepared
in respectable yields from 5,6-diamino-1,10-phenan-
throline[17–19] (obtained in high yield by the reduction of
1,10-phenanthroline-5,6-dione dioxime with sodium dithio-
nite[20] or formamidinesulfinic acid[21]) and picolinic acid or
its methoxy derivative, respectively (Scheme 1). Because of
solubility problems, air sensitivity, and poor reactivity of
the amine groups, the acylation is performed under inert
conditions in DMF, with DMAP[22] as the acylation cata-
lyst, phenylphosphonic acid dichloride[23–26] as the acti-
vation reagent for the carboxylic group, and TEA as base.
The Ru2+ complexes [Ru(bpy)2(H2L1,2)]2+ and [Ru-
(H2L1)3]2+ are obtained by the usual methods and in high
yields.[10] Low-spin Fe2+ complexes have also been obtained
but are not discussed here in detail. The red mononuclear
Ru2+ complexes have the characteristic MLCT transitions
1
at around 450 nm, they show resonances in the H NMR
spectra for the amide protons at around 10.5 ppm and have
the expected vibrations for amide bonds in the infrared
spectra at approximately 1680 and 1570 cm–1, as well as the
amide N–H transitions at approximately 3300 cm–1. Upon
coordination of metal ions to the L1 (L2) sites, the N–H
vibration disappears, the amide transitions shift to a lower
energy (ca. 30–50 cm–1), and the MLCT transitions are
shifted to a higher energy.
The EPR spectra of the mono- and tris-CuII complexes
are similar to each other and typical for tetragonal CuII
sites, with g and A values (gʈ = 2.213, Aʈ = 180×10–4 cm–1)
that are typical for tetrahedrally distorted coordination
sites.[9] The similarity of the EPR spectra indicates that
there is no CuII···CuII magnetic exchange interaction and
only a very weak, i.e. negligible, dipolar coupling interac-
tion (Figure 1b). A model of the structure (Figure 1a), ob-
tained by force field calculations,[27,28] visualizes the CuII
planes that are distorted because of the repulsion of the α-
H atoms of the pyridine donors and indicates a distance of
ca. 13 Å between the CuII centers.
Figure 1. (a) Structural model of [Ru{(L1)Cu}3]2+; (b) X-band EPR
spectrum of [Ru{µ-(L1)Cu}3](PF6)2 (ca. 10–3 , DMF-H2O-glass
(2:1), 110 K); and (c) relative fluorescence intensities (λex = 450 nm,
λem = 620 nm) in aqueous solution at pH 7 (lutidine buffer) of
[Ru(H2L1)3](PF6)2 alone (10 µ), and after addition of 1 or 2 equiv.
CuSO4.
Fluorescence Measurements
The luminescence spectra of [Ru(bpy)2(H2L1)]2+
,
[Ru(bpy)2(H2L2)]2+, and [Ru(H2L1)3]2+ are as expected for
Ru2+ polypyridine chromophores (transition at ca. transitions at similar energies and are known to strongly
620 nm,[13] see Figure 1c); also shown in Figure 1c is the bind to amide donors already at physiological pH.[10,29]
efficient fluorescence quenching of [Ru(H2L1)3]2+ with Cu2+
To fully characterize the L1- and L2-based Cu2+ sensors,
([Ru2+]/[Cu2+] = 1:0, 1:1, 1:2). Similar effects are observed the luminescence intensities (aqueous solutions, [Ru2+] =
with [Ru(bpy)2(H2L1)]2+ and [Ru(bpy)2(H2L2)]2+, i.e. these 10–5 ) were studied as a function of pH, buffer base, anion,
complexes are, as expected, good on/off sensors for metal and Mn+ concentration (M = Cu2+, Ni2+, Co2+, Fe2+/3+
,
ions, specifically for Cu2+ and Ni2+, which have electronic Zn2+, Al3+, Nd3+, Mn2+, Pb2+, alkali, and alkaline earth
Eur. J. Inorg. Chem. 2006, 4442–4448
© 2006 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
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P. Comba, R. Krämer, A. Mokhir, K. Naing, E. Schatz
FULL PAPER
metal ions; see Table 1 for an overview of the most relevant
results.). Buffer bases such as acetate, citrate, carbonate,
phosphate, and lutidine as well as EDTA do not quench
the fluorescence. Aminoalkylsufonates (e.g., MOPS, MES)
lead to an approximately 50% reduction of the lumines-
cence intensity, i.e., these are not suited as buffer bases in
our systems. Usual inorganic anions or carboxylates do not
affect the fluorescence intensity (see Table 1 and above). In
addition, Al3+, Nd3+, Mn2+, Pb2+, and group 1 and 2 cat-
ions do not alter the luminescence spectra. Interestingly,
protonation of the pyridine donors and deprotonation of
an amide site lead to drastic changes in the luminescence
properties (Figure 2). This is in contrast to other Ru(bpy)2-
amide sensors,[10] which have pH-independent luminescence
intensities over a pH range of 2–12. This indicates that the
published and present systems probably differ with respect
to the mechanism of quenching of the excited state [electron
(PET) vs. energy transfer (EET)].[12]
Figure 2. pH-dependence of the relative fluorescence intensity of
10 µ aqueous solutions of the complexes (λex = 450 nm, λem
=
620 nm) [Ru(bpy)2(H2L1)]2+ (᭿), [Ru(H2L1)3]2+ (᭡), and [Ru-
(bpy)2(H2L2)]2+ (᭹).
Table 1. Reduction of the fluorescence intensity (in %) of [Ru-
(bpy)2(H2L1)]2+ as a function of added metal ions and pH.
mately zero at pH Ͼ 14, pKa Ϸ 11.5) suggests a deproton-
ation of an amide donor, and this also occurs in the ex-
pected range [pKa(25 °C) Ϸ 12].[33]
Added metal ion
pH
% Reduction of
fluorescence intensity of
[Ru(bpy)2(H2L1)]2+
Figure 3 shows the pH-dependent luminescence of
[Ru(bpy)2(H2L1)]2+ together with that of the [Ru(bpy)2-
(H2L1)]2+/Cu2+ system (1 equiv. Cu2+). Also shown in Fig-
ure 3 is the Cu2+-concentration dependence of the fluores-
cence intensity at pH 4.9 (acetate buffer). At pH 5, no other
metal ion leads to any fluorescence quenching, i.e. at pH 5
the [Ru(bpy)2(H2L1)]2+ on/off fluorescence sensor is selec-
1 equiv. Cu2+
5
5
5
5
5
5
5
5
5
5
7
7
7
7
7
7
7
7
7
7
7
7
7
7
99
99
2
1
0
5
1
98
99
99
98
70
90
80
3
80
85
40
0
0
0
99
99
99
2 equiv. Cu2+
10 equiv. Co2+
10 equiv. Fe2+
1 equiv. Ni2+
10 equiv. Ni2+
10 equiv. Zn2+
tive for Cu2+
All three systems, [Ru(bpy)2(H2L1)]2+
.
10 equiv. Fe2+ + 1 equiv. Cu2+
100 equiv. Ni2+ + 1 equiv. Cu2+
10 equiv. Zn2+ + 1 equiv. Cu2+
1 equiv. Cu2+
,
[Ru(bpy)2-
(H2L2)]2+, and [Ru(H2L1)3]2+, show very similar behavior
with respect to the metal-ion-induced fluorescence quench-
ing, specifically in terms of the metal-ion- and pH-depend-
encies and the competition with other ligands (Table 1): (i)
at pH 5 (acetate buffer), Cu2+ is the only metal ion that
leads to significant quenching; the addition of an excess of
any other metal ion does not have any influence on the
fluorescence intensity observed with Cu2+ alone; (ii) at pH
7 (lutidine buffer), the reduction of the fluorescence inten-
sity with one equivalent of Cu2+ is Ϸ100%, those due to
Ni2+, Fe2+/3+, Co2+, and Zn2+ are significantly smaller (40–
85%), all other metal ions studied do not lead to any
quenching; the kinetics of complex formation with Ni2+ is
1 equiv. Co2+
10 equiv. Co2+
10 equiv. Fe2+
10 equiv. Mn2+
1 equiv. Ni2+
10 equiv. Ni2+
1 equiv. Zn2+
10 equiv. Pb2+
10 equiv. Cu2+
10 equiv. Mg2+
1 equiv. Cu2+ + 10 equiv. Co2+
1 equiv. Cu2+ + 10 equiv. Fe2+
1 equiv. Cu2+ + 10 equiv. Pb2+
very slow, full equilibration (pH 7; 1 or 10 equiv. Ni2+
needs at least 1 h (complexation of all other metal ions is
)
From the plot in Figure 2, it follows that for [Ru(bpy)2- fast, i.e., equilibration within minutes); (iii) at pH 7, acetate
(H2L1)]2+ the luminescence intensity is virtually constant does not lead to any significant reduction of the quenching
over the pH range 4.5–8.5. For [Ru(bpy)2(H2L2)]2+ and efficiency of Cu2+, with citrate there is some competition,
[Ru(H2L1,2)3]2+ the pH ranges of approximately constant and with EDTA fluorescence quenching is only observed
luminescence are similar (pH 4.7–9.0). At a lower pH, the after complexation with EDTA is complete [from se-
fluorescence intensity drops sharply to nearly zero at pH Ͻ miquantitative experiments and the known stability con-
2. The sigmoidal curves suggest pKa values of Ϸ3, which is stants logKML(Cu–acetate) = 1.75,[31] logKML(Cu–citrate)
in the expected range for substituted pyridine groups = 4.5,[32] logKML(Cu–EDTA) = 19.2,[33] an approximate
[pKa(20–25 °C) = 2.1–2.4].[30] The decrease in the lumines- value of logKML([Ru(bpy)2{(H2L1)Cu}]2+) = 12 2 may be
cence intensity at high pH (luminescence intensity approxi- deduced].
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© 2006 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
Eur. J. Inorg. Chem. 2006, 4442–4448

Synthesis of New Phenanthroline-Based Heteroditopic Ligands
FULL PAPER
dard methods; solvents and chemicals for spectroscopy were of the
highest possible grade and used as purchased. 1,10-Phenanthroline-
5,6-dione dioxime was obtained by oxidation of 1,10-phenan-
throline to 1,10-phenanthroline-5,6-dione[37] and subsequent reac-
tion with hydroxylamine.[18] (4-Chloro-2-pyridyl)carboxylic acid
methyl ester and (4-methoxy-2-pyridyl)carboxylic acid methyl ester
were obtained as described from picolinic acid.[38]
UV/Vis/NIR spectra (CH3CN, ambient temperature) were recorded
with a Cary 1E or a JASCO V-570 spectrophotometer. IR spectra
(KBr pellets) were obtained with a Perkin–Elmer 16C FTIR instru-
ment. 1H NMR spectra were recorded at room temperature with a
Bruker ARX 200 or a Bruker Avance 500 spectrometer; the chemi-
cal shifts are relative to the solvent that is used as the internal
standard. Electrochemical data were obtained by cyclic voltamme-
try [100 mV/sec., complex solutions (2×10–3 ), ambient tempera-
ture, tetrabutylammonium hexafluorophosphate (0.1 ) in
CH3CN], measured with a BAS100B electrochemical analyzer
(data analysis with Digisim), by using a glassy carbon working elec-
trode, a Pt-wire auxiliary, and a Ag/AgNO3 reference electrode
(0.01  AgNO3); ferrocene was used as an external standard. EPR
spectra were recorded with a Bruker ELEXSYS E500 spectrometer
[frozen solutions (approx. 10–3 ) in DMF/H2O = 2:1] at 110 K.
Mass spectra were recorded with a Finnigan 8400 or a JEOL
JMS700 sector field instrument (EI or FAB) with a nitrobenzyl
alcohol matrix (Nibeol, NBA) for the FAB spectra; electrospray
mass spectra were recorded with a Finnigan TSQ 700 triple-quad-
rupole or a Q-Tof Ultima API mass spectrometer (Micromass/
Waters, ESI) with analyte solutions in acetonitrile or methanol in
the concentration range 10–6–10–5 . For HR-EI, HR-FAB, and
HR-ESI spectra deviations from the theoretical mass are generally
smaller than 5 mD, the internal standards used are reported with
the experimental data. Emission spectra were recorded with a Var-
ian Cary Eclipse fluorescence spectrophotometer at an excitation
wavelength of 450 nm (intensities not calibrated). Fluorimetric ti-
trations were performed in aqueous solutions (equilibrated in air,
µ = 0.1; NaCl; the concentrations of the ruthenium complexes were
10–5 ). Metal ions were added as the chloride, perchlorate, or sul-
fate salts, and there was no dependence on the type of anion within
this group. Standard HCl and NaOH solutions were used for ad-
justing the pH. Buffers at pH 4.7–5 and 7 were made by using the
acetate/acetic acid and the lutidine/lutidinium couples, respectively.
Figure 3. (a) pH-dependence of the luminescence of [Ru(bpy)2-
(H2L1)]2+ (10 µ aqueous solution) with or without 1 equiv. of
Cu2+, λex = 450 nm, λem = 620 nm. (b) Fluorimetric titration of
[Ru(bpy)2(H2L1)]2+ (10–5 ) with Cu2+ in acetate buffer (100 equiv.)
at pH 4.9.
Syntheses
5,6-Diamino-1,10-phenanthroline[17–19]
Method A: A suspension of phenanthroline-5,6-dione dioxime
(2.88 g, 12 mmol) in ethanol (80 mL) was heated under N2 (70 °C).
A solution of sodium dithionite (85%, 9 g, 45 mmol) in aqueous
ammonia (3%, 80 mL) was quickly added. An additional amount
of sodium dithionite (85%, 3 g, 15 mmol) in aqueous ammonia
(3%, 40 mL) solution was added when the yellow product started
to precipitate as yellow flakes after dissolution of the dioxime. The
reaction was then kept for 45 min at 85 °C. After being cooled to
ambient temperature, the product was filtered under N2, washed 3
Conclusions
The synthesis of a rigid ditopic ligand with a 1,10-phen-
anthroline and a bis(pyridinamide) coordination site, based
on a general strategy, which may be used to prepare a vari-
ety of 1,10-phenanthroline-derived ditopic ligands with a
range of donor sets, has led to Ru2+-polypyridine-based
fluorescence on/off sensors that are highly selective for Cu2+
in aqueous solution at low pH. The rational design of the times with diluted ammonia and then with THF, and dried over-
night under high vacuum. Yield: 2.17 g (10.3 mmol, 86%), deep
yellow solid.
structure and donor set of the host, which, upon coordina-
tion of a metal ion, leads to fluorescence quenching,[34–36]
should make possible the development of systems that show
a range of specific selectivities in various pH regions.
Method B: Ethanol (150 mL, 50%) and a concentrated ammonia
solution (10 mL) were added to a mixture of phenanthroline-5,6-
dione dioxime (2.4 g, 10 mmol) and thiourea S,S-dioxide (5 g,
46.3 mmol) under nitrogen whilst stirring. The mixture was placed
in a preheated (80 °C) oil bath and left to react for 45 min. The 5,6-
diamino-1,10-phenanthroline started to precipitate after Ϸ15 min.
After being cooled to room temperature, the product was isolated
Experimental Section
Materials and Measurements: Commercially available chemicals
were used without further purification; solvents were dried by stan-
Eur. J. Inorg. Chem. 2006, 4442–4448
© 2006 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
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4445

P. Comba, R. Krämer, A. Mokhir, K. Naing, E. Schatz
FULL PAPER
as described above. Yield: 1.79 g (8.1 mmol, 81%).
C12H10N4·1⁄6H2O (213.23): calcd. C 67.59, H 4.88, N 26.27; found
C 67.81, H 4.62, N 26.03. MS (EI+): m/z = 210 [M+].
throline (0.21 g, 1 mmol) and (4-chloro-2-pyridyl)carboxylic acid
potassium salt (0.59 g, 3 mmol). Yield: 0.37 g crude product. HR-
ESI-MS: calcd. for [M + H+] (C24H15Cl2N6O2) 489.0634; found
489.0610 (–2.4 mD, standard: H3PO4).
Potassium Salts of Substituted Picolinic Acids: KOH (0.95 equiv.)
in a minimum amount of EtOH was added to a stirred solution
of the methyl ester of the corresponding substituted picolinic acid
derivative in dry ethanol (2 mL/mmol). After 6 h, Et2O (1/5 vol-
ume) was added. The product was filtered, washed with EtOH/
Et2O, and dried under high vacuum.
Tris[5,6-bis(2-pyridylcarboxamido)-1,10-phenanthroline]ruthenium
Hexafluorophosphate, [Ru(H2 L1 )3 ](PF6)2: A mixture of
RuCl3·3H2O (0.026 g, 0.1 mmol) and 5,6-bis(2-pyridylcarbox-
amido)-1,10-phenanthroline (0.15 g, 0.35 mmol) was heated (160 °C)
in ethylene glycol (5 mL) for 30 min. After being cooled to room
temperature, the mixture was diluted with water (1/6 volume), and
the excess ligand was removed by filtration. The complex was pre-
cipitated by the addition of NH4PF6, filtered off, washed with small
amounts of H2O and Et2O, and dried under high vacuum.
Yield: 0.11 g (0. 06 mmol, 66 %) black-violet powder.
C72H48F12N18O6P2Ru·6H2O (1760.25): calcd. C 49.12, H 3.44, N
14.32; found C 49.29, H 3.54, N 13.87. HR-FAB-MS: calcd. for
[M – PF6–] (C72H48F6N18O6PRu) 1507.2689; found 1507.2656
(–3.3 mD, standard: PEG1500). 1H NMR (500 MHz, CD3CN): δ
= 7.61 (dd,3J = 7.5 Hz, 3J = 4.5, 6 H, py-H), 7.72 [m(br), 6 H,
Potassium (4-Cloro-2-pyridyl)carboxylate: Yield: 84%. M.p. Ͼ
350 °C. C6H3ClKNO2 (195.64): calcd. C 36.83, H 1.55, N 7.16;
found C 36.98, H 1.82, N 7.22. MS (ESI-): m/z = 156 [M – H–].
1H NMR (200 MHz, D2O): δ = 7.63 (dd, 3J = 5.3 Hz, 4J = 1.9 Hz,
4
3
1 H), 7.99 (d, J = 1.90 Hz, 1 H), 8.55 (d, J 5.3 Hz, 1 H) ppm.
Potassium (4-Methoxy-2-pyridyl)carboxylate: (4-Methoxy-2-pyr-
idyl)carboxylic acid methyl ester (0.84 g, 5 mmol) and KOH
(0.27 g) were added together to give (4-methoxy-2-pyridyl)carbox-
ylic acid potassium salt (0.76 g). Yield: 80%. M.p. Ͼ 350 °C.
C7H6KNO3·¼H2O (195.73): calcd. C 42.95, H 3.35, N 7.16; found
C 43.06, H 3.21, N 7.17. MS (ESI-): m/z = 152 [M – H–]. 1H NMR
3
phen-H], 8.01 (t, J = 7.5 Hz, 6 H, py-H), 8.19 [s(sh), 6 H, phen-
3
3
H], 8.20 (d, J = 7.5 Hz, 6 H, py-H), 8.65 (d, J = 4.5 Hz, 6 H, py-
3
3
(200 MHz, D2O): δ = 3.92 (s, 3 H, OCH3), 7.07 (dd, J = 5.8 Hz,
H), 8.69 (d, J = 7.8 Hz, 6 H, phen-H), 10.71 (s, 6 H, NH) ppm.
4J = 2.5 Hz, 1 H), 7.46 (d, 4J = 2.5 Hz, 1 H), 8.38 (d, 3J = 5.76 Hz,
IR (KBr): 3280 (s) (N–H); 3076 (m), 3054 (m) (C–H); 1680 (s),
1570 (m) (C=Oamide); 1620 (m) (C=N); 1590 (m), 1496 (s) (C=C);
844 (s) (PF6–) cm–1. UV/Vis (CH3CN): λmax = 451 nm (ε =
2.2×104 Lmol–1 cm–1).
1 H) ppm.
5,6-Bis(2-pyridylcarboxamido)-1,10-phenanthroline, H2L1: Picolinic
acid (1.11 g, 9 mmol) and DMAP (0.12 g, 1 mmol, 33 mol-%) in
absolute DMF (25 mL) were added to a stirred suspension/solution
of 5,6-diamino-1,10-phenanthroline (0.63 g, 3 mmol) in a 100-mL
Schlenk flask under nitrogen at ambient temperature. TEA
(1.4 mL, 10 mmol) was then added by syringe, followed by the ad-
dition of phenylphosphonic acid dichloride (0.9 mL, 6.4 mmol) and
more TEA (2.8 mL, 20 mmol) over a period of 5 h. After an ad-
ditional 4 h, the reaction was quenched by the addition of water
(1 mL). The product was isolated by precipitation (addition of
H2O, 5 volumes), filtration, washing with H2O, and drying under
high vacuum. Yield: 0.68 g (1.62 mmol, 54%). M.p. 294–298 °C.
C24H16N6O2·12⁄3 H2O (450.45): calcd. C 63.99, H 4.33, N 18.66,
found C 64.01, H 4.10, N 18.39. MS (ESI+): m/z = 421 [M + H+].
Bis(2,2Ј-bipyridine)[5,6-bis(2-pyridylcarboxamido)-1,10-phenanthro-
line]ruthenium Hexa-fluorophosphate, [Ru(bpy)2(H2L1)](PF6)2:
Ru(bpy)2Cl2·2H2O (0.15 g, 0.3 mmol) and 5,6-bis(2-pyridylcarbox-
amido)-1,10-phenanthroline (0.15 g, 0.35 mmol) were refluxed in
50% aqueous ethanol (20 mL) under nitrogen for 4 h. After being
evaporated to near dryness, the residue was treated with water
(10 mL), and the excess ligand was removed by filtration. The com-
plex was precipitated with NH4PF6, filtered off, washed with H2O
and Et2O, and dried under vacuum. Yield: 0.27 g (0.233 mmol,
78%) orange-red powder. C44H32F12N10O2P2Ru·2H2O (1159.80):
calcd. C 45.56, H 3.13, N 12.08; found C 45.40, H 3.13, N 11.90.
HR-FAB-MS: calcd. for [M – PF6–] (C44H32F6N10O2PRu)
979.1395; found 979.1415 (+2.0 mD, standard: PEG1000). 1H
NMR (500 MHz, CD3CN): δ = 7.29 (ddd, 3J = 7.3 Hz, 3J = 5.4 Hz,
3
3
1H NMR (500 MHz, [D7]DMF): δ = 7.70 (ddd, J = 7.6 Hz, J =
4.7 Hz, 4J = 1.2 Hz, 2 H, py-H), 7.85 (dd, 3J = 8.3 Hz, 3J = 4.2 Hz,
3
4
2 H, phen-H), 8.11 (td, J = 7.7 Hz, J = 1.5 Hz, 2 H, py-H), 8.25
3
3
4
4J = 1.0 Hz, 2 H, bpy-H), 7.46 (ddd, J = 7.3 Hz, J = 5.4 Hz, J
(ddd,3J = 7.7 Hz, J = 1.2 Hz, J = 0.6 Hz, 2 H, py-H), 8.62 (dd,
4
5
3
3
4
= 1.0 Hz, 2 H, bpy-H), 7.61 (ddd, J = 7.5 Hz, J = 4.8 Hz, J =
3J = 8.3 Hz, J = 1.6 Hz, 2 H, phen-H), 8.75 (ddd, J = 4.7 Hz, J
= 1.5 Hz, 5J = 0.6 Hz, 2 H, py-H), 9.21 (dd, 3J = 4.2 Hz, 4J =
1.6 Hz, 2 H, phen-H), 11.10 (s, 2 H, NH) ppm. IR (KBr): 3298
(m), 3236 (m) (N–H); 3076 (w), 3050 (m) (C–H); 1676 (s), 1570 (m)
(C=Oamide); 1616 (m) (C=N); 1590 (m), 1496 (m) (C=C) cm–1.
4
3
4
1.0 Hz, 2 H, py-H), 7.63 (d, J = 5.4 Hz, 2 H, bpy-H), 7.75 (dd, 3J
3
= 8.4 Hz, 3J = 5.2 Hz, 2 H, phen-H), 7.85 (d, 3J = 5.4 Hz, 2 H,
bpy-H), 8.00 (ddd, 3J = 8.2 Hz, 3J = 7.3 Hz, 4J = 1.0 Hz, 2 H, bpy-
3
3
4
H), 8.02 (ddd, J = 8.2 Hz, J = 7.3 Hz, J = 1.0 Hz, 2 H, bpy-H),
8.10 (ddd, J = 8.0 Hz, J = 7.5 Hz, J = 0.9 Hz, 2 H, py-H), 8.12
3
3
4
3
4
3
(dd, J = 5.2 Hz, J = 0.8 Hz, 2 H, phen-H), 8.19 (d, J = 8.0 Hz,
2 H, py-H), 8.51 (d, 3J = 8.2 Hz, 2 H, bpy-H), 8.54 (d, 3J = 8.2 Hz,
2 H, bpy-H), 8.65 (d, 3J = 4.8 Hz, 2 H, py-H), 8.66 (d, 3J = 8.4 Hz,
2 H, phen-H), 10.67 (s, 2 H, NH) ppm. IR (KBr): 3322 (s) (N–H);
3076 (m) (C–H); 1684 (m), 1570 (w) (C=Oamide); 1622 (m) (C=N);
5,6-Bis[(4-methoxy-2-pyridyl)carboxamido]-1,10-phenanthroline,
H2L2: Obtained as described above by using 5,6-diamino-1,10-
phenanthroline (0.21 g,1 mmol). Yield: 0.25 g, (0.52 mmol, 52%).
M.p. 246–249 °C. C26H20N6O4·2H2O (516.51): calcd. C 60.46, H
4.68, N 16.27, found C 60.57, H 4.76, N 15.96. MS (ESI+): m/z =
1604 (m), 1496 (m) (C=C); 842 (s) (PF6 ) cm–1. UV/Vis (CH3CN):
–
1
481 [M + H+]. H NMR (500 MHz, [D7]DMF): δ = 4.00 (s, 6 H,
λmax = 450 nm (ε Ϸ 1.3×104 Lmol–1 cm–1).
3
4
4
OCH3), 7.26 (dd, J = 5.7 Hz, J = 2.6 Hz, 2 H, py-H), 7.73 (d, J
= 2.6 Hz, 2 H, py-H), 7.85 (dd, 3J = 8.4 Hz, 3J = 4.2 Hz, 2 H,
Bis(2,2Ј-bipyridine){5,6-bis[(4-methoxy-2-pyridyl)carboxamido]-
1,10-phenanthroline}ruthenium Hexafluorophosphate, [Ru(bpy)2-
(H2L2)](PF6)2: Obtained as described above by using Ru(bpy)2-
Cl2·2H2O (0.09 g, 0.173 mmol) and 5,6-bis[(4-methoxy-2-pyridyl)-
carboxamido]-1,10-phenanthroline (0.1 g, 0.2 mmol). Yield: 0.19 g
(0.152 mmol, 88 %) orange-red powder. C46H36F12N10O4P2Ru·
3
3
phen-H), 8.57 (d, J = 5.7 Hz, 2 H, py-H), 8.59 (dd, J = 8.4 Hz,
4J = 1.5 Hz, 2 H, phen-H), 9.20 (dd, J = 4.2 Hz, J = 1.5 Hz, 2
H, phen-H), 11.02 (s, 2 H, NH) ppm. IR (KBr): 3298 (s) (N–H);
3090 (w), 3066 (w), 3010 (w), 2934 (w) (C–H); 1684 (s), 1566 (m)
(C=Oamide); 1602 (s), 1496 (s) (C=N, C=C) cm–1.
3
4
5,6-Bis[(4-chloro-2-pyridyl)carboxamido]-1,10-phenanthroline: Ob-
tained as described above by using 5,6-diamino-1,10-phenan-
3.5H2O (1246.87): calcd. C 44.31, H 3.48, N 11.23; found C 44.02,
–
H 3.15, N 11.06. HR-FAB-MS: calcd. for [M – PF6
]
4446
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© 2006 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
Eur. J. Inorg. Chem. 2006, 4442–4448

Synthesis of New Phenanthroline-Based Heteroditopic Ligands
FULL PAPER
(C46H36F6N10O4PRu) 1039.1608; found 1039.1649 (+4.1 mD, stan-
dard: PEG1000); calcd. for [M – 2 PF6–] (C46H36N10O4PRu)
894.1966; found 894.1955 (–1.1 mD). 1H NMR (500 MHz,
[Ru(µ-L1Cu)3](PF6)2: Cu(AcO)2·H2O (0.012 g). Yield after
recrystallization from DMF/MeOH: 0.029 g (0.014 mmol, 69%)
dark brown solid. C72H42Cu3F12N18O6P2Ru·2DMF·5H2O·MeOH
CD3CN): δ = 3.92 (s, 6 H, OCH3), 7.12 (dd, 3J = 5.2 Hz, 4J = (2105.06): calcd. C 45.07, H 3.35, N 13.31; found C 45.21, H 3.46,
2.8 Hz, 2 H, py-H), 7.29 [m(br), 2 H, bpy-H], 7.46 [m(br), 2 H, N 13.15. HR-ESI-MS: calcd. for [M – 2 PF6–] (C72H42Cu3-
3
4
bpy-H], 7.63 (d, J = 4.2 Hz, 2 H, bpy-H), 7.70 (d, J = 2.8 Hz, 2 N18O6Ru) 1545.0466; found 1545.0432 (–3.4 mD, standard:
3
3
H, py-H), 7.74 (dd, J = 8.2 Hz, J = 4.8 Hz, 2 H, phen-H), 7.85
(d, 3J = 4.2 Hz, 2 H, bpy-H), 8.02 [m(br), 2 H, bpy-H], 8.10 [m(br),
2 H, bpy-H], 8.11 (d, 3J = 4.8 Hz, 2 H, phen-H), 8.46 (d, 3J =
H3PO4). IR (KBr): 3066 (w) (C–H); 1650 (sh) (C=Oamide); 1620 (s)
(C=N); 1596 (s) (C=C); 842 (s) (PF6–) cm–1. UV/Vis (CH3CN):
λmax = 419 nm (ε Ϸ 1.0×104 Lmol–1 cm–1), λmax = 473 nm (ε Ϸ
3
3
5.2 Hz, 2 H, py-H), 8.51 (d, J = 7.9 Hz, 2 H, bpy-H), 8.54 (d, J 0.9×104 Lmol–1 cm–1).
3
= 7.9 Hz, 2 H, bpy-H), 8.63 (d, J = 8.2 Hz, 2 H, phen-H), 10.67
[Ru(µ-L1Ni)3](PF6)2: Ni(AcO)2·4H2O (0.015 g). Yield: 0.031 g
(s 2 H, NH) ppm. IR (KBr): 3318 (s) (N–H); 3074 (m), 2932 (w)
(C–H); 1684 (m), 1566 (m) (C=Oamide); 1614 (m) (C=N); 1600 (s),
–
(0.017 mmol, 85%) red solid. HR-ESI-MS: calcd. for [M – 2 PF6 ]
(C72H42N18Ni3O6Ru) 1530.0639; found 1530.0640 (+0.1 mD, stan-
dard: H3PO4).
1308 (s) (C=C); 840 (s) (PF6–) cm–1. UV/Vis (CH3CN): λmax
447 nm (ε Ϸ 1.9×104 Lmol–1 cm–1).
=
[Ru(µ-L1Pd)3](PF6)2: Pd(benzonitrile)2Cl2 (0.023 g) in CH3CN
[Ru(bpy)2(µ-L1M)](PF6)2, M = Cu2+, Ni2+, Pd2+: [Ru(bpy)2-
(H2L1)](PF6)2·2H2O (0.034 g, 0.03 mmol) and the corresponding
metal salt (0.03 mmol) were refluxed in MeOH (15 mL) for 20 min.
After being cooled to room temperature, the dinuclear complexes
were precipitated by addition of Et2O, isolated by centrifugation or
filtration, and dried under high vacuum.
(4 mL), followed by TEA (0.1 mL). Yield: 0.037 g (0.022 mmol,
–
74%) red solid. ESI-MS: calcd. for [M – 2 PF6 ] (C72H42N18O6P-
d3Ru) 1673.97; found 1674.
Tris[5,6-bis(2-pyridylcarboxamido)-1,10-phenanthroline]iron Hexa-
fluorophosphate, [Ru(H2L1)3](PF6)2: A mixture of FeSO4·7H2O
(0.028 g, 0.1 mmol), 5,6-bis(2-pyridylcarboxamido)-1,10-phenan-
throline (0.15 g, 0.35 mmol), hydroxylammonium chloride (0.01 g),
and sulfuric acid (50 µL) was stirred in H2O (10 mL) for 6 h at
ambient temperature. After filtration (excess ligand), the complex
was precipitated from the dark red solution by addition of
NH4PF6, collected on a filter, washed with small amounts H2O and
Et2O, and dried under high vacuum. Yield: 0.15 g (0.09 mmol,
90%) bordeaux red powder. C72H48F12FeN18O6P2·4H2O (1679.00):
calcd. C 51.50, H 3.36, N 15.02; found C 51.67, H 3.55, N 15.13.
[Ru(bpy)2(µ-L1Cu)](PF6)2: Cu(AcO)2·H2O (0.006 g). Yield: 0.022 g
(0.017 mmol, 57 %) dark brown solid. C44H30CuF12N10O2P2Ru·
6H2O (1293.39): calcd. C 40.86, H 3.27, N 10.83; found C 40.63,
H 3.03, N 10.60. IR (KBr): 3074 (m) (C–H); 1654 (m) (C=Oamide);
1624 (m) (C=N); 1600 (m), 1488 (m) (C=C); 838 (PF6 ) cm–1.
–
[Ru(bpy)2(µ-L1Ni)](PF6)2: Ni(AcO)2·4H2O (0.0075 g). Yield:
0.027 g (0.023 mmol, 75%) bright red solid.
[Ru(bpy)2(µ-L1Pd)](PF6)2: Pd(benzonitrile)2Cl2 (0.0115 g) in
CH3CN (2 mL), followed by 0.05 mL TEA. Yield: 0.031 g
(0.024 mmol, 80%) orange-red solid. C44H30F12N10O2P2PdRu·
2MeOH (1292.26): calcd. C 42.75, H 2.96, N 10.84; found C 42.59,
H 3.16, N 11.12. IR (KBr): 3062 (m) (C–H); 1684 (w) (C=Oamide);
–
HR-ESI-MS: calcd. for [M – 2PF6 ] (C72H48FeN18O6) 1316.3354;
found 1316.3366 (+1.2 mD, standard: H3PO4). 1H NMR
3
3
(500 MHz, CD3CN): δ = 7.62 (dd, J = 7.5 Hz, J = 4.2 Hz, 6 H,
3
py-H), 7.69 [m(br), 6 H, phen-H], 7.82 (d, J = 3.4 Hz, 6 H, phen-
H), 8.01 (t, J = 7.5 Hz, 6 H, py-H), 8.21 (d, J = 7.5 Hz, 6 H, py-
H), 8.65 (d, J = 4.2 Hz, 6 H, py-H), 10.74 (s, 6 H, NH) ppm. IR
3
3
1626 (m) (C=N); 1600 (m), 1494 (w) (C=C); 842 (s) (PF6 ) cm–1.
–
3
[Ru(bpy)2(µ-L2M)](PF6)2, M = Cu2+, Ni2+, Pd2+: Obtained as de-
scribed above, but with [Ru(bpy)2(H2L2)](PF6)2·3.5H2O (0.038 g,
0.03 mmol).
(KBr): 3274 (m) (N–H); 3074 (w), 3054 (w) (C–H); 1570 (m), 1680
(s) (C=Oamide); 1622 (m) (C=N); 1588 (m), 1500 (s) (C=C); 844 (s)
( P F 6 – ) c m – 1 . U V / Vi s ( C H 3 C N ) : λ m a x = 5 1 5 n m ( ε Ϸ
0.8×104 Lmol–1 cm–1).
[Ru(bpy)2(µ-L2Cu)](PF6)2: Cu(AcO)2·H2O (0.006 g). Yield: 0.027 g
(0.02 mmol, 68 %) red-brown solid. C46H34CuF12N10O2P2Ru·
3H2O·1.5MeOH (1319.42): calcd. C 42.34, H 3.44, N 10.39; found
C 42.40, H 3.64, N 10.61. IR (KBr): 3072 (w), 2926 (w) (C–H);
1656 (m) (C=Oamide); 1634 (s) (C=N); 1604 (s), 1310 (m) (C=C);
[Fe(µ-L1M)3](PF6)2, M = Cu2+, Ni2+, Pd2+: [Fe(LpicH2)3](PF6)2·
4H2O (0.034 g, 0.02 mmol) and the corresponding metal salt
(0.06 mmol) were refluxed in MeOH (15 mL) for 20 min. After
cooling, the tetranuclear complexes were precipitated by addition
of Et2O, isolated by centrifugation or filtration, and dried under
high vacuum.
842 (s) (PF6 ) cm–1.
–
[Ru(bpy)2(µ-L2Ni)](PF6)2: Ni(AcO)2·4H2O (0.0075 g). Yield:
0.029 g (0.022 mmol, 74 %) red solid. C46H34NiF12N10O2P2Ru·
3H2O (1268.02): calcd. C 42.68, H 3.11, N 10.82; found C 42.69,
H 3.16, N 10.77. IR (KBr): 3074 (m), 2934 (w) (C–H); 1640 (m)
(C=Oamide); 1612 (s) (C=N); 1584 (w), 1310 (m) (C=C); 838 (s)
[Fe(µ-L1Cu)3](PF6)2: Cu(AcO)2·H2O (0.012 g). Yield: 0.03 g
(0.0157 mmol, 79%) dark red-brown solid. C72H42Cu3F12FeN18
-
O6P2·6H2O (1899.62): calcd. C 45.52, H 2.87, N 13.27; found C
–
45.56, H 3.04, N 13.17. HR-ESI-MS: calcd. for [M – 2PF6
]
–
(PF6 ) cm–1.
(C72H42Cu3FeN18O6) 1499.0772; found 1499.0804 (+3.2 mD, stan-
dard: H3PO4). IR (KBr): 3068 (m) (C–H); 1654 (m) (C=Oamide);
1622 (s) (C=N); 1596 (s) (C=C); 844 (s) (PF6–) cm–1. UV/Vis
[Ru(bpy)2(µ-L2Pd)](PF6)2: Pd(benzonitrile)2Cl2 (0.0115 g) in
CH3CN (2 mL), followed by 0.05 mL TEA. Yield: 0.03 g
(0.022 mmol, 74%) orange-red solid. C46H34PdF12N10O2P2Ru·
4H2O (1333.77): calcd. C 40.62, H 3.11, N 10.30; found C 40.45,
H 3.13, N 10.22. IR (KBr): 3066 (m), 2926 (w) (C–H); 1654 (sh)
(C=Oamide); 1626 (s) (C=N); 1604 (s), 1308 (m) (C=C); 842 (s)
(CH3CN): λmax = 387 nm (ε Ϸ 1.0 × 104 L mol–1 cm–1), λmax
524 nm (ε Ϸ 0.9×104 L mol–1 cm–1).
=
[Fe(µ-L1Ni)3](PF6)2: Ni(AcO)2·4H2O (0.015 g). Yield: 0.025 g
(0.0132 mmol, 66 %) red solid. C72H42F12FeN18Ni3O6P2·
–
(PF6 ) cm–1.
2H2O·3MeOH (1906.09): calcd. C 47.18, H 3.06, N 13.21; found C
–
[Ru(µ-L1M)3](PF6)2, M = Cu2+, Ni2+, Pd2+: The synthesis was car-
ried out as described above, but with [Ru(H2L1)3](PF6)2·6H2O
(0.035 g, 0.02 mmol), along with double the amount of the corre-
sponding metal salts and double the volume of solvent.
47.22, H 2.92, N 12.96. ESI-MS: calcd. for [M – 2 PF6
]
(C72H42FeN18Ni3O6) 1484; found 1483.9. IR (KBr): 3078 (w) (C–
H); 1660 (sh) (C=Oamide); 1636 (s) (C=N); 1604 (w), 1586 (m)
–
(C=C); 842 (s) (PF6 ) cm–1. UV/Vis (CH3CN): λmax = 451 nm (ε Ϸ
Eur. J. Inorg. Chem. 2006, 4442–4448
© 2006 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
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4447

P. Comba, R. Krämer, A. Mokhir, K. Naing, E. Schatz
FULL PAPER
1.3×104 Lmol–1 cm–1), λmax = 485 nm (ε Ϸ 1.3×104 Lmol–1 cm–1),
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λmax = 527 nm (ε Ϸ 1.3×104 Lmol–1 cm–1).
[Fe(µ-L1Pd)3](PF6)2: Pd(benzonitrile)2Cl2 (0.023 g) in CH3CN
(4 mL), followed by TEA (0.1 mL). Yield: 0.032 g (0.0164 mmol,
82%) red solid. C72H42F12FeN18O6P2Pd3·9H2O (2082.29): calcd. C
41.53, H 2.90, N 12.11; found C 41.28, H 2.76, N 11.97. ESI-MS:
–
calcd. for [M – 2 PF6 ] (C72H42FeN18O6 Pd3) 1628; found 1628. IR
(KBr): 3064 (m) (C–H); 1650 (sh) (C=Oamide); 1626 (s) (C=N); 1598
(s) (C=C); 844 (m) (PF6 ) cm–1.
–
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Acknowledgments
Generous financial support by the Deutsche Forschungsgemein-
schaft (DFG) and a generous gift of palladium and ruthenium salts
by Degussa AG are gratefully acknowledged.
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Received: May 19, 2006
Published Online: September 12, 2006
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Eur. J. Inorg. Chem. 2006, 4442–4448