Rapid and highly sensitive dual-channel detection of cyanide by bis-heteroleptic ruthenium(II) complexes

Article abstract of DOI:10.1021/ic2022853

Two new ruthenium complexes [Ru(bipy)₂(PDA)]²⁺ (1) and [Ru(phen)₂(PDA)]²⁺ (2) (PDA = 1,10-phenanthroline-4,7- dicarboxaldehyde) have been synthesized to detect cyanide based on the well-known formation of cyanohydrins. Both 1[PF₆]₂ and 2[PF₆]₂ were fully characterized by various spectroscopic techniques and their solid state structures determined by single-crystal X-ray diffraction. Their anion binding properties in pure and aqueous acetonitrile were thoroughly examined using two different channels, i.e., UV-vis absorption and photoluminescence (PL). After addition of only 2 equiv of CN^-, the PL intensity of 1[PF₆]₂ and 2[PF₆] ₂ was enhanced ～55-fold within 15 s along with a diagnostic blue shift of the emission by more than 100 nm. PL titrations of 1[PF ₆]₂ and 2[PF₆]₂ with CN^- in CH₃CN furnished the very high overall cyanohydrin formation constants log β_[CN^-_] = 15.36 ± 0.44 (β_[CN^-_] = 2.3 × - 10¹⁵ M^-2) and log β_[CN^-_] = 16.37 ± 0.53 (β_[CN^-_] = 2.3 × 10¹⁶ M^-2), respectively. For both probes, the second constant, K₂, is about 57-84 times less than K₁, suggesting that the cyanohydrin reaction is stepwise. The stepwise mechanism is further supported by results of a ¹H NMR titration of 2[PF ₆]₂ with CN^-. The high selectivity of 2[PF ₆]₂ for CN^- was established by PL in the presence of other competing anions. Furthermore, the color change from orange-red to yellow and the appearance of a orange luminescence, which can be observed by the naked eye, provides a simple real-time method for cyanide detection. Finally, theoretical calculations were carried out to elucidate the details of the electronic structure and transitions involved in the ruthenium probes and their cyanide adducts.

Full text of DOI:10.1021/ic2022853

Article
pubs.acs.org/IC
Rapid and Highly Sensitive Dual-Channel Detection of Cyanide
by Bis-heteroleptic Ruthenium(II) Complexes
Snehadrinarayan Khatua,† Debabrata Samanta,† Jan W. Bats,‡ and Michael Schmittel*,†
†Center of Micro and Nanochemistry and Engineering, Organische Chemie I, Universitat Siegen, Adolf-Reichwein-Strasse 2,
̈
D-57068 Siegen, Germany
‡Institut fur Organische Chemie und Chemische Biologie, Johann Wolfgang Goethe-Universitat, Max-von-Laue Strasse 7,
̈
̈
D-60438 Frankfurt am Main, Germany
S
* Supporting Information
ABSTRACT: Two new ruthenium complexes [Ru(bipy)2(PDA)]2+ (1) and
[Ru(phen)2(PDA)]2+ (2) (PDA = 1,10-phenanthroline-4,7-dicarboxaldehyde)
have been synthesized to detect cyanide based on the well-known formation of
cyanohydrins. Both 1[PF6]2 and 2[PF6]2 were fully characterized by various
spectroscopic techniques and their solid state structures determined by single-
crystal X-ray diffraction. Their anion binding properties in pure and aqueous
acetonitrile were thoroughly examined using two different channels, i.e., UV−
vis absorption and photoluminescence (PL). After addition of only 2 equiv of
CN−, the PL intensity of 1[PF6]2 and 2[PF6]2 was enhanced ∼55-fold within
15 s along with a diagnostic blue shift of the emission by more than 100 nm.
PL titrations of 1[PF6]2 and 2[PF6]2 with CN− in CH3CN furnished the very
−
high overall cyanohydrin formation constants log β[CN = 15.36
0.44
]
(β[CN ] = 2.3 × 1015 M−2) and log β[CN ] = 16.37 0.53 (β[CN ] = 2.3 × 1016
M−2), respectively. For both probes, the second constant, K2, is about 57−84
times less than K1, suggesting that the cyanohydrin reaction is stepwise. The
−
−
−
1
stepwise mechanism is further supported by results of a H NMR titration of
2[PF6]2 with CN−. The high selectivity of 2[PF6]2 for CN− was established by
PL in the presence of other competing anions. Furthermore, the color change from orange-red to yellow and the appearance of a
orange luminescence, which can be observed by the naked eye, provides a simple real-time method for cyanide detection. Finally,
theoretical calculations were carried out to elucidate the details of the electronic structure and transitions involved in the
ruthenium probes and their cyanide adducts.
phosphorescent ruthenium(II) polypyridine complexes as
chemosensors or probes12 has recently attracted enormous
interest owing to their advantageous photophysical properties,
such as visible excitation wavelengths, large Stoke shifts,
relatively long excited state lifetimes, suitable redox properties
for electrochemiluminescence, and high stability in aqueous
media compared with those of pure organic luminophores. In
recent years, a large number of chromogenic and luminescent
receptors/probes based on ruthenium(II) polypyridine com-
plexes has been developed for the selective and sensitive
sensing of metal cations,13 anions,14 molecular oxygen,15 and
biologically relevant molecules.16
While bisheteroleptic ruthenium complexes have previously
been used for both cation and anion detection, only a few are
selective and sensitive toward the cyanide ion. In many cases,
however, fluoride and acetate were strongly interfering
anions.17 Recently, addition of anions, such as cyanide
(CN−), to an electron-deficient carbonyl unit has been
INTRODUCTION
■
Cyanide as an extremely toxic inorganic anion is harmful to the
environment and human health.1 However, its wide range of
application, particularly in gold mining, electroplating, and
various chemical industries, leads to unavoidable environmental
spills.2 Due to its serious toxicity and wide use, development of
further new probes for highly selective cyanide detection and
quantification are desirable.3 Due to the known limitations of
various colorimetric and fluorometric cyanide receptors,4 such
as slow reaction rate,4a,b special requirements (e.g., heating),4c,d
and poor selectivity regarding fluoride or acetate as interfering
anions,4a,b,e,f reaction-based sensors or chemodosimeters attract
great attention.5 Most chemodosimeters for cyanide so far are
based on dyes equipped with a metal binding unit6 or on
covalent bond formation.7
Ruthenium(II) polypyridyl complexes of 2,2′-bipyridine
(bpy), 1,10-phenanthroline (phen), and related ligands have
interesting photophysical, photochemical, and electrochemical
properties that make them attractive for development of
luminescent sensors,4b,8 dye-sensitized solar cells (DSSC),9
photoinduced switches,10 and photoactive devices.11 Use of
Received: October 21, 2011
© XXXX American Chemical Society
A
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Chart 1. Chemical Structures of the Ligand and Ruthenium Complexes
Figure 1. Crystal structure of (a) compound 1[PF6]2 and (b) compound 2[PF6]2 (thermal ellipsoids were drawn at the 30% probability level). Only
non-carbon and non-hydrogen atoms except fluorine are labeled here. View of the three-dimensional (3-D) crystal packing of (c) compound 1[PF6]2
−
and (d) compound 2[PF6]2 along the crystallographic a axis. Solvent molecules and counter PF6 ions are omitted for clarity.
successfully applied in the design of colorimetric or turn-on
fluorescent probes. Cyanide has a particularly strong affinity to
CO (see its well-known formation of a cyanohydrin),7a,b,d
and thus, the interference of acetate and fluoride may be
reduced successfully.18 Moreover, to establish higher kinetic
reactivity and equilibrium constants, stronger electron-with-
drawing groups, such as the −C(O)CF3 group, are advised.19
Instead, the electron deficiency of a functional group or the
acidity of a specific proton of an organic ligand may be
significantly increased when it is coordinated to a positive metal
center like Ru2+, Co2+, etc.20
As part of our ongoing research in multichannel probes based
on ruthenium(II) and iridium(III) diimine complexes,21 we
recently started to evaluate bis-heteroleptic ruthenium(II)
complexes as anion probes. Due to the above-mentioned
advantages of ruthenium(II) complexes as probes and of the
carbonyl group as a selective colorimetric and fluorescent
cyanide reaction site, we designed the two ruthenium
complexes [Ru(bipy)2(PDA)]2+ (1) and [Ru(phen)2(PDA)]2+
(2) (PDA = 1,10-phenanthroline-4,7-dicarboxaldehyde). In the
current work, their synthesis and aptness for luminescence
detection of CN− based on the well-known cyanohydrin
B
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formation at the aldehyde group are presented. As expected,
both 1[PF6]2 and 2[PF6]2 reacted preferably with cyanide even
in the presence of competitive anions, namely, F−, Cl−, Br−, I−,
CH3CN under N2 atmosphere with 1,1′-dimethylferrocene as
ox
internal standard (E1/2 = −0.09 V vs FeCp20/+). Compound
1[PF6]2 shows a quasi-reversible (ΔEp = 72 mV) Ru2+/Ru3+
OAc−, H2PO4 , HSO3 . The two aldehyde groups of both
complexes reacted with cyanide in a stepwise manner, as
disclosed, for example, by 1H NMR titration. Theoretical
calculations were made to assign the electronic transitions in 1
and 2 and their cyanide adducts. The results indicate a partial
MLCT switching after reaction with cyanide.
−
−
ox
0/+
redox couple at E1/2 = +1.038 V vs FeCp2 (Figure S16,
Supporting Information). The 128 mV anodic shift in
23
0/+
comparison to [Ru(bipy)3]2+ (E1/2 = +0.91 V vs FeCp2
)
is readily explained by the stronger π-acceptor quality of ligand
PDA, effectively decreasing the HOMO energy level. Similarly,
for 2[PF6]2 a quasi-reversible redox wave at E1/2ox = +1.04 V vs
0/+
FeCp2
for Ru2+/Ru3+ is observed with a peak to peak
RESULTS AND DISCUSSION
separation (ΔEp) of 74 mV. The redox wave is anodically
shifted by only 30 mV in comparison to [Ru(phen)3]2+
(E1/2 = +1.01 V vs FeCp20/+). The two PDA-centered
■
Synthesis and Characterization. The anion-responsive
phenanthroline PDA was prepared according to a reported but
modified procedure.22 Ruthenium compounds 1[PF6]2 and
2[PF6]2 were synthesized by refluxing PDA with cis-Ru-
(bpy)2Cl2·2H2O and cis-Ru(phen)2Cl2, respectively, in ethanol/
water (2:1) under nitrogen followed by anion exchange of Cl−
red
(LC) reduction potentials E1/2 for 1[PF6]2 and 2[PF6]2
0/+
were found at −1.10/−1.43 and −1.05/−1.36 V vs FeCp2
,
respectively. In contrast, the reduction waves for the bipy
ligands (E1/2 = −1.89/−2.08, −2.28 V vs FeCp20/+) and
red
0/+
phen ligands (E1/2red = −1.81 V and Epc = −2.03 V vs FeCp2
)
−
with PF6 (Chart 1). Dark red and black crystals of 1[PF6]2
were observed at more negative potential (see Figure S16,
Supporting Information).
and 2[PF6]2 were obtained from CH3COCH3/CHCl3/CH2Cl2
(3:2:1) in 63% and 60% yield, respectively. Both 1[PF6]2 and
2[PF6]2 were fully characterized by elemental analysis, 1D (1H,
13C) and 2D NMR (1H−1H COSY, 1H−13C HSQC, and
1H−13C HMBC) spectroscopy (Figures S4−S13, Supporting
Information), ESI-MS spectrometry (Figure S14 and S15,
Supporting Information), electrochemical studies (Figure S16,
Supporting Information), and single-crystal X-ray diffrac-
tion (Figure 1). Photophysical properties were determined by
UV−vis and PL spectroscopy (Figure 2).
Crystal Structures. Compounds 1[PF6]2 and 2[PF6]2 were
found to crystallize in the triclinic and monoclinic space group
P1 and P2 /n, respectively. Their structures reveal that both
̅
1
ruthenium centers adopt a similar octahedral geometry
through tridentate coordination of two ancillary bipyridines/
phenanthrolines and one PDA ligand (Figure 1a and 1b). The
Ru−N bond distances in 1[PF6]2 and 2[PF6]2 are in the range
of 2.043(6)−2.070(5) Å, with trans N−Ru−N angles in the
range of 170.80(17)−175.84(18)°. Similar bond lengths and angles
were also observed in formerly reported ruthenium polypyridyl
complexes.24 Analysis of the crystal packing in both 1[PF6]2
and 2[PF6]2 reveals that the complexes form noncovalent 3D
networks (Figure 1c and 1d) which are held together by weak
C−H···O and C−H···F hydrogen bonds as well as by π−π
stacking interactions of two bipyridines/phenanthrolines of
neighboring complexes. The occurrence of C−H···F hydrogen
bonds indicates that the counteranion PF6− plays an important
role in formation of the 3D networks.
Photophysical Properties. UV−vis spectra of 1[PF6]2 and
2[PF6]2 in CH3CN display sharp bands at 287 (ε = 7.4 × 104)
and 264 nm (ε = 8.8 × 104), respectively, assigned to
intraligand (IL) π−π* transitions. Additionally, in both spectra
a broad metal-to-ligand charge-transfer (MLCT) absorption
is observed in the 370−600 nm range consisting of two or
more MLCT bands. For 2[PF6]2, a band at λmax = 473 nm (ε =
1.9 × 104) and a shoulder at 435 nm (ε = 1.7 × 104) are
observed, whereas for 1[PF6]2 it is impossible to provide
an exact absorption maximum due to excessive broadening
(Figure 2). Deconvolution of the broad absorption spanning
from 370 to 600 nm furnishes two bands at λmax = 472
(ε = 1.5 × 104) and 435 nm (ε = 1.4 × 104). A time-dependent
DFT (TD-DFT) calculation was performed to assign those
bands (vide infra). Compounds 1[PF6]2 and 2[PF6]2 show a
rather poor emission intensity at 732 nm upon excitation at 473
and 472 nm, respectively. It is noteworthy that the PL maxima
and shapes are independent of the wavelength of excitation
(from 400 to 473 nm), which implies that the emission occurs
from the same MLCT excited state.
Figure 2. UV−vis (black line, red line) and PL (blue line, green line)
spectra of 1[PF6]2 and 2[PF6]2, respectively, measured in acetonitrile
at room temperature.
The 1D and 2D NMR spectra of 1[PF6]2 and 2[PF6]2,
recorded in acetone-d6 at room temperature, clearly show all
expected resonances for the phenanthroline and bipyridine
ligands. In the 13C spectra of 1[PF6]2 and 2[PF6]2 all peaks are
fully assigned with the help of HSQC and HMBC. For 1[PF6]2,
the ESI-MS clearly shows two peaks at m/z = 794.6 (calcd
794.6) and 324.8 (calcd. 324.8) that are assigned to 1·(PF6)+
and 12+, respectively. Similarly for 2[PF6]2, peaks are observed
at m/z = 842.1 (calcd 842.7) and 348.3 (calcd 348.3). For both
compounds, the experimental isotopic distribution of the singly
and doubly charged species is well matching with the calculated
one (Figures S14 and S15, Supporting Information). The electro-
chemical properties of 1[PF6]2 and 2[PF6]2 were examined by
cyclic voltammetry (CV) using a Pt working electrode in dry
Anion Detection in UV−Vis and Photoluminescence
(PL) Channels. The aptitude of 1[PF6]2 and 2[PF6]2 to serve
as probes for different anions (2.0 equiv) was tested by UV−vis
and PL spectroscopy in CH3CN at room temperature. Both
1[PF6]2 and 2[PF6]2 gave a similar response to anions and
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Figure 3. (a) UV−vis absorption spectra of 2[PF6]2 (20 μM) with different anions (2.0 equiv). (Inset) Photograph showing the color change from
orange red to yellow upon addition of CN−. (b) UV−vis absorption titration of 2[PF6]2 (20 μM) with CN− solution (0−2.0 equiv) in CH3CN at
25 °C. (Inset) Plot of A473/A435 (ratio of absorbance at 473 and 435 nm) against the amount of added CN− (lines serve to illustrate the change in
stoichiometry).
Figure 4. (a) PL spectra of 2[PF6]2 (20 μM) with different anions (2.0 equiv). (Inset) Photograph showing the orange luminescence upon addition
of CN−. (b) PL titration of 2[PF6]2 (20 μM) with CN− solution (0−2.0 equiv) in CH3CN at 25 °C. (Inset) Plot of the PL intensity change (I − I0)
at 614 nm upon addition of CN− (lines serve to illustrate the change in stoichiometry).
equally similar UV−vis and PL titration profiles with specific
anions. For brevity, the present discussion will be mostly
confined to compound 2[PF6]2 (see Supporting Information
for corresponding data of compound 1[PF6]2). In the UV−vis
channel, 2[PF6]2 shows notable absorption changes only
with CN−. Significant blue shifts of λmax of 2[PF6]2 (Δλ =
23−38 nm) and the prominent orange-red to yellow color
change can be readily observed by the naked eye upon addition
of 2.0 equiv of cyanide (Figure 3a, inset). In contrast, no
significant changes of λmax and the color were observed in the
presence of other anions, such as F−, Cl−, Br−, I−, AcO−,
HCO3 , H2PO4 , and HSO3 (Figure 3a). This points to a
selective reaction of CN− with the −CHO groups of 2[PF6]2,
which was furthermore monitored by UV−vis titration to
understand the cause of the color change. Addition of
increasing amounts of CN− (0−2.0 equiv) to the CH3CN
solution of 2[PF6]2 (20 μM) at room temperature reveals a
gradual decrease of the absorbance at 473 nm and appearance
of two bands at 435 (ε = 1.9 × 104) and 447 nm (ε = 1.8 ×
104) (obtained by deconvolution). No further change is
observed after addition of more than 2.0 equiv of CN− ions
(Figure 3b). During the course of the UV−vis titration two
isosbestic points were clearly observed in the MLCT region. A
first isosbestic point was observed at ∼455 nm during addition
of 0−1 equiv of CN− and a second one at 469 nm when more
than 1.0 equiv of CN− was added (Figure S17a, Supporting
Information). A plot of the absorbance ratio at 473 and 435 nm
(A473/A435) as a function of the amount of cyanide clearly
shows that A473/A435 decreases linearly up to 1.0 equiv of CN−
and then with a different slope again from 1.0 to 2.0 equiv of
cyanide. Thereafter, the ratio becomes constant, clearly
indicating a 1:2 binding stoichiometry of 2[PF6]2 and CN−.
The observed relationship should allow for a quantitative
determination of cyanide in the UV−vis channel. Similarly for
1[PF6]2, the broad MLCT band is blue shifted to 435 and 450
nm (obtained by deconvolution) after 2.0 equiv of CN−
addition (Figure S18 in Supporting Information).
For both 1[PF6]2 and 2[PF6]2 it is expected that the lower
energy MLCT band at ∼473 nm is due to a metal (d orbital) to
PDA ligand (π* orbital) charge transfer since the electron-
withdrawing character of the two CHO groups and their π
conjugation with the phenanthroline should efficiently decrease
the LUMO energy. On the other hand, the higher energy band
at ∼434 nm is attributed to a metal (d orbital) to ancillary
−
−
−
D
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Figure 5. PL titration of 2[PF6]2 adding incremental amounts of CN−: (a) 0−1.0 and (b) 1.0−2.0 equiv. (Insets) Plot of I/I0 vs [CN−] shows a
good linear relationship from 0 to 1.0 and 1.0 to 2.0 equiv.
bipy/phen ligand (π* orbital) charge transfer. A significant
enhancement of the LUMO energy level is expected after
cyanide addition to the −CHO group due to the much less
electron-withdrawing character of the cyanohydrin groups and
concomitant loss of extended π conjugation. Hence, after
reaction with cyanide, partial or full MLCT switching from
ruthenium(II) → PDA to ruthenium(II) → bipy/phen(π*) is
expected. To get more details of the changes in the transition,
time-dependent DFT (TD-DFT) calculations were performed
showing indeed partial MLCT switching from ruthenium(II) →
PDA to Ru(II) → bipy/phen(π*) (vide infra).
π(CO) bond due to the negative charge in PDA ligand. As a
consequence, reaction with cyanide becomes more exothermic,
as not a full π(CO) bond has to be cleaved on the way to the
cyanohydrin. The very high overall bond formation constants
are in line with CN− detection through creation of a dynamic
covalent bond.
The PDA ligand contains not only one but two reactive
−CHO groups. As reported earlier for a similar organic
probe,26 cyanide may react with both groups at the same rate.
On the other hand, the possibility of a stepwise reaction cannot
be ignored. During the PL titration of 2[PF6]2 at first a clear
isoemissive point was found at 712 nm up to 1.0 equiv of added
CN−, while a second isoemissive point emerged red shifted to
745 nm upon addition of further CN−. This suggests the
existence of two different equilibria during the course of the
titration (Figure 5a and 5b), as equally suggested by the dual-
slope relationship (Figure 3b) and two isosbestic points at 455
and 469 nm (Figure S17, Supporting Information) in the UV−
vis absorption titration. It is thus reasonable to assume that the
two cyanohydrin units are formed in two steps during the
titration: first one −CHO group in the complex is attacked
by CN− to form the monocyanohydrin, i.e., 1:1 adduct, then
the remaining −CHO group of the 1:1 adduct is attacked by
CN− to yield the 1:2 adduct. As stated earlier, for both 1 and 2
the second binding constant K2 is approximately 57/84 times
smaller than K1, in full agreement with a stepwise CN−
addition.
When the PL intensity of 2[PF6]2 at 614 nm is plotted
against the amount of added CN−, the graph shows two linear
relationsships with different slope, again as in the UV−vis
titration; the first one is from 0 to 1.0 equiv of CN− and the
second from 1.0 to 2.0 equiv of CN−. No more intensity change
is observed after more than 2.0 equiv of CN− has been added,
confirming formation of 1:2 adduct, [2-(CN)2]2+. (Figure 4b,
inset). The plot of the PL intensity change (I − I0) at 614 nm
for 2[PF6]2 as a function of the cyanide concentration shows a
good linear relationship in the range of 0−1 equiv of cyanide;
this indicates that 2[PF6]2 could be used to quantitatively
detect the CN− concentration in an unknown sample (Figure 5,
insets).
As stated earlier, compound 2[PF6]2 shows a rather weak
emission at 732 nm. Treatment of 2[PF6]2 with 2.0 equiv of
various anions shows a notable behavior only with CN−
resulting in a ∼118 nm blue shift of the emission maximum
(Figure 4a). The CN− detection ability of 2[PF6]2 was
interrogated through PL titration studies in detail. The
titration of 2[PF6]2 (λexc = 455 nm; isosbestic point of UV−
vis titration) shows the gradual disappearance of the PL band at
732 nm with increasing amounts of CN− ion and the
appearance of the new band at 614 nm. No more changes
are observed after addition of more than 2.0 equiv of CN−
(Figure 4b). The PL intensity is enhanced ∼52.5-fold (at 614 nm)
after addition of 2.0 equiv of CN−. Similarly for 1[PF6]2, the PL
intensity is enhanced ∼55-fold at 624 nm along with a ∼108 nm
blue shift after addition of 2.0 equiv of CN− (Figure S19, in
Supporting Information). The cyanohydrin formation con-
stants for CN− to 1 and 2 were calculated from PL titration
data using SPECFIT,25 which provided K1 = 3.6 2.5 × 108 M−1
(log K1 = 8.56 0.37) and K2 = 6.3 1.0 × 106 M−1 (log β =
15.36
0.44; β = 2.3 × 1015 M−2) for 1 (average of three
individual titrations) and K1 = 1.4 1.2 × 109 M−1 (log K1 =
9.14 0.46) and K2 = 1.7 0.3 × 107 M−1 (log β = 16.37
0.53; β = 2.3 × 1016 M−2) for 2 (average of three individual
titrations).
It is instructive to compare the above data with results from
the absorption titrations; for 1 we obtain log K = 6.91 0.10,
log β = 13.43
0.18 and for 2 log K = 7.98
0.14, log
β = 14.37 0.24. Notably, the constants from the absorption
measurements are significantly lower than those obtained from
PL by 1−2 orders of magnitude. This difference is readily
rationalized: In the photoexcited complexes 1[PF6]2 and
2[PF6]2, the MLCT state involves a partial weakening of the
Selectivity and Sensitivity. To confirm the high selectivity
of 2[PF6]2 toward cyanide a competition study was performed.
As displayed in Figure 6, no remarkable PL intensity
E
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shows a higher reactivity as measured by its full response within
15 s, necessitating only the stoichiometric amount (2 equiv) for
complete reaction.
1
Reaction with Cyanide Studied by H NMR Spectros-
copy and ESI Mass Spectrometry. To obtain further insight
1
into the nature of the reaction of cyanide with 2[PF6]2, H
NMR titration was carried out. The incremental addition of
tetra-n-butylammonium cyanide (TBACN) to a solution of
2[PF6]2 (2.38 mM) in CD3CN resulted in incremental upfield
shifts of all aromatic proton signals (Figure 8). The spectral
shifts practically stop after addition of 2.0 equiv of cyanide. To
1
explain the distinctive changes of the H NMR signals during
the titration process, we propose formation of two cyanohy-
drins functions in the 4,7 positions of PDA (Scheme 1). During
the 1H NMR titration of 2[PF6]2 with 0−1.0 equiv of CN− the
intensity of the sharp singlet at δ = 10.58 ppm corresponding to
the aldehyde protons (1-H, 1′-H) slowly decreases with CN−
concentration and a new peak for the cyanohydrin proton,
−CH(CN)OH (1a-H) appears at δ = 4.53 ppm. At the same
time, a new signal typical for an aldehyde proton (1″-H) shows
up at δ = 10.57 ppm. Simultaneous appearance of the
cyanohydrin (1a-H) and a new aldehyde proton (1″-H) clearly
indicates that the complex loses its symmetry by forming a
1:1 adduct. The initial signal of the 5,6 protons (5-H, 6-H) of
the PDA ligand in 2 at δ = 9.36 ppm gradually disappears, and
new signals for the 5,6 protons (5a-H, 6a-H) emerge
Figure 6. Behavior of 2[PF6]2 toward CN− and other anions as
measured by PL in CH3CN.
enhancement was observed upon addition of other possibly
competing anions (F−, Cl−, Br−, I−, H2PO4 , HSO3 , OAc−,
−
−
−
HCO3 ; all added in 2 equiv) to the solution of 2[PF6]2 in
CH3CN in the absence of cyanide. Reversely, addition of 2.0
equiv of CN− to 2[PF6]2 in the presence of an excess of other
anions (10 equiv) entails a PL enhancement that was well
reproducible. Therefore, 2[PF6]2 may be considered as a highly
selective probe for CN−.
Moreover, 2[PF6]2 shows a high sensitivity toward CN− due
to the large PL increase, suggesting one to determine the
detection limit (DL) for cyanide. For 2[PF6]2, the PL intensity
changes (I − I0) with increasing amounts of cyanide yielded a
detection limit as low as ca. 0.18 μM in CH3CN (Figure S20,
Supporting Information). The time course of the PL response
of 1[PF6]2 and 2[PF6]2 upon addition of 2.0 equiv of cyanide
in CH3CN at room temperature was monitored (Figure 7),
3
as doublets at δ = 9.13 (d, J = 9.5 Hz, 1H) and 9.28 ppm
3
(d, J = 9.5 Hz, 1H).
Nonequivalence of the 5-H, 6-H protons during titration
confirms formation of a 1:1 adduct as well as the stepwise
reaction. In complex 2, the 2-H, 9-H and 3-H, 8-H protons
appear as sharp doublets at 8.41 and 8.06 ppm. During titration
with up to 1.0 equiv of cyanide, the two doublets shift upfield
and separate into two sets due to the unsymmetry of the 1:1
adduct. In the later stage of the titration from 1.0 to 2.0 equiv of
CN− all signals for the 1:1 adduct in PDA slowly dis-
appear, except that for the cyanohydrins protons −CH(CN)-
OH (1a-H).
After addition of 2.0 equiv of CN−, upfield shifts are
observed for the PDA ligand ring protons. The signals for 5-H,
6-H at 9.36 ppm, 2-H, 9-H at 8.42 ppm, and 3-H, 8-H at 8.01
ppm were upfield shifted to ∼8.85 (for 5b-H, 6b-H), 8.07 (for
2b-H, 9b-H), and 7.68 ppm (for 3b-H, 8b-H), respectively. On
the other hand, the signals for the ancillary phenanthroline
ligands in 2 remain almost unchanged. The new set of signals,
the disappearance of −CHO (1-H, 1′-H), and appearance of
new cyanohydrins protons strongly imply formation of the 1:2
adduct, [2-(CN)2]2+. It is noted that the 1:2 adduct forms
parallel in small amounts at the same time the 1:1 adduct is
generated. During the PL titration (vide supra) the two dif-
ferent isoemissive points clearly point to two different equilibria
Figure 7. Time course of the photoluminescence response of
1[PF6]2 and 2[PF6]2 upon addition of 2.0 equiv of cyanide in CH3CN
at 25 °C.
1
and a stepwise cyanide addition. Thus, H NMR titration data
strongly support our assumption of a stepwise cyanide addition.
Formation of a 1:2 adduct was further confirmed by ESI-MS.
Addition of a slight excess of TBACN to 2[PF6]2 in CH3CN
revealed a singly positive ion peak at m/z 777.8 that is
identified as 1:2 adduct with a cyanide counterion, [{2-
(CN)2}2+·(CN)−]+ (calcd 777.7; found, 777.8) (Figure S21,
Supporting Information).
showing that the maximum of PL for both 1[PF6]2 and 2[PF6]2
was reached within 15 s. No further changes were observed
from 1 to 15 min. This observation points to an extremely fast
reaction of 1[PF6]2 and 2[PF6]2 with cyanide. Very recently,
Lin et al.27 also reported on a highly reactive CN− probe that
showed its maximum fluorescence response in less than 1 min
but required 5 equiv of CN− instead of stoichiometric amounts
(1 equiv) to complete the reaction. In contrast, probe 2[PF6]2
Detection of CN− in Aqueous Solution. For practical use
of probe 2[PF6]2, finally PL titrations were carried out in
aqueous solution. As before in acetonitrile, 2[PF6]2 is weakly
emissive at 606 nm in CH3CN/H2O (95:5 v/v) upon
F
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1
Figure 8. Partial H NMR spectra showing the titration of 2[PF6]2 with CN− in CD3CN at room temperature. The asterisks (*) and number (#)
signs are used to index specific proton signals of the intermediate 1:1 adduct.
Scheme 1. Cyanide Detection by Probe 2[PF6]2 Based on
Cyanohydrins Formation
gradual enhancement of the intensity at 606 nm. However,
unlike the titration process in CH3CN, here ∼5.0 equiv of
CN− is needed to complete the reaction. A study of the
time dependence shows that the PL intensity continuously
increases up to 15 min, implying a much slower reaction than
in pure CH3CN, where the reaction was completed within
15 s (Figure S22, Supporting Information). This result is con-
sistent with previously reported CN− probes, where the strong
hydration of CN− in aqueous solution reduces its
nucleophilicity.18c To set up a test for aqueous solutions,
the CN− reaction was also checked in acetonitrile with
lower water content. In 3% aqueous solution (CH3CN:H2O;
97:3 v/v), the reaction requires ∼3 min to reach the final
value, and for completion ∼2.5 equiv of CN− is required. In
1% aqueous solution (CH3CN:H2O; 99:1 v/v), CN− shows a
very high reactivity toward 2[PF6]2 that is almost identical to
that in pure CH3CN (Figure S22, Supporting Information).
Using such conditions, i.e., CH3CN:H2O = 99:1 (v/v),
2[PF6]2 is well suited to selectively detect CN− in aqueous
solution and shows equally a good selectivity in competition
tests (Figure 9). Actually, 2[PF6]2 is even slightly more
selective and sensitive in acetonitrile after mixing in 1% of
water than in the pure organic solvent itself and may be thus
of use in real-world applications.
excitation at 455 nm (isosbestic point of the UV−vis titration),
Computational Study. Computational studies were
carried out to gain further understanding of the photophysical
and a PL titration with increasing amounts of CN− shows a
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PDA-(CN)2 (π*) character, respectively (Figure S23,
Supporting Information).
To obtain insight into the electronic transitions responsible
for the absorption spectra of complexes 1 and 2 and their
cyanohydrin adducts, 1-(CN)2 and 2-(CN)2, time-dependent
DFT (TD-DFT) calculations on optimized geometries in
CH3CN were performed. The transitions in the visible region
between 370 and 600 nm are assigned to various metal-to-
ligand charge-transfer bands in the singlet state (1MLCT). In
Table S1 (see Supporting Information) the computed vertical
excitation energies and composition of the related transitions
assigned to the experimental UV−vis spectra in CH3CN are
displayed. Only transitions characterized by an oscillator
strength (f) larger than 0.06 are considered. With these data
in hand, the experimental broad MLCT absorptions of 1 from
370 to 600 nm may be understood. The TD-DFT calculations
for 1 indicate that the experimental MLCT band at ∼472 nm
(2.63 eV) arises from a strong transition characterized as
HOMO−1→ LUMO+1 (f = 0.3) (440 nm, 2.81 eV). Another
band at 435 nm (2.85 eV) is due to the weaker transition from
HOMO−2 → LUMO+2 (f = 0.12) (387 nm, 3.20 eV). In
1-(CN)2, the calculated strong transition at 418 nm (2.97 eV),
which is due to the HOMO−1 → LUMO (f = 0.12) transition,
is assigned to the experimental absorption band at 450 nm
(2.77 eV). The other two transitions from HOMO−2 →
LUMO+2 (f = 0.11) and HOMO−2 → LUMO+3 (f = 0.11)
are responsible for the other absorption at 435 nm (2.85 eV).
Similarly, for compound 2 the calculation shows the absorp-
tions at 473 (2.62 eV) and 435 nm (2.85 eV) to be related to
the MLCT bands from HOMO−2 → LUMO+1
(f = 0.3) (442 nm, 2.81 eV) and the HOMO−2 → LUMO
+3 (f = 0.09) (386 nm, 3.21 eV), respectively. In 2-(CN)2, the
experimental λmax at 447 nm (2.86 eV) corresponds to a
transition that relates the metal-based d orbital (HOMO−1) to
the π* of the PDA-(CN)2 (LUMO + 1) (f = 0.07) (414 nm,
2.99 eV).
Figure 9. Behavior of 2[PF6]2 toward CN− and other anions as
measured by PL in 1% aqueous acetonitrile solution.
properties. Selected calculated molecular orbital diagrams
of 1, 1-(CN)2, 2, and 2-(CN)2 are shown in Figure 10 (and
Figure S23, Supporting Information). In all compounds, the
relevant occupied molecular orbitals HOMO, HOMO−1, and
HOMO−2 are mainly located on the ruthenium(II) center.
The two highest lying MOs, i.e., HOMO and HOMO−1,
relate to the ruthenium(II) dz orbital whereas the HOMO−2
corresponds to the ruthenium(II) t2g set (see Figure S23,
Supporting Information). The unoccupied molecular orbitals
LUMO and LUMO+1 of complexes 1 and 2 have PDA (π*)
character, whereas the LUMO+2 and LUMO+3 orbitals cor-
respond to the ancillary bipy/phen ligands. In 2-(CN)2, the
LUMO and LUMO+1 are mainly located on PDA-(CN)2
(π*) whereas the LUMO+2 and LUMO+3 have phen (π*)
character. For 1-(CN)2, the LUMO and LUMO+1 have
mixed-ligand character, i.e., PDA-(CN)2 (π*) and bipy (π*),
and the LUMO+2 and LUMO+3 have bipy (π*) and
Figure 10. View of the frontier molecular orbitals (MOs) of 1, 1-(CN)2, 2, and 2-(CN)2 [isovalue = 0.05].
H
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examine low-energy excitations at the ground-state geometry in
acetonitrile at the same level of calculation as employed for geometry
optimizations.
Another MLCT band at 435 nm (2.85 eV) is due to com-
bination of three major transitions, HOMO−2 → LUMO+2
(f = 0.06) (406 nm, 3.05 eV), HOMO−2 → LUMO+3
(f = 0.09) (396 nm, 3.13 eV), and HOMO−1 → LUMO+3
(f = 0.1) (400 nm, 3.09 eV), respectively. All transitions are
determined to be singlet MLCT transitions (1MLCT) involving
the metal-based HOMO, HOMO−1, and HOMO−2 and the
ligand-based LUMO, LUMO+1, LUMO+2, and LUMO+3.
Synthesis. Synthesis of 1,10-Phenanthroline-4,7-dicarboxalde-
hyde (PDA).22 A mixture of 4,7-dimethyl-1,10-phenanthroline
(208 mg, 1.00 mmol) and selenium dioxide (448 mg, 4.00
mmol) in dioxane containing 4% H2O (25 mL) was heated
under reflux for 3 h and then filtered through Celite (2 cm bed)
while kept hot. A light yellow solid separated in the cold filtrate
and recrystallized from dioxane to furnish 1,10-phenanthroline-
4,7-dicarboxaldehyde (PDA) as yellow needles. Yield: 154 mg
(65%). FTIR in KBr disk (ν/cm−1): 3224, 2360, 1699, 1504,
1222, 1087, 848. ESI-MS: [C14H8N2O2 + H]+: calcd m/z,
CONCLUSIONS
■
Two new ruthenium complexes have been prepared to detect
cyanide based on a cyanohydrin chemodosimeter reaction, and
their mechanism of operation is carefully elucidated. Both
complexes show high selectivity and sensitivity toward CN− in
pure or 1% aqueous CH3CN using either the UV−vis or the PL
channel. The immediate color change from orange-red to
yellow and orange luminescence can be observed by the naked
eye after CN− addition. The high overall binding constant for
1-(CN)2 and 2-(CN)2 and immediate ∼55 fold PL intensity
enhancements point to a high sensitivity of CN− detection. The
reactivity of 1[PF6]2 and 2[PF6]2 to CN− is very high at room
temperature, just requiring stoichiometric amounts for
complete reaction within 15 s. The reactivity is higher than
that of a recently reported fast CN− probe.27 The calculated
detection limit implies that the probe can detect CN−even at
the sub-micromolar level and in the presence of many other
anions. As the complex has two reacting units, a stepwise
reaction is observed, which is supported by absorption, PL, and
1H NMR titration. Finally, theoretical calculations furnish
detailed insights into the electronic structures and transitions
involved in the compounds and their cyanide adducts. The
results indicate a partial MLCT switching after cyanide addition
to the carbonyl groups.
1
237.07; found m/z, 237.10. H NMR (400 MHz, CDCl3): δ =
10.64 (s, 2H, 1-H, 1′-H), 9.54 (d, 3J = 4.4, 2H, 2-H, 9-H), 9.23
3
(s, 2H, 5-H, 6-H), 8.10 (d, J = 4.4, 2H, 3-H, 8-H). 13C NMR
(100 MHz, CDCl3): δ = 192.4, 151.2, 146.8, 136.8, 127.2,
125.3, 124.9.
Synthesis of [Bis(2,2′-bipyridine)(4,7-diformyl-1,10-
phenanthroline)ruthenium(II) Dihexafluorophosphate] (1[PF6]2).
cis-[Ru(bipy)2]Cl2·2H2O32 (0.13 g, 0.25 mmol) and 1,10-phenanthro-
line-4,7-dicarboxaldehyde [PDA] (59 mg, 0.25 mmol) were refluxed in
60 mL of degassed aqueous ethanol (ethanol/water = 2:1) at 90 °C for
14 h under N2. An excess of NH4PF6 (500 mg) was added, and the
mixture was stirred for another 1 h. Thereafter, the solution was
concentrated under reduced pressure. The dark red-colored solid was
separated from the aqueous solution by filtration, washed with distilled
water, and dried under vacuum. Finally, recrystallization of the solid
from acetone/chloroform provided a black red crystalline complex
(154 mg, 63% yield). Diffraction-quality single crystals were obtained
from an acetone, chloroform, and dichloromethane (3:2:1) mixture.
Anal Calcd for C34H24F12N6O2P2Ru·0.3CHCl3 (Mw = 978.95): C,
42.08; H, 2.50; N, 8.58. Found: C, 42.34; H, 2.60; N, 8.59. FTIR in
KBr (ν/cm−1): 3055, 2306, 1704, 1610, 1428, 1263, 898, 840, 745.
ESI-MS [C34H24N6O2Ru]2+: calcd, m/z = 324.8; found, m/z = 324.8.
ESI-MS [C34H24N6O2RuPF6]+: calcd, m/z = 794.6; found. m/z =
794.6. 1H NMR (400 MHz, acetone-d6): δ = 10.75 (s, 2H, 1-H, 1′-H),
3
9.46 (s, 2H, 5-H, 6-H), 8.92 (d, J = 5.4 Hz, 2H, 2-H, 9-H), 8.88 (d,
3J = 8.2 Hz, 2H, 3′-H), 8.84 (d, 3J = 8.2 Hz, 2H, 3″-H), 8.37 (d, 3J = 5.4
Hz, 2H, 3-H, 8-H), 8.30 (dt, 3J = 8.0, 4J = 1.5 Hz, 2H, 4′-H), 8.18 (dt,
semicovered, 3J = 8.0, 4J =1.5 Hz, 2H, 4″-H), 8.17−8.15 (m, 2H, 6′-H),
EXPERIMENTAL SECTION
■
Materials and Physical Measurements. All chemicals were used
as received from commercial suppliers (Aldrich, Alfa Aesar and Acros).
1H and 13C NMR spectra were measured on a Bruker Avance
spectrometer using residual protic solvent as the internal standard.
ESI-MS spectra were measured on a LCQ Deca Thermo Quest
instrument. Infrared spectra were recorded using a Varian 1000 FT-IR
instrument. Elemental analysis measurements were done using the EA
3000 CHNS. UV−vis and PL spectra were recorded on a Varian Cary
50 Bio UV−vis spectrometer and Varian Cary Eclipse fluorescence
spectrometer.
3
3
4
7.90−7.89 (m, 2H, 6″-H), 7.67 (ddd, J =7.9, J =5.6 Hz, J =1.2 Hz,
2H, 5′-H), 7.39 (ddd, J = 7.9, J =5.6 Hz, J =1.2 Hz, 2H, 5″-H). 13C
NMR (100 MHz, acetone-d6): δ = 193.8 (C-1, C-1′), 158.9 (4C, C-2′,
C-2″), 156.5 (C-2, C-9), 154.1 (2C, C-6′), 153.8 (2C, C-6″), 150.7
(C-11, C-12), 140.6 (2C, C-4′), 140.5 (2C, C-4″), 138.2 (C-4, C-7),
131.1 (C-3, C-8), 130.0 (2C, C-5′), 129.8 (2C, C-5″), 129.2 (C-13,
C-14), 128.5 (C-5, C-6), 126.5 (2C, C-3′), 126.5 (2C, C-3″).
3
3
4
Synthesis of [Bis(1,10-phenanthroline)(4,7-diformyl-1,10-
phenanthroline)]ruthenium(II) Dihexafluorophosphate] (2[PF6]2).
A mixture of cis-[Ru(phen)2]Cl2 (0.13 g, 0.25 mmol) and 1,10-
phenanthroline-4,7-dicarboxaldehyde [PDA] (59 mg, 0.25 mmol) was
refluxed in 60 mL of degassed aqueous ethanol (ethanol/water = 2:1)
at 90 °C for 14 h under N2. An excess of NH4PF6 (500 mg) was
added, and the mixture was stirred for another 1 h. Then the solution
was concentrated under reduced pressure. From the concentrated
aqueous solution the dark red solid was filtered off, washed with
distilled water, and dried under vacuum. Recrystallization from
acetone/chloroform provided the black red crystalline complex
(162.0 mg, 60% yield). Diffraction-quality black-colored single crystals
were obtained from an acetone, chloroform, and dichloromethane
(3:2:1) mixture. Anal. Calcd for C38H24F12N6O2P2Ru·0.77CHCl3
(Mw = 1079.56): C, 43.13; H, 2.31; N, 7.78, Found: C, 43.22; H,
2.03; N, 7.62. FTIR in KBr disk (ν/cm−1): 3093, 1703, 1508, 1429,
1267, 957, 837, 739. ESI-MS [C38H24N6O2Ru]2+: calcd, m/z = 348.3;
found, m/z = 348.3. ESI-MS [C38H24N6O2RuPF6]+: calcd, m/z =
842.7; found, m/z = 842.1. 1H NMR (400 MHz, acetone-d6):
δ(ppm) = 10.72 (s, 2H, 1-H, 1′-H); 9.47 (d, 2H, 5-H, 6-H), 8.89 (d,
J = 5.4 Hz, 2H, 2-H, 9-H), 8.83 (dd, J = 8.3, 2.2 Hz, 2H, 4′-H, 4″-H),
8.83 (dd, J = 8.3, 2.2 Hz, 2H, 7′-H, 7″-H), 8.43 (dd, semicovered,
Electrochemical experiments were performed using a standard
three-electrode setup (Pt working electrode, Pt auxiliary electrode,
silver wire as quasi-reference electrode) connected to a Princeton
Applied Research model 362 potentiostat. Experiments were carried
out on a 1.0 mM solution of 1[PF6]2 or 2[PF6]2 in dry degassed
acetonitrile with 0.1 M tetra-n-butylammonium hexafluorophosphate
(Bu4NPF6) as the supporting electrolyte. All potentials were measured
at a scan rate of 100−200 mV s−1 and referenced to 1,1′-
dimethylferrocene as the internal standard that has E1/2 = −0.09 V
0/+
vs FeCp2
.
DFT Calculations. All geometry optimizations were performed
with the TURBOMOLE28 program package using DFT. The B3LYP/
6-31G(d) exchange correlation functional29 was used for C, H, N,
together with the LANL2DZ30 for ruthenium. All geometries were
fully optimized in the ground states (closed-shell singlet So). Time-
dependent density functional (TD-DFT) calculations using the
polarizable continuum model (PCM) nonequilibrium version,31 in
which the cavity is created by the united atom topological model as
implemented in G03 for the lowest singlet−singlet and singlet−triplet
excitations, were performed with a spin-restricted formalism to
I
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J = 5.3, 1.2 Hz, 2H, 2′-H, 2″-H), 8.43 (s, 4H, 5′-H, 5″-H, 6′-H, 6″-H),
8.39 (dd, J = 5.3, 1.2 Hz, 2H, 9′-H, 9″-H), 8.25 (d, J = 5.4 Hz, 2H, 3-H,
8-H), 7.83 (dd, J = 8.3, 5.3 Hz, 2H, 3′-H, 3″-H), 7.80 (dd, J = 8.3, 5.3
Hz, 2H, 8′-H, 8″-H). 13C NMR (100 MHz, acetone-d6): δ = 193.8
(C-1, C-1′), 157.0 (C-2, C-9), 155.3 (C-2′, C-2″), 154.9 (C-9′, C-9″),
151.1 (C-11, C-12), 149.6 (C-11′, C-11″), 149.4 (C-12′, C-12″), 139.5
(C-4′, C-4″ or C-7′, C-7″), 139.4 (C-7′, C-7″ or C-4′, C-4″), 138.1(C-4,
C-7), 133.1 (C-13′, C-13″, C-14′, C-14″), 131.0 (C-3, C-8), 130.2
(C-5′, C-5″), 130.2 (C-6′, C-6″), 129.1 (C-13, C-14), 128.5 (C-3′,
C-3″), 128.3(C-8′, C-8″), 128.2 (C-5, C-6).
Crystallographic Studies. X-ray data of 1[PF6]2 and 2[PF6]2 were
collected at 166 and 170 K, respectively, with a SIEMENS SMART 1K
area detector diffractometer using graphite-monochromated Mo Kα
radiation (λ = 0.71073 Å). An empirical absorption correction was
applied using the SADABS program.33 Structures were solved by direct
methods using the program SHELXS-9734 and refined by full matrix
least-squares calculations (F2) using the SHELXL-9735 software. All
non-H atoms were refined anisotropically against F2 for all
reflections. All hydrogen atoms were placed at their calculated
positions and refined isotropically. Crystal data for 1[PF6]2 and
2[PF6]2 are given in Table 1. Selected bond lengths and angles
Table 2. Selected Bond Lengths [Angstroms] and Angles
[degrees] for Compounds 1[PF6]2 and 2[PF6]2 Around the
Ru(II) Center
compound 1[PF6]2
Ru(1)−N(2)
Ru(1)−N(6)
2.045(5)
2.051(4)
Ru(1)−N(1)
Ru(1)−N(4)
2.051(4)
2.059(5)
Ru(1)−N(3)
2.057(5)
Ru(1)−N(5)
2.058(4)
N(2)−Ru(1)−N(1)
N(1)−Ru(1)−N(6)
N(1)−Ru(1)−N(4)
N(2)−Ru(1)−N(3)
N(6)−Ru(1)−N(3)
N(2)−Ru(1)−N(5)
N(6)−Ru(1)−N(5)
N(3)−Ru(1)−N(5)
79.31(18)
95.88(17)
97.78(18)
98.38(18)
170.80(17)
97.14(17)
78.81(17)
94.81(17)
N(2)−Ru(1)−N(6)
N(2)−Ru(1)−N(4)
N(6)−Ru(1)−N(4)
N(1)−Ru(1)−N(3)
N(4)−Ru(1)−N(3)
N(1)−Ru(1)−N(5)
N(4)−Ru(1)−N(5)
89.06(18)
175.84(18)
94.22(18)
90.84(18)
78.60(17)
173.73(18)
86.02(17)
compound 2[PF6]2
Ru(1)−N(1)
Ru(1)−N(3)
Ru(1)−N(5)
2.058(6)
2.044(6)
2.062(6)
95.6(2)
90.6(2)
94.8(2)
172.9(2)
95.6(2)
89.4(2)
94.8(2)
95.5(2)
Ru(1)−N(2)
Ru(1)−N(4)
Ru(1)−N(6)
N(2)−Ru(1)−N(1)
N(2)−Ru(1)−N(5)
N(1)−Ru(1)−N(5)
N(3)−Ru(1)−N(4)
N(5)−Ru(1)−N(4)
N(3)−Ru(1)−N(6)
N(5)−Ru(1)−N(6)
2.043(6)
2.065(6)
2.070(5)
78.8(2)
N(2)−Ru(1)−N(3)
N(3)−Ru(1)−N(1)
N(3)−Ru(1)−N(5)
N(2)−Ru(1)−N(4)
N(1)−Ru(1)−N(4)
N(2)−Ru(1)−N(6)
N(1)−Ru(1)−N(6)
N(4)−Ru(1)−N(6)
Table 1. Crystal Data for Compounds 1[PF6]2 and 2[PF6]2
97.3(2)
1[PF6]2
2[PF6]2
173.6(2)
79.9(3)
empirical formula
fw
C35H25Cl3F12N6O2P2Ru
1058.97
C42H31Cl3F12N6O3P2Ru
1165.09
88.7(2)
temperature
wavelength
cryst syst
166(2) K
170(2) K
173.2(2)
80.0(2)
0.71073 Å
0.71073 Å
triclinic
monoclinic
P21/n
space group
unit cell dimens
P−1
a = 11.3135(11) Å
b = 12.8239(17) Å
c = 14.7083(17) Å
α = 101.288(9)°
β = 93.655(10)°
γ = 92.021(12)°
2085.9(4) Å3
2
a = 11.5251(5) Å
b = 26.3548(13) Å
c = 16.9055(8) Å
α = 90°
β = 90.1070(10)°
γ = 90°
5134.9(4) Å3
4
ASSOCIATED CONTENT
* Supporting Information
■
S
Crystallographic information files (CIF), all NMR data, UV−
vis and PL titration data for 1[PF6]2, CV data for 1[PF6]2 and
2[PF6]2. This material is available free of charge via the Internet
at http://pubs.acs.org.
vol
Z
AUTHOR INFORMATION
Corresponding Author
*E-mail: schmittel@chemie.uni-siegen.de.
■
density (calcd),
Mg/m3
1.686
1.507
F(000)
1052
2328
cryst size
0.60 × 0.60 × 0.36 mm3
0.65 × 0.65 × 0.20 mm3
Notes
theta range
1.93−26.75°
1.43−26.75°
The authors declare no competing financial interest.
reflns collected
independent reflns
completeness to θ
abs corr
27 281
50 012
8251 [R(int) = 0.0598]
26.75° (93.1%)
semiempirical
0.766 and 0.521
10 380 [R(int) = 0.0739]
95.0%
ACKNOWLEDGMENTS
■
S.K. is grateful to the Alexander von Humboldt Foundation for
financial support, while additional support was provided by the
DFG (Schm 647/17-1). We thank Soumen Samanta
semiempirical
0.885 and 0.636
Tmax and Tmin
refinement method full-matrix least-squares
full-matrix least-squares
on F2
on F2
(Universitat Siegen) for his help with Specfit calculations.
̈
data/restraints/
parameters
8251/0/551
10 380/6/622
1.036
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■
goodness-of-fit on
1.071
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