Li+, Cu+, and Ag+ oligonuclear structures with the sterically demanding bis(3,5-tertbutylpyrazol-1-yl)dithioacetate heteroscorpionate ligand

Article abstract of DOI:10.1021/ic100886x

The heteroscorpionate N₂S₂ donor ligand bis(3,5-tertbutylpyrazol-1-yl)dithioacetate (L) was prepared as a Li⁺ trinuclear complex, which co-crystallizes with tetrahydrofuran (THF) solvent molecules: [Li(L)]₃(2.25)THF. When [Li(L)]₃ was reacted with AgBF₄ or [Cu(CH₃CN)₄]BF ₄, the oligonuclear species [Ag(L)]₃ and [Cu ₅(L)₄]BF₄ were isolated and structurally characterized. The Ag⁺ complex presents an irregular trinuclear structure in which three AgL moieties define a central trigonal site that may potentially host a fourth metal ion. The Cu⁺ complex exhibits a highly symmetric pentanuclear structure in which four equivalent CuL moieties shape an internal tetrahedral site occupied by an additional Cu⁺ ion. According to electrospray-mass spectrometry (ESI-MS) and ¹H diffusion NMR spectroscopy, the Ag⁺ and Cu⁺ complexes maintain oligonuclear structures in solution. In particular, the Cu⁺ pentanuclear complex, once dissolved, rapidly equilibrates with the tetranuclear species [Cu₄(L)₃]⁺. This is confirmed by the presence of two sets of NMR signals, which demonstrated a change in ratio at different complex concentrations effected by a NMR dilution titration. Variable temperature NMR experiments (210-303 K) defined the activation parameters associated with the fluxional behavior of [Cu₅(L)₄]BF ₄ and [Cu₄(L)₃]⁺, and these results are consistent with intramolecular rearrangements in both species (ΔS ^? < 0).

Full text of DOI:10.1021/ic100886x

Inorg. Chem. 2010, 49, 7007–7015 7007
DOI: 10.1021/ic100886x
þ
þ
þ
Li , Cu , and Ag Oligonuclear Structures with the Sterically Demanding
Bis(3,5-tertbutylpyrazol-1-yl)dithioacetate Heteroscorpionate Ligand
Irene Bassanetti, Marcello Gennari, Luciano Marchi ꢀo ,* Mattia Terenghi, and Lisa Elviri
Dipartimento di Chimica Generale ed Inorganica, Chimica Analitica, Chimica Fisica, Universit aꢀ degli Studi di
Parma, viale G. P. Usberti 17/a, I 43100 Parma, Italy
Received May 5, 2010
þ
The heteroscorpionate N S donor ligand bis(3,5-tertbutylpyrazol-1-yl)dithioacetate (L) was prepared as a Li
2
2
trinuclear complex, which co-crystallizes with tetrahydrofuran (THF) solvent molecules: [Li(L)] (2.25)THF. When
3
3
[
isolated and structurally characterized. The Ag complex presents an irregular trinuclear structure in which three AgL
Li(L)] was reacted with AgBF or [Cu(CH CN) ]BF , the oligonuclear species [Ag(L)] and [Cu (L) ]BF were
3 4 3 4 4 3 5 4 4
þ
þ
moieties define a central trigonal site that may potentially host a fourth metal ion. The Cu complex exhibits a highly
symmetric pentanuclear structure in which four equivalent CuL moieties shape an internal tetrahedral site occupied by
þ
þ
1
an additional Cu ion. According to electrospray-mass spectrometry (ESI-MS) and H diffusion NMR spectroscopy,
þ
þ
the Ag and Cu complexes maintain oligonuclear structures in solution. In particular, the Cu pentanuclear complex,
once dissolved, rapidly equilibrates with the tetranuclear species [Cu (L) ] . This is confirmed by the presence of two
þ
4
3
sets of NMR signals, which demonstrated a change in ratio at different complex concentrations effected by a NMR
dilution titration. Variable temperature NMR experiments (210-303 K) defined the activation parameters associated
þ
with the fluxional behavior of [Cu (L) ]BF and [Cu (L) ] , and these results are consistent with intramolecular
3
rearrangements in both species (ΔS < 0).
5
4
4
4
q
3
-5
6-10
11-13
Introduction
catalysis,
and supramolecular chemistry.
class of compounds is the hydrotris(pyrazolyl)borate anion
bioinorganic chemistry,
magnetism,
1
4-16
1,2
The first member of this
Scorpionate ligands are a versatile class of compounds
that have found applications in many research fields, including
17
(
Tp), in which the three nitrogen atoms can occupy a
18
trigonal face of a coordination polyhedron. Throughout
the years, a number of modifications have been contrived to
tunethe donor ability of Tp, which primarily consist of (a) the
introduction of steric hindrance on the pyrazole rings and (b)
*
(
To whom correspondence should be addressed. E-mail: marchio@unipr.it.
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(
the replacement of pyrazole with other moieties bearing
(
19-33
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(
the coordination properties of the B-centered scorpionates
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r 2010 American Chemical Society
Published on Web 07/06/2010
pubs.acs.org/IC

7
008 Inorganic Chemistry, Vol. 49, No. 15, 2010
Bassanetti et al.
þ
þ
Scheme 1. Ligand Synthesis
soft metal ions, such as Cu and Ag . The presence of the
dithioacetate group renders this ligand potentially N2S2
tetradentate because both sulfur atoms can be involved in
metal binding for this moiety. Furthermore, the bispyrazole
(
N ) and dithioacetate (S ) donor systems are linked by the
2 2
tetrahedral central carbon atom, which introduces divergent
binding sites at an angle of ∼109°. These features represent
the main reason for the formation of oligonuclear complexes
þ
þ
þ
with Li , Cu , and Ag . In addition, the presence of bulky
t-Bu groups on the pyrazole rings provides additional steric
and hydrophobic protection to the central core of these
homoleptic complexes.
particular, C-centered heteroscorpionate ligands have been
34
35-38
39-41
prepared that exhibit Cp, phenol/alcohol,
thioether,
42-44
or a carboxyl and thiocarboxyl
residues in addition to
Because the X-ray structures of [Li(L)] , [Ag(L)] , and
the N donor system. Furthermore, polytopic ligands desig-
3
3
2
[
Cu (L) ]BF indicate that L tends to support oligomers
ned to produce supramolecular architectures have also been
5 4 4
45-47
(through S-bridging), we wished to investigate the nuclearity
described.
of these species in solution. This study was performed by
In the present work, we have studied the coordination
properties of the C-centered heteroscorpionate ligand bis-
4
9-51
means of electrospray-mass (ESI-MS) spectrometry
52-54
combined with dilution, diffusion,
and variable tem-
(3,5-tertbutylpyrazol-1-yl)dithioacetate (L, Scheme 1). Homo-
1
perature H NMR experiments. The silver complex occurs in
solution as a trinuclear entity whereas the copper complex
exhibits a pentanuclear-tetranuclear equilibrium. According
to the X-ray characterization, the disposition of the ML units
in the oligonuclear structures provides a central cavity that
may host an additional metal ion. In the silver complex, the
shape of this cavity is suitable for a relatively small cation
favoring a trigonal planar geometry, whereas in the copper
complex, the tetrahedral central site is already occupied by a
logous ligands have been previously reported, and their
binding properties were assessed mainly with early transition
44,48
metals and in the presence of co-ligands.
Because the
chemistry of this class of scorpionateshas been littleexplored,
we wish to extend the investigation concerning the coordina-
tion capabilities of L with late transition metals, which are
likely to exploit the affinity of the dithioacetate groups for
(
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þ
0
þ
0
Cu ion. The possibility that mixed MM L (M = Cu , M =
þ
Ag ) complexesmay formwas further exploredwith ESI-MS
4
(
spectrometry.
(
Experimental Section
(
General Procedures. 3,5-Di-tert-butylpyrazole was obtained
from 2,2,6,6-tetramethyl-3,5-heptanedione and hydrazine hy-
(
55
drate using a reported literaturemethod. Bis(3,5-t-butylpyrazol-
1-yl)methane was prepared according to the general method
employed for the synthesis of bis(pyrazolyl)methanes via reac-
tion of azoles with CH Cl under phase transfer catalysis con-
(
(
(
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Sanchez, A.; Sanchez-Barba, L.; Rodriguez, A. M.; Maestro, M. A.
56,57
ditions.
3 4 4
[Cu(CH CN) ]BF was prepared as previously
J. Am. Chem. Soc. 2004, 126, 1330–1331.
5
8
described. All other reagents and solvents were commercially
available. Tetrahydrofuran (THF) and MeOH were distilled
over Na/benzophenone and CaH , respectively, and carbon
(
35) Hoffman, J. T.; Carrano, C. J. Inorg. Chim. Acta 2006, 359, 1248–
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(
2
˚
disulfide was stored over 3 A molecular sieves before use. The
2
004, 260–266.
syntheses were performed under inert gas (N
techniques. Single crystals of the complexes were obtained in
a glovebox (N ). Infrared spectra were recorded from 4000
2
) using Schlenk
(
37) Higgs, T. C.; Carrano, C. J. Inorg. Chem. 1997, 36, 291–297.
(
38) Gennari, M.; Tegoni, M.; Lanfranchi, M.; Pellinghelli, M. A.;
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2
-1
(
to 700 cm on a Perkin-Elmer FT-IR Nexus spectrometer
equipped with a Smart Orbit HATR accessory (diamond
crystal). H NMR spectra were recorded on a Bruker Avance
4
277–4279.
(
40) Hammes, B. S.; Carrano, C. J. Chem. Commun. 2000, 1635–1636.
1
(
41) Gennari, M.; Tegoni, M.; Lanfranchi, M.; Pellinghelli, M. A.;
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Hermosilla, F.; Diez-Barra, E.; Lara-Sanchez, A.; Fernandez-Lopez, M.;
(
(
49) Spasojevic, I.; Boukhalfa, H.; Stevens, R. D.; Crumbliss, A. L. Inorg.
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6
26, 16–23.
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(
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Article
Inorganic Chemistry, Vol. 49, No. 15, 2010 7009
Table 1. Summary of X-ray Crystallographic Data for [Li(L)]
3
3 (2.25)THF, [Cu5(L)
4 4 3
]BF , and [Ag(L)]
[Li(L)]
3
(2.25)THF
[Cu
5
(L)
4
]BF
4
[Ag(L)]
3
3
empirical formula
formula weight
color, habit
C
81
H
135Li
3
N
12 2.25
O S
6
C
96
H
156BCu
5
F
4
N
S
16 8
72 3 12 6
C H117Ag N S
1666.75
red, prism
1526.19
orange, block
2195.36
red, prism
crystal size, mm
crystal system
space group
0.23 ꢀ 0.18 ꢀ 0.15
monoclinic
C2/c
27.095(1)
15.709(1)
46.906(2)
90
110.35(1)
90
18719(2)
8
293(2)
0.37 ꢀ 0.22 ꢀ 0.20
tetragonal
I4
20.830(3)
20.830(3)
13.270(2)
90
90
90
5758(2)
2
293(2)
0.45 ꢀ 0.35 ꢀ 0.20
triclinic
P1
˚
a, A
15.396(2)
15.833(2)
21.295(3)
68.871(2)
83.645(3)
61.547(2)
4245(1)
2
˚
b, A
˚
c, A
R,deg.
β, deg.
γ, deg.
3
˚
V, A
Z
T, K
173(2)
1.304
0.877
3
F (calc), Mg/m
1.083
0.193
1.266
1.108
-
1
μ, mm
θ range, deg.
no. of rflcn/obsv
GoF
1.52 to 24.72
15986/10161
1.019
0.0594
0.1461
1.38 to 26.53
5981/5055
1.007
0.0377
0.0964
1.51 to 27.90
19567/13098
1.006
0.0323
0.0596
a
R1
wR2
a
P
P
P
P
a
2
2 2
2 2 1/2
2
2
2
2
2
R1 = ||F
o
| - |F
c
||/ |F
o
|, wR2 = [ w(F
o
- F
c
) / w(F
o
) ] , w = 1/[σ (F
o
) þ (aP) þ bP], where P = [max(F
o
,0) þ 2F
c
]/3.
3
00 spectrometer using standard Bruker pulse sequences. Chemi-
15 min, the mixture was filtered, washed with MeOH (5 mL), dried
and collected ([Ag(L)] , 160 mg, 0.096 mmol, 66%). IR (cm ):
2962s, 2904w, 2871w, 1545 m, 1458 m, 1361s, 1319w, 1252 m,
1228s, 1105 m, 1084 m, 1064 m, 992s, 875w, 851w, 798vs, 750s. H
-
1
cal shifts are reported in parts per million (ppm) referenced to
residual solvent protons. Elemental analyses (C, H, N) were
performed with a Carlo Erba EA 1108 automated analyzer.
3
1
Synthesis of [Li(L)]
3
(2.25)THF. n-BuLi (6 mL, 1.6 M in
NMR (300 MHz, (CD
18H, CH ), 6.16 (s, 2H, CH pz), 7.86 (s, 1H, CHcentral). Anal.
Calcd. for C72 Ag (1666.78): C, 51.88; H, 7.07; N, 10.08.
Found: C, 51.62; H, 6.93; N, 9.94. ESI-MS (p.i., CH OH, m/z,
Na , 1705.25, 32
3 2 3
) CO, 300 K): δ 1.29 (s, 18H, CH ), 1.41 (s,
3
hexane, 9.60 mmol) was slowly added to a solution of bis(3,5-t-
butylpyrazol-1-yl)methane (3.13 g, 8.40 mmol) in THF (100 mL)
at -78 °C. After stirring the orange solution for 15 min, carbon
3
H N
117 12
S
6
3
3
3
þ
þ
disulfide (0.60 mL, F = 1.266 g/cm , 9.98 mmol) was slowly
I%): 1666.33, 12 [Ag(L)]
3
; 1689.25, 100 [Ag(L)]
3
þ
þ
added, and the resulting deep red solution was allowed to warm
to room temperature with stirring. After 3 h, the solvents were
removed in vacuo, and the residue was washed with hexane (2 ꢀ
[Ag(L)] K , 1773.42, 7 [Ag (L)
3 4
3
] . Red crystals suitable for X-ray
2 2
data collection were obtained by layering MeOH over a CH Cl
solution of the product at -18 °C.
X-ray Crystallography. A summary of data collection and
1
(
(
5 mL), dried and collected as a pale orange powder ([Li(L)]
3
3
-
1
2.25)THF, 2.6 g, 1.70 mmol, 61%). IR (cm ): ∼3300 m, br
structure refinement for [Li(L)]3 (2.25)THF, [Cu (L) ]BF , and
5 4 4
3
H
2
O), 2960 m, 2905 m, 2871 m, 1650 m, 1541 m, 1463 m, 1364 m,
3
[Ag(L)] is reported in Table 1. Single crystal data were collected
1
319 m, 1253 m, 1228 m, 1088s, 1060s, 1007s, 878s, 853s. H
1
with a Bruker Smart 1000 and with a Bruker Smart APEXII area
˚
NMR (300 MHz, CDCl ) δ 1.21 (s, 18H, CH ), 1.43 (s, 18H,
detector diffractometers (Mo KR; λ = 0.71073 A). Cell para-
3
3
CH (t-Bu), 1.89 (m, 4H, CH (THF)), 3.82 (m, 4H, OCH -
meters were refined from the observed setting angles and
detector positions of selected strong reflections. Intensities were
integrated from several series of exposure frames that covered
3
2
2
(THF)), 5.96 (s, 2H, CH pz), 7.07 (s, 1H, CHcentral). According
to the intensities of the signals the THF content is consistent
5
9
with ∼2.2 molecules for each [Li(L)] complex. Anal. Calcd for
the sphere of reciprocal space. An absorption correction was
3
6
0
C
1
72
H
117
N
12
S
6
Li
3
2.25THF (1526.24): C, 63.74; H, 8.91; N,
1.01. Found: C, 63.31; H, 8.49; N, 11.48. Dark orange single
applied using the program SADABS with minimum and maxi-
mum transmission factors of 0.845-1.000 ([Li(L)] (2.25)-
3
3
crystals suitable for X-ray data collection were obtained by
layering hexane over a THF solution of the product, which
corresponded to [Li(L)]
THF), 0.865-1.000 ([Cu
5
(L) ]BF
4
4
) and 0.663-1.000 ([Ag(L)]
3
).
61
The structures were solved by direct methods (SIR97) and
refined with full-matrix least-squares (SHELXL-97) using
6
2
3
3
(2.25)THF.
6
3
Synthesis of [Cu
420 mg, 1.33 mmol) in MeOH (30 mL) was added to a solution
of [Li(L)] (2.25)THF (500 mg, 0.328 mmol) in MeOH (10 mL),
5
(L)
4
](BF
4
). A solution of [Cu(CH
3
4
CN) ]BF
4
the Wingx software package. Non-hydrogen atoms were re-
fined anisotropically, and the hydrogen atoms were placed at
(
their calculated positions. The crystals of [Li(L)] (2.25)THF
3
3
3
3
and a dark brown precipitate was formed. After 0.5 h, the
solution was filtered, washed with MeOH (5 mL), dried and
were grown from a THF solution, and one molecule of this
solvent of crystallization was found disordered in three posi-
tions with site occupancy factors of 0.33 for each fragment.
Another molecule of THF was located on a binary axis and was
refined with a site occupancy factor of 0.25. Ortep diagrams
-
1
collected ([Cu
5
L
4
](BF
4
), 465 mg, 0.212 mmol, 86%). IR (cm ):
2
1
2
953s, 2904w, 2855w, 1534 m, 1452 m, 1364s, 1321w, 1255 m,
222s, 1079s, 1052vs, 1014s, 794s. H NMR (300 MHz, CD Cl ,
1
2
2
3
30 K): δ 0.94-1.36 (m br, 36H, CH ), 5.94 (s, 1H, CH pz), 6.01
(
C H N S Cu BF (2195.44): C, 52.52; H, 7.16; N, 10.21.
s, 1H, CH pz), 7.43 (s, 1H, CHcentral). Anal. Calcd. for
(
59) SMART (control) and SAINT (integration) software for CCD sys-
tems; Bruker AXS: Madison, WI, 1994.
60) Area-Detector Absorption Correction; Siemens Industrial Automation
9
6
156 16
8
5
4
3
Found: C, 52.26; H, 6.70; N, 9.95. ESI-MS (p.i., CH OH, m/z,
(
þ
þ
I%): 1597.68, 34 [Cu
4
(L)
3
] ; 2107.90, 100 [Cu
5
(L)
4
] . Dark red
Inc.: Madison, WI, 1996.
single crystals suitable for X-ray data collection were obtained
by layering hexane over a solution of the product in CH Cl .
Synthesis of [Ag(L)] . [Li(L)] (2.25)THF (223 mg, 0.146 mmol)
and AgBF (90 mg, 0.462 mmol), were dissolved in MeOH
4
(15 mL), and the initial red solution yielded a red precipitate. After
(61) Altomare, A.; Burla, M. C.; Camalli, M.; Cascarano, G. L.;
Giacovazzo, C.; Guagliardi, A.; Moliterni, A. G. G.; Polidori, G.; Spagna,
R. J. Appl. Crystallogr. 1999, 32, 115–119.
2
2
3
3
3
(
62) Sheldrick, G. M. SHELX97, Programs for Crystal Structure Anal-
ysis, Release 97-2; University of G €o ttingen: G €o ttingen, Germany, 1997.
(63) Farrugia, L. J. J. Appl. Crystallogr. 1999, 32, 837–838.

7
010 Inorganic Chemistry, Vol. 49, No. 15, 2010
Bassanetti et al.
6
4
65
were prepared using the ORTEP-3 and Mercury 2.0 pro-
grams. CCDC 773133-773135 contains the supplementary
crystallographic data for this paper.
Results and Discussion
69
The synthesis of L follows a reported procedure, based
on the reaction between differently substituted bis(pyrazol-1-
yl)methanes and butyl lithium in THF followed by treatment
ESI-MS experiments. An LTQ XL linear ion trap mass spec-
trometer (Thermo Electron Corporation, San Jos ꢀe , CA) equi-
pped with an ESI/API Ion Max source was used. The ESI source
was connected to a solvent delivery system (Finnigan Surveyor,
MS Pump Plus) that was used to pump a continuous flow of
methanol (200 μL min- ). Instrumental tuning was performed
by direct infusion of a freshly prepared methanolic solution
with CS at low temperature (Scheme 1). The heteroscorpio-
2
nate ligands previously prepared according to this method
include bis(3,5dimethylpyrazol-1-yl)dithioacetate and bis-
(3,5diphenylpyrazol-1-yl)dithioacetate. These ligands have
been employed primarily with early transition metals, such
as Ti, Y, and Sc, and they behave as N S donors that form
mononuclear complexes.
of L are virtually identical to those of the aforementioned
heteroscorpionates, but the increased steric hindrance pro-
vided by the t-Bu residues is expected to affect the geometry
of the resulting complexes. The lithium complex crystallizes
1
5 4 4
(1 nM) of pure [Cu (L) ]BF into the continuous flow of meth-
anol from the pump. The most abundant ion at m/z 2108, which
2
44,70,71
The coordination capabilities
þ
corresponds to the [Cu
5
(L)
4
]
metal cluster, was used to opti-
mize source ionization efficiency and lens ion transmission.
Working parameters were set as follows: spray voltage, 3.5 kV;
capillary voltage, 15 V; capillary temperature, 200 °C; tube lens,
6
5 V. Samples were analyzed in flow injection mode by means
of a six-port valve equipped with a 2 μL sample loop. Mass
spectra were recorded in full scan analysis mode in the range
as a trinuclear species [Li(L)] , whereas the less hindered
3
bis(3,5diphenylpyrazol-1-yl)dithioacetate ligand affords a
mononuclear complex in the presence of adventitious water.
1
000-2500 m/z.
þ
5 4 4 4
For titration experiments of [Cu (L) ]BF with AgBF , six
The formation of oligomeric structures with Li is not new
solutions were prepared in methanol and incubated at room
temperature for 15 h; each solution contained a fixed concen-
tration of [Cu (L) ]BF (50 μM) and an increasing concentra-
for this type of ligand; the bis(3,5dimethylpyrazol-1-yl)-
acetate ligand (N O donor) has also yielded a tetranuclear
2
5
4
4
44
complex. Treatment of [Li(L)] with 3 equiv of AgBF4
3
tion of AgBF
final [Ag ]/[[Cu
4
(20, 40, 60, 80, 100, 250 μM), which resulted in
(L) ]BF ] ratios of 0.40, 0.85, 1.30, 1.70, 2.10,
þ
yielded a trinuclear [Ag(L)] complex. The same reaction was
3
5
4
4
þ
attempted with Cu by treating [Li(L)] with 3 equiv of
and 5.30, respectively.
PGSE Measurements. H PGSE (pulsed gradient spin echo)
3
1
[
Cu(CH CN) ]BF ; however, the pentanuclear [Cu (L) ]BF
3 4 4 5 4 4
NMR measurements were performed for [Ag(L)] and for a
3
complex precipitated from the reaction mixture. The synth-
esis was optimized by using a slight excess of copper (Cu/L
ratio of 1.3), which is consistent with the 5/4 Cu/L ratio
þ
þ
mixture of [Cu
standard stimulated echo (STE) sequence on a Bruker Avance
00 spectrometer was employed (room temperature without
4
(L)
3
] /[Cu
5
(L)
4
]
(ratio 1/0.6) in CD
2
Cl
2
. A
1
3
reported in the X-ray structure. As discussed in the H NMR
spinning). The most intense signals were taken into account
during the data processing. The dependence of the resonance
intensity (I) on the gradient strength (g) is described by the
following equation:
section (vide infra), the [Cu (L) ]BF complex is in equilib-
5
4
4
þ
rium with a [Cu (L) ] tetranuclear entity in CD Cl solu-
4
3
2
2
tion. The propensity to generate oligonuclear species appears
to be characteristic of L, arising from (a) the bridging ability
of the thioacetate group, (b) the steric hindrance in the form
of t-Bu residues, and (c) the absence of ancillary ligands. The
2
2
2
-
Dγ g δ ðΔ - δ=3Þ
I ¼ I0e
þ
þ
Cu and Ag complexes are dark redair-stable solids that are
soluble in common organic solvents.
where I = observed intensity (attenuated signal intensity), I
0
=
reference intensity (unattenuated signal intensity), D=diffusion
coefficient, γ=nucleus gyromagnetic ratio, g=gradient stren-
gth, δ=gradient duration, and Δ = diffusion delay. The para-
meters δ (1.6 ms) and Δ (60 ms) were kept constant during the
experiments, whereas g was varied from 2 to 95% in 16 steps. All
spectra were acquired using 16 K points and processed with a
line broadening of 1.0 Hz. PGSE data were treated by applying a
Solid-State Structures. Relevant geometric parameters
for [Li(L)] (2.25)THF, [Cu (L) ]BF , and [Ag(L)] are
3
3
5
4
4
3
reported in Tables 2-4, and the molecular structures of
the three compounds are depicted in Figures 1-3. The
Li complex is trinuclear, and each metal is surrounded
þ
5
4
by two nitrogen and two sulfur atoms, which define a
Li S ring that is in a chair conformation (Figure 1). Each
ligand chelates in the N S coordination mode on one
procedure reported in the literature, which uses an internal
standard (tetrakis(trimethylsilyl)silane, TMSS; rH
TMSS
(hydro-
(van der Waals radius) = 4.28
3 3
TMSS
dynamic radius) ≈ rvdW
2
6
A). The van der Waals volume (VvdW
6
67
) and the solvent-
of [Ag(L)] and [Cu (L) ]BF were
˚
metal and bridges a second metal with the same sulfur
atom. The other sulfur atom does not participate in metal
chelation and points outside the Li S hexa-atomic ring.
6
)
8
excluded volume (VSE
3
5
4
4
computed from the atomic coordinates derived using X-ray
geometries. The X-ray volumes (VX-ray) were computed by
dividing the unit cell volume by the number of oligonuclear
entities contained in the unit cell. Because there is no crystal-
lization solvent for [Ag(L)] and [Cu (L) ]BF , this latter pro-
3 5 4 4
cedure should provide reliable values for the molecular volume.
3
3
The Li-N bond distances are not equivalent; one bond is
significantly longer than the other (Table 2). This inequi-
valence is also observed for the Li-S distances; the Li-S
chelate
ꢁ
˚
is significantly longer than the Li-Sbridge (∼0.06 A). The
metal geometry can be described as trigonal pyramidal
with the metal residing in the coordination plane. Another
characteristic feature of the complex is the non-symmetric
(
(
64) Farrugia, L. J. J. Appl. Crystallogr. 1997, 30, 568.
65) Macrae, C. F.; Edgington, P. R.; McCabe, P.; Pidcock, E.; Shields,
G. P.; Taylor, R.; Towler, M.; van de Streek, J. J. Appl. Crystallogr. 2006, 39,
53–457.
66) Dinnebier, R. E.; Dollase, W. A.; Helluy, X.; Kummerlen, J.; Sebald,
A.; Schmidt, M. U.; Pagola, S.; Stephens, P. W.; Van Smaalen, S. Acta
Crystallogr., Sect B: Struct. Sci. 1999, B55, 1014–1029.
4
(69) Otero, A.; Fernandez-Baeza, J.; Antinolo, A.; Tejeda, J.; Lara-
Sanchez, A. J. Chem. Soc., Dalton Trans. 2004, 1499–1510.
(70) Otero, A.; Fernandez-Baeza, J.; Antinolo, A.; Tejeda, J.; Lara-
Sanchez, A.; Sanchez-Barba, L.; Rodriguez, A. M. J. Chem. Soc., Dalton
Trans. 2004, 3963–3969.
(71) Otero, A.; Fernandez-Baeza, J.; Antinolo, A.; Tejeda, J.; Lara-
Sanchez, A.; Sanchez-Barba, L.; Martinez-Caballero, E.; Rodriguez,
A. M.; Lopez-Solera, I. Inorg. Chem. 2005, 44, 5336–5344.
(
(
(
67) Bondi, A. J. Phys. Chem. 1964, 68, 441–451.
68) VSE takes into account that the cavities and inlets of the solute are not
accessible by the solvent so that VSE > VvdW. Connolly, M. L. J. Am. Chem.
Soc. 1985, 107, 1118–1124.

Article
Inorganic Chemistry, Vol. 49, No. 15, 2010 7011
˚
Table 2. Selected Bond Lengths (A) and Angles (deg) for [Li(L)]
3
3 (2.25)THF
Li(1)-N(21)
2.077(5)
2.130(5)
87.9(2)
142.8(2)
129.3(2)
Li(1)-S(19)
2.539(5)
2.580(5)
90.54(19)
91.68(18)
89.59(16)
Li(1)-N(22)
Li(1)-S(13)
N(21)-Li(1)-N(22)
N(21)-Li(1)-S(19)
N(22)-Li(1)-S(19)
N(21)-Li(1)-S(13)
N(22)-Li(1)-S(13)
S(19)-Li(1)-S(13)
Li(2)-N(24)
2.073(6)
2.144(6)
88.2(2)
141.7(3)
130.1(3)
Li(2)-S(13)
2.535(5)
2.620(6)
89.1(2)
91.9(2)
89.39(17)
Li(2)-N(25)
Li(2)-S(16)
N(24)-Li(2)-N(25)
N(24)-Li(2)-S(13)
N(25)-Li(2)-S(13)
N(24)-Li(2)-S(16)
N(25)-Li(2)-S(16)
S(13)-Li(2)-S(16)
Li(3)-N(27)
2.109(6)
2.144(5)
87.6(2)
146.3(2)
126.1(2)
Li(3)-S(16)
2.535(5)
2.606(5)
89.1(2)
92.08(19)
91.24(16)
Li(3)-N(28)
Li(3)-S(19)
N(27)-Li(3)-N(28)
N(27)-Li(3)-S(16)
N(28)-Li(3)-S(16)
N(27)-Li(3)-S(19)
N(28)-Li(3)-S(19)
S(16)-Li(3)-S(19)
˚
Table 3. Selected Bond Lengths (A) and Angles (deg) for [Cu
5
(L)
4
]BF
4
0
Cu(1)-N(21)
1.970(2)
2.293(1)
2.1633(9)
2.684(3)
2.3106(8)
S(12)-Cu(1)-S(22)
N(21)-Cu(1)-S(12)
N(21)-Cu(1)-S(22)
113.40(3)
106.73(8)
139.88(8)
Cu(1)-S(12)
0
0
Cu(1)-S(22)
Cu(1)-N(23)
Cu(2)-S(12)
0
S(12) -Cu(2)-S(12)
S(12) -Cu(2)-S(12)
106.20(2)
116.23(4)
0
00
0
00
=
y-1/2; -xþ1/2; -zþ1/2. = -yþ1/2; xþ1/2; -zþ1/2.
˚
Table 4. Selected Bond Lengths (A) and Angles (deg) for [Ag(L)]
3
Ag(1)-N(23)
2.421(2)
2.523(2)
Ag(1)-S(28)
Ag(1)-S(12)
2.4644(7)
2.5939(7)
86.59(5)
130.64(2)
86.64(4)
Ag(1)-N(21)
N(23)-Ag(1)-S(28)
132.90(5) N(23)-Ag(1)-S(12)
S(28)-Ag(1)-S(12)
127.80(4) N(21)-Ag(1)-S(12)
N(23)-Ag(1)-N(21) 72.56(6)
S(28)-Ag(1)-N(21)
Ag(2)-N(26)
2.399(2)
2.616(2)
Ag(2)-S(22)
Ag(2)-S(15)
2.4606(7)
2.5938(7)
Ag(2)-N(24)
N(26)-Ag(2)-S(22)
N(26)-Ag(2)-S(15)
S(22)-Ag(2)-S(15)
147.16(4) N(26)-Ag(2)-N(24) 69.18(6)
89.87(5)
116.87(2) S(15)-Ag(2)-N(24)
S(22)-Ag(2)-N(24)
125.16(5)
90.64(4)
3
Figure 1. Top, ORTEP drawing of [Li(L)] (2.25)THF at the 30%
3
thermal ellipsoids probability level. The hydrogen atoms and the crystal-
lization solvent molecules are omitted for clarity. Bottom, a spacefilling
Ag(3)-N(27)
2.344(2)
2.622(2)
Ag(3)-S(25)
Ag(3)-S(18)
2.4399(7)
2.5967(7)
Ag(3)-N(29)
3
representation of [Li(L)] (2.25)THF; top view (left) and bottom view
3
N(27)-Ag(3)-S(25)
N(27)-Ag(3)-S(18)
S(25)-Ag(3)-S(18)
137.50(5) N(27)-Ag(3)-N(29) 73.59(7)
95.34(4)
123.51(2) S(18)-Ag(3)-N(29)
(
right).
S(25)-Ag(3)-N(29)
126.19(5)
78.71(4)
by the t-Bu groups and the appropriately sized THF
molecule.
placement of the two pyrazole rings that provide the N2
system. This placement has consequences for the overall
shape of the trinuclear assembly; three t-Bu groups
located on one side of the Li S moiety diverge from the
The copper complex exhibits a pentanuclear structure
in which four CuL units provide an internal tetrahedral
pocket that is occupied by an additional Cu ion, and the
þ
3
3
þ
positive charge of the [Cu (L) ] moiety is balanced by a
5
4
molecular center, whereas the other three t-Bu groups on
the opposite side of the Li S moiety are converging
-
BF4 anion. The complex crystallizes in the tetragonal I4
space group, and the asymmetric unit is represented by
one CuL entity (Figure 2). Each peripheral metal presents
a trigonal planar geometry defined by a nitrogen and a
sulfur atom of one ligand and by a bridging sulfur atom
of another ligand. The nitrogen atom of one pyrazole
ring does not take part in the metal coordination because
3
3
toward the center (Figure 1). In the first case, a hydro-
phobic pocket is generated that hosts a THF solvent
molecule. This is a surprising finding for two reasons:
THF, when present, is usually bound to lithium, and
7
2
Li-S interactions are less common than Li-O bonds.
In a previous report, the less sterically hindered bis(3,5-
diphenylpyrazol-1-yl)dithioacetate ligand yielded a tetra-
hedral mononuclear Li complex (N O coordination)
ꢁ
˚
of a particularly long (2.684(8) A) Cu-N distance, and
the metal is located inside the trigonal plane; the con-
siderable mismatch between the nitrogen lone pair and
the copper atom is further evidence that this pyrazole ring
is non-coordinating. The metal at the center (Cu(2)) is
within a nearly perfect tetrahedral geometry, and the
Cu-S bond distances are significantly longer than those
of the peripheral copper atoms. The Cu S cluster is
þ
2
-
2
that lacked interaction of the -CS2 moiety with the
metal in the presence of THF and adventitious water. In
Li(L)] (2.25)THF, the preference for sulfur over oxygen
by the Li atom may plausibly be related to favorable
interactions between the hydrophobic pocket formed
4
4
[
3
3
þ
5
8
surrounded by a hydrophobic shield provided by the 16
t-Bu groups.
(
72) CCDC 2010 Release.

7
012 Inorganic Chemistry, Vol. 49, No. 15, 2010
Bassanetti et al.
Figure 2. ORTEP drawing of [Cu
soids probability level. The methyl groups of the t-Bu residues, the BF
anion, and the hydrogen atoms are omitted for clarity. Symmetry codes:
5 4 4
(L) ]BF at the 30% thermal ellip-
-
4
0
00
000
=
y-1/2; 1/2-x; 1/2-z, = -x; 1-y; z, = 1/2-y; 1/2þx; 1/2-z.
5 4 4 3
Figure 4. ESI-MS spectra of [Cu (L) ]BF and [Ag(L)] dissolved in
methanol.
ꢁ
˚
ꢁ
˚
ꢁ
˚
that measure 4.11 A, 3.75 A, and 3.43 A, respectively. The
distance between these sulfur atoms and their centroid is
ꢁ
˚
in the 1.96-2.36 A range.
Solution Studies. To confirm the presence of oligo-
nuclear species in solution, we have performed ESI-MS
and H NMR experiments on [Cu (L) ]BF and [Ag(L)]
1
5
4
4
3
crystals dissolved in methanol and CD Cl , respectively.
2
2
According to ESI-MS experiments, the peaks in the pro-
file of the copper complex confirm the presence of the
pentanuclear [Cu (L) ] cation (2107.9 m/z) as well as the
þ
5
4
þ
presence of a tetranuclear species [Cu (L) ] (1597.6 m/z)
4
3
(Figure 4). The ESI-MS technique provides detailed
Figure 3. ORTEP drawing of [Ag(L)]
probability level. The hydrogen atoms are omitted for clarity.
3
at the 30% thermal ellipsoids
information on the species present in solution; however,
some ambiguities remain as to whether the experimental
conditions influence the peak intensities and the fragmen-
tation pathways. This is particularly evident in the present
case because the tetranuclear species may be a unique
species or the result of fragmentation of the pentanuclear
The molecular structure of the silver complex is tri-
nuclear (Figure 3). Each metal exhibits a geometry that is
intermediate between trigonal pyramidal and tetrahedral;
this geometry is achieved by the N S donor set of one
2
ligand and by a sulfur atom of a second ligand. Two
1
complex. To resolve this uncertainty, a detailed H NMR
investigation was performed on [Cu (L) ]BF (298 K) in
5
4
4
Ag-N bond distances are observed; one bond is signifi-
CD Cl solution. Two sets of signals are evident, which
2 2
ꢁ
˚
cantly longer than the other (range 0.10-0.28 A) and may
be responsible for the distortion from the ideal trigonal
planar geometry. Each silver atom lies out of the trigonal
is consistent with the presence of at least two species
(Figure 5). According to a H NMR dilution titration
1
(concentration range 0.005-0.0001 M, Supporting In-
formation), one of the two sets of signals becomes pre-
dominant over the other during dilution or concentration
of the solution. This result suggests that the two species
are in equilibrium. A plausible explanation for this result
is that the signals occurring at high concentration are
ꢁ
˚
ꢁ
˚
ꢁ
˚
NS planes by 0.41 A (Ag(1)), 0.32 A (Ag(2)) and 0.26 A
2
(
gen atom. Similar to the copper complex, both sulfur
Ag(3)), respectively, and points toward the apical nitro-
-
atoms in the -CS2 group of the ligand are bound to a
metal. The three bridging sulfur atoms are located at the
periphery of the Ag C S dodecatomic ring, whereas the
chelating sulfur atoms point toward the center of the
þ
those of the [Cu (L) ] entity, whereas those signals pre-
5
3
3
6
4
vailing after dilution can be assigned to a species of lower
nuclearity, which is presumably the tetranuclear complex
molecule, which form an irregular S triangle with sides
3

Article
Inorganic Chemistry, Vol. 49, No. 15, 2010 7013
þ
Table 5. Hydrodynamic Volumes (V
Species in CD Cl
X-ray (VX-ray) Volumes, Determined As Described in the Text
H
) of [Ag(L)]
3
, [Cu
4
(L)
3
] , and [Cu
5
(L)
4
]BF
4
2
2
, and the van der Waals (VvdW), Solvent-Excluded (VSE) and
3
˚
(A )
3
3
3
˚
˚
˚
V
H
V
vdW (A )
V
SE (A )
V
X-ray (A )
[
[
[
Ag(L)]
3
1720(30)
2330(30)
2630(20)
1254
2096
2123
þ
]
]BF
a
Cu
Cu
4
(L)
(L)
3
5
4
4
1629
2700
3012
a
þ
þ
The V
of [Cu (L)
H
of [Cu
4
(L) ] and [Cu
3
5
(L)
4
] have similar values, and the V
H
þ
þ
4
3
]
is greater than that of [Ag(L)]
3
. The large V
H
of [Cu (L)
4 3
]
is most likely a consequence of the dynamic equilibrium involving the
4 3 5 4
Cu (L) ] and [Cu (L) ] species.
þ þ
75,76
[
0
77
3
Figure 6. Optimized molecular structure of the [Cu(L )] complex.
Densityfunctional: B3LYP, basis set:Cu, S (lanl2dz) C,H,N (6-31G(d);in
0
L , the t-Bu of L are replaced by H atoms to save computational
ꢁ
˚
resources). Selected bond distances: Cu-N, 2.16-2.22 A range; Cu-Sbridge
,
ꢁ
˚
ꢁ
˚
2
.31-2.32 A range; Cu-Schelate, 2.47-2.51 A range.
0
geometry of the [Cu(L )] model was optimized by DFT cal-
3
0
culations (Figure 6). The three copper atoms of [Cu(L )]
are in a distorted tetrahedral environment, and the overall
3
shape of the molecule resembles that of [Ag(L)] , but the
3
0
pyrazole rings in [Cu(L )] are symmetrically bound to the
3
metal. Additionally, the inner triangular cavity delineated
0
by three sulfur atoms in [Cu(L )] may accommodate
3
1
Figure 5. Top, variable temperature H NMR spectra of [Cu (L)
(
5
4
]BF
ratio of 1/0.6). Bottom, stacking plot of H PGSE
NMRspectrafor thesamesolutionat roomtemperature(295K) usingthe
internal reference tetrakis(trimethylsilyl)silane (TMSS). Solvent: CD Cl
4
þ
another Cu ion because the distances from the centroid
of this triangle to the sulfur atoms varies in the 2.04-2.29
A range. The smaller species arising in solution may be
þ þ
4 3 5 4
[Cu (L) ] /[Cu (L) ]
1
ꢁ
˚
2
2
.
The intensity in the 6-8 ppm region has been increased 8-fold for clarity.
either [Cu(L)] , which is analogous to the silver trimer, or
3
þ
[
Cu (L) ] , which is found in the ESI-MS spectrum.
4
3
observed in the ESI-MS spectrum. This is further con-
firmed by H PGSE NMR experiments for a solution in
Conclusive evidence supporting the structural assign-
ment for the two sets of NMR signals associated with
1
þ
which both species were present in nearly equivalent quan-
tity. This analysis confirms that both entities are relatively
large because the hydrodynamic volumes (V ) measure
[Cu (L) ]BF and [Cu (L) ] is provided by the variable
5
4
4
4
3
temperature experiment performed in the 200-303 K
range (Figure 5). The signals (a) and (p) correspond to
the central methinic proton for both complexes, and (b)
and (r) are the signals of the central CH of the pyrazole
ring. When the temperature is lowered, the “high dilu-
tion” singlets (a) and (b) split into three and six reso-
nances, respectively. This change is consistent with loss of
H
ꢁ ꢁ
˚
3
˚
3
2
630(20) A and 2330(30) A , respectively (Table 5). A
comparison of the molecular volumes calculated using
different methods suggests that the larger species corre-
sponds to the pentanuclear complex [Cu (L) ]BF seen in
5
4
4
the X-ray structures. The actual hydrodynamic volume is
intermediate between the VvdW and the solvent-excluded
volume VSE and is very close to the volume calculated by
taking intoaccount theoccupancyoftheunitcell(Table5).
The second species is slightly smaller, and it is reasonable
to suggest that it corresponds to the tetranuclear complex.
A proper structural assignment for this species used the
þ
the 3-fold symmetry of the [Cu (L) ] complex at low
3
4
temperature, which implies the loss of chemical equiva-
lence of the three methinic and the six pyrazole protons.
The absence of molecular symmetry between the three
CuL units can be appreciated by examination of the
0
optimized [Cu(L )] structure. The kinetic parameters of
3
structure of [Ag(L)] as a model for a copper trinuclear
3
entity via simple substitution of the metal ions, and the
the exchange process were determined from complete line
shape analysis: ΔH = þ42(2) kJ mol , ΔS = -35(5) J
q
-1
q

7
014 Inorganic Chemistry, Vol. 49, No. 15, 2010
Bassanetti et al.
-
1
-1 73,74
q
mol
K
.
The negative ΔS value obtained from
Scheme 2. Description of the Possible Structures for the Charged
Species As Derived from the ESI-MS Analysis
this experiment suggests that it is most likely related to a
non-dissociative fluxional mechanism that could be asso-
ciated to the distortion of the Cu C S dodecatomic ring
3
3 6
(
Figure 6).
The “high concentration” NMR signals (r) and (p)
behave differently because they are associated with the
pentanuclear species [Cu (L) ]BF . On the basis of sym-
5
4
4
metry considerations made for the X-ray structure, the
four CuL units are equivalent, but the two pyrazole rings
within each unit are not equivalent. Binding of only one
pyrazole to the metal could potentially explain the 2-fold
splitting of the (r) signals observed at low temperature.
The mutual partial rotation of the two pyrazoles with
respect to each other, which results in continuous ex-
change of the coordination to the metal ion, makes them
chemically equivalent at high temperature. The kinetic
q
parameters of the fluxional process are ΔH = þ57(2)
-
1
q
-1 -1
kJ mol , ΔS = -16(4) J mol
K
. In the Supporting
confirms the large size of the silver complex in solution,
which is consistent with the X-ray structure (Table 5). The
Information, we report the VT spectra of two solutions
containing different [Cu (L) ]BF concentrations, in
1
VT H NMR experiments performed in the 298-230 K
range do not indicate any signal multiplicity as found for
the [Cu (L) ] complex. These results remain suggestive
5
4
4
þ
þ
which the [Cu (L) ] /[Cu (L) ] ratios are ∼9/1 and
4
3
5
4
þ
∼
1/9, to better appreciate the splitting of the t-Bu
resonances.
Ag(L)]3 exhibits more straightforward behavior in
4
3
of even smaller values for the activation parameters for
the silver trinuclear complex when compared to the
copper species.
ESI-MS Titrations. On the basis of the structure of
[Cu (L) ]BF , the four metals at the exterior of the cluster
5 4 4
[
solution because it does not give rise to oligomer-oligomer
equilibria. The ESI-MS confirms the presence of the silver
cation [Ag (L) ] (Figure 4), which most likely originates
þ
4
3
during the ESI-MS ionization process via aggregation of
the neutral [Ag(L)] complex with Ag ; however, the
are coordinately different from the central metal. In
addition, the Cu-S distances for the inner metal suggest
þ
3
most abundant species are those deriving from the neutral
[
that other metal ions may be hosted by an empty [Cu(L)]
4
Ag(L)] complex. In [Ag(L)] , the distances between the
3
tetranuclear complex. To preserve or minimally affect the
3
nþ nþ
species, M
should have a preference for tetrahedral geometry and
ꢁ
˚
inner sulfur atoms and their centroid (1.96-2.36 A) are
too small for an optimal interaction with an additional
Ag ion; however, [Ag(L)] may still be able to host a
3
structure of the resulting [MCu
4
(L)
4
]
þ
should be small enough to avoid the collapse of the entire
structure. Similar to BF in [Cu (L) ]BF , the charge on
-
fourth metal ion in its center, for example, by a slight
rotation of the CS2 groups that enlarges the inner cavity
4
5
4
4
-
M can also be compensated for by non-coordinating
anions. We chose to employ Ag for this study, and the
þ
(
[
Scheme 2). Another structural hypothesis for the
Ag (L) ] species consists of the interaction of the addi-
þ
formation of copper-silver adducts may be seen in
4
3
þ
tional metal with one of the three S atoms that point
toward the exterior of the complex (taking as reference
the [Ag(L)] structure), which are not buried by the t-Bu
Figure 7, which reports the change in the [Cu
spectrum as a function of the Ag concentration. The
5
(L)
4
] mass
þ
þ
peak at 2151.6 m/z corresponds to the [AgCu (L) ]
4 4
3
1
groups (Figure 3). The H PGSE NMR experiment
cation, and the peak at 1641.5 m/z is a result of the
fragmentation of the former, corresponding to [AgCu -
3
þ
(
L) ] . This latter complex may already be present in
3
(
73) Sandstrom, J. Dynamic NMR Spectroscopy; Academic Press: London,
982.
74) Reich, H. J. WINDNMR software: NMR Spectrum Calculations,
Version 7.1.11; 2005.
solution; however, in this case, the structural considera-
1
þ þ
tions made for the [Cu (L) ] and [Ag (L) ] cations
4 3 4 3
(
would no longer be valid. As shown in Scheme 2, the very
small S triangle formed by the [Cu(L)] complex would
(75) Avram, L.; Cohen, Y. J. Am. Chem. Soc. 2005, 127, 5714–5719.
(76) Cabrita, E. J.; Berger, S. Magn. Reson. Chem. 2002, 40, S122–S127.
(77) Frisch, M. J.; Trucks, G. W.; Schlegel, H. B.; Scuseria, G. E.; Robb,
3
3
þ
þ
be unlikely to host Ag ; however, the additional Ag ion
may interact with the outer sulfur atoms. When the
concentration of Ag is increased to a [Ag ]/[[Cu (L) ]-
BF ] ratio >5, the predominant species are [AgCu (L) ]
4
at 1641.7 m/z, [Ag Cu (L) ] at 1685.7 m/z, [Ag Cu(L) ]
2
M. A.; Cheeseman, J. R.; Montgomery, Jr., J. A.; Vreven, T.; Kudin, K. N.;
Burant, J. C.; Millam, J. M.; Iyengar, S. S.; Tomasi, J.; Barone, V.;
Mennucci, B.; Cossi, M.; Scalmani, G.; Rega, N.; Petersson, G. A.; Nakat-
suji, H.; Hada, M.; Ehara, M.; Toyota, K.; Fukuda, R.; Hasegawa, J.;
Ishida, M.; Nakajima, T.; Honda, Y.; Kitao, O.; Nakai, H.; Klene, M.; Li,
X.; Knox, J. E.; Hratchian, H. P.; Cross, J. B.; Bakken, V.; Adamo, C.;
Jaramillo, J.; Gomperts, R.; Stratmann, R. E.; Yazyev, O.; Austin, A. J.;
Cammi, R.; Pomelli, C.; Ochterski, J. W.; Ayala, P. Y.; Morokuma, K.;
Voth, G. A.; Salvador, P.; Dannenberg, J. J.; Zakrzewski, V. G.; Dapprich,
S.; Daniels, A. D.; Strain, M. C.; Farkas, O.; Malick, D. K.; Rabuck, A. D.;
Raghavachari, K.; Foresman, J. B.; Ortiz, J. V.; Cui, Q.; Baboul, A. G.;
Clifford, S.; Cioslowski, J.; Stefanov, B. B.; Liu, G.; Liashenko, A.; Piskorz,
P.; Komaromi, I.; Martin, R. L.; Fox, D. J.; Keith, T.; Al-Laham, M. A.;
Peng, C. Y.; Nanayakkara, A.; Challacombe, M.; Gill, P. M. W.; Johnson,
B.; Chen, W.; Wong, M. W.; Gonzalez, C.; Pople, J. A. Gaussian 03, Revision
C.02; Gaussian, Inc.: Wallingford, CT, 2004.
þ
þ
5
4
þ
þ
3
3
þ
þ
2
3
3
3
at 1729.5 m/z, and [Ag (L) ] at 1775.5 m/z. According to
4
3
the ESI-MS, these peaks originate from the parent ions of
very low intensity that are found at the following m/z
þ
values: 2198.8 m/z ([Ag Cu (L) ] ), 2239.6 m/z ([Ag Cu -
2
2
3
4
3
þ
þ
(L) ] ), and 2284.3 m/z ([Ag Cu(L) ] ), respectively.
4
4
4
þ
When the Ag concentration is increased, more extensive
fragmentation of the tetranuclear species occurs because
the most intense peaks are those associated with the
þ
mixed trinuclear species. Interestingly, the [Ag (L) ]
5
4

Article
Inorganic Chemistry, Vol. 49, No. 15, 2010 7015
reports have shown that this type of ligand behaves as a N2S
donor with early transition metal ions because the dithio-
acetate group employs only one sulfur atom for metal
44,70,71
binding.
By restricting rotation along the C-C axis,
the t-Bu groups on the pyrazole ring of L direct the CS2
moiety to a favorable position that chelates the metal center
with a sulfur atom. The second sulfur is then available for
binding an additional metal ion in a direction that is nearly
perpendicular to the bis-pyrazole system. This steric control
has important structural consequences for the nuclearity of
the resulting complexes; oligonuclear species are preferen-
þ
þ
þ
tially formed with Li , Cu , and Ag . Co-crystallized THF
þ
molecules are present in the Li crystals, but these molecules
were not found to participate in the metal coordination, in
þ
contrast to previous reports for most structures in which Li
and THF are present. The lithium and silver complexes are
trinuclear and form a trigonal internal cavity surrounded by
three sulfur groups; in contrast, the copper complex is
pentanuclear, and four equivalent CuL units delineate a
þ
regular tetrahedral site that is occupied by a fifth Cu ion.
This [Cu (L) ]BF complex, once dissolved, rapidly equili-
5
4
4
þ
brates with the tetranuclear species [Cu (L) ] . According to
4
3
the electroneutrality principle, the presence of both species in
solution can be accounted for by the following equilibrium:
þ
þ
3
[Cu (L) ] = [Cu(L)] þ 3[Cu (L) ] . The low temperature
5
4
3
4
3
1
H NMR spectrum suggests that only one set of signals is
present for the tetranuclear entity, and the neutral [Cu(L)]3
and charged [Cu (L) ] entities must rapidly exchange a
labile copper ion. By employing Ag instead of Cu , the
highest nuclearity that is achieved is three (see ESI-MS data).
þ
4
3
þ
þ
This is also confirmed by the ESI-MS titration of a
þ
[
Cu (L) ]BF solution with Ag , which demonstrates that
5
4
4
þ
þ
the mixed trinuclear Cu /Ag species predominates when
the silver concentration increases.
In summary, we have explored the coordination capabili-
ties of the new heteroscorpionate ligand bis(3,5-tertbutyl-
pyrazol-1-yl)dithioacetate; the ligand was prepared as a
lithium salt and behaved as a N S donor with the two soft
2
2
þ
þ
transition metal ions Cu and Ag , exhibiting an ability to
form stable oligonuclear structures.
þ
5 4 4
Figure 7. ESI-MS spectra collected at different [Ag ]/[[Cu (L) ]BF ]
ratios: (a) 0.85; (b) 1.70; (c) 5.3.
Acknowledgment. This work was supported by the Mini-
stero dell’Istruzione, dell’Universit ꢀa e Ricerca (Rome,
Italy).
species is never observed in any of the experimental con-
ditions employed. This absence suggests that the highest
nuclearity for the silver complex is three, as observed in
the X-ray molecular structure.
Supporting Information Available: Crystallographic infor-
mation files (CIF) for [Li(L)]3 (2.25)THF, [Cu (L) ]BF and
3
5
4
4
[
(
Ag(L)] . Cartesian coordinates of the optimized structures
0
B3LYP/lanl2dz-6-31G(d)) of the model complex [Cu(L )]
VT H NMR spectra of [Cu (L) ]BF in CD Cl . This mat-
5 4 4 2 2
3
Conclusions
3
.
1
We have investigated the coordination properties of the
heteroscorpionate ligand bis(3,5-tertbutylpyrazol-1-yl)dithio-
acetate (L), which possesses a N S donor set. Previous
erial is available free of charge via the Internet at http://
pubs.acs.org.
2
2