Copper complexes of 1,3-bis(2-pyridyl)-1-thiapropane (bpt) and pyridine-2(1H)-thione. Crystal structure of [{Cu(μ-O2CMe)2(bpt)}2] and metal-promoted cleavage of bpt

Article abstract of DOI:10.1039/a700711f

The reactivity of the asymmetric thioether 1,3-bis(2-pyridyl)-1-thiapropane [1-(2-pyridyl)-2-(2-pyridyl-sulfanyl)ethane] (bpt) with copper-(I) and -(II) starting materials has been investigated. Reaction with [Cu(NCMe)₄]PF₆ in MeCN gave a cluster formulated as [Cu₄(bpt)₆][PF₆]₄, whilst reaction in tetrahydrofuran resulted in partial cleavage of bpt to give the mixed thionato-thioether complex [Cu₂(SC₅H₄N)(bpt)]PF₆ [SC₅H₄NH = pyridine-2(1H)-thione]. Reaction with [Cu₂(μ-O₂CMe)₄] in MeOH gave the dimer [{Cu(μ-O₂CMe)₂-(bpt)}₂], whose crystal structure shows that the bpt ligands are monodentate and co-ordinated via the N atom remote from the thioether. The compound bpt undergoes cleavage with other copper(II) salts such as Cu(BF₄)₂, ultimately giving the hexameric copper(I) complex [Cu₆(SC₅H₄N)₆]. The details of this reaction have been investigated. Reaction of SC₅H₄NH with Cu(NO₃)₂ in the presence of HNO₃ gave [Cu(NO₃)(SC₅H₄NH²)], which in turn reacted progressively with PPh₃ to give [Cu(NO₃)(SC₅H₄NH)₂(PPh₃)] and the known complex [Cu(SC₅H₄NH)₂(PPh₃) ₂]NO₃, whose crystal structure has been determined. Other complexes of SC₅H₄NH with copper(I) and a range of anions have been prepared, and the crystal structure of the dimer [Cu₂(SC₅H₄NH)₆]-[MeC ₆H₄SO₃]₂ is reported.

Full text of DOI:10.1039/a700711f

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Copper complexes of 1,3-bis(2-pyridyl)-1-thiapropane (bpt) and
pyridine-2(1H)-thione. Crystal structure of [{Cu(ì-O2CMe)2(bpt)}2]
and metal-promoted cleavage of bpt †
Sian C. Davies, Marcus C. Durrant,* David L. Hughes, Kerstin Leidenberger, Christian Stapper
and Raymond L. Richards
Nitrogen Fixation Laboratory, John Innes Centre, Norwich Research Park, Colney, Norwich,
UK NR4 7UH
The reactivity of the asymmetric thioether 1,3-bis(2-pyridyl)-1-thiapropane [1-(2-pyridyl)-2-(2-pyridyl-
sulfanyl)ethane] (bpt) with copper-() and -() starting materials has been investigated. Reaction with
[Cu(NCMe)4]PF6 in MeCN gave a cluster formulated as [Cu4(bpt)6][PF6]4, whilst reaction in tetrahydrofuran
resulted in partial cleavage of bpt to give the mixed thionato–thioether complex [Cu2(SC5H4N)(bpt)]PF6
[SC5H4NH = pyridine-2(1H)-thione]. Reaction with [Cu2(µ-O2CMe)4] in MeOH gave the dimer [{Cu(µ-O2CMe)2-
(bpt)}2], whose crystal structure shows that the bpt ligands are monodentate and co-ordinated via the N atom
remote from the thioether. The compound bpt undergoes cleavage with other copper() salts such as Cu(BF4)2,
ultimately giving the hexameric copper() complex [Cu6(SC5H4N)6]. The details of this reaction have been
investigated. Reaction of SC5H4NH with Cu(NO3)2 in the presence of HNO3 gave [Cu(NO3)(SC5H4NH)2], which
in turn reacted progressively with PPh3 to give [Cu(NO3)(SC5H4NH)2(PPh3)] and the known complex
[Cu(SC5H4NH)2(PPh3)2]NO3, whose crystal structure has been determined. Other complexes of SC5H4NH with
copper() and a range of anions have been prepared, and the crystal structure of the dimer [Cu2(SC5H4NH)6]-
[MeC6H4SO3]2 is reported.
Type 1 copper centres are found in a variety of copper
metalloproteins, including blue copper oxidases,1 plasto-
cyanins2 and nitrite reductases.3 Their roles as electron-transfer
agents are associated with the distinctive properties of the
copper atom, which is generally co-ordinated by two histidine,
one cysteinate and one methionine ligand in a highly distorted
tetrahedral or trigonal-pyramidal environment.4 Model studies
using simple copper complexes to mimic this arrangement have
highlighted the remarkably flexible nature of the copper with
regard to its co-ordination geometry, a phenomenon termed
plasticity.5,6 We have previously reported the crystal structure
of a molybdenum(0) complex of the asymmetric thioether
1,3-bis(2-pyridyl)-1-thiapropane
[1-(2-pyridyl)-2-(2-pyridyl-
sulfanyl)ethane] (bpt),7 in which the four- and six-membered
chelate rings formed by the tridentate N2S-donor bpt ligand
result in a highly distorted octahedral geometry around the
metal centre. In the hope of preparing structurally distorted
copper complexes of bpt, we have now investigated the chem-
istry of this thioether with a number of copper-() and -()
starting materials.
Fig. 1 Crystal structure of [{Cu(µ-O2CMe)2(bpt)}2] 1
copper atoms is essentially five-co-ordinate square pyramidal,
and the geometrical properties of the complex are in good
agreement with the literature values for related complexes.8–10 It
is noteworthy that in complex 1 copper() prefers to co-
ordinate the harder pyridine nitrogen donor over the thioether
sulfur. Furthermore, the pyridine ring remote from the sulfur is
preferred for co-ordination. This is evidently due primarily to
electronic rather than steric effects, since molecular models
show that the steric difference between the two possible isomers
is minimal. It has been argued 11 that since the pyridine rings in
this type of complex are staggered with respect to the orthog-
onal planes of the carboxylate ligands, pyridine is acting essen-
tially as a pure σ donor; in this case the inductively electron-
withdrawing properties of the thioether compared to the alkyl
group could account for the choice of pyridine donor in com-
plex 1.
Results and Discussion
Reactions of bpt with copper(II)
The preparation and spectroscopic properties of bpt have been
described previously.7 Reaction of bpt with copper() acetate
gave the dimeric adduct [{Cu(µ-O2CMe)2(bpt)}2] 1. Its molecu-
lar structure, determined by X-ray crystallography, is shown in
Fig. 1, and selected bond lengths and angles are given in Table 1.
In this complex the bpt ligand is monodentate, behaving as a
simple pyridine; the structure is a classic example of a carb-
oxylate-bridged dinuclear copper() adduct,8 closely related to
that of [{Cu(µ-O2CMe)2(py)}2] (py = pyridine).9 The molecule
lies about a centre of symmetry; the geometry around the
The room-temperature magnetic moment of complex 1 was
measured as 1.35 µB, typical for complexes of this type.11 Even
though the copper centres in 1 are paramagnetic, it was possible
to observe the non-co-ordinated ends of the bpt ligands by
NMR spectroscopy (Tables 4 and 5). Together with the low
† Non-SI unit employed: µB ≈ 9.27 × 10Ϫ24 J TϪ1
.
J. Chem. Soc., Dalton Trans., 1997, Pages 2409–2418
2409

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Nu–
Table 1 Selected dimensions (bond lengths in Å, angles in Њ) in [{Cu(µ-
O2CMe)2(bpt)}2] 1 with estimated standard deviations (e.s.d.s) in
parentheses*
H
N
N
Cu
Cu
S
SC5H4N
(a) About the Cu atom
C5H4N
Cu ؒ ؒ ؒ CuЈ
Cu᎐O(11)
Cu᎐O(12Ј)
2.651(1)
1.974(3)
1.958(3)
Cu᎐O(21)
Cu᎐O(22Ј)
Cu᎐N(31)
1.979(3)
1.960(3)
2.217(3)
Scheme 1
plex of pyridine-2(1H)-thione (SC5H4NH), namely [Cu6(SC5-
H4N)6] 2 (Fig. 2). The structure of this complex was originally
obtained by Kitagawa et al.,13 who prepared it by the reaction
of the copper() salt [Cu(NCMe)4]PF6 with SC5H4NH in
acetone.
In order to explain the formation of complex 2 from
copper() plus bpt, we examined the reaction of CuSO4 with
bpt in more detail. Upon boiling an equimolar mixture of the
reactants in methanol–water solution for 4 h, [Cu6(SC5H4N)6]
was obtained in 50% yield. The green colour of the reaction
solution suggested that the remaining copper() had not
reacted; the solution was acidic, and contained 2-vinylpyridine
as shown by 1H NMR spectroscopy and its characteristic
odour. The overall reaction can therefore be written as in
equation (1) where dpds is bis(2-pyridyl) disulfide and vpy is
O(11)᎐Cu᎐O(12Ј)
O(11)᎐Cu᎐O(21)
O(11)᎐Cu᎐O(22Ј)
O(11)᎐Cu᎐N(31)
O(12Ј)᎐Cu᎐O(21)
167.5(1)
90.6(1)
87.3(1)
92.8(1)
88.5(1)
O(12Ј)᎐Cu᎐O(22Ј)
O(12Ј)᎐Cu᎐N(31)
O(21)᎐Cu᎐O(22Ј)
O(21)᎐Cu᎐N(31)
O(22Ј)᎐Cu᎐N(31)
90.9(1)
99.7(1)
167.6(1)
91.4(1)
100.9(1)
(b) In the acetate ligands
O(11)᎐C(1)
C(1)᎐O(12)
C(1)᎐C(11)
1.246(5)
1.253(5)
1.515(7)
O(21)᎐C(2)
C(2)᎐O(22)
C(2)᎐C(21)
1.255(5)
1.254(5)
1.495(7)
Cu᎐O(11)᎐C(1)
O(11)᎐C(1)᎐O(12)
CuЈ᎐O(12)᎐C(1)
122.1(3)
125.8(4)
124.5(3)
Cu᎐O(21)᎐C(2)
O(21)᎐C(2)᎐O(22)
CuЈ᎐O(22)᎐C(2)
124.8(3)
125.0(4)
122.2(3)
(c) In the bpt ligand
CuSO4 ϩ 2bpt
C(32)᎐C(321)
C(321)᎐C(322)
1.501(6)
1.528(6)
C(322)᎐S(42)
S(42)᎐C(42)
1.799(5)
1.769(5)
1
–
6[Cu6(SC5H4N)6] ϩ ¹dpds ϩ 2vpy ϩ H2SO4 (1)
¯
²
Cu᎐N(31)᎐C(32)
Cu᎐N(31)᎐C(36)
N(31)᎐C(32)᎐C(321) 117.5(4)
C(33)᎐C(32)᎐C(321) 122.0(4)
C(32)᎐C(321)᎐C(322) 113.6(4)
129.6(3)
112.2(3)
C(321)᎐C(322)᎐S(42) 116.1(3)
2-vinylpyridine. The cleavage of bpt to SC5H4NH and vpy is the
reverse of the reaction used for its preparation, and is evidently
promoted by both copper-() and -() (see below). The reaction
is reminiscent of the metal-promoted cleavage of RSCH2-
CH2SR groups to give a thiolate plus vinyl thioether;14 it might
involve the formation of a chelate ring incorporating the pyri-
dine nitrogen and the thioether sulfur, which would render the
protons of the ethylene linkage susceptible to nucleophilic
attack as shown in Scheme 1.
C(322)᎐S(42)᎐C(42)
S(42)᎐C(42)᎐N(41)
S(42)᎐C(42)᎐C(43)
102.7(2)
119.3(3)
117.2(4)
(d) Torsion angles in the bpt ligand
N(31)᎐C(32)᎐C(321)᎐C(322)
C(33)᎐C(32)᎐C(321)᎐C(322)
C(32)᎐C(321)᎐C(322)᎐S(42)
C(321)᎐C(322)᎐S(42)᎐C(42)
C(322)᎐S(42)᎐C(42)᎐N(41)
C(322)᎐S(42)᎐C(42)᎐C(43)
Ϫ94.2(4)
85.8(5)
Ϫ71.7(4)
Ϫ89.3(4)
18.8(4)
These observations led us to consider the co-ordination
chemistry of copper with SC5H4NH in more detail.
Ϫ160.5(4)
* Primed atoms are related by the operation: 1 Ϫ x, 1 Ϫ y, 1 Ϫ z.
Reactions of pyridine-2(1H)-thione with copper
The co-ordination chemistry of SC5H4NH and other hetero-
cyclic thioamides with copper is an active research area which
has recently been reviewed in detail.15 Although the reaction
of SC5H4NH with Cu(O2CMe)2 was investigated as long ago
as 1900,16 the exact nature of the product has proved elusive,
being successively formulated as [Cu2(SC5H4N)2],16 [{Cu(SC5-
H4N)}n]17 and [Cu4(SC5H4N)4].18 The last formulation was
based primarily on the mass spectrum of the complex, which
showed [Cu4(SC5H4N)4]ϩ as the highest mass ion, with the
correct 63/65Cu isotopic ratio for a Cu4 species. Further support
for a tetrameric structure has been deduced from the observa-
tion that the complex can be prepared from the crystallographi-
cally characterised species [Cu2(SC5H4NH)6]Cl2.19 The cation
of this complex is a dimer with a Cu2S2 core, which could serve
as a basis for formation of a Cu4S4 heterocubane. The cation of
the bromide analogue is isostructural,20 and that of the toluene-
p-sulfonate [Cu2(SC5H4NH)6][MeC6H4SO3]2, characterised by
X-ray crystallography during the course of the present study
(complex 3, see Fig. 3 and Table 2), is basically the same (see
below). Notwithstanding these observations, we now identify
[{Cu(SC5H4N)}n] as the hexamer [Cu6(SC5H4N)6], as confirmed
by its crystal structure. Although we were able to observe the
molecular ion in the mass spectrum of authentic [Cu6(SC5-
H4N)6], this peak had only 0.24% of the intensity of the largest
peak {that of [Cu2(SC5H4N)2]ϩ} and 0.44% of the intensity of
the [Cu4(SC5H4N)4]ϩ peak; the largest peak above m/z 700 was
that of [Cu5(SC5H4N)4]ϩ, with an intensity of 0.51% of that of
the [Cu2(SC5H4N)2]ϩ peak. It would appear that under the
fairly severe conditions required to observe the mass spectrum
Fig. 2 Crystal structure of [Cu6(SC5H4N)6] 2
solution conductivity12 of 1 (Table 3), these observations sug-
gest that the solid-state structure is retained in solution.
Reaction of bpt with other copper() starting materials such
as CuSO4 and Cu(BF4)2 in alcohol–water mixtures initially gave
green solutions, but no copper() complexes could be isolated.
In time the solutions precipitated an orange solid, insoluble in
all organic solvents tested. When the reaction was carried out in
dimethyl sulfoxide (dmso) solution crystals suitable for X-ray
crystallography were obtained and found to be a known com-
2410
J. Chem. Soc., Dalton Trans., 1997, Pages 2409–2418

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Table 2 Selected dimensions (bond lengths in Å, angles in Њ) in [Cu2-
(SC5H4NH)6][MeC6H4SO3]2 3 with e.s.d.s in parenthesesa
(a) About the copper atom
Cu ؒ ؒ ؒ CuЈ
Cu᎐S(1)
Cu᎐S(1Ј)
2.744(1)
2.406(1)
2.403(1)
Cu᎐S(2)
Cu᎐S(3)
2.307(1)
2.304(1)
S(1)᎐Cu᎐S(1Ј)
S(1)᎐Cu᎐S(2)
S(1)᎐Cu᎐S(3)
110.4b
118.3b
97.0b
S(1Ј)᎐Cu᎐S(2)
S(1Ј)᎐Cu᎐S(3)
S(2)᎐Cu᎐S(3)
107.8b
118.5b
105.0b
(b) In the ligands
S(1)᎐C(11)
1.717(3)
Cu᎐S(1)᎐CuЈ
69.6b
Cu᎐S(1)᎐C(11)
CuЈ᎐S(1)᎐C(11)
Cu᎐S(2)᎐C(21)
Cu᎐S(3)᎐C(31)
109.6(1)
113.9(1)
116.0(1)
109.1(1)
S(2)᎐C(21)
S(3)᎐C(31)
1.710(3)
1.698(4)
(c) In proposed hydrogen bonds
Fig. 4 View of the hydrogen-bonding scheme in complex 3. The
H ؒ ؒ ؒ O and H ؒ ؒ ؒ S hydrogen bonds are shown with the thinner lines.
The scheme continues in double-linked chains through the crystal
N(12) ؒ ؒ ؒ O(41Љ)
N(22) ؒ ؒ ؒ O(42)
N(32) ؒ ؒ ؒ S(1Ј)
2.765(3)
2.731(4)
3.689(3)
H(12) ؒ ؒ ؒ O(41Љ)
H(22) ؒ ؒ ؒ O(42)
H(32) ؒ ؒ ؒ S(1Ј)
1.80
1.83
2.79
quite different, 69.6Њ in 3 versus 74.3(1) or 74.6(1)Њ in the chlor-
ide, 73.8(1)Њ in the bromide. The principal differences, however,
are in the orientations of the pyridine rings, a consequence of
the different hydrogen-bonding schemes and packing of the
anions, halide versus toluene-p-sulfonate, with respect to the
cations. Two N᎐H ؒ ؒ ؒ X hydrogen bonds and an intramolecular
hydrogen bond are recorded for the halide structures; similarly,
all three crystallographically independent N᎐H groups in 3 are
involved in hydrogen bonds, two to oxygen atoms of neigh-
bouring anions (in quite different directions from the halide
structures) and the third a rather longer, intramolecular
N᎐H ؒ ؒ ؒ S contact, involving different groups from those in the
halides. The hydrogen bonding connects the ions in sheets in
the halides, but in 3 the linking is in chains (Fig. 4).
N(12)᎐H(12) ؒ ؒ ؒ O(41Љ) 165.8
N(22)᎐H(22) ؒ ؒ ؒ O(42) 151.8
N(32)᎐H(32) ؒ ؒ ؒ S(1Ј) 152.8
a
The primes indicate the symmetry relations: Ј 1 Ϫ x, 1 Ϫ y, Ϫz;
Љ 1 Ϫ x, Ϫy, Ϫz. b E.s.d. is less than 0.05Њ.
The in situ reduction of copper() with an excess of SC5-
H4NH is a useful method for the preparation of SC5H4NH
complexes of copper(), which can give different products from
those obtained by the direct reaction of the analogous copper()
salt. For example, reaction of CuCl2 and CuBr2 with SC5H4NH
was reported to give [CuCl(SC5H4NH)] and [CuBr2(SC5H4-
NH)2] respectively,17,19 whereas the analogous reactions with
CuCl and CuBr gave [CuCl(SC5H4NH)3] and [CuBr(SC5H4-
NH)2] respectively.17 In contrast to these results, we found that
reaction of CuBr2 and SC5H4NH gives [CuBr(SC5H4NH)] 4.
The low conductivity of complex 4 in dimethylformamide
(dmf) solution suggests that the bromine atoms are co-
ordinated; the complex is probably polymeric in the solid state,
with bridging through both sulfur and bromine atoms to give a
copper co-ordination number of four. The choice of anion is
critical to the stoichiometry of the product, thus reaction of
CuSO4 with 3 equivalents of SC5H4NH gives [Cu2(SC5H4-
NH)4]SO4 5, or alternatively [Cu(SC5H4NH)2]BPh4 6 if NaBPh4
is added to the reaction solution. These complexes are all
air-stable, diamagnetic solids; [Cu2(SC5H4NH)4]SO4 is readily
soluble in water, but the solution soon precipitates [Cu6-
(SC5H4N)6] with concomitant liberation of acid. Addition of
a trace of sulfuric acid to solutions of 5 significantly retards the
Fig. 3 Crystal structure of the cation of [Cu2(SC5H4N)6][MeC6-
H4SO3]2 3
of this complex (370 ЊC) it suffers extensive degradation;
indeed, the same mass spectrum is also observed for quite
unrelated complexes (see below).
It is noteworthy that although the crystal structure of
complex 3 shows it to be a centrosymmetric dimer with four
1
terminal and two bridging SC5H4NH ligands, its H and 13C
NMR spectra show only one type of SC5H4NH ligand, even in
weakly co-ordinating solvents such as dichloromethane. This
suggests that in solution, either [Cu2(SC5H4NH)6]2ϩ dissociates
to the known 21 [Cu(SC5H4NH)3]ϩ cation, or that the terminal
and bridging SC5H4NH ligands exchange rapidly. Either way,
the bridging thione bonds must be readily broken in solution.
In the crystal we note that there are significant variations in
the geometries of the cations of the halide salts (which are
essentially identical19,20) and of complex 3. In our complex the
four Cu᎐Sbridging bonds are equal at 2.405(1) Å (Table 2). The
Cu᎐Sterminal distances are also the same, at 2.305(1) Å. The
Cu ؒ ؒ ؒ CuЈ distance, at 2.744(1) Å, is considerably shorter
than in the chloride, 2.907(2)19 or 2.950(2)20 Å, and bromide,
2.907(2) Å,20 and correspondingly the Cu᎐S᎐CuЈ angles are
1
decomposition process; the H NMR spectrum of 5 was not
significantly affected by this measure. Similarly, the tetraphenyl-
borate complex 6 rapidly starts to decompose upon dissolution
in organic solvents such as dmso; [Cu6(SC5H4N)6] is precipi-
tated and the solution becomes acidic. Further evidence of
decomposition is observed in the 1H and 13C NMR spectra of 6,
which show the formation of a species which we identify as
HSC5H4NHϩBPh4Ϫ. This is itself unstable, reacting further to
give benzene and (presumably) a SC5H4NHؒBPh3 adduct.
Although the initial decomposition of 6 is rapid, as the acidity
J. Chem. Soc., Dalton Trans., 1997, Pages 2409–2418
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Table 3 Colours, melting points, conductivities and analyticala data for the complexes
Analysis (%)
Complex
[{Cu(µ-O2CMe)2(bpt)}2]
Colour
Green
M.p./ЊC
162d,e
ΛM b/S cm2 molϪ1
C
H
N
X c
—
1
2
3
4
5
6
7
8
9
8
48.4
4.4
6.9
(48.3)
(4.6)
(7.0)
f
[Cu6(SC5H4N)6]
Orange
Orange
Orange
Yellow
Yellow
Yellow
Yellow
Yellow
Orange
Yellow
305d
152
—
34.6
(34.6)
2.3
(2.3)
7.8
(8.1)
—
[Cu2(SC5H4NH)6][MeC6H4SO3]2
[CuBr(SC5H4NH)]
100
25
46.2
(46.5)
3.8
(3.9)
7.1
(7.4)
10.6g
(11.2)
184d,e
159e
74d
23.6
(23.6)
1.9
(2.0)
5.4
(5.5)
—
[Cu2(SC5H4NH)4]SO4ؒ2H2O
[Cu(SC5H4NH)2]BPh4ؒH2O
[Cu2(SO4)(SC5H4NH)2]
[Cu(NO3)(SC5H4NH)2]
[Cu(SC5H4NH)2]PF6
71
34.4
(34.1)
3.0
(3.4)
7.8
(8.0)
17.5g
(18.1)
45h
37
65.9
(65.5)
5.0
(5.2)
4.5
(4.5)
11.1
(10.3)
142d
146d
175d
126k
118
27.4
(27.0)
2.3
(2.3)
6.4
(6.3)
21.5
(21.6)
41
34.5
(34.5)
2.8
(2.9)
12.1
(12.1)
17.8
(18.4)
64
28.4
(27.9)
2.1
(2.3)
6.4
(6.5)
31i, j
(34)
10 [Cu(NO3)(SC5H4NH)(py)]
49l
49
38.8
(38.0)
3.2
(3.2)
13.1
(13.3)
10.2
(10.2)
11 [Cu(NO3)(SC5H4NH)2(PPh3)]
54.9
4.1
6.4
10.5
(55.1)
(4.1)
(6.9)
(10.5)
12 [Cu(SC5H4NH)2(PPh3)2]NO3
13 [Cu2(bpt)3][PF6]2ؒC3H6O
Yellow
Yellow
127
140
69
—
—
—
—
141
41.6
3.7
7.4
25.9i
(41.7)
(3.8)
(7.5)
(25.8)
14 [Cu2(SC5H4N)(bpt)]PF6ؒ0.25C3H6O
15 [Cu(py)4]PF6
Orange
146
73
71
35.1
(34.8)
2.7
(2.9)
6.7
(6.9)
24.0i
(23.6)
Pale green
169d
46.0
3.7
10.6
27.9i
(45.8)
(3.8)
(10.7)
(27.6)
a
Calculated values in parentheses. b In dmf; accepted ranges12 for 1:1 and 1:2 electrolytes are 65–90 and 130–170 S cm2 molϪ1 respectively. c X = S
unless stated otherwise. d Decomposes. e Shows signs of decomposition below this temperature. f Insufficient solubility for measurement. g Copper
analysis. h ΛM for NaBPh4 measured under the same conditions = 47 S cm2 molϪ1
.
i PF6 analysis. j The poor solubility of this complex limited the
precision of the determination. Melts with decomposition. l Sample dissolved by heating to 100 ЊC then allowing to cool to room temperature
k
before measurement.
of the solution increases the rate decreases, allowing obser-
vation of its 13C-{1H} NMR spectrum.
ture. However, if a sample of the complex, whether freshly pre-
pared or not, is transferred to a stoppered tube, it turns green
overnight. The decomposition may not be as advanced as it
appears, since the microanalysis and IR spectrum of the green
material were only marginally different from those of the unde-
composed compound. Upon removing the stopper the charac-
teristic odour of NO2 was noted. This suggests that the reaction
may be autocatalytic; if the compound is left in air any NOx
formed is free to escape, whereas in a stoppered tube it would be
more likely to attack the complex.
During the course of these studies we noted that although
[Cu6(SC5H4N)6] is often readily precipitated, some of the
copper()–SC5H4NH products evidently stay in solution in these
reactions. Speculating that this may be associated with the
formation of the acid by-product, we investigated these reac-
tions in the presence of the conjugate acid. Reaction of CuSO4
with SC5H4NH in the presence of H2SO4 gave a new complex
formulated as [Cu2(SO4)(SC5H4NH)2] 7. This compound has a
different stoichiometry from that of 5, [Cu2(SC5H4NH)4]SO4;
moreover whilst complex 5 is a 1:1 electrolyte in dmf, 7 is non-
conducting. Only a relatively small excess of acid is required for
the isolation of complex 7; use of more than 2 equivalents leads
to the formation of an orange tar rather than a yellow powder.
Reaction of Cu(NO3)2 with SC5H4NH in the presence of HNO3
gave the new complex [Cu(NO3)(SC5H4NH)2] 8. This material
exhibits an unusual stability pattern. The freshly prepared
complex is bright yellow and indefinitely stable if stored in a
sealed ampoule. It also shows no deterioration if left in air for
several weeks, and is unaffected by light and atmospheric mois-
Complexes 7 and 8 were investigated as starting materials for
further synthesis. The sulfato complex 7 reacts with HX (X = Br
or Cl) to give [CuBr(SC5H4NH)] and the known complex19
[CuCl(SC5H4NH)] respectively; however reaction with HPF6
gives
a product with different stoichiometry, [Cu(SC5-
H4NH)2]PF6 9. This species is presumably formed via a dispro-
portionation reaction. Although solutions of complex 7 in
water are stable for up to 1 h, treatment with salts such as
NaBF4 or Na(SC6H2Pri3-2,4,6) led to the immediate precipi-
tation of [Cu6(SC5H4N)6]. The nitrato-complex 8 reacts with an
excess of pyridine to give [Cu(NO3)(SC5H4NH)(py)] 10 and
2412
J. Chem. Soc., Dalton Trans., 1997, Pages 2409–2418

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Table 4 Proton NMR data a
Compound
SC5H4NH b
δ(J/Hz)
12.10 (s, 1 H, H1), 7.52 (‘d’, 1 H, H6), 7.37 (m, 2 H, H3,4), 6.72 (‘t’, 1 H, H5)
HSC5H4NHϩ b,c 8.44 (m, 1 H, H6), 8.25 (‘t’, 1 H, H4), 7.87 (‘d’, 1 H, H3), 7.66 (‘t’, 1 H, H5)
bpt d
8.54 (‘d’, 1 H, H6), 8.43 (‘d’, 1 H, H6), 7.59 (‘t’, 1 H, H4), 7.47 (‘t’, 1 H, H4), 7.20 (‘d’, 1 H, H3), 7.18 (‘d’, 1 H, H3), 7.13 (‘t’, 1 H, H5),
6.97 (‘t’, 1 H, H5), 3.58 (t, JH H = 7.4, CH2C5H4N), 3.18 (t, JH H = 7.4, CH2S)
8.47 (br, 1 H, H6), 7.58 (‘t’, 1 H, H4), 7.25 (‘d’, 1 H, H3), 7.07 (‘t’, 1 H, H5), 3.86 (br, 2 H, CH2)
14.22 (br s, 3 H, H1), 7.97 (‘d’, 3 H, H6), 7.64 (m, 6 H, H3,4), 7.47 (d, 2 H, O3SC6H4Me), 7.10 (d, 2 H, O3SC6H4Me), 7.07 (‘t’, 3 H,
H5), 2.27 (s, 3 H, O3SC6H4Me)
1e
3 f
4g
5i
14.46h (br s, 1 H, H1), 8.27 (‘d’, 1 H, H6), 7.86 (m, 2 H, H3,4), 7.26 (‘t’, 1 H, H5)
14.42h (br s, 1 H, H1), 8.08 (‘d’, 1 H, H6), 7.70 (m, 2 H, H3,4), 7.15 (‘t’, 1 H, H5)
14.23h (br s, 1 H, H1), 7.99 (‘d’, 2 H, H6), 7.61 (m, 4 H, H3,4), 7.17 (m, 8 H, BPh4), 7.04 (‘t’, 2 H, H5), 6.91 (t, 8 H, BPh4), 6.78 (t, 4 H,
BPh4)
6 f,j
7i
8 f
14.70 (br s, 1 H, H1), 8.14 (br, 1 H, H6), 7.71 (br, 1 H, H4), 7.54 (br, 1 H, H3), 7.17 (br, 1 H, H5)
14.27 (br s, 1 H, H1), 8.01 (br, 1 H, H6), 7.64 (br m, 1 H, H4), 7.58 (br m, 1 H, H3), 7.06 (‘t’, 1 H, H5)
8.28 (br, 1 H, H6), 7.77 (br, 2 H, H3,4), 7.33 (br, 1 H, H5)
9e,k
11b
12 f
13b,l
13.00 (br s, 2 H, H1), 7.76 (‘d’, 2 H, H6), 7.31–7.46 (m, 19 H, H3,4, PPh3), 6.87 (m, 2 H, H5)
14.00 (br s, 2 H, H1), 7.82 (‘d’, 2 H, H6), 7.46–7.24 (m, 34 H, H3,4, PPh3), 6.89 (‘t’, 2 H, H5)
8.48 (m, 1 H, H6), 8.41 (m, 1 H, H6), 7.70 (m, 1 H, H4), 7.58 (m, 1 H, H4), 7.25 (m, 3 H, H3,5), 7.08 (m, 1 H, H5), 3.52 (t, JH H = 7.1,
2 H, CH2C5H4N), 3.15 (t, JH H = 7.1, 2 H, CH2S)
14 f,l
8.73–8.01 (br m, 3 H, H6), 7.85 (‘t’, 1 H, H4), 7.66 (‘t’, 1 H, H4), 7.52–6.75 (br m, 7 H, H4,3,5), 3.49 (br, 2 H, CH2C5H4N), 3.17 (br,
2 H, CH2S)
15b
8.53 (br, 2 H, H2), 7.82 (m, 1 H, H4), 7.42 (br, 2 H, H3)
a
br = Broad, s = singlet, d = doublet, t = triplet, m = multiplet; multiplicities in inverted commas are pseudo-multiplicities, generally showing second-
order couplings also, but valuable for peak assignments. b In CD3CN. c Acidified with MeSO3H. d In CD2Cl2. e In (CD3)2CO; spectrum of complex 1
shows other very broad features above δ 8. f In (CD3)2SO. g In (CD3)2NCDO. h Shown to exchange with D2O. i In (CD3)2SO plus a little concentrated
H2SO4. j Spectrum also contains a minor component at δ 8.47, 7.80 and 7.27, possibly HSC5H4NHϩBPh4Ϫ (see text). H1 will be exchanged in this
k
solvent. l Spectrum also shows solvent of crystallisation.
Table 5 13C-{1H} NMR data a
Compound
δ(J/Hz)
SC5H4NH
HSC5H4NHϩ
bpt
179.2 (C2), 138.6 (C6), 138.0 (C4), 134.1 (C3), 113.8 (C5)
154.5 (C2), 146.9 (C6), 142.8 (C4), 129.0 (C3), 123.8 (C5)
159.9 (C2), 158.8 (C2), 149.3 (C6), 149.2 (C6), 136.0 (C4), 135.8 (C4), 123.0 (C3), 121.9 (C3), 121.3 (C5), 119.2 (C5), 37.8
(CH2C5H4N), 29.1 (CH2S)
1
3
159.8 (C2), 150.3 (C6), 137.0 (C4), 122.8 (C3), 120.3 (C5)
171.0 (C2), 145.6 (C6), 140.2 (O3SC6H4Me), 139.3 (O3SC6H4Me), 137.7 (C4), 131.7 (C3), 128.1 (O3SC6H4Me), 125.5 (O3SC6H4Me),
116.4 (C5), 20.8 (O3SC6H4Me)
4b
5
6
7
8
146.4 (C6), 144.9 (C4), 137.5 (C3), 123.1 (C5)
167.9 (C2), 141.1 (C6), 139.9 (C4), 131.4 (C3), 117.9 (C5)
171.4 (C2), 163.4 (q, JCB = 49, BPh4), 140.1 (C6), 139.2 (C4), 135.6 (BPh4), 131.8 (C3), 125.3 (br, BPh4), 121.5 (BPh4), 116.2 (C5)
162.0 (C2), 139.7 (C6), 138.5 (C4), 128.9 (C3), 117.2 (C5)
171.0 (C2), 140.2 (C6), 139.3 (C4), 131.7 (C3), 116.4 (C5)
9
11
164.8 (C2), 143.8 (C6), 141.8 (C4), 132.4 (C3), 121.1 (C5)
171.5 (C2), 139.8 (C6), 139.1 (C4), 133.3 (d, JCP = 16, PPh3), 132.7 (d, JCP = 28, PPh3), 131.9 (C3), 130.2 (PPh3), 128.9 (d, JCP = 9,
PPh3), 116.1 (C5)
12
173.0 (C2), 139.1 (C6), 138.8 (C4), 133.3 (d, JCP = 16, PPh3), 133.0 (d, JCP = 22, PPh3), 131.2 (C3), 130.1 (PPh3), 128.8 (d, JCP = 9,
PPh3), 115.3 (C5)
13c
160.9 (C2), 158.9 (C2), 150.5 (C6), 150.2 (C6), 137.9 (C4), 137.5 (C4), 124.7 (C3), 123.3 (C3), 122.9 (C5), 120.9 (C5), 38.1
(CH2C5H4N), 30.2 (CH2S)
14c,d
15
36.9 (CH2C5H4N), 30.3 (CH2S)
150.5 (C2), 137.8 (C4), 125.7 (C3)
a
All resonances are singlets unless stated otherwise; solvents as in Table 4. b C2 is probably obscured by the solvent. c Spectrum also shows solvent of
crystallisation. d Spectrum also shows a set of aromatic signals at δ 160–120, but the sample was not sufficiently stable to allow for detailed analysis.
with PPh3 to give [Cu(NO3)(SC5H4NH)2(PPh3)] 11. Both of
these complexes have only limited stability in solution; on
standing, a solution of [Cu(NO3)(SC5H4NH)(py)] in pyridine
precipitated a mixture of [Cu6(SC5H4N)6] and pyridinium
nitrate, whilst attempted crystallisation of [Cu(NO3)(SC5-
H4NH)2(PPh3)] from ethanol gave, as the isolated product in
low yield, the known complex [Cu(SC5H4NH)2(PPh3)2]NO3 12,
originally prepared by the reaction of Cu(PPh3)2NO3 with
SC5H4NH.22 The crystal structure of complex 12 is shown in
Fig. 5, and selected dimensions are given in Table 6. The struc-
ture of the analogous perchlorate complex, [Cu(SC5H4NH)2-
(PPh3)2]ClO4ؒ2CHCl3,23 shows very similar tetrahedral co-
ordination and dimensions about the copper atom. Whereas the
{Cu(PPh3)2(S)2} fragments of the cations of the two complexes
can be reasonably well superimposed, the orientations of the
SC5H4NH ligands are quite different and, as in complex 3 and
its analogues, these appear to be determined by hydrogen-
bonding contacts. In complex 12 dimeric units are formed by
the linking of pairs of cations through pairs of anions by
hydrogen bonding about a centre of symmetry (Table 6). The
links to both cations are made through one oxygen atom,
O(51), of the nitrate ion; the other two O atoms are not
involved. In the perchlorate one of the SC5H4NH ligands is
hydrogen bonded to an anion; the other is intramolecularly
bonded to the sulfur atom of the first SC5H4NH ligand. The
intermolecular hydrogen bonding scheme is thus limited to
single cation–anion units.
The higher conductivity of the ionic nitrate complex 12 com-
pared to the other nitrato complexes 8, 10 and 11 (Table 3)
suggests that the nitrate is probably co-ordinated in these
last three. Reaction of SC5H4NH with copper() nitrite in
nitrous acid gave only [Cu6(SC5H4N)6], as did the equivalent
reaction with copper() methanesulfonate in methanesulfonic
acid.
J. Chem. Soc., Dalton Trans., 1997, Pages 2409–2418
2413

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thiolate-bridged clusters [Cu4(SR)6]2Ϫ (R = alkyl or aryl).24
Molecular models derived from the crystallographically estab-
lished {Cu4(SPh)6} moiety suggest that a [Cu4(bpt)6]4ϩ cluster
is feasible in steric terms. Well characterised examples of
thioether-bridged copper() species, although rare, are not
unknown; the clusters [Cu4Br4(ddtp)2] [ddtp = 1,5-bis(3Ј,5Ј-
Table 6 Selected dimensions (bond lengths in Å, angles in Њ) in
[Cu(SC5H4NH)2(PPh3)2]NO3 12 with e.s.d.s in parentheses*
(a) About the copper atom
Cu᎐S(1)
Cu᎐S(2)
2.397(2) Cu᎐P(3)
2.358(2) Cu᎐P(4)
2.308(2)
2.294(2)
dimethylpyrazolyl)-3-thiapentane]25 and [{CuI CuIICl5(tht)3}n]
3
(tht = tetrahydrothiophene)26 are examples.
S(1)᎐Cu᎐S(2)
S(1)᎐Cu᎐P(3)
S(2)᎐Cu᎐P(3)
100.3(1) S(1)᎐Cu᎐P(4)
101.3(1) S(2)᎐Cu᎐P(4)
104.1(1) P(3)᎐Cu᎐P(4)
106.7(1)
120.6(1)
120.4(1)
The reaction of bpt with [Cu(NCMe)4]PF6 in tetrahydro-
furan (thf) resulted in the precipitation of an orange product
formulated empirically as [Cu2(SC5H4N)(bpt)]PF6 14, in which
half of the bpt reagent has evidently undergone metal-
promoted cleavage to give a pyridine-2-thionate ligand (see
above). This was confirmed by the identification of 2-
vinylpyridinium hexafluorophosphate in the supernatant by 1H,
13C-{1H} and 31P NMR spectroscopy, hence the overall reaction
(b) In the SC5H4NH ligands
S(1)᎐C(11)
S(2)᎐C(21)
1.703(6) Cu᎐S(1)᎐C(11)
1.708(7) Cu᎐S(2)᎐C(21)
108.0(2)
110.2(2)
(c) In the phosphine ligands
1
can be written as in equation (2). The H NMR spectrum of
P(3)᎐C(31a)
P(3)᎐C(31b)
P(3)᎐C(31c)
1.831(6) P(4)᎐C(41a)
1.840(6) P(4)᎐C(41b)
1.829(6) P(4)᎐C(41c)
1.832(6)
1.823(6)
1.827(6)
2[Cu(NCMe)4]PF6 ϩ 2bpt
[Cu2(SC5H4N)(bpt)]PF6 ϩ vpy ϩ HPF6 (2)
Cu᎐P(3)᎐C(31a)
Cu᎐P(3)᎐C(31b)
C(31a)᎐P(3)᎐C(31b)
Cu᎐P(3)᎐C(31c)
C(31a)᎐P(3)᎐C(31c)
C(31b)᎐P(3)᎐C(31c)
112.6(2) Cu᎐P(4)᎐C(41a)
115.3(2) Cu᎐P(4)᎐C(41b)
102.8(3) C(41a)᎐P(4)᎐C(41b)
115.9(2) Cu᎐P(4)᎐C(41c)
104.9(3) C(41a)᎐P(4)᎐C(41c)
103.8(3) C(41b)᎐P(4)᎐C(41c)
112.4(2)
112.6(2)
103.7(3)
122.1(2)
101.2(3)
102.7(3)
complex 14 confirms the presence of the SC5H4N ligand in that
the ratio of aromatic to aliphatic protons is 3:1 rather than the
2:1 expected for bpt alone. As with complex 13, the mass spec-
trum of 14 showed [Cu4(SC5H4N)4]ϩ as the highest mass ion. In
the absence of X-ray structural information no firm conclu-
sions can be drawn about the structure of this complex,
although one possibility is a modification of the [Cu6(S-
C5H4N)6] cluster 2 in which three of the SC5H4N ligands are
replaced by bpt ligands.
(d) Proposed hydrogen-bonding contacts
N(12) ؒ ؒ ؒ O(51)
H(12) ؒ ؒ ؒ O(51)
2.872(8) N(22) ؒ ؒ ؒ O(51Ј)
2.26(7) H(22) ؒ ؒ ؒ O(51Ј)
2.800(8)
2.05(6)
N(12)᎐H(12) ؒ ؒ ؒ O(51)
132(6)
N(22)᎐H(22) ؒ ؒ ؒ O(51Ј) 167(6)
H(12) ؒ ؒ ؒ O(51) ؒ ؒ ؒ H(22Ј) 136(2)
1H NMR, 13C NMR and IR Spectra
* The prime indicates the symmetry relation: 1 Ϫ x, 1 Ϫ y, 1 Ϫ z.
As an aid to interpretation of the spectra of the SC5H4NH
complexes, we also prepared and characterised the simple tet-
rakis(pyridine)copper() species [Cu(py)4]PF6 15. Although the
potentially hazardous perchlorate analogue, [Cu(py)4]ClO4, is
known and has been characterised by X-ray crystallography,27
equilibrium and enthalpy measurements28 and 63Cu NMR
1
spectroscopy,29 to the best of our knowledge the H and 13C
NMR and IR properties of the [Cu(py)4]ϩ cation have not pre-
viously been described. In complex 15, where the ligands are
necessarily co-ordinated through nitrogen, the pyridine H3/5
and H4 protons exhibit chemical shifts intermediate between
those of free pyridine, which are relatively shielded, and those
of the pyridinium salt C5H5NHϩClϪ, which are relatively
deshielded.30 In contrast, the chemical shift of the pyridine H2/6
protons in 15 is not intermediate between those for free py and
C5H5NHϩClϪ, but rather is very close to the value for free py;
this additional shielding is presumably a consequence of the
proximity of these protons to the metal. Turning to the com-
plexes of SC5H4NH, 3–9, 11 and 12, in each case the chemical
shifts of all four aryl protons are intermediate between those of
free SC5H4NH and HSC5H4NHϩO3SMeϪ (Table 4); the obser-
vation that, unlike the H2/6 protons of compound 15, the H6
protons do not show an additional shielding, is consistent with
co-ordination of SC5H4NH through sulfur rather than through
nitrogen in these complexes. The 13C NMR spectra of the py
and SC5H4NH complexes (Table 4) show very similar effects.
The infrared spectra of the complexes of both bpt and
SC5H4NH give little by way of diagnostic information, beyond
confirmation of the presence of pyridine groups and the
various anions. No ν(SH) band was observed, consistent
with the co-ordination of SC5H4NH through S in the thione
tautomer rather than through N in the pyridinethiol tautomer
(see below). Clearly, given the possibility of protonation of the
Fig. 5 Crystal structure of the cation of [Cu(SC5H4NH)2(PPh3)2]NO3
12
Reactions of bpt with copper(I)
The products obtained from the reaction of bpt with [Cu(NC-
Me)4]PF6 depend on the reaction solvent. When equimolar
amounts of bpt and the copper salt were allowed to react
in acetonitrile no identifiable products were obtained; how-
ever, the use of an excess of bpt afforded a pale yellow
material formulated empirically as [Cu2(bpt)3][PF6]2 13.
1
The H and 13C-{1H} NMR spectra showed only one set of
bpt resonances, suggesting a symmetrical structure in solu-
tion, whilst the mass spectrum again showed only [Cu4-
(SC5H4N)4]ϩ as the highest molecular weight ion, presumably
due to the necessarily high inlet temperature of 370 ЊC. The
stoichiometry of complex 13 recalls the well known class of
pyridine N, even if ν(C᎐N) of the pyridine ring could be
᎐
unambiguously assigned, a shift in frequency between the
complexes and free SC5H4NH could not be taken as evidence
for co-ordination of this atom.
2414
J. Chem. Soc., Dalton Trans., 1997, Pages 2409–2418

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For all the complexes of SC5H4NH in Table 7, in which the
pyridine nitrogen is not co-ordinated but is protonated, very
broad lines were observed, with linewidth at half maximum
values in the range of 750–1050 Hz. The chemical shifts of the
SC5H4NH ligands lie in the range of δ Ϫ177 to Ϫ192, consist-
ent with retention of the thione tautomer upon co-ordination.
In the case of the nitrato-complexes 8 and 11 the large differ-
ence in linewidths between the nitrato- and SC5H4NH peaks
was reflected in disparate peak heights; for some of the other
complexes, such as the sulfato salt 5, the SC5H4NH peak was
probably too broad to observe at all. For complex 15, in which
the pyridine ligands are of necessity N-bonded to the metal, no
signals were observed in the 14N NMR spectrum, even when
recorded at 100 ЊC. The linewidth probably exceeds 2500 Hz in
this case. We were likewise unable to observe any 14N signals for
the bpt complexes 13 and 14.
Table 7 Nitrogen-14 NMR data for selected compounds and related
speciesa
Compound
δb
SC5H4NH
Ϫ182 (170)c
HSC5H4NHϩO3SMeϪ
Ϫ184 (140)d
NaϩSC5H4NϪ
Ϫ94 (2400)d
3
Ϫ177 (770)
6
Ϫ180 (1050)
8
11
Ϫ10 (55), Ϫ182 (830)
Ϫ4 (40), Ϫ192 (800)
a
Referenced to external MeNO2. Data obtained on Me2SO–(CD3)2SO
solutions unless stated otherwise. b Linewidth at half maximum (Hz) in
parentheses. c In CCl4. d In EtOH–CD3OD.
Conclusion
The chemistry of copper with SC5H4NH and related hetero-
cyclic thiones is known for its very high degree of product
variability depending on kinetic factors such as solvent, pH,
anion, stoichiometry, etc.15 This versatility is associated with
the ready formation of a variety of Cu᎐S᎐Cu bridging
modes, together with the plasticity of copper co-ordination
geometries and the high substitution lability of both bridging
and terminal SC5H4NH ligands. These considerations appear
to apply equally to the thioether ligand bpt, with the added
complication of the possibility of cleavage by both copper-()
and -(); for complex 14 this leads to a product in which half of
the bpt is cleaved but the other half remains intact. The source
of this remarkable specificity is probably the low solubility of
the product in the reaction solvent, thf.
Scheme 2
14N NMR Spectra of pyridine-2(1H) -thione and its complexes
The tosylate salt 3 provides a basis for consideration of the
structures of the other SC5H4NH complexes in this study. Thus
removal of two terminal SC5H4NH ligands from the [Cu2-
(µ-SC5H4NH)2(SC5H4NH)4]2ϩ core of 3 would allow all the
SC5H4NH ligands to become bridging, giving a cationic poly-
mer as shown in Scheme 3, A; this is probably the structure of
the complexes of stoichiometry [Cu(SC5H4NH)2]ϩ in which the
SO42Ϫ, BPh4Ϫ and PF6Ϫ anions are non-co-ordinating, 5, 6 and 9
respectively. If the anion is also able to act as a bridging ligand,
as in the bromide complex 4 and the sulfato-complex 7, the
Cu :SC5H4NH stoichiometry can be reduced further to 1:1
whilst retaining an approximately tetrahedral geometry at
copper, as shown for complex 4 in Scheme 3. Complexes 8 and
10, in which the nitrate groups appear to be co-ordinated, might
involve a single bridging SC5H4NH ligand, as in Scheme 3, B,
whilst the introduction of triphenylphosphine co-ligands evi-
dently gives monomeric complexes 11 and 12, perhaps due to
steric factors.
It has long been recognised that SC5H4NH exists in tautomeric
equilibrium with pyridine-2-thiol (HSC5H4N).31,32 The sub-
stantially higher dipole moment of the thione compared to the
thiol tautomer 33 is readily explained in terms of a resonance
hybrid for SC5H4NH involving a contribution from the zwit-
terionic form;34 these are illustrated in Scheme 2, along with
the thionium cation and thionate anion formed by protonation
and deprotonation respectively of SC5H4NH. It should be
noted that, with all these species, valence-bond representations
are only approximate descriptions. The SC5H4NH
HSC5H4N equilibrium has been probed by a variety of tech-
niques, including 14N and 15N NMR spectroscopies.35,36 Com-
parison of the 14N chemical shifts of SC5H4NH in acetone and
methanol solutions (δ ca. Ϫ187) with those of its N- and S-
methylated derivatives 1-methylpyridine-2-thione (δ ca. Ϫ189)
and 1-(2-pyridyl)-1-thiaethane [2-(methylsulfanyl)pyridine]
(NC5H4SMe, δ Ϫ79 and Ϫ88 in acetone and methanol
respectively) allowed Stefaniak 35 to deduce that SC5H4NH is
95 ± 5% in the SC5H4NH form in these solvents. We have
obtained data for the species shown in Scheme 2 and also for
selected complexes (Table 7). It is important to note here that
dissolved dinitrogen gives an 14N peak at δ Ϫ71 ppm, exactly
in the region where substituted pyridines are expected to
appear. For compounds which have moderate solubilities or
large linewidths, the dinitrogen peak can have comparable
intensity, hence samples were prepared under argon or sealed
under vacuum.
Finally, the stabilities of many of the complexes of
SC5H4NH in solution depend critically on pH. In acid con-
ditions the nitrogen atoms of the S-co-ordinated SC5H4NH
ligands are protonated, preventing involvement of the nitrogen
atom in co-ordination. Once the proton is removed to give
the anion, Cu᎐N bonds can readily be formed due to the
facile displacement of other SC5H4NH ligands and the highly
insoluble S,N-co-ordinated hexamer [Cu6(SC5H4N)6]
2 is
readily precipitated from solution; as a result, this complex acts
as a thermodynamic sink into which the other complexes tend
to fall.
The 14N chemical shift of the thionium cation is virtually
unchanged compared to that of SC5H4NH, and close to that
of the pyridinium cation (δ Ϫ172 in dmso). In contrast, the
thionate anion exhibits substantial deshielding compared to
SC5H4NH, with a chemical shift similar to those of substituted
pyridines such as NC5H4SMe (see above). The severe line
broadening of this signal may be associated with the high non-
bonding electron density at N as well as the presence of the
sodium cation.37
Experimental
The compounds bpt 7 and [Cu(NCMe)4]PF6 38 were prepared by
the literature procedures. All other chemicals were obtained
from commercial sources. Pyridine was distilled from NaOH
under a nitrogen atmosphere before use. Reactions were carried
out in air unless noted otherwise.
J. Chem. Soc., Dalton Trans., 1997, Pages 2409–2418
2415

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[{Cu(SC5H4NH)2}2(ì-SC5H4NH)2][MeC6H4SO3]2 3. Cop-
per() oxide (0.17 g, 2.1 mmol) was dissolved in a solution of
toluene-p-sulfonic acid hydrate (0.40 g, 2.1 mmol) in water
(10 cm3). The solution was filtered, and added to a solution of
SC5H4NH (1.05 g, 9.4 mmol) in EtOH (20 cm3). The resulting
solution was stirred for 30 min, then the solvent was removed
in vacuo, giving a red tar. This was stirred thoroughly with
acetone, then allowed to settle and the solvent was decanted off;
the procedure was repeated, giving an orange solid. This was
filtered off and washed with acetone followed by Et2O.
Recrystallisation from EtOH gave analytically pure [Cu2-
(SC5H4NH)6][MeC6H4SO3]2 3 (0.82 g, 69%). IR: 1565m,
1210m, 1167m, 1129m, 1030m, 1009m, 990m, 752m, 683m,
569m and 486m cmϪ1
.
[CuBr(SC5H4NH)] 4. A solution of SC5H4NH (1.00 g, 9.0
mmol) in MeOH (20 cm3) was added to a solution of CuBr2
(1.00 g, 4.5 mmol) in water (35 cm3), giving immediate precipi-
tation. The mixture was stirred for 3 h, then filtered. The solid
was washed with water, then MeOH and finally Et2O, and dried
in vacuo as [CuBr(SC5H4NH)] 4 (1.06 g, 93%). The product is
soluble only in strongly co-ordinating solvents such as dmso
and dmf. IR: 1603m, 1586s, 1510m, 1266m, 1159w, 1130s,
1034w, 1001w, 741s, 621w and 477m cmϪ1
.
Complex 4 was also prepared by the addition of concen-
trated hydrobromic acid (1.0 cm3) to a freshly prepared solution
of 7 (0.1 g, 0.24 mmol) in water (20 cm3). The resulting mixture
was stirred for 30 min, and the precipitate was isolated as above
(0.081 g, 71%).
[Cu2(SC5H4NH)4]SO4ؒ2H2O 5. A solution of SC5H4NH
(2.80 g, 25.2 mmol) in MeOH (50 cm3) was added portionwise
over 5 min to a solution of CuSO4ؒ5H2O (2.0 g, 8.0 mmol) in
water (30 cm3). The orange solution was stirred for 5 h, giving a
thick yellow suspension. This was filtered, and the solid was
dried to constant weight in vacuo as [Cu2(SC5H4NH)4]-
SO4ؒ2H2O 5 (2.22 g, 79%). IR: 1602m, 1578s, 1255m, 1166m,
1136s (br), 1081m, 1031m, 991w, 879m, 750s, 595w and 483w
Scheme 3 B, X = SC5H4NH or py
Infrared spectra were recorded on Nujol mulls using KBr
plates in the range 4600–400 cmϪ1 and a Shimadzu FTIR-
1
8101M spectrophotometer, H, 13C, 14N and 31P NMR spectra
at 270.17, 67.94, 19.52 and 109.38 MHz respectively on a JEOL
GSX270 spectrometer. The 1H and 13C chemical shifts are
quoted relative to external SiMe4, 14N shifts relative to external
MeNO2. Magnetic susceptibilities were obtained in solution by
1H NMR spectroscopy using the Evans method.39 Fast atom
bombardment (FAB) mass spectra were kindly provided by Dr.
Ali Abdulsadda of the School of Chemistry and Molecular
Science, University of Sussex. Conductivities and melting
points were obtained using a Portland Electronic conductivity
meter and an Electrothermal melting-point apparatus respect-
ively.
Microanalyses (C, H, N and S) were determined by Mr. C. J.
Macdonald (Nitrogen Fixation Laboratory) or Mr. A. Saunders
(University of East Anglia). Copper analyses were obtained
from Southern Science Ltd. on samples dissolved in concen-
trated HNO3. Quantitative 31P NMR measurements were car-
ried out on samples dissolved in dmso containing a constant
amount of PBu4Br as reference and calibrated using a set of
NBu4PF6 standards prepared using the same solvent.
cmϪ1
.
[Cu(SC5H4NH)2]BPh4ؒH2O 6. A solution of SC5H4NH (2.80
g, 25.2 mmol) in MeOH (30 cm3) was added to a solution of
CuSO4ؒ5H2O (2.0 g, 8.0 mmol) in water (30 cm3), giving a clear,
deep orange solution. This was stirred for 5 min, then filtered,
and a solution of NaBPh4 (2.74 g, 8.0 mmol) in water (50 cm3)
was added. The resulting suspension was stirred for 10 min,
then filtered. The solid was washed with water, dried by vacuum
aspiration, then stirred with Et2O (100 cm3). The mixture was
filtered and the Et2O extraction repeated twice. The solid was
then dried to constant weight in vacuo as [Cu(SC5H4NH)2]-
BPh4ؒH2O 6 (4.99 g, 100%). IR: 1603m, 1575s, 1504m, 1262m,
1131s, 1031w, 997w, 849w, 733s, 705s, 604m and 482w cmϪ1
.
[Cu2(SO4)(SC5H4NH)2] 7. The salt CuSO4ؒ5H2O (1.12 g, 4.49
mmol) was dissolved in 2.24 mol dmϪ3 H2SO4 (1.0 cm3, 2.24
mmol) plus the minimum amount of water. A solution of
SC5H4NH (1.0 g, 8.99 mmol) in MeOH (35 cm3) was added in
one portion, giving an orange solution. This was stirred for 5 h,
to no visible effect, then filtered, and added to acetone (200
cm3); the resulting precipitate was immediately filtered off,
washed with acetone and dried in vacuo as [Cu2(SO4)-
(SC5H4NH)2] 7 (0.94 g, 94%). IR: 1593s, 1516w, 1264w, 1129s
Preparations
[{Cu(ì-O2CMe)2(bpt)}2] 1. The compound bpt (1.25 g, 5.8
mmol) was added to a solution of Cu(O2CMe)2ؒH2O (1.10 g,
5.5 mmol) in MeOH (75 cm3) and the solution was boiled under
reflux for 2 h. The hot solution was filtered and concentrated in
vacuo to ca. 10 cm3. Addition of an excess of Et2O gave a pre-
cipitate; this was filtered off, washed with Et2O and dried in
vacuo. The crude product was dissolved in hot acetone; the
resulting solution was filtered and left to evaporate, giving
crystals of [{Cu(µ-O2CMe)2(bpt)}2] (1.2 g, 55%). IR: 1618s,
1573s, 1557m, 1283m, 1128m, 771m, 756w, 681m, 627w, 593w,
(br), 1036m, 858m, 760m, 577m, 486w and 438w cmϪ1
.
[Cu(NO3)(SC5H4NH)2] 8. A solution of Cu(NO3)2ؒ2.5H2O
(3.31 g, 14.2 mmol) in water (5 cm3) plus concentrated HNO3
(0.5 cm3, 7.7 mmol) was added to a solution of SC5H4NH (5.0
g, 45 mmol) in EtOH (100 cm3). The resulting suspension was
stirred for 10 min, then filtered, and the bright yellow solid was
washed with EtOH followed by Et2O and dried in vacuo as
506w and 484w cmϪ1
.
2416
J. Chem. Soc., Dalton Trans., 1997, Pages 2409–2418

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[Cu(NO3)(SC5H4NH)2] 8 (4.81 g, 97%). The complex can be
recrystallised as very fine needles from dmf acidified with
HNO3. IR: 1593s, 1507w, 1314s, 1260m, 1132m, 1084w, 1034w,
vacuo. The filtrate was concentrated to near dryness in vacuo
and taken up in [2H6]acetone for NMR studies (see Results and
Discussion). The orange precipitate was dissolved in acetone;
the solution was filtered, and Et2O was added to the filtrate; the
resulting precipitate was filtered off, washed with Et2O and
dried in vacuo as [Cu2(SC5H4N)(bpt)]PF6ؒ0.25C3H6O 14 (0.67 g,
82%). IR: 1710w (acetone), 1606w, 1585m, 1556w, 1422m,
826w, 750s, 617m, 482m and 442w cmϪ1
.
[Cu(SC5H4NH)2]PF6 9. Aqueous HPF6 (1.0 cm3 of 60% w/w)
was added dropwise to a rapidly stirred, filtered solution of
[Cu2(SO4)(SC5H4NH)2] (0.10 g, 0.22 mmol) in water (20 cm3).
The resulting suspension was stirred for 10 min, then filtered.
The solid was washed with water, dried by vacuum aspiration,
then extracted with several portions of Et2O. The product was
then dried to constant weight in vacuo as [Cu(SC5H4NH)2]PF6 9
(0.078g, 81%). The complex is soluble in acetone, but only
moderately soluble in dmso. IR: 1582m, 1512w, 1265w, 1161w,
1278w, 1160w, 1128m, 840s, 759m, 721m, 557m and 483w cmϪ1
.
[Cu(py)4]PF6 15. Pyridine (30 cm3) was added to solid [Cu-
(NCMe)4]PF6 (1.0 g, 2.68 mmol) under a nitrogen atmosphere.
The solution was stirred for 20 min, then filtered, and the filtrate
was concentrated in vacuo to ca. 10 cm3, then kept at Ϫ20 ЊC
overnight. The microcrystalline precipitate was filtered off,
washed with Et2O and dried in vacuo as [Cu(py)4]PF6 15 (0.97 g,
69%). IR: 1575s, 1482m, 1443m, 1215m, 1154w, 1067m, 1038m,
1005w, 885m, 845s, 750s, 700s, 623w, 558s and 415m cmϪ1. The
solid complex is reasonably stable to air, but solutions are
rapidly oxidised, turning green within seconds.
1129m, 1084w, 845s, 756m, 722m, 559m and 484w cmϪ1
.
[Cu(NO3)(SC5H4NH)(py)] 10. This preparation was carried
out under a nitrogen atmosphere. A suspension of [Cu-
(NO3)(SC5H4NH)2] (0.36 g, 1.03 mmol) in pyridine (25 cm3)
was boiled under reflux for 1 h. The resulting suspension was
filtered to remove [Cu6(SC5H4N)6] (ca. 0.14 g, 78%) and the
filtrate was concentrated to ca. 5 cm3 in vacuo. Addition of an
excess of Et2O precipitated a red tar. The solvent was decanted
off and the residue dried in vacuo for several hours, then stirred
with Et2O for 1 h. The mixture was filtered to give a yellow
powder, which was dried in vacuo. The crude product was dis-
solved in hot pyridine, and an excess of Et2O was added; the
precipitate was filtered off, washed with Et2O and dried in vacuo
as [Cu(NO3)(SC5H4NH)(py)] 10 (0.043 g, 13%). IR: 1578m,
1547m, 1414m, 1313(sh), 1267m, 1125m, 1084w, 1038w, 1003w,
Crystallography
The crystal structure analysis of [Cu2(SC5H4NH)6]-
[MeC6H4SO3]2 3 is described in detail here. The analyses of the
other samples followed similar procedures; major variations for
complexes 1 and 12 are given with their crystal data below.
Crystal data. C30H30Cu2N6S6ؒ2C7H7O3S, M = 1136.4, mono-
clinic, space group P21/n (equivalent to no. 14), a = 16.881(1),
b = 9.9724(8), c = 14.887(1) Å, β = 97.604(6)Њ, U = 2484.0(4) Å3,
Z = 2, Dc = 1.519 g cmϪ3, F(000) = 1168, µ(Mo-Kα) = 12.3
cmϪ1, λ(Mo-Kα) = 0.710 69 Å.
822w, 754s, 681m, 608w, 490w and 442w cmϪ1
.
Crystals are deep yellow, rectangular plates. One, ca.
0.11 × 0.20 × 0.48 mm, was mounted on a glass fibre and, after
preliminary photographic examination, transferred to an
Enraf-Nonius CAD4 diffractometer (with monochromated
radiation) for determination of accurate cell parameters (from
the settings of 25 reflections, θ = 12–13Њ, each centred in four
orientations) and for measurement of diffraction intensities to
θmax = 25Њ. There were 4364 unique reflections, 2982 of which
were ‘observed’ with I > 2σI.
During processing, corrections were applied for Lorentz-
polarisation effects, slight crystal deterioration (5.0% overall),
absorption (by semiempirical ψ-scan methods) and to eliminate
negative net intensities (by Bayesian statistical methods). The
structure was determined by the heavy-atom method using the
SHELX program 40 and refined (on F) by full-matrix least-
squares methods. Hydrogen atoms were included in idealised
positions; those on pyridine and phenyl rings were set to ride on
their parent C or N atoms, and those in the methyl groups were
refined with geometrical constraints. The isotropic thermal
parameters of all the H atoms were allowed to refine freely, and
the non-H atoms were refined with anisotropic thermal param-
eters. Refinement was smooth and rapid, converging with
R = 0.062 and Rg = 0.04440 for all 4364 reflections weighted
w = σFϪ2. In the final difference map the highest peaks were
between the anion and cation (ca. 0.55 e ÅϪ3) and within the
anion (ca. 0.37 e ÅϪ3).
[Cu(NO3)(SC5H4NH)2(PPh3)] 11. This preparation was done
under a nitrogen atmosphere. Methanol (25 cm3) was added to
a solid mixture of [Cu(NO3)(SC5H4NH)2] (0.50 g, 1.44 mmol)
and PPh3 (0.40 g, 1.52 mmol) and the mixture was boiled under
reflux for 10 min, giving an orange solution. This was allowed
to cool, then filtered. The filtrate was concentrated to ca. 2 cm3
in vacuo, and Et2O was added, causing separation of a yellow
tar. The supernatant was decanted off and the solid dried in
vacuo for several hours, then stirred with Et2O (20 cm3). This
gave a powder, which was filtered off, washed with Et2O and
dried in vacuo as [Cu(NO3)(SC5H4NH)2(PPh3)] 11 (0.54 g,
61%). IR: 1565s, 1306m, 1130s, 1024w, 754s, 695m, 617m,
517m, 484m and 446w cmϪ1
.
Recrystallisation of [Cu(NO3)(SC5H4NH)2(PPh3)] by slow
diffusion of Et2O into an EtOH solution gave, in low yield,
crystals of [Cu(SC5H4NH)2(PPh3)2]NO3 12, whose IR spectrum
was virtually identical to that of the starting complex.
[Cu2(bpt)3][PF6]2ؒC3H6O 13. The compound bpt (1.25 g, 5.78
mmol) was added to a solution of [Cu(NCMe)4]PF6 (1.0 g, 2.68
mmol) in MeCN (40 cm3). The mixture was stirred under a
nitrogen atmosphere for 24 h, then filtered to remove
[Cu6(SC5H4N)6]. The filtrate was concentrated in vacuo to ca. 5
cm3 and an excess of Et2O was added, causing precipitation of
a yellow oil. The mixture was kept at Ϫ20 ЊC overnight, where-
upon the oil solidified; the solid was filtered off, washed with
Et2O and dried in vacuo. The crude product apparently con-
tained some HPF6; it was purified by repeatedly dissolving in
acetone and precipitating with Et2O as [Cu2(bpt)3][PF6]2ؒC3H6O
13 (0.42 g, 28%). IR: 1709m (acetone), 1605m, 1586m, 1428m,
1279w, 1225m, 1167m, 1136w, 941w, 882m, 839s, 768m, 727m,
Scattering factor curves for neutral atoms were taken from
ref. 41. Computer programs used in this analysis have been
noted above and in Table 4 of ref. 42, and were run on a Micro-
VAX 3600 machine in the Nitrogen Fixation Laboratory, Uni-
versity of Sussex, Brighton.
558s and 484w cmϪ1
.
[{Cu(ì-O2CMe)2(bpt)}2] 1. Crystal data. C32H36Cu2N4O8S2,
M = 795.9, monoclinic, space group P21/n (equivalent to
no. 14), a = 27.330(3), b = 7.8772(6), c = 8.0866(7) Å, β =
[Cu2(SC5H4N)(bpt)]PF6ؒ0.25C3H6O 14. The compound bpt
(1.25 g, 5.78 mmol) was added to a solution of [Cu(NCMe)4]-
PF6 (1.0 g, 2.68 mmol) in thf (40 cm3) under a nitrogen atmos-
phere and the mixture was boiled under reflux for 4 h. The
orange precipitate was filtered off, washed with thf and dried in
93.480(8)Њ, U = 1737.7(3) Å3, Z = 2, Dc = 1.521
g ,
cmϪ3
F(000) = 820, µ(Mo-Kα) = 14.0 cmϪ1
Crystals are well defined, green plates; sample selected was
.
J. Chem. Soc., Dalton Trans., 1997, Pages 2409–2418
2417

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S. Stötzel and K. Wieghardt, J. Chem. Soc., Chem. Commun., 1989,
1600.
0.04 × 0.21 × 0.26 mm. Total number of unique reflec-
tions = 3061, ‘observed’ reflections (I > 2σI) 2080. No crystal
deterioration. Structure determined by the heavy-atom method
using SHELX. Refinement of F using SHELXN; final R and Rg
values were 0.071 and 0.056 for all 3601 reflections weighted
w = (σF2 ϩ 0.00043F 2)Ϫ1. The final difference map showed peaks
of ca. 0.5 e ÅϪ3, close to Cu and O in an acetate ligand.
15 E. S. Raper, Coord. Chem. Rev., 1994, 129, 91.
16 W. Marckwald, W. Klemm and H. Trabert, Ber. Dtsch. Chem. Ges.,
1900, 33, 1556.
17 I. P. Evans and G. Wilkinson, J. Chem. Soc., Dalton Trans., 1974,
946.
18 N. Lenhart and H. Singer, Z. Naturforsch., Teil B, 1975, 30, 284.
19 E. C. Constable and P. R. Raithby, J. Chem. Soc., Dalton Trans.,
1987, 2281.
20 G. A. Stergioudis, S. C. Kokkou, P. J. Rentzeperis and P. Karagian-
nidis, Acta Crystallogr., Sect. C, 1987, 43, 1685.
[Cu(SC5H4NH)2(PPh3)2]NO3 12. Crystal data. C46H40CuN3-
¯
O3P2S2, M = 872.5, triclinic, space group P1 (no. 2), a =
10.156(2), b = 13.060(1), c = 16.038(2) Å, α = 97.500(8), β =
21 S. C. Kokkou, S. Fortier, P. J. Rentzeperis and P. Karagiannidis,
Acta Crystallogr., Sect. C, 1983, 39, 178.
94.269(12), γ = 90.861(11)Њ, U = 2102.6(5) Å3, Z = 2, Dc = 1.378
g cmϪ3, F(000) = 940, µ(Mo-Kα) = 7.3 cmϪ1
.
22 P. Karagiannidis, P. Aslanidis, P. Papastefanou, D. Mentzafos,
A. Hountas and A. Terzis, Inorg. Chim. Acta, 1989, 156, 265.
23 P. Karagiannidis, P. Aslanidis, S. Papastefanou, D. Mentzafos,
A. Hountas and A. Terzis, Polyhedron, 1990, 9, 2833.
24 I. G. Dance, G. A. Bowmaker, G. R. Clark and J. K. Seadon,
Polyhedron, 1983, 2, 1031; G. Henkel, B. Krebs, P. Betz, H. Fietz and
K. Saatkamp, Angew. Chem., Int. Ed. Engl., 1988, 27, 1326.
25 A. L. E. Stoffels, W. G. Haanstra, W. L. Driessen and J. Reedijk,
Angew. Chem., Int. Ed. Engl., 1990, 29, 1419.
26 E. W. Ainscough, A. M. Brodie, J. M. Husbands, G. J. Gainsford,
E. J. Gabe and N. F. Curtis, J. Chem. Soc., Dalton Trans., 1985, 151.
27 K. Nilsson and Å. Oskarsson, Acta Chem. Scand., Ser. A, 1982, 36,
605.
Beautiful, yellow triangular prisms, crystal size 0.14 × 0.30 ×
0.33 mm. Total number of unique reflections = 7381,
‘observed’ reflections (I > 2σI) 3930. No crystal deterioration.
Structure determined by automated Patterson methods using
SHELXS;43 refinement on F using SHELXN; final R and Rg
values were 0.086 and 0.089 for 5750 reflections (with I > σI)
weighted w = (σF2 ϩ 0.00250F 2)Ϫ1. The final difference map
showed peaks at ca. 0.55 e ÅϪ3 close to both cation and anion.
Atomic coordinates, thermal parameters, and bond lengths
and angles have been deposited at the Cambridge Crystallo-
graphic Data Centre (CCDC). See Instructions for Authors,
J. Chem. Soc., Dalton Trans., 1997, Issue 1. Any request to the
CCDC for this material should quote the full literature citation
and the reference number 186/535.
28 S. Ahrland, S. Ishiguro and I. Persson, Acta Chem. Scand., Ser. A,
1986, 40, 418.
29 D. S. Gill, L. Rodehüser and J.-J. Delpuech, J. Chem. Soc., Faraday
Trans., 1990, 2847.
30 C. J. Pouchert and J. Behnke, The Aldrich Library of 13C and
1H FT NMR Spectra, 1st edn., Adrich Chemical Company Inc.,
Milwaukee, 1993.
Acknowledgements
31 A. Albert and G. B. Barlin, J. Chem. Soc., 1959, 2384.
32 S. Stoyanov, I. Petkov, L. Antonov, T. Stoyanova, P. Karagiannidis
and P. Aslanidis, Can. J. Chem., 1990, 68, 1482 and refs. therein.
33 M. J. Nowak, L. Lapinski, H. Rostkowska, A. Les and L. Adamow-
icz, J. Phys. Chem., 1990, 94, 7406.
34 J. S. Kwiatkowsi, J. Mol. Struct., 1971, 10, 245.
35 L. Stefaniak, Org. Magn. Reson., 1979, 12, 379.
36 L. Stefaniak, G. A. Webb, C. Brevard, M. Bourdonneau,
R. Lejeune, L. Thunus and C. L. Lapière, Magn. Reson. Chem.,
1985, 23, 790.
We thank the BBSRC for financial support for this work.
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J. Chem. Soc., Dalton Trans., 1997, Pages 2409–2418