[Tl(OPPh3)2][Au(C6F5) 2]: The first extended unsupported gold-thallium linear chain

Article abstract of DOI:10.1039/a806077k

Li[Au(C₆F₅)₂] reacts with TlNO₃ in the presence of OPPh₃ affording a complex of stoichiometry [AuTl(C₆F₅)₂-(OPPh₃) ₂]_n, which presents different luminescence properties depending on the conditions and whose crystal structure reveals the existence of unsupported Au-Tl bonds forming a polymeric linear chain.

Full text of DOI:10.1039/a806077k

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[Tl(OPPh3)2][Au(C6F5)2]: the first extended unsupported gold–thallium linear
chain
Olga Crespo,a Eduardo J. Fernández,b Peter G. Jones,c Antonio Laguna,*a José M. López-de-Luzuriaga,b
Aránzazu Mendía,b Miguel Mongeb and Elena Olmosb
a Departamento de Química Inorgánica, Instituto de Ciencia de Materiales de Aragón, Universidad de Zaragoza-CSIC, E-50009
Zaragoza, Spain. E-mail: alaguna@posta.unizar.es
b Departamento de Química, Universidad de La Rioja, Obispo Bustamante 3, E-26001 Logroño, Spain
c Institüt für Anorganische und Analytische Chemie der Technischen Universität, Postfach 3329, D-38023 Braunschweig, Germany
Li[Au(C6F5)2] reacts with TlNO3 in the presence of OPPh3
affording complex of stoichiometry [AuTl(C6F5)2-
(OPPh3)2]n, which presents different luminescence proper-
ties depending on the conditions and whose crystal structure
reveals the existence of unsupported Au–Tl bonds forming a
polymeric linear chain.
reduction of the gold(III) centre and the oxidation of the
triphenylphosphine.
a
The structure of 1 was determined by single-crystal X-ray
diffraction15‡ (Fig. 1). The two independent gold atoms lie on
inversion centres and thus display exact linear co-ordination by
the C6F5 groups with Au–C distances of 2.058(5), 2.053(6) Å,
whereas the thallium centre is bonded to two OPPh3 ligands
[O(1)–Tl–O(2) = 80.61(3)°] with typical Tl–O distances of
2.483(3) and 2.550(4) Å. The compound forms a one-
dimensional polymer parallel to the crystallographic x axis.
Including the metal–metal interactions, the geometry at gold is
almost square planar and that at thallium is distorted trigonal
bipyramidal with a vacant equatorial co-ordination site, pre-
sumably associated with the stereochemically active lone pair.
The Tl–Au distances [Au(1)–Tl = 3.0358(8), Au(2)–Tl =
3.0862(8) Å] are nearly equal and similar to the sum of thallium
and gold metallic radii (3.034 Å). They are similar to those
There is a renewed interest in mixed gold–transition metal
compounds because of their fascinating and unique chemical
and physical properties. A central issue in their chemistry is the
study of closed-shell metal–metal interactions, which have been
attributed to correlation effects that are strengthened by the
relativistic effects for gold.1 Structural and theoretical evidence
has been accumulated for an entire family of cation–cation
interactions between d8–d10–s2 systems.2 Particularly inter-
esting are extended linear chain compounds, because the
rationalization of the bonding of these structures still remains as
a challenge.3,4 For instance, Tl2Pt(CN)4,5 with a Tl–Pt distance
of 3.14 Å, was expected to be ionic with some covalent
character6 although correlation effects and the crystal-field
contributions seem to be also important.7 In contrast,
[AuTl{Ph2P(S)CH2}2],3,8 with a shorter Tl–Au distance (3.003
Å), displays mainly ionic bonds between Tl+ and [AuX2]2
moieties.2 This latter unit is also present in the polymeric
species [AgAuX2L2],9,10 where X is a pentafluorophenyl group,
thus avoiding any bridging effect. Mössbauer spectroscopic
studies of such species indicate that [Au(C6F5)2]2 groups act as
Lewis bases; the presence of perfluorophenyl groups seems to
be the key for their donor properties,11 which are similar to
those postulated for dinuclear units of the form [Au(y-
lide)]2.12–14
found in [AuTl(Ph2P(S)CH2)2]n [Tl–Au(intramolecular)
=
2.959(2), Tl–Au(intermolecular) = 3.003(2) Å],3,8 where two
‘supporting’, Ph2P(S)CH2 ligands are C-bonded to each gold
centre and S-bonded to each thallium atom of a linear chain in
which the metallic centres exhibit similar geometries as in 1.
Complex 1 may be considered as containing [Au(C6F5)2]2 and
Despite the results previously reported, [Au(C6F5)2]2 has not
hitherto been employed in the synthesis of other heterometallic
compounds. We report here the synthesis and characterization
of [Tl(OPPh3)2][Au(C6F5)2] (1), the first extended unsupported
gold–thallium linear chain. This material is formed by reacting
a mixture of triphenylphosphine oxide and a solution of TlNO3
in MeOH with a freshly prepared solution of Li[Au(C6F5)2] in
diethyl ether at 278 °C. The LiNO3 formed is filtered off and
the colourless solution is layered with pentane. Yellow-green
crystals of complex 1 are collected after three days in a 40%
yield. Compound 1 shows analytical and spectroscopic data in
accordance with the proposed structure† and behaves as a 1:1
electrolyte in acetone. The absence of colour in ether or acetone
solution implies that the interactions between the metal centres
are restricted to the solid state.
Fig. 1 Molecular structure of complex 1. Selected distances (Å) and angles
(°): Au(1)–C 2.058(5), Au(2)–C 2.053(6), Au(1)–Tl 3.0358(8), Au(2)–Tl
3.0862(8), Tl–O(1) 2.483(3), Tl–O(2) 2.550(4), C(11)–Au(1)–Tl 90.8(2),
C(11)i–Au(1)–Tl 89.2(2), C(81)–Au(2)–Tlii 88.0(2), C(81)–Au(2)–Tl
92.0(2), O–Tl–O 80.61(13), O(1)–Tl–Au(1) 94.73(11), O(2)–Tl–Au(1)
86.16(11), O(1)–Tl–Au(2) 99.04(11), O(2)–Tl–Au(2) 105.55(11), Au(1)–
Tl–Au(2) 163.163(8). Symmetry operators: i 2x, 2y + 1, 2z; ii 2x + 1, 2y
+ 1, 2z.
In contrast, when the same reaction is carried out with the
NBu4+ instead of the lithium salt, the complex is not formed and
the gold( ) starting material is recovered unaltered. However,
I
treatment of [Au(C6F5)2Cl(PPh3)] with equimolecular amounts
of thallium acetylacetonate surprisingly affords complex 1. The
mechanism of such a reaction is not clear, but it involves the
Chem. Commun., 1998
2233

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halogenated solvents and irradiated with UV light, the emission
is also quenched but, upon evaporation of the solvent, it does not
regenerate the green product, but instead an uncharacterized
grey solid appears which shows an emission at higher energy
(476 nm). If the process of dissolution in CH2Cl2 is carried out
in the dark, the green product is recovered without any change.
This promising result seems to indicate that under UV radiation
the excited state is able to react with halocarbons in an electron
transfer reaction, perhaps making this product appropriate for
practical applications.
We are grateful to Professor J. P. Fackler, Jr. for his helpful
discussions and the facilities for using his laboratory material.
This work was supported by the D.G.E.S. (PB97-
1010-C02-02), the University of La Rioja (API-98/B09) and the
Fonds der Chemischen Industrie.
Notes and References
† Selected data for 1: (Calc. for C48H30AuF10O2P2Tl: C, 44.51; H, 2.33.
Found: C, 44.14; H, 2.00%). IR: n(PNO): 1178 (vs); C6F5: 1503 (vs), 957
(vs), 784 (m) cm21 31P{1H} NMR (CDCl3): d 30.0 (s, OPPh3); 19F NMR
.
Fig. 2 Excitation and emission spectra of complex 1 in the solid state at 293
K (dashed line) and at 77 K (solid line) (excitation in curve A, emission in
curve B)
(CDCl3): d 2115.4 (m, Fo), 2158.6 (t, J 20 Hz, Fp), 2161.8 (m, Fm). MS
(FAB+): m/z(%) = 761(5) [M]+; MS (ES): m/z(%) = 531(100) [M]2. L
(5.0 3 1024 , acetone): 113 W21 cm2 mol21
.
M
‡ Crystal data for 1: C48H30AuF10O2P2Tl, T = 2100 °C, M = 1292.00,
monoclinic, space group P21/n, a 12.112(3), b 27.006(3), c
13.515(2) Å, b = 91.891(12)°, V = 4418.2(14) Å3, Z = 4, m = 7.11 mm21
=
=
=
[Tl(OPPh3)2]+ ions, which are linked by weak M–MA bonds thus
forming the first unsupported Au–Tl linear chain. Four weak
Tl···F contacts (3.313–3.488 Å) may also contribute to the
stability of the system.
,
10486 reflections (Siemens P4 diffractometer, Mo-Ka radiation, 2qmax 50°,
w-scans), 7764 unique. Refinement on F2 using all reflections; program
system SHELXL-93. Final R = 0.0305, Rw = 0.0456, for 581 parameters
and 544 restraints; max. Dr 0.6 e Å23. CCDC 182/1021.
Furthermore,
the
heteronuclear
complexes
[AuTl(Ph2P(S)CH2)2] and [Au2Pb(Ph2P(S)CH2)4]3,8 with d10
and s2 electronic configurations are luminescent and also form
linear Au–M linear chains. Similarly, complex 1 luminesces
both at room temperature (293 K) (excitation at 421 nm,
emission at 494 nm) and at 77 K (maximum excitation at 403
nm, emission at 494 and 530 nm) in the solid state (Fig. 2). The
excitation and emission spectra for 1 are virtually mirror images
of each other with only a small separation between excitation
and emission peaks, suggesting that the dominant emission in
this complex is perhaps fluorescence.
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Previous Fenske–Hall molecular orbital calculations for a
gold–thallium complex3,8 indicated that although no formal
metal–metal single bond is present, the HOMO is a s* orbital
mainly of Tl(
I
) and the LUMO is a s orbital of both Au( ) and
I
Tl(
I
) orbitals. Thus, a feature of this excited state is that the
transfer of an electron from an antibonding orbital to a bonding
orbital results in a net increase of intermetallic bonding in the
excited state, but the luminescence spectrum suggests that there
is no change in the Au–Tl distances in this linear chain
species.
Neither the gold(
I
) nor Tl( ) precursor complexes are
I
luminescent under similar conditions suggesting that the
emission is a result of interactions between the metals.
Moreover, when the product is dissolved in non-halogen
solvents the green colour of the solid disappears and the
resultant colourless solution is non-emissive. Evaporation of the
solvents regenerates the colour and its optical properties.
Another interesting feature is when 1 is saturated with
Received in Basel, Switzerland, 3rd August 1998; 8/06077K
2234
Chem. Commun., 1998