Coordination of new disulfide ligands to CuIand CuII: Does a CuII μ-thiolate complex form?

Article abstract of DOI:10.1016/j.ica.2014.12.033

Interest in dinuclear Cu^II μ-thiolate and Cu^I disulfide complexes is triggered by their similarity with the Cu_A site and the possibility to control this redox equilibrium. Three new disulfide ligands L1, L3 and L4 were synthesized and reacted with Cu^I salts to investigate whether thiolate or disulfide species would form. The nature of L1 precludes the formation of Cu^II μ-thiolate species, resulting in the formation of [Cu₂^I(L1)(CH₃CN)](BF₄)₂ which was characterized via single crystal X-ray crystallography. Pyrazole-containing ligands L3 and L4 form Cu^I complexes that are stable in solution in air for hours with half-wave potentials of approximately +0.55 V versus Ag/AgCl, indicating high stability of the Cu^I state rather than the Cu^II state. The half-wave potentials of the Cu^I complexes with L1 and L2 are less positive, indicating that in order to allow formation of both Cu^II μ-thiolate and Cu^I disulfide species, a half-wave potential of roughly 0 V versus Ag/AgCl would be ideal. Furthermore, Cu^II crystal structures with L1, L2, L3 and L4 and different counterions were compared and analyzed. Pyrazolyl-containing ligands L3 and L4 form complexes that are very similar to the complexes with pyridyl-containing ligands L1 and L2.

Full text of DOI:10.1016/j.ica.2014.12.033

Inorganica Chimica Acta 428 (2015) 193–202
Contents lists available at ScienceDirect
Inorganica Chimica Acta
journal homepage: www.elsevier.com/locate/ica
Coordination of new disulfide ligands to CuI and CuII:
Does a CuII
l-thiolate complex form?
Erica C.M. Ording-Wenker a, Maxime A. Siegler b, Elisabeth Bouwman a,
⇑
a Leiden Institute of Chemistry, Gorlaeus Laboratories, Leiden University, P.O. Box 9502, 2300 RA Leiden, The Netherlands
b Department of Chemistry, Johns Hopkins University, Baltimore, MD 21218, United States
a r t i c l e i n f o
a b s t r a c t
Interest in dinuclear CuII -thiolate and CuI disulfide complexes is triggered by their similarity with the
l
Article history:
Received 24 October 2014
Received in revised form 9 December 2014
Accepted 10 December 2014
Available online 7 February 2015
CuA site and the possibility to control this redox equilibrium. Three new disulfide ligands L1, L3 and L4
were synthesized and reacted with CuI salts to investigate whether thiolate or disulfide species would
form. The nature of L1 precludes the formation of CuII
l-thiolate species, resulting in the formation of
[CuI2(L1)(CH3CN)](BF4)2 which was characterized via single crystal X-ray crystallography. Pyrazole-contain-
ing ligands L3 and L4 form CuI complexes that are stable in solution in air for hours with half-wave poten-
tials of approximately +0.55 V versus Ag/AgCl, indicating high stability of the CuI state rather than the CuII
state. The half-wave potentials of the CuI complexes with L1 and L2 are less positive, indicating that in order
Keywords:
Copper
Coordination chemistry
Thiolate
Disulfide
to allow formation of both CuII -thiolate and CuI disulfide species, a half-wave potential of roughly 0 V ver-
l
sus Ag/AgCl would be ideal. Furthermore, CuII crystal structures with L1, L2, L3 and L4 and different coun-
terions were compared and analyzed. Pyrazolyl-containing ligands L3 and L4 form complexes that are very
similar to the complexes with pyridyl-containing ligands L1 and L2.
Redox chemistry
Ó 2015 Elsevier B.V. All rights reserved.
1. Introduction
analyze the electron shuttling capabilities remains a challenge.
Alternatively, the redox reaction of dinuclear CuII
l-thiolate and
Many biological redox processes involve copper and sulfur,
because of their ability to mediate efficient electron transfer. Cop-
per can cycle between CuI and CuII, while cysteine thiolate ligands
can be reversibly oxidized to form sulfur radicals or disulfide
bonds. For example, Type-1 copper centers are electron transfer
agents in nature that contain a thiolate ligand and are found in
both mononuclear proteins such as azurin and plastocyanin as well
as multicopper enzymes like ascorbate oxidase and NOꢀ2 reductase
[1,2]. Another example is the CuA site, found in cytochrome c
oxidase and N2O reductase, which contains a cysteine-bridged
CuI disulfide complexes is investigated. This conversion, in which
CuII is reduced to CuI and the thiolate ligands are oxidized to form
a disulfide bond, takes place intramolecularly and in some cases
can be reversed in a controlled manner [11–13]. It has been
reported that small ligand changes can determine the formation
of either a CuII -thiolate or a CuI disulfide complex [14]. To further
l
investigate the effect of ligand changes on the formation of either
CuII or CuI species we have synthesized three new disulfide ligands
L1, L3 and L4. These ligands show similarities to the ligand LSSL,
that has been shown to form a stable CuII
reacted with CuI (Fig. 1) [15,16].
l-thiolate complex when
bis(l
-thiolato) dicopper center that can cycle between the CuICuI
and Cu1.5Cu1.5 redox states [3–6]. To understand and mimic the
electron shuttling capabilities of these enzymes, bioinorganic
chemistry research has been directed towards synthesis of model
systems. Several synthetic models have been reported for the CuA
site; the isolated complexes contain a CuICuI, CuIICuII or even a
Cu1.5Cu1.5 core, the latter containing a completely delocalized elec-
tron between the two copper centers [7–10]. However, changing
the oxidation state of these models to form stable species and to
Ligand L1 only differs from LSSL in the bond between the two
methyl groups in the -position with respect to the sulfur atoms.
This connection generates a six-membered ring, which inhibits
a
the intramolecular, but perhaps not the intermolecular formation
of CuII
l-thiolate species. We further investigated the replacement
of pyridyl groups by pyrazolyl moieties in L3. The difference
between L3 and L4 lies in the methyl groups on the pyrazole rings,
as addition of a methyl group to a pyridyl moiety has shown to
have a large effect on the complex formation [14]. Ligand L2 was
used for comparative purposes, because of its ability to form both
⇑
CuII -thiolate and CuI disulfide complexes [13]. The three new
l
Corresponding author.
E-mail address: bouwman@chem.leidenuniv.nl (E. Bouwman).
ligands have been reacted with CuI salts to study ligand effects
http://dx.doi.org/10.1016/j.ica.2014.12.033
0020-1693/Ó 2015 Elsevier B.V. All rights reserved.

194
E.C.M. Ording-Wenker et al. / Inorganica Chimica Acta 428 (2015) 193–202
Fig. 1. Schematic representation of the reaction between LSSL and [CuI] forming a CuII
l-thiolate species and ligands L1, L2, L3 and L4.
on the formation of CuII
l
-thiolate species. Furthermore, new CuII
diffractometer (equipped with Atlas detector) with Cu Ka radia-
complexes with all four ligands are reported.
tion (k = 1.54178 Å) under the program CrysAlisPro (Version
1.171.36.24 or 1.171.36.28 Agilent Technologies, 2012–2013). The
same program was used to refine the cell dimensions and for data
reduction. The structures were solved with the program SHELXS-
2013 (Sheldrick, 2013) [20] and were refined on F2 with SHELXL-
2013 (Sheldrick, 2013) [20]. Analytical numeric absorption correc-
tions based on a multifaceted crystal model were applied using Cry-
sAlisPro. The temperature of the data collection was controlled using
the system Cryojet (manufactured by Oxford Instruments). The H
atoms were placed at calculated positions using the instructions
AFIX 13, AFIX 23, AFIX 43, AFIX 137 or AFIX 147 with isotropic dis-
placement parameters having values 1.2 or 1.5 times Ueq of the
attached C or O atoms.
2. Experimental
2.1. General procedures
Reagents and solvents were purchased from commercial sources.
[CuI(CH3CN)4](BF4), L2, (3R,6S)-meso-3,6-bis(tert-butyloxycarbony-
laminomethyl)-1,2-dithiacyclohexane, N-hydroxymethylpyrazole
and N-hydroxymethyl-3,5-dimethylpyrazole were synthesized
according to literature procedures [13,17–19]. NMR spectra were
recorded on a Bruker 300 DPX spectrometer. NMR experiments
under argon were carried out using a J. Young NMR tube. IR spectra
were obtained on a Perkin Elmer UATR (Single Reflection Diamond)
Spectrum Two device (4000–700 cmꢀ1; resolution 4 cmꢀ1). Mass
spectrometry was measured using a Finnigan Aqua Mass Spectrom-
eter (MS) with electrospray ionization (ESI). Sample introduction
was achieved through a Dionex ASI-100 automated sample injector
with an eluent flow rate of 0.2 mL/min. Elemental analyses were
performed using a Perkin Elmer 2400 Series II CHNS/O analyzer or
were performed by the Mircoanalytical laboratory Kolbe in Ger-
many. UV–Vis absorbance spectra were recorded on a Varian
Cary50 spectrophotometer. Cyclic voltammetry was performed
with an Autolab PGstat10 potentiostat controlled by GPES4 soft-
ware. A three electrode arrangement with a glassy carbon working
electrode (3 mm diameter), an Ag/AgCl double junction reference
electrode and a Pt wire counter electrode were used in different sol-
vents with 0.1 M NBu4PF6 as the electrolyte. In these conditions the
Fc/Fc+ couple was found to be located at +439 mV with a peak-to-
peak separation of 65 mV in CH3CN. Potentials are given relative
to the Ag/AgCl electrode.
The reflection intensities for [CuI2I(L2)(H2O)(F)(BF4)](BF4)2 were
measured using a KM4/Xcalibur (detector: Sapphire3) with enhanced
graphite-monochromated Mo K
a radiation (k = 0.71073 Å) at 110(2)
K
under the program CrysAlisPro (Version 1.171.35.11 Oxford
Diffraction Ltd., 2011). The same program was used to refine the cell
dimensions and for data reduction. The structure was solved with the
program SHELXS-97 (Sheldrick, 2008) [20] and was refined on F2 with
SHELXL-97 (Sheldrick, 2008) [20]. Analytical numeric absorption
corrections based on a multifaceted crystal model were applied using
CrysAlisPro. The temperature of the data collection was controlled
using the system Cryojet (manufactured by Oxford Instruments).
The H atoms (unless otherwise specified) were placed at calculated
positions using the instructions AFIX 23 or AFIX 43 with isotropic
displacement parameters having values 1.2 times Ueq of the attached
C atoms. The H atoms attached to the coordinated water molecule
(O1W) were located from difference Fourier maps; their atomic
coordinates were refined freely using the DFIX restraints to keep
the O–H and Hꢁ ꢁ ꢁH distances within acceptable ranges.
2.2. X-ray crystallography
2.3. Ligand and complex synthesis
The reflection intensities for [CuI2(L1)(CH3CN)](BF4)2, [Cu4II(L1)2
(Cl)4(CuIICl4)2], [Cu2II(L3)(Cl)2]n(BF4)2n and [Cu2II(L4)(CH3CN)2(BF4)2]n
(BF4)2n were measured at 100(2) or 110(2) K using a SuperNova
2.3.1. Synthesis of L1
This ligand was synthesized using modified literature
procedures [19,21]. A mixture of (3R,6S)-meso-3,6-bis(tert-butyl-

E.C.M. Ording-Wenker et al. / Inorganica Chimica Acta 428 (2015) 193–202
195
oxycarbonylaminomethyl)-1,2-dithiacyclohexane (0.913 g, 2.41
mmol) and trifluoroacetic acid (5 mL) was stirred for 30 min at RT.
The reaction was concentrated in vacuo yielding a viscous oil, to
which dichloromethane (80 mL) and 2-pyridinecarboxaldehyde
(1.4 mL, 14.5 mmol) were added. To this emulsion NaBH(OAc)3
(4.50 g, 21.2 mmol) was added in three portions after which the
reaction mixture was stirred for 24 h at RT. The reaction was
quenched by addition of NaHCO3 (sat.) and stirred for 15 min.
The layers were separated and the aqueous layer was extracted
two times with dichloromethane. The combined organic layers
were dried over MgSO4 and then evaporated to dryness yielding
a yellow oil with white powder. From this impure product, L1
could be crystallized with ethyl acetate yielding a white powder
(0.986 g, 1.82 mmol, 75%). Crystals suitable for X-ray structure
determination were obtained by crystallization from ethyl acetate.
The crystal structure of L1 is reported in the Supporting Informa-
tion. 1H NMR (300 MHz, CD3CN, RT): d 1.47 (br, 2H, S-CH-CH2-
CH2), 1.67 (m, 2H, S-CH-CH2-CH2), 2.52 (br, 2H, S-CH-CH2-N),
2.76 (br, 2H, S-CH-CH2-N), 3.03 (q, J = 6 Hz, 2H, S-CH), 3.72 (m,
8H, N-CH2-Py), 7.17 (m, 4H, Py-H5), 7.53 (d, J = 8 Hz, 4H, Py-H3),
7.68 (td, J = 8 Hz, 1 Hz, 4H, Py-H4), 8.43 (d, J = 4 Hz, 4H, Py-H6).
1H NMR (300 MHz, CDCl3, RT): d 1.50 (br, 2H, S-CH-CH2-CH2),
1.70 (m, 2H, S-CH-CH2-CH2), 2.72 (m, 4H, S-CH-CH2-N), 2.95 (br,
2H, S-CH), 3.77 (m, 8H, N-CH2-Py), 7.08 (m, 4H, Py-H5), 7.52 (d,
J = 8 Hz, 4H, Py-H3), 7.59 (td, J = 8 Hz, 1 Hz, 4H, Py-H4), 8.43 (d,
J = 5 Hz, 4H, Py-H6). 13C NMR (75 MHz, CDCl3, RT): d 28.5 (S-CH-
CH2-CH2), 41.8 (br, S-CH), 56.5 (br, S-CH-CH2-N), 60.7 (N-CH2-Py),
122.1 (Py-C5), 123.4 (Py-C3), 136.5 (Py-C4), 148.9 (Py-C6), 159.4
(Py-C1). ESI-MS found (calculated) for [M+H]+ m/z 542.7 (543.2);
[M+2H]2+ m/z 272.1 (272.6); [M+Na]+ m/z 565.0 (565.2). IR (neat,
cmꢀ1): 3050w, 3009w, 2907w, 2821m, 1589s, 1569m, 1473m,
1440m, 1432m, 1369m, 1249m, 1116m, 1048m, 984m, 964m,
873m, 768vs, 761vs, 746s, 615m, 519m. Elemental analysis calcd
for L1: C 66.39, H 6.31, N 15.48, S 11.82; Found: C 66.21, H 6.35,
N 15.21, S 11.81.
(s, 4H, N-C(CH3)-CH). 13C NMR (75 MHz, CD3CN, RT): d 11.2 (C-
CH3), 13.7 (C-CH3), 36.9 (S-CH2), 49.9 (S-CH2-CH2), 66.3 (N-CH2-
Pz), 106.4 (N-C(CH3)-CH), 140.7 (N-C(CH3)), 147.8 (N-C(CH3)).
ESI-MS found (calculated) for [MꢀC5H4+Na]+ m/z 543.0 (543.3);
[Mꢀ2 C5H4+Na]+ m/z 479.0 (479.3); [Mꢀ3 C5H4+Na]+ m/z 414.9
(415.2); [Mꢀ4 C5H4+Na]+ m/z 350.9 (351.2). IR (neat, cmꢀ1):
2919m, 1555s, 1456s, 1421s, 1376s, 1314s, 1248s, 1096s, 1029s,
975s, 779vs, 732s, 626m.
2.3.4. Synthesis of [CuI2(L1)(CH3CN)](BF4)2ꢁCH3CN
The synthesis of [CuI2(L1)(CH3CN)](BF4)2 was carried out using
standard Schlenk-line techniques under an argon atmosphere. To a
suspension of L1 (38.0 mg, 0.070 mmol) in 5 mL CH3CN was added
[CuI(CH3CN)4](BF4) (44.1 mg, 0.140 mmol). To the resulting bright
yellow solution was added 40 mL diethyl ether, which resulted in
precipitation. The product was filtered and washed with diethyl
ether yielding [CuI2(L1)(CH3CN)](BF4)2 as a yellow powder (9.5 mg,
0.011 mmol, 15%). Crystals suitable for X-ray structure determina-
tion were obtained by slow vapor diffusion of diethyl ether into an
acetonitrile solution containing the complex under oxygen-free con-
ditions. 1H NMR (300 MHz, CD3CN, RT): d 1.61 (br, 2H, S-CH-CH2-
CH2), 1.86 (br, 2H, S-CH-CH2-CH2), 2.78 (br, 4H, S-CH-CH2-N), 3.07
(br, 2H, S-CH), 3.87 (br, 8H, N-CH2-Py), 7.36 (br, 4H, Py-H3), 7.45
(br, 4H, Py-H5), 7.86 (t, J = 7 Hz, 4H, Py-H4), 8.60 (br, 4H, Py-H6).
ESI-MS found (calculated) for [MꢀCH3CNꢀ2 BF4]2+ m/z 334.1
(334.0); [MꢀCuꢀCH3CNꢀ2 BF4]+ m/z 605.2 (605.2). IR (neat,
cmꢀ1): 2907w, 1604m, 1571w, 1480w, 1439m, 1302w, 1284w,
1263w, 1048vs, 1033vs, 958m, 771s, 648w, 520m. Elemental Anal.
Calc. for [CuI2(L1)(CH3CN)](BF4)2: C, 43.45; H, 4.22; N, 11.08;
S, 7.25.; Found: C, 42.59; H, 4.14; N, 10.75; S, 7.35%.
2.3.5. Synthesis of [CuI2(L3)](BF4)2
Measurements of [CuI2(L3)](BF4)2 have been carried out in situ by
adding two equivalents of [CuI(CH3CN)4](BF4) to L3 in acetonitrile.
Attempts to isolate the complex resulted in the formation of an oil.
1H NMR (300 MHz, CD3CN, RT): d 2.56 (t, J = 7 Hz, 4H, S-CH2), 2.97
(t, J = 7 Hz, 4H, S-CH2-CH2), 5.12 (s, 8H, N-CH2-Pz), 6.39 (t, J = 2 Hz,
4H, N-CH-CH), 7.63 (d, J = 2 Hz, 4H, N-CH), 7.76 (d, J = 2 Hz, N-CH).
13C NMR (75 MHz, CD3CN, RT): d 36.5 (S-CH2), 49.6 (S-CH2-CH2),
68.2 (N-CH2-Pz), 107.2 (N-CH-CH), 132.6 (N-CH), 141.5 (N-CH).
ESI-MS found (calculated) for [MꢀCuꢀ2 BF4]+ m/z 535.2 (535.1).
2.3.2. Synthesis of L3
Cystamine dihydrochloride (1.90 g, 8.43 mmol), N-hydrox-
ymethylpyrazole (3.32 g, 33.9 mmol) and triethylamine (1.76 g,
17.5 mmol) dissolved in dichloromethane (50 mL) were stirred
for 24 h at RT. The reaction mixture was extracted with water
(30 mL) three times, after which the organic layer was dried over
MgSO4 and the solvent was evaporated. This yielded L3 as a color-
less oil (3.96 g, 8.38 mmol, 99%), which was used without further
purification. 1H NMR (300 MHz, CD3CN, RT): d 2.65 (t, J = 7 Hz,
4H, S-CH2), 2.94 (t, J = 7 Hz, 4H, S-CH2-CH2), 5.07 (s, 8H, N-CH2-
Pz), 6.27 (t, J = 2 Hz, 4H, N-CH-CH), 7.47 (d, J = 1 Hz, 4H, N-CH),
7.63 (d, J = 2 Hz, N-CH). 13C NMR (75 MHz, CD3CN, RT): d 37.1 (S-
CH2), 50.2 (S-CH2-CH2), 68.9 (N-CH2-Pz), 106.6 (N-CH-CH), 130.8
(N-CH), 140.1 (N-CH). ESI-MS found (calculated) for [M+Na]+ m/z
495.0 (495.2); [MꢀC3+Na]+ m/z 459.0 (459.2); [Mꢀ2 C3+Na]+ m/z
422.9 (423.2); [Mꢀ3 C3+Na]+ m/z 387.0 (387.2); [Mꢀ4 C3+Na]+
m/z 350.9 (351.2). IR (neat, cmꢀ1): 3110w, 2941w, 1513m,
1393m, 1251m, 1121m, 1084s, 1046s, 962m, 743vs, 653m, 614s.
2.3.6. Synthesis of [CuI2(L4)](BF4)2
Measurements of [CuI2(L4)](BF4)2 have been carried out in situ by
adding two equivalents of [CuI(CH3CN)4](BF4) to L4 in acetonitrile.
Attempts to isolate the complex resulted in the formation of an oil.
1H NMR (300 MHz, CD3CN, RT): d 2.32 (s, 24H, C-CH3), 2.78 (t,
J = 7 Hz, 4H, S-CH2), 2.94 Hz (t, J = 7 Hz, 4H, S-CH2-CH2), 4.86 (s,
8H, N-CH2-Pz), 6.05 (s, 4H, N-C(CH3)-CH). 13C NMR (75 MHz, CD3CN,
RT): d 11.7 (C-CH3), 14.0 (C-CH3), 36.6 (S-CH2), 50.1 (S-CH2-CH2),
62.6 (N-CH2-Pz), 107.7 (N-C(CH3)-CH), 142.7 (N-C(CH3)), 150.4
(N-C(CH3)). ESI-MS found (calculated) for [½ MꢀBF4]+ m/z 355.1
(355.1); [MꢀCuꢀ2 BF4]+ m/z 647.4 (647.3).
2.3.7. Synthesis of [CuI4I(L1)2(Cl)4(CuIICl4)2]ꢁ2 CH3OH
To a suspension of L1 (36.6 mg, 0.067 mmol) in 10 mL CH3CN
was added solid CuCl2ꢁ2 H2O (35.0 mg, 0.202 mmol). The mixture
was stirred for 1 h during which L1 dissolved and a green precipi-
tate formed. The precipitate was filtered and washed with acetoni-
trile and diethyl ether yielding [CuI4I(L1)2(Cl)4(CuIICl4)2] as a light
green powder (0.061 g, 0.064 mmol, 96%). Crystals suitable for
X-ray structure determination were obtained by vapor diffusion of
diethyl ether into a methanol solution of the complex. ESI-MS found
(calculated) for [Cu2(L1)Cl2]2+ m/z 370.1 (370.0). IR (neat, cmꢀ1):
3490m, 3065w, 2939m, 1608s, 1572w, 1482m, 1444s, 1287m,
1160w, 1093w, 1052w, 1030m, 899w, 855w, 778vs, 765s, 730w,
2.3.3. Synthesis of L4
L4 was synthesized in the same manner as L3 starting from N-
hydroxymethyl-3,5-dimethylpyrazole (2.89 g, 23.1 mmol), cysta-
mine dihydrochloride (1.27 g, 5.64 mmol) and triethylamine
(1.6 mL, 11.5 mmol) in 50 mL dichloromethane. This yielded L4
as a viscous, colorless oil (3.22 g, 5.51 mmol, 98%), which was used
without further purification. 1H NMR (300 MHz, CD3CN, RT): d 2.11
(s, 12H, C-CH3), 2.20 (s, 12H, C-CH3), 2.40 (t, J = 7 Hz, 4H, S-CH2),
2.86 Hz (t, J = 7 Hz, 4H, S-CH2-CH2), 4.88 (s, 8H, N-CH2-Pz), 5.81

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E.C.M. Ording-Wenker et al. / Inorganica Chimica Acta 428 (2015) 193–202
656w, 497w, 478w. Elemental Anal. Calc. for [CuI4I(L1)2(Cl)4(CuII-
Cl4)2]: C, 38.09; H, 3.62; N, 8.88; S, 6.78. Found: C, 39.03; H, 3.63;
N, 9.23; S, 7.15%. UV–Vis in CH3OH at 0.1 mM [Cu] concentration:
256 nm (11600 Mꢀ1 cmꢀ1), 290 nm (3600 Mꢀ1 cmꢀ1), 710 nm
(90 Mꢀ1 cmꢀ1). UV–Vis in N,N-dimethylformamide at 0.1 mM [Cu]
concentration: 290 nm (3900 Mꢀ1 cmꢀ1), 730 nm (110 Mꢀ1 cmꢀ1).
3. Results and discussion
3.1. Ligand synthesis
Ligand L1 was synthesized from the enantiomerically pure
compound
(3R,6S)-meso-3,6-bis(tert-butyloxycarbonylaminom-
X-band EPR powder spectrum (RT,
m = 9.859 GHz): giso = 2.12.
ethyl)-1,2-dithiacyclohexane, which was synthesized based on a
reported 7-step reaction [19]. The amine groups were deprotected
using trifluoroacetic acid, after which a reductive amination with
2-pyridinecarboxaldehyde gave L1 in 75% yield. The synthetic
scheme for L1 can be found in Fig. S1. L1 is a meso compound con-
taining two stereocenters. Recrystallization of the compound from
ethyl acetate resulted in colorless crystals that were suitable for
X-ray structure determination; the crystallographic data are
presented in the Supporting Information. The crystal structure con-
firms that the ligand is enantiomerically pure, containing an R and
2.3.8. Synthesis of [CuI2I(L2)(H2O)(F)(BF4)](BF4)2
To a solution of L2 (0.056 g, 0.103 mmol) in 1.5 mL methanol
was added a solution of [CuII(H2O)6](BF4)2 (0.072 g, 0.208 mmol)
in water (1 mL), resulting in a dark blue solution. Slow vapor diffu-
sion of diethyl ether into this complex solution resulted in dark
blue crystals of [CuI2I(L2)(H2O)(F)(BF4)](BF4)2 (0.069 g, 0.071 mmol,
69%) that were suitable for X-ray structure determination. ESI-MS
found (calculated) for [½(MꢀH2OꢀFꢀ3 BF4)]+ m/z 335.0 (335.1);
[MꢀCuꢀH2OꢀFꢀ3 BF4]+ m/z 607.3 (607.2). IR (neat, cmꢀ1): 3517w,
2806w, 2362w, 1616m, 1575w, 1487w, 1447m, 1320w, 1306w,
1046vs, 1029vs, 1012vs, 954m, 925m, 764m, 723w, 656m, 520m,
425m. Elemental analysis calcd for [CuI2I(L2)(H2O)(F)(BF4)](BF4)2: C
37.17, H 3.95, N 8.67, S 6.62; Found: C 37.52, H 4.28, N 8.70, S
6.49. UV–Vis in H2O at 0.1 mM [Cu] concentration: 256 nm
S
stereocenter. The two di-(2-pyridylmethyl)amine moieties
attached to the six-membered ring are in equatorial and axial posi-
tion, which is expected to be the most stable isomer. Refluxing L1
overnight in ethanol results in a 1:1 mixture of the R,S: R,R/S,S iso-
mers, as confirmed by 1H NMR; a longer reflux time does not
change this enantiomeric ratio. The pyrazole-containing ligands
L3 and L4 were synthesized from N-hydroxymethylpyrazole
and N-hydroxymethyl-3,5-dimethylpyrazole respectively [18].
Reaction of the hydroxymethylpyrazoles with cystamine dihydro-
chloride and triethylamine resulted in L3 and L4 in almost
quantitative yields, which were sufficiently pure for further use.
Interestingly, ESI-MS spectra of both ligands showed signals
indicating loss of one, two, three or four of the carbon fragments
originating from the pyrazole groups to form –NH–NH2 moieties.
This means that the net weight loss is C3 for the loss of each carbon
fragment of L3 and C5H4 for L4. The synthetic schemes for L3 and
L4 are provided in Figs. S2 and S3.
(
e
= 11800 Mꢀ1 cmꢀ1), 640 nm (
at 0.1 mM [Cu] concentration: 260 nm
620 nm (
= 200 Mꢀ1 cmꢀ1). X-band EPR spectrum (powder, RT,
= 9.858 GHz): giso = 2.11; X-band EPR spectrum (in CH3CN, RT,
= 9.875 GHz): giso = 2.11.
e
= 90 Mꢀ1 cmꢀ1). UV–Vis in CH3CN
(
e
= 12,000 Mꢀ1 cmꢀ1),
e
m
m
2.3.9. Synthesis of [CuI2I(L3)(Cl)2]n(BF4)2nꢁ2n CH3CN
L3 (0.202 g, 0.43 mmol) was dissolved in 5 mL methanol. To this
solution solid [CuII(H2O)6](BF4)2 (0.149 g, 0.43 mmol) and CuCl2ꢁ2
H2O (0.073 g, 0.43 mmol) were added and the mixture was stirred
for 10 min. The formed precipitate was filtered and washed with
methanol and diethyl ether giving the product [CuI2I(L3)(Cl)2]n
(BF4)2n (0.342 g, 0.41 mmol, 94%) as a light blue powder. Crystals
suitable for X-ray structure determination were obtained by slow
vapor diffusion of diethyl ether into a CH3CN solution containing
the complex. ESI-MS found (calculated) for [½ MꢀBF4ꢀCl]+ m/z
298.8 (299.0); [½ MꢀBF4+Cl]+ m/z 370.8 (371.0); [MꢀCuꢀClꢀ2
BF4]+ m/z 569.9 (570.1); [Mꢀ2 BF4]2+ m/z 334.9 (335.0). IR (neat,
cmꢀ1): 3131w, 1521w, 1477w, 1426w, 1404w, 1272m, 1036vs,
987s, 920m, 765vs, 639w, 607m, 520m. Elemental Anal. Calc. for
[CuI2I(L3)(Cl)2](BF4)2ꢁH2O: C, 27.86; H, 3.51; N, 16.24; S, 7.44. Found:
C, 28.09; H, 3.49; N, 16.28; S, 7.49%. UV–Vis in CH3CN at 0.1 mM [Cu]
3.2. Synthesis and analyses of CuI complexes
Addition of two equivalents of [CuI(CH3CN)4](BF4) to L1
resulted in a bright yellow solution, which turns green in the pres-
ence of air due to oxidation of CuI to CuII. Slow vapor diffusion of
diethyl ether into the yellow solution under argon atmosphere
yielded crystals suitable for X-ray structure determination, which
confirmed a CuI complex (see Fig. 2) with formula [Cu2I (L1)(CH3-
CN)](BF4)2ꢁCH3CN. Crystallographic data and selected bond distances
are given in Tables 1 and 2.
The two copper centers in [CuI2(L1)(CH3CN)](BF4)2 have different
coordination geometries. Cu1 coordinates to one of the di-(2-pyri-
dylmethyl)amine moieties of the ligand and an acetonitrile group,
resulting in a strongly flattened tetrahedral geometry with an N4
environment and one N–Cu–N angle of 153°. Cu2 coordinates to
the other di-(2-pyridylmethyl)amine moiety and a sulfur donor of
the ligand. This gives Cu2 an N3S environment in a trigonal–pyrami-
dal geometry. The 6-membered ring in the backbone of L1 shows the
same chair conformation within the complex as in the free ligand
with one axial and one equatorial substitution. The 1H NMR spec-
trum of [CuI2(L1)(CH3CN)](BF4)2 shows slightly broadened peaks in
the diamagnetic region, indicating that the ligand induces quite a
steric environment limiting free rotation (Fig. S6). The much more
rigid structure of L1 compared to LSSL may possibly hinder the for-
concentration: 215 nm (11800 Mꢀ1 cmꢀ1), 284 nm (
cmꢀ1), 670 nm ( = 90 Mꢀ1 cmꢀ1). X-band EPR spectrum (powder,
RT, = 9.839 GHz): g\ = 2.09, g|| = 2.21; X-band EPR spectrum (in
CH3CN, RT, = 9.875 GHz): giso = 2.10.
e -
= 3 700 Mꢀ1
e
m
m
2.3.10. Synthesis of [CuI2I(L4)(CH3CN)2(BF4)2]n(BF4)2nꢁ2n CH3CNꢁn
C4H10O
L4 (19 mg; 0.033 mmol) was dissolved in 2 mL acetonitrile giv-
ing a colorless solution. To this solution [CuII(H2O)6](BF4)2 (23 mg;
0.066 mmol) was added resulting in
a clear turquoise blue
solution. Slow vapor diffusion of diethyl ether into this reaction
mixture resulted in blue crystals that were suitable for X-ray
structure determination. The crystals of the complex turn into oil
when the lattice solvent molecules evaporate from the crystal, thus
precluding elemental analysis. ESI-MS found (calculated) for [½
MꢀCH3CNꢀ2 BF4]+ m/z 355.2 (355.1); [MꢀCH3CNꢀ4 BF4]2+ m/z
375.2 (375.6). UV–Vis in CH3CN at 0.1 mM [Cu] concentration:
204 nm (17500 Mꢀ1 cmꢀ1), 223 nm (19800 Mꢀ1 cmꢀ1), 272 nm (1
600 Mꢀ1 cmꢀ1), 335 nm (800 Mꢀ1 cmꢀ1), 650 nm (120 Mꢀ1 cmꢀ1).
mation of a CuII
l-thiolate structure. Furthermore, coordination of
both copper ions to the sulfur centers is needed for electron transfer
to occur and the crystal structure of [CuI2(L1)(CH3CN)](BF4)2
shows that at least in the solid state this is not the case for one
of the two copper ions. However, it cannot be ruled out that
both copper centers are bound to sulfur when the complex is in
solution.
X-band EPR spectrum (in CH3CN, RT,
m = 9.876 GHz): giso = 2.10.

E.C.M. Ording-Wenker et al. / Inorganica Chimica Acta 428 (2015) 193–202
197
Fig. 2. Schematic drawing and projection of the cationic part of [CuI2(L1)(CH3CN)](BF4)2ꢁCH3CN. Displacement ellipsoids are set at 50% probability level. Hydrogen atoms are
omitted for clarity. Py = 2-pyridyl.
Table 1
Crystallographic and structure refinement data for complexes [CuI2(L1)(CH3CN)](BF4)2, [CuI4I(L1)2(Cl)4(CuIICl4)2], [CuI2I(L2)(H2O)(F)(BF4)](BF4)2, [Cu2II(L3)(Cl)2]n(BF4)2n and
[CuI2I(L4)(CH3CN)2(BF4)2]n(BF4)2n
.
[CuI2(L1)(CH3CN)] (BF4)2
[CuI4I(L1)2(Cl)4
[CuI2I(L2)(H2O)(F)
(BF4)](BF4)2
[CuI2I(L3)(Cl)2]n (BF4)2n
[CuI2I(L4)(CH3CN)2
(BF4)2]n(BF4)2n
(CuIICl4)2]
Empirical formula
[C32H37Cu2N7S2](BF4)2ꢁCH3CN C60H68Cl12Cu6N12S4ꢁ [C30H38BCu2F5N6OS2](BF4)2 [C20H28Cl2Cu2N10S2](BF4)2ꢁ [C32H50B2Cu2F8N12S2](BF4)2ꢁ
2 CH3OH
1954.88
monoclinic
P21/c
2 CH3CN
926.35
2 CH3CNꢁC4H10
O
Formula weight
Crystal system
Space group
a (Å)
b (Å)
c (Å)
925.56
969.29
1297.50
monoclinic
Cc
monoclinic
P21/c
monoclinic
P21/n
triclinic
P1
ꢀ
22.0386(4)
16.8210(2)
11.37505(17)
90
111.2630(18)
90
13.25184(17)
17.8395(3)
18.4599(2)
90
94.7369(12)
90
13.7798(8)
12.7963(7)
22.5595(13)
90
106.871(6)
90
13.1387(3)
22.9250(5)
13.3035(3)
90
110.399(3)
90
12.4961(3)
14.7450(3)
16.3715(2)
98.5626(14)
102.8998(16)
92.7244(15)
2897.40(10)
2
a
(°)
b (°)
c
(°)
V (Å3)
3929.80(11)
4
4349.13(10)
2
3806.7(4)
4
3755.78(16)
4
Z
Z0
1
½
1
1
1
Dcalc (g ꢁ cm3)
1.564
1.493
1.691
1.638
1.487
T (K)
100(2)
100(2)
110(2)
110(2)
110(2)
Crystal size (mm)
l
0.22 ꢂ 0.16 ꢂ 0.15
0.19 ꢂ 0.17 ꢂ 0.09
0.47 ꢂ 0.11 ꢂ 0.06
0.36 ꢂ 0.27 ꢂ 0.26
0.30 ꢂ 0.25 ꢂ 0.17
(mmꢀ1
)
2.994
6.249
1.327
4.439
2.442
No. of reflections
11933
25534
30434
22451
30654
measured
No. of unique reflections 6492
8535
7206
10469
8201
7364
7084
10374
9646
No. of reflections
6421
observed [I > 2r(I)]
No. of parameters
508
448
521
472
854
R1/wR2 [I > 2 (I)]
R1/wR2 [all reflections]
r
0.0246/0.0663
0.0248/0.0665
1.053
0.0571/0.1599
0.0641/0.1683
1.050
0.0552/0.1218
0.0780/0.1328
1.106
0.0372/0.0858
0.0384/0.0862
1.169
0.0498/0.1377
0.0533/0.1401
1.065
Goodness of fit (GOF)
D
q
(e ꢁ Åꢀ3
)
–0.32 /0.60
–1.28 /1.50
–0.69 /0.86
–0.43 /0.47
–0.83 /0.95
Upon addition of two equivalents of [CuI(CH3CN)4](BF4) to L3 or
L4, colorless solutions are obtained that are stable for several hours
in the presence of air; these solutions most likely contain the spe-
cies [CuI2(L3)](BF4)2 and [Cu2I (L4)](BF4)2, respectively. Unfortunately,
all crystallization attempts for both complexes resulted in the forma-
tion of residual colorless oils. Both 1H and 13C NMR spectra show the
presence of diamagnetic species with peaks that are shifted com-
pared to the resonances of the free ligand (Figs. S7 and S8). These
results show that displacement of the pyridyl moieties by pyrazolyl
groups leads to ligands that stabilize CuI, even in the presence of air.
As L1, L3 and L4 form CuI disulfide complexes when reacted
with CuI their redox potentials were compared with that of
[CuI2(L2)](BF4)2. We reported the formation of this unique CuI
complex, that is formed upon heating a solution containing the
All four complexes show a quasi-reversible wave that can be
attributed to the CuI/CuII redox-couple with relatively large peak
separations varying from 140–160 mV (Table 3). The compounds
[CuI2(L3)](BF4)2 and [CuI2(L4)](BF4)2 also show smaller waves at
higher oxidation potentials that are scan-rate dependent and can
possibly be attributed to association/dissociation of either acetoni-
trile or the sulfur group of the ligand (Figs. S9 and S10).
When comparing the E1/2 values of the four complexes it can be
seen that E1/2 is much more positive for [CuI2(L3)](BF4)2 (E1/
2 = +0.58 V) and [CuI2(L4)](BF4)2 (E1/2 = +0.52 V) than for the two pyr-
idyl-containing complexes. This confirms that the CuI oxidation state
is stabilized by L3 and L4, in agreement with the oxidation-insensitive
nature of these compounds. The oxidation potential of [CuI2(L3)](BF4)2
is slightly higher than that of [CuI2(L4)](BF4)2, which is in agreement
with the presence of the electron-donating methyl groups in L4. The
half-wave potential of [Cu2I (L1)(CH3CN)](BF4)2 is more positive than
that of [CuI2(L2)](BF4)2, showing that L1 stabilizes CuI better than L2.
CuII
l-thiolate complex of L2 [13]. The cyclic voltammograms of
[CuI2(L1)(CH3CN)](BF4)2, [Cu2I (L3)](BF4)2 and [CuI2(L4)](BF4)2 are
depicted in Fig. 3. The half-wave potentials (E1/2) and the peak-to-
peak separations (
D
Ep) of the CuI complexes containing either L1,
Apparently to allow formation of both CuII
l
-thiolate and CuI disulfide
L2,[13] L3 or L4 are given in Table 3.
species, the half-wave potential needs to be roughly around 0 V

198
E.C.M. Ording-Wenker et al. / Inorganica Chimica Acta 428 (2015) 193–202
Table 2
Selected bond distances (Å) and bond angles (°) for complexes [CuI2(L1)(CH3CN)](BF4)2, [CuI4I(L1)2(Cl)4(CuIICl4)2], [CuI2I(L2)(H2O)(F)(BF4)](BF4)2, [Cu2II(L3)(Cl)2]n(BF4)2n and
[CuI2I(L4)(CH3CN)2(BF4)2]n(BF4)2n
.
[CuI2(L1)(CH3CN)](BF4)2
[CuI4I(L1)2(Cl)4
[CuI2I(L2)(H2O)(F)(BF4)](BF4)2
[CuI2I(L3)(Cl)2]n
(BF4)2n
[CuI2I(L4)(CH3CN)2
(BF4)2]n(BF4)2n
(CuIICl4)2]
Cu1–Cu2
5.7535(6)
6.0370(8)
3.6658(8)
2.7791(11)
2.0420(13)
2.063(3)
1.987(3)
1.995(3)
2.2635(11)
2.8951(11)
2.8141(11)
2.069(3)
4.9571(9)
5.8687(5)
3.5128(6)
2.9522(9)
2.0491(10)
2.126(2)
1.934(2)
1.940(2)
2.2538(7)
2.8136(8)
2.8278(9)
2.117(2)
1.949(2)
1.938(2)
2.2562(7)
2.8438(8)
8.2073(7)
Cu1–Cu1⁄/Cu2⁄
Cu1–S1
3.1251(8)
2.0637(10)
2.443(3)
2.020(3)
2.043(3)
1.947(3)
2.7496(14)
2.0442(19)
2.036(4)
2.001(4)
2.005(4)
1.984(3)
2.598(3)
2.7837(14)
2.039(4)
1.989(4)
1.999(4)
1.913(3)
2.7761(8)
2.0436(10)
2.095(2)
1.978(3)
1.968(2)
S1–S2
Cu1–N1
Cu1–N11/N12
Cu1–N21/N22
Cu1–N3/Cl1/O1
Cu1–Cl1⁄/Cl2⁄/F2/F5⁄
Cu2–S2
1.975(3)
2.4456(17)
5.5963(9)
2.085(2)
1.971(3)
1.958(3)
2.433(9)
1.976(3)
2.4450(18)
83.85(7)
94.83(7)
2.2324(8)
2.181(2)
2.021(3)
1.993(3)
Cu2–N2
Cu2–N31/N32
Cu2–N41/N42
Cu2–Cl2/F1
1.985(3)
1.985(3)
2.2362(10)
2.8914(11)
Cu2–Cl6/Cl1#/N4
Cu2–F5⁄/F7
2.775(3)
85.59(11)
100.99(11)
93.00(12)
175.90(7)
82.76(16)
93.07(16)
171.96(15)
165.01(16)
84.48(12)
105.45(12)
96.41(11)
165.45(7)
S1–Cu1–N1
67.35(6)
127.33(8)
85.14(9)
83.61(9)
98.61(9)
83.30(9)
169.32(3)
81.96(13)
83.49(13)
178.47(9)
165.01(13)
81.72(9)
81.05(7)
94.23(7)
86.51(8)
169.62(3)
81.96(9)
81.93(9)
176.55(7)
163.55(10)
83.04(7)
87.49(7)
95.54(7)
171.61(3)
S1–Cu1–N11/N12
S1–Cu1–N21/N22
S1–Cu1–N3/Cl1⁄/F2/Cl2⁄/F5⁄
N1–Cu1–N11/N12
N1–Cu1–N21/N22
N1–Cu1–N3/Cl1/O1
N11/N12–Cu1–N21/N22
S2–Cu2–N2
S2–Cu2–N31/N32
S2–Cu2–N41/N42
S2–Cu2–Cl6/F5⁄/Cl1#
F1–Cu2–F7
94.18(7)
86.30(9)
172.15(5)
82.15(11)
82.93(10)
175.50(10)
161.61(11)
76.39(10)
76.46(10)
153.15(11)
122.36(11)
90.50(7)
114.08(8)
126.87(8)
89.96(9)
86.74(10)
170.51(3)
173.5(3)
N2–Cu2–N31/N32
N2–Cu2–N41/N42
N2–Cu2–Cl2/F1/N4
N31/N32–Cu2–N41/N42
83.44(10)
82.69(10)
81.23(13)
82.37(14)
179.03(10)
163.57(14)
83.37(17)
95.13(16)
171.03(15)
157.81(16)
82.02(9)
81.76(9)
176.72(7)
163.01(10)
82.01(10)
81.59(10)
170.02(10)
163.46(11)
117.26(11)
Symmetry operation ⁄ = [1 ꢀ x, 1 ꢀ y, 1 ꢀ z] for [Cu4II(L1)2(Cl)4(CuIICl4)2]; [ꢀx, 1 ꢀ y, 1 ꢀ z] for [Cu2II(L2)(H2O)(F)(BF4)](BF4)2; [½ + x, ½ ꢀ y, ½ + z] for [CuI2I(L3)(Cl)2]n(BF4)2n
;
[x, 1 + y, z] for [CuI2I(L4)(CH3CN)2(BF4)2]n(BF4)2n. Symmetry operation # = [ꢀ½ + x, ½ ꢀ y, ꢀ1/2 + z] for [CuI2I(L3)(Cl)2]n(BF4)2n
.
Fig. 3. Cyclic voltammograms of (a) [CuI2(L1)(CH3CN)](BF4)2 and (b) [CuI2(L3)](BF4)2 (black) and [CuI2(L4)](BF4)2 (red) in acetonitrile at 2.0 mM [Cu] concentration. Scan rate
100 mV/s; potentials are given vs. Ag/AgCl. (For interpretation of the references to color in this figure legend, the reader is referred to the web version of this article.)
Table 3
3.3. Synthesis and analyses of CuII complexes
Electrochemical data for CuI complexes with L1, L2, [13] L3 and L4 in CH3CN at
2.0 mM [Cu] concentration. Potentials are given vs Ag/AgCl.
CuII compounds of the ligands L1, L2, L3 and L4 were also syn-
Complex
E1/2 (V)
DEp (mV)
thesized and characterized; single crystals were obtained for the
[CuI2(L1)(CH3CN)](BF4)2
[CuI2(L2)](BF4)2 [13]
[CuI2(L3)](BF4)2
+0.25
+0.07
+0.58
+0.52
150
150
140
160
compounds [Cu4II(L1)2(Cl)4(CuIICl4)2], [CuI2I(L2)(H2O)(F)(BF4)](BF4)2,
[CuI2I(L3)(Cl)2]n(BF4)2n and [CuI2I(L4)(CH3CN)2(BF4)2]n(BF4)2n
.
The
crystallographic and structure refinement data of the CuII complexes
are provided in Table 1. Selected bond distances and angles are given
in Table 2.
[CuI2(L4)](BF4)2
Upon addition of two equivalents of CuIICl2ꢁ2 H2O to L1 in
CH3CN, a green precipitate formed, which is insoluble in CH3CN.
Crystals suitable for X-ray structure determination were grown
by dissolving the green powder in CH3OH and slowly diffusing
(versus Ag/AgCl); more negative potentials will lead to unstable CuI
complexes and more positive potentials will lead to stabilization of
the CuI complexes.

E.C.M. Ording-Wenker et al. / Inorganica Chimica Acta 428 (2015) 193–202
199
diethyl ether into this solution. The compound was found to be
hexanuclear with the formula [CuI4I(L1)2(Cl)4(CuIICl4)2]ꢁ2 CH3OH. A
displacement ellipsoid plot is depicted in Fig. 4.
0.3723(8). The final structure refinement was performed using the
HKL5 format.
Cu1 is in a slightly distorted octahedral geometry in an N3SOF
environment. The elongated Jahn–Teller axis has S1 and F2 at the
axial positions at 2.7496(14) and 2.598(3) Å, respectively. Cu2 is
in a slightly distorted square-pyramidal geometry, but when taking
into account a somewhat longer interaction between Cu2 and F5⁄
(2.775(3) Å) the geometry can be considered to be octahedral with
S2 (2.7837(14) Å) and F5⁄ on the elongated Jahn–Teller axis. The
dinuclear molecule is connected to the neighboring molecule,
which forms a centrosymmetric dimer via a set of four O–Hꢁ ꢁ ꢁF
hydrogen bonds. One of the two hydrogens (H2) of the water mol-
ecule bound to Cu1 is intramolecularly hydrogen-bonded to the
Fꢀ counterion coordinated to Cu2 (1.71(3) Å). The other hydrogen
(H1) is found to be a bifurcated H-bond donor to F5 (intramolecu-
lar hydrogen bond with Hꢁ ꢁ ꢁF = 2.04(3) Å) and F1 (intermolecular
hydrogen bond with Hꢁ ꢁ ꢁF = 2.39(5) Å) atoms. This allows the for-
mation of a quite unique tetranuclear complex with four hydrogen
bonds between the cationic units as well as two stabilizing Cu2–
F5⁄ bonds (Fig. 5).
One third of the added CuII ions appeared not to coordinate to
L1, but to form the counterion CuIICl42ꢀ. The use of three instead
of two equivalents of CuIICl2ꢁ2 H2O in the complex synthesis leads
to a yield of ca. 96% of the hexanuclear compound. It is remarkable
that the formation and coordination of CuIICl42ꢀ is preferred over
coordination of terminal Clꢀ ions. However, it must be noted that
the elemental analysis of the powder indicates the presence of
1
approximately
of terminal Clꢀ counterions instead of CuCl24ꢀ in
4
the crude precipitate.
The compound [Cu4II(L1)2(Cl)4(CuIICl4)2]ꢁ2 CH3OH crystallizes in
the monoclinic space group P21/c and is mostly ordered. The com-
pound is located on an inversion center, and thus has three crystal-
lographically independent metal centers. The crystal lattice contains
some methanol molecules that are disordered over two orientations
(the occupancy factor of the major component of the disorder refines
to 0.834(9)) and some other very disordered solvent molecules1.
In contrast to [CuI2(L1)(CH3CN)](BF4)2, the two copper ions in
[CuI4I(L1)2(Cl)4(CuIICl4)2] that are bound to the ligand are coordinated
to sulfur creating a very similar coordination environment for both
Cu1 and Cu2. The copper ions have a slightly distorted octahedral
geometry with an N3SCl2 coordination environment. The CuII ions
are in an elongated Jahn–Teller distorted octahedron with S and Cl
at the axial positions at 2.7791(11) (Cu1–S1)/2.8141(11) (Cu2–S2)
and 2.8951(11) (Cu1–Cl1⁄)/2.8914(11) Å (Cu2–Cl6), respectively.
The di-(2-pyridylmethyl)amine moieties are coordinated in a merid-
ional fashion in the equatorial plane with CuII-N(pyr) distances of ca.
2.0 Å. The two symmetry related Cu1 ions are bridged by two chlo-
UV–Vis spectra of [Cu2II(L2)(H2O)(F)(BF4)](BF4)2 in either H2O or
CH3CN show two absorptions around 260 nm (LMCT CuII S) and
630 nm (CuII d–d transition).
As the use of CuCl2ꢁ2 H2O can lead to formation of CuCl24ꢀ and
the use of [CuII(H2O)6](BF4)2 might result in Fꢀ abstraction, further
experiments were carried out starting from one equivalent of
CuCl2ꢁ2 H2O and one equivalent of [CuII(H2O)6](BF4)2. Reaction of
a 1:1 mixture of these salts to L3 resulted in the formation of the
polymeric complex [Cu2II(L3)(Cl)2]n(BF4)2nꢁ2n CH3CN, as shown by
X-ray structure determination (see Fig. 6). Starting from the ligand
L4 the very similar compound [CuI2I(L4)(Cl)2]n(BF4)2n was obtained,
of which the crystal structure, synthetic procedure, crystallographic
data and selected bond distances and angles are reported in the
Supporting Information.
ride ions over an inversion center resulting in a planar Cu(
arrangement with a Cu1–Cu1⁄ distance of 3.6658(8) Å. The di-(2-
pyridylmethyl)amine moieties bound to the Cu( -Cl)2Cu core are
l-Cl)2Cu
l
stacked parallel to each other at a distance of 2.692 Å. The angle
between the N11–N1–N21 and N31–N2–N41 meridional planes of
Cu1 and Cu2 is 44.21°.
The ligand L3 coordinates to copper in a fashion very similar to
L1 in [CuI4I(L1)2(Cl)4(CuIICl4)2] or LSSL in the previously reported
complex [CuI4I(LSSL)2(Cl)4](BF4)4 [29]. The angle between the equato-
rial planes of the copper ions (angle between N12–N1–N22 and
[CuI4I(L1)2(Cl)4(CuIICl4)2] dissolved in CH3OH yields a light blue
solution with UV–Vis absorptions at 256 nm (LMCT CuII S or Cl),
290 nm (LMCT CuII S or Cl) and 710 nm (CuII d–d transition). The
LMCT for CuIICl24ꢀ, which is expected to be around 400 nm, is not
observed [22–24]. This indicates that in solution the chlorides might
dissociate to a situation where there is just CuIICl2 present with and
without coordinated L1. When [CuI4I(L1)2(Cl)4(CuIICl4)2] is dissolved
in DMF, similar absorption bands are observed and again bands indi-
cating the presence of CuIICl42ꢀ are not present.
N32–N2–N42 planes) is somewhat larger at 59.74°. The Cu(l-Cl)2Cu
core that is formed by the two bridging chlorides is nearly planar
with a small torsion angle of 0.87(3)°. The distance between Cu1
and Cu2⁄ is 3.5128(6) Å. Both copper centers are in a slightly distorted
octahedral geometry with an N3SCl2 environment. The elongated
Jahn–Teller axis, like in previously discussed crystal structures, is
occupied by the S atom (Cu1–S1 2.9522(9) Å; Cu2–S2 2.8278(9) Å)
and the chloride ion (Cu1–Cl2⁄ 2.8136(8) Å; Cu2–Cl1⁄ 2.8438(8) Å).
The UV–Vis spectrum of [CuI2I(L3)(Cl)2]n(BF4)2n in acetonitrile
shows absorptions at 215 nm (LMCT CuII S or Cl), 284 nm (LMCT
CuII S or Cl) and 670 nm (CuII d–d transition).
When [CuII(H2O)6](BF4)2 is added to L2 a dark blue solution is
formed, from which crystals suitable for X-ray structure determi-
nation were grown. These crystals have the formula [CuI2I(L2)
(H2O)(F)(BF4)](BF4)2 (see Fig. 5) and were isolated in 69% yield indi-
cating that this is the main product of complex formation. CuII pre-
fers five or six coordination, while the ligand only provides four
donor atoms per copper ion. In this case, this results in coordination
of the solvent (H2O), coordination of the usually non-coordinating
BFꢀ4 counterion and an Fꢀ ion that has been abstracted from BFꢀ4 .
Fluoride abstraction from BFꢀ4 is a well-known phenomenon that
has been reported before [25–28]. [CuI2I(L2)(H2O)(F)(BF4)](BF4)2 crys-
tallizes in the monoclinic space group P21/c. The crystal was found to
be twinned non-merohedrally, and the twin relationship corre-
sponds a twofold axis found along the reciprocal-space vector a⁄.
The batch scale factor of the minor component refines to
When two equivalents of [CuII(H2O)6](BF4)2 were added to L4 in
CH3CN and diethyl was allowed to slowly evaporate into the
complex solution, blue crystals suitable for X-ray structure determi-
nation were formed with the formula [CuI2I(L4)(CH3CN)2(BF4)2]n
(BF4)2nꢁ2n CH3CNꢁn C4H10O (Fig. 7). In this case no fluoride ions were
abstracted, but CH3CN and BFꢀ4 molecules coordinate to each copper
ion. The complex could not be isolated as a powder, because the com-
pound turns into an oil upon evaporation of the lattice (and/or coordi-
nating) solvent molecules. It is important that the complex solution
remained within high concentration before vapor diffusion started,
as an oil would be obtained rather than crystals, which is likely caused
by the formation of monomers and oligomers instead of the polymeric
ꢀ
structure. The compound crystallizes in the triclinic space group P1
1
The H atoms of the minor component of the disorder of the lattice methanol
and is partly disordered. Three of the four crystallographically inde-
pendent counterions are found to be disordered over two orientations
(see CIF file in the Supporting Information for occupancy factors of the
major/minor components).
molecules could not be found from difference Fourier maps; see CIF file for occupancy
factors. For the very disordered solvent molecules (possibly diethyl ether), their
contributions have been taken out using the program SQUEEZE for the final
refinement. All details of the SQUEEZE refinement are provided in the final CIF file.

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E.C.M. Ording-Wenker et al. / Inorganica Chimica Acta 428 (2015) 193–202
Fig. 4. Schematic drawing and displacement ellipsoid plot (50% probability level) of [CuI4I(L1)2(Cl)4(CuIICl4)2]ꢁ2 CH3OH. Hydrogen atoms and lattice solvent molecules are
omitted for clarity. Symmetry operation ⁄ = [1 ꢀ x, 1 ꢀ y, 1 ꢀ z]. Py = 2-pyridyl.
Fig. 5. Schematic drawing (with distances in Å) and projection of the cationic part of [CuI2I(L2)(H2O)(F)(BF4)](BF4)2 showing the weaker bonds between two cationic subunits
with dotted lines. Displacement ellipsoids are set at 50% probability level. The non-coordinating counterions and hydrogen atoms (except for those of the coordinated water
molecules) are omitted for clarity. Symmetry operation ⁄ = [ꢀx, 1 ꢀ y, 1 ꢀ z]. Py = 2-pyridyl.
Fig. 6. Schematic drawing and displacement ellipsoid plot (50% probability level) of two of the repeating units in the cationic polymer chain of [CuI2I(L3)(Cl)2]n(BF4)2nꢁ2n
CH3CN. Hydrogen atoms, counterions and lattice solvent molecules are omitted for clarity. Symmetry operation ⁄ = [½ + x, ½ ꢀ y, ½ + z] and # = [ꢀ½ + x, ½ ꢀ y, ꢀ1/2 + z]. Pz = 1-
pyrazolyl.

E.C.M. Ording-Wenker et al. / Inorganica Chimica Acta 428 (2015) 193–202
201
Fig. 7. Displacement ellipsoid plot (50% probability level) of [Cu2II(L4)(CH3CN)2(BF4)2]n(BF4)2nꢁ2n CH3CNꢁn C4H10O. Hydrogen atoms, non-coordinating counterions and lattice
solvent molecules are omitted for clarity. Symmetry operation ⁄ = [x, 1 + y, z] and # = [x, ꢀ1 + y, z]. Pz = 1-(3,5-dimethyl)pyrazolyl.
The polymeric structure formed from L4 with [CuII(H2O)6](BF4)
differs from the structure containing halide ions [CuI2I(L4)(Cl)2]n
(BF4)2n. The equatorialplanes of the copper centers are only at an angle
of 25.58°, whereas they are at an angle of 59.74° in [CuI2I(L3)(Cl)2]n
(BF4)2n. Both copper ions are in a slightly distorted octahedral geome-
try and are coordinated to the di-(N-pyrazolylmethyl)amine moiety of
the ligand and one CH3CN solvent molecule in the equatorial plane.
One BFꢀ4 counterion and either another BF–4 ion or one of the disulfide
Satomsoftheligandarein theaxial positions. Thus, Cu2is coordinated
by two BFꢀ4 ions, one of which is bridging towards a neighboring Cu1⁄
ion. The distance between these copper centers is 6.9966(6) Å, which
is shorter than the Cu1–Cu2 distance (8.2073(7) Å). The BFꢀ4 ions are
on the elongated Jahn–Teller axis of Cu2, but the Cu–F distances are
significantly shorter (2.433(9) and 2.4450(18) Å), than those of
ꢃ2.8 Å found in the other CuII structures described in this paper.
The UV–Vis spectrum of [CuI2I(L4)(CH3CN)2(BF4)2]n(BF4)2n in CH3-
CN shows multiple absorption bands. Four bands are in the LMCT
region at 204, 223, 272 and 335 nm; the absorption at 650 nm can
be attributed to a CuII d–d transition.
the graduate research schools NIOK, HRSMC, and EPL. We thank
John van Dijk and Theo van der Kaaij for ESI-MS analysis and Jos
van Brussel for elemental analysis. We thank undergraduate stu-
dents Stefan de Weger, Mark Boers, Jordi Keijzer, Jacob Boon and
Quentin Siberie for the synthesis of L3 and L4.
Appendix A. Supplementary material
CCDC 1030414–1030420 contain the supplementary crystallo-
graphic data for [Cu2I (L1)(CH3CN)](BF4)2, [CuI4I(L1)2(Cl)4(CuIICl4)2],
[Cu2II(L2)(H2O)(F)(BF4)](BF4)2, [Cu2II(L3)(Cl)2]n(BF4)2n [Cu2II(L4)(CH3-
,
CN)2(BF4)2]n(BF4)2n, [CuI2I(L4)(Cl)2]n(BF4)2n and L1. These data can
be obtained free of charge from The Cambridge Crystallographic
Data Centre via www.ccdc.cam.ac.uk/data_request/cif. Supplemen-
tary data associated with this article can be found, in the online ver-
sion, at http://dx.doi.org/10.1016/j.ica.2014.12.033.
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Acknowledgements
This research has been financially supported by the National
Research School Combination NRSC-Catalysis, a joint activity of

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