Proton and Electron Transfer in the Formation of a Copper Dithiolene-Based Coordination Polymer

Dithiolene-Based Coordination Polymer

Article

Proton and Electron Transfer in the Formation of a Copper

Stefan Hen ﬂ ing, Anastasia Kultaeva, Andreas P ö ppl, Jennifer Klose, Berthold Kersting,

Kostiantyn V. Domasevitch, and Harald Krautscheid*

Cite This: Inorg. Chem. 2021, 60, 9008 −9018

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sı Supporting Information

ABSTRACT: Metal bis(dithiolene) complexes are promising building blocks for electrically

conductive coordination polymers. N-Heterocyclic dithiolene complexes allow their cross-linking

via the coordination of N-donor atoms to additional transition metal ions. In this study, we

−

present the formal copper(II) and copper(III) 6,7-quinoxalinedithiolene complexes [Cu(qdt) ]

and [Cu(qdt)₂]²⁻(qdt : 6,7-quinoxalinedithiolate), as well as the 2D coordination polymer

2−

Cu[Cu(Hqdt)(qdt)] (3). The dithiolene complexes were isolated as (Bu N) [Cu(qdt) ] (1),

Na[Cu(qdt) ]·4H O (2a), [Na(acetone) ][Cu(qdt) ] (2b), and [Ni(MeOH) ][Cu(qdt) ] ·

2 2

H O (2c). Their crystal structures reveal nearly planar complexes with a high tendency of π-

stacking. For a better understanding of their coordination behavior, the electronic properties are

investigated by UV−vis−NIR spectroscopy, cyclic voltammetry, and DFT simulations. The

synthesis of the 2D coordination polymer 3 involves the reduction and protonation of the

monoanionic copper(III) complex. A combination of powder X-ray diﬀraction, magnetic

susceptibility measurements, as well as IR and EPR spectroscopy conﬁrm that formal

−

[Cu (Hqdt)(qdt)] units link trigonal planar copper(I) atoms to a dense 2D coordination polymer. The electrical conductivity

−7

of 3 at room temperature is 2 × 10 S/cm. Temperature dependent conductivity measurements conﬁrm the semiconducting

behavior of 3 with an Arrhenius derived activation energy of 0.33 eV. The strong absorption of 3 in the visible and NIR regions of

the spectrum is caused by the small optical band gap of E_g_,_o_p_t= 0.65 eV, determined by diﬀuse reﬂectance spectroscopy. This study

sheds light on the coordination chemistry of N-heterocyclic dithiolene complexes and may serve as a reference for the future design

and synthesis of dithiolene-based coordination polymers with interesting electrical and magnetic properties.

INTRODUCTION

has been provided by Kato. Contrary to the numerous

studies on the variation of counterions, there exist only a few

reports that describe further coordination toward metal ions.

The incorporation of metal dithiolene complexes as building

blocks in conjugated coordination polymers could, however,

lead to materials with interesting cooperative properties.

Dithiolene based coordination polymers reported in the

literature mostly consist of nitrogen containing dithiolene

complexes, which are further coordinating to alkali metal

■

For almost six decades, square planar metal bis(dithiolene)

complexes have been attracting great interest due to their

outstanding and sometimes unusual optical, electrical, and

−4

magnetic properties.

They are characterized by an

electronically delocalized M(S C ) core that can be further

2 2

extended by various substituents. Often, dithiolene complexes

can be isolated in a series with diﬀerent total charges due to the

ligands contributing to redox reactions. This behavior has been

described as “non-innocence” and can be attributed to a

similarity in energies of the metal and ligand frontier

1−29

ions.

In these cases, however, the interaction between

nitrogen and alkali metal atoms is of a rather ionic nature,

which limits through-bond charge delocalization. One example,

which provided great incentive for research on transition metal

ion based coordination polymers, was published by Takaishi et

−8

orbitals.

In N-heterocyclic dithiolene complexes, the

electron transfer can further be coupled to the transfer of

−12

protons.

Metal dithiolene complexes ﬁnd application in

al. They synthesized the ﬁrst electrically conductive (6 ×

mainly two ﬁelds. First, especially N-heterocyclic dithiolene

complexes serve in bioinorganic modeling studies, as the active

sites of many metalloenzymeslike the molybdenum and

tungsten-dependent oxidoreductasescontain metal dithio-

0⁻S/cm at 300 K) and porous coordination polymer

Received: March 24, 2021

Published: June 2, 2021

3,14

lene moieties.

Second, dithiolene metal complexes are

widely investigated for their potential application in electronic

devices. Several compounds have been characterized as

15,16

17−19

metallic molecular crystals

or even superconductors.

A detailed overview of conducting metal dithiolene complexes

2021 American Chemical Society

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Inorg. Chem. 2021, 60, 9008−9018

Inorganic Chemistry

Article

Table 1. Crystal and Structure Reﬁnement Data of 1, 2b, 2c, and 3

compound

(Bu N) [Cu(qdt) ] (1)

[Na(acetone) ][Cu(qdt) ] (2b)

[Ni(MeOH) ][Cu(qdt) ] ·2 H O (2c)

Cu[Cu(Hqdt)(qdt)] (3)

space group

P2 /c

822.53(3) pm

1650.51(4) pm

1868.12(6) pm

90°

92.860(3)°

90°

830.54(3) pm

969.33(2) pm

1021.13(3) pm

86.914(3)°

81.084(3)°

83.408(5)°

806.23(5)

808.56(2) pm

1797.12(3) pm

1588.62(4) pm

90°

98.124(2)°

90°

432.695(8) pm

828.14(2) pm

2208.82(7) pm

90°

95.799(1)°

90°

volume/10 pm³

2533.0(1)

2285.22(9)

787.44(4)

180 K

0.029

0.069

180 K

0.031

0.087

180 K

0.033

0.100

293 K

R_w_p= 0.033

R_p= 0.026

R1 (I > 2σ(I))

wR2 (all data)

The structure was solved and reﬁned using powder XRD data (Rietveld method).

−

Cu[Cu(pdt) ] (pdt : 2,3-pyrazinedithiolate). The copper(III)

Information (chapter 1). Formal nickel(II) and nickel(III)

dithiolene complexes with this ligand have been described by

III

−

dithiolene complex [Cu (pdt) ] , reported by Ribas et al.,

served as a linker moiety. It bears four nitrogen donor

coordination sites and can be reduced to the corresponding

copper(II) complex at −0.72 V vs Fc/Fc . Comproportiona-

tion with Cu ions results in the formation of Cu [Cu (pdt) ].

Just one year later, in 2010, Kobayashi et al. reported the

isostructural coordination polymer Cu [Ni (pdt) ]. It

33,34

Das et al.

Deprotonation of H qdt with hydroxide ions and

a subsequent reaction with Cu ions resulted in the red

complex [Cu(qdt) ] , isolated and characterized as

2−

(Bu N) [Cu(qdt) ] (1). Oxidation with iodine aﬀorded the

corresponding copper(III) complex, namely, the one-fold

−

negatively charged green complex [Cu(qdt)₂ ] which was

exhibits permanent porosity, but a 4 orders of magnitude

lower electrical conductivity with also a higher activation

energy for charge transport. This may be explained by the

weaker reducing power of [Ni(pdt)₂]²compared to its copper

analogue and the associated lower charge carrier delocalization

identiﬁed by NMR spectroscopy (Figures SI-1, SI-2 ). It was

crystallized as Na[Cu(qdt) ]·4H O (2a) from a mixture of

acetone/methanol (10:1, v/v) and as [Na(acetone) ][Cu-

−

(qdt) ] (2b) by diﬀusion of Et O into an acetone solution of

−

2a. Concerning the coordination behavior of [Cu(qdt) ] , we

in the coordination polymer. Since the building units are

redox-active, the electrical conductivity could be increased by 4

orders of magnitude via partially oxidizing the framework with

found that the diﬀusion-controlled reaction of 2a with certain

divalent transition metal acetates in methanol resulted in the

formation of crystalline materials. The dark, octahedral crystals

of the reaction product with Ni(OAc) ·4H O consist of

−

iodine to reach a value of 1 × 10 S/cm at 323 K (two-probe,

ﬁlm). Whereas the synthesis of Cu [Cu (pdt) ] and

[Ni(MeOH) ][Cu(qdt) ] ·2H O (2c). The microcrystalline

6 2 2 2

Cu [Ni (pdt) ] includes the transfer of electrons, classical

coordination polymer Cu[Cu(Hqdt)(qdt)] (3) was obtained

by the solvothermal reaction of 2a with CuI and

triphenylphosphine (PPh ) in acetonitrile. The use of PPh

acid−base reactions may equally play an important role in the

formation of N-heterocyclic dithiolene based coordination

polymers. This was shown for the N−H protonated copper(I)

was required for the isolation of phase pure 3. If the synthesis

complex [Cu(H pdt) ] . The reaction with additional Cu⁺

2−

of 3 is performed without PPh , qdt is oxidized to the bis-

ions, in this case, leads to the 1D coordination polymer

Cu(Hpdt)] and is accompanied by a deprotonation of the

disulﬁde (qdt) , while a coordination polymer similar to that of

[

is formed. The similar, but slightly larger unit cell and the

H pdt ligands. Apart from the cited examples, dithiolene

absence of N−H stretching vibrations indicate the composition

as Cu [Cu(qdt) ] (SI, chapter 8). Temperature dependent

complexes have to date seldomly been used for the strategic

design of transition metal ion-based coordination polymers. To

explore the structure determining properties of dithiolene

complexes in polymeric assemblies, we investigated the

coordination behavior of the N-heterocyclic dithiolene

PXRD measurements of the coordination polymer 3 reveal its

thermal stability up to 490 °C (Figure SI-21 ).

Crystal Structures of 1 and 2a−2c. Compounds 1 and

a−2c were characterized via single crystal X-ray diﬀraction

−

2−

complex [Cu(qdt) ] (qdt : 6,7-quinoxalinedithiolate) to-

and display structural properties that are typical for dithiolene

complexes. The tetrabutylammonium salt of the copper(II)

ward Cu ions. In the ﬁrst part, the manuscript focuses on the

structural and electronic characterization of the formal

dithiolene complex 1 crystallizes in space group P2 /c (no. 14)

−

copper(II) and copper(III) complexes [Cu(qdt) ] and

with two formula units per unit cell (Table 1) and is

−

[

(

[

Cu(qdt) ] , isolated as (Bu N) [Cu(qdt) ] (1), Na[Cu-

qdt) ]·4H O (2a), [Na(acetone) ][Cu(qdt) ] (2b), and

Ni(MeOH) ][Cu(qdt) ] ·2H O (2c). The second part of

isostructural to the previously reported nickel(II) analogue

(

Bu N) [Ni(qdt) ]. The formal copper(II) atom exhibits a

4 2 2

2 2

square planar coordination with the angle S1−Cu1−S2 =

0.24 ° (Figure 1). Selected bond lengths are summarized in

Table SI-10. Compared to the average Ni−S distance in

this manuscript deals with the characterization of the

physicochemical properties of the 2D coordination polymer

Cu[Cu(Hqdt)(qdt)] (3).

(

Bu N) [Ni(qdt) ] (216.9(2) pm), the Cu−S distances are

considerably longer (Cu1−S1 = 225.91(5) pm, Cu1−S2 =

226.15(6) pm), but in good agreement with those of other

homoleptic bis(dithiolene) copper(II) complexes.

RESULTS AND DISCUSSION

■

Synthesis. The synthesis of H qdt (H qdt: 6,7-quinox-

alinedithiol) was performed according to the literature with

small variations that are described in the Supporting

Crystals of Na[Cu(qdt) ]·4H O (2a) were obtained as

2 2

intergrown dark green needles. Their diﬀraction data set only

009

Inorg. Chem. 2021, 60, 9008−9018

Inorganic Chemistry

is observed (Figure 2 a). The Cu −S distances are

Article

chelating unit C S and the CuS unit, being 9.54(5)° (Figure

̅ ̅

b). The complexes are connected to chains in [111] direction

by the coordination of the diagonal opposite nitrogen atoms

N1 to sodium ions (Na1−N1 = 252.9(2) pm; Figure 2a). The

sodium ions exhibit a slightly distorted octahedral coordination

sphere with the oxygen atoms of two pairs of symmetry

equivalent acetone molecules, occupying the equatorial

Figure 1. Ellipsoid representation (50% probability) of the [Cu-

(

qdt)₂]²anion in 1. Symmetry code: a (2 − x, −y, 1 − z).

−

positions of the NaN O octahedron (Na1−O1 = 238.5(1),

Na1−O2 = 247.8(2)). Each chain in 2b is linked to two

neighboring chains via oﬀset π···π stacking interactions of the

aromatic quinoxaline units with an atom to plane distance

ranging from 328.8(8) pm to 334.5(2) pm (Figure 2c). As

depicted in perpendicular view to the quinoxaline planes, the

oﬀset of the stacking is more dominant in the short axis of the

quinoxaline units.

allowed the determination of a structure model, which is

described in the SI (chapter 11). Slow diﬀusion of Et O into a

solution of 2a in acetone resulted, however, in prismatic, green

crystals with good diﬀraction data quality. [Na(acetone) ]-

[

Cu(qdt) ] (2b) crystallizes in space group P1 (no. 2) with

one formula unit per unit cell (Table 1). The copper atom

resides on an inversion center, and a perfectly planar

coordination environment for the formal copper(III) atoms

Single crystals of 2c were obtained by the slow diﬀusion of

Ni(OAc) ·4H O into a solution of 2a in methanol. As

determined by X-ray single crystal structure analysis, this

compound crystallizes in the monoclinic space group P2 /c

(

no. 14) with two formula units per unit cell (Table 1, Figure

). Similar to the structure of 2b, the complex is nearly planar

with marginally varying Cu −S distances and S −Cu −S angles

Figure 2. (a) Ellipsoid representation (50% probability) of [Cu-

−

(

qdt) ] units in 2b, linked by Na ions, which are coordinated by

four acetone molecules each. Symmetry codes: a (2 − x, −y, 2 − z), b

−

(

1 − x, 1 − y, 1 − z). (b) [Cu(qdt) ] with viewing direction parallel

to the short axis of the complex. (c) Schematic representation of the

oﬀset π-stacking interactions between the coordination chains in 2b.

The view is perpendicular toward the quinoxaline planes.

18.77(5) pm and 216.91(5) pm, about 8 pm shorter than

Figure 3. (a) Ellipsoid representation (50% probability) of [Cu-

−

in the corresponding copper(II) complex in 1, but similar to

(qdt)

]

in 2c with hydrogen bonds to methanol and water

24,36

molecules. Symmetry codes: a (0.5 + x, 0.5 − y, − 0.5 + z), b (1.5

those reported in related copper(III) dithiolene complexes,

and also similar to the Ni−S distance in the isoelectronic

nickel(II) complex (Bu N) [Ni(qdt) ]. Besides the signiﬁ-

cant shortening of Cu−S bond lengths, the C−S and C1−C2

bond lengths change only slightly upon oxidation from the

copper(II) to the copper(III) complex. A comparison of bond

lengths in 1 and 2b is provided in Table SI-10 . The distortion

from planarity of the whole complex in 2b can be described by

the angle δ between the least-squares planes spanned by the

−

x, 0.5 + y, 1.5 − z). (b) Double layer of hydrogen bond connected

dithiolene complexes in 2c. The darker shaded complexes lie atop the

brighter ones. The view is perpendicular to the planes of the

complexes. Methyl groups, as well as hydrogen atoms that do not

participate in hydrogen bonding, are omitted for clarity. (c) Stacking

−

of [Cu(qdt)₂] complexes between double layers, viewed in

perpendicular direction to the plane of the complex. The darker

shaded complex lies atop the brighter one. Hydrogen atoms are

omitted for clarity.

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Inorg. Chem. 2021, 60, 9008−9018

Inorganic Chemistry

with shoulders directed toward higher energies (Figure 5 ).

Article

ranging from 217.63(8) pm to 219.18(6) pm and 86.73(2)° to

with respect to the adjacent sulfur p orbitals. The LUMO

1.59(2)°, respectively (Table SI-11 ). Curiously, the anionic

(−0.69 eV; Figure 4a) is formed by the metal d orbital and a

complexes do not interact directly with the Ni ions but are

imbedded in an extended network of hydrogen bonds, π-

stacking, and weak intermolecular Cu···S interactions. Figure

combination of sulfur p and p orbitals, σ antibonding to the

metal d_x_yorbital. These ﬁndings are in line with molecular

orbital representations of similar diamagnetic d metal

24,39,41,42

a displays hydrogen bonds of the complex with one water

bis(dithiolene) complexes.

The σ* character of the

(

O4b) and two methanol molecules (O1 and O2a). Donor−

LUMO is consistent with the about 8 pm longer Cu−S bond

length, observed in the crystal structure of the reduced

complex in 1. With regard to further investigations of the

coordination chemistry, it is noteworthy that the lone pair

electrons of sulfur atoms are mainly described by the HOMO

(−2.69 eV), HOMO−1 (−3.13 eV), HOMO−2 (−3.28 eV),

and HOMO−3 (−3.51 eV), whereas the unshared pair of

electrons of the nitrogen atoms appear much more stabilized at

the HOMO−5 (−4.35 eV), HOMO−6 (−4.36 eV), HOMO−

13 (−5.98 eV), HOMO−14 (−6.03 eV), and HOMO−15

(−6.16 eV; Figure SI-3).

UV−vis−NIR absorption investigations of 1 and 2a uncover

strong charge transfer excitations and support the delocalized

electronic structure of both complexes. The electronic

absorption spectrum of 2a in acetonitrile reveals two main

excitations at 415 nm (log ε = 4.90) and 273 nm (log ε = 4.77)

acceptor distances are summarized in Table SI-12 and range

between 272.7(3) pm and 282.2(3) pm. The Ni²ion, residing

on an inversion center, is coordinated by three crystallo-

graphically diﬀerent methanol oxygen atoms (O1, O2, O3)

and exhibits a regular octahedral coordination. Ni−O distances

lie in between 204.4(2) pm and 205.4(2) pm; O−Ni−O

angles are close to 90° (Table SI-11 ). The hydroxy hydrogen

atoms of four methanol molecules of each [Ni(MeOH)₆]

octahedron link the dithiolene complexes into an oﬀset π-

stacked double layer (Figure 3b). The arrangement can be

described as a herringbone motif, in which the complexes are

packed with their long axis perpendicular to each other. The

atom to plane distance between stacked quinoxaline groups is

in the range of 348 to 359 pm. The double layers are stacked

via additional π···π stacking interactions between adjacent

quinoxaline units of 354.3(2) to 367.4(2) pm with a slightly

lesser oﬀset in both the short and the long axis of the ligand.

This is shown in Figure 3c represented by two stacked

dithiolene complexes belonging to adjacent double layers. Both

shifts in the diﬀerent π···π interactions can be explained by

additional weak dipole−dipole interactions between copper

and sulfur atoms. As represented in Figure 3b, copper and

sulfur atoms in one double layer lie almost on top of each other

with a distance of 338.52(1) pm. The shortest Cu···S distance

between the double layers is slightly longer (350.32(1) pm).

Both interatomic distances are longer than the sum of their van

der Waals radii (320 pm).

Electronic Properties of [Cu(qdt) ] and [Cu(qdt) ] .

−

2−

Since the frontier molecular orbitals are essential to under-

standing the electrical and optical properties of dithiolene

−

complexes, DFT calculations of [Cu(qdt) ] were performed

at the B3LYP-D3BJ/ZORA-def2-TZVP level of theory. The

−

^g^e^o^m^e^t^r^y^o^p^tⁱ^mⁱ^z^a^tⁱ^oⁿ^o^f^[^C^u⁽^q^d^t⁾2^] in the gas phase

Figure 5. UV−vis−NIR spectrum of 2a in acetonitrile (solid line) and

reproduces well the experimentally determined bond lengths

and angles of the complex in the solid state (Table SI-2 ). The

slight overestimation of the M−S bond lengths of about 2.5

pm is not unusual for DFT calculations and has already been

The HOMO (−2.69 eV) of

Cu(qdt)₂] (Figure 4b) is a π orbital, extended over the

in methanol (dashed line).

Although the shoulder of the strongest absorption band is not

well resolved in acetonitrile, it becomes more pronounced in

the protic solvent methanol. Furthermore, the absorption at

415 nm displays an about 14 nm bathochromic shift when the

solvent is changed from acetonitrile to methanol. An

explanation might be that methanol molecules form hydrogen

bonds with the electronegative nitrogen atoms of the

quinoxaline unit, stabilizing the excited states of the dithiolene

,38−40

observed in similar systems.

−

[

whole complex. It consists of ligand p_zorbitals with a

considerable contribution from the Cu d orbital, antibonding

complex, and lowering the energy needed for the excitation.

TD-DFT simulations predict one-electron excitations at 250,

70, 311, 341, and 440 nm. The transitions are displayed as

transition diﬀerence densities in Table SI-3 . They visualize

mostly ligand-to-metal charge transfer (LMCT) excitations, in

which electron density is transferred from sulfur orbitals to the

unoccupied Cu d orbital, and metal-to-ligand charge transfer

(

MLCT), intraligand charge transfer (ILCT), and π → π*

transitions from the Cu d_x_zand S p to the aryl p orbitals.

Besides the absorption at the blue edge of the spectrum, 2a

exhibits two weaker broad absorption bands at 608 nm (log ε

= 2.58) and 1016 nm (log ε = 2.58; Figure SI-7).

−

Figure 4. LUMO (a) and HOMO (b) of [Cu(qdt) ] . The surface

isovalue is 0.03.

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Inorg. Chem. 2021, 60, 9008−9018

Inorganic Chemistry

2.0 to 0.25 V vs Fc/Fc (Figure 6 ) show two chemically

Article

In comparison to the green solution of 2a, a solution of 1 in

acetone appears red. The color is related to the absorption

maximum at 466 nm for solutions of 1 (Figure SI-8 , left). This

bathochromic shift is explained by TD-DFT simulation of

to the formation of the formal copper(I) species of the

complex. The potentials for the current maxima and minima

are separated by 161 mV at v = 25 mV/s. The distance

increases with increasing scan rates. This is typical for a quasi-

−

[Cu(qdt)₂] that predicts LMCT and MLCT transitions at

reversible electron transfer and slow kinetics at the electrode.

96 and 494 nm, respectively (Table SI-4). Exposed to air, the

A structural change within the complex anion from a square

planar to a tetrahedral coordination, typical for copper(I)

complexes, might be a reason for the slow electron transfer.

Scanning further anodically, one more-electron oxidation

band at 466 nm successively vanishes, while the characteristic

band for the copper(III) complex at 415 nm appears. The

reaction proceeds within several minutes; isosbestic points

evidence a constant stoichiometry and the direct trans-

process starting at 0.25 V vs Fc/Fc can be observed and is

formation of [Cu(qdt)₂]²to [Cu(qdt) ] (Figure SI-8, right).

−

represented in Figure SI-5. It appears irreversible and is

combined with a chemical reaction and structural changes in

the oxidized state. The formation of noninteger oxidation

products has been found in other, similar dithiolene

−

The proton acceptor behavior of [Cu(qdt)₂] was

monitored by spectrophotometric titration experiments with

aqueous hydrochloric acid. A good photometric response was

observed in solutions of 2a in acetone and DMSO (Figure SI-

8−50

complexes.

The reduction and redissolution of this

). The decrease of the absorption at 420 nm was

oxidized species, covering the electrode, is observed in two

accompanied by the emergence of a new band at 479 nm in

DMSO and 498 nm in acetone. Whereas the addition of 1

equiv of HCl to the acetone solution already induced a

considerable change in the UV−vis−NIR spectrum, in DMSO,

steps at −1.0 and −1.1 V vs Fc/Fc .

Concerning the electronic properties, signiﬁcant similarities

to literature known complexes should be pointed out. First, the

−

observed reduction potential for [Cu(qdt) ] is the very same

−

5000 equiv was needed to observe a ﬁrst eﬀect. The isosbestic

as that of its smaller analogue [Cu(pdt) ] (Figure SI-4 ). It

−

points suggest the direct protonation of [Cu(qdt)₂] to

Cu(Hqdt)(qdt)]. By the addition of aqueous NaOH, this

reaction is reversed.

is, however, much more negative than that of the copper

−

/2−

[

maleonitriledithiolate [Cu(S C (CN) ) ]

couple (E₁_/₂=

2 2

−0.06 V vs Fc/Fc ), which exhibits an air-stable dianionic

form (Table SI-6). Compared to corresponding redox

potentials of the copper dithiolene complexes [Cu(S C H ) ]

−

The complex [Cu(qdt) ] not only accepts protons but also

−

electrons. The cyclic voltammograms of 2a in the range of

−

4 2

−

and [Cu(S C Me ) ] , the observed reduction in [Cu(qdt) ]

2 6 4 2 2

occurs at less cathodic potentials (Table SI-6). The observed

trend may be explained by the diﬀerent extent of the electron

withdrawing eﬀect of diﬀerent dithiolene ligand substituents.

In general, substituents with stronger electron withdrawing

properties cause a greater decrease in the energy of the frontier

molecular orbitals and facilitate reduction processes. The

1,51,52

reduced anionic complex is stabilized.

Second, compared

2−

to the isoelectronic [Ni(qdt) ] , in which the redox active

orbital is the HOMO, in the CV of 2a, no reversible

oxidation of the complex can be observed within the

electrochemical window of DMSO. The redox active orbital

−

in [Cu(qdt) ] is the LUMO. Since the HOMO in

2−

[

Ni(qdt)₂] is delocalized over the whole complex, the ligand

can be regarded as noninnocent in combination with nickel(II)

atoms, whereas in combination with copper(III) atoms, the

reduction takes place at the CuS unit. The ligand can be

considered innocent in this case.

Crystal structure of Cu[Cu(Hqdt)(qdt)] (3). The copper-

Figure 6. Cyclic voltammograms of 2a between −2.0 and 0.25 V vs

−

(

III) complex [Cu(qdt) ] served as a building block for the

Fc/Fc in DMSO at diﬀerent scan rates.

construction of the 2D coordination polymer Cu[Cu(Hqdt)-

qdt)] (3). The crystal structure of 3 was solved and re ﬁ ned

(

reversible redox processes (p1, p2). The electrochemical

on the basis of its powder X-ray diﬀraction pattern (Figure SI-

22 ). Compound 3 crystallizes in the monoclinic space group

parameters derived from the cyclic voltammetry studies are

provided in Table SI-5 . At E₁

= −0.70 V vs Fc/Fc ,

P2 /c (no. 14) with one-half of the formula unit as an

/2,p1

−

2−

[

Cu(qdt) ] is reduced to [Cu(qdt) ] . Reduction potentials

lower than −0.38 V vs Fc/Fc indicate the susceptibility to

asymmetric unit (Table 1). Figure 7 shows the copper

dithiolene complex with its connectivity toward the crystallo-

graphically diﬀerent copper atoms (Cu1) on a general position.

Free reﬁnement of the Cu1 occupancy resulted in a value of

0.488(8) per formula unit and was set to 0.5, in agreement

with the elemental analysis. Important bond lengths of the

crystal structure are shown in Table SI-13. As expected, the

overall D₂_hsymmetry of the dithiolene complex was retained,

despite a slight distortion reﬂected in the Cu−S distances

(Cu2−S1 = 229.1(5) pm and Cu2−S2 = 224.1(6) pm). Both

bonds are longer than in the starting material 2a, where the

average Cu−S distance is 217.8(9) pm. This is explained by

aerial oxidation of the reduced species. This is consistent

with the photometric response of solutions of 1 to aerial

exposure. The diﬀerence between the reduction and oxidation

potential of this redox event at E₁_/₂_,_p₁is 91 mV and does not

change with the scan rate, indicating a fast electron transfer at

the electrode. Both the oxidation and reduction reaction of p1

produce reaction products that do not precipitate on the

electrode surface but remain in solution, as indicated by

5,46

Randles-Sevci

k plots (Figure SI-6).

At E₁_/₂_,_p₂= −1.65 V vs

Fc/Fc , a second redox process, p2, is observed. It is attributed

012

Inorg. Chem. 2021, 60, 9008−9018

Inorganic Chemistry

Article

Figure 7. Coordination of the dithiolene complex in 3 to Cu1. The

trigonally coordinated Cu1 atoms are in a general position with site

occupation factor 0.5. Hydrogen atoms are omitted for clarity.

Symmetry codes: a (−x, 1 − y, 1 − z), b (1 − x, 1 − y, 1 − z), c (1 −

x, −y, 1 − z).

the reduction of the complex to a formal copper(II) dithiolene

species with typical Cu−S distances of around 225.0 to 230.8

pm. The other copper atoms, Cu1, are connecting the

complexes in a trigonal planar coordination, distorted,

however, toward pyramidal: Cu1 is located 23.0(7) pm

above the plane spanned by the coordinating atoms N1c,

S1b, and S2. The Cu1−N1c distance of 198(1) pm is, within

the accuracy limits of powder diﬀraction data, similar to that of

typical three coordinated copper(I) atoms with unsaturated

Figure 8. (a) Connectivity of dithiolene complexes via Cu1 (site

occupation factor of 0.5) into a 2D network. (b) Stacking of

dithiolene complex moieties in 3, viewed along their long axis, and (c)

along their short axis. Hydrogen atoms are omitted for clarity.

packed structure. Besides weak van der Waals interactions, no

further signiﬁcant electronic attraction is observed between the

layers.

54,55

nitrogen ligands (191−202 pm).

Likewise, the Cu1−S

bond lengths (Cu1−S1b = 221.5(9) pm, Cu1−S2 = 229(1)

pm) are similar to literature reported Cu−S distances of

Oxidation States in 3. The combination of magnetic

susceptibility data, IR, and EPR spectra shows that copper(I)

atoms are linked by protonated formally one-fold negatively

56−61

trigonally coordinated copper(I) atoms (222−235 pm).

The Cu···Cu distances between the dithiolene copper atom

−

charged copper(II) complexes, [Cu (Hqdt)(qdt)] . Evidence

for the assumed protonation of one ligand was gained by IR

spectroscopy of the deuterium labeled compound 3. The

synthesis of the coordination polymer was executed in the

Cu2 and the trigonally coordinated Cu1 alternate between

369.5(7) and 280.4(7) pm. The latter is surprisingly short and

raises the question about the metal···metal interaction.

Comparable short Cu···Cu distances of about 293 pm are

reported for mixed-valence (Cu···Cu)³units in model systems

presence of a small amount of D O to yield 3-D (Experimental

Section). Phase purity was conﬁrmed via X-ray powder

diﬀraction (Figure SI-20 ). The N−H proton of

of the biological Cu electron transfer site, a complex involved

62,63

in the respiratory chain of eukaryotes.

In these cases, both

Cu [Cu (Hqdt)(qdt)] is considered acidic and expected to

exchange with its heavier isotope, whereas C−H protons

should remain unaﬀected. Figure 9 displays both IR spectra of

copper ions are bridged by two μ thiolate functions and

exhibit the same distorted tetrahedral coordination environ-

ment. The complexes are best described as delocalized mixed

1.5

valence Cu Cu systems. The structure of 3, on the contrary,

exhibits distinct and typical coordination environments for Cu

and Cu , which points toward a valence-trapped state, with no

direct metal···metal interactions. Stibrany et al. reported a

similar system in which two distorted square planar cis-

N(amine) S(thiolate)₂coordinated copper(II) atoms and

three trigonal planar S(thiolate) Cl coordinated copper(I)

atoms are linked by μ and μ thiolate functions. The Cu ···Cu

distance in this case is 282.31(9) pm and similar to that

observed in 3.

Figure 9. IR spectrum of 3 (black) and of its deuterated analogue 3-D

Via the coordination to Cu1, a dense 2D network

perpendicular to [001] is formed (Figure 8). All dithiolene

units in one layer are oriented in the same direction and are

stacked along the crystallographic a axis (Figure 8). The

distance between parallel quinoxaline units is 341 pm. The

oﬀset of the π-stacking in 3 is predominant in the direction of

the long axis of the complex (230 pm) and less along the short

axis of the complex (90 pm)resulting in a staircase like

assembly in one stack (Figure 8b,c). The shortest Cu···S

distance between adjacent complexes is 379.4(5) pm and is

considerably longer than the sum of the atoms ’ van der Waals

(red).

3 (black) and its deuterium exchanged analogue 3-D (red).

−

The N−H stretching frequency in 3 of 3198 cm is lower than

−

in most N-heterocycles, e.g., in pyrrole (3450 cm ). It is,

however, similar to the more acidic tetrazoles, which display

−1

N−H stretching frequencies at about 3145 cm . Assuming

an equal bond strength for isotope exchanged bonds, the

model of a harmonic oscillator predicts the stretching

−

frequency of the heavier N−D couple at 2335 cm . Since

there are no other signals in this part of the spectrum, the

appearance of the N−D stretching mode is clear and distinct

radii (320 pm). As depicted in Figure SI-23, the layers are

arranged in a staggered, interdigitated fashion to a densely

013

Inorg. Chem. 2021, 60, 9008−9018

Inorganic Chemistry

and is centered, close to the estimated value, at 2313 cm .

gradually decreases to reach 0.43 μ at 2 K (Figure 11 ). This

Article

−

(S = 1/2; μ_e_f_f= 1.73 μ , g = 2.0). Upon cooling, the value

−

Below 1600 cm , most frequencies remain unaﬀected upon

deuteration. However, some of the bands lose intensity, while a

−

few new ones appear at 1519, 1262, 772, and 627 cm . They

may be tentatively attributed to in plane and out of plane

deformation vibrations involving H and D atoms.

These ﬁndings clearly show that the dithiolene coordination

polymer 3 bears acidic N−H groups. EPR and magnetic

susceptibility measurements indicate that the protonated

dithiolene complexes additionally possess unpaired electrons

and must have been reduced during the formation of 3. The X-

band cw EPR spectrum of a powder sample of 3 measured at

93 K (Figure 10 ) exhibits a typical anisotropic pattern for

Figure 11. Temperature dependence of the eﬀective magnetic

moment μ_e_f_f(black squares) and the magnetic susceptibility (blue

circles) for 3 at H = 0.5 T.

behavior is attributed to antiferromagnetic exchange inter-

actions between the copper(II) complexes. The increase in χ_M

at low temperatures implies the presence of a paramagnetic

impurity. A Curie−Weiss ﬁt of the inverse magnetic

susceptibility data of 3 from 300 to 70 K results in a Curie

constant of C = 0.43 K and an asymptotic Curie temperature of

Θ = −99 K (Figure SI-10). Taking into account the one-

Figure 10. X-band cw EPR spectrum of 3 at 293 K (black) and

simulation (red).

dimensional stacking of Cu complexes, a ﬁt of the magnetic

susceptibility to the appropriate Bonner−Fisher model of an

S = 1/2 inﬁnite isotropic Heisenberg chain with the

Cu²⁺(3d , S = 1/2) in a magnetically nondiluted powder.

67,68

polynomial expression derived by Hall was attempted

3,65

The

Cu hyperﬁne interaction between the electron spin S

1/2 and the nuclear spin I = 3/2 was not resolved due to

(Figure SI-11 ). Excluding the low temperature data and ﬁxing

g = 2.04 (derived by EPR spectroscopy), the least-squares ﬁt

−

the high metal atom concentration. In this case, the substantial

magnetic exchange interactions between the neighboring

copper(II) atoms average their nuclear spin conﬁguration,

and consequently the hyperﬁne splitting is not observed in the

resulted in a value of |J| = 58(1) cm for the electronic spin−

spin coupling constant. The large coupling constant is not

unusual for polymeric assemblies of dithiolene complexes. In

the N−Cu −N bridged dithiolene coordination polymer

EPR spectrum. The principal values of the Cu g tensor,

obtained by simulation, are g = 2.020(1), g = 2.022(1), and g

Cu [Cu (pdt) ], the coupling constant between the

−

dithiolene copper(II) atoms was determined to be 113 cm ,

with g = 2.007.

2.083(1), typical for a planar Cu S coordination unit with

69,70

D₂_hsymmetry or lower.

The results of the EPR spectrum

Electrical Conductivity of Cu[Cu(Hqdt)(qdt)] (3). Metal

bis(1,2-dithiolene) complexes are known for their extended

frontier orbitals and the resulting delocalization of electrons.

They have been intensively studied as molecular conductors

simulation support the assumption of a paramagnetic copper

dithiolene species in 3.

A variable temperature magnetic susceptibility measurement

of 3 further corroborates that the coordination polymer

contains paramagnetic copper(II) complexes and shows that

they are antiferromagnetically coupled. Magnetic exchange

interactions in 3 can be found in the a direction of uniformly

and constitute a unique category of conducting materials.

The coordination polymer 3 bears one loosely bound unpaired

electron in the formal copper(II) complex, which is expected

to be further delocalized in the network via the coordination to

copper(I) atoms. The electrical conductivity at 25 °C on a

pressed pellet was measured with two contacts to be 2 × 10⁻

S/cm. Compared to the reported dithiolene coordination

stacked copper(II) complexes through Cu −S−Cu −S−Cu

bonds with a syn−syn bridging mode. The through-space

distance between the copper(II) centers is 432.70(1) pm.

Additionally, each complex is linked statistically to two others

−

polymer Cu[Cu(pdt) ] (σ = 6 × 10 S/cm, 25 °C), the

of the two neighboring stacks via S−Cu −N bonds, resulting in

electrical conductivity of 3 appears rather low. Since the herein

described material shows connectivity only in two dimensions,

the electrical conductivity is expected to display large

anisotropy. This fact, as well as the presence of intergrain

boundaries, limit the conductivity derived by measurements on

a pellet. In a temperature dependent conductivity measure-

ment, 3 was conﬁrmed to be semiconducting with an

Arrhenius temperature dependence (Figure SI-16). The

Cu ···Cu through-space distances of 828.14(2) pm and

34.37(2) pm (Figure SI-24). These magnetic interactions are,

however, considered weak. In agreement with Cu1−S and

Cu2−S bond lengths typical for oxidation states + I and + II,

respectively, the eﬀective magnetic moment μ at room

eff

temperature is 1.61 μ per Cu [Cu (Hqdt)(qdt)] formula unit

and is slightly less than that of one noninteracting Cu ion

014

Inorg. Chem. 2021, 60, 9008−9018

Inorganic Chemistry

The Supporting Information is available free of charge at

Article

activation energy derived from the linear region between 300

and 364 K is 0.33 eV. This is consistent with the optical band

gap E_g_,_o_p_t= 0.61 eV, assigned by extrapolation of the

absorption decay observed in the diﬀuse reﬂectance spectrum

of 3 (Figure SI-17).

at 40 °C until the ﬁrst small crystals appeared. Crystallization was

completed overnight at 6 °C. After ﬁltration and washing with cold

methanol and diethyl ether, dark green crystals of compound 2a were

isolated.

Yield: 835 mg, 1.54 mmol, 32%. EA found: C, 35.58%; H, 2.74%;

N, 10.45%. Calculated for (C H N S O CuNa): C, 35.38%; H,

−

.98%; N, 10.32%. HR-MS (ESI): m/z 446.893 [Cu(qdt) ] . H

CONCLUSION

The copper quinoxalinedithiolene complex [Cu(qdt) ]

■

NMR (400 MHz, DMSO-d

2 H, CHarom). C NMR (100 MHz, DMSO-d ): δ [ppm] 122.8 (s, 2

): δ [ppm] 7.62 (s, 2 H, CHarom), 8.64 (s,

−

/2−

^C^,^Carom⁾^,¹⁴⁰^.⁴⁽^s^,²^C^,^Carom⁾^,¹⁴³^.²⁽^s^,²^C^,^Carom), 152.3 (s, 2 C,

was explored for its structure directing properties in the

formation of polymeric assemblies. Its planar structure, the

extended π-system, and the polar Cu−S bonds make this

dithiolene complex ideal for π···π and intermolecular Cu···S

interactions, as observed for 2a, 2b, 2c, and 3. Typical for

C_a_r_o_m). UV/vis/NIR (acetonitrile): λ [nm] (log ε) 273 (4.77), 415

−

(

4.90), 608 (2.58), 1016 (2.58). IR (KBr): v

̃ [cm ] 3510 (m), 3342

m), 3186 (m), 1644 (m), 1454 (s), 1422 (m), 1354 (s), 1334 (m),

182 (s), 1149 (w), 1101 (s), 1037 (s), 978 (w), 930 (m), 880 (m),

91 (m), 673 (m), 626 (w), 419 (m).

−

^dⁱ^t^hⁱ^o^l^eⁿ^e^c^o^m^p^l^e^x^e^s^,^[^C^u⁽^q^d^t⁾2^] displays reversible one-

[Na(acetone) ][Cu(qdt) ] (2b). Crystals of 2b were obtained via

electron reduction processes at mild potentials, accompanied

by small structural changes of the complex. This property, as

slow diﬀusion of diethyl ether into a solution of 2a in acetone.

[Ni(MeOH) ][Cu(qdt) ] ·2H O (2c). A 2 mL glass vial with

2 2

well as the Lewis and the Brønsted basicity of the nitrogen

Ni(OAc) ·4H O (6.2 mg, 0.025 mmol, 1 equiv) was placed in a 20

2 2

−

mL glass vial with 2a (13.6 mg, 0.025 mmol, 1 equiv). Both were ﬁlled

slowly with methanol. After 1 week, black crystals of 2c formed on the

outer wall of the small vial.

atoms in [Cu(qdt) ] , have been shown to play all together an

important role in the formation of compound 3. In the

−

synthesis of 3, the copper(III) complex [Cu(qdt) ] is reduced

Cu[Cu(Hqdt)(qdt)] (3). A Teﬂon lined steel autoclave was loaded

with 2a (54.3 mg, 0.10 mmol, 1 equiv) and a solution of CuI (19.0

and protonated at one nitrogen atom. The resulting para-

magnetic dithiolene complex anions are linked by trigonally

planar coordinated copper(I) atoms to a dense 2D

coordination polymer with antiferromagnetic exchange inter-

actions and a room temperature electrical conductivity of 2 ×

mg, 0.10 mmol, 1 equiv) and Ph P (104.9 mg, 0.40 mmol, 4 equiv) in

5 mL of acetonitrile. The autoclave was sealed, and the reaction

mixture was heated to 100 °C within 20 h. The temperature was kept

at a constant level for 1 h before cooling the autoclave to room

temperature during a period of 2 h. The resulting black microcrystal-

line solid was isolated via decantation. The product was washed

thoroughly with acetonitrile and methanol before being dried under

reduced pressure.

−

S/cm.

This study presents a large variety of parameters to address

for a strategic synthesis of polymeric dithiolene structures. We

anticipate that dithiolene complexes will be more widely

perceived as tunable building blocks for the synthesis of more-

dimensional coordination polymers with highly interesting

electronic and magnetic properties.

Yield: 40 mg, 0.078 mmol, 78%. EA found: C, 37.67%; H, 1.67%;

N, 10.79%, S: 24.89%, Cu: 24.9%. Calculated for (C H Cu N S ): C,

4 4

7.48%; H, 1.77%; N, 10.93%, S: 25.02, Cu: 24.79%. IR (KBr): v

−

[cm ] = 3197 (w), 3082 (w), 3040 (w), 3020 (w), 1590 (w), 1551

m), 1467 (w), 1446 (s), 1438 (s), 1404 (m), 1370 (w), 1353 (m),

(

EXPERIMENTAL SECTION

Experimental details and the synthesis of H qdt are provided in the

Supporting Information.

1337 (m), 1313 (m), 1313 (m), 1219 (m), 1203 (s), 1189 (m), 1175

■

(

s), 1081 (s), 1055 (w), 1038 (m), 979 (w), 928 (w), 876 (m), 860

m), 781 (m), 763 (w), 752 (w), 672 (w), 666 (w), 616 (w), 596

w), 540 (w), 502 (w), 429 (m).

Bu N) [Cu(qdt) ] (1). H qdt (1.36 g, 7.0 mmol, 1 equiv) was

4 2 2 2

Cu[Cu(Dqdt)(qdt)] (3-D). On the basis of the synthetic protocol

deprotonated with KOH (786 mg, 14.0 mmol, 2 equiv) in 40 mL of

methanol and 40 mL of acetone. To the red solution, a solution of

CuCl ·2H O (597 mg, 3.5 mmol, 0.5 equiv) in 10 mL of methanol

of compound 3, two drops of D O were added to the reaction mixture

before the autoclave was heated in the oven.

−

IR (KBr): v

w), 1590 (w), 1550 (m), 1519 (m), 1446 (s), 1439 (s), 1405 (m),

353 (m), 1321 (m), 1264 (m), 1207 (s), 1173 (m), 1080 (s), 1038

m), 979 (w), 959 (w), 928 (w), 875 (m), 854 (m), 772 (m), 666

m), 627 (w), 616 (w), 589 (w), 540 (w), 502 (w), 429 (m).

̃ [cm ] 3198 (w), 3084 (w), 3036 (w), 3021 (w), 2313

was added dropwise. The solution was ﬁltered, and 2.42 g (7.5 mmol,

.1 equiv) of (Bu N)Br was added. After removal of the solvent, the

(

red solid was extracted with 100 mL of acetone. Layering with diethyl

ether resulted in dark red needle-shaped crystals of 1.

Yield: 1.92 g, 2.1 mmol, 59%. T : 181 °C. EA, found: C, 61.16%;

H, 8.45%; N, 8.94%. Calculated for (C H N S Cu): C, 61.78%; H,

6 4

−

.66%; N, 9.01%. HR-MS (ESI): m/z 446.893 [Cu(qdt) ] . UV/vis/

ASSOCIATED CONTENT

Supporting Information

https://pubs.acs.org/doi/10.1021/acs.inorgchem.1c00914.

■

−

NIR (acetone): λ [nm] (log ε) = 479 (4.71). IR (KBr): v

009 (w), 2957 (m), 2934 (m), 2871 (m), 1560 (w), 1469 (m), 1454

m), 1435 (s), 1410 (s), 1378 (m), 1361 (w), 1340 (m), 1329 (w),

269 (w), 1218 (w), 1177 (s), 1156 (s), 1122 (w), 1073 (s), 1029

s), 977 (w), 932 (m), 900 (w), 878 (m), 801 (w), 785 (m), 744 (m),

[cm ]

sı

(

Details concerning the experimental part and ligand

synthesis, NMR spectroscopy, DFT calculations, cyclic

voltammetry, UV−vis−NIR spectroscopy, EPR spec-

68 (m), 630 (w), 604 (m), 523 (w), 526 (w), 482 (w), 435 (w).

Na[Cu(qdt) ]·4H O (2a). H qdt (1.89 g, 9.73 mmol, 1 equiv) was

suspended in 68 mL of degassed acetonitrile and deprotonated with

an aqueous solution of 2 M NaOH (14 mL, 28 mmol, 2.9 equiv).

After 3 h of vigorous stirring, Cu(ClO ) ·6 H O (1.80 g, 4.86 mmol,

troscopy, magnetic characterization, inﬂuence of PPh in

the formation of 3, electrical conductivity measurement,

diﬀuse reﬂectance spectroscopy, single crystal structure

analysis, and X-ray powder diﬀraction and Rietveld

reﬁnement (PDF)

.5 equiv) was added to the brown slurry to aﬀord a dark red solution.

Iodine (617 mg, 2.43 mmol, 0.25 equiv) was added, and the solvent

was removed under reduced pressure. The resulting dark brown

precipitate was redissolved in 85 mL of methanol. After stirring for 4 h

at room temperature in an open beaker, a dark crystalline precipitate

formed from the red solution. It was ﬁltered oﬀ and dried under

reduced pressure. The crude product was dissolved in 150 mL of

acetone and ﬁltered through a bed of Celite. The dark green solution

was diluted with 40 mL of methanol and concentrated under vacuum

Accession Codes

CCDC 2065438−2065442 contain the supplementary crys-

tallographic data for compounds 1, 2b, 2c , 3 and (qdt) . These

data can be obtained free of charge via www.ccdc.cam.ac.uk/

data_request/cif , or by emailing data_request@ccdc.cam.ac.

015

Inorg. Chem. 2021, 60, 9008−9018

Inorganic Chemistry

Article

uk , or by contacting The Cambridge Crystallographic Data

Centre, 12 Union Road, Cambridge CB2 1EZ, UK; fax: + 44

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DOI: 10.1002/0471471933.

4) Rauchfuss, T. B. Synthesis of Transition Metal Dithiolenes in

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223 336033.

(

AUTHOR INFORMATION

Corresponding Author

■

Dithiolene Chemistry. In Dithiolene Chemistry; Stiefel, E. I., Ed.; John

Wiley & Sons, Inc, 2003; pp 1−54.

Harald Krautscheid − Institute for Inorganic Chemistry,

orcid.org/0000-0002-5931-5440; Email: krautscheid@

rz.uni-leipzig.de

(5) Ward, M. D.; McCleverty, J. A. Non-innocent behaviour in

mononuclear and polynuclear complexes: consequences for redox and

electronic spectroscopic properties. J. Chem. Soc., Dalton Trans. 2002,

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(6) Butin, K. P.; Beloglazkina, E. K.; Zyk, N. V. Metal complexes

Authors

with non-innocent ligands. Russ. Chem. Rev. 2005, 74 (6), 531−553.

Stefan Henﬂing − Institute for Inorganic Chemistry,

Universität Leipzig, D-04103 Leipzig, Germany

Anastasia Kultaeva − Felix Bloch Institute for Solid State

Physics, Universität Leipzig, D-04103 Leipzig, Germany;

Faculty of Chemistry and Biochemistry, Ruhr University

Bochum, D-44801 Bochum, Germany

Andreas Pöppl − Felix Bloch Institute for Solid State Physics,

Universität Leipzig, D-04103 Leipzig, Germany;

orcid.org/0000-0003-2354-2542

Jennifer Klose − Institute for Inorganic Chemistry, Universität

Leipzig, D-04103 Leipzig, Germany

Berthold Kersting − Institute for Inorganic Chemistry,

Universität Leipzig, D-04103 Leipzig, Germany

Kostiantyn V. Domasevitch − Department of Inorganic

Chemistry, University of Kiev, UA-25033 Kiev, Ukraine;

orcid.org/0000-0002-8733-4630

(7) Coucouvanis, D.; Paital, A. R.; Zhang, Q.; Lehnert, N.; Ahlrichs,

R.; Fink, K.; Fenske, D.; Powell, A. K.; Lan, Y. Synthesis, electronic

structure, and structural characterization of the new, ″non-innocent ″

4,5-dithio-catecholate ligand, its metal complexes, and their oxidized

4,5-dithio-o -quinone derivatives. Inorg. Chem. 2009, 48 (18), 8830−

8844.

9) Kimura, Y.; Hayashi, M.; Yoshida, Y.; Kitagawa, H. Rational

8) Eisenberg, R.; Gray, H. B. Noninnocence in metal complexes: a

dithiolene dawn. Inorg. Chem. 2011, 50 (20), 9741−9751.

Design of Proton-Electron-Transfer System Based on Nickel

Dithiolene Complexes with Pyrazine Skeletons. Inorg. Chem. 2019,

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10) Kennedy, S. R.; Goyal, P.; Kozar, M. N.; Yennawar, H. P.;

Hammes-Schiffer, S.; Lear, B. J. Effect of Protonation upon Electronic

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Ni(2,3-pyrazinedithiol) ]. Inorg. Chem. 2016, 55 (4), 1433−1445.

Steady-State Spectroscopic Analysis of Proton-Dependent Electron

Transfer on Pyrazine-Appended Metal Dithiolenes [Ni(pdt)₂ ],

Complete contact information is available at:

https://pubs.acs.org/10.1021/acs.inorgchem.1c00914

12) Henfling, S.; Kempt, R.; Klose, J.; Kuc, A.; Kersting, B.;

Pd(pdt) ], and [Pt(pdt) ] (pdt = 2,3-Pyrazinedithiol). Inorg. Chem.

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Author Contributions

All authors have given approval to the ﬁnal version of the

manuscript.

Funding

The work was supported by Studienstiftung des Deutschen

Volkes (doctoral grant for S.H.), Deutsche Forschungsgemein-

schaft, and Universitat Leipzig (research proﬁle area ‘Complex

Matter’).

Krautscheid, H. Dithiol-Dithione Tautomerism of 2,3-Pyrazinedithiol

in the Synthesis of Copper and Silver Coordination Compounds.

Inorg. Chem. 2020, 59 (22), 16441 −16453.

(13) Basu, P.; Burgmayer, S. J. N. Recent developments in the study

of molybdoenzyme models. JBIC, J. Biol. Inorg. Chem. 2015, 20 (2),

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DOI: 10.1002/9783527664160.ch13 .

14) Schulzke, C.; Ghosh, A. C. Molybdenum and Tungsten

Oxidoreductase Models. In Bioinspired Catalysis: Metal-Sulfur

Complexes ; Weigand, W., Ed.; Wiley-VCH, 2014; pp 349−382.

Notes

The authors declare no competing ﬁnancial interest.

15) Kato, R.; Kobayashi, H.; Kobayashi, A.; Sasaki, Y. Crystal

ACKNOWLEDGMENTS

■

Structure of a new Molecular Conductor (DBTTF)[Ni(dmit) 2 ].

Chem. Lett. 1985, 14 (1), 131−134.

(16) Olk, R.-M.; Kirmse, R.; Hoyer, E.; Faulmann, C.; Cassoux, P.

Synthese und Eigenschaften von molekularen Leitern auf der Basis

von dmit-isologen Chelaten Kristall- und Moleklstruktur des

Tetramethylammonium-bis-[bis-(1,3-dithiol-2-selon-4,5-

diselenolato)nickelat]; [(CH ) N][Ni(dsise) ] . Z. Anorg. Allg. Chem.

We gratefully acknowledge ﬁnancial support from Studien-

stiftung des deutschen Volkes (doctoral grant for S.H.),

Deutsche Forschungsgemeinschaft (DFG) and Universität

Leipzig. A.P. and A.K. acknowledge ﬁnancial support within

the priority program 1601 (Increasing Sensitivity with EPR) of

the DFG. The authors thank Dr. Oliver Kluge and Oliver

Erhart for advice concerning the Rietveld reﬁnement. Manuela

Roßberg, Ramona Oehme, Dr. Maik Icker with his team, and

Heike Rudzik are acknowledged for the elemental analysis, the

measurement of mass spectra and NMR spectra, and ICP-OES

analysis, respectively. The authors further thank URZ Leipzig

for the generous allocation of computer time.

2 2

(

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