J. Am. Chem. Soc. 2001, 123, 9689-9691
Chart 1. Structure of the Trinuclear Compounds Studied
9689
Chemistry and Optoelectronic Properties of Stacked
Supramolecular Entities of Trinuclear Gold(I)
Complexes Sandwiching Small Organic Acids
Manal A. Rawashdeh-Omary, Mohammad A. Omary,† and
John P. Fackler, Jr.*
Department of Chemistry, Texas A&M UniVersity
College Station, Texas 77843
cyanides may directly bind to the “exposed” linear 2-coordinate
Au(I) centers.9 However, DFT calculations that we have carried
out8 clearly show that the donor regions in the trinuclear Au(I)
compounds are located at the center of the nine-membered ring
and that they extend to regions in space above and below the
ring plane, as opposed to being localized on the Au atoms. Indeed,
we show here that a charge-transfer complex with a columnar
structure does form when a small tetracyano-substituted organic
acceptor reacts with 1. Previous attempts for the reaction with
cyano-substituted organic acceptors have lead to the rupture of
the trinuclear Au(I) unit and formation of mononuclear cations.10
We also show here that the liquid organic acid C6F6 forms a
stacked complex with 2 and quenches its luminescence, thus
suggesting a potential sensing action.
A saturated solution containing 7.0 mg (0.034 mmol) of 7,7,8,8-
tetracyanoquinodimethane (TCNQ) dissolved in 1 mL of CH2-
Cl2 was prepared and warmed in a water bath until dissolution.
A 35 mg (0.033 mmol) sample of 1 was added to the light-yellow
CH2Cl2 solution, and an intense green color was observed
immediately. Crystallization from CH2Cl2/ether produced dark
crystals that were analyzed by X-ray crystallography and scanning
electron microscopy (SEM).
The product, 3, of the reaction of 1 with TCNQ was
characterized by elemental analysis11 and X-ray crystallogra-
phy12,13 as [1]2TCNQ. The crystal structure of 3 is shown in Figure
1. The TCNQ molecule is sandwiched between two units of 1
from each side, in a face-to-face manner so that a molecule of 3
is best represented by the formula (π-1)(µ-TCNQ)(π-1). The
cyanide groups are clearly not coordinated to the gold atoms. The
distance between the centroid of TCNQ to the centroid of the
Au3 unit is 3.964 Å. The packing of 3 shows a stacked linear-
chain structure, as shown in Figure 1, with a repeat pattern of
‚‚‚(Au3)(Au3)(µ-TCNQ)(Au3)(Au3)(µ-TCNQ)‚‚‚ The stacking in
3 is similar to the previously reported7,8 sandwich adducts of 1
with Tl+, Ag+, and Hg3(µ-C6F4)3, all of which also show a
‚‚‚BBABBA‚‚‚ infinite chain pattern with intermolecular auro-
philic bonding between four out of the six Au atoms in adjacent
Au3 units. A striking difference in 3, however, is the two very
short intermolecular Au‚‚‚Au distances of 3.152 Å (identical for
the two aurophilic bonds). The intermolecular Au‚‚‚Au distance
in 3 is even shorter than the intramolecular distances in the
compound, which were found to be 3.475, 3.471, and 3.534 Å.
The adjacent Au3 units in 3, as well as in the previously reported
adducts of 1 with Tl+, Ag+, and Hg3(µ-C6F4)3, form a chair-type
structure as opposed to the face-to-face (nearly eclipsed) pattern
reported in Balch’s studies9 of the nitro-9-fluorenones adducts
with the trinuclear Au(I) alkyl-substituted carbeniate complexes.
Rossana Galassi, Bianca R. Pietroni, and Alfredo Burini*
Dipartimento di Scienze Chimiche
UniVersity of Camerino, Via S. Agostino
1-062032- Camerino, Italy
ReceiVed May 25, 2001
Extended linear-chain inorganic compounds have special
chemical and physical properties.1,2 This has led to new develop-
ments in fields such as supramolecular chemistry, acid-base
chemistry, luminescent materials, and various optoelectronic
applications. Among the recent examples are the developments
of a vapochromic light-emitting diode from linear-chain Pt(II)/
Pd(II) complexes,3 a luminescent switch consisting of an Au(I)
dithiocarbamate complex that possesses a luminescent linear-chain
form only in the presence of vapors of organic solvents,4 mixed-
metal (Ag/Au) compounds that exhibit different colors and
emissions when different organic solvents are introduced or
removed,5 and the discovery of a new phenomenon, solvolumi-
nescence,6 in a trinuclear Au(I) complex whose extended-chain
structure is responsible for storage of energy and release of it as
long-lived orange phosphorescence upon contact with solvent.
We have been studying trinuclear Au(I) compounds with
aromatic-substituted imidazolate, 1, and carbeniate, 2, bridging
ligands (Chart 1). These compounds are colorless and do not form
extended-chain structures. However, we have recently reported
that they can produce brightly colored complexes by sandwiching
naked Tl+ and Ag+ ions to form linear-chain complexes with
fascinating luminescence properties such as luminescence thermo-
chromism.7 More recent results have demonstrated that the
electron-rich trinuclear Au(I) complexes can interact with the
neutral inorganic Lewis acid Hg3(µ-C6F4)3 to produce infinite
linear-chain complexes.8 We have then focused our efforts on
studying the reactivity of 1 and 2 with small organic Lewis acids
and electron acceptors. Balch and co-workers have recently
demonstrated that trinuclear Au(I) compounds with alkyl-
substituted carbeniate bridging ligands can interact with the large
organic acceptors nitro-9-fluorenones.9 It was suggested that
cyano-substituted acceptors should be avoided because the
† Permanent address: Department of Chemistry, University of North Texas,
Denton, TX 76209.
(1) Extended Linear Chain Compounds; Miller, J. S., Ed.; Plenum Press:
New York, 1982; Vols. 1-3.
(2) Hoffmann, R. Angew. Chem., Int. Ed. Engl. 1987, 26, 846.
(3) Kunugi, Y.; Mann, K. R.; Miller, L. L.; Exstrom, C. L. J. Am. Chem.
Soc. 1998, 120, 589.
(4) Mansour, M. A.; Connick, W. B.; Lachicotte, R. J.; Gysling, H. J.;
Eisenberg, R. J. Am. Chem. Soc. 1998, 120, 1329.
(5) Laguna, A. Personal communications.
(6) Vickery, J. C.; Olmstead, M. M.; Fung, E. Y.; Balch, A. L. Angew.
Chem., Int. Ed. Engl. 1997, 36, 1179.
(7) (a) Burini, A.; Bravi, R.; Fackler, J. P., Jr.; Galassi, R.; Grant, T. A.;
Omary, M. A.; Pietroni, B. R.; Staples, R. J. Inorg. Chem. 2000, 39, 3158.
(b) Burini, A.; Fackler, J. P., Jr.; Galassi, R.; Pietroni, B. R.; Staples, R. J.
Chem. Commun. 1998, 95.
(10) Jiang, F.; Olmstead, M. M.; Balch, A. L. J. Chem. Soc., Dalton Trans.
2000, 4098.
(11) Anal. Calcd (found) for C72H58N16Au6: C, 37.13 (36.60); H, 2.51
(2.34); N, 9.62 (9.25).
(12) Crystallographic data were obtained using a Siemens SMART CCD
diffractometer, Mo KR radiation (λ ) 0.71069 Å), T) 110(2) K.
(13) Crystal data for 3: triclinic, space group P-1, a ) 11.581(5) Å, b )
11.688(5) Å, c ) 13.572(5) Å, R )106.249(5)°, â ) 107.005(5)°, γ )94.076-
(5)°, V ) 1663.0(12) Å3, Z ) 2, Fcalc) 2.326 g cm-3, 7716 data, R1 ) 0.0579
(all data).
(8) Burini, A.; Fackler, J. P., Jr.; Galassi, R.; Grant, T. A.; Omary, M. A.;
Rawashdeh-Omary, M. A.; Pietroni, B. R.; Staples, R. J. J. Am. Chem. Soc.
2000, 122, 11264.
(9) Olmstead, M. M.; Jiang, F.; Attar, S.; Balch, A. L. J. Am. Chem. Soc.
2001, 123, 3260.
10.1021/ja016279g CCC: $20.00 © 2001 American Chemical Society
Published on Web 09/07/2001