Dual fluorescence from an Isonido ReIII rhenacarborane phosphine complex, [7,10-μ-H-7-CO-7,7-(PPh3)2-isonido-7,8,9- ReC2B7H9]

Article abstract of DOI:10.1021/ic061071n

The complex [7,10-μ-H-7-CO-7,7-(PPh₃)₂-isonido-7, 8,9-ReC₂B₇H₉] has been synthesized by treatment of the complex salt [NHMe₃][3,3-Cl₂-3,3-(CO) ₂-closo-3,1,2-ReC₂B₉H₁₁] with PPh₃ in refluxing THF (tetrahydrofuran) and isolated as intensely colored orange-red microcrystals. Spectroscopic NMR and IR data have suggested that the product has a highly asymmetric structure with two inequivalent PPh₃ ligands and a single CO ligand. Measurement of ¹¹B NMR spectra in particular have indicated seven distinct boron vertexes, although the resulting cage degradation by removal of two BH vertexes was confirmed only following X-ray crystallographic analysis, which revealed the pentadecahedral isonido-7,8,9-ReC₂B₇ architecture. The ¹¹B NMR resonances span an enormous chemical shift range (Δδ = 113), and this appears to be a direct consequence of the deshielding of the boron vertex directly opposite the quadrilateral ReCCB aperture. The new complex has been shown by electrochemical measurements to undergo a reversible one-electron oxidation. Digitally simulated cyclic voltammograms support a proposed square scheme (E_1/2 = 0.58, 0.69 V vs ferrocene) involving a reversible isonido-closo transition of the metallacarborane cage. Most unusually for a metallacarborane complex, ambient temperature solutions in CH₂Cl ₂ and DMF have been shown to be intensely turquoise-blue fluorescent (λ_em = 442 nm, Φ= 0.012). Fluorescence spectroscopy measurements in MeTHF (2-methyltetrahydrofuran) glass at 77 K have indicated that the likely cause of such a broad emission is dual fluorescence (λ_em = 404,505 nm), with both emissions displaying vibronic structure. Following excited-state lifetime decay analysis, the emissive behavior has been accredited to metal-perturbed ¹IL states, with the lower energy emission arising from a slight geometric distortion of the initially excited complex.

Full text of DOI:10.1021/ic061071n

Inorg. Chem. 2006, 45, 7339−7347
Dual Fluorescence from an Isonido ReIII Rhenacarborane Phosphine
Complex, [7,10- -H-7-CO-7,7-(PPh3)2-isonido-7,8,9-ReC2B7H9]
µ
Steven W. Buckner,† Matthew J. Fischer,† Paul A. Jelliss,*,† Rensheng Luo,‡ Shelley D. Minteer,†
Nigam P. Rath,‡ and Aleksander Siemiarczuk§
Department of Chemistry, Saint Louis UniVersity, St. Louis, Missouri 63103, Department of
Chemistry and Biochemistry, UniVersity of Missouri-St. Louis, St. Louis, Missouri 63128, and
Fast Kinetics Application Laboratory, Photon Technology International (Canada), Inc.,
347 Consortium Court, London, Ontario, Canada N6E 2S8
Received June 14, 2006
The complex [7,10-µ-H-7-CO-7,7-(PPh3)2-isonido-7,8,9-ReC2B7H9] has been synthesized by treatment of the complex
salt [NHMe3][3,3-Cl2-3,3-(CO)2-closo-3,1,2-ReC2B9H11] with PPh3 in refluxing THF (tetrahydrofuran) and isolated as
intensely colored orange-red microcrystals. Spectroscopic NMR and IR data have suggested that the product has
a highly asymmetric structure with two inequivalent PPh3 ligands and a single CO ligand. Measurement of 11B
NMR spectra in particular have indicated seven distinct boron vertexes, although the resulting cage degradation by
removal of two BH vertexes was confirmed only following X-ray crystallographic analysis, which revealed the
pentadecahedral isonido-7,8,9-ReC2B7 architecture. The 11B NMR resonances span an enormous chemical shift
range (∆δ ) 113), and this appears to be a direct consequence of the deshielding of the boron vertex directly
opposite the quadrilateral ReCCB aperture. The new complex has been shown by electrochemical measurements
to undergo a reversible one-electron oxidation. Digitally simulated cyclic voltammograms support a proposed square
scheme (E1
)
0.58, 0.69 V vs ferrocene) involving a reversible isonido
cage. Most unusually for a metallacarborane complex, ambient temperature solutions in CH2Cl2 and DMF have
been shown to be intensely turquoise-blue fluorescent (λem 442 nm, Φ ) 0.012). Fluorescence spectroscopy
measurements in MeTHF (2-methyltetrahydrofuran) glass at 77 K have indicated that the likely cause of such a
−closo transition of the metallacarborane
/
2
)
broad emission is dual fluorescence (λem
excited-state lifetime decay analysis, the emissive behavior has been accredited to metal-perturbed IL states, with
)
404, 505 nm), with both emissions displaying vibronic structure. Following
1
the lower energy emission arising from a slight geometric distortion of the initially excited complex.
Introduction
is merely an isolobal replacement for the simple BH vertex.2
Irrespective of one’s viewpoint, an expanding array of
aesthetically fascinating metallacarborane structures have
been discovered and rationalized (in most cases) using the
Wade-Williams protocol for cage-cluster counting.3 We
report herein a novel isonido-ReC2B7 complex, which
exhibits exceptional optoelectronic properties for this class
of complex. While a range of sandwich and half-sandwich
MC2B9 metallacarboranes have been electrochemically ana-
lyzed,4 reports of luminescence from metallacarborane
complexes are few and far between.5 Our own efforts in this
For 40 or so years, it has been known that carborane cages
can mimic cyclopentadienide ligands in their haptotropic
binding to d-block metal-ligand fragments.1 From the
perspective of the boron chemist, the metal-ligand moiety
* To whom correspondence should be addressed. E-mail: jellissp@slu.edu.
† Saint Louis University.
‡ University of Missouri-St. Louis.
§ Photon Technology International, Inc.
(1) (a) Hosmane, N. S. Pure Appl. Chem. 2003, 75, 1219. (b) Grimes, R.
N. Coord. Chem. ReV. 2000, 200-202, 773. (c) Grimes, R. In
ComprehensiVe Organometallic Chemistry II; Abel, E. W., Stone, F.
G. A., Wilkinson, G., Eds.; Pergamon Press: Oxford, UK, 1995; Vol.
1, Chapter 9. (d) Callahan, K. P.; Hawthorne, M. F. AdV. Organomet.
Chem. 1976, 14, 145. (e) Hawthorne, M. F. Pure Appl. Chem. 1973,
39, 475. (f) Hawthorne, M. F.; Young, D. C.; Andrews, T. D.; Howe,
D. V.; Pilling, R. L.; Pitts, A. D.; Reintjes, M.; Warren, L. F., Jr.;
Wegner, P. A. J. Am. Chem. Soc. 1968, 90, 879.
(2) O’Neill, M. E.; Wade, K. In ComprehensiVe Organometallic Chem-
istry; Wilkinson, G., Abel, E. W., Stone, F. G. A., Eds.; Pergamon
Press: Oxford, UK, 1982; Vol. 1, Section 1.
(3) (a) Wade, K. AdV. Inorg. Chem. Radiochem. 1976, 18, 1. (b) Williams,
R. E. AdV. Inorg. Chem. Radiochem. 1976, 18, 67.
10.1021/ic061071n CCC: $33.50
Published on Web 08/08/2006
© 2006 American Chemical Society
Inorganic Chemistry, Vol. 45, No. 18, 2006 7339

Buckner et al.
Scheme 1. Synthesis of [7,10-µ-H-7-CO-7,7-(PPh3)2-isonido-7,8,9-
ReC2B7H9] (2)
area are just beginning to yield dividends, with results so
far limited to strong phosphorescence at low temperature (77
K) only.6 We nevertheless report surprisingly strong fluo-
rescence from the new isonido-ReC2B7 complex in solution
at ambient temperatures, which, from analysis of emission
characteristics and lifetimes at ambient and liquid nitrogen
temperatures, appears to be anomalously bifurcated.
Figure 1. Molecular geometry of complex 2. Selected bond lengths (Å)
and angles (deg): Re(7)-C(1) 1.924(4), Re(7)-B(3) 2.142(5), Re(7)-C(8)
2.248(4), Re(7)-B(4) 2.357(5), Re(7)-B(2) 2.377(5), Re(7)-B(10) 2.413-
(5), Re(7)-P(1) 2.4507(10), Re(7)-P(2) 2.4625(11), Re(7)-H(7) 1.69(6),
C(8)-C(9) 1.522(7), B(10)-C(9) 1.659(7), C(1)-O(1) 1.156(5); C(1)-
Re(7)-C(8) 109.98(18), C(1)-Re(7)-B(10) 161.82(19), C(8)-Re(7)-
B(10) 63.21(17), C(1)-Re(7)-P(1) 91.67(14), B(3)-Re(7)-P(1) 102.55-
(14), C(8)-Re(7)-P(1) 158.36(12), B(10)-Re(7)-P(1) 96.18(13), C(1)-
Re(7)-P(2) 88.90(13), B(3)-Re(7)-P(2) 152.07(14), C(8)-Re(7)-P(2)
79.40(12), B(2)-Re(7)-P(2) 149.18(14), B(10)-Re(7)-P(2) 105.47(13),
P(1)-Re(7)-P(2) 101.52(4), C(9)-B(10)-Re(7) 92.8(3), O(1)-C(1)-Re-
(7) 177.6(4), C(9)-C(8)-Re(7) 103.5(3), C(8)-C(9)-B(10) 100.5(4).
Results and Discussion
Treatment of the recently reported complex salt [NHMe3]-
[3,3-Cl2-3,3-(CO)2-closo-3,1,2-ReC2B9H11] (1)6a with PPh3
in refluxing THF (tetrahydrofuran) yielded, as one of two
products, the bright orange-red complex [7,10-µ-H-7-CO-
7,7-(PPh3)2-isonido-7,8,9-ReC2B7H9] (2) in low yield (Scheme
1). The second product has not been formally identified yet
but is apparently formed in even lower yield.
coordinating CCBBB face, although deboronation was not
a consequence on this occasion.6a The [NHMe3]+ counterion
could also feasibly act as a source of the base NMe3 under
the conditions of the reaction.
Despite NMR and IR measurements that were straight-
forward in appearance, the identity of complex 2 was not
formally deduced until single crystals were procured for
X-ray crystallographic analysis. The structure is shown in
Figure 1 along with pertinent structural parameters. Most
striking is the excision of two BH vertexes from the starting
material to yield a ReC2B7 cage system. The source of cage
degradation is debatable because PPh3 would not normally
be expected to act as a potent enough base to promote
deboronation. However, such a mechanism may be facilitated
by the marginally elevated +3 oxidation state (vide infra)
of rhenium in compound 1. In this respect, it should be noted
that our own observations of the reactivity of the ReIII-
carborane complex [3-I-3,3,3-(CO)3-closo-3,1,2-ReC2B9H11]
revealed it to be especially susceptible to nucleophilic attack
under mildly basic conditions at the â-B vertex of the
The cage structure of complex 2 is not perfectly deltahe-
dral, with an open quadrilateral face defined by the vertexes
Re(7)C(8)C(9)B(10) and with the opposite corners clearly
nonbonded (Re(7)-C(9) 2.994, C(8)-B(10) 2.446 Å, cf. Re-
(7)-C(8) 2.248(4), C(9)-B(10) 1.659(7) Å). One of these
edges, Re(7)-B(10), is bridged by an endopolyhedral proton
H(7), which was located in the difference Fourier map. The
asymmetry caused by this facial configuration is compounded
by the orientation of the tripodal Re(CO)(PPh3)2 vertex with
respect to the carborane cage. Thus one of the PPh3 ligands
is directly trans (B(3)-Re(7)-P(2) 152.07(14)°) to the boron
atom B(3) of the lower pentagonal belt, while the other lies
approximately in the plane defined by the Re(7)C(8)C(9)B-
(10) face, transoid to the facial carbon C(8) (C(8)-Re(7)-
P(1) 158.36(12)°). The carbonyl ligand is disposed transoid
to the cage B(10) vertex (C(1)-Re(7)-B(10) 161.82(19)°)
and is essentially linear (Re(7)-C(1)-O(1) 177.6(4)°).
Routine PSE (polyhedral skeletal electron) counting
procedures,2,3 with a d7 ML3 Re(CO)(PPh3)2 vertex contribut-
ing 1 PSE, yield a structure prediction of n + 1 closo. The
observed polyhedral distortion, however, leads to the isonido
assignment, contrary to the Wade-Williams formalism. That
said, consideration of formal valency leads us to conclude
that the complex notionally results from the combination of
(4) (a) For a review of the electrochemistry of many prototypical
metallacarboranes and carboranes see: Morris, J. H.; Gysling, H. J.;
Reed, D. Chem. ReV. 1985, 85, 51. (b) Geiger, W. E., Jr.; Smith, D.
E. J. Electroanal. Chem. 1974, 50, 31.
(5) (a) Hawthorne, M. F.; Zink, J. I.; Skelton, J. M.; Bayer, M. J.; Liu,
C.; Livshits, E.; Baer, R.; Neuhauser, D. Science 2004, 303, 1849.
(b) Crespo, O.; Gimeno, M. C.; Jones, P. G.; Laguna, A.; Lo´pez-de-
Luzuriaga, J. M.; Monge, M.; Pe´rez, J. L.; Ramo´n, M. A. Inorg. Chem.
2003, 42, 2061. (c) Bitner, T. W.; Wedge, T. J.; Hawthorne, M. F.;
Zink, J. I. Inorg. Chem. 2001, 40, 5428. (d) Hong, E.; Jang, H.; Kim,
Y.; Jeoung, S. C.; Do, Y. AdV. Mater. 2001, 13, 1094. (e) Calhorda,
M. J.; Crespo, O.; Gimeno, M. C.; Jones, P. G.; Laguna, A.; Lo´pez-
de-Luzuriaga, J. M.; Perez, J. L.; Ramon, M. A.; Veiros, L. F. Inorg.
Chem. 2000, 39, 4280.
(6) (a) Fischer, M. J.; Jelliss, P. A.; Phifer, L. M.; Rath, N. P. Inorg.
Chim. Acta 2005, 358, 1531. (b) Fischer, M. J.; Jelliss, P. A.; Orlando,
J. H.; Phifer, L. M.; Rath, N. P. J. Lumin. 2005, 114, 60. (c) Jelliss,
P. A.; Mason, J.; Nazzoli, J. M.; Orlando, J. H.; Vinson, A. Inorg.
Chem. 2006, 45, 370.
(7) (a) Ellis, D. D.; Jeffery, J. C.; Jelliss, P. A.; Kautz, J. A.; Stone, F. G.
A. Inorg. Chem. 2001, 40, 2041. (b) Ellis, D. D.; Jelliss, P. A.; Stone,
F. G. A. Organometallics 1999, 18, 4982. (c) Blandford, I.; Jeffery,
J. C.; Jelliss, P. A.; Stone, F. G. A. Organometallics 1998, 17, 1402.
7340 Inorganic Chemistry, Vol. 45, No. 18, 2006

Rhenacarborane Dual Fluorescence
Chart 1. Isonido-, Closo-, and Hypercloso-MCxB9-x (x ) 0-2) Cage
Section). Thus, a single νmax(CO) absorption was observed
Frameworks.a
at 1928 cm-1, suggesting CO loss upon reaction with PPh3.
An H{11B} NMR spectrum verified the presence of two
1
PPh3 ligands with a customary multiplet integrating 30:7:
2:1 with the terminal cage B-H and C-H proton, and
endo-H proton singlets, respectively. The endo-H atom was
identified by its broad, metal-perturbed shift at δ -7.61,
which despite this broadening, showed doublet coupling 2JHH
) 14 Hz. This was matched by the appearance of a second
2
doublet in the same spectrum, also with JHH ) 14 Hz at δ
1.67, identified as one of the terminal cage B-H protons.
The observation of seven and two distinct signals for the
terminal cage B-H and C-H hydrogens, respectively,
reflects the high degree of asymmetry observed in the above-
described crystal structure. As a further consequence of this,
the 31P{1H} NMR spectrum revealed two distinct resonances
(δ 12.0 and 12.5) and the 11B{1H} spectrum seven reso-
nances. However, the latter spectrum was conspicuous in
that its most downfield signal was extraordinarily deshielded
(δ 86.7) relative to the remaining range of signals (δ -3.2
to -26.4). This was at first misleading because such an
isolated displacement is often indicative of exopolyhedral
substitution for hydrogen at a boron vertex.14 This finding
was initially all the more puzzling because the aforemen-
tioned complex reported by Stone, [5,8-Me2-7,7-(PEt3)2-
isonido-7,5,8-PtC2B7H7], displayed 11B resonances in a much
narrower range (δ 28.4 to -1.6). However, a fully coupled
a Boron vertexes are unmarked, and open isonido faces are emphasized
with bold lines. bReference 8. cReference 9. dReference 10. eThis work.
g
fNot reported to date. Reference 13.
a nido-C2B7H92- ligand with a [ReIII(H)L3]2+ metal-ligand
fragment. The intense color of the compound is certainly
commensurate with a ReIII formulation; simple ReICxB11-x
(x ) 1, 2) complexes are well-known to be weakly colored
or more usually colorless.1a,7
The pentadecahedral isonido cage architecture, although
rarely reported in the literature, has been established for
metallaborane (IA),8 metallamonocarborane (IB),9 and met-
alladicarborane (IC)10 systems of Ru, Os, Ir, and Pt only
(Chart 1). A 10-vertex isonido rhodathiaborane has also been
recently described by Barton and co-workers.11 These
structures have also been invoked in closo-isocloso trans-
formations of MCxB9-x (x ) 0-2) systems.12 Complex 2 is
the first rhenium, pre-platinum-block MC2B7 metalladicar-
borane in the isonido class ID and notably comprises a
configuration with both carbon vertexes in the quadrilateral
face. Interestingly, the parent closo species, IIA, has not
yet been reported, although Hawthorne and co-workers
have characterized closo and hypercloso ruthenacarborane
species with structures IIB and IIC, respectively.13 Stone
and co-workers have disclosed the synthesis of the only other
isonido metalladicarborane, [5,8-Me2-7,7-(PEt3)2-isonido-
7,5,8-PtC2B7H7], produced as the isomer type IC with one
facial carbon vertex.10 Although arguably the first isonido
species to be reported, it has not been credited as such. Just
two other isonido-MCxB9-x (x ) 0-2) structures share the
phenomenon of bridging endopolyhedral hydrogens, those
of [7,7,9-(PPh3)3-isonido-7-IrB9H10] and [3-Cl-7,9-(PPh3)2-
7,10-µ-(o-Ph2PC6H4)-isonido-7-IrB9H10] (both metallaborane
type IA), which tentatively bear them on opposite Ir-B and
B-B faces of the quadrilateral aperture.8b
1
11B NMR spectrum of complex 2 showed JHB > 100 Hz
for all resonances, indicating a terminal hydrogen atom
remains fully engaged at this vertex. Furthermore, 11B NMR
spectra of several isonido-MC2B8 species (M ) Ru, Os) have
shown similarly wide 11B chemical shift ranges (ca. δ 62 to
-42 on average) with one particularly deshielded signal.15
Although an additional vertex is present compared with
complex 2, the comparison may be more suitable because
they too possess a quadrilateral isonido-MCCB face, i.e., 1
boron + 2 carbon facial vertexes. The full 11B chemical shift
range for complex 2 (∆δ ) 113) appears to be the largest
yet observed for a metalla(car)borane complex. Because of
limited solubility in addition to some very short T1 relaxation
constants for the identified 11B resonances (0.69-2.30 ms),
suitable 2D 11B{1H}-11B{1H} COSY and 1H-11B{1H}
HETCOR NMR spectra could not be obtained. However,
1H NMR spectra measured with systematically selective 11
B
decoupling permitted correlation of the cage 1H resonances
with those of the 11B NMR spectrum (Scheme 2). These
experiments notably linked the endo-H(7) proton to the 11
B
Complex 2 was also characterized by IR, NMR, and UV-
vis spectroscopies and by microanalysis (see Experimental
resonance at δ -4.3. Furthermore, a 2D 1H{11B}-1H{11B}
COSY NMR spectrum (Figure 2) of complex 2 revealed a
strong correlation between resonances at δ -7.61 (the endo-
H(7) proton) with the signal at δ 1.67, which correlates with
the 11B resonance at δ -4.3. Because only the facial B(10)
vertex should display any coupling to both a terminal and
the endo-bridging proton, this 11B resonance (δ -4.3) may
(8) (a) Bould, J.; Brint, P.; Kennedy, J. D.; Thornton-Pett, M. Acta
Crystallogr. 1990, C46, 1010. (b) Bould, J.; Kennedy, J. D.; Thornton-
Pett, M. J. Chem. Soc., Dalton Trans. 1992, 563.
(9) Crook, J. E.; Greenwood, N. N.; Kennedy, J. D.; McDonald, W. S. J.
Chem. Soc., Chem. Commun. 1981, 933.
(10) Green, M.; Spencer, J. L.; Stone, F. G. A.; Welch, A. J. J. Chem.
Soc., Chem. Commun. 1974, 571.
(11) Volkov, O.; Rath, N. P.; Barton, L. Organometallics 2003, 22, 2548.
(12) King, R. B. Inorg. Chem. 1999, 38, 5151.
(13) Jung, C. W.; Baker, R. T.; Knobler, C. B.; Hawthorne, M. F. J. Am.
Chem. Soc. 1980, 102, 5782.
(14) Brew, S. A.; Stone, F. G. A. AdV. Organomet. Chem. 1993, 35, 135.
(15) Brown, M.; Gru¨ner, B.; Sˇt´ıbr, B.; Fontaine, X. L. R.; Thornton-Pett,
M.; Kennedy, J. D. J. Organomet. Chem. 2000, 614-615, 269.
Inorganic Chemistry, Vol. 45, No. 18, 2006 7341

Buckner et al.
1
1
Scheme 2. Correlations through Selectively Decoupled H{11B} NMR Spectra (Solid Lines) and a H{11B}-1H{11B} COSY NMR Spectrum (Dotted
Line)a
a Correlations between terminal-only protons are not indicated. Boron vertex numbers from the cage structure (right) are shown along the top line.
electron oxidation (E1/2 ) 0.67 V, ∆Ep ) 82 mV (0.02 V
s-1) vs ferrocene, ∆Ep ) 90 mV (0.02 V s-1)). Reversibility
was confirmed by DPV (differential pulse voltammetry)
scans in both directions (Supporting Information), which gave
an integrated charge ratio, qpa/qpc ) 1.07 in addition to the
peak current ratio at the slowest scan rate measured (0.02 V
s-1), ipa/ipc ) 1.02. Diffusion control was established in both
scanning directions with linear ν1/2 - |ip| plots (Supporting
Information). The peak current ratios are observed to increase
gradually with increasing scan rate to ipa/ipc ) 1.39 at 1.50
V s-1, suggestive of an EBCrev mechanism at minimum.
Supporting this assertion, the oxidative peak displacement,
∆Epa ) 55 mV decade-1 increase in scan rate, close to the
theoretical 59 mV expected for a reversible chemical reaction
following a one-electron redox event.16
Closer inspection of the CV traces, however, reveals
distortion of the reductive wave at the higher scan rates so
that an EBCrevEA square scheme mechanism may be more
appropriate. Given the isocloso rhenacarborane system under
scrutiny, a logical chemical reaction would result from the
expected plasticity of the cage to yield a formally closo
architecture, accomplished by the formation of an additional
connectivity between Re(7) and C(9) to give a type IIA
structure (Chart 1). From the perspective of PSE counting
rules, where one would conclude such a formal nido structure
for complex 2 (isonido or otherwise) is anomalously electron
deficient, this outcome is the likely mitigation of what could
be viewed as even further loss of PSE. One presumption
made in this mechanism is that the bridging hydrogen atom
H(7) is displaced from the closing nido face to become a
terminal hydride ligand on the Re atom, with this conse-
quence perhaps even facilitating the redox-driven deforma-
tion. Such a conclusion is borne out of the apparent inability
of endopolyhedral hydrogen atoms to bridge deltahedral (3-
vertex) faces in stable carboranes. Thus, a likely scenario
for the square scheme mechanism is given in Scheme 3 and
is supported by digital CV simulation studies (Supporting
Information).
Figure 2. 2D 1H{11B}-1H{11B} COSY NMR spectrum of complex 2 in
CD2Cl2. Off-diagonal correlations indicated on one side by boxes, cage
CH’s denoted by an asterisk.
Figure 3. Cyclic voltammograms for a CH2Cl2 solution (0.68 mM) of
complex 2 at scan rates 0.02, 0.10, 1.00, and 1.50 V s-1 relative to Ag/
AgNO3 (MeCN, 10 mM).
Despite the mechanistic complexity, the same solution was
shown to be stable to repeated potential cycling and the CV
scan fully reproducible over a period of several hours. If
the redox process is metal centered, this would represent an
unusual reversible ReIV/III event for such a carbonyl-bearing
unequivocally be assigned to B(10). The remaining off-
1
diagonal peaks in the 2D H{11B}-1H{11B} COSY NMR
spectrum permitted reasonably confident assignment of the
other 11B chemical shifts, as indicated in Scheme 2.
CV (cyclic voltammetry) measurements (Figure 3) with
CH2Cl2 solutions of complex 2 revealed a reversible one-
(16) (a) Bard, A. J.; Faulkner, L. R. Electrochemical Methods: Funda-
mentals and Applications; Wiley: New York, 2000. (b) Astruc, D.
Electron Transfer and Radical Processes in Transition-Metal Chem-
istry; VCH: New York, 1995.
7342 Inorganic Chemistry, Vol. 45, No. 18, 2006

Rhenacarborane Dual Fluorescence
Scheme 3. Square Scheme (EBCrevEA) Mechanism in the Oxidation of
Complex 2a
Figure 5. Fluorescence decay for sampled emission wavelengths from a
solution of complex 2 in CH2Cl2 at 298 K, λex ) 360 nm. Curve fits are
shown in addition to instrument response function (solid lines).
a Potentials quoted relative to ferrocene.
to blue emission, solutions of 2 characteristically luminesce
turquoise-blue when placed over a hand-held UV lamp with
a long-wave source, reflecting the broadness of the emission
(peakwidth-at-half-height ) 5900 cm-1). Time-based experi-
ments showed no variation of emission intensity over a period
of 400 s, confirming that the emissive species is not a
dissociative photoproduct and that the lumophore is in fact
optically stable. Thus, free PPh3, which actually luminesces
much more weakly at λem ≈ 475 nm (Φ ) 0.003 in benzene
at 298 K),18 is not the species responsible for emission in
this case. This was also confirmed by careful NMR analysis,
which showed no decomposition of complex 2 upon pro-
longed photolysis at λex ) 360 nm and the absence of free
PPh3.
Comparison of the excitation/emission peak shapes, even
on an energy scale, reveals a perceptible asymmetry. Thus,
the emissive excited-state species may not share the same
ground-state nuclear arrangement of the parent complex,
which is feasible given the redox characteristics of complex
2 discussed above and the d-d phosphorescence observed
for the complex [3-CO-3,3-{κ2-Me2N(CH2)2NMe2}-closo-
3,1,2-RuC2B9H11].6c This phenomenon, however, may neces-
sarily be the consequence of the mixing of multiple excited
states of complex 2. This was evidenced by decay lifetime
measurements in CH2Cl2 measured at ambient temperatures
(Figure 5, Table 1). Sampling at a variety of wavelengths
along the emission profile revealed monoexponential, very
short-lived fluorescence at the high-energy extreme (τ ) 0.39
ns at λem ) 400 nm), with biexponential decay at the
emission peak (τ1 ) 0.44 ns (74%) and τ2 ) 1.1 ns (26%)
at λem ) 442 nm). At lower energies (λem ) 500 and 560
nm), the shorter lifetime component (g71%) approaches 1
ns along with a minor contribution (e29%) from super-3.0
ns decay. Clearly, all emitting states are fluorescent with a
net result that is apparent from Figure 5: the emission tail
is evidently longer-lived than at the high-energy extreme.
Measurements in MeTHF (2-methyltetrahydrofuran) glass
at 77 K (Figure 4) resulted in two distinct structured
Figure 4. UV-vis spectrum of complex 2 in CH2Cl2 (solid black line)
(left ordinate). Photoluminescence spectra in CH2Cl2 (50 µM, 298 K):
excitation (λem ) 442 nm) (solid magenta line); emission (λex ) 360 nm)
(solid blue line). Photoluminescence spectra in MeTHF (50 µM, 77 K):
excitation (λem ) 504 nm) (dotted red line); excitation (λem ) 405 nm)
(dotted pink line); emission (λex ) 368 nm) (dotted green line). Photolu-
minescence intensity (right ordinate) normalized relative to maximum
excitation intensities.
organometallic complex. Chemical oxidation of CH2Cl2
solutions of complex 2 with the ammoniumyl salt [N(p-C6H4-
Br)3][SbCl6] did indeed reveal a clean displacement of the
CO stretching absorption to νmax(CO) ) 2039 cm-1. A
change of ∆ν ) +111 cm-1 is consistent with a metal-
centered oxidation.6c,17 Solutions of 2+, however, appear to
not be stable to isolation procedures, with IR spectra showing
quantitative reformation of neutral complex 2 over a period
of several hours.
Perhaps even more uncharacteristic in this field of orga-
nometallic chemistry is the ambient-temperature lumines-
cence of CH2Cl2 solutions of complex 2 (Figure 4). Thus,
complex 2 strongly emits light at λem ) 442 nm (Φ ) 0.012)
with excitation at λex ) 360 nm (Stokes shift ) 5330 cm-1)
with no irregular concentration dependence. Photolumines-
cence results were reproducible from multiple batches of
pure, chromatographed complex 2, as ascertained by spec-
troscopic and microanalytical data. Although λem corresponds
(17) (a) Connelly, N. G.; Johnson, G. A. J. Organomet. Chem. 1974, 77,
341. (b) Carriedo, G. A.; Riera, V.; Connelly, N. G.; Raven, S. J. J.
Chem. Soc., Dalton Trans. 1987, 1769.
(18) (a) Segers, D. P.; DeArmond, M. K.; Grutsch, P. A.; Kutal, C. Inorg.
Chem. 1984, 23, 2874. (b) Changenet, P.; Plaza, P.; Martin, M. M.;
Meyer, Y. H.; Rettig, W. Chem. Phys. 1997, 221, 311.
Inorganic Chemistry, Vol. 45, No. 18, 2006 7343

Buckner et al.
Table 1. Decay Lifetime Analysis for Complex 2
translational motion should be highly restricted (Supporting
Information). Any 405 nm emission from complex 2 was
masked by the strong anthracene luminescence.
T/K (solvent)
λ
em/nma
τ1/ns (a1/%)b
τ2/ns (a2/%)b
ø2 c
298 (CH2Cl2)
400
442d
500
560
405
504
543
585
0.39 (100)
0.44 (74)
0.81 (89)
0.86 (71)
0.18 (92)
0.40 (88)
0.36 (77)
0.49 (72)
-
1.37
1.29
1.22
0.97
0.97
0.99
1.39
0.82
1.1 (26)
3.2 (11)
3.0 (29)
0.74 (8)
4.7 (12)
4.3 (23)
5.1 (28)
An IR spectrum of complex 2 in CH2Cl2 does indeed
display medium-intensity absorptions at 1430 and 1434 cm-1,
which are nominally assigned to aryl C-C n stretching
modes in the phosphine ligand and tend to be invariant
between the free PPh3 ligand and its coordination com-
pounds.19 This would thus seem to identify the PPh3 ligand-
(s) as a critical component of the lumophore in complex 2.
However, the only report of Re-phosphine luminescence is
that of d-d emission from the ReI complexes [Re(Cl)L2-
(CO)3] (L ) PPh3, P(o-C6H4Me)3; L2 ) Et2P(CH2)2PEt2),20
which due to the strength and energy of the excitation, as
well as its frozen (77 K) glass behavior described above, is
most unlikely to be responsible for the luminescence of
complex 2. What is more, there have been no reports of
emission from a complex with a mononuclear ReIII center.
Indeed, this oxidation state might be considered to be
photophysically benign for mononuclear rhenium complexes
with only ReI and ReVII centers being acknowledged as
established lumophores.21 The observed 77 and 298 K
emissions are nevertheless consistent with metal-perturbed
1IL dual fluorescence (Scheme 4a), with the impact of the
metal evident from the Huang-Rhys factor for the longer-
wavelength emission, normally >1.0 for pure IL progres-
sions.22 Specifically σReP-σPC* singlet emission is proposed,
where contribution from P-C σ* antibonding orbitals to the
excited state is suggested. Given the propensity of these
orbitals to also engage with the metal dπ orbitals (as well as
P 3d orbitals of course),23 the total asymmetry of the complex
no doubt assists in any relaxation of Laporte selection rules.
The P-C σ* component would be consistent with the
vibronic structure observed at 77 K in Figure 4 because aryl
C-C n stretching modes at ca. 1430 cm-1 in aryl phosphines
(coordinated or uncoordinated) cannot occur independently
from P-C bond deformation (Figure 7). The stimulation of
these stretching modes by occupation of an orbital with P-C
σ* character can thus be readily appreciated.
77 (MeTHF)
a Emission wavelength for decay sampling. Excitation, λex ) 360 (298
K) and 368 nm (77 K). b Lifetime(s) τn with percent contribution, an, shown
in parentheses. c ø2 (Marquardt-Levenberg) fit. d Emission peak, Φ442
)
0.012.
Figure 6. Fluorescence decay for sampled emission wavelengths from a
solution of complex 2 in MeTHF at 77 K, λex ) 368 nm. Curve fits are
shown in addition to instrument response function (solid lines).
emissions at λꢀm ) 405 and 504 nm. The latter (Stokes shift
) 7260 cm-1) comprises obvious vibrational fine structure
(∆ν ) 1425 cm-1, Huang-Rhys factor, I0,1/I0,0 ) 0.75),
while the former (Stokes shift ) 2470 cm-1) shows less
resolved structure (∆ν ≈ 1400 cm-1). It should be noted
that, while the emission spectra at 298 and 77 K are radically
different, the corresponding excitation spectra differ only
slightly in λex (∆λ ) 8 nm) and not at all in line shape.
Moreover, the excitation appears to correspond with a
moderately strong absorption shoulder (λmax ) 355 nm, ꢀ )
7200 M-1 cm-1) in the UV-vis spectrum also measured in
CH2Cl2 at 298 K (Figure 4) that is solvent independent.
Decay lifetime measurements in MeTHF measured at 77 K
(Figure 6, Table 1) ruled out any phosphorescent contribution
to the lower energy emission especially, despite the mod-
erately large Stokes shift. Thus, the 405 nm violet emission
is exceedingly short-lived, and though formally biexponen-
tial, is dominated by the τ ) 0.18 ns (92%) decay. Sampling
of the lower energy green emission reveals somewhat longer
biexponential contributions with τ ) 0.40 (88%) and 4.7 ns
(12%) at λem ) 504 nm and only slight variation of these
The excitation for complex 2 (λex ) 360 nm) also lies at
considerably lower energy than ligand-isolated π-π* or
n-aπ transitions.18 The observed emissions are likewise
inconsistent with σ-aπ (Re-P σ-bond f aryl π* orbital)
states observed in other luminescent metal-phosphine
complexes from the late d block, which show some solvent
dependency (especially for the 3σ-aπ phosphorescence), and
(19) (a) Crayston, J. A.; Davidson, G. Spectrochim. Acta 1986, 42A, 1311.
(b) Deacon, G. B.; Green, J. H. S. Spectrochim. Acta 1968, 24A, 845.
(c) Whiffen, D. H. J. Chem. Soc. 1956, 1350.
(20) Ramsis, M. N. Monatsh. Chem. 1993, 124, 849.
(21) Vogler, A.; Kunkely, H. Coord. Chem. ReV. 2000, 200-202, 991.
(22) (a) Miskowski, V. M.; Houlding, V. H. Inorg. Chem. 1989, 28, 1529.
(b) Miskowski, V. M.; Houlding, V. H. Coord. Chem. ReV. 1991, 111,
145. (c) Miskowski, V. M.; Houlding, V. H.; Che, C.-M.; Wang, Y.
Inorg. Chem. 1993, 32, 2518. (d) Buchner, R.; Cunningham, C. T.;
Field, J. S.; Haines, R. J.; McMillin, D. R.; Summerton, G. C. J. Chem.
Soc., Dalton Trans. 1999, 711.
(23) (a) Orpen, A. G.; Connelly, N. G. J. Chem. Soc., Chem. Commun.
1985, 1310. (b) Pacchioni, G.; Bagus, P. S. Inorg. Chem. 1992, 31,
4391. (c) Crabtree, R. H. In The Organometallic Chemistry of the
Transition Metals; Wiley: New York, 2001; Ch. 4, pp 92-93.
parameters at longer wavelength peaks/shoulders at λem
)
543 and 585 nm. The longest decay measured (5.1 ns (28%))
in the emission tail is still clearly fluorescent. Nevertheless,
the highly structured green emission all but disappeared (89%
decrease in integrated intensity) when measurements were
carried out with a high concentration (10 mM) of the well-
known triplet quencher, anthracene, even at 77 K where
7344 Inorganic Chemistry, Vol. 45, No. 18, 2006

Rhenacarborane Dual Fluorescence
Scheme 4. Energy Level Diagrams for (a) Dual Fluorescence of Complex 2 at 77 K and (b) Fluorescence Quenching by Singlet-Triplet Energy
Transfer to Anthracene
do not display similarly structured emissions, irrespective
of temperature.18a,24 Both absorption and emission spectra
for complex 2 are completely solvent-invariant in λ, with
the spectra in DMF, for instance, appearing the same as those
in Figure 4, suggesting little or no charge transfer. The
quenching observed upon the addition of anthracene at 77
K must result from rapid intermolecular singlet-triplet
energy transfer (kET > 109 s-1) as indicated in Scheme 4b.
photophysical behavior of 2, especially given our observation
of very similar luminescence characteristics with the recently
isolated ReIII complex [3-Cl-3-CO-3,3-(PMe3)2-closo-3,1,2-
ReC2B9H11].25 However, we expect to continue our inves-
tigations with the isolation and characterization of further
rhenacarborane-phosphine complexes.
Conclusion
1
Efficient diversion of energy from the upper S2 state of
Complex 2 has been synthesized and thoroughly charac-
terized by X-ray crystallography and by NMR, IR, and UV-
vis spectroscopic analysis, revealing an asymmetric isonido-
7,8,9-ReC2B7 structure, comprising a tripodal Re(CO)(PPh3)2
vertex. Electrochemical measurements in CH2Cl2 solution
have revealed a reversible one-electron square scheme with
an associated isonido-closo transformation, which is not
altogether surprising from the viewpoint of metallacarborane
cage PSE counting. The strong ambient temperature fluo-
rescence, on the other hand, was unexpected given this class
of complex and especially the oxidation state of the metal
(ReIII). The short fluorescent lifetimes, with major compo-
nents in the sub-nanosecond regime, are no doubt a major
contributor to the observed respectable quantum yield in
solution at room temperature. At present, the involvement
of the carborane ligand with the lumophore appears to be
trivial, but with the opening of this avenue of investigation,
it may be prudent at some point to investigate previously
reported metallacarborane complexes for potentially interest-
ing photophysical behavior. For our part, we continue to
probe this and other related rhenacarborane phosphine
complexes for their candidacy as redox and dye mediators
in biofuel and photovoltaic cells, respectively.
complex 2 to the energy-matched anthracene 3A1 excited state
effectively shuts down intersystem crossing to 1S1, and thus,
the dual fluorescence is mostly quenched.
From excitation measurements, it seems that the lower
excited state 1S1 is not directly accessible by absorption from
the 1S0 ground state, as there are no further excitation peaks
at lower energy, despite the presence of moderately weak
absorptions in the UV-vis spectrum at λmax ) 424 and 493
nm. This would ultimately suggest a small but significant
and rapid nondissociative nuclear displacement resulting from
the primary excitation at λex ) 360 nm. The most likely
scenario is a minor adjustment in metal coordination
geometry. However, given that the excitation involves
displacement of electron density from an orbital directly
involved in PSE cage-cluster bonding to an orbital which is
not, some cage deformation, namely an isonido-closo
conversion might also be feasible. Such a modification was
of course invoked in the redox chemistry of complex 2 (vide
supra), and simulation experiments support a rapid structure
reassignment, although we cannot say at this point whether
it is fast enough to accommodate the fluorescent state
observed for complex 2. We have previously implicated cage
deformation in the d-d phosphorescence of [3-CO-3,3-
{κ2-Me2N(CH2)2NMe2}-closo-3,1,2-RuC2B9H11], although
this complex displays a much longer decay lifetime (τ )
0.77 ms), albeit at 77 K.6c At this point, our inclination is to
favor an ancillary role for the carborane cage in the
Experimental Section
General Considerations. Solvents (CH2Cl2, DMF, hexanes,
MeCN, THF, MeTHF) were distilled over appropriate drying agents
under argon prior to use. All reactions were carried out under a
dry, oxygen-free argon atmosphere using Schlenk line and glovebox
techniques. Complex 1 was prepared using the literature method.6a
The reagent PPh3 was purchased from Aldrich and used as received.
(24) (a) Kunkely, H.; Vogler, A. J. Am. Chem. Soc. 1995, 117, 540. (b)
Kunkely, H.; Vogler, A. Coord. Chem. ReV. 2002, 230, 243.
(25) Buckner, S. W.; Fischer, M. J.; Jelliss, P. A.; Minteer, S. M.; Rath,
N. P. Unpublished results. See Supporting Information for preliminary
data for this complex.
Figure 7. Aryl C-C n stretching mode in the PPh3 ligand. The notation
is taken from ref 19c.
Inorganic Chemistry, Vol. 45, No. 18, 2006 7345

Buckner et al.
Instrumentation. All solution measurements were made at 298
K unless otherwise stated. IR measurements were made using
solution cells in a Perkin-Elmer RX-I FTIR spectrometer. NMR
measurements were recorded using a Varian Gemini 300 MHz
stroboscopic detection system with an R928 photomultiplier. The
decays were analyzed with a PTI FeliX32 advanced analysis
package utilizing a discrete multiexponential fitting function and
iterative reconvolution.
1
spectrometer, H (300.0 MHz); 13C (75.4 MHz);11B (96.3 MHz);
Synthesis of [7,10-µ-H-7-CO-7,7-(PPh3)2-isonido-7,8,9-ReC2-
B7H9]. Compound 1 (0.10 g, 0.20 mmol) and PPh3 (0.16 g, 0.59
mmol) were combined in a three-necked flask fitted with a
condenser, which is in turn connected to an Ar/vacuum Schlenk
line. The reactants were dissolved in dry distilled THF (30 mL)
and heated to reflux for 24 h. After the mixture cooled to room
temperature, solvent was removed in vacuo. The residue was
dissolved in CH2Cl2/hexanes (10 mL, 1:1) and chromatographed
on alumina (Brockmann IV) at -25 °C. Elution with the same
solvent mixture removed an intense orange-red fraction. Solvent
was reduced in volume to 2 mL and hexanes added (5 mL) to afford
bright orange-red microcrystals of 2 (0.03 g, 18%), which were
washed with hexanes (3 × 20 mL) and dried in vacuo. X-ray-quality
crystals were grown from a CH2Cl2 solution of 2 layered with
hexanes. A second rhenacarborane-carbonyl product was eluted
from the column using neat CH2Cl2 but has not yet been identified.
Data for 2 (298 K): IR (CH2Cl2) (cm-1) νmax(BH) 2550m, νmax(CO)
1928s, νmax(CC-n) 1430m, 1434m; 1H{11B} NMR (CD2Cl2) δ
7.73-7.04 (m, 30 H, Ph), 10.80, 3.80, 2.12, 1.67*, 0.61, 0.13, -1.69
1
31P (121.4 MHz), or a Bruker ARX 500 MHz spectrometer, H
(500.1 MHz); 13C (125.6 MHz);11B (160.5 MHz); 31P (202.5 MHz).
Selective decoupling experiments and 2D spectra were exclusively
measured on the latter instrument. Electrochemical experiments
were performed with a CH Instruments CHI620B electrochemical
analyzer. All potentials were recorded relative to an Ag/AgNO3
(MeCN, 10 mM) reference electrode at 298 K and quoted relative
to an internal ferrocene standard. All solutions were studied in a
three-electrode cell under Ar in distilled, deoxygenated solvents
and contained 0.1 M [NBun ][PF6] as supporting electrolyte. All
4
CV and DPV measurements were made on a glassy carbon disk
working electrode with a surface area of 7.07 mm2, which was
frequently polished, rinsed, and dried between measurements. The
Pt wire counter electrode was precleaned by soaking in concentrated
HNO3, rinsed with distilled water, and then flame-dried. Cyclic
voltammograms were run both with initial positive and negative
scan polarities, and showed little variation with this parameter.
Digital simulations were carried out using DigiElch.26 UV-vis
spectral measurements (800 f 220 nm) were made with a Shimadzu
2530 UV-visible absorption spectrophotometer. Photoluminescence
measurements were made with a Photon Technologies QM4
fluorescence spectrophotometer with a Xe arc lamp light source
and digital PMT detector. Emission and reference source gain
excitation corrections were applied to all steady-state data. Slit
widths were typically set at 5 nm. Appropriate cutoff filters were
used to eliminate peaks due to solvent Raman-shifted bands and
excitation harmonics when possible. Solution samples at ambient
temperatures were measured in a quartz sample cuvette with
Schlenk attachment to deoxygenate samples. Samples measured at
77 K were degassed and analyzed in a quartz NMR tube with
Schlenk attachment and set in quartz-bottomed Dewar flask in an
argon-filled sample chamber. The quantum yield was assessed by
comparison of integrated peak intensities between those of complex
2 for the full range of emission wavelengths and the singlet emission
from deoxygenated 9-cyanoanthracene in hexane, which has Φem
) 1.00. The concentration of the complex 2 solution was adjusted
to give an accurately measured absorbance of ca. 0.1 A at λex. A
standard solution of 9-cyanoanthracene was similarly created and
its integrated emission intensity measured using an optical density
(OD1) filter at the emission monochromator entrance at consistently
fixed slit widths for all measurements. Quantum yields were then
calculated according to
(s × 7, 7 H, cage BH, * 2JH H ) 14), 3.27, 2.64 (s × 2, 2 H, cage
7
10
CH), -7.61 (d br, 1 H, endo-H, 2JH H ) 14); 13C{1H} NMR (CD2-
7
10
1
Cl2) δ 208.8 (CO), 134.5, 134.2 (d × 2, Ci(Ph), JPC ) 47, 47),
2
133.6, 133.5 (d × 2, Co(Ph), JPC ) 11, 10), 135.8, 135.2 (d × 2,
4
3
Cp(Ph), JPC ) 2, 2), 128.2, 127.7 (d × 2, Cm(Ph), JPC ) 10, 9),
45.5, 39.5 (br × 2, cage C); 31P{1H} NMR (CD2Cl2) δ 12.5, 12.0
(s × 2); 11B{1H} NMR (CD2Cl2) δ (T1) 86.7 (0.69 ( 0.03 ms),
-2.8 (1.20 ( 0.08 ms), -4.0 (2.30 ( 0.08 ms), -11.9 (1.20 (
0.06 ms), -18.3 (1.14 ( 0.04 ms), -24.2 (1.10 ( 0.06 ms), -26.4
(1.21 ( 0.05 ms) (s × 7); UV-vis. (CH2Cl2) λmax (nm) (ꢀ × 10-3
(M-1 cm-1)) 266sh (17.3), 276sh (16.0), 297 (13.9), 355sh (7.2),
424 (1.5), 493 (1.5); Anal. Calcd for C39H40B7OP2Re: C, 55.2; H,
4.8. Found: C, 54.8; H, 5.0.
X-ray Crystallography. A crystal of 2 was mounted onto a glass
fiber in a random orientation. Preliminary examination and data
collection were performed using a Siemens SMART charge-coupled
device (CCD) detector system single-crystal X-ray diffractometer
equipped with a sealed-tube X-ray source using graphite-mono-
chromated Mo KR radiation (λ ) 0.71073 Å). Preliminary unit
cell constants were determined with a set of 45 narrow-frame scans
(0.3° in ω). A total of 4026 frames of intensity data were collected
at a crystal-to-detector distance of 4.91 cm. The double-pass method
of scanning was used to reduce noise. The collected frames were
integrated using an orientation matrix determined from the narrow-
frame scans. The SMART software package was used for data
collection, and SAINT27 was used for frame integration. Analysis
of the integrated data did not show any decay. Final cell constants
were determined by a global refinement of the x, y, z centroids of
thresholded reflections from the entire dataset. Absorption correc-
tions were applied to the data using equivalent reflections (SAD-
ABS).28 The SHELX-9729 software package was used for structure
solutions (by direct methods) and refinement. Full-matrix least-
squares refinement was carried out by minimizing ∑ w(Fo2 - Fc2)2.
The non-hydrogen atoms were refined anisotropically to conver-
gence. Noncage hydrogen atoms were included in calculated
positions and treated using appropriate riding models. Cage
Iint,x/fx
Φem
)
(Iint,c/fc) × 100
where Iint ) integrated intensity, f ) fraction of light absorbed for
a solution of complex 2 (x) and of 9-cyanoanthracene (c). Integrated
emission intensities, Iint, were thus corrected for self-absorption
using transmission data parameters from the UV-vis absorption
spectra over the width of the emission band. Accurate fluorescence
decays from compound 2 were measured with a PTI model TM-
3/2005 lifetime fluorescence spectrophotometer. The instrument
employed a PTI GL-330 pulsed nitrogen laser pumping a PTI GL-
302 tunable dye laser as an excitation source and a proprietary
(27) SAINT; Bruker Analytical X-ray: Madison, WI, 2002.
(28) Blessing, R. H. Acta Crystallogr. 1995, A51, 33.
(29) Sheldrick, G. M. SHELX-97; University of Go¨ttingen: Go¨ttingen,
Germany, 1997.
(26) Rudolph, M. DigiElch ver. 2.0; Friedrich-Schiller-Universita¨t: Jena,
Germany, 2005.
7346 Inorganic Chemistry, Vol. 45, No. 18, 2006

Rhenacarborane Dual Fluorescence
Table 2. Crystallographic Data for Complex 2
for Figure 1. A complete list of positional and isotropic displacement
coefficients for the hydrogen atoms, anisotropic displacement
coefficients for the non-hydrogen atoms, and bond distances and
angles are available in CIF format as Supporting Information.
CCDC 288357 also contains 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.
empirical formula
fw
C39H40B7OP2Re
848.52
cryst dimens (mm)
cryst color, shape
cryst syst, space group
0.18 × 0.15 × 0.13
red, rectangular prism
monoclinic, P21/c
10.2488(3)
21.7109(7)
16.2333(5)
98.594(2)
3571.53(19)
4
1.578
a (Å)
b (Å)
c (Å)
â (deg)
V (Å3)
Z
Acknowledgment. This material is based upon work
funded in part by the U.S. Government. Research Corpora-
tion (Cottrell Grant No. CC5748) is also acknowledged for
the purchase of the fluorescence spectrophotometer. We
thank Prof. Lawrence Barton (UMSL) for helpful discussions.
D
calcd (g cm-3
)
µ(Mo KR) (mm-1
T (K)
)
3.525
165(2)
θ range (deg)
reflns collcd
1.58-28.00
85321
indept reflns (Rint
)
8626 (0.065)
0.0720, 0.0432
0.0749, 0.0582
1.257
wR2, R1a (I > 2σ(I))
wR2, R1a (all data)
GOF on F2
Supporting Information Available: Further electrochemical
measurement and analysis of 2 (DPVs, ν1/2 - |ip| plots, CV digital
simulation details). Photoluminescence spectrum of 2 with an-
thracene quenching. Tables of crystallographic data, including
fractional coordinates, bond lengths, and angles, anisotropic
displacement parameters, and hydrogen atom coordinates of 2 in
CIF file format. This material is available free of charge via the
Internet at http://pubs.acs.org.IC061071N
largest diff. peak and hole (e Å-3
)
1.613, -2.723
a Refinement was block full-matrix least-squares on all F2 data: wR2
) [∑{w(Fo - Fc )2}/∑w(Fo )2]1/2 where w-1 ) σ2(Fo ). The value R1 )
∑|Fo| - |Fc|/∑|Fo|.
2
2
2
2
hydrogens, including the endopolyhedral hydrogen H(7), were
located from the difference Fourier map and included in the final
refinement. The structure refinement parameters are given in Table
2, and selected bond angles and distances are given in the legend
IC061071N
Inorganic Chemistry, Vol. 45, No. 18, 2006 7347