Proton-induced reversible modulation of the luminescent output of rhenium(I), iridium(III), and ruthenium(II) tetrazolate complexes

Article abstract of DOI:10.1021/ic402187e

One of the distinct features of metal-tetrazolate complexes is the possibility of performing electrophilic additions onto the imine-type nitrogens of the coordinated five-membered ring. These reactions, in particular, provide a useful tool for varying the main structural and electronic properties of the starting tetrazolate complexes. In this paper, we demonstrate how the use of a simple protonation-deprotonation protocol enables us to reversibly change, to a significant extent, the light-emission output and performance of a series of Re(I)-tetrazolate-based phosphors of the general formulation fac-[Re(N ^∧N)(CO)₃L], where N^∧N denotes diimine-type ligands such as 2,2′-bipyridine (bpy) or 1,10-phenanthroline (phen) and L represents a series of different 5-aryl tetrazolates. Indeed, upon addition of triflic acid to these neutral Re(I) complexes, a consistent blue shift (Δλ_max ca. 50 nm) of the emission maximum is observed and the protonated species also display increased quantum yield values (4-13 times greater than the starting compounds) and longer decay lifetimes. This alteration can be reversed to the initial condition by further treating the protonated Re(I) complex with a base such as triethylamine. Interestingly, the reversible modulation of luminescent features by the same protonation- deprotonation mechanism appears as a quite general characteristic of photoactive metal tetrazolate complexes, even for compounds in which the 2-pyridyl tetrazolate ligands coordinate the metal center with a bidentate mode, such as the corresponding Ir(III) cyclometalates [Ir(C^∧N)₂L] and the Ru(II) polypyridyl derivatives [Ru(bpy)₂L]⁺. In these cases, the protonation of the starting materials leads to red-shifted and more intense emissions for the Ir(III) complexes, while almost complete quenching is observed in the case of the Ru(II) analogues.

Full text of DOI:10.1021/ic402187e

Article
pubs.acs.org/IC
Proton-Induced Reversible Modulation of the Luminescent Output of
Rhenium(I), Iridium(III), and Ruthenium(II) Tetrazolate Complexes
Melissa V. Werrett,† Sara Muzzioli,‡ Phillip J. Wright,† Antonio Palazzi,‡ Paolo Raiteri,† Stefano Zacchini,‡
Massimiliano Massi,*,† and Stefano Stagni*,‡
†Department of Chemistry, Curtin University, GPO Box U 1987, Perth, Australia, 6845
‡Department of Industrial Chemistry “Toso Montanari”, University of Bologna, Viale Risorgimento 4, I-40136 Bologna, Italy
S
* Supporting Information
ABSTRACT: One of the distinct features of metal−tetrazolate complexes is the possibility of performing electrophilic additions
onto the imine-type nitrogens of the coordinated five-membered ring. These reactions, in particular, provide a useful tool for
varying the main structural and electronic properties of the starting tetrazolate complexes. In this paper, we demonstrate how the
use of a simple protonation−deprotonation protocol enables us to reversibly change, to a significant extent, the light-emission
output and performance of a series of Re(I)-tetrazolate-based phosphors of the general formulation fac-[Re(N∧N)(CO)3L],
where N∧N denotes diimine-type ligands such as 2,2′-bipyridine (bpy) or 1,10-phenanthroline (phen) and L represents a series
of different 5-aryl tetrazolates. Indeed, upon addition of triflic acid to these neutral Re(I) complexes, a consistent blue shift
(Δλmax ca. 50 nm) of the emission maximum is observed and the protonated species also display increased quantum yield values
(4−13 times greater than the starting compounds) and longer decay lifetimes. This alteration can be reversed to the initial
condition by further treating the protonated Re(I) complex with a base such as triethylamine. Interestingly, the reversible
modulation of luminescent features by the same protonation−deprotonation mechanism appears as a quite general characteristic
of photoactive metal tetrazolate complexes, even for compounds in which the 2-pyridyl tetrazolate ligands coordinate the metal
center with a bidentate mode, such as the corresponding Ir(III) cyclometalates [Ir(C∧N)2L] and the Ru(II) polypyridyl
derivatives [Ru(bpy)2L]+. In these cases, the protonation of the starting materials leads to red-shifted and more intense emissions
for the Ir(III) complexes, while almost complete quenching is observed in the case of the Ru(II) analogues.
ions such as tricarbonyl Re(I) diimines2 and, to a greater extent,
INTRODUCTION
■
cyclometalated Ir(III) derivatives.3 Overall, the synergistic
Among the reasons that might explain the tremendous scientific
effect that arises from the combination of the “right” metal
developments in the chemistry of some specific classes of
with the appropriately modified set of ligands has driven the
octahedral d6 metal complexes, namely, Ru(II) polypyridyls,
cyclometalated Ir(III) derivatives, and tricarbonyl Re(I)
diimines, the modulation of their photophysical properties by
variation of the set of the coordinated ligands is of crucial
application of these classes of photoactive d6 metal complexes
in some of the most challenging research fields: these include
the conversion of solar energy,4 the design of emitting
molecules for lighting devices and displays,5 the development
importance. In particular, the relevance of the role played by
of new luminescent markers and probes for biological imaging,6
the coordinated ligands is evident when considering that the
and, to a more general meaning, the proposition of new families
photophysical behavior of Ru(II) polypyridyls, which represent
of luminescent sensors.7 In the latter context, the sensing ability
the paradigm of luminescent metal complexes, is governed by
metal-to-ligand charge transfer (MLCT) excited states.1 The
of metal complexeswhich is meant herein as the variation of
contribution of the ligands in determining the nature of the
excited states becomes even more appreciable on passing to
isoelectronic complexes containing third-row transition metal
Received: August 27, 2013
Published: December 20, 2013
© 2013 American Chemical Society
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the luminescence output induced by external stimulican be
achieved by different mechanisms that might involve the
occurrence of proton-coupled electron transfer (PCET)8 or the
quenching of the emission originating from triplet excited states
(e.g., O2 sensors)9 or from the analyte-induced perturbation of
the “actor” ligand influencing the emissive excited state.10 In
particular, following our work centered on the study of the
coordination chemistry of tetrazolate ligands in Ru(II)
polypyridyls,11 Ir(III)cyclometalates,12 Re(I)-diimine,13 and
Pt(II)-cyclophane compounds,14 we could observe how, in all
cases, the tetrazolate ligands actually behaved as “actor” ligands,
since their role in determining electronic properties and, in
particular, the luminescent performances of the corresponding
complexes was of relevant importance. From this point of view,
an emblematic example is represented by the series of
tetrazolate-based Ir(III) cyclometalates.12 In those cases, the
tuning of the emitted color spans over a 100 nm range and
could be induced by introducing different substituted
tetrazolates in the structure of the corresponding Ir(III)
cyclometalated fragments. The color variation efficiently
demonstrates the participation of the tetrazolate ligand in the
composition of the emitting MLCT states. As a consequence,
any reversible or irreversible modification occurring to the
coordinated tetrazolate moieties might lead to the further
modulation of the luminescent properties of the corresponding
complexes. This behavior was observed in our investigation
both for the Ru(II) and, particularly, for the Ir(III) tetrazolate
complexes we have reported so far,11,12 in which the
regioselective addition of a methyl group to the coordinated
tetrazolate ring resulted in the enhancement of emission
intensity and shift of the emission maxima. Similarly, we
described how methylation influences the quantum yield of
square-planar Pt(II) tetrazolate complexes.14 It has to be
pointed out that all these modifications displayed an irreversible
character. The opportunity to extend similar effects in a
reversible manner prompted us to perform protonation and
deprotonation reactions onto tricarbonyl Re(I) diimine
tetrazolate derivatives of the general formula fac-[Re(N∧N)-
(CO)3L] (see Scheme 1), for which no studies dealing with
their reactivity toward electrophilic agents has been reported
yet. In order to determine whether the reversible switching of
the luminescence output that was displayed by Re(I) tetrazolate
complexes might represent a general and peculiar feature of
luminescent metal tetrazolate species, we have also extended
this study to the cases of the isoelectronic Ir(III) cyclo-
metalated and Ru(II) polypyridyl tetrazolate complexes.
RESULTS AND DISCUSSION
■
Spectroscopic Characterization. All of the starting
neutral Re(I) complexes were synthesized using a method
differing from the ones previously reported.13a,c The method
does not involve the use of a silver salt for halogen abstraction,
rather just a solvent mixture of ethanol/water (75:25 v/v) in
the presence of triethylamine. In most cases the complexes
were simply filtered off after 24 h at reflux and did not require
further purification; if purification was required, it was
accomplished with the use of flash chromatography. By
following this procedure, the new fac-[Re(bpy)(CO)3Tcya]
complex was prepared and characterized spectroscopically.
Moreover, its structure has been confirmed via X-ray
crystallography (Figure S1 and Table S1, Supporting
Information). The geometry and bonding parameters of fac-
[Re(bpy)(CO)3Tcya] are in agreement with those previously
reported for analogous neutral complexes.13a
The protonation reactions (Scheme 2) have been performed
by adding a slight excess (ca. 1.5 equiv) of triflic acid to
dichloromethane solutions of the starting neutral Re(I)
tetrazolate complexes maintained at −50 °C.
In contrast with that reported by Szczepura and co-workers
in the case of the addition of HBF4 to hexanuclear Re(III)
clusters containing 5-aryl tetrazolate moieties,15 the protonation
of the tricarbonyl Re(I) diimine tetrazolate complexes
described herein occurred even at low temperature. In
particular, all the protonation procedures could be monitored
by solution-state IR spectroscopy. Indeed, the formation of the
targeted protonated species was witnessed by the shift toward
higher wavenumbers of the CO stretchings on passing from the
neutral to the cationic complexes. In all cases, the facial
configuration of the CO ligands was retained. This appeared
evident by considering that, apart from the expected shift of the
CO bands, the profile of each IR spectrumthat always
consisted of one sharp band centered at ca. 2040 cm−1, assigned
to the totally symmetric in-phase stretching A′(1), and a
broader one at ca. 1937 cm−1 that is the result of the
superimposition of the totally symmetric out-of-phase stretch-
ing A′(2) and the asymmetric stretching A″ (Figure 1 and
Table 1)did not change upon protonation.
Scheme 1. Complexes and Their Acronyms
The protonated Re(I) complexes were then characterized by
1H and 13C NMR spectroscopy, and the comparative analysis of
the obtained spectra with those of each starting complex
indicated that, as expected, the addition of H+ is directed to the
coordinated tetrazolate, which behaves as a Brønsted-type base.
On comparing the corresponding starting and protonated
Re(I) complexes (see Supporting Information, Figures S2−S7),
it is possible to observe that the most evident variations
occurring upon protonation are localized on the phenyl ring
conjugated with the tetrazole group. Taken together, these
spectroscopic features suggest that the protonation reaction
occurs chemoselectively to the tetrazolate ligand. Also, on the
basis of our previous studies dealing with the protonation of a
series of [Ru(tpy)(bpy)L]+ complexes, in which the tetrazolate
ligands adopt the same monocoordinate binding mode, we
assume that the N(4) atom of the coordinated tetrazolate ring
likely represents the privileged site where the electrophilic
attack occurs. Reliable evidence for such regioselective
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Scheme 2. Protonation Reaction of the Re(I)-Tetrazolate Complexes and Atom Labeling
Figure 1. Monitoring the protonation of fac-[Re(bpy)(CO)3Tph]: solution IR spectra showing the CO stretchings pattern of the protonated
compound fac-[Re(bpy)(CO)3TphH]+ (black trace) compared to those of the mixture containing both the protonated species and the neutral
starting complex fac-[Re(bpy)(CO)3Tph] (red trace).
Table 1. Stretching Frequencies (cm−1) of the CO Bands of
All the Re(I) Complexes Reported in This Work
range nor in the one typical of the starting compounds (δCt =
a
161−165 ppm). However, quite decisive support of our
hypothesis came from the analysis of the structures of the
Re(I) protonated complexes obtained by X-ray diffraction,
whose detailed descriptions are given in the following section.
Crystal Structures. The molecular structures of the fac-
[Re(phen)(CO)3TphH]+, fac-[Re(phen)(CO)3TcyaH]+, fac-
[Re(phen)(CO)3TbdzH]+, fac-[Re(bpy)(CO)3TcyaH]+, and
fac-[Re(bpy)(CO)3TbdzH]+ cationic complexes have been
determined by single-crystal X-ray diffractometry on their fac-
[Re(phen)(CO)3TphH][CF3SO3] (Figure 2), fac-[Re(phen)-
(CO)3TphH][CF3SO3]·0.25Et2O (Figure 3), fac-[Re(phen)-
(CO)3TcyaH][CF3SO3] and fac-[Re(phen)(CO)3TbdzH]-
[CF3SO3] (Supporting Information, Figures S8 and S9,
respectively), fac-[Re(bpy)(CO)3TcyaH][CF3SO3] (Figure
4), and fac-[Re(bpy)(CO)3TbdzH][CF3SO3] (Figure 5) salts.
A selection of the most relevant bonding and angle parameters
is reported in Table 2. The structure of fac-[Re(phen)-
(CO)3TphH]+ has been determined both in fac-[Re(phen)-
(CO)3TphH][CF3SO3] (Figure 2) and in the solvate fac-
[Re(phen)(CO)3TphH][CF3SO3]·0.25Et2O (Figure 3). The
Re centers in all the complexes display an octahedral geometry,
being coordinated to three CO ligands (in a relative fac
arrangement), a cis-chelating dinitrogen ligand, and an aryl-
substituted protonated tetrazolate ring. The tetrazolate ligand is
bound to the Re center through N(2), and protonation occurs
CO A′(1)
CO A′(2)/A″
fac-[Re(phen)(CO)3Tph]
fac-[Re(phen)(CO)3TphH]+
fac-[Re(bpy)(CO)3Tph]
2029
2039
2029
2039
2029
2040
2029
2040
2030
2040
2029
2040
1922
1936
1924
1936
1923
1938
1922
1937
1923
1937
1923
1938
fac-[Re(bpy)(CO)3TphH]+
fac-[Re(phen)(CO)3Tbdz]
fac-[Re(phen)(CO)3TbdzH]+
fac-[Re(bpy)(CO)3Tbdz]
fac-[Re(bpy)(CO)3TbdzH]+
fac-[Re(phen)(CO)3Tcya]
fac-[Re(phen)(CO)3TcyaH]+
fac-[Re(bpy)(CO)3Tcya]
fac-[Re(bpy)(CO)3TcyaH]+
a
Values are relative to solution-state (dichloromethane as the solvent)
IR spectra recorded at room temperature.
protonation might be obtained from the analysis of the 13C
NMR spectra, in which the tetrazole carbon (Ct) resonance
should be found in the 154−158 ppm16,11d,f chemical shift
range, which is diagnostic for the presence of a substituent at
the N(4) atom. Unfortunately, for the majority of the
protonated species the Ct resonance could not be detected in
the 13C NMR spectra, neither in the expected chemical shift
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Figure 2. Molecular structure of fac-[Re(phen)(CO)3TphH]-
[CF3SO3] with key atoms labeled. Displacement ellipsoids are at the
30% probability level. The [CF3SO3]− anion is omitted for clarity.
Figure 5. Molecular structure of fac-[Re(bpy)(CO)3TbdzH][CF3SO3]
with key atoms labeled. Displacement ellipsoids are at the 30%
probability level. The [CF3SO3]− anion is omitted for clarity.
always at N(4) as previously found in analogous Ru(II)
complexes.11a,c Also the bonding parameters determined for the
aryl-substituted protonated tetrazolate rings compare very well
to those previously found in the protonated Ru(II) complexes.
The five-membered tetrazole rings are perfectly planar [mean
deviations from the N(1) N(2) N(3) N(4) C(4) least-squares
planes in the range 0.0016−0.0071 Å].
Conversely, the N(1)−C(4)−C(5)−C(6) torsion angles are
very different in the six crystal structures, i.e., −172.4(3)° in fac-
[Re(phen)(CO)3TphH][CF3SO3], −25.2(6)° in fac-[Re-
(phen)(CO)3TphH][CF3SO3]·0.25Et2O, −1.9(6)° in fac-[Re-
(phen)(CO)3TcyaH][CF3SO3], 2.4(10)° in fac-[Re(phen)-
(CO)3TbdzH][CF3SO3], −21.0(10)° in fac-[Re(bpy)-
(CO)3TcyaH][CF3SO3], and −160.4(7)° in fac-
[Re(bpy)(CO)3TbdzH][CF3SO3]. An absolute value of this
torsion angle close to 0° or 180° indicates coplanarity between
the protonated tetrazolate and aryl ring, whereas significant
deviations from these values are indicative of loss of coplanarity.
The fact that the experimental values are rather spread and, in
particular, the fact that for the same fac-[Re(phen)-
(CO)3TphH]+ cation two very different torsion angles have
been found in the fac-[Re(phen)(CO)3TphH][CF3SO3]
(−172.4(3)°) and fac-[Re(phen)(CO)3TphH][CF3SO3]·
0.25Et2O (−25.2(6)°) salts suggest that the relative orienta-
tions of the protonated tetrazolate and aryl rings in the solid
state are mainly determined by packing effects rather than by
electronic conjugation. In particular, in all six crystal structures
H-bonds are present involving the N(4)−H(4) group as a
donor and the O atoms of the [CF3SO3]− anions as acceptors
(Table 3). Similarly, the orientation of the aryl-substituted
protonated tetrazolate ligand with respect to the Re(phen)-
(CO)3 framework is very different in the six crystal structures
(see C(2)−Re(1)−N(2)−N(1) torsion angle in Table 2),
suggesting free rotation around the Re(1)−N(2) bond in
solution, whereas the geometry found in the solid state is
determined by H-bonds and other crystal-packing effects.
Photophysical Properties. The relevant absorption and
emission data of all the complexes are listed in Tables 4 and 5.
The UV−vis absorption profiles of the Re(I) compounds
reported herein are quite similar for all the complexes, with
Figure 3. Molecular structure of fac-[Re(phen)(CO)3TphH]-
[CF3SO3]·0.25Et2O with key atoms labeled. Displacement ellipsoids
are at the 30% probability level. The [CF3SO3]− anion and the Et2O
molecule are omitted for clarity.
Figure 4. Molecular structure of fac-[Re(bpy)(CO)3TcyaH][CF3SO3]
with key atoms labeled. Displacement ellipsoids are at the 30%
probability level. The [CF3SO3]− anion is omitted for clarity.
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Table 2. Selected Bond Lengths (Å) and Angles (deg) for fac-[Re(phen)(CO)3TphH][CF3SO3] (1), fac-
[Re(phen)(CO)3TphH][CF3SO3]·0.25Et2O (2), fac-[Re(phen)(CO)3TcyaH][CF3SO3] (3), fac-
[Re(phen)(CO)3TbdzH][CF3SO3] (4), fac-[Re(bpy)(CO)3TcyaH][CF3SO3] (5), and fac-[Re(bpy)(CO)3TbdzH][CF3SO3] (6)
1
2
3
4
5
6
Re(1)−C(1)
Re(1)−C(2)
Re(1)−C(3)
Re(1)−N(2)
Re(1)−N(5)
Re(1)−N(6)
C(1)−O(1)
C(2)−O(2)
C(3)−O(3)
N(1)−N(2)
N(2)−N(3)
N(3)−N(4)
N(1)−C(4)
C(4)−N(4)
C(4)−C(5)
Re(1)−C(1)−O(1)
Re(1)−C(2)−O(2)
Re(1)−C(3)−O(3)
C(1)−Re(1)−N(5)
C(2)−Re(1)−N(2)
C(3)−Re(1)−N(6)
N(5)−Re(1)−N(6)
sum of angles at N4C
sum of angles at C(4)
N(1)−C(4)−C(5)−C(6)
C(2)−Re(1)−N(2)−N(1)
1.914(3)
1.922(3)
1.917(3)
2.182(2)
2.172(2)
2.169(2)
1.150(4)
1.140(4)
1.142(4)
1.345(3)
1.300(3)
1.330(3)
1.322(4)
1.336(4)
1.464(4)
179.3(3)
177.6(3)
179.3(3)
172.45(11)
178.71(11)
172.58(11)
75.83(9)
540.0(5)
359.9(5)
−172.4(3)
−1(5)
1.911(5)
1.915(5)
1.910(5)
2.188(3)
2.168(3)
2.182(3)
1.149(6)
1.141(6)
1.149(6)
1.349(5)
1.298(4)
1.333(5)
1.328(5)
1.335(5)
1.462(6)
178.6(5)
178.4(5)
176.7(5)
172.57(19)
177.13(17)
172.55(18)
75.77(12)
540.0(7)
360.0(7)
−25.2(6)
157.0(3)
1.931(5)
1.907(4)
1.921(4)
2.193(3)
2.183(3)
2.183(3)
1.146(6)
1.142(5)
1.146(5)
1.358(4)
1.294(4)
1.335(4)
1.324(5)
1.334(5)
1.461(5)
179.4(5)
176.6(4)
178.2(4)
171.81(16)
175.60(15)
172.86(15)
75.34(11)
540.0(7)
359.9(5)
−1.9(6)
1.920(8)
1.903(7)
1.924(10)
2.191(5)
2.187(5)
2.195(6)
1.139(8)
1.151(7)
1.141(10)
1.359(7)
1.286(7)
1.336(7)
1.322(7)
1.312(8)
1.478(8)
178.2(7)
177.5(7)
178.6(9)
171.9(3)
175.8(2)
173.7(3)
75.29(19)
540.0(11)
359.9(10)
2.4(10)
1.913(7)
1.890(8)
1.919(7)
2.168(5)
2.174(5)
2.181(5)
1.151(7)
1.170(8)
1.150(8)
1.347(7)
1.317(7)
1.324(7)
1.315(8)
1.333(7)
1.466(9)
177.8(7)
179.2(6)
177.4(6)
173.2(2)
179.7(2)
172.7(2)
74.30(18)
540.0(11)
359.9(10)
−21.0(10)
−147.7(5)
1.912(8)
1.914(8)
1.910(9)
2.190(5)
2.161(5)
2.160(6)
1.160(9)
1.154(9)
1.156(9)
1.349(7)
1.296(7)
1.341(7)
1.324(8)
1.348(8)
1.452(9)
179.1(7)
179.1(6)
178.6(9)
173.2(3)
177.4(2)
172.7(3)
75.0(2)
539.9(11)
360.0(10)
−160.4(7)
32.0(5)
24.2(3)
66.4(5)
reduction is likely to be caused by the decreased σ donation
and/or increased π acceptance of the protonated tetrazolate.
The overall effect is hence a stabilization of the 5d orbitals on
the metal with consequent widening of the HOMO−LUMO
gap.
Table 3. Hydrogen Bonds for fac-
[Re(phen)(CO)3TphH][CF3SO3], fac-
Re(phen)(CO)3TphH][CF3SO3]·0.25Et2O, fac-
[Re(phen)(CO)3TcyaH][CF3SO3], fac-
[Re(phen)(CO)3TbdzH][CF3SO3], fac-
[Re(bpy)(CO)3TcyaH][CF3SO3], and fac-
[Re(bpy)(CO)3TbdzH][CF3SO3]
If the changes of the absorption features occurring upon
protonation were somewhat expected, the extent of the
modifications of the luminescence properties was actually
surprising. Upon excitation of the 1MLCT band at ca. 370 nm,
each of the starting neutral Re(I) complexes display a single
broad and featureless orange-red emission centered between
584 nm (as for complexes fac-[Re(phen)(CO)3Tbdz] and fac-
[Re(phen)(CO)3Tcya]) and 606 nm ( fac-[Re(bpy)-
(CO)3Tph]). According to our previous studies,13 the
phosphorescent emission originates from excited states of
triplet metal−ligand-to-ligand charge transfer (3MLLCT)
nature, where the main contributors to the HOMO-type
orbitals involved in the lowest energy transitions are the metal
5d and the tetrazolate π system and the main contributor for
the LUMO-type orbitals is the π* system of the diimine ligand.
The conversion of the neutral Re(I) tetrazolate complexes into
their conjugated acids dramatically changes the luminescence
properties, in a similar manner for both the bpy and phen
complexes. Indeed, the moderately intense orange-red emission
of the neutral compounds shifts to a bright green color, with
emission maxima blue-shifted of ca. 50 nm (Table 4 and
Figures 7 and 8).
d(N−H)
d(H···O)
d(N···O) ∠(NHO)
fac-[Re(phen)
0.863(18)
1.818(19)
2.681(3)
179(3)
(CO)3TphH][CF3SO3]
fac-[Re(phen)
0.873(19)
1.88(2)
2.752(4)
175(4)
(CO)3TphH][CF3SO3]·
0.25Et2O
fac-[Re(phen)
(CO)3TcyaH][CF3SO3]
0.85(2)
0.86
1.87(2)
1.89
2.720(4)
2.729(7)
2.732(7)
2.673(8)
175(4)
164(4)
168(6)
176(7)
fac-[Re(phen)
(CO)3TbdzH][CF3SO3]
fac-[Re(bpy)(CO)3TcyaH]
[CF3SO3]
0.87(2)
0.87(2)
1.88(3)
1.80(2)
fac-[Re(bpy)(CO)3TbdzH]
[CF3SO3]
intense ligand-centered (LC) π−π* transitions occurring in the
high-energy UV region and weaker charge transfer (CT) bands
tailing in the visible part of the spectrum. When compared to
the initial neutral complexes, the UV−vis absorption spectra of
the protonated cationic compounds display the expected
hypsochromic shift of the MLCT transition, which is
accompanied by an analogous variation of the LC-based
absorption bands (see Figure 6 and Figures S10−S13,
Supporting Information). This behavior can be rationalized
by considering that the protonation of the tetrazolate ring
reduces the overall electron density on the rhenium center. The
This behavior might be explained as a protonation-mediated
reduction, or complete removal, of the contribution of the
tetrazolate ligand in the composition of the emitting excited
states. Indeed, we have previously observed13a the same blue-
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a
Table 4. Absorption and Emission Spectral Data of All the Re(I) Complexes
bc
,
cd
,
absorption
emission 298 K
emission 77 K
complex
λmax (nm); 10−4ε (M−1 cm−1
)
λ (nm)
τ (μs) dear
τ (μs) air
Φ dear
Φ air
λ (nm)
τ (μs)
6.75
[Re(phen)(CO)3Tph]
259 (1.560)
363 (0.196)
254 (1.325)
335 (0.240)
251 (1.570)
285 (0.895)
373 (0.166)
245 (1.556)
319 (0.520)
352 (0.185)
274 (1.115)
360 (0.114)
257 (1.650)
342 (0.180)
284 (0.890)
369 (0.090)
254 (1.010)
319 (0.310)
350 (0.120)
272 (1.413)
366 (0.060)
272 (1.262)
351 (0.940)
296 (1.020)
372 (0.120)
266 (1.291)
592
0.517
0.268
0.072
0.045
534
[Re(phen)(CO)3TphH]+
[Re(bpy)(CO)3Tph]
538
606
2.505
0.092
1.293
0.085
0.470
0.030
0.328
0.028
500
528
5.25
2.97
[Re(bpy)(CO)3TphH]+
548
0.660
0.596
0.135
0.120
502
3.54
[Re(phen)(CO)3Tcya]
[Re(phen)(CO)3TcyaH]+
[Re(bpy)(CO)3Tcya]
[Re(bpy)(CO)3TcyaH]+
584
534
598
546
0.518
2.948
0.139
0.874
0.382
1.819
0.107
0.655
0.070
0.540
0.025
0.204
0.060
0.296
0.021
0.103
528
508
526
534
6.75
5.42
3.64
2.32 (47)
4.74 (53)
[Re(phen)(CO)3Tbdz]
[Re(phen)(CO)3TbdzH]+
[Re(bpy)(CO)3Tbdz]
[Re(bpy)(CO)3TbdzH]+
584
534
596
546
0.775
2.186
0.124
0.825
0.343
1.333
0.105
0.612
0.053
0.206
0.021
0.276
0.043
0.105
0.015
0.145
516
496
528
502
8.00
9.57
3.55
3.38
319 (0.410)
a
b
All data for complexes in 10−5 M CH2Cl2 solutions. “Air” denotes air-equilibrated samples, “dear” means degassed (O2-free) samples; quantum
c
yields are measured versus rhodamine 101 in ethanol. For the biexponential excited-state lifetimes (τ), the relative weights of the exponential curve
are reported in parentheses. In frozen CH2Cl2 matrixes.
d
a
Table 5. Absorption and Emission Spectral Data of All the Ir(III) and Ru(II) Complexes
b,
c
cd
,
absorption
emission 298 K
emission 77 K
λmax (nm); 10−4ε (M−1 cm−1
)
λ (nm)
τ (μs) dear
τ (μs) air
Φ dear
Φ air
λ (nm)
τ (μs)
3.58
Ir(PyrTz)
258 (1.738)
391 (0.192)
253 (1.880)
385 (0.257)
250 (1.520)
368 (0.200)
239 (1.437)
303 (0.567)
291 (1.701)
370 (0.272)
475 (0.311)
287 (1.515)
441 (0.346)
484, 512
0.423
0.080
0.038
0.032
476, 510
[Ir(PyrTzH)]+
FIrN4
594
458, 488
536
0.158
0.161
0.351
0.100
0.105
0.226
0.102
0.056
0.182
0.057
0.034
0.138
477, 510
450, 482
448, 478
2.93
3.14 (26)
4.85 (74)
4.23
[FIrN4H]+
e
e
e
e
e
e
e
[Ru(bpy)2(PyrTz)]+
653
0.220
0.077
n.d.
0.004
n.d.
597
5.23
[Ru(bpy)2(PyrTzH)]2+
n.d.
n.d
n.d
n.d.
n.d.
n.d.
a
b
All data for complexes in 10−5 M CH2Cl2 solutions. “Air” denotes air-equilibrated samples, “dear” means degassed (O2 free) samples; quantum
c
yields are measured versus quinine bisulfate in 1 N H2SO4. For the biexponential excited-state lifetimes (τ), the relative weights of the exponential
curve are reported in parentheses. In frozen CH2Cl2 matrixes. Data from ref 11e.
d
e
shift of the emission maxima by comparing the emission
profiles of the neutral Re(I)-tetrazolate complexes of the type
fac-[Re(bpy)(CO)3L] with that of the corresponding solvate
complex fac-[Re(bpy)(CO)3(CH3CN)]+.13a This hypothesis is
further corroborated by TD-DFT computational calculations
(see next section).
In accordance with the energy gap law,17 such a
tremendously improved performance, the progress of which
can be observed by partitioning the addition of triflic acid into
several aliquots (Figure 8 and Figures S10−S13, Supporting
Information), is at first evidenced by considering that the
protonated compounds display quantum yield values (Φ) that
are 4−13 times higher than those of the starting material. Also,
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Figure 6. UV−vis absorption profiles of the protonated fac-[Re(N∧N)(CO)3TphH]+ complexesred traces; N∧N = bpy (left), N∧N = phen
(right)compared to those of the corresponding neutral precursors (black traces).
Figure 7. Protonation−deprotonation scheme (top) of fac-[Re(N∧N)(CO)3L]-type complexes and (bottom) images of the cuvettes containing the
starting fac-[Re(phen)(CO)3Tph] (left) the protonated fac-[Re(phen)(CO)3TphH]+ (right) and an the intermediate mixture of the two complexes
(middle). λexc = 365 nm.
Figure 8. Steady-state emission spectra showing the blue shift and the increase of emission intensity occurring upon the transformation of fac-
[Re(bpy)(CO)3Tph] (left) and fac-[Re(phen)(CO)3Tph] (right), denoted as [Re], into the corresponding protonated species, denoted as [ReH]+.
a quite similar result is deduced from the interpretation of the
time-resolved analysis, that again enlightens the elongation of
lifetime fitting decays (τ) of the phosphorescent emissions on
going from the neutral species (relative to air-equilibrated
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Inorganic Chemistry
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samples, τ ranges from 85 to 107 ns for the bpy-containing
complexes or from 268 to 382 ns for the phen-based ones) to
the corresponding protonated complexes (τ of bpy complexes
spans between 595 and 655 ns, whereas τ spans between 1.3
and 1.8 μs for the phen complexes). Again, the emissions that
are displayed by the new protonated species are sensitive to the
presence of oxygen, and their originating from an excited state
reported for Ir(PyrTz), with the only difference being
represented by the pronounced improvement of the quantum
yield values of the couple FIrN4/[FIrN4H]+ with respect to
that observed in the cases of the nonfluorinated complexes
Ir(PyrTz) and [Ir(PyrTzH)]+ (Figure 10 and Table 5). It is
important to note that, apart from the red shift of the emission,
protonation likely causes significant changes in the nature of
the emitting excited states of Ir(III) tetrazolate complexes.
Upon protonation, the vibronically structured emission profiles
of Ir(PyrTz) and FIrN4, which reflect the presence of closely
3
with prevalent MLCT character is suggested by the blue shift
of the emission maxima that is observed from the same samples
frozen at 77 K (Table 4 and Figures S14−S16, Supporting
Information).
3
3
spaced LC and MLCT emissive states, turn to broad and
featureless emission spectra, which are more typical of pure CT
states. This behavior might be explained in consideration of the
reduction or total loss of the 3LC contribution in the
composition of the emitting excited states, which takes place
on going from the neutral starting complex to the cationic
product. In addition, the variation of the nature of the emitting
excited states that occurs upon protonation of both Ir(PyrTz)
and FIrN4 can be also experimentally deduced from the
comparison of the emission profiles obtained at room
temperature with those of the same complexes frozen at 77
K (Table 5 and Figures S19 and S20, Supporting Information).
It is indeed possible to observe how the rigidochromic blue
shift of the emission maxima, which is typical for MLCT-based
excited states, was more evident for the cationic protonated
complexes [Ir(PyrTzH]+ and [FIrN4H]+ (Figure S20,
Supporting Information) than that observed in the cases of
the corresponding neutral precursors (Figure S19, Supporting
Information). However, these considerations are supported by
computational calculations (vide infra), the results of which also
indicate that the tetrazolate ligand is the main contributor to
the LUMO-type orbitals of the protonated complex.
As might be expected for such reactions, the protonated
compounds can be reconverted to the corresponding initial
neutral complexes by treatment with a base, e.g., triethylamine
(Figure 7). Importantly, such behavior introduces the
possibility of reversibly modulating the luminescent features
of neutral Re(I) tetrazolate complexes via a protonation−
deprotonation regime.
These results prompted us to determine whether such a
reversible modulation of the luminescence performances might
be regarded as a general feature of luminescent metal
tetrazolate complexes. To investigate the generality of this
behavior, we first took into consideration the protonation of
one of the cyclometalated Ir(III)-tetrazolate complexes that we
have reported previously,12a namely, Ir(PyrTz); see Table 5,
Figure 9, and Figure S17, Supporting Information.
Finally, our investigation was completed with the analysis of
the influence played by the protonation of a Ru(II)-based metal
tetrazolate complex such as [Ru(PyrTz)]+ (Table 5, Figure 11,
and Figures S22 and S23, Supporting Information). As we
reported earlier,11e this Ru(II) complex, when excited at 460
nm, displays a typically MLCT-shaped broad emission profile
centered at λmax = 653 nm. In sharp contrast with what we
observed in the case of the methylation of the same
substrate,11e this radiative process is completely quenched
upon protonation (Figure 11). A similar behavior might be
attributed to the occurrence in the protonated complex
3
[Ru(bpy)2(PyrTzH)]2+ of thermally populated MC excited
states or, more likely, to the shift of the MLCT-centered
emission toward the near-infrared (NIR) region, the presence
of which cannot be detected, in agreement with the predictions
of the energy gap law.17 Unfortunately, by now it has not been
possible to circumstantiate these attributions by means of TD-
DFT calculations, whose results are not yet decisive. However,
even though the reasons for such an apparently anomalous
quenching phenomenon are not yet fully elucidated, it is
important to note that, as a very important and common
feature of all the other metal-tetrazolate complexes described
herein, the emission of light from the Ru(II)-tetrazole complex
[Ru(bpy)2(PyrTzH)]2+ can be experimentally restored upon its
treatment with one molar equivalent of triethylamine, thereby
leading to the re-formation of the starting Ru(II)-tetrazolate
species [Ru(bpy)2(PyrTz)]+ (Figure 11).
Figure 9. Protonation−deprotonation scheme (top) of Ir(III)-
tetrazolate complexes and (bottom) images of the cuvettes containing
the starting FIrN4 (left) and the protonated [FIrN4H]+ (right). λexc
=
365 nm.
As can be seen in Figures 9 and 10, the blue-green emitting
Ir(III) tetrazolate neutral complex Ir(PyrTz) can be gradually
transformed into the corresponding protonated species [Ir-
(PyrTzH)]+, which displays an equally intense and red-shifted
emission, following a trend that is quite similar to the one we
previously observed for the methylation of the same
complex.12a Again, the proton-induced modulation is fully
reversible (Figure 9). An analogous effect is observed when
performing the same protonation−deprotonation reactions
onto the fluorinated Ir(III) tetrazolate complex that is usually
denoted as FIrN4.18 Also in this case, protonation red shifts the
sky-blue emission of the latter species to the same extent as that
TD-DFT Calculations. To further support the interpreta-
tion of the photophysical results, the energetics and absorption
spectra of the complexes were simulated with time-dependent
density functional theory using GAUSSIAN09.19 It must be
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Figure 10. Steady-state emission spectra showing the changes in the emission profiles of FIrN4 (left) and Ir(PyrTz) (right) occurring upon their
transformation to [FIrN4H]+ and [Ir(PyrTzH)]+, respectively.
Figure 11. [Ru(bpy)2(PyrTz)]+: protonation−deprotonation procedure (top) and graphics showing the quenching of the emission occurring upon
transformation of [Ru(bpy)2(PyrTz)]+, [Ru]+, into the protonated [Ru(bpy)2(PyrTzH)]2+, [RuH]2+, (bottom).
noted that for the fac-[Re(bpy)(CO)3TphH]+ complex, single
crystals suitable for X-ray diffraction analysis could not be
obtained. However, the TD-DFT calculations of this species
were carried out by assuming that the protonation trend was
the same as the other protonated Re(I) complexes, for which
X-ray structures were available. According to our previous
studies, the lowest energy excited states for the neutral rhenium
complexes were characterized by an MLCT nature, partially
mixed with LLCT character (MLLCT).13a,b For the protonated
rhenium species investigated here, the lowest energy excited
state seems to originate predominantly from HOMO−n →
LUMO transitions, where n = 0−2 (Figures 12 and 13 and
Supporting Information Figures S24−S35 and corresponding
Tables S4−S9). Importantly, in this case, the contribution from
the tetrazole π system in the HOMO−n orbitals is lost and they
are exclusively composed of 5d orbitals of the Re center. On the
other hand, as expected, the LUMO orbital is localized on the
diimine ligand. Therefore, the lowest energy excited state is
assigned to an MLCT process. The decrease in electron density
experienced by the tetrazolate ring upon protonation indirectly
causes the stabilization of the HOMO−n orbitals on the Re
center. The high-energy transition seen in the absorption
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Figure 12. Localization of the HOMO and LUMO orbitals for the three fac-[Re(phen)(CO)3LH]+ complexes.
Figure 13. Localization of the HOMO and LUMO orbitals for the three fac-[Re(bpy)(CO)3LH]+ complexes.
spectra can be assigned to a mixture of LLCT and π−π* LC
transitions.
where n = 0−1 and m = 0−3 (Figure 14 and Supporting
Information Figures S38 and S39 and Table S11). This
indicates that the lowest energy transitions possess mainly
MLCT and LLCT character, with a significant reduction in the
contribution from the LC transition. This again supports the
transition from a structured emission from the neutral FIrN4
complex to a broad structureless emission upon protonation.
In order to provide a general picture of the behavior of these
two classes of tetrazolate complexes, the energies of the frontier
molecular orbitals for fac-[Re(phen)(CO)3Tph] and FIrN4
have been plotted along with their respective protonated
complexes (Figure 15). In the case of the Re complex, it is
apparent how the protonation of the tetrazole ring causes a
strong stabilization of the HOMO orbital by indirectly reducing
the electron density on the Re center. On the other hand, the
LUMO localized on the phen ligand is only marginally affected.
The orbital contours of the neutral and protonated complexes
also highlight how the lowest excited state changes its character
from MLLCT to MLCT upon protonation. In the case of the Ir
complex, the tetrazole ring is directly involved in the
composition of the LUMO orbital; hence the protonation
The neutral Ir(PyrTz) has been calculated previously and
supports the assignment of the lowest energy transitions
12b
3
3
possessing a mixture of LC and MLCT character.
The
lowest excited state for the protonated species [Ir(PyrTzH)]+
appears to originate from predominantly HOMO → LUMO+m
transitions, where m = 0−2 (Figure 14 and Supporting
Information Figures S36−S37 and Table S10). This confirms
that the lowest excited state is composed mainly of transitions
of an MLCT and LLCT nature. There is also a small
contribution from the LC, but this reduced contribution in
comparison to the neutral analogue can explain the shift to a
broad and structureless emission upon protonation. The lowest
energy transitions for the FIrN4 complex appear to originate
from HOMO → LUMO+m transitions, where m = 0−2
(Figure 14). This supports the assignment of the lowest excited
state to be predominantly 3MLCT and 3LC in character, with a
small contribution from LLCT. In the corresponding
[FIrN4H]+ complex, the lowest energy transitions appear to
originate from primarily HOMO−n → LUMO+m transitions,
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Figure 14. Localization of the HOMO and LUMO orbitals for the [Ir(PyTzH)]+, FIrN4, and [FIrN4H]+ complexes.
Figure 15. Calculated energy levels and orbital contours for the HOMO and LUMO orbitals of the fac-[Re(phen)(CO)3Tph] and FIrN4 and their
protonated versions obtained from the TD-DFT calculations. The energies of the Kohn−Sham HOMO orbitals for the nonprotonated and
protonated complexes have been positioned by aligning the lowest energy orbitals that are not perturbed by the protonation.
causes its stabilization with consequent reduction in the
HOMO−LUMO gap. As a consequence, the ligand-centered
character of the excited state is lost, as it can be deduced from
the analysis of the respective orbital contours.
from neutral Re(I) tetrazolate complexes as the result of their
conversion into the corresponding protonated cationic
derivatives. This perturbation, which might be properly
described as a “luminescence boosting reaction”, can be
efficiently removed by the addition of a base to the protonated
complexes, taking the system back to the initial stage. A quite
similar variation of the luminescent performances, even if to a
less “dramatic” extent, occurs in the case of Ir(III) tetrazolate
complexes, the luminescence features of which can be again
reversibly modulated by the means of the same protonation−
deprotonation mechanism. Interestingly, the luminescence
modulation of these Ir(III) complexes is not just a matter of
CONCLUSIONS
■
Within the framework of our studies about the reactivity of
metal tetrazolate complexes, we have investigated the proton-
induced reversible modulation of the luminescence properties
of fac-tricarbonyl diimine Re(I) tetrazolates. In particular, we
have shown that by protonation reaction it was possible to blue
shift and dramatically increase the intensity of light emission
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monochromators, and a Peltier-cooled Hamamatsu R928P photo-
multiplier tube (185−850 nm). Emission and excitation spectra were
corrected for source intensity (lamp and grating) and emission spectral
response (detector and grating) by a calibration curve supplied with
the instrument. The wavelengths for the emission and excitation
spectra were determined using the absorption maxima of the metal-to-
ligand charge transfer (MLCT) transition bands (emission spectra)
and at the maxima of the emission bands (excitation spectra).
According to the approach described by Demas and Crosby,20
luminescence quantum yields (Φem) were measured in optically dilute
solutions (OD < 0.1 at excitation wavelength) obtained from
absorption spectra on a wavelength scale [nm] and compared to the
reference emitter by the following equation:21
shifting the emission color and/or varying the intensity of the
radiative processes, but it involves also the substantial change of
the nature of the emitting excited states, which reversibly passes
from closely spaced 3LC/3MLCT combination (neutral
3
3
species) to an admixture of MLCT and LLCT-type excited
states (as for the protonated complexes). Yet a different
behavior is displayed by a polypyridyl Ru(II) tetrazolate
complex such as [Ru(bpy)2L]+, for which the application of
the protonation−deprotonation reaction’s protocol causes the
reversible ON−OFF switching of the emissive performances. In
all cases, the presence of such pronounced electrophile
sensitivity reflects the important role played by the tetrazolate
ligands in determining the extent of the HOMO−LUMO gap.
In general, these findings might be quite important for further
widening the application perspectives of metal tetrazolate
complexes. Indeed, the chance of modulating the emission
color in connection with the variation of the charge of the
complexes involves the presence of species that likely display
different solubility in aqueous solvents. If the color change
would occur in a biologically useful pH range (6−8), both
Ir(III) and, particularly, Re(I) tetrazolate complexes might have
all the characteristics for behaving as imaging and/or sensing
agents. In this context, studies about the influence of pH on the
luminescence behavior and the efficiency of cell uptake of
luminescent metal tetrazolate complexes are currently being
undertaken.
2
⎡
⎤
⎥
⎦
⎡
⎤⎡
⎤
⎡
⎤
Ar(λr) Ir(λr) nx
D
D
r
x
⎢
Φ = Φ⎢
⎥⎢
A (λ ) I (λ )
⎥
⎢
⎣
⎥
⎦
x
r
2
⎣
⎦⎣
⎦ n
⎣
x
x
x
x
r
where A is the absorbance at the excitation wavelength (λ), I is the
intensity of the excitation light at the excitation wavelength (λ), n is
the refractive index of the solvent, D is the integrated intensity of the
luminescence, and Φ is the quantum yield. The subscripts r and x refer
to the reference and the sample, respectively. The quantum yield
determinations were performed at identical excitation wavelengths for
the sample and the reference, therefore canceling the I(λr)/I(λx) term
in the equation. All the Re(I) complexes were measured against an
ethanol solution of rhodamine 101 used as reference (Φr = 1),22 while
quinine bisulfate in 1.0 N sulfuric acid was used as reference (Φr =
0.546)23 for the Ir(III) complexes. Emission lifetimes (τ) were
determined with the single photon counting technique (TCSPC) with
the same Edinburgh FLSP920 spectrometer using pulsed picosecond
LEDs (EPLED 295 or EPLED 360, fhwm <800 ps) as the excitation
source, with repetition rates between 1 kHz and 1 MHz, and the
above-mentioned R928P PMT as detector. The goodness of fit was
assessed by minimizing the reduced χ2 function and by visual
inspection of the weighted residuals. To record the 77 K luminescence
spectra, the samples were put in quartz tubes (2 mm diameter) and
inserted in a special quartz dewar filled with liquid nitrogen. The
solvent (dichloromethane) used in the preparation of the solutions for
the photophysical investigations was of spectrometric grade. Degassed
solutions were prepared by gently bubbling argon gas into the
prepared sample for 15 min before measurement. Experimental
uncertainties are estimated to be 8% for lifetime determinations,
20% for quantum yields, and 2 and 5 nm for absorption and
emission peaks, respectively.
EXPERIMENTAL SECTION
■
General Considerations. All the reagents and solvents were
obtained commercially (e.g., Aldrich) and used as received without any
further purification, unless otherwise specified. The preparation of the
starting Ir(III) complexes, namely, Ir(PyrTz)12a and FIrN4,16 and the
Ru(II) species [Ru(PyrTz)][PF6]11e was accomplished by following
methods reported in the literature. All the reactions were carried out
under an argon atmosphere following Schlenk protocols. Where
required, the purification of the Re complexes was performed via
column chromatography with the use of neutral alumina as the
stationary phase. ESI-mass spectra were recorded using a Waters ZQ-
4000 instrument (ESI-MS, acetonitrile as the solvent). IR spectra were
recorded as dichloromethane (DCM) solutions, using a NaCl (5 mm)
disc on a Perkin-Elmer Spectrum 2000 FT-IR spectrometer. Nuclear
magnetic resonance spectra (consisting of H and 13C experiments)
1
COMPUTATIONAL CALCULATIONS
were always recorded using a Varian Mercury Plus 400 instrument
(1H, 400.1; 13C, 101.0 MHz) at room temperature. 1H and 13C
chemical shifts were referenced to residual solvent resonances. With
the exception of the new complex fac-[Re(bpy)(CO)3Tcya], the
spectroscopic data of the neutral Re(I) complexes fac-[Re(N∧N)-
(CO)3L], where N∧N is bpy or phen, L = Tph, Tbdz,13a and fac-
[Re(phen)(CO)3Tcya],13c have been described previously. However,
for comparison purpose, their ESI-MS, IR, and NMR data have also
■
The TD-DFT calculations were performed using the B3LYP
functional,24 the Stuttgart-Dresden effective core potential for Re,25
and the 6-311++G** basis set for the other atoms. The presence of
the solvent was then mimicked by using the PCM implicit solvation
model26 with parameters appropriate for dichloromethane.
Synthesis. Warning! Tetrazole derivatives are used as components for
explosive mixtures.16 In this lab, the reactions described here were only
run on a few grams’ scale and no problems were encountered.
However, great caution should be exercised when handling or heating
compounds of this type.
1
been reported herein. It has to be noted that the analysis of the H
NMR spectra of the protonated Re(I) complexes indicates the
presence of tiny but detectable amounts of decomposition byproducts
(see Supporting Information, Figures S2−S7), which likely derive from
tetrazole displacement processes that could be likely promoted by the
addition of a slight excess of triflic acid to the complexes prior to the
preparation of the samples. However, the contamination of the desired
product was never found to be higher than ca. 8−10% (as in the
batches containing the complexes fac-[Re(N∧N)(CO)3TphH]+; see
Supporting Information, Figures S6 and S7).
The formation of the tetrazolate anions [Tph]−, [Tcya]−, and
[Tbdz]− was achieved by the addition of equimolar amounts of
triethylamine to a suspension of the neutral 5-substituted tetrazoles in
absolute ethanol (5 mL). The resulting pale yellow solutions were
used without any further purification.
General Procedure for the Preparation of the Neutral fac-
[Re(N∧N)(CO)3L]-Type Complexes. A 0.100 g amount of fac-
∧
∧
Relative to the description of the 1H NMR spectra (see further on),
the atom numbering always refers to Scheme 2.
Photophysics. Absorption spectra were recorded at room
temperature using a Perkin-Elmer Lambda 35 UV/vis spectrometer.
Uncorrected steady-state emission and excitation spectra were
recorded on an Edinburgh FLSP920 spectrometer equipped with a
450 W xenon arc lamp, double excitation and single emission
[Re(NN)(CO)3Br] (0.20 mmol for N N = bpy; 0.19 mmol if N N =
phen) was dissolved in 20 mL of an ethanol/water mixture (3:1 v/v)
under an argon atmosphere. A 5.0 mL portion of an ethanol/water
(3:1 v/v) solution containing 1.5 equiv of the appropriate tetrazolate
salt was added dropwise. Once the addition was completed, the
resulting suspension was stirred at the reflux temperature for 20 h.
After this time, the mixture was cooled to rt and filtered through a
̂
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Inorganic Chemistry
Article
glass frit, affording the desired complexes as a yellow microcrystalline
powder. In most cases, the product complexes did not require any
further purification process, the exceptions being fac-[Re(bpy)-
(CO)3Tbdz] and fac-[Re(phen)(CO)3Tcya]. These latter compounds
were obtained as the second fractions upon performing alumina-filled
column chromatographies using acetonitrile as the eluent.
fac-[Re(bpy)(CO)3Tph]. Yield: 0.072 g, 63%. ESI-MS (m/z) = 595
[M + Na]+. IR (ν, cm−1, CH2Cl2, rt): 2029 s (CO, A′(1)), 1924 s br
(CO, A′(2)/A″), 1606 w (tetrazole CN). 1H NMR (δ, ppm,
acetone-d6): 9.25 (2H, d, J = 5.2 Hz, H2,2′), 8.69 (2H, d, J = 8.0 Hz,
−50 °C for 30 min, the mixture was left to stir overnight at rt. The
solvent was then removed by rotary evaporation, affording generally
oily yellow, i.e., Re(I) and Ir(III), or red, as for Ru(II), residues that
were identified as the expected protonated complexes.
fac-[Re(phen)(CO)3TphH][SO3CF3]. Yield: 0.051 g, 82%. ESI-MS
(m/z) = 597 [M − SO3CF3]+; 149 [SO3CF3]−. IR (ν, cm−1, CH2Cl2,
rt): 2039 s (CO, A′(1)), 1936 br (CO, A′(2)/A″), 1606 w (tetrazole
CN). 1H NMR (δ, ppm, acetone-d6): 9.75 (2H, d, J = 4.8 Hz, H2,2′),
9.07 (2H, d, J = 8.0 Hz, H4,4′), 8.37 (2H, s, phen H5,5′), 8.28−8.24
(2H, m, phen H3,3′), 7.69 (2H, d, J = 7.6 Hz, Hortho), 7.56−7.54 (1H,
m, Hpara), 7.43−7.39 (2H, m, Hmeta). 13C NMR (δ, ppm, acetone-d6):
197.0, 156.4, 156.2, 148.8, 141.8, 134.1, 132.7, 131.0, 129.6, 128.8,
128.5. Crystals suitable for X-ray analysis were obtained by slow
diffusion of diethyl ether into a solution of the complex in
dichloromethane and a few drops of dilute triflic acid solution. By
using this procedure, two different crystals of the same complex were
obtainedfac-[Re(phen)(CO)3TphH][CF3SO3], C23H14F3N6O6ReS,
and fac-[Re(phen)(CO)3 TphH][CF3 SO3 ]·0. 25Et2 O,
C24H16.5F3N6O6.25ReS, respectivelywhich are distinguished by the
presence of diethyl ether in the unit cell. Anal. Calcd for
C23H14F3N6O6ReS (745.660): C, 37.04; H, 1.89; N, 11.27. Found:
C, 37.15; H, 1.80; N. 11.09.
H
5,5′), 8.35 (2H, t, J = 7.2 Hz, H4,4′), 7.82−7.79 (4H, m, H3,3′ and
Hortho), 7.32−7.24 (3H, m, Hmeta and Hpara). 13C NMR (δ, ppm,
acetone-d6): 163.7, 157.5, 154.7, 141.2, 131.5, 129.2, 128.9, 128.7,
126.8, 124.7.
fac-[Re(phen)(CO)3Tph]. Yield: 0.085 g, 75%. ESI-MS (m/z) = 619
[M + Na]+. IR (ν, cm−1, CH2Cl2, rt): 2029 s (CO, A′(1)), 1922 s br
(CO, A′(2)/A″), 1606 w (tetrazole CN). 1H NMR (δ, ppm, acetone-
d6): 9.65 (2H, d, J = 4.8 Hz, H2,2′), 8.96 (2H, d, J = 8.2 Hz, H4,4′), 8.30
(2H, s, H5,5′), 8.19−8.15 (2H, m, H3,3′), 7.63 (2H, d, J = 7.2 Hz,
Hortho), 7.22−7.20 (3H, m, 2Hmeta and Hpara). 13C NMR (δ, ppm,
acetone-d6): 163.4, 155.1, 148.3, 140.3, 131.7, 131.3, 129.1, 128.9,
128.7, 127.4, 126.6.
fac-[Re(bpy)(CO)3Tbdz]. The complex was purified via alumina-
filled column chromatography using a 100% acetonitrile solvent
system as eluent (second fraction, yellow). Yield: 0.067 g, 56%. ESI-
MS (m/z) = 623 [M + Na]+. IR (ν, cm−1, CH2Cl2, rt): 2029 s (CO,
A′(1)), 1922 br (CO, A′(2)/A″), 1699 s (aldehyde CO), 1607 w
(tetrazole CN). 1H NMR (δ, ppm, acetone-d6): 10.01 (1H, s,
−CHO), 9.27 (2H, d, J = 5.5 Hz, H2,2′), 8.71 (2H, d, J = 8.4 Hz, H5,5′),
8.37 (2H, t, J = 7.8 Hz, H4,4′), 8.01 (2H, d, J = 8.0 Hz, Hortho), 7.87
(2H, d, J = 8.4 Hz, Hmeta), 7.83 (2H, t, J = 5.6 Hz, H3,3′). 13C NMR (δ,
ppm, acetone-d6): 192.4, 163.0, 157.5, 154.7, 141.3, 137.2, 136.7,
130.6, 128.7, 127.1, 124.7.
fac-[Re(phen)(CO)3Tbdz]. Yield: 0.097g, 82%. ESI-MS (m/z) = 647
[M + Na+]. IR (ν, cm−1, CH2Cl2, rt): 2029 s (CO, A′(1)), 1923 br
(CO, A′(2)/A″), 1699 s (aldehyde CO), 1610 w (tetrazole CN).
1H NMR (δ, ppm, acetone-d6): 9.96 (1H, s, −CHO), 9.67 (2H, d, J =
5.2 Hz, H2,2′), 8.98 (2H, d, J = 8.4 Hz, H4,4′), 8.32 (2H, s, H5,5′), 8.20−
8.17 (2H, m, H3,3′), 7.84 (2H, d, J = 8.8 Hz, Hmeta), 7.80 (2H, d, J = 8.4
Hz, Hortho). 13C NMR (δ, ppm, acetone-d6): 192.4, 162.8, 155.2, 148.2,
140.4, 137.1, 136.6, 131.7, 130.5, 128.7, 127.4, 127.0.
fac-[Re(bpy)(CO)3Tcya]. Yield: 0.090 g, 75%). ESI-MS (m/z) = 620
[M + Na+]. IR (ν, cm−1, CH2Cl2, rt): 2229 w (CN), 2029 s (CO,
A′(1)), 1923 br (CO, A′(2)/A″), 1606 w (tetrazole CN). 1H NMR
(δ, ppm, acetone-d6): 9.27 (2H, d, J = 5.5 Hz, H2,2′), 8.71 (2H, d, J =
8.40 Hz, H5,5′), 8.37 (2H, t, J = 8 Hz, H4,4′), 7.96 (2H, d, J = 9.2 Hz,
Hortho), 7.83−7.79 (2H, m, H3,3′), 7.72 (2H, d, J = 7.5 Hz, Hmeta). 13C
NMR (δ, ppm, acetone-d6): 162.5, 157.4, 154.7, 141.3, 135.5, 133.3,
128.7, 127.3, 124.7, 119.3, 112.3. Crystals suitable for X-ray analysis
(identified as fac-[Re(bpy)(CO)3(Tcya)], C21H12N7O3Re) were
obtained by slow diffusion of diethyl ether into a solution of the
complex in dichloromethane. Anal. Calcd for C21H12N7O3Re
(596.570): C, 42.28; H, 2.03; N, 16.43. Found: C, 42.25; H, 1.88;
N, 16.26.
fac-[Re(phen)(CO)3Tcya]. The complex was purified via alumina-
filled column chromatography using pure acetonitrile as the eluent
(second fraction, yellow). Yield: 0.050 g, 42%. ESI-MS (m/z) = 644
[M + Na+]. IR (ν, cm−1, CH2Cl2, rt): 2229 w (CN), 2030 s (CO,
A′(1)), 1923 br (CO, A′(2)/A″), 1606 w (tetrazole CN). 1H NMR
(δ, ppm, acetone-d6): 9.67 (2H, d, J = 4.0 Hz, H2,2′), 8.97 (2H, d, J =
7.2 Hz, H4,4′), 8.31 (2H, s, H5,5′), 8.20−8.16 (2H, m, H3,3′), 7.81 (2H,
d, J = 6.4 Hz, Hortho), 7.65 (2H, d, J = 4.0 Hz, Hmeta). 13C NMR (δ,
ppm, acetone-d6): 162.4, 155.2, 148.2, 140.4, 135.3, 133.2, 131.7,
128.7, 127.4, 127.1, 119.3, 112.2.
fac-[Re(bpy)(CO)3TphH][SO3CF3]. Yield: 0.045 g, 70%. ESI-MS (m/
z) = 573 [M − SO3CF3]+; 149 [SO3CF3]−. IR (ν, cm−1, CH2Cl2, rt):
2039 s (CO, A′(1)), 1936 br (CO, A′(2)/A″), 1606 w (tetrazole C
1
N). H NMR (δ, ppm, acetone-d6): 9.31 (2H, d, J = 5.2 H6,6′), 8.78
(2H, d, J = 8.4 Hz H3,3′), 8.43−8.39 (2H, m, H4,4′), 7.90−7.83 (4H, m,
H5,5′ and Hortho), 7.54−7.49 (3H, m, Hmeta and Hpara). 13C NMR (δ,
ppm, acetone-d6): 196.8, 194.3, 159.2, 157.5, 155.0, 141.9, 132.4,
130.1, 129.1, 127.9, 125.4, 123.3. Anal. Calcd for C21H14F3N6O6ReS
(721.640): C, 34.95; H, 1.96; N, 11.64. Found: C, 35.20; H, 2.09; N,
11.77.
fac-[Re(phen)(CO)3TbdzH][SO3CF3]. Yield: 0.042 g, 68%. ESI-MS
(m/z) = 625 [M − SO3CF3]+; 149 [SO3CF3]−. IR (ν, cm−1, CH2Cl2,
rt): 2040 s (CO, A′(1)), 1938 br (CO, A′(2)/A″), 1709 s (aldehyde
CO), 1607 w (tetrazole CN). 1H NMR (δ, ppm, acetone-d6): 10.04
(1H, s, −CHO), 9.74 (2H, d, J = 5.2 Hz, H2,2′), 9.04 (2H, d, J = 8.2
Hz, H4,4′), 8.36 (2H, s, H5,5′), 8.26−8.23 (2H, m, H3,3′), 7.95 (2H, d, J
= 8.4 Hz, Hortho), 7.90 (2H, d, J = 8.4 Hz, Hmeta). 13C NMR (δ, ppm,
acetone-d6): 192.3, 155.7, 148.2, 141.0, 139.3, 132.0, 130.9, 128.9,
128.5, 127.7. Crystals suitable for X-ray analysis (identified as fac-
[Re(phen)(CO)3TbdzH][CF3SO3], C24H14F3N6O7ReS) were ob-
tained by slow diffusion of diethyl ether into a solution of the
complex in dichloromethane and a few drops of dilute triflic acid
solution. Anal. Calcd for C24H14F3N6O7ReS (773.670): C, 37.26; H,
1.82; N, 10.86. Found: C, 37.33; H, 1.90; N, 11.12.
fac-[Re(bpy)(CO)3TbdzH][SO3CF3]. Yield: 0.035g, 56%. ESI-MS
(m/z) = 601 [M − SO3CF3]+; 149 [SO3CF3]−. IR (ν, cm−1,
CH2Cl2, rt): 2040 s (CO, A′(1)), 1937 br (CO, A′(2)/A″), 1709 s
(aldehyde CO), 1606 w (tetrazole CN). 1H NMR (δ, ppm, acetone-
d6): 10.11 (1H, s, −CHO), 9.34 (2H, d, J = 5.6 Hz, H6,6′), 8.81 (2H, d,
J = 8.2 Hz, H3,3′), 8.45−8.43 (2H, m, H4,4′), 8.07 (4H, s, Hortho and
Hmeta), 7.91−7.88 (2H, m, H5,5′). 13C NMR (δ, ppm, acetone-d6):
196.4, 192.4, 157.5, 155.1, 154.9, 142.4, 142.1, 139.9, 131.0, 129.2,
129.0, 125.3. Crystals suitable for X-ray analysis (identified as fac-
[Re(bpy)(CO)3TbdzH][CF3SO3], C22H14F3N6O7ReS) were obtained
by slow diffusion of diethyl ether into a solution of the complex in
dichloromethane and a few drops of dilute triflic acid solution. Anal.
Calcd for C22H14F3N6O7ReS (749.651): C, 35.25; H, 1.88; N, 11.21.
Found: C, 35.31; H, 1.92; N 11.30.
fac-[Re(phen)(CO)3TcyaH][SO3CF3]. Yield: 0.039 g, 64%. ESI-MS
(m/z) = 622 [M − SO3CF3]+; 149 [SO3CF3]−. IR (ν, cm−1, CH2Cl2,
rt): 2233 w (CN), 2040 s (CO, A′(1)), 1937 br (CO, A′(2)/A″),
1606 w (tetrazole CN). 1H NMR (δ, ppm, acetone-d6): 9.76 (2H, d,
J = 5 Hz, H2,2′), 9.07 (2H, d, J = 8.4 Hz, H4,4′), 8.37 (2H, s, H5,5′),
8.28−8.25 (2H, m, H3,3′), 7.91 (4H, s, Hmeta and Hortho). 13C NMR (δ,
ppm, acetone-d6): 196.3, 155.8, 148.1, 141.2, 134.1, 132.0, 129.0,
128.9, 127.8, 127.6, 126.8, 118.3, 116.5. Crystals suitable for X-ray
analysis (identified as fac-[Re(phen)(CO)3TcyaH][CF3SO3],
C24H13F3N7O6ReS) were obtained by slow diffusion of diethyl ether
General Procedure for the Protonation of Re(I), Ir(III), and
Ru(II) Tetrazolate Complexes. In a typical procedure,27 0.050 g of
the appropriate Re(I), Ir(III), or Ru(II) metal tetrazolate precursor
was dissolved in 15 mL of dichloromethane. The resulting solution
was cooled to −50 °C, and an excess (1.5 equiv) of HOSO2CF3 (0.124
M solution in dichloromethane) was added. After being maintained at
241
dx.doi.org/10.1021/ic402187e | Inorg. Chem. 2014, 53, 229−243

Inorganic Chemistry
Article
into a solution of the complex in dichloromethane and a few drops of
dilute triflic acid solution. Anal. Calcd for C24H13F3N7O6ReS
(770.672): C, 37.40; H, 1.70; N, 12.72. Found: C, 37.33; H, 1.63;
N, 12.42.
fac-[Re(bpy)(CO)3TcyaH][SO3CF3]. Yield: 0.026 g, 42%. ESI-MS
(m/z) = 598 [M − SO3CF3]+; 149 [SO3CF3]−. IR (ν, cm−1, CH2Cl2,
rt): 2233 w (CN), 2040 s (CO, A′(1)), 1938 br (CO, A′(2)/A″),
1606 w (tetrazole CN). 1H NMR (δ, ppm, acetone-d6): 9.32 (2H, d,
J = 5.4 Hz, H6,6′), 8.78 (2H, d, J = 8.4 Hz, H3,3′), 8.44 (2H, t, J = 8 Hz,
related positions, and the independent image has been refined
isotropically with a 0.25 occupancy factor.
CCDC-943783 (for fac-[Re(bpy)(CO)3Tcya]), -943784 (for fac-
[Re(phen)(CO)3TphH][CF3SO3]), -943785 (for fac-[Re(phen)-
(CO)3TphH][CF3SO3]·0.25Et2O), -943786 (for −[Re(phen)-
(CO)3TcyaH][CF3SO3]), -943787 (for fac-[Re(phen)(CO)3TbdzH]-
[CF3SO3]), -943788 (for fac-[Re(bpy)(CO)3TcyaH][CF3SO3]), and
-943789 (for −[Re(bpy)(CO)3TbdzH][CF3SO3]) contain the
supplementary crystallographic data for this paper. These data can
be obtained free of charge from the Cambridge Crystallographic Data
Centre via www.ccdc.cam.ac.uk/data_request/cif.
H
4,4′), 8.04 (2H, d, J = 8.8 Hz, Hortho), 7.94−7.88 (4H, m, Hmeta and
bpy H5,5′). 13C NMR (δ, ppm, acetone-d6): 157.5, 154.9, 154.1, 141.7,
140.7, 133.7, 129.0, 128.2, 125.0, 118.8, 114.5. Crystals suitable for X-
ray analysis (identified as fac-[Re(bpy)(CO)3TcyaH][CF3SO3],
C22H13F3N7O6ReS) were obtained by slow diffusion of diethyl ether
into a solution of the complex in dichloromethane. Anal. Calcd for
C24H13F3N7O6ReS (746.650): C, 35.39; H, 1.75; N, 13.13. Found: C,
35.31; H, 1.90; N, 13.22.
ASSOCIATED CONTENT
* Supporting Information
■
S
X-ray crystallographic data for the complexes fac-[Re(bpy)-
(CO)3Tcya], fac-[Re(phen)(CO)3TphH][CF3SO3], fac-[Re-
(phen)(CO)3TphH][CF3SO3]·0.25Et2O, fac-[Re(phen)-
(CO)3TcyaH][CF3SO3], fac-[Re(phen)(CO)3TbdzH]-
[CF3SO3], fac-[Re(bpy)(CO)3TcyaH][CF3SO3], and fac-
[Re(bpy)(CO)3TbdzH][CF3SO3] in CIF format. Table of
bonding and angle parameters for fac-[Re(bpy)(CO)3Tcya],
crystal data and collection details for all the X-ray crystal
[FIrN4H][SO3CF3]. Yield: 0.048 g, 80%). ESI-MS (m/z) = 719 [M −
1
SO3CF3]+; 149 [SO3CF3]−. H NMR (δ, ppm, acetonitrile-d3): 8.49
(1H, d, J = 7.6 Hz), 8.12−8.24 (3H, m), 8.01 (1H, d, J = 5.2 Hz), 7.92
(2H, t, J = 7.6 Hz), 7.74 (1H, d, J = 5.6 Hz), 7.66−7.59 (2H, m),
7.13−7.07 (2H, m), 6.72−6.65 (2H, m), 5.75−5.71 (2H, m). Anal.
Calcd for C29H17F7N7O3SIr (868.762): C, 40.09; H, 1.97; N, 11.28.
Found: C, 40.20; H, 2.09; N, 11.39.
[Ir(PyrTzH)][SO3CF3]. Yield: 0.052 g, 85%. ESI-MS (m/z) = 648 [M
− SO3CF3]+; 149 [SO3CF3]−. 1H NMR (δ, ppm, acetonitrile-d3): 8.33
(1H, d, J = 7.6 Hz), 8.02−7.99 (3H, m), 7.80−7.72 (5H, m) 7.61 (1H,
d, J = 4.8 Hz), 7.55 (1H, d, J = 4.8 Hz), 7.32−7.29 (1H, m), 7.01−6.87
(5H, m), 6.83−6.79 (1H, m), 6.33 (1H, d, J = 7.6 Hz), 6.28 (1H, d, J =
7.6 Hz). Anal. Calcd for C29H21F3N7O3SIr (796.800): C, 43.71; H,
2.65; N, 12.30. Found: C, 43.65; H, 2.60; N, 12.60.
1
structures described herein, H NMR spectra of all the Re(I)-
based species, emission spectra recorded at rt and at 77 K, and
computational calculations. This material is available free of
charge via the Internet at http://pubs.acs.org.
AUTHOR INFORMATION
Corresponding Authors
■
[Ru(bpy)2(PyrTzH)][SO3CF3]2. Yield: 0.045 g, 75%. ESI-MS: (m/z)
280 [M]2+; 145 [PF6]−, 149 [SO3CF3]−. 1H NMR (CD3CN, 400
MHz): 8.49 (2H, t, J = 7.2 Hz), 8.44−8.41 (2H, m), 8.35 (1H, d, J =
7.6 Hz), 8.05−7.94 (5H, m), 7.87−7.83 (2H, m), 7.79 (1H, d, J = 5.6
Hz), 7.69 (1H, d, J = 5.2 Hz), 7.62 (1H, d, J = 5.2 Hz), 7.41−7.29
(5H, m) ppm. An accurate determination of the bulk composition by
elemental analysis could not be obtained due to the uncertain nature
of the anionic counterpart, which is likely formed by one triflate
*E-mail: stefano.stagni@unibo.it.
̧
*E-mail: m.massi@curtin.edu.au.
Notes
The authors declare no competing financial interest.
ACKNOWLEDGMENTS
■
M.V.W. and P.J.W. thank Curtin University and the Australian
Government for funding through an APA. M.V.W. also thanks
Boehringer Ingelheim Fonds for the Travel Grant and the
Graduate Women (WA) for the Mary and Elsie Stevens
Scholarship. P.R. thanks the Australian Research Council for
funding his fellowship under the Discovery Program
(DP0986999). P.R. and P.J.W. thank the National Computa-
tional Infrastructure for the provision of computer time. S.M.
−
−
(CF3SO3 ) and one hexafluorophosphate (PF6 ) ion, as can be
observed in the negative ion ESI-MS spectrum reported in Supporting
Information, Figure S23.
X-ray Crystallography. Crystal data and collection details for fac-
[Re(bpy)(CO)3Tcya], fac-[Re(phen)(CO)3TphH][CF3SO3], fac-[Re-
(phen)(CO)3TphH][CF3SO3 ]·0.25Et2O, fac-[Re(phen)-
(CO)3TcyaH][CF3SO3], fac-[Re(phen)(CO)3TbdzH][CF3SO3], fac-
[Re(bpy)(CO)3TcyaH][CF3SO3], and fac-[Re(bpy)(CO)3TbdzH]-
[CF3SO3] are reported in Tables S2 and S3 (Supporting Information).
The diffraction experiments were carried out on a Bruker APEX II
diffractometer equipped with a CCD detector and using Mo Kα
radiation, except fac-[Re(bpy)(CO)3Tcya], for which an Oxford
Diffraction Gemini diffractometer was employed. Data were corrected
for Lorentz polarization and absorption effects (empirical absorption
correction SADABS).28 Structures were solved by direct methods and
̀
thanks the Italian Ministero dell’Istruzione, Universita e Ricerca
(M.I.U.R.)(PRIN 2009) for a Post-Doc grant. The Toso
Montanari Foundation and the Australian Research Council are
gratefully acknowledged for the financial support.
REFERENCES
■
refined by full-matrix least-squares based on all data using F2.29
H
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using a riding model, except N-bonded hydrogens, which were located
in the Fourier map and refined isotropically using the 1.2-fold Uiso
value of the parent N atom; N−H distances were restrained to 0.89 Å
(s.u. 0.02). All non-hydrogen atoms were refined with anisotropic
displacement parameters. Similar U restraints were applied to the C,
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[Re(bpy)(CO)3TcyaH][CF3SO3], and fac-[Re(bpy)(CO)3TbdzH]-
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−
[CF3SO3] (s.u. 0.01). The O and F atoms of the CF3SO3 anion
fac-[Re(phen)(CO)3TphH][CF3SO3], fac-[Re(phen)(CO)3TphH]-
[CF3SO3]·0.25Et2O, fac-[Re(phen)(CO)3TcyaH][CF3SO3], fac-[Re-
(phen)(CO)3TbdzH][CF3SO3], and fac-[Re(bpy)(CO)3TbdzH]-
[CF3SO3] were restrained to an isotropic-like behavior (ISOR line
in SHELXL; s.u. 0.01). The Et2O molecule in fac-[Re(phen)-
(CO)3TphH][CF3SO3]·0.25Et2O is disordered over four symmetry-
242
dx.doi.org/10.1021/ic402187e | Inorg. Chem. 2014, 53, 229−243

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