{Tl[Au(C6Cl5)2]}n: A vapochromic complex 01

Article abstract of DOI:10.1021/ja028734u

The X-ray structure of {Tl[Au(C₆Cl₅)₂]}_n, 1, consists of 1-D linear polymer chains parallel to the crystallographic z axis. The crystal structure of 1 has channels that run parallel to these chains with interatom distances in the range 3.231-4.076 A. There are holes in these channels with diameters as large as 10.471 A, which can accommodate a variety of solvents. Complex 1 displays reversible vapochromic emission and absorption spectral behavior when the solid is exposed to a variety of organic vapors such as acetone, acetonitrile, triethylamine, acetylacetone, tetrahydrothiophene, 2-fluoropyridine, tetrahydrofuran, and pyridine. Complex 1 is luminescent at room temperature and at 77 K in the solid state. UV excitation at 495 nm leads to an emission at 531 nm. Copyright

Full text of DOI:10.1021/ja028734u

Published on Web 01/31/2003
{Tl[Au(C6Cl5)2]}n: A Vapochromic Complex
Eduardo J. Ferna´ndez,† Jose´ M. Lo´pez-de-Luzuriaga,† Miguel Monge,† M. Elena Olmos,†
Javier Pe´rez,† Antonio Laguna,*,‡ Ahmed A. Mohamed,§ and John P. Fackler, Jr.*,§
Departamento de Qu´ımica, UniVersidad de La Rioja, Grupo de S´ıntesis Qu´ımica de La Rioja, UA-CSIC, Madre de
Dios 51, E-26004 Logron˜o, Spain, Departamento de Qu´ımica Inorga´nica-ICMA, UniVersidad de Zaragoza-CSIC,
E-50009 Zaragoza, Spain, and Department of Chemistry and Laboratory for Molecular Structure and Bonding,
Texas A&M UniVersity, P.O. Box 30012 College Station, Texas 77842-3012
Received September 27, 2002 ; E-mail: fackler@mail.chem.tamu.edu
Recently, synthetic efforts have been directed toward the
preparation of polymeric materials with special optico-electronic
properties.1 Some of these materials are sensors for volatile organic
compounds (VOC).2 Materials that show appreciable selectivity and
tunable changes of color or emission in the presence of VOCs are
of particular interest.3 Here we report on a luminescent, polymeric,
semiconducting gold-thallium complex with a solid-state structure
that permits reversible interactions and related color changes with
a variety of VOCs.
By reacting equimolar quantities of [NBu4][Au(C6Cl5)2] with
TlPF6 in tetrahydrofuran, the compound {Tl[Au(C6Cl5)2]}n, 1, is
obtained as a pale yellow solid.4
Figure 1. Crystal structure of 1 viewed down the crystallographic z axis.
Inset: The polymeric molecular structure of 1.
The X-ray structure5 of complex 1 consists of 1-D linear polymer
chains parallel to the crystallographic z axis, with unsupported Au-
Tl interactions between the [Au(C6Cl5)2] anions and Tl(I) cations
(Figure 1). The Au-Tl distances (3.0044(5) and 2.9726(5) Å) are
shorter than the sum of Au(I) and Tl(I) ionic radii (2.96 Å)6 and
Au-Tl distances in related systems (3.0161(2)-3.1887(6) Å)7 but
similar to those observed in [TlAu(Ph2P(S)CH2)2]n 8 [Au-Tl(intra)
) 2.959(2) Å; Au-Tl(inter) ) 3.003(2) Å] and longer than those
found in the metallocryptate [TlAu2(P2-phen)3](PF6)3 (P2-phen )
2,9-bis(diphenylphosphino)-1,10-phenantroline)9 [2.9171(5) and
2.9109(5) Å]. Each Au(I) atom is coordinated to two pentachlo-
rophenyl groups with a normal Au-C distance (2.063(6) Å). The
Tl center is not further coordinated, although this structure is
stabilized by eight long Tl‚‚‚Cl contacts (3.2441(15)-3.6786(15)
Å). Four additional Au‚‚‚Cl contacts (3.3388(15) and 3.3688(16)
Å) may also contribute to the stability of the system. Finally, the
crystal structure of 1 has channels that run parallel to the z axis
(Figure 1) with interatom distances in the range 3.231-4.076 Å.
There are holes with diameters as large as 10.471 Å (the static
Au-Au distance between chains) which can accommodate the
molecules which enter the lattice.
Solid complex 1 is luminescent at room temperature (RT) and
at 77 K. UV excitation at 495 nm leads to an RT emission at 531
nm. The emission is shifted to 547 nm at 77 K. This observed
thermochromism is similar to observations found in other gold-
thallium extended linear chains7a,b,8 and is assumed to be a result
of the thermal contraction that occurs when the temperature is
lowered. The shortened Au-Tl distance at low temperatures in the
absence of ligands coordinated to Tl causes the overlap between
the Au(I) and Tl(I) orbitals to increase. This reduces the HOMO-
LUMO gap, thereby lowering the energy of the emission band.
Compound 1 is not luminescent when dissolved in THF.
Figure 2. Comparison between emission spectra of crystals and powder
of 1 at 77 K. Inset: SEM images of X-ray size crystals (left) and bulk
powder (right) of 1 taken without coating with a conducting film.
and 123 ns. The longer lifetime is suggestive of phosphorescence;
however, the Stokes shift between the maxima of excitation and
emission bands is only 1370 cm-1. The emission spectrum is
independent of the excitation wavelength in the range from 300 to
500 nm.
A very interesting spectral feature is the observed shift of the
emission energy of 1 with particle size. At 77 K, the bulk powder
shows an emission at 547 nm, while X-ray quality crystals display
an emission at 560 nm (see Figure 2). In addition, when the crystals
are gently crushed, the band shifts to higher energies. It is generally
observed in semiconductors that a reduction in the spatial confine-
ment of the electrons increases their kinetic energy. This produces
a larger band gap, an effect known as the quantum size effect.10
The scanning electron microscope (SEM) images taken of the
microcrystalline solid (Figure 2) and larger single crystals show
clear SEM images without coating with a conductor. These data
suggest that the material is not an insulator.11 TD-DFT calculations
carried out for Tl[Au(C6Cl5)2]2 (see the Supporting Information)
show that the high oscillator strength transitions are between orbitals
The decay at 298 K of the emission centered at 531 nm has
been fitted with two exponential functions giving lifetimes of 1039
† Universidad de La Rioja.
‡ Universidad de Zaragoza-CSIC.
§ Texas A&M University.
9
2022
J. AM. CHEM. SOC. 2003, 125, 2022-2023
10.1021/ja028734u CCC: $25.00 © 2003 American Chemical Society

C O M M U N I C A T I O N S
The solids resulting from the exposure of 1 to VOCs display
this new absorption band in the range 455-600 nm, at energies
similar to the maxima observed in the excitation spectra, suggesting
that these bands give rise to the luminescence. This observation
supports the premise that the luminescence observed has its origin
in the Au-Tl interactions.
These preliminary results illustrate the potential applications of
Au(I)-Tl(I) compounds as candidates for the detection of various
VOCs.
Acknowledgment. This work was supported by the Spanish
DGI (BQU2001-2409) and the Robert A. Welch Foundation of
Houston, TX.
Figure 3. Powder samples of compound 1 deposited on filter paper and
exposed to selected organic vapors: (1) 2-flouropyridine, (2) THF, (3)
acetone, (4) acetylacetone, (5) acetonitrile, (6) pyridine, (7) triethylamine,
(8) THT.
Supporting Information Available: X-ray crystallographic files
for 1 (CIF); luminescence, absorption data, and TD-DFT results (PDF).
This material is available free of charge via the Internet at http://
pubs.acs.org.
located in the metal centers along the metal chain. Measurement
for a single crystal failed to establish conductivity; hence semi-
conductivity is suggested.
References
Complex 1 displays a vapochromic behavior with reversible
changes12 of color when the solid is exposed to a variety of organic
vapors. Acetone, acetonitrile, triethylamine, acetylacetone, tetrahy-
drothiophene (THT), 2-fluoropyridine, tetrahydrofuran (THF), and
pyridine vapors (see Figure 3) have been used. The color changes
back to that of the starting material upon heating to 100 °C over a
period that requires from a few seconds for acetone to 10 min for
pyridine. In all cases, the process is found to be completely
reversible with no detectable degradation of the starting material
after 10 exposure/heating cycles. The exchange of color is even
deeper under UV light, and the substances display a strong
luminescence under these conditions (see the Supporting Informa-
tion).
(1) Extended Linear Chain Compounds; Miller, J. S., Ed.; Plenum Press: New
York, 1982; Vols. 1-3.
(2) Buss, C. E.; Mann, K. R. J. Am. Chem. Soc. 2002, 124, 1031 and references
therein.
(3) (a) Mansour, M. A.; Connick, W. B.; Lachicotte, R. J.; Gysling, H. J.;
Eisenberg, R. J. Am. Chem. Soc. 1998, 120, 1329. (b) Beauvais, L. G.;
Shores, M. P.; Long, J. R. J. Am. Chem. Soc. 2000, 122, 2763. (c) Cariati,
E.; Bu, X.; Ford, P. C. Chem. Mater. 2000, 12, 3385. (d) Evju, J. K.;
Mann, K. R. Chem. Mater. 1999, 11, 1425.
(4) Anal. Calcd (found) for C12AuCl10Tl: C, 16.1 (16.0). ΛM (acetonitrile)
) 109 Ω-1 cm2 mol-1. Yield: 65%.
(5) Crystallographic data were obtained using a Nonius Kappa CCD diffrac-
tometer, Mo KR radiation (λ ) 0.71073 Å), T ) -100 °C. Crystal data:
orthorhombic, Pccn, a ) 14.7106(8), b ) 10.4709(4), c ) 11.9540(6) Å,
V ) 1841.31(15) Å3, Z ) 4, dcalc ) 3.246 Mg/m3, 3371 measured
reflections, 1870 independent reflections (Rint ) 0.0306), R1 ) 0.0282
and wR2 ) 0.0571, goodness-of-fit on F 2 ) 1.055.
Exposure of solid complex 1 to the RT vapor pressure of the
above VOCs shifts the RT emission band from 531 to 507 (THF,
ex 473), 511 (NEt3, ex 463), 513 (NCMe, ex 491), 532 (acetone,
ex 444), 567 (THT, exc 485), 627 (2-fluoropyridine, ex 400), 646
(pyridine, ex 560), and 650 (acetylacetone, ex 550) nm, respectively.
These shifts presumably are associated with a weak interaction of
the Tl(I) centers with the VOCs. Each band shifts to the red when
the measurements are made at 77 K. In addition, analysis of the
UV-vis absorption and IR spectra is in accord with the presence
of an interaction between VOCs and the metallic centers. A dilute
solution (5 × 10-4 M) of complex 1 in THF displays only
absorptions due to the [Au(C6Cl5)2]- units, centered in the pen-
tachlorophenyl rings;7b the UV-vis spectra in the solid state of
both [NBu4][Au(C6Cl5)2] and 1 display a pattern similar to that of
the bands at 217, 235, 288, and 311 nm for the Au material and
217, 240, 291, and 311 nm for Au-Tl complex 1. Complex 1 shows
an additional peak at 343 nm that can be assigned to a transition
between levels formed as a consequence of the intermetallic
interaction (see the Supporting Information).
(6) Pauling, L. The Chemical Bond; Cornell University Press: Ithaca, New
York, 1967. Lide, D. R. CRC Handbook of Chemistry and Physics, 73rd
ed.; CRC Press: Boca Raton, FL, 1993.
(7) (a) Crespo, O.; Ferna´ndez, E. J.; Jones, P. G.; Laguna, A.; Lo´pez-de-
Luzuriaga, J. M.; Mend´ıa, A.; Monge, M.; Olmos, E. Chem. Commun.
1998, 2233. (b) Ferna´ndez, E. J.; Jones, P. G.; Laguna, A.; Lo´pez-de-
Luzuriaga, J. M.; Monge, M.; Olmos, E.; Pe´rez, J. Inorg. Chem. 2002,
41, 1056. (c) Ferna´ndez, E. J.; Laguna, A.; Lo´pez-de-Luzuriaga, J. M.;
Monge, M.; Olmos, E.; Pe´rez, J. J. Am. Chem. Soc. 2002, 124, 5942.
(8) (a) Wang, S.; Fackler, J. P., Jr.; King, C.; Wang, J. C. J. Am. Chem. Soc.
1988, 110, 3308. (b) Wang, S.; Garzo´n, G.; King, C.; Wang, J. C.; Fackler,
J. P., Jr. Inorg. Chem. 1989, 28, 4623.
(9) Catalano, V. J.; Bennett, B. L.; Kar, H. M.; Noll, B. C. J. Am. Chem.
Soc. 1999, 121, 10235.
(10) Blasse, G.; Grabmaier, B. C. Luminescent Materials; Springer-Verlag:
New York, 1994; pp 216-218. A similar, but somewhat more complex,
emission has been observed for the linear chain complex, [Au(TPA)2Au-
(CN)2]n. See: Assefa, Z.; Omary, M. A.; McBurnett, B. G.; Mohamed,
A.; Fackler, J. P., Jr.; Patterson, H. H.; Staples, R. J. Inorg. Chem. 2002,
41, 6274-6280.
(11) Scanning Electron Microscopy and X-ray Microanalysis; Goldstein, J. I.,
et al., Eds.; Plenum Press: New York, 1992.
(12) Crystallizations from different solvents give different structures and
different coordination of the ligands to Tl.
JA028734U
9
J. AM. CHEM. SOC. VOL. 125, NO. 8, 2003 2023