Conducting neutral gold bisdithiolene complex [Au(dspdt)2]

Article abstract of DOI:10.1039/d0dt02931a

[Au(dspdt)2] (dspdt = 2,3-dihydro-5,6-selenophenedithiolate) is an unprecedented example of a neutral gold bisdithiolene complex with a unique structure composed of interacting dimer and trimer chains displaying relatively high electrical conductivity (0.

Full text of DOI:10.1039/d0dt02931a

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Conducting neutral gold bisdithiolene complex
[Au(dspdt)2]•†
Cite this: Dalton Trans., 2020, 49,
13737
Mariana F. G. Velho,a,b Rafaela A. L. Silva,a Graça Brotas,a Elsa B. Lopes,
a,c
Isabel C. Santos, a,c Ana Charas,b Dulce Belo
*
a,c and Manuel Almeida
*
a,c
Received 20th August 2020,
Accepted 21st September 2020
[Au(dspdt)2] (dspdt = 2,3-dihydro-5,6-selenophenedithiolate) is an unprecedented example of a neutral
gold bisdithiolene complex with a unique structure composed of interacting dimer and trimer chains dis-
playing relatively high electrical conductivity (0.1 S cm−1 at room temperature).
DOI: 10.1039/d0dt02931a
rsc.li/dalton
been largely unsuccessful. Almost all such solids behave as
insulators or poor semiconductors, except in a few cases if
Introduction
Considering very significant developments in the field of mole- under high pressure.11,16,17 This failure arises because the
cular conducting materials during the last decades several typical intermolecular interactions are relatively weak and lead
hundred molecular metals and superconductors are presently to electron bandwidths significantly smaller than the on-site
known.1 The large majority of molecular conductors are com- electron repulsion interactions. Therefore, half-filled bands
pounds based on two components, such as charge transfer generated from singly occupied states (SOMO bands) in mole-
salts, in which at least one electron donor or acceptor molecule cular solids behave invariably as Mott-insulators.
becomes partially oxidised and builds in the solid an extended
The first well-succeeded examples of single component
network of interactions, leading to partially filled bands molecular solids with metallic properties at ambient pressure
responsible for electrical conducting properties. In contrast, have been provided by molecules with small HOMO–LUMO
the possibility to achieve metallic properties in molecular gaps and large intermolecular interactions. These conditions
solids based on a single component, as in elemental metals, is allow the overlap between the valence and conduction bands,
a much less explored possibility.2–5
which become partially filled as in a semimetal. This possi-
The difficulty in obtaining molecular metals based on bility was early suggested for [M(dmit)2] (M: Ni, Pd, dmit = 4,5-
single components arises from the fact that the large majority dimercapto-1,3-dithiole-2-thione) complexes,18 and later found
of stable molecules are characterised by a large HOMO–LUMO in the first single component molecular metal characterised as
gap and these frontier orbitals led, in the solid state, to a single crystal, a neutral nickel bisdithiolene complex [Ni
valence and conductions bands, respectively, separated by (tmdt)2], (tmdt
= trimethylenetetrathiafulvalenedithiolate),
large energy gaps. In this context, radical species were since based on an highly extended dithiolene ligand fused with a
early pointed out as good candidates, since the unpaired elec- TTF moiety.3 Metallic behaviour has also been observed in
trons could lead to partially filled bands without the need of neutral bisdithiolene complexes of nickel and other metals
charge transfer to or from any other molecular unit.6 However, based on similar type of ligands with TTF moieties.4 Although
in spite of several attempts using delocalised planar radicals this type of extended ligands are regarded as good candidates,
based on phenalenyl-7,8 and thiazolyl-based radicals,9–11 as they have low-HOMO–LUMO gaps and can promote large
coupled TTFs (TTF = tetrathiafulvalene) and radical units,12 or intermolecular interactions, highly conducting properties have
neutral gold bisdithiolene complexes13–15 this possibility has also been observed at ambient pressure in a few gold com-
plexes with smaller ligands,2,5 in other purely organic mole-
cular units such as catechol functionalised19 or zwiterionic
aCentro de Ciências e Tecnologias Nucleares, Instituto Superior Técnico,
TTF derivatives.20 A stable and highly conducting metallic
Universidade de Lisboa, E.N. 10, P-2695-066 Bobadela LRS, Portugal.
state was recently achieved at ambient pressure in a neutral
E-mail: dbelo@ctn.tecnico.ulisboa.pt, malmeida@ctn.tecnico.ulisboa.pt
bInstituto de Telecomunicações, Instituto Superior Técnico, Av. Rovisco Pais 1,
P-1049-001 Lisboa, Portugal
gold bisdithiolene complex with a thiazoldithiolate ligand, as
a consequence of a larger superposition of SOMO and
SOMO−1 bands, with electron transfer from the last to the
first one.5
cDepartamento de Engenharia e Ciências Nucleares, Instituto Superior Técnico,
Universidade de Lisboa, E.N. 10, P-2695-066 Bobadela LRS, Portugal
†Electronic supplementary information (ESI) available: Fig. S1–S8 and Tables
S1–S9. CCDC 2015926–2015928. For ESI and crystallographic data in CIF or
other electronic format see DOI: 10.1039/d0dt02931a
Here we report a selenium derivative of [Au(α-tpdt)2]
(α-tpdt = 2,3-thiophenedithiolate),2 [Au(dspdt)2] (dspdt = 2,3-
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ring ethyl groups (Fig. S1†). The crystal structure of 1 is com-
posed by head-to-tail columns, running along a (Fig. S2b†).
Along the columns the molecules are connected by C–H⋯S
hydrogen bonds. Between columns, neighbouring molecules
are connected through an intricate 3D network of S⋯S and
S⋯Se short contacts (Fig. S2a/c†).
Chart 1 Chemical structures of gold bisdithiolene complexes with
thiophene and selenacyclopentane, respectively.
The monoanionic gold complex, nBu4N[Au(dspdt)2] 2, was
prepared following a general procedure, commonly used to
prepare similar bisdithiolene complexes (Scheme 1).2 The
ligands were obtained in solution from 1 by an hydrolytic clea-
vage with sodium methoxide in methanol, followed by
addition of potassium tetrachloroaurate(III), leading to the pre-
cipitation of the corresponding tetrabutylammonium (2a) or
tetraphenylphosphonium (2b) salts after treatment with
nBu4NBr or Ph4PBr, respectively. The tetraphenylphosphonium
salt is easier to prepare and has a more reasonable yield than
2a, which could only be obtained as a few dark brown needle
shaped crystals suitable for X-ray diffraction, demonstrating
the formation of the anionic complex (Tables S3–S6 and
Fig. S3, S4†).
dihydro-5,6-selenophenedithiolate) (Chart 1). This new deriva-
tive displays an unusual structural arrangement composed of a
combination of interacting dimer and trimer columns and
semiconducting properties with relatively high electrical con-
ductivity associated with the splitting of closely spaced energy
bands derived from SOMOs.
Results and discussion
The key compound to prepare [Au(dspdt)2] is thione 1 (5,6-
dihydroselenolo[2,3-d]-1,3-dithiole-2-thione), obtained by
a
In the crystal structure of 2a, the anionic complex presents
a square planar coordination geometry (Fig. 1) with S–Au dis-
tances of 2.32 Å and a small boat distortion due to hydrogen
bonds between the cations involving sulphur and selenium
atoms. The selenium atoms appear disordered over two equi-
populated positions denoting either cis–trans disorder or most
likely an orientation disorder of trans configuration. The
crystal structure is composed by consecutive anionic grid
layers, growing in the bc plane. Apart a few intermittent Se⋯Se
short contacts between anions, the molecules in the layers are
separated at distances slightly above the sum of the van der
Waals radii. There is no interactions between anions in neigh-
bouring layers. The cations occupy the empty space in this
honeycomb anionic structure, contacting with the anions
throughout several S⋯H–C hydrogen. Further details are given
in Tables S3–S6 and Fig. S3, S4.†
modified version of previously described procedure
a
(Scheme 1).21 The synthesis of 1 is based on a previously
reported procedure by Jigami et al.,21 however with some modi-
fications since for us the method described to obtain the first
intermediate (A) was not reproducible. The synthesis of this
compound starts with a cyclization reaction of commercial
available 2-(3-butynyloxy)tetrahydro-2H-pyran with nBuLi,
sulphur and carbon disulphide, giving the 1,3-dithiole-2-
thione ring. This reaction was performed without the reported
addition of tetramethylethylenediamine or MeOH.21
Afterwards, selenium powder was added and the reaction was
quenched with MeI, giving A.
Selected single crystals enabled the determination of the
crystal structure of 1 by X-ray diffraction (Tables S1, S2 and
Fig. S1, S2†). The molecule is planar, with exception of the
The redox properties of 2, studied by cyclic voltammetry,
show a pair of redox waves centred at E1/2, of 42.5 mV vs. Ag/
AgNO3 (E1/2(Fc/Fc+) = 357 mV), (Fig. 4) ascribed to the couple
[Au(dspdt)2]−/[Au(dspdt)2]0 indicating the possibility to obtain
the neutral complex 3 as a stable compound.
Indeed, the oxidation of the monoanionic complex 2 to give
the neutral complex 3 could be carried out with iodine in solu-
Scheme 1 Synthesis of the thione 1 and monoanionic (2) and neutral
(3) gold complexes [Au(dspdt)2]: (i) nBuLi, THF, −78 °C; (ii) S, 0° C;
(iii) CS2, −78° C; (iv) Se then MeI, 0° C; (v) HCl (aq.), acetone/MeOH;
(vi) TsCl, pyridine; (vii) NaI, DMF, 80 °C; (viii) DDQ, toluene, reflux.
(viii) MeONa, KAuCl4 in MeOH, nBu4NBr (2a) or Ph4PBr (2b) in MeOH;
(ix) treatment with an iodine solution in acetone or electrochemical oxi-
dation at constant potential.
Fig. 1 (a) Top and side view of the [Au(dspdt)2]− complex in 2a, (b)
short contacts between anion pairs in plane b, c.
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Fig. 4 Nearby dimer and trimer columns in 3 viewed along a axis.
Fig. 2 Cyclic voltammetry of [Au(dspdt)2]− in CH2Cl2, 0.5 × 10−3 M with
nBu4NPF6 0.1 M as supporting electrolyte, E [V] vs. Ag/AgNO3, Pt elec-
trode and scan rate 100 mV s−1. The ferrocene/ferrocenium (Fc/Fc+)
couple was measured in the same conditions, displaying a E1/2 = 357 mV
vs. Ag/AgNO3.
The neutral complexes are arranged as centrosymmetric A–
A dimers and B–C–B trimers, where the molecules overlap par-
allel to each other with a metal-over-metal mode with short
interplane distances of 3.581 Å and 3.622 Å respectively, and
with several intermolecular atomic distances well below the
sum of van der Waals radii (Table S9†).
The unit cell contains 20 neutral complex units organised
in four trimers and four dimers, as shown in Fig. 3. The crystal
structure is composed of columns along b of closely spaced
side-by-side dimers and columns of trimers (Fig. 2 and
Fig. S6†). The dimer and trimer columns alternate in the a,c
plane in such a way that each trimer column is surrounded by
4 next neighbour dimer columns and each dimer column is
surrounded by 4 columns of trimers. The arrangement in
dimers is quite common in neutral gold bisdithiolene
complexes,13,14 as well as in other radical species, driven by
the strong pairing interaction of SOMOs. However, the for-
mation of trimers is quite uncommon and the present struc-
tural type composed of a mixture of dimer and trimer columns
is to the best of our knowledge unprecedented.
Fig. 3 Crystal structure of 3, [Au(dspdt)2]•, viewed along b axis. Only
one trans configuration for the disordered Se atoms was considered.
The thin blue lines denote short contacts.
Electrical conductivity was measured in small single crys-
tals and showed a value of 0.1 S cm−1 at room temperature, fol-
lowing a semiconducting behaviour with an activation energy
of 95 meV (Fig. 5). This conductivity, although not as large as
other single component compounds behaving as metals at
ambient pressure, such as [Au(α-tpdt)2] (7 S cm−1 in polycrys-
tion, giving a dark fine powder. As an alternative, the oxidation
can be done electrochemically at a constant potential (300 mV
vs. Ag/AgNO3) yielding small dark needle crystals (up to 0.5 ×
0.03 × 0.03 mm3) suitable for X-ray diffraction.
talline sample),2 [Au(tmdt)2] (50
S
cm−1 in crystalline
The asymmetric unit of 3 contains two neutral complex
units A and B in general position and half complex C with the
gold atom in an inversion center (Fig. S5†). As often observed
in similar thiophenic complexes the Se atoms appear dis-
ordered between two positions, most likely resulting from the
usual orientation disorder of trans configuration.22,23 With
exception of a small distortion in the ethylene groups the com-
plexes are essentially planar with unit B presenting a small
boat type distortion. The Au–S bond lengths (∼2.31 Å) are com-
parable to other neutral gold bisdithiolene complexes (Tables
S7 and S8†). A comparative analysis between the bond lengths
in the neutral and monoanionic gold complexes shows a short-
ening of the Scoord–C bond length (1.75 Å in 2 and 1.69 Å in 3),
while the Au–S remains essentially the same, denoting a
ligand centered oxidation process.23
Fig. 5 Temperature dependence of electrical resistivity, ρ, of [Au(dspdt)2]•.
Dalton Trans., 2020, 49, 13737–13743 | 13739
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sample)24 and [Au(Me-thiazdt)2] (Me-thiazdt = N-methyl-1,3-
thiazoline-2-thione-4,5-dithiolate, 750 S cm−1 in single crys-
tals),5 is rather large for a single-component material based on
a gold complex.25–27
The electrical properties of this compound can be under-
stood in view of the intermolecular electronic interactions and
the resulting electronic band structure. With 20 molecules in
the unit cell, each with different possible configurations of Se
atoms, the number of different intermolecular interactions is
rather large. Their magnitude is expected to be quite different,
depending on the type of contacts, and can be estimated using
an extended Hückel approach.28–31 For sake of simplicity in
the analysis of the different intramolecular interactions, only
one trans configuration was considered.
As seen in Table 1 the largest |βHOMO–HOMO| energy inter-
actions are between closely spaced face-to-face molecules in
the trimer (β1 = 907 meV) and dimer (β6 = 998 meV). Along b
the trimers are arranged in columns with side-by-side inter-
actions β2, β3 and β4, with values of 114, 100 and 28 meV,
respectively. The dimers along the columns present also side-
Fig. 6 Calculated band structure of [Au(dspdt)2]•, 20 SOMO bands near
the Fermi level (dashed line). The. Γ, X, Y and M and refer to the (0, 0, 0),
(21, 0, 0), (0, 21, 0), (21, 21, 0), points in k-space, respectively.
by-side interactions of smaller magnitude, β5 = 17 and β7
=
36 meV. In addition, there are intercolumn interactions β7–β13,
with values listed in Table 1. The intercolumn interactions are
quite anisotropic being more significant along the long axis of
the dimers reaching 100 meV for β8, while they are signifi-
cantly smaller along a.
middle one half filled. Therefore, the chains of radical dimers
are expected to lead to semiconducting properties due to the
large dimer gap, while the trimer chains will behave as Mott
insulators, as observed in all molecular materials with half-
filled bands due to on-site electron–electron repulsion inter-
actions larger than the bandwidth. The above situation,
expected for isolated chains, contrasts with the present case
where, due to the significant intercolumn interactions between
dimers and trimer chains, there is a strong splitting of the
bands in sets of 4, with the Fermi level crossing the four
central bands at different wave vectors.
Although 3 is highly conducting for a solid composed of a
single neutral species, it is not metallic as predicted by this
ideal model without electron correlation effects, but rather
semiconducting with relatively high conductivity and low acti-
vation energy. Although the Fermi level lies close to the lower
set of dimer bands, the compound is still in the range of Mott-
insulator with unpaired electrons localized in each trimer. In
addition, the disorder in the Se atoms position, not taken into
account in the calculations, where only one trans configuration
for the complexes was assumed, may also contribute to the
electronic localisation.
Based on the intermolecular interactions it is possible to
estimate the electronic band structure using a tight-binding
extended Hückel approach.28–31 The 20 donor molecules in the
unit cell lead to 20 bands derived from the SOMO orbital
around the Fermi level, as shown in Fig. 6 (additional band
structures and Fermi surface in Fig. S7 and S8†). These bands
result from a combination of mixed trimer and dimer parallel
bands that due to intercolumn interactions are considerably
split and partially overlapping. The two upper sets of 4 bands
result from an avoided crossing between the upper trimer and
the dimer SOMO bands, with larger and smaller dispersions,
respectively. The Fermi level crosses the central four bands,
mostly due to the nonbonding SOMO combination of the
trimers. The Fermi level is very close to the top of a lower set
of four bands along Γ–X, derived mainly from the lower dimer
orbitals.
This band structure can be understood recalling that a
single chain of strong radical dimers has two SOMO bands,
the lower one full and the upper one empty. On the other end
a single chain of trimers will lead to three SOMO bands, the
Experimental
General information
Table 1 βHOMO–HOMO energy interactions represented in Fig. 3 and
Fig. 2, in eV
All reactions were carried out under a nitrogen atmosphere
with dry solvents, unless otherwise stated. All solvents were
dried and distilled following the standard procedures.32 All the
reagents used on the synthesis, including the starting material
2-(3-butynyloxy)tetrahydro-2H-pyran, were purchased from
commercial sources and used without any additional
purification.
β (eV)
β1
β2
β3
β4
β5
β6
β7
0.907
β8
0.114
β9
0.100
β10
0.028
β11
0.017
β12
0.998
β13
0.036
β14
0.103
0.006
0.010
0.011
0.004
0.027
0.041
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Paper
Synthesis of 4-Methylseleno-5-[2-(tetrahydropyran-2-yloxy) 10−3 M) and tetrabutylammonium hexafluorophosphate (0.1
ethyl]-1,3-dithiole (A). Modified procedure based on the one M) undergo an electrochemical oxidation process at a constant
described by Jigami et al.:21 To a solution of 2-(3-butynyloxy) potential of 300 mV, during 4000 s. At the end, compound 3
tetrahydro-2H-pyran (1.26 mL, 7.80 mmol) in THF (47 mL) was was collected has small dark needles. FTIR (KBr), cm−1: 1256
added a solution of nBuLi in hexane (1.6 M, 5.0 mL) at −78° C (s, H2C-CH2 ligand), 1358 (m, C–H aliph), 1637 (m, CvC).
and the mixture was stirred for 30 min at the same tempera-
Cyclic voltammetry studies
ture. Then sulphur (250 mg, 7.80 mmol) was added and the
mixture was allowed to slowly warmed to 0° C over a period of Cyclic voltammetry data were obtained using a BAS C3 Cell
2 h and stirred at this temperature for other 2 h. Carbon disul- Stand. The voltammograms were obtained at room tempera-
phide (0.5 mL, 7.80 mmol) and selenium (616 mg, 7.80 mmol) ture with variable scan rates in the range of 20–500 mV s−1
,
were added at −78 °C and the mixture was again warmed to 0° platinum wire working and counter electrodes and a Ag/AgNO3
C over a period of 2 h and then stirred at the same temperature (0.01 M AgNO3 and 0.1 M nBu4NPF6 in acetonitrile) reference
for another hour. The reaction was quenched with methyl electrode, in which the Ag+ ion electrode was separated from
iodide (0.5 mL, 7.80 mmol) and after stirring 1 h at 0° C, water the bulk solution by a Vycor™ frit. The measurements were
(12 mL) was added to the mixture. The mixture was extracted performed on fresh solutions with
a concentration of
with CH2Cl2, washed with brine and dried with MgSO4. The 0.5 × 10−3 M, in dichloromethane, that contained nBu4NPF6
product was purified by column chromatography on silica gel (0.1 M) as a supporting electrolyte. Ferrocene was added
1
with CH2Cl2, giving 1.46 g of A as a yellow oil. Yield 52%. H directly to the solution after analysis to allow the potentials
NMR (300 MHz, CDCl3): δ 4.60 (br tr, J = 3.04, 1H), 3.89 (m, normalization in situ, relatively to the ferrocene/ferrocenium
1H), 3.76 (m, 1H), 3.50 (m, 2H), 3.06 (m, 2H), 2.30 (s, 3H), couple redox potential. Under the experimental conditions the
1.5–1.9 (m, 6H).
ferrocene/ferrocenium (Fc/Fc+) couple was found to bet E1/2
=
Synthesis of [nBu4N][Au(dspdt)2] (2a). Compound 1 (100 mg, 357 mV vs. Ag/AgNO3.
0.42 mmol) was added to a solution of sodium methoxide in
methanol, obtained by a complete reaction of metallic sodium
X-ray crystallography
(46 mg, 2 mmol) in methanol (10 mL). After stirred at 40 °C Crystallographic and experimental details of data collection
for 45 min, solution of potassium tetrachloroaurate and crystal structure determinations for the compounds 1, 2a
a
(79.3 mg, 0.21 mmol) in methanol (1 mL) was added and the and 3 are given in Table 2. Suitable crystals of these com-
mixture was stirred for an extra 1 h. The mixture was filter into pounds were mounted on a loop in Fomblin protective oil and
a
solution of tetrabutylammonium bromide (67.7 mg, data were collected on a Bruker APEX II area detector diffract-
0.21 mmol) in methanol (5 mL). There was no visible for- ometer at 150 K using graphite-monochromated Mo Kα (α =
mation of precipitate. The golden-brown solution was then 0.71073 Å) in the φ and ω scans mode. Cell parameters were
cooled and kept under a low flux of nitrogen. Maintaining retrieved using Bruker SMART and refined using Bruker SAINT
these conditions during several days was possible to collect on all observed reflections.33 Absorption corrections were
dark brown crystals suitable for single crystals X-ray studies. applied using SADABS.34 The structures were solved by direct
FTIR (KBr), cm−1: 685 (w, C–S), 736 (s, C–H aliph), 875 (m, C– methods using either SHELXS-9735 or SIR 9736 and refined
H aliph), 1241 (s, H2C–CH2 ligand), 1380 (m, C–H aliph), 1458 using full-matrix least squares refinement against F2 using
(m, C–H aliph), 1632 (m, CvC), 2858 (m, C–H aliph), 2954 (m, SHELXL-2014.37 In the former case, all programs are included
C–H aliph). UV-Vis (CHCl3): λmax = 370, 418 nm.
in the package of programs WINGX-v2014.1.38 All non-hydro-
Synthesis of [PPh4][Au(dspdt)2] (2b). This compound was gen atoms were refined anisotropically, unless it was men-
prepared following the same procedure as for 2a, using tetra- tioned in the cif files of the structures, and all hydrogen atoms
phenylphosphonium bromide (105.7 mg, 0.252 mmol) in were placed in idealized positions and allowed to refine riding
methanol (1 mL), instead of tetrabutylammonium bromide. on the parent carbon atom. Molecular graphics and packing
After standing for a few hours, the reaction mixture was fil- diagrams were prepared using MERCURY-4.3.39 (CCDC
tered and the collected solid was washed with methanol and 2015926, 2015927 and 2015928† contain supplementary crys-
diethyl ether. Compound 2b (96 mg) was obtained as a brown- tallographic data for 1, 2a and 3 respectively).
ish powder. Yield 50%. Elemental analysis calcd (%) for
Electric transport properties
C32H28AuPS4Se2: C 41.48, H 3.04, S 13.84; found C 40.53, H
2.99, S 13.11.
Electrical conductivity measurements were made along the
Synthesis of [Au(dspdt)2]• (3). Procedure a: To a solution of needle axis of the crystals in the temperature range of
2b (30 mg, 0.032 mmol) in acetone (3 mL) was added a solu- 200–310 K, using a measurement cell attached to the cold
tion of iodine (9 mg, 0.036 mmol) in acetone (1 mL). The stage of a closed cycle helium refrigerator. A four-in-line
mixture was stirred for 15 min and the collected solid was contact standard configuration DC method was used to
washed with acetone, yielding 24.3 mg (86%) of 3 as black crys- perform these measurements, using a Keithley 224 current
talline powder. Elemental analysis calcd (%) for C8H8AuS4Se2: source to apply through the sample both direct and reverse DC
C 16.36, H 1.37, S 21.84; found C 18.35, H <2.0, S 20.26. currents, and Keithley 619 electrometer to measure the corres-
Procedure b: A dichloromethane solution containing 2a (0.5 × ponding voltage drop, the current used was 1 µA.
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Table 2 Selected crystal data and data collection parameters for 1, 2a and 3
1
2a
3
Empirical formula
Crystal size (mm)
Formula weight
Cryst. system
Space group
a [Å]
b[Å]
c [Å]
α [°]
C5H4S3Se1
0.35 × 0.10 × 0.06
239.22
Orthorhombic
Pbca
C24H44N1S4Se2Au
0.20 × 0.02 × 0.02
829.73
Monoclinic
P21/c
C40H40S20Se10Au5
0.14 × 0.02 × 0.02
2936.35
Monoclinic
C2/c
40.7970(14)
6.4600(2)
29.1807(9)
90
7.4929(2)
9.4015(3)
11.7270(3)
16.9268(5)
90
17.8349(5)
17.9831(5)
90
β [°]
90
90
98.102(2)
90
2985.22(15)
4, 1.846
7.661
125.8850(10)
90
6230.8(4)
4, 3.130
18.278
γ [°]
V [Å3]
1487.34(7)
8, 2.137
5.791
Z, DCal (mg m−3
)
µ (mm−1
)
Tmin/Tmax
F (000)
θ range (°)
0.2364/0.7226
928
0.310/0.862
1624
0.184/0.711
5340
3.44–25.34
−5/9; −14/12; −20/20
7754/1354 (0.0407)
1354/0/82
R1 = 0.0184, wR2 = 0.0449
1.054
2.935–25.680
−9/11; −21/21; −21/21
29 859/5637 (0.0654)
5637/22/313
R1 = 0.0343, wR2 = 0.0586
1.037
3.419–26.371
−50/50; −7/8; −36/36
24 508/6326 (0.0993)
6326/112/381
R1 = 0.0522, wR2 = 0.0804
0.969
Index range (h, k, l)
Refle. collected/unique (Rint
Data/restraints/parameters
Final R indices [I > 2σ(I)]
GOF on F2
)
Largest diff. peak, hole/e Å−3
CCDC reference†
0.327, −0.278
2015926
1.425, −1.471
2015927
1.425, −1.471
2015928
Intermolecular energy interactions and band structure
calculations for 3
Conflicts of interest
There are no conflicts to declare.
The electronic band structure and intermolecular energy inter-
actions were calculated using the freeware PrimeColor
Software, CAESAR,28 which employs the extended Hückel
method29–31 with a basis set consisting of Slater type orbitals
of double-ζ quality. The exponents, contraction coefficients,
and atomic parameters were taken from previous reported
work.18
Acknowledgements
This work was partially supported by FCT (Portugal) through
Contracts UIDB/04349/2020, UIDB/50008/2020 and PTDC/
QUI-QIN/29834/2017, PhD grant PD/BD/135314/2017 to
M. F. G. V. Fruitful discussions with E. Canadell are also
acknowledged.
Conclusions
Notes and references
In conclusion, [Au(dspdt)2] is a rare case of a conducting com-
pound based only on a single neutral unit with a new struc-
tural type composed of dimers and trimers. At variance with
other single-component molecular metals, where the metallic
properties arise from the overlap of HOMO and LUMO or
SOMO−1 and SOMO bands, the highly conducting properties
of [Au(dspdt)2] result from the splitting of several quasi-one-
dimensional SOMO bands from dimers and trimers that
become non-degenerate due to the multiple interactions
between chains in the unit cell. For slightly larger inter-
molecular interactions, which can be induced by high
pressure, truly metallic properties are expected to be easily
achieved in this situation. Although a crystal structure determi-
nation was never possible in [Au(α-tpdt)2], this new alternative
mechanism to high conductivity may explain the conducting
metallic properties observed in that compound and other
neutral gold complexes with small ligands.
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