Charge-transfer salts of ferrocene derivatives with bis(maleonitriledithiolato)metallate(III) complexes ([M(mnt)2]-, M = Ni, Pt): A ground-state high-spin [(Ni(mnt)2)2]2- dimer

Article abstract of DOI:10.1002/(SICI)1522-2675(19990908)82:9<1324::AID-HLCA1324>3.0.CO;2-F

New hexamethylated ferrocene derivatives containing thioether moieties (1,1'-bis[(tert-butyl)thio]-2,2',3,3',4,4'-hexamethylferrocene (3a,b)) or fused S-heteropolycyclic substituents (rac-1-[(1,3-benzodithiol-2- yliden)methyl]-2,2',3,3',4,4'-hexamethylferrocene (5) and rac-1-[1,2-bis(1,3- benzodithiol-2-yliden)ethyl]2,2',3,3',4,4'-hexamethylferrocene (14)), as well as a series of ferrocene-substituted vinylogous tetrathiafulvalenes (1,1'- bis[1,2-bis(1,3-benzodithiol-2-yliden)ethyl]ferrocene (6a), 1,1'-bis[1-(1,3- benzodithiol-2-yliden)-2(5,6-dihydro-1,3-dithiolo[4,5-b][1,4]dithiin-2- yliden)ethyl]ferrocene (6b), [1,2-bis(1,3-benzodithiol-2- yliden)ethyl]ferrocene (21a), [1-(1,3-benzodithiol-2-yliden)-2-(5,6-dihydro- 1,3-dithiolo[4,5-b][1,4]dithiin-2-yliden)ethyl]ferrocene (21b), [1,2-bis(5,6- dihydro-1,3-dithiolo[4,5-b][1,4]dithiin-2-yliden)ethyl]ferrocene (21c), [1(5,6-dihydro-1,3-dithiolo[4,5-b][1,4]dithiin-2-yliden)-2-(1,3-benzodithiol- 2-yliden)ethyl]ferrocene (21d)) were prepared and fully characterized. Their redox properties show that some of them are easily oxidized and undergo transformation to paramagnetic salts containing bis(maleonitriledithiolato)- metallate(III) anions [M(mnt)₂]- (M=Ni, Pt; bis[2,3-dimercapto-κS)but-2- enedinitrilato(2^-)]nickelate (1^-) or -platinate (1^-). The derivatives [3a][Ni(mnt)₂] (26), [3a][Pt(mnt)₂] (27), [Fe{(n⁵- C₅Me₄S)₂S}][Ni(Mnt)₂] (28), [Fe{(n⁵c₅Me₄s)₂S}[Pt(mnt)₂] (29), [5] [Ni(mnt)₂]·ClCH₂CH₂Cl (30), [6a] [Ni(mnt)₂] (31), [6a] [Ni(mnt)₂]. CICH₂CH₂Cl (31a), [6a] [Pt(mnt)₂] [32), and [6b] [Ni(mnt)₂] (33) were prepared and fully characterized, including by SQUID (superconducting quantum interference device) susceptibility measurements. X-Ray crystal-structural studies of the neutral ferrocene derivatives 6a,b, 21c,d, and 1,1'-bis[1- (1,3-benzodithiol-2-yliden)-2-oxoethyl]ferrocene (23), as well as of the charge-transfer salts 26-28, 30, and 31a, are reported. The salts 28 and 30 display both a D⁺A^-A^-D⁺ structural motif, however, with a different relative arrangement of the [{Ni(mnt)₂}₂]^2- dimers, thus giving rise to different but strong antiferromagnetic couplings. Salt 26 exhibits isolated ferromagnetically coupled [{Ni(mnt)₂}₂]^2- dimers. Salt 27 displays a D⁺A^-D⁺A^- structural motif in all three space dimensions, and a week ferromagnetic ordering at low temperature. Salt 31a, on the contrary, shows segregated stacks of cations and anions. The cations are connected with each other in two dimensions, and the anions are separated by a 1,2-dichloroethane molecule.

Full text of DOI:10.1002/(SICI)1522-2675(19990908)82:9<1324::AID-HLCA1324>3.0.CO;2-F

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Helvetica Chimica Acta ± Vol. 82 (1999)
Charge-Transfer Salts of Ferrocene Derivatives with
Bis(maleonitriledithiolato)metallate(III) Complexes ([M(mnt)2] , M ˆ Ni,
Pt): A Ground-State High-Spin [(Ni(mnt)2)2]2 Dimer
by Stefan Zürcher, Jeannine Petrig, Mauro Perseghini, Volker Gramlich, Michael Wörle, Dieter von Arx,
and Antonio Togni*
Laboratory of Inorganic Chemistry, ETH Zentrum, Swiss Federal Institute of Technology, CH-8092 Zürich,
Tel: 016322236, Fax: 016321090, e-mail: togni@inorg.chem.ethz.ch
New hexamethylated ferrocene derivatives containing thioether moieties (1,1'-bis[(tert-butyl)thio]-
2,2',3,3',4,4'-hexamethylferrocene (3a,b)) or fused S-heteropolycyclic substituents (rac-1-[(1,3-benzodithiol-
2-yliden)methyl]-2,2',3,3',4,4'-hexamethylferrocene (5) and rac-1-[1,2-bis(1,3-benzodithiol-2-yliden)ethyl]-
2,2',3,3',4,4'-hexamethylferrocene (14)), as well as a series of ferrocene-substituted vinylogous tetrathiafulva-
lenes (1,1'-bis[1,2-bis(1,3-benzodithiol-2-yliden)ethyl]ferrocene (6a), 1,1'-bis[1-(1,3-benzodithiol-2-yliden)-2-
(5,6-dihydro-1,3-dithiolo[4,5-b][1,4]dithiin-2-yliden)ethyl]ferrocene (6b), [1,2-bis(1,3-benzodithiol-2-yliden)-
ethyl]ferrocene (21a), [1-(1,3-benzodithiol-2-yliden)-2-(5,6-dihydro-1,3-dithiolo[4,5-b][1,4]dithiin-2-yliden)-
ethyl]ferrocene (21b), [1,2-bis(5,6-dihydro-1,3-dithiolo[4,5-b][1,4]dithiin-2-yliden)ethyl]ferrocene (21c), [1-
(5,6-dihydro-1,3-dithiolo[4,5-b][1,4]dithiin-2-yliden)-2-(1,3-benzodithiol-2-yliden)ethyl]ferrocene (21d)) were
prepared and fully characterized. Their redox properties show that some of them are easily oxidized and
undergo transformation to paramagnetic salts containing bis(maleonitriledithiolato)-metallate(III) anions
[M(mnt)2] (M ˆ Ni, Pt; bis[2,3-dimercapto-kS)but-2-enedinitrilato(2 )]nickelate (1 ) or -platinate (1 ).
The derivatives [3a][Ni(mnt)2] (26), [3a][Pt(mnt)2] (27), [Fe{(h5-C5Me4S)2S}][Ni(Mnt)2] (28), [Fe{(h5-
C5Me4S)2S}][Pt(mnt)2] (29), [5] [Ni(mnt)2] ´ ClCH2CH2Cl (30), [6a] [Ni(mnt)2] (31), [6a] [Ni(mnt)2] ´
ClCH2CH2Cl (31a), [6a] [Pt(mnt)2] [32), and [6b] [Ni(mnt)2] (33) were prepared and fully characterized,
including by SQUID (superconducting quantum interference device) susceptibility measurements. X-Ray
crystal-structural studies of the neutral ferrocene derivatives 6a,b, 21c,d, and 1,1'-bis[1-(1,3-benzodithiol-2-
yliden)-2-oxoethyl]ferrocene (23), as well as of the charge-transfer salts 26 ± 28, 30, and 31a, are reported. The
‡
‡
salts 28 and 30 display both a D A A D structural motif, however, with a different relative arrangement of the
[{Ni(mnt)2}2]2 dimers, thus giving rise to different but strong antiferromagnetic couplings. Salt 26 exhibits
isolated ferromagnetically coupled [{Ni(mnt)2}2]2 dimers. Salt 27 displays a D A D A structural motif in all
three space dimensions, and a week ferromagnetic ordering at low temperature. Salt 31a, on the contrary, shows
segregated stacks of cations and anions. The cations are connected with each other in two dimensions, and the
anions are separated by a 1,2-dichloroethane molecule.
‡
‡
1. Introduction. ± We recently reported synthesis and characterization of
bis(maleonitriledithiolato)metallate(III) salts [M(mnt)2] (M ˆ Ni, Co, Pt; bis[2,3-
di(mercapto-kS)-but-2-enedinitrilato(2 )]metallate(2 )) with the octamethylferro-
cenyl thioethers [1] 1 and 2, as well as with ferrocenes containing S-heterocycles [2 ± 3]
related to the basic tetrathiafulvalene (TTF) structure. These compounds were shown
to display weak ferromagnetic or antiferromagnetic interactions. The physical proper-
ties of such materials strongly depend on the relative arrangement of cations and anions
in the solid state. In turn, the three-dimensional structure is influenced by the nature
and size of the S-containing substituents on the ferrocene. In continuation of these
investigations concerning charge-transfer (CT) complexes with ferrocene electron

Helvetica Chimica Acta ± Vol. 82 (1999)
1325
donors [1 ± 7], a series of bis(maleonitriledithiolato)nickelate and -platinate complexes
with a variety of new ferrocenes (see 3 ± 6) were prepared. The aim of the present study
was to further explore how subtle changes at the electron-donor molecular level
influence the material properties of the corresponding CT complexes. Thus, the present
work was conducted on two main lines. First, in the ferrocenyl thioether series, the new
hexamethyl derivatives 3 and 4 were prepared, thus allowing a comparison with their
octamethyl counterparts. Can such a minor structural change significantly alter the
properties of the corresponding CT complexes? Second, a more drastic modification of
the benzodithiol-containing derivatives, i.e., towards branched compounds comprising
up to four heterocyclic units (see 6), could lead to multiple intermolecular interactions
in the solid state.
2. Results and Discussion. ± 2.1. Synthesis of Ferrocene Derivatives as Electron
Donors. 2.1.1. Hexamethylated Ferrocenes. As opposed to tetramethylcyclo-penta-1,3-
diene, 1,2,3-trimethylcyclopenta-1,3-diene (10) is not stable and dimerizes slowly at
room temperature and upon distillation. Because the retro-Diels-Alder reaction of
dimeric 10 does not occur as easily as for dicyclopentadiene, this compound is more
difficult to access [8][9]. However, 10 may be obtained by distillation of trimethylcy-
clopent-2-en-1-ols (9) at atmospheric pressure and at 1708 and has to be used directly,
after removal of the co-distilled water with sodium sulfate. Thus, for the synthesis of
1,1'-bis[(tert-butyl)thio]-2,2',3,3',4,4'-hexamethylferrocene (3), a strategy for the direct
conversion of trimethylcyclopentenone 7 to the S-substituted ligand 8 was needed. As

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illustrated in Scheme 1, 8 was obtained in moderate yields applying a reported method
[10][11]. The synthesis of the corresponding ferrocenes 3 was then achieved
analogously to that of the octamethylated counterparts [1]. The product obtained
was a 1:1 mixture of two diastereoisomers, i.e., an achiral meso-form 3a and a pair of
enantiomers 3b that could be distinguished by NMR spectroscopy. In particular, the
cyclopenta-2,4-dien-1-yl (Cp) protons of 3a and 3b show distinctly different chemical
1
shifts in the H-NMR spectrum. Upon recrystallization from hexane, an enriched
sample (diastereoisomer ratio of 85 :15) was obtained. However, the configurational
assignment of the diastereoisomers could be made only via an X-ray crystallographic
study of the corresponding CT [Ni(mnt)2] salt (vide infra) obtained from the enriched
mixture. This revealed that the enriched component is the meso-form 3a, thus making a
complete assignment of the 1H-NMR spectra of the two compounds possible.
Reduction of the [Ni(mnt)2] salt with sodium dithionite afforded the ferrocene 3a
quantitatively, and contaminated with only 6% of 3b.
Scheme 1
The 1,1',2,2',3,3'-hexamethylferrocene (11) was needed as a starting material for the
preparation of the corresponding mono- and dialdehydes, intermediates in the
synthesis of donor molecules containing fused S-heterocycles such as, e.g., 5 [2 ±
4][6][12]. As opposed to what was observed for the octamethylated derivatives
previously reported from our laboratory [4][6], it was anticipated that the S-
heterocycles in the hexamethylated series would assume an orientation coplanar with
the Cp ring and, therefore, be in conjugation with the ferrocene. Hexamethylferrocene
11 was obtained in moderate yield from crude 10 as shown in Scheme 2. The dilithiation
of 11, but not of the corresponding octamethyl derivative, with butyllithium (BuLi) in
the presence of N,N,N',N'-tetramethylethylenediamine (TMEDA) appears to be
possible. However, the followup products upon reaction with DMF and sulfur,
respectively, i.e., the dialdehyde 15 and the trithioferrocene 16, could be isolated in
yields of a few percent only. Even the use of stronger bases such as tert-butyllithium or
ꢀLickorꢁ [13] did not improve these preparations. Further work with 15 and 16 was,
therefore, discontinued. On the other hand, monosubstitution of 11 could be achieved
more easily. Thus, the monoaldehyde 12 was prepared via a Vilsmeier reaction, as
in the case of the octamethylated derivative [14 ± 16]. The following Wittig-Horner
reaction afforded the new ferrocene donor 5 in good yield. In an attempt to further
formylate 5 under Vilsmeier conditions, we found a selective functionalization of the
olefinic C H bond, and not at the second Cp ring. This reaction opens the possibility to

Helvetica Chimica Acta ± Vol. 82 (1999)
1327
prepare a new class of donor molecules belonging to the class of vinylogous tetrathia-
fulvalenes [17 ± 26]. Indeed, aldehyde 13 reacted in an additional Wittig-Horner
reaction to give the new donor 14. Finally, one should note that compounds 5 and 12 ±
14 are chiral and that they were obtained as racemates.
Scheme 2
2.1.2. Ferrocenes Containing Vinylogous Tetrathiafulvalenes. The formylation
reaction described above prompted us to prepare a series of vinylogous TTF
compounds based on non-methylated ferrocene, for which the accessibility of mono-
and 1,1'-disubstituted derivatives was known [2]. Thus, the monosubstituted ferrocenes
19a and 19b were prepared in very good yields from 17 and 18a or 18b, respectively
(Scheme 3). As expected, these compounds could be selectively converted under
Vilsmeier conditions to the aldehydes 20a and 20b, respectively, in high yields.
However, aldehyde 20b required the reagent oxalyl chloride instead of phosphoric

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trichloride, which gave no detectable product. From the intermediates 20a,b, the four
vinylogous ferrocenyl tetrathiafulvalenes 21a ± d were prepared in moderate to good
yields by Wittig-Horner reactions.
Scheme 3
Finally, from the known precursor 22a, the ferrocene derivatives 6a and 6b
containing two vinylogous tetrathiafulvalenes were obtained in good yields via 23
(Scheme 4). In contrast, 22b did not react under the same conditions as 22a, neither
with oxalyl chloride nor with phosphoric trichloride. It appears that ferrocene oxidation
of 22b prevails under these conditions, as indicated by the green color of the reaction
mixture.

Helvetica Chimica Acta ± Vol. 82 (1999)
1329
Scheme 4
2.1.3. Synthesis of Charge-Transfer Complexes 26 ± 33. The preparation of
[M(mnt)2] salts 26 ± 33 (M ˆ Ni, Pt) containing the donors 3 ± 6 was achieved
according to the published procedure by reaction with the ferrocenium bis(maleoni-
triledithiolato)metallates 24 or 25 (see Scheme 5) [1][3]. With the new ferrocene-
bridged, vinylogous bis(tetrathiafulvalene) 6a and [Ni(mnt)2] salt 24, two different
products 31 and 31a were obtained in ratios close to 1 : 1 from dichloroethane solutions.
One of them, 31a, is the dichloroethane adduct which crystallized in nice prismatic
plates, whereas the second one, 31, is the solvent-free 1 : 1 salt, obtained as extremly
thin needles. The [Pt(mnt)2] salt 32 of 6a and the [Ni(mnt)2] salt 33 of 6b could be
isolated in only moderate yields. All new [M(mnt)2] salts described in this study

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Helvetica Chimica Acta ± Vol. 82 (1999)
1
display sharp nÄ(CN) bands in the narrow range between 2205 and 2209 cm . This is
also true for the starting monoanionic forms (Et4N)[M(mnt]2]. The IR opacity of the
1
dichloroethane adduct 31a down to 3000 cm is indicative of a semiconductor-like
behavior of this compound.
Scheme 5
2.2. Cyclovoltammetric Measurements. Routine cyclovoltammetric measurements
in CH2Cl2 solution were carried out for all new ferrocene compounds, to check their
ability to form CT complexes. Redox potentials are reported in Table 1. The ferrocenes
3a,b, 5, 6a,b, 11, 12, 15, and 16 all show one reversible one-electron oxidation. The redox
potential increases by ca. 0.3 V per aldehyde group, and ca. 0.1 V per thioether group,
as compared to the corresponding non-substituted derivatives.
The two donors 5 and 14 show two reversible oxidation waves. The lower one
concerns the ferrocene unit, whereas the second process corresponds to an oxidation of
the S-substituent. Cyclovoltammograms for the three compounds 5, 13, and 14 are
depicted in Fig. 1. The two one-electron processes in 5 are separated by 0.78 V
(Table 1). In 14, the oxidation of the ferrocene occurs at a slightly higher potential than
in 5. This can be explained by the larger steric hindrance of the substituent on 14, such
that a coplanar geometry with the Cp ring is no longer possible, thus reducing the
delocalization of the positive charge on the substituent. The second oxidation step,
which is a reversible two-electron oxidation, is lowered by 0.14 V, as compared to 5.
Thus the two potentials are separated by only 0.61 V. The aldehyde group of 13
increases the redox potential of the ferrocene by 0.13 V. This is much less than the effect
of an aldehyde group directly attached to the Cp ring. Moreover, 13 shows a second
irreversible oxidation at a potential of ‡ 1.09 V.

Helvetica Chimica Acta ± Vol. 82 (1999)
1331
a
‡
Table 1. Formal Electrode Potentials (vs. Fc/Fc ) for Ferrocene Derivatives in Dichloromethane Solution )
Compound
E8'(0!n‡) [V]
DEp [mV]
ipc/ipa
E8'(n‡ !m‡) [V]
DEp [mV]
ipc/ipa
(reduced form)
3a,b
4
5
0.19b)(0!1)
0.10c)(0!1)
0.35c)(0!1)
0.16c)(0!1)
104
272
132
106
0.95
1.00
0.96
1.05
‡ 0.43c)(1!2)
(‡ 0.24)b)(1!2)
(‡ 0.33)b)(2!3)
(‡ 0.70)b)(3!4)
140
1.13
6a
(‡ 0.80)b
(4!5)
(‡ 0.37)b)(5!3)VIIbe)
(‡ 0.04)b)(3!1)VIIae)
(‡ 0.14)c)(3!1)
6b
0.16d)(0!1)
98
1.8
(‡ 0.13)d)(1!2)
(‡ 0.21)d)(2!3)
‡ 0.57d)(3!4)VIae)
224
164
(
0.03)d)(3!1)VIbe)
(‡ 0.05)b)(3!1)
11
12
13
14
15
16
19a
19b
20a
20b
21a
0.34b)(0!1)
0.03c)(0!1)
0.22c)(0!1)
0.32c)(0!1)
‡ 0.23b)(0!1)
0.03c)(0!1)
0.07b)(0!1)
0.08c)(0!1)
‡ 0.04c)(0!1)
‡ 0.03b)(0!1)
0.08b)(0!1)
404
120
205
136
92
112
110
96
0.96
0.97
1.39
1.02
0.94
0.98
0.69
0.88
0.97
0.81
0.96
(‡ 1.09)b)(1!2)
‡ 0.29c)(1!2)
0.97
‡ 0.455b)(1!2)
‡ 0.30c)(1!2)
(‡ 0.78)b)(1!2)
(‡ 0.84)b)(1!2)
‡ 0.20b)(1!2)
‡ 0.36b)(2!3)
‡ 0.13b)(1!2)
‡ 0.34b)(2!3)
‡ 0.08c)(1!2)
‡ 0.34c)(2!3)
‡ 0.14c)(1!2)
‡ 0.35c)(2!3)
(‡ 0.78)b)(1!2)
119
192
0.31
1.6
58
200
98
86
166
56
118
90
130
138
168
21b
21c
21d
23
0.07b)(0!1)
0.10c)(0!1)
107
90
0.10c)(0!1)
137
102
‡ 0.02b)(0!1)
0.97
a) All experiments were carried out in dry CH2Cl2/0.1m (Bu4N)BF4 vs. 0.05m Fc/Fc reference electrode
with E8' ˆ‡ 0.042 V for ferrocene, and a Pt working electrode (all values are corrected for 0 V). Values in
brackets are Epa or Epc (anodic or cathodic peak potentials), assigned only to irreversible oxidation steps.
DEp is the difference between Epa and Epc and ipc/ipa is the ratio between cathodic and anodic current indicative
of the reversibility of the redox process. b) Scan rate 100 mV/s. c) Scan rate 20 mV/s. d) Scan rate 50 mV/s).
e) See Fig. 3 for peak identification.
‡
The two mono-substituted ferrocenes 19a and 19b can both be oxidized twice.
The first one-electron oxidation again is probably located on the ferrocene
moiety, whereas the second corresponds to an electron removal from the substituent
[2][6]. The potential of the first oxidation is ca. 100 mV higher than in the doubly
substituted analogues. The two oxidation steps are not completely reversible, as
shown by the ratio of the anodic and cathodic currents of 0.31 and 1.6, respectively
(Table 1).

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Fig. 1. Cyclovoltammograms of the three ferrocene donors 5, 13, and 14
Both aldehydes 20a and 20b can be reversibly oxidized at a potential of ‡ 0.04 and
‡ 0.03 V, respectively (Table 1). Here again, the potentials increase by ca. 110 mV with
respect to that of the precursors because of the acceptor group. At a potential of ‡ 0.78
and ‡ 0.84 V, respectively, a second irreversible oxidation occurs similarly to what is
observed for the aldehydes 13 and 23. The latter can be reversibly oxidized at a potential
of ‡ 0.02 V, and an irreversible oxidation occurs at ‡ 0.78 V (see below, Fig. 3).
The four vinylogous tetrathiafulvalenes 21a ± d show three oxidation waves (Fig. 2).
Because the three waves are overlapping, the ratios of the anodic and cathodic currents
could not be determined. However, since the cycles overall are closed, probably no

Helvetica Chimica Acta ± Vol. 82 (1999)
1333
decomposition of the compounds occurs. In all four cases, the reduction wave at the
highest potential is very steep, and the corresponding current is higher than expected
for a normal one-electron reduction step. Such effects can be detected when a
conducting species precipitates at the electrode. Such behavior has been reported,
for example, for [Ni(dmit)2] derivatives [27] (dmit2 ˆ 1,3-dithiol-2-thione-4,5-
dithiolato ˆ 4,5-di(mercapto-kS)-1,3-dithiol-2-thione).
Fig. 2. Cyclovoltammograms of the four vinylogous TTF derivatives 21a ± d
Donor 6a displays an interesting redox behavior (see Fig. 3), as it is possible to
oxidize this compound in five descrete one-electron steps (steps I ± V). However, the
waves corresponding to the oxidations from 6a1‡ to 6a3‡ (steps II and III) and from 6a3‡

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Helvetica Chimica Acta ± Vol. 82 (1999)
Table 2. Experimental Data for the X-Ray Diffraction Studies of 6a,b, 21c,d, 23, 26 ± 28, 30, and 31a
6a
6b
C40H30Cl4FeS12 C22H18FeS8
1093.01 594.76
21c
21d
23
Empirical formula
Mr
C42H26FeS8
843.00
C24H28FeS6
554.62
C28H18FeO2S4
570.51
Crystal size/mm
Crystal system
Space group (No.)
Temp.
a/Š
0.57 Â 0.27 Â 0.19 0.3 Â 0.3 Â 0.06 0.1 Â 0.02 Â 0.02 0.2 Â 0.1 Â 0.1 0.7 Â 0.3 Â 0.3
triclinic
triclinic
orthorhombic
P212121 (19)
room temp.
11.799(10)
12.869(7)
15.478(12)
90
90
90
2350(3)
4
orthorhombic monoclinic
Å
Å
P1 (2)
P1 (2)
P212121 (19)
room temp.
11.7920(3)
12.9689(4)
15.1203(4)
90
P21/c (14)
room temp.
12.804(5)
14.716(6)
13.443(6)
90
111.42(3)
90
2358(2)
4
room temp.
14.170(3)
14.364(3)
20.603(4)
99.33(3)
106.27(3)
109.52(3)
3639.5(13)
4
room temp.
10.327(5)
13.002(7)
17.059(9)
90.70(2)
98.84(2)
98.43(2)
2238(2)
2
b/Š
c/Š
a/deg
b/deg
g/deg
90
90
3
V/Š
2312.34(11)
4
Z
3
1(calc.)/g cm
m/mm
1.538
1.622
1.681
1.593
1.607
1
0.906
10.388
1.363
1.206
1.021
Diffractometer
Stoe image
plate diffraction
system
Picker Stoe
Syntex P21
Siemens Smart Syntex P21
Platform with
CCD detector
Wavelength l/Š
MoKa,
CuKa,
MoKa,
MoKa,
MoKa,
l ˆ 0.71073
3.96 ± 24.71
21561
l ˆ 1.54178
1.31 ± 25.00
4601
l ˆ 0.71073
2.06 ± 20.03
1281
l ˆ 0.71073
2.07 ± 32.89
7850
l ˆ 0.71073
2.14 ± 20.04
2203
q Range/deg
Measured reflections
Observed reflections
(n)a)
10865
4601
1281
7850
2203
Parameters refined (p) 919
523
281
255
316
Abs. correction
m, max/min trans.
wR2 (I > 2s(I)b)
R1 (I > 2s(I)c)
none
integration
0.581/0.111
0.1515
0.0530
1.046
integration
0.652/0.590
0.0513
0.0198
1.012
empirical
(SADABS)
0.0656
0.0341
0.889
integration
0.774/0.717
0.0620
0.0232
1.062
0.1139
0.0480
1.022
G.o.f. on F^ 2d)
Res. electron density
0.564
0.731
0.160
0.234
0.164
3
eŠ
to 6a5‡ (steps IV and V) strongly overlap. Furthermore, the reduction part of the cycle
shows only three waves, where two two-electron reductions (steps VI and VIIb) and
one one-electron reduction (step VIIIb) can be detected. A two-electron reduction
wave is observed also deriving from cation 6a3‡ (VIIa), however at a peak potential
higher by ca. 100 mV, as compared to the potential of the corresponding step (VIIb)
observed in the full cycle. As in the case of the monosubstituted analogues 21a ± d, the
closed redox cycles indicate that no compound degradation is occurring.
2.3. Solid-State Structure of Neutral Donor Molecules and Charge-Transfer Salts.
2.3.1. Preamble. Single-crystal X-ray diffraction studies were carried out for the five
neutral ferrocene derivatives 23, 6a,b, and 21c,d, and the five CT salts 26 ± 28, 30, and
31a. Table 2 gives the relevant crystal and data-collection parameters. Bond distances
and angles of each asymmetric unit were found to fall in the expected ranges and shall,
therefore, not be discussed in detail. It was mainly of interest to see how the geometry
and orientation of the substituents on the ferrocenes-moiety change in going from the

Helvetica Chimica Acta ± Vol. 82 (1999)
1335
Table 2. (cont.)
26
27
28
30
31a
Empirical formula
C32H28FeN4NiS6 C32H38FeN4PtS6 C26H24FeN4NiS7 C34H30Cl2FeN4NiS6 C52H30Cl2FeN4NiS12
Mr
785.59
921.96
731.48
872.44
1281.02
0.6 Â 0.4 Â 0.2
monoclinic
C2/c (15)
room temp.
8.309(4)
23.202(12)
27.982(14)
90
94.52
90
5378
4
Crystal dimens/mm
Crystal system
Space group (No.)
Temp.
a/Š
b/Š
c/Š
a/deg
b/deg
g/deg
0.3 Â 0.24 Â 0.16 0.2 Â 0.2 Â 0.2
0.4 Â 0.3 Â 0.25 0.4 Â 0.25 Â 0.04
monoclinic
P21/n (14)
room temp.
12.48290(10)
16.9929(3)
18.54960(19)
90
orthorhombic
Pbca (61)
room temp.
13.297(39)
16.849(5)
17.301(9)
90
90
90
3876(3)
4
1.580
monoclinic
P21/c (14)
room temp.
9.804(5)
11.392(8)
27.96(2)
90
triclinic
Å
P1 (2)
room temp.
9.537(5)
11.120(6)
18.691(9)
83.39(4)
77.83(3)
75.46(49)
1872(2)
2
102.4630(10)
90
3842.03
93.89(6)
90
3116
3
V/Š
Z
1(calc.)/g cm
m/mm
4
4
3
1.358
1.220
1.559
1.563
1.548
8.424
1.582
8.202
1
4.329
Diffractometer
Siemens Smart
Platform with
CCD detector
MoKa,
Syntex P21
Syntex P21
Picker Stoe
Picker Stoe
Wavelength l/Š
q Range/deg
Measured reflections 4685
Observed reflections 4685
MoKa,
l ˆ 0.71073
2.28 ± 20.04
1819
MoKa,
l ˆ 0.71073
1.93 ± 17.53
2164
CuKa,
l ˆ 1.54178
1.21 ± 25.00
3845
CuKa,
l ˆ 1.54178
1.59 ± 25.00
2772
l ˆ 0.71073
1.64 ± 21.98
1819
1990
3845
2772
Parameters refined
(p)
399
209
371
433
327
Abs. correction
m, max/min trans.
wR2 (I > 2s(I)b)
R1 (I > 2s(I)c)
G.o.f. on F^ 2d)
empirical
(SADABS)
0.0954
0.0433
1.043
none
empirical
(y scan)
0.0676
0.0315
0.889
integration
0.712/0.173
0.1436
0.0554
1.049
integration
0.207/0.061
0.1346
0.0507
1.130
0.0480
0.0221
0.689
Res. electron density 0.366
eŠ
0.509
0.407
0.856
0.435
3
a) (jFo j> 4.0s(jFj )).
b) wR2 ˆ[s(w(Fo2 Fc2 )2 ]/s[w(Fo2 )2]1/2
.
c) R1 ˆsjjFoj jFcjj/sjFoj.
d) G.o.f.ˆSˆ
2
2
[s (w(Fo2 Fc2)2]/(n p)]1/2
.
neutral to the oxidized form, and how the arrangement of these groups influences the
ordering of the anions.
2.3.2. Neutral Donor Molecules. First, it is important to note that the vinylogous
TTF fragment seems to be very flexible, such that weak packing forces have a strong
influence on its conformation. Thus, in all measured structures, except for the
isomorphous 21c and 21d, the relative arrangement of this fragment is different,
1
although H-NMR spectra in solution indicate free rotation of these substituents.
The dialdehyde 23 crystallizes in the monoclinic space group P21/c, and a view of the
molecule is shown in Fig. 4. The two Cp rings are almost parallel (interplanar angle
2.58), eclipsed, and rotated by only 3.98 against each other. Thus, the two substituents
lie one above the other; however, they are not coplanar with the respective Cp plane,
but rotated by 36 and 308, and the two benzodithiol fragments R and R' are not parallel,

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Fig. 3. Cyclovoltammograms of the two ferrocene-bridged vinylogous TTF derivatives 6a and 6b and of their
precursor 23
with an interplanar angle 14.48. The distances between the planes of the two
neighboring benzene rings are between 3.88 and 4.52Š, which is larger than a van der
Waals stacking distance. The two aldehyde groups lie in the same plane as the
benzodithiol fragments, as indicated by the distances of the O-atoms from the
corresponding planes of 0.3 Š for O(1) and 0.02 Š for O(1'). There are quite short
contacts between the S- and O-atoms of 2.66 and 2.61 Š, respectively. Also, the bond
distances C(6) C(14) and C(6') (14') are shorter than expected (1.440(4) and
1.436(5) Š, resp.). Both anomalies may indicate a contribution of a thienium/enolate
resonance structure, thus with an attractive S O interaction.
Crystals of the ferrocene-bridged vinylogous TTF derivative 6a are triclinic (space
Å
group P1) with two different molecules per asymmetric unit. These two molecules,

Helvetica Chimica Acta ± Vol. 82 (1999)
1337
Fig. 4. ORTEP Plot of dialdehyde 23 with the atom-numbering scheme. Thermal ellipsoids are drawn at the 30%
probability level; H-atoms are omitted.
indicated hereafter as MA and MB, with the benzodithiol fragments R1 and R1' (closer
to the Cp ring), and R2 and R2' (further away from the Cp ring), respectively, are
enantiomers (Fig. 5). The molecules are pseudo-C2-symmetric with eclipsed and
parallel Cp rings that are rotated against each other by 79 (MA) and 688 (MB). The
benzene rings in the fragments R1 and R1' stack in a ꢀface-to-faceꢁ geometry with
distances of 3.64 (MA) and 3.89 Š (MB), slightly larger than van der Waals contacts.
The corresponding interplanar angles are 2.7 (MA) and 2.98 (MB). On the other hand,
the fragments R2 and R2' are almost perpendicular to the fragments R1 and R1', with
torsion angles C(7) C(6) C(14) C(15) of 83 and 798 (MA), and 948 and 868
(MB ), thus indicating that there is no conjugation between R1 and R2.
The very similar ferrocene-bridged TTF derivative 6b also crystallizes in the
Å
triclinic space group P1. However, crystals contain two CH2Cl2 molecules per
asymmetric unit, one of which is highly disordered (see Fig. 6). Again, the two Cp
rings are eclipsed (interplanar angle 5.88) and rotated against each other by 868. The
two fragments R1/R1' and R2/R2' are again not coplanar. The torsion angle
C(8) C(6) C(7) (15) is 688 (and 1418 for the corresponding angle of R1' and
R2'). With respect to 6a, the most striking difference is that the two benzene rings of the
fragments R1 and R1' in 6b show an ꢀedge-to-faceꢁ interaction with an interplanar angle
of 608 and a distance of the two ring centers of 5.1 Š.
The vinylogous ferrocenyl-substituted TTF derivatives 21c and 21d are isomor-
phous and crystallize in the non-centrosymmetric space group P212121. A view of the
asymmetric unit of 21c and 21d, along with the atom-numbering scheme, is depicted in
Fig. 7. Like the compounds 6a and 6b, the vinylogous TTF substituents are not planar,
and the fragment R1 is not coplanar to the respective Cp ring. The interplanar angle
between R1 and R2 is 588 for 21c and 568 for 21d. The torsion angle
C(7) C(6) C(12) C(13) is 648 ( 678), and the plane of R1 forms an angle with
the Cp ring of 428 (488).
2.3.3. Charge-Transfer Complexes. The apparently small difference between [meso-
Fe{h5-C5Me3(StBu)}2][Ni(mnt)2] (26) and the corresponding octamethylated deriva-
tive [1] has a remarkably strong influence on the relative arrangement of the molecules
‡
‡
in the solid state. Thus, whereas the latter displays a typical D A D A structure, in 26

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Fig. 5. ORTEP Plot of the asymmetric unit with the two enantiomers MA and MB in 6a, with the atom-numbering
scheme. Thermal ellipsoids are drawn at the 30% probability level; H-atoms are omitted.

Helvetica Chimica Acta ± Vol. 82 (1999)
1339
Fig. 6. ORTEP Plot of the asymmetric unit of the ferrocene bridged vinylogous TTF derivative 6b, with the atom-
numbering scheme. Thermal ellipsoids are drawn at the 30% probability level; for clarity reasons, the second
position of the C-atom C2M in the disordered solvent molecule (occupancy 25%), as well as H-atoms, are
omitted.
there are layers of ferrocenium cations alternating with layers of [(Ni(mnt)2)2]2 anion
pairs, running diagonally through the unit cell. A projection along the b axis of a pair of
such layers is depicted in Fig. 8, and a projection along the a axis is given in Fig. 9. It is
apparent that the anion dimers are well separated from each other. Within each dimer,
the two anions are arranged in such a way that each Ni-atom lies above the CˆC bond
of the neighboring unit (see also below, Fig. 17). A consequence of this arrangement is
that two pairs of S-atoms lie above each other with intermolecular S S distances of
3.72 Š, and that the Ni Ni distance becomes quite large (4.54 Š). Another feature of
this structure is that the [Ni(mnt)2] units quite strongly deviate from planarity, as
indicated by the interplanar angle between the two mnt ligands of 10.48. To the best of
our knowledge, this type of structure in [Ni(mnt)2] dimers has never been observed
before and, as we will see, has an important effect on the magnetic properties of the CT
complex 26. Finally, the cations show a pseudo-centrosymmetric conformation, with
parallel Cp rings (interplanar angle <0.58) rotated against each other by 1788.
The platinum derivative 27 crystallizes in the orthorhombic space group Pbca, with
both the Fe- and the Pt-atoms on symmetry centers. Thus, every cation is completely
‡
‡
surrounded by six anions, resulting in a three-dimensional D A D A motif. A
projection of a layer perpendicular to the c axis is depicted in Fig. 10. Within such a
layer, four [Pt(mnt)2] anions assume a propeller-like arrangement around the cation
(symmetry center), with an interplanar angle of 748 within each pair. One of the nitrile

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groups points almost directly to the Pt-atom of the neighboring anion, with a Pt
N
distance of 5.77 Š. The same N-atom has an equal distance to the Fe-center. The three
different Fe Pt distances are 6.65 Š along a, 8.42 Š along b, and 8.65 Š along c,
corresponding to half-cell constants. The Cp ring of the cation is almost parallel to the
anions in the a direction (interplanar angle 7.28).
Fig. 7. ORTEP Plot of the asymmetric unit of the vinylogous TTF derivatives 21c and 21d with the atom-
numbering scheme. Thermal ellipsoids are drawn at the 30% probability level; H-atoms are omitted.

Helvetica Chimica Acta ± Vol. 82 (1999)
1341
Fig. 8. Perspective view of a ferrocenium and [Ni(mnt)2]-layer of 26 projected along the b axis
The CT complex 28 of the 1,1',2,2,',3,3,',4,4'-octamethyl-5,5'-trithioferrocene (4)
and [Ni(mnt)2] crystallizes in the monoclinic space group P21/c and displays a
‡
‡
‡
‡
D D A A D D A A motif. The structure consists of alternating planes of almost
perpendicular stacks. A projection along one of the stacking directions is depicted in
Fig. 11, and a side view of a stack is detailed in Fig. 12. Two anions from two neigh-
boring layers form an interplanar angle of 748. The [Ni(mnt)2] dimers have structural
features as previously found in other compounds [1][28][29], with each Ni-atom
interacting with a S-atom of the companion fragment at a distance of 3.78 Š.

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Fig. 9. Perspective view of a ferrocenium and [Ni(mnt)2]-layer of 26 projected along the a axis
Furthermore, the Ni-atoms show a weak interaction with the terminal S-atom of the
trithio unit at a distance of 3.86 Š. The Cp ring of the cation is almost perfectly parallel to
the anion plane, with an interplanar angle of less than 28. The cations within a pair are
facing each other with an intermolecular distance between the middle disordered S-atoms
of 3.53 Š, similar to what was found for the corresponding [FeCl4] and (TCNQF4)
salts [5][7] ((TCNQF4) ˆ ꢀ2,3,5,6-tetrafluorotetracyanoquinodimethanideꢁ).
A comparable description may be applied to the structure of the triclinic 30,
‡
‡
‡
‡
Å
crystallizes in the space group P1. Again a D D A A D D A A motif is observed,
however, with the anions being almost congruent one above the other, with Ni Ni
(3.64 Š) and S S (3.56 Š and 3.65 Š) interactions, as shown in Fig. 13. As opposed to
the octamethylated derivatives previously reported by Hobi et al. [4][6], the S-
heterocycle in the cation resulting from 5 is almost coplanar to the Cp ring, with an

Helvetica Chimica Acta ± Vol. 82 (1999)
1343
Fig. 10. Perspective view of a layer of cations and anions perpendicular to the c axis in 27
interplanar angle between the Cp ring and the heterocycle of 118. A cation/anion
interaction exists, as represented by a Ni S contact distance of 3.80 Š of one of the two
S-atoms. The other one has short-range interactions (3.66 and 3.59 Š) with two S-atoms
of a [Ni(mnt)2] dimer in the neighboring layer. Two neighboring donor molecules
constitute an enantiomeric pair, with a symmetry center located between the two
parallel benzene rings. The planes of the latter are separated from each other by ca.
3.66 Š, slightly larger than typical van der Waals contacts. Finally, there is one
dichloroethane molecule per donor/acceptor unit with a Cl
C C Cl torsion angle of
638. Th solvent molecules form a zig-zag arrangement parallel to the b axis, with
alternating short (3.35 Š) and long (3.45 Š) Cl Cl-distances.
Compound 31a crystallizes in the monoclinic space group C2/c with segregated
stacks of donor and acceptor molecules. The acceptor stacks contain intercalated
dichloroethane molecules, thus leading to a large Ni Ni distance of 8.31 Š. The
ferrocene molecules adopt a chiral conformation and lie on the twofold axes parallel to
the b axis. All molecules aligned on one such C2 axis show the same orientation and
absolute configuration. Thus, enantiomerically pure stacks of each enantiomer
alternate along the c axis, as evident from both the projection of the unit cell along
the a axis in Fig. 14 and a projection along the C2 axis in Fig. 15. The overall
conformation of the ferrocenium cations is very different from that of the neutral

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Fig. 11. Perspective view of the unit cell of 28, projected along one stacking direction
molecule 6a. The two Cp rings show an eclipsed conformation with the two substituents
directly above each other, and a relatively large opening of 138 in the direction of the
substituents. Thus, the distances C(3) C(4') and C(4) C(3') are shortened to 3.17 Š
and C(1) C(1') is elongated to 3.69 Š from the value of 3.37 Š in ferrocene. The
orientation of the two heterocyclic fragments R1 is such that only the five-membered

Helvetica Chimica Acta ± Vol. 82 (1999)
1345
‡
‡
Fig. 12. Side view of a A A D D A A stack in 28
rings overlap to a significant extent, with relatively short distances of 3.75 Š between
S(2) and S(2'). The two fragments R1 and R2 are now more planar than in the neutral
molecule. The torsion angle around the bond C(6) C(14) within the vinylogous TTF
unit is 1478 (838, 948 in neutral 6a). Thus, this unit approaches coplanarity of the two
heterocycles (interplanar angle of 348) much more than does the neutral molecule,
where the two fragments are almost perpendicular to each other. A significant
conjugation and hence delocalization of positive charge is therefore possible, despite
the rotation by 478 of the substituents with respect to the Cp ring. Donor-donor
intermolecular interactions are also apparent. Along the a axis, e.g., the atoms S(1) in
fragments R1 are separated by 3.57 Š, which is significantly shorter than van der Waals
distance (3.7 ± 4.1 Š). Moreover, along the c axis, the fragments R2 show a plane-to-
plane distance of 3.5 Š, which corresponds to the van der Waals distance of the S- and

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Helvetica Chimica Acta ± Vol. 82 (1999)
Fig. 13. Perspective view of a layer of 30, projected perpendicular to the layer plane. Contacts which are shorter
than van der Waals distances are indicated by dotted lines. The dichloroethane molecules fill the empty space
‡
‡
between two D A A D packages.
C-atoms. This leads to a two-dimensional network of stacking interactions between
donor molecules (Fig. 14). The perfectly planar anions, which lie on a symmetry center,
fill the space between the layers of the ferrocenes and are, therefore, strongly
separated. The shortest contact of a S-atom of the anion and R2, e.g., is more than 4 Š.
2.4. Magnetic Measurements. Magnetic-susceptibility measurements were carried
out for the CT complexes 26 ± 31a with a SQUID (superconducting quantum
interference device) susceptometer in the temperature range between 2 and 300 K at
a constant external field of 1000 Gauss. All compounds except 31a obey a modified
Curie-Weiss expression (Eqn. 1), where q is the sum of core diamagnetism and
temperature-independent paramagnetism (TIP)1). For all compounds, q is positive,
meaning that TIP is larger than the diamagnetic component.
C
cmol
ˆ
‡ q
q
ꢀ1†
T
1
)
q ˆ sum of cDIA and cTIP; hgAi ˆ 2.01 [37].

Helvetica Chimica Acta ± Vol. 82 (1999)
1347
Fig. 14. Perspective view of the unit cell of 31a, projected along the a axis. Numbering of the atoms and fragments
as described in the text.

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Helvetica Chimica Acta ± Vol. 82 (1999)
Fig. 15. Perspective view of a ferrocenium layer of 31a, projected along the b axis. There are short contacts
between the S-atoms S(1) (3.57 Š, dotted lines) of the fragments R1.
A plot of cmolT vs. T for the six compounds is shown in Fig. 16. The magnetic
properties of the CT complexes are strongly influenced by the relative arrangement of
the molecular components in the crystal. In principle, there are two main structural
‡
‡
classes, i.e., one with separated single anions and cations assuming a D A D A
arrangement, and showing ferromagnetic interactions (e.g. 27) [1][30], and a second
group containing dimers of anions, this being the more common case. This second
group can in turn be divided in two subgroups: those with isolated dimers displaying a
‡
‡
D A A D motif (for example 28 and 30), and those with segregated stacks of anion
dimers and columns of cations. For this second category, many examples have been
reported [1][3][28][30 ± 32]. Weiher and co-workers [31] found in 1964 that the
tetraethylammonium salts of [{M(mnt)2}2]2 (M ˆ Ni, Pt) have a singlet ground state
(S ˆ 0) with a thermally populated excited triplet state (S ˆ 1). These authors used the

Helvetica Chimica Acta ± Vol. 82 (1999)
1349
equation developed by Figgis and Martin [33] (Eqn. 2)2) to calculate the molar
magnetic susceptibility of dimeric [{M(mnt)2}2]2 complexes, and found an energy gap
1
between singlet and triplet state JAA (S ˆ 0 ! S ˆ 1) for (Et4N)[Ni(mnt)2] of 620 cm .
2
Nb2hgAi SAꢀSA ‡ 1†
cmol
ˆ
‡ cDIA ‡ cTIP
ꢀ2†
J
AA=kT
kTꢀ3 ‡ e
†
Twenty years later, Ramakrishna [34] showed that this is not a sufficiently accurate
description because, in a stack of anions with alternating distances, alternating J values
should be observed. It has been shown that these values are extremely sensitive to the
packing arrangement of the dimers. Unfortunately, it is not easy to discern the two
different values from only temperature-dependent susceptibility measurements,
because there are too many parameters to fit. However, Eqn. 2 can be used as long
as the observed J values are interpreted as average values for all possible interactions.
A survey of the magnetic data of the new compounds, together with some selected
literature data, are given in Table 3.
Fig. 16. SQUID Susceptibility data for compounds 26 ± 30 and 31a measured in an external field of 1000 G. The
lines correspond to the calculated values either with Eqn. 1 (26, 27) or Eqn. 4 (28 ± 30, 31a).
With the assumption that there are no interactions between the ferrocenium donors
and the [{Ni(mnt)2}2]2 dimers, the magnetic susceptibility of both components is
additive (Eqn. 3) [35]. This assumption is meaningful whenever the metal-metal
distances between donors and acceptors are sufficiently large. For both contributions,
cdonor and cacceptor, a term as in Eqn. 2 can be used to calculate the molar magnetic
susceptibility of the compounds containing [{M(mnt)2}2]2 dimers, as given by Eqn. 4.
2
Â
)
N, Avogadro constant; b, Bohr magneton; hgAi, average Lande factor of the acceptors; SA, spin of the
acceptors; k, Boltzmann constant; JAA, energy difference between ground and excited state; cDIA
diamagnetic susceptibility; cTIP, temperature-independent paramagnetic susceptibility.
,

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Table 3. Survey of the Observed Magnetic Data for the Charge-Transfer Complexes 26 ± 30 and 31a, as well as for Some
Selected Previously Reported Compounds
6
Curie constant meff
Weiss Const. q JAA
JDD
[cm
hgDi
q ´ 10
1
1
1
1
1
C [cm3Kmol
]
[mbmol
]
[K]
[cm
]
]
[cm3mol
]
26
27
28
29
30
31a
0.917(5)
0.554(4)
0.559(5)
0.6048(4)
0.402(6)
0.451(5)
±
2.71
2.10
2.11
2.20
1.79
1.90
‡ 1.3(2)
‡ 3.0(49)
‡ 0.7(3)
0.197(4)
‡ 1.3(6)
6.0(59)
±
±
±
±
±
2.40
1.37
2.588(5)
1031(17)
631(18)
607(25)
302(8)
1000
630(33)
96(1)
620
490
350
6(1)
771(4)
0.27(5)
<
0.459(9) 2.9035(9) 1047(3)
1.01(7)
2.34(3)
2.192(8)
2.280(3)
2.06[37]
2.06[37]
2.04[37]
2.65(4)
477(36)
1889(4)
260
150
220
(Et4N)[Ni(mnt)2] [29][31]
(Ph3MeP)[Ni(mnt)2] [28][31]
(Et4N)[Pt(mnt)2] [31][32]
[1][Ni(mnt)2] [1][7]
[Fe(h5-C5H4CHCHPhSMe)2]- 0.480(4)
[Ni(mnt)2] [3][6]
±
±
±
±
±
±
±
0.88(2)
2.65
1.96
0.7(9)
‡ 0.7(4)
‡ 0.6(4)
720(50)
626(15)
0.81(3)
2.692(4)
cmol ˆ cdonor ‡ cacceptor ‡ cDIA ‡ cTIP
ꢀ3†
ꢀ4†
2
2
Nb2 hgDi SDꢀSD ‡ 1† hgAi SAꢀSA ‡ 1†
cmol
ˆ
‡
J
DD=KT
JAA=KT
kT 3 ‡ e
3 ‡ e
We shall address the CT complexes 28 and 30 first, as they contain isolated
‡
‡
[Ni(mnt)2] dimers displaying a known arrangement within the D A A D motif.
Furthermore, although the crystal structure of 29 is not known, the magnetic data
strongly indicate that its structure must be very similar to that of 28. Thus, for these
compounds, the Curie constants C are too small for one unpaired electron per donor
1
and acceptor molecule (C ˆ 0.559(5) cm3K/mol and meff ˆ 2.11 mBmol for 283); C ˆ
1
0.6048(4) cm3K/mol meff ˆ 2.20 mBmol
for 29; C ˆ 0.402(6) cm3K/mol and meff
ˆ
1
1.79 mBmol for 30). By fitting the observed data with Eqn. 4, strong antiferromagnetic
interactions for all three compounds result, as expected (28: JAA
1000 cm and JDD
1.01(7) cm ). The higher value of JAA for 30, as compared
to 28, can be explained by the relatively strong direct Ni Ni interaction, whereas in 28,
a Ni Ni interaction is found. In the Pt derivative 29, the coupling constant JAA is too
1
ˆ
302(8) cm and
1
1
1
JDD
ˆ
0.27(5) cm ; 29: JAA
<
ˆ
0.459(9) cm ; 30: JAA
ˆ
1
1
630(33) cm and JDD
ˆ
S
large for it to be obtained by means of magnetic-susceptibility measurements. In other
words, in the measured temperature range below 300 K, only the contribution of the
cation is observed. Because of the relatively short distances of one S-atom of the donors
‡
to the Ni-atom of the acceptors in 28 and 30, a D A interaction could be expected.
However, below 100 K, the triplet state of the [{Ni(mnt)2}] dimers is no longer
thermally populated, such that the contribution of an interaction between donor and
acceptor has no significant influence on the magnetic susceptibility below this
temperature.
The magnetic behavior of 31a is more complex, as it does not obey the Curie-Weiss
expression (Eqn. 1). Nevertheless, a Curie constant C of 0.451(5) cm3K/mol (meff
1.90 mBmol ) and a negative Weiss constant q of 6.0(5) K could be determined. The
ˆ
1
As obtained from high-temperature data according to meff ˆ (3kcmol ´ T/Nb2)1/2), calculated per 1 mol of Fe.
3
)

Helvetica Chimica Acta ± Vol. 82 (1999)
1351
cT vs. T plot (Fig. 16) shows a steady decrease with a small plateau at about 25 K and a
strong drop below 10 K. This behavior points out strong antiferromagnetic interactions.
Although it is possible to obtain perfect coincidence between values calculated with
Eqn. 4 and the observed measured data, the resulting values for JAA and JDD probably
do not have any physical meaning. It is indeed known from the crystal structure (vide
supra) that there are several contacts between the donor molecules and also between
donors and acceptors, possibly leading to magnetic couplings.
As opposed to the above compounds, 26 shows a strong increase in cTas a function
of T below 20 K (Fig. 16). The Curie constant C of 0.917(5) cm3K/mol (meff
ˆ
1
2.71 mBmol ) indicates that there has to be an unpaired electron per donor and
acceptor molecule (S ˆ 2  1/2 spin system). Thus, the hitherto unknown arrangement
of the [Ni(mnt)2] anions within a dimer changes the sign of the spin-spin interaction.
This is the first time that an isolated [{Ni(mnt)2}2]2 dimer with a ferromagnetic (S ˆ 1)
ground state has been found. A comparable situation was reported for the [Ni(dmit)2]
salt of decamethylferrocenium [36]. This observation can now help to explain the
unusually weak antiferromagnetic interaction in the previously described compound
[1] [Ni(mnt)2] [1]. In this compound, stacks of [{Ni(mnt)2}2]2 dimers are found, like in
(Et4N)[Ni(mnt)2]. However, the interdimer interaction is probably a ferromagnetic
one as in 26, of almost the same magnitude as the antiferromagnetic intradimer
interaction. Such an alternation of ferromagnetic and antiferromagnetic interactions
1
leads to the overall weak antiferromagnetic JAA value of only 6(1) cm . A summary
of the observed magnetic properties of [Ni(mnt)2] dimers in different CT complexes,
along with a view of the different dimer arrangements, is depicted in Fig. 17.
Compound 27 shows behavior similar to that of its companion 26, with the
difference that the Curie constant C is too small for it to indicate the presence of one
1
unpaired electron per molecular unit (C ˆ 0.554(4) cm3K/mol, meff ˆ 2.10 mBmol ).
Â
This can be explained only with an exceptionally small average Lande factor hgDi for
the ferrocenium cation of only 1.37 (hgAi for [Pt(mnt)2] ˆ 2.04 [37]). Below 20 K,
again a strong increase is observed in the cT vs. T plot (Fig. 16), indicating a weak but
significant ferromagnetic ordering at low temperature, as shown also by the positive
‡
‡
Weiss constant q of ‡ 3.04(4) K. This observation is in accord with the D A D A
arrangement of the molecules found in the solid state.
3. Conclusions.± We have shown that it is possible to achieve ferromagnetic
interactions in molecular materials containing [M(mnt)2] anions by two completely
different interaction pathways. One of them is the already known mechanism relying
‡
‡
upon a D A D A structural motif, as in compound 27. The second one is based on the
new dimer arrangement found in [meso-Fe{h5-C5HMe3(StBu)}2][Ni(mnt)2] (26),
leading to a dimer with a ferromagnetic ground state. Therefore, it should be possible,
in principle, to obtain a one dimensional stack of ferromagnetically coupled
[M(mnt)2] anions, as long as the cation would favor such a relative arrangement of
the anions. However, we have seen how serendipitous and unpredictable the structural
properties of [M(mnt)2] CT complexes are, also in view of the structural variety of the
ferrocenyl donor molecules. Thus, the goal remains to find ferromagnetic compounds
‡
‡
with higher Tcꢁs than for the D A D A complexes of decamethyl ferrocene with
TCNE (tetracyanoethylene ˆ ethenetetracarbonitrile) and TCNQ ( ˆ tetracyano-

1352
Helvetica Chimica Acta ± Vol. 82 (1999)
Fig. 17. Different arrangements of [{Ni(mnt)2}2]2 dimers, with their magnetic interaction parameters J. In the
ferromagnetically coupled compound 26, the value of J could not be determined, because of an over-
parameterization.
quinodimethane ˆ 2,2'-(cyclohexa-2,5-diene-1,4-diylidene) bis[propanedinitrile]) re-
ported by Miller and others [38 ± 41]. We are currently performing quantum-
mechanical calculations aimed at finding the relative energy differences in the three
different dimer arrangements, and to calculate the triplet/singlet energy gap in 26.
Experimental Part
General. Experimental techniques were described earlier [2]. NMR: at 250.13 (1H) and 62.895 MHz (13C)
for CDCl3 solns. at 258, unless stated otherwise; d in ppm rel. to SiMe4 (ˆ 0 ppm), J in Hz. MS: m/z (rel. %).
1-[(tert-Butyl)thio]-2,3,4-trimethylcyclopenta-1,3-diene (8). A soln. of 2,3,4-trimethylcyclopent-2-en-1-one
[8][9][42 ± 46] (7; 4.958 g, 39.9 mmol) in THF (100 ml) was mixed with titanium tetrachloride (6.77 g,

Helvetica Chimica Acta ± Vol. 82 (1999)
1353
35.7 mmol) at 08, and sodium 1,1-dimethylethanethiolate (4.475 g, 39.9 mmol) and Et3N (5.56 mL, 39.9 mmol)
were added dropwise. The mixture was warmed to r.t. and stirred overnight. The solvent was evaporated and the
residue distilled at 1108/3 ´ 10 2 mbar in a bulb-to-bulb distillation apparatus: 4.56 g (58%) of 8. Bad smelling
yellow oil. 1H-NMR: 1.28 (s, t-Bu); 1.83 (s, 1 Me); 1.94 (s, 1 Me); 2.01 (s, 1 Me); 3.02 (m, CH2). 13C-NMR: 11.30
(Me); 13.39 (Me); 13.56 (Me); 31.44 (Me3C); 46.95 (Me3C); 52.16 (CH2); 124.83 (MeC); 136.40 (MeC);
.
‡
138.85 (MeC); 142.65 (tBuSC). EI-MS: 196.3 (42; M ), 140 (100), 125, 107.
1,1'-Bis[(tert-butyl)thio]-2,2',3,3',4,4'-hexamethylferrocene (mixture of diastereoisomers 3a/3b). The same
procedure as for 1,1'-bis[(tert-butyl)thio]-2,2',3,3',4,4',5,5'-octamethylferrocene [1] was applied, with 8 (4.15 g,
21.1 mmol), THF (30 ml), a freshly prepared lithium diisopropylamide (LDA) soln. (from (iPr)2NH (4.5 ml),
1.6m BuLi in hexane (17 ml), and THF (25 ml)), and anh. iron(II) chloride (2.08 g, 29.6 mmol): 2.89 g (70%) of
3a/3b 1:1. M.p. 1018. By recrystallization from hexane, the meso-form 3a could be enriched to a meso/rac ratio of
85 :15 after one recrystallization.
Data of 3a: 1H-NMR: 1.15 (s, 2 t-Bu); 1.79 (Me); 1.84 (Me); 1.86 (Me); 3.67 (s, 2 CH (Cp)). 13C-NMR:
10.32 (Me); 10.99 (Me); 11.75 (Me); 30.84 (Me3C); 44.89 (Me3C); 74.94 (CH (Cp)); 78.07 (tBuSC); 83.11 (MeC
(Cp)); 83.48 (MeC (Cp)); 86.05 (MeC (Cp)).
Data of 3b: 1H-NMR: 1.15 (s, 2 t-Bu); 1.80 (s, 2 Me); 1.81 (s, 2 Me); 1.85 (s, 2 Me); 3.78 (s, 2 CH (Cp)).
13C-NMR (62.895 MHz, CDCl3): 10.09 (Me); 10.49 (Me); 11.90 (Me); 30.82 (Me3C); 44.94 (Me3C); 74.78 (CH
(Cp)); 77.62 (tBuSC); 83.31 (MeC (Cp)); 83.40 (MeC (Cp)); 86.04 (MeC (Cp)).
Data of 3a/3b: IR (KBr): 3072, 2957, 2897, 1655, 1472, 1456, 1377, 1360, 1290, 1169, 1032, 977, 836, 750, 696,
.
‡
518, 457. EI-MS: 446 (100, M ), 390, 334, 301, 299, 193, 162, 105. Anal. calc. for C24H38FeS2 (893.1): C 64.55,
H 8.58, S 14.36; found: C 64.68, H 8.51, S 14.41.
Synthesis of 3a by Reduction of the Corrresponding [Ni(mnt)2] Salt 26. [3a][Ni(mnt)2] (26; 754 mg) was
vigorously stirred in sodium dithionite soln./tBuOMe until the black crystals dissolved. The red aq. soln.
containing [Ni(mnt)2]2 was separated and the org. phase dried (MgSO4) and evaporated: 425 mg (99%) of 3a.
M.p. 134 ± 1368. 1H-NMR: meso/rac 94 :6.
2,3,4-Trimethylcyclopent-2-en-1-ol (9) [47]. To a soln. of 7 (10 g, 80 mmol) in Et2O (100 ml), LiAlH4 (3.4 g,
90 mmol) was added in portions. The resulting mixture was stirred for 24 h at r.t. Then, 2n HCl was slowly added
until the excess of LiAlH4 was hydrolyzed. The org. phase was filtered over Celite, and the lithium and
aluminium salts were washed with tBuOMe. The combined org. phase was evaporated and the residue distilled
at 948/4 mbar in a bulb-to-bulb distillation apparatus. 8.74 g (87%) of 9 cis/trans ca. 3 :1. GC/EI-MS: 126 (20,
.
‡
M
), 111, 43, 29, 15 (100).
1,1',2,2',3,3'-Hexamethylferrocene (11). At 1 atm/1708 (bath) 9 (7.5 g, 59 mmol) was distilled. At this temp.,
trimethylcyclopentadiene distilled together with H2O (boiling temp. 928) directly into a cooled Schlenk tube
788), to prevent Diels-Alder dimerization. When the distillation was complete, pentane was added to the
(
distillate and the soln. dried (MgSO4) and evaporated at 08. 5 g (47.8 mmol, 81%) of 1,2,3-trimethylcyclopenta-
1,3-diene (10). This product was immediately cooled to 788, mixed with THF (10 ml) and 2m LDA in THF/
ethylbenzene (31 ml, 62 mmol), and stirred for 15 min. Anh. iron(II) chloride (4.6 g, 36 mmol) was added in
one portion and the mixture allowed to warm to r.t. The resulting mixture was dissolved in tBuOMe and treated
wtih 2n HCl and brine. The residue from the org. phase was chromatographed (silica gel, hexane): 2.4 g (30%)
1
of 11. IR (KBr): 3068, 2902, 1475, 1377, 1030, 802, 474. H-NMR: 1.79 (s, 2 Me); 1.85 (s, 4 Me); 3.61 (s, 4 CH
(Cp)). 13C-NMR: 9.66 (Me); 12.19 (Me); 68.44 (CH (Cp)); 80.82 (MeC); 82.01 (MeC). EI-MS: 270 (100,
.
‡
M
), 255, 160, 148, 135, 105, 91. Anal. calc. for C16H22Fe (270.2): C 71.12, H 8.21; found: C 71.10, H 8.14.
rac-1-Formyl-2,2',3,3',4,4'-hexamethylferrocene (12). A mixture of 11 (2.4 g, 8.8 mmol), DMF (14 ml), and
POCl3 (2.4 ml, 26.4 mmol) was stirred overnight. A sat. NaOAc soln. was added and the resulting mixture stirred
for an additional hour. The product was extracted with CH2Cl2 and chromatographed (silica gel, hexane/AcOEt
3 :1): 1.65 g (63%) of 12. M.p. 1288. IR (KBr): 3065, 2965, 2907, 1666, 1412, 1380, 1157, 1033, 844, 799, 744, 721,
684, 656, 612, 510, 470. 1H-NMR: 1.69 (s, Me); 1.76 (s, Me); 1.77 (s, Me); 1.88 (s, Me); 1.94 (s, Me); 2.09 (s, Me);
3.65 (d, 1 CH (Cp)); 3.69 (d, 1 CH (Cp)); 4.25 (s, 1 CH (Cp)); 9.89 (s, CHO). 13C-NMR: 194.54 (CHO): 87.89
(MeC (Cp)); 87.35 (MeC (Cp)); 84.39 (MeC (Cp)); 83.98 (MeC (Cp)); 83.29 (MeC (Cp)); 82.43 (MeC (Cp));
75.02 (MeC (Cp)); 70.24 (CH (Cp)); 69.98 (CH (Cp)); 69.82 (CH (Cp)); 12.25 (Me); 11.73 (Me); 11.59 (Me);
.
‡
10.25 (Me); 9.66 (Me); 9.17 (Me). EI-MS: 298 (100, M ), 269, 255, 240, 163, 148, 107, 91, 79, 56. Anal. calc. for
C17H22FeO (298.2): C 68.47, H 7.44; found: C 68.33, H 7.42.
rac-1-[(1,3-Benzodithiol-2-ylidene)methyl]-2,2',3,3',4,4'-hexamethylferrocene (5). A soln. of dimethyl 1,3-
benzodithiol-2-ylphosphonate [48 ± 50] (18a; 106 mg, 0.404 mmol) in THF (15 ml) was mixed with 1m BuLi in
hexane (0.26 ml, 0.416 mmol) at 788. Then a soln. of 12 (120 mg, 0.404 mmol) in THF (5 ml) was added
dropwise. After 1.5 h, the mixture was warmed to r.t., and a sat. NH4Cl soln. (6 ml) and CH2Cl2 (35 ml) were