Plasticity in [(R4-xR1 x) 4N]4[Cu4{S2C2(CN) 2}4] (x = 0-4) is molded by a guest cation on an elastic anionic host

Article abstract of DOI:10.1002/ejic.200800094

The elastic anion [Cu₄(mnt)₄]^4- {mnt = maleonitriledithiolato, [S₂C₂(CN)₂] ^2-} serves as a host to a series of guest cations [(R _4-xR¹ _x)₄

Full text of DOI:10.1002/ejic.200800094

FULL PAPER
DOI: 10.1002/ejic.200800094
Plasticity in [(R4–xR1 ) N]4[Cu4{S2C2(CN)2}4] (x = 0–4) is Molded by a Guest
xC4ation on an Elastic Anionic Host
Biplab K. Maiti,[a] Kuntal Pal,[a] and Sabyasachi Sarkar*[a]
Keywords: Cation template / Plasticity / Elasticity / Host–guest systems / Supramolecular chemistry
The elastic anion [Cu4(mnt)4]4– {mnt = maleonitriledithiolato,
[S2C2(CN)2]2–} serves as a host to a series of guest cations
[(R4–xR1x)4N]+ (R = Et, R1 = Me; x = 0–4) to form the complexes
[(R4–xR1x)4N]4[Cu4{S2C2(CN)2}4]. The molecular structural
design information stored in the cation is molded to the elas-
tic anionic host-framework through H-bonding to create a
plastic supramolecular entity. The reaction of CuCl with
Na2(mnt) in a 1:1 metal/ligand ratio, followed by interaction
with the respective cation, gives the cation-dependent
tetranuclear host-guest assemblies [Me4N]4[Cu4(mnt)4] (1),
Vis spectra in solution and their identical cyclic voltammetric
redox behaviors also imply the presence of a common entity.
The ESI mass spectra in acetonitrile confirm the presence of
this common {Cu4(mnt)4} core. The elastic {Cu4(mnt)4} core
participates in extensive hydrogen bonds in the presence of
different quaternary cations in solution during the crystalli-
zation process and the cation determines the final shape of
the anion in the solid state. Depending on the length and
nature (symmetric or non-symmetric) of the alkyl groups at-
tached to the quaternary cation, the overall geometry of the
anion assumes different degrees of openness in a partially
opened umbrella shape. The {Cu4(mnt)4} moiety is cleaved
by treatment with PPh3 to give a monomer, which has been
isolated as [Et4N][Cu(mnt)PPh3] (6).
[Me3EtN]4[Cu4(mnt)4]
(2),
[Me2Et2N]4[Cu4(mnt)4]
(3),
[MeEt3N]4[Cu4(mnt)4] (4) and [Et4N]4[Cu4(mnt)4] (5), which
have been characterized by X-ray structural studies in the
solid state. The host cavity shrinks and expands, with varying
Cu···Cu separations ranging from 2.754 to 3.952 Å, to accom-
modate the relevant guest ion during the crystallization pro-
cess. All these complexes show identical 13C NMR and UV/
(© Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim,
Germany, 2008)
traditional methods that produce only a rigid host cavity
that is based on guest size selectivity. Recently, however,
Raymond and co-workers have described the elasticity of a
host cavity in solution where an encapsulated guest may
be exchanged from the cavity by deformation of the host
framework.[8] We envisioned a different situation where the
plasticity of the host cavity may be melted (used in terms
of plastic melting) to accommodate different guests by map-
ping the size and shape of the guest during the remolding
process. Such a process requires disruption of the noncoval-
ent interactions between the guest and the host during melt-
ing process whilst retaining the nature of the host frame-
work. During this guest-exchange process the melted host
(on dissolution) can regenerate an elastic relaxed host
framework, which effectively remolds itself in the presence
of a new guest during re-crystallization.
The discrete metallacycles to be used as hosts were syn-
thesized on the basis of a rational ligand-directed ap-
proach.[9] We decided to use Na2(mnt) as a chelate ligand
as sulfur has the possibility of linking a soft transition
metal ion in diverse bridging modes,[10–12] such as µ2-S and
µ3-S. On the basis of the above idea we developed a series
of compounds based on a partially opened umbrella-shaped
tetranuclear core, {Cu4mnt4}, where the openness is con-
trolled by several noncovalent interactions with the hydro-
gen atoms of the cation. The X-ray structures of all these
Introduction
The metal-assisted self-assembly of metallacycles, hel-
icates, racks, ladders, grids, and cages is an impressive
achievement in molecular design and assembly.[1] It has be-
come now apparent that by proper manipulation of the
noncovalent interactions between anions[2] or cations[3] the
course of the assembly process may follow the chemistry of
molecular information. The involvement of reversible dy-
namic covalent and noncovalent connections means that a
particular combination of metal ion or ligand can be as-
sembled in a process where the cation templates like a target
lock or kinetic selection.[4] Such ionic recognition may lead
to the binding of a guest to a host and this binding may
further involve a complex interplay of subtle noncovalent
interactions.[5] Numerous synthetic host–guest systems are
potentially useful in separation processes, recognition, ca-
talysis, and sensor technologies;[6] indeed, guest-exchange
processes have been reported for a number of supramolec-
ular metal–ligand hosts.[7] Synthetic chemistry has evolved
[a] Department of Chemistry, Indian Institute of Technology Kan-
pur,
Kanpur-208016, India
Fax: +91-512-259-7265
E-mail: abya@iitk.ac.in
Supporting information for this article is available on the
WWW under http://www.eurjic.org or from the author.
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complexes show the maintenance of the plasticity of the
opened umbrella-shaped {Cu4mnt4} core upon encapsulat-
ing tetraalkylammonium cationic species of varying sizes
and shapes. Uniquely, the rigid tetranuclear complexes sever
several hydrogen bonds on dissolution, thereby liberating
the relaxed tetranuclear core and losing their structural
plasticity. On addition of an excess of a new tetraalkylam-
monium cation, its hydrogen atoms impart newer forces for
association with the tetranuclear core and these alter the
placement of the core cations to impart a new structural
motif for the tense tetranuclear core that leads to a reshap-
ing of the fold of the umbrella on recrystallization. Such
reversibility shows the plasticity of the tetranuclear core
when accommodating a new cation. This process is revers-
ible and different shapes of the partially opened umbrella
can be molded by different guest cations. The tetranuclear
core can be ruptured in solution by addition of PPh3, which
acts as a blocker to prevent Cu–S bond formation and
yields [Et4N][Cu(mnt)PPh3].
Previously known structurally characterized tetranuclear
CuI complexes such as [Cu4(dtc)4],[13] [Cu4(dtp)4],[14]
[Cu4(S2CC7H7)4],[15] and [Cu4(i-mnt)4]4– [16] (dtc: dithiocar-
bamato, dtp: dithiopropionato, i-mnt: isomaleonitriledi-
thiolato, mnt: maleonitriledithiolato) have in common that
their copper atoms are disposed almost at the vertices
of a distorted tetrahedron. Compounds 1–5 are the first
structurally characterized tetranuclear CuI complexes with
four dianionic 1,2-dithiolato ligands, which results in the
formation of anionic species. An X-ray-structural analysis
shows that the cations used as a guest in 1–5 play a decisive
role in molding the final shape of the tetranuclear anionic
frame. The plasticity of the {Cu4(mnt)4} framework only
exists in the solid state Ϫ the 13C NMR and UV/Vis spectra
and cyclic voltammetric studies indicate the existence
of a common unit in solution, namely tetranuclear
{Cu4(mnt)4}, as determined by ESI mass spectrometry.
Scheme 1. Schematic representation of the cation-assisted self-as-
sembly process.
ing one of them in CH3CN, adding an excess of the alter-
nate cation, and precipitating the new complex by adding
diethyl ether (Scheme 2). These core conversions were con-
firmed by measuring the unit cell dimensions and melting
point. Complexes 1–5 are smoothly converted into
[Cu(mnt)(PPh3)]– with the respective counter cation upon
treatment with four equivalent of PPh3 in dichloromethane
(Scheme 3). Compounds 1–5 are highly susceptible towards
oxygen in solution, which leads to the oxidation of the cop-
per(I) ion, whereas 6 is more stable and reacts only slowly
with oxygen in solution. On aging, all these complexes with
a {Cu4mnt4} core slowly lose an mnt2– anion to form [CuII-
(mnt)2]2–, along with a more stable cubane core,[11,12] espe-
cially in the presence of traces of air.[16] This reaction can
be followed by electronic spectroscopy (see Figure S1 in the
Supporting Information).
Scheme 2. Transformation from tetramer to monomer.
Results and Discussion
Synthesis
The tetranuclear host–guest assemblies 1–5 were synthe-
sized by treating CuCl with Na2(mnt) in a 1:1 molar ratio in
water. The desired yellowish-orange compound precipitated
upon addition of an aqueous solution of the respective qua-
ternary ammonium bromide (cations Me4N+, Me3EtN+,
Me2Et2N+, MeEt3N+, and Et4N+; Scheme 1) in high yield.
Interestingly, addition of a cation such as Bu4N+ gave the
trinuclear complex [Bu4N]3[Cu3(mnt)3][17] instead.
Scheme 3. Interconversion between 1 and 5.
Solution UV/Vis Study
The electronic absorption spectra (Figure 1) of 1–5 in
Compounds 1–5 isolated from the aqueous reaction me- acetonitrile are identical and superimposable, with a com-
dium and recrystallized from acetonitrile/diethyl ether were mon charge-transfer band at 377 nm.
found to be structurally identical, as confirmed by compar-
This suggests that 1–5 generate a common species in
ing the respective pairs of XRD patterns (see Figure S11 in solution upon breaking of all the hydrogen-bonding inter-
the Supporting Information) and by checking their melting actions. However, the released tetramer appears to be stable
points. These results assured us that the single crystals used and further fragmentation to yield a monomer, dimmer, or
in the diffraction analyses retained the tetranuclear form other forms, which may remain in equilibrium, cannot be
isolated originally from the aqueous medium. All these detected. A charge-transfer band is observed at 372 nm for
compounds can easily be interconverted simply by dissolv- 6.
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Plasticity in [(R4–xR1x)4N]4[Cu4{S2C2(CN)2}4]
Figure S3 in the Supporting Information). These oxidations
are copper-centered and presumably not due to the oxi-
dation of µ1-S/µ2-S bridging sulfur.
Figure 1. The electronic absorption spectra of 1 (0.25ϫ10–4 ), 2
Figure 2. Left: full-scan CV spectra of 5 (1ϫ10–3 ; solid line) and
6 (4ϫ10–3 ; broken line); right: CV (solid line) and DPP (broken
line, current height reduced by 1/3 with respect to CV) of 1–5. All
spectra were recorded at a scan rate of 100 mVs–1 over the potential
range of interest (0 to +0.40 V) in acetonitrile with KPF6 as the
supporting electrolyte.
(0.25ϫ10–4 ),
3
(0.25ϫ10–4 ),
4
(0.25ϫ10–4 ),
5
(0.25ϫ10–4 ), and 6 (1ϫ10–4 ) in CH3CN solution.
It is known that metal sulfido complexes can incorporate
elemental sulfur to form polysulfide complexes,[16] therefore
we added one equivalent of elemental sulfur to a solution
of 5 during the CV study. The color of the solution dark-
ened from yellow to orange but there was no change in the
redox peak positions in CV or DPP compared to those
found for pure 5. The addition of one equivalent of PPh3
to the solution caused the color to revert to that of 5. The
formation of PPh3S in this reaction was subsequently con-
firmed. A similar reaction between a polysulfido copper
complex and PPh3 has been reported,[16] therefore the spe-
cies generated upon addition of elemental sulfur in the pres-
ent case must be similar, with the coordinated sulfide ligand
being converted into a polysulfide from which sulfur can be
abstracted by PPh3 to yield PPh3S. As the peak position
remains unaltered upon addition of elemental sulfur, these
redox processes cannot be related to copper as in that case
the position of the sulfide-dependent redox peak should
change due to formation of the polysulfide entity. The ready
aerobic oxidation of these complexes indicates the ease of
oxidation of CuI. The only information that can be ex-
tracted from this study, therefore, is the presence of com-
mon copper-containing species in solution for all com-
plexes.[18] However, the presence of two structurally dif-
ferent species containing copper(I) in two different environ-
ments, or one complex containing two nonequivalent cop-
per(I) centers, both of which could account for these two
successive oxidation processes, cannot be differentiated.
The choice of species in solution has been narrowed down
however. Compound 6 displays one anodic peak, Epa, at
0.30 V vs. Ag/AgCl due to an irreversible oxidation.
Electrochemistry
Cyclic voltammetric analysis was performed to deter-
mine the number of electroactive copper-containing species
as the oxidation of copper(I) should vary in different envi-
ronments. Thus, the presence of a monomer, dimmer, or
tetramer, etc. will lead to the appearance of different metal
oxidation based peak potentials. Any geometry changes due
to the presence of a further quaternary cation were avoided
by using KPF6 as the supporting electrolyte and performing
the measurements in acetonitrile to maintain the identity
of the species detected by electronic spectroscopy. CV was
performed for 1–5 in CH3CN solution containing 0.1 
KPF6 as the supporting electrolyte. Ferrocene was used as
an internal standard and the potentials were referenced to
the Ag/AgCl electrode. Electrochemical measurements at
platinum and glassy carbon working electrodes gave similar
results for complex 5 (Figure S2 in the Supporting Infor-
mation).
Complexes 1–5 exhibit identical electrochemical re-
sponses, a result which is in agreement with the results of
the electronic spectral study. The CV of all tetranuclear
complexes (Figure 2) show two anodic peaks (Epa) at 0.22
and 0.32 V vs. Ag/AgCl. Both these processes have the cor-
responding cathodic peaks (Epc) at 0.15 and 0.24 V, respec-
tively, which suggests that we are dealing with two sequen-
tial one-electron oxidations (∆E = 70 mV in each case). The
first oxidation process overlaps with the second oxidation
process. Differential pulse polarography (DPP) of these spe-
cies showed oxidation processes at 0.19 and 0.27 V, close to
the E1/2 values of the two processes found in the CV studies.
Cyclic voltammetry of compound 5 in CH3CN (0.2 , sup-
porting electrolyte, KPF6) at scan rates of 50–400 mVs–1
showed two peaks at the same positions but with current
intensities that are strongly affected by the scan rate (Fig-
NMR Spectroscopy
The 13C NMR spectra of all complexes were recorded in
ure S2 in the Supporting Information). The intensities and argon-purged [D6]DMSO and in CD3CN; key peaks are
peak positions are independent of the number of scans (see listed in Table 1. CD3CN masks the CN peak of the mnt2–
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B. K. Maiti, K. Pal, S. Sarkar
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ligand but it is nevertheless used, along with DMSO, as ligand is in an identical environment in solution on the
a common solvent for most of the solution studies. NMR NMR timescale. The results of the electronic spectroscopy
measurements were carried out with varying concentrations and CV studies have allowed us to narrow the possible spe-
(30 and 50 m) of complex 1 to the saturation limit (ca. cies in solution down to least two, and the 13C NMR results
50 m) to identify the presence of intermediate species due reduces that possibility still further to enantiomeric
to concentration-dependent equilibria. The 13C NMR spec- forms.[17]
tra were identical in both cases.
The NMR spectrum of 6 is noticeably different. Thus,
the CN and C=C signals are both shifted down-field to δ
= 125.21 and 120.86 ppm, respectively, due to a change in
the coordination mode of the dithiolene and PPh3 ligands.
The CN signal is less shifted than C=C as it is further away
from the coordination site. The 13C NMR assignment of
the respective cations of 1–6 in [D6]DMSO is straightfor-
ward (Table 1). The 13C NMR spectrum of 6 in [D6]DMSO
also exhibits resonances due to the PPh3 moiety
Table 1. 13C NMR spectroscopic data of all compounds.
Ligand (mnt)
Cation
α-CH2
Compd.
CN
C=C
CH3
β-CH3
1
2
3
4
5
6
124.67
124.67
124.67
124.67
124.67
125.21
120.12
120.12
120.12
120.12
120.12
120.86
59.48
51.73
48.99
50.3
–
–
–
60.54
58.04
53.7
51.49
51.55
8.16
7.83
11.3
7.15
7.16
–
Electrospray Mass Spectrometry
The 13C NMR spectra of 1–5 in [D6]DMSO (Table 1)
show two resonances at δ = 120.12 ppm for C=C carbon
Self-assembled supramolecular host-guest complexes
atoms and at δ = 124.67 ppm for the CN moiety. The CN have been characterized by electrospray ionization mass
and C=C groups present in the coordinated mnt2– ligand in spectrometry.[19] The high symmetry inherent to most
1–5 are in different structurally imposed environments in supramolecular assemblies can lead to difficulties in as-
the solid, which suggested to us that they should display sessing the exact stoichiometry of host-guest complexes by
four 13C peaks; only two 13C peaks are observed in [D6]- solution-based characterization methods. Mass spectrome-
DMSO. This is due to a rapid positional change of the sul- try, however, allows for a convenient assessment of the exact
fur atoms, where Cu–S bonds arising due to µ1-S and µ2-S stoichiometry based on the mass and isotopic composition
bridging interchange their positions faster than the NMR of the ions observed. The ESI mass spectra in the negative
timescale, which means that the sulfur atoms of the mnt2– ion mode were acquired under mild conditions using a nee-
ligand are equivalent in solution on the NMR timescale dle voltage of 2.5 kV and a cone voltage of 40 V. The ESI
(clockwise and anticlockwise copper–sulfur binding mass spectrum of complex 5 in CH3CN shows a signal at
modes).[17] In contrast, only a clockwise or anticlockwise m/z 1203.99 due to [Et4N]3[Cu4(mnt)4]– along with frag-
structure is found in the solid state. The appearance of con- ments assigned to [Et4N]2[Cu3(mnt)3]–, [Et4N][Cu2(mnt)2]–,
centration-independent CN and C=C peaks at the same po- and [Cu(mnt)]– at m/z 870.90, 538.10, and 203, respectively
sition for all tetramers shows that the coordinated mnt2– (Figure 3).
Figure 3. Electrospray mass spectrum of 5 in CH3CN. The ion signals displayed correspond to [Cu(mnt)]– (I) at m/z 203, [Et4N][CuII-
(mnt)2]– (II) at m/z 474.35, [Et4N][Cu2(mnt)2]– (III) at m/z 538.10, [Et4N]2[Cu8(mnt)6]2– (IV) at m/z 803.66, [Et4N]2[Cu3(mnt)3]– (V) at m/z
870.90, and [Et4N]3[Cu4(mnt)4]– (VI) at m/z 1203.99 (parent ion peak). The experimental and theoretical isotopic distribution patterns of
VI are shown in the inset.
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Plasticity in [(R4–xR1x)4N]4[Cu4{S2C2(CN)2}4]
Changing the needle voltage to 3.5 kV whilst keeping low the plane [four µ2-S atoms are located above the plane
cone voltage the same resulted in fragmentation of all the at a distance of 0.755 Å (S1) and 0.882 Å (S3) and four µ1-
complex into the [Cu(mnt)]– ion (m/z = 203). The identity S atoms are located below the plane at a distance of 1.954 Å
of the tetramer and monomer forms was confirmed by (S1) and 1.849 Å (S4)]. The overall dimensions and shape
comparing these m/z peaks with their simulated isotopic of the core of the macrocyclic entity can be extracted by
distribution pattern using the program ISOPRO3.0.[20] The considering the four coplanar metal ions as the hypothetical
ESI mass spectra of 1–4 show similar fragmentation pat- corners of a quadrilateral. The four Cu–Cu–Cu angles (two
terns (see Supporting Information). In addition, due to the pairs; 86.8° and 93.2°) are close to 90° but the separations
presence of traces of oxygen,[16] mass fragments assignable between two adjacent copper atoms are not identical (two
to [CuII(mnt)2] and [Cu8(mnt)6] species are observed. The pairs of opposite distance; 2.875 and 3.087 Å) therefore the
parent ion peak of 6, which appears at m/z 465, is due to molecule contains a nearly perfect rectangular-planar ar-
[Cu(mnt)(PPh3)]– and the peak at m/z 203 is again due to rangement. The four {Cu(mnt)} building blocks assemble
[Cu(mnt)]– formed by loss of PPh3 from the former. The in a clockwise fashion and these units are connected
PPh3-bound CuI center in 6 resists aerial oxidation and so through four S atoms with Cu–S–Cu angles (two pairs) of
species like [CuII(mnt)2] and [Cu8(mnt)6] were not detected 88.3° and 80.4°. The four Cu(mnt) planes are not co-planar
in its ESI mass spectrum. The presence of the parent tetra- with the Cu4 plane but deviate (two pairs) by 65.1° and
meric {Cu4(mnt)4} unit as a common entity in the low en- 59.9° from this plane; the two {Cu(mnt)} planes approach
ergy ESI mass spectra of all the complexes strongly support each other with angles of 71.7° and 83.7°. Thus, the struc-
its existence in solution. Application of a slightly higher ture of this cyclic tetramer resembles a partly opened um-
needle voltage to all these complexes results in the presence brella and exhibits C2 symmetry.
of only a monomeric unit. The existence of a common tet-
rameric unit in solution therefore reveals the identity of the
common species found by 13C NMR, electronic spec-
troscopy, and by CV. This suggests that complexes 1 to 5
form a common, relaxed tetranuclear species on dissol-
ution.
Solid-State Structure of [Me4N]4[Cu4(mnt)4] (1)
The structure of the anion in 1 is illustrated in Figure 4
and selected bond lengths and angles are provided in the
corresponding figure caption. Compound 1 crystallizes in
the monoclinic system, space group C2/c. The asymmetric
unit of 1 contains four half tetramethylammonium cations
and one half of a [Cu4(mnt)4] anion. One of the four
[Me4N]+ cations is disordered. The N atom of this cation
suffers positional disorder at a special position and it was
refined using a negative part instruction. This [Me4N]+ cat-
ion is located inside the cavity of the anion host. The four
CuI ions and mnt ligands form a discrete tetranuclear com-
plex in which each mnt ligand forms a µ1-S bond to a Cu
Figure 4. Structure (ORTEP drawing) of the anionic unit (top) and
Cu4S4 core (bottom) of 1. Thermal ellipsoids are drawn at the 50%
probability level. Selected bond lengths [Å] and angles [°]: Cu1–S1
atom and a µ2-S bond to the same Cu atom to form a five-
membered chelate ring.[21] This mnt ligand further binds to
2.2087(14), Cu1–S3 2.2411(14), Cu1–S2 2.2469(13), Cu2–S3
2.2117(14) Cu2–S4 2.2565(13), Cu1···Cu2 2.8755(11); S3–Cu1–S2
97.09(5), S4–Cu2–Cu1 119.97(4), S3–Cu2–S4 121.78(5), S3–Cu2–
Cu1 50.22(4), S1–Cu1–S3 135.04(5), S1–Cu1–S2 121.88(5), S1–
Cu1–Cu2 131.46(4), S3–Cu1–Cu2 49.33(4), S2–Cu1–Cu2 99.62(4),
Cu2–S3–Cu1 80.45(4).
an adjacent Cu atom to build a Cu4S4 eight-membered ring.
The average S···S bite distance in mnt is 3.353 Å and the
average S–Cu–S angle is 96.8°.[11] The tetrameric unit con-
tains a central Cu4S4 eight-membered ring comprising alter-
nate copper and sulfur atoms. This octameric ring is non-
planar and is arranged in a crown-like configuration.[22]
Each copper atom is coordinated to three sulfur atoms (one
µ1-S and two µ2-S) and the copper atoms are displaced by
0.244 (Cu1) and 0.307 Å (Cu2) from the S3 basal plane in
a distorted trigonal planar geometry. The Cu–S dis-
Solid-State Structure of [Me3EtN]4[Cu4(mnt)4] (2)
The structure of the anion in 2 is illustrated in Figure 5
tance[11,12,23,24] (2.242 Å) associated with the five-membered and selected bond lengths and angles are provided in the
chelate ring is slightly larger than the bridging Cu–S dis- corresponding figure caption. Compound 2 crystallizes in
¯
tance (2.211 Å). However, the four Cu atoms can be consid- the triclinic system, space group P1. The asymmetric unit of
ered as planar with the S atoms alternating above and be- 2 contains four trimethylethylammonium cations and one
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B. K. Maiti, K. Pal, S. Sarkar
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[Cu4(mnt)4] anion. One of the four [Me3EtN]+ cations is 55.3°, 57.8°, and 41.4° from this plane; the two
located inside the cavity of the anion host. The chelating {Cu(mnt)}planes approach each other with angles of 86.4°,
coordination mode, ligand orientation, and Cu–S distances 47.5°, 58.5°, and 87.7°. Thus, the structure of this cyclic
in the anion of 2 are similar to those found in 1 even though tetramer resembles a partly opened umbrella and exhibits
its size and shape are quite different to those of 1. The four C1 symmetry.
pseudo-trigonal copper centers are displaced from the S3-
basal plane by 0.157 (Cu1), 0.178 (Cu2), 0.210 (Cu3), and
0.106 Å (Cu4) can be considered to form a plane with the
S atoms alternating above and below this plane [four µ2-S
Solid-State Structure of [Me2Et2N]4[Cu4(mnt)4] (3)
The structure of the anion in 3 is illustrated in Figure 6
and selected bond lengths and angles are provided in the
corresponding figure caption. Compound 3 crystallizes as
tetrameric units in the monoclinic system, space group
P21/c. The asymmetric unit of 3 contains four diethyldi-
methylammonium cations and one [Cu4(mnt)4] anion. One
of the four [Me2Et2N]+ cations is located inside the cavity
of the anion host. The bite distance, bite angles, and Cu–S
distances are similar to those in 1. Interestingly, the binding
mode and relative orientation (anticlockwise) of the mnt
groups are opposite to those in 1, which suggests that the
counteraction (Me2Et2N+) changes the conformation (size
and shape) of the anion of 3 from that in 1. The four almost
atoms are located above the plane at a distance of 0.381
(S1), 0.973 (S3), 0.576 (S5), and 1.047 Å (S7) and four µ1-
S atoms are located below the plane at a distance of 1.435
(S2), 1.865 (S4), 1.775 (S8), and 1.775 Å (S6)]. The metal-
defined quadrilateral in 2 is unsymmetrical in shape with
four different Cu···Cu separations of 3.641, 2.846, 3.905,
and 2.753 Å and four Cu–Cu–Cu angles of 76.8°, 93°,
79.7°, and 88.9°. The four {Cu(mnt)} building blocks are
connected through four S atoms with Cu–S–Cu angles of
110.3°, 79.7°, 125.2°, and 76.8°. The four {Cu(mnt)} planes
are not co-planar with the Cu4 plane but deviate by 62.9°,
Figure 5. Structure (ORTEP drawing) of the anionic unit (top) and
Cu4S4 core (bottom) of 2. Thermal ellipsoids are drawn at the 50%
probability level. Selected bond lengths [Å] and angles [°]: Cu1–
S3 2.202(2), Cu1–S1 2.219(3), Cu1–S2 2.2403, Cu2–S5 2.196(3),
Cu1···Cu2 2.8464(17), Cu2–S4 2.240(3), Cu2–S3 2.242(2), Cu3–S7
2.205(3), Cu3–S5 2.239(3), Cu3–S6 2.245(3), Cu3···Cu4 2.7539(17),
Cu4–S1 2.180(3), Cu4–S7 2.229(2), Cu4–S8 2.236(3); Cu3–S7–Cu4
76.80(8), Cu4–S1–Cu1 125.22(11), Cu1–S3–Cu2 79.64(8), Cu2–S5–
Cu3 110.35(10), S3–Cu1–S1 138.17(9), S3–Cu1–S2 124.24(9), S1–
Cu1–S2 95.96(9), S3–Cu1–Cu2 50.80(7), S1–Cu1–Cu2 110.87(8),
S2–Cu1–Cu2 133.46(8), S5–Cu2–S4 126.07(10), S5–Cu2–S3
Figure 6. Structure (ORTEP drawing) of the anionic unit (top) and
Cu4S4 core (bottom) of 3. Thermal ellipsoids are drawn at the 50%
probability level. Selected bond lengths [Å] and angles [°]: Cu1–S8
2.213(2), Cu1–S2 2.231(2), Cu1–S1 2.247(2), Cu1···Cu2 2.7840(15),
Cu2–S6 2.196(2), Cu2–S8 2.230(2), Cu2–S7 2.246(2), Cu3–S4
2.203(2), Cu3–S6 2.232(2), Cu3–S5 2.233(2), Cu3···Cu4 2.7824(15),
Cu4–S2 2.194(2), Cu4–S3 2.233(2), Cu4–S4 2.236(2); S8–Cu1–S2
133.63(8), S8–Cu1–S1 127.24(8), S2–Cu1–S1 95.58(8), S8–Cu1–
Cu2 51.48(6), S2–Cu1–Cu2 111.32(7), S1–Cu1–Cu2 136.04(7), S6–
Cu2–S8 135.59(8), S6–Cu2–S7 126.49(8), S8–Cu2–S7 96.78(8), S6–
Cu2–Cu1 117.60(7), S8–Cu2–Cu1 50.94(6), S7–Cu2–Cu1
135.49(10), S4–Cu2–S3 96.38(9), S5–Cu2–Cu1 123.20(8), S4–Cu2– 102.74(7), S4–Cu3–S6 131.65(8), S4–Cu3–S5 129.97(8), S6–Cu3–S5
Cu1 99.70(8), S3–Cu2–Cu1 49.56(6), S7–Cu3–S5 137.76(10), S7– 96.41(8), S4–Cu3–Cu4 51.72(6), S6–Cu3–Cu4 113.81(7), S5–Cu3–
Cu3–S6 123.31(10), S5–Cu3–S6 96.04(9), S7–Cu3–Cu4 51.99(7), Cu4 127.60(7), S2–Cu4–S3 132.98(8), S2–Cu4–S4 128.79(8), S3–
S5–Cu3–Cu4 123.03(8), S6–Cu3–Cu4 120.32(8), S1–Cu4–S7 Cu4–S4 96.83(8), S2–Cu4–Cu3 115.02(7), Cu1–S8–Cu2 77.59(7),
135.33(10), S1–Cu4–S8 126.02(10), S7–Cu4–S8 97.92(9), S1–Cu4–
Cu3 113.97(8), S7–Cu4–Cu3 51.21(7), S8–Cu4–Cu3 105.83(8).
Cu4–S2–Cu1 126.56(10), Cu3–S4–Cu4 77.62(7), Cu2–S6–Cu3
124.53(9), S3–Cu4–Cu3 101.89(7), S4–Cu4–Cu3 50.65(6).
2412
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Plasticity in [(R4–xR1x)4N]4[Cu4{S2C2(CN)2}4]
trigonal planar Cu centers can be considered as being ne-
arly rectangular [the four Cu–Cu–Cu angles (91.6°, 87.7°,
92.3°, and 88.4°) are close to 90° and the opposite distances
between two adjacent copper atoms are nearly identical
(3.952, 2.784, 3.919, and 2.782 Å)]. Eight S atoms alternate
above and below this rectangle, with four µ2-S atoms lo-
cated above the rectangle at a distance of 0.457 (S2), 1.216
(S4), 0.399 (S6), and 1.088 Å (S8) and four µ1-S atoms lo-
cated below the plane at a distance of 1.389 (S1), 1.536 (S3),
1.616 (S5), and 1.700 Å (S7). The four {Cu(mnt)} building
blocks are connected through bridging S atoms with Cu–
S–Cu angles of 126.6°, 77.6°, 124.5°, and 77.5°. The four
{Cu(mnt)} planes are not co-planar with the Cu4 plane but
deviation from it by 56.8°, 47.6°, 58.5°, and 39.9°; the two
{Cu(mnt)} planes approach each other with angles of 82.4°,
88.9°, 46.3°, and 45.5°. Thus, the structure of this cyclic
tetramer resembles a partly opened umbrella and exhibits
approximate C2 symmetry.
Solid-State Structure of [MeEt3N]4[Cu4(mnt)4] (4)
Figure 7. Structure (ORTEP drawing) of the anionic unit (top) and
Cu4S4 core (bottom) of 5. Thermal ellipsoids are drawn at the 50%
probability level. Selected bond lengths [Å] and angles [°]: Cu1–S2
2.1801(19), Cu1–S1 2.2215(19); S2–Cu1–S1 131.33(7).
The molecular structure of 4 was determined by single-
crystal X-ray diffraction study. However, the quality of the
crystal was poor[25]and this complex suffers from serious
disorder of the cationic part, which prevents a discussion of
the metrical parameters of the complex. However, from the
crystal data, the basic structure of the anion in 4 similar to
that of 3.
Solid-State Structure of [Et4N][Cu(mnt)(PPh3)] (6)
The structure of the anion in 6 is illustrated in Figure 8
and selected bond lengths and angles are provided in the
corresponding figure caption. Compound 6 crystallizes in
the monoclinic system, space group P21/n. The asymmetric
unit of 6 contains one tetraethylammonium cation and one
Solid-State Structure of [Et4N]4[Cu4(mnt)4] (5)
The structure of the anion in 5 is illustrated in Figure 7 [Cu(mnt)PPh3] anion. The complex has C1 symmetry. The
and selected bond lengths and angles are provided in the copper atom is coordinated to one P and two µ1-S atoms
corresponding figure caption. Compound 5 crystallizes as in a trigonal planar geometry. The mnt ligand has two dis-
tetrameric units in the tetragonal system, space group tinct S atoms, with an S···S distance of 3.342 Å and an S–
P4/n. The asymmetric unit of 5 contains four quarters of a Cu–S angle of 97.8°. The Cu–S bond length is 2.217 Å and
tetraethylammonium cation and one quarter of a [Cu4- Cu–P bond length[26] is 2.168 Å.
(mnt)4] anion. One of the four [Et4N]+ cations is disordered
over the carbon atoms and was refined with the free part
instruction. The larger countercation in this complex helps
to change the host conformation of 5 from that in 1. The
four trigonal-planar Cu centers can be considered as form-
ing a square with four identical Cu–Cu–Cu angles (90°) and
four identical (3.865 Å) Cu···Cu separations. Eight S atoms
alternate above and below this square, with four µ2-S atoms
located above it at a distance of 0.540 Å and four µ1-S
atoms located below it at a distance of 1.249 Å. The four
{Cu(mnt)} building blocks are connected through four S
atoms with four identical Cu–S–Cu) angles of 122°. The
four {Cu(mnt)} planes are not co-planar with the Cu4 plane
Figure 8. Structure (ORTEP drawing) of the anionic unit of 6.
but deviate from it by 36.4°; the two {Cu(mnt)} planes ap-
Thermal ellipsoids are drawn at the 50% probability level. Selected
proach each other with an angle 49.7°. Thus, the structure
bond lengths [Å] and angles [°]: Cu1–P1 2.1683(8), Cu1–S2
2.2166(9), Cu1–S1 2.2176(8); P1–Cu1–S2 128.77(3), P1–Cu1–S1
133.34(3), S2–Cu1–S1 97.81(3).
of this cyclic tetramer resembles a partly opened umbrella
and exhibits C4 symmetry.
Eur. J. Inorg. Chem. 2008, 2407–2420
© 2008 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
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2413

B. K. Maiti, K. Pal, S. Sarkar
FULL PAPER
IR Spectroscopy
lattice (total 18 cations) by C–H···S (dC–S = 3.63–4.02 Å
and ЄC–H···S = 118–176°) and C–H···N (dC–N = 3.12–
3.83 Å and ЄC–H···N = 110–177°) hydrogen-bonding in-
teractions. These bonds play a key role in shaping the dif-
ferent supramolecular topology of 2.
A different structural topology is observed for 3 in com-
parison with 1 or 2 due to the presence of a different
counter-cation. The host framework in 3 is stabilized by C–
H···S (dC–S = 3.65–4.01 Å and ЄC–H···S = 112–171°) and
The IR spectra of 1–6 show the presence a ν(CN) stretch-
ing band[11,17] at 2190 cm–1 and bands due a ν(Cu–S)
stretch in the far IR region below 300 cm–1. A detailed vi-
bration analysis was not attempted but the simple pattern
of the IR band due to the Cu–S linkages shows some inter-
esting features. The appearance of the band in the range
276–280 cm–1 is due to the interaction of the three-coordi-
nate copper–sulfur bond.[27] Figure S12 (see Supporting In-
formation) shows the variation of the ν(Cu–S) absorption
due to the structural variations in 1–6. This absorption ap-
pears at 280 cm–1 (m) in 1, 278 cm–1 (s), with a shoulder at
273 cm–1, in 2, 276 cm–1 (s), with a shoulder at 269 cm–1, in
3, 278 cm–1 (s), with a shoulder at 285 cm–1, in 4, 279 cm–1
(s) in 5, and 277 cm–1 (s) in 6. This trend reflects the shape
of the {Cu4S4} core structure in the solid state. Thus, the
regular symmetric {Cu4S4} core in 1 and 5 shows a single
ν(Cu–S) band whereas the dissymmetric cores found in 2–
4 result in a band with another band as shoulder.
Hydrogen Bonding
The hydrogen atoms of the tetraalkylammonium cations
are extensively involved in hydrogen bonds[28] with the S
and N atoms of the coordinated mnt ligand. These hydro-
gen bonds are like spokes and control the final topology of
the complex anion as a reversely held, partly opened um-
brella where the N atom of a sheet-anchored cation is
placed at the focal point and the {Cu4S4} crown ring forms
the outer rim. There is another important position of an-
other cation just on top of the other face of the partly
opened umbrella. The main interactions are from the hy-
drogen atoms present in the alkyl groups of these two cat-
ions and the sulfurs of the mnt ligands. The hydrogen bonds
arising from these two oppositely placed (one inside the
partly opened umbrella and the other outside the face of
the umbrella) cations are like a bunch of spokes that control
the opening or closing of the {Cu4S4} core. The even or odd
number of carbon atoms of the chain in the alkyl groups
of the quaternary cation further controls the symmetry or
dissymmetry of the {Cu4} core. Thus, the two sheet-an-
chored Me4N+ cations in 1 lie above and below the host
framework and methyl hydrogen atoms are only involved
in hydrogen-bond formation with the S-atoms of the host-
framework (dC–S = 3.64–4.01 Å and ЄC–H···S = 114–161°),
as shown in Figure 9. These distances and angles indicate
weak hydrogen bonding.[28,29] In addition, the other cations
(total 18) present in the lattice are also involved in hydrogen
bonds with either S or N or show both C–H···S (dC–S
=
3.36–4.01 Å and ЄC–H···S = 112–171°) and C–H···N
(dC–N = 3.16–3.74 Å and ЄC–H···N = 103–177°) interac-
tions.
Figure 9. View of the crystal structures of 1 (a), 2 (b), 3 (c), and 5
(d) showing the interactions between the host framework and the
cations above and below it; left: hydrogen bonds are shown as
broken lines and the position of the cation above and below the
virtual Cu4 plane is indicated by a red arrow; right: those cations
in the lattice involved in the formation of H-bonds with S and N
atoms of the mnt ligands are shown as blue balls. Color code: C:
The Me3EtN+ cation in 2 lies above and below the host
framework and forms weak C–H···S interactions (dC–S
=
3.52–4.02 Å and ЄC–H···S = 125–172°) with the S atoms
of this framework, as shown in Figure 9. The host frame-
work is further stabilized by other cations present in the black; N: blue; S: yellow; Cu: cyan; H: green.
2414 Eur. J. Inorg. Chem. 2008, 2407–2420
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© 2008 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim

Plasticity in [(R4–xR1x)4N]4[Cu4{S2C2(CN)2}4]
C–H···N (dC–N = 3.18–3.74 Å and ЄC–H···N = 108–177°) 92.34% increase in areaquad. for 5 with respect to that of 1.
interactions, as illustrated in Figure 9. The C–H groups of This effect is reflected in the {Cu4S4} molecular core, as
the Me2Et2N+ cations interact with the adjacent S and N shown in Figure 10.
of host framework.
The Et4N+ ion in compound 5 lies at the center of the
two sides of the host framework, which forms C–H···S hy-
drogen-bonding interactions with the C–H groups of the
¡cation (Figure 9). Moreover, weak C–H···S (dC–S = 3.49–
4.03 Å and ЄC–H···S = 122–168°) and C–H···N (dC–N
=
3.34–3.73 Å and ЄC–H···N = 107–166°) hydrogen-bonding
interactions are found between the host and neighboring
cations present in the lattice. These varied interactions with
this different tetraalkylammonium cation lead to a different
topology.
The distances between the central nitrogen of the bottom
cation (inside the partly opened umbrella) in 1, 2, 3, and 5
and the corresponding Cu4 plane are 5.359, 4.509, 4.480,
and 3.747 Å, respectively, which means that the Et4N+ cat-
ion lies much closer to the Cu4 plane than any of the other
cations studied here. This is due to the four arms of the
Et4N+ cation acting as a spacer that stretches outward uni-
formly in four different directions, which causes the um-
brella shape to open the most.
It is understandable that such a partly opened umbrella
structure will not be stable in solution as solvation forces
are likely to overcome the energy of these hydrogen bonds,
thereby causing melting in the plasticity of the host. The
existence of a hydrophobic surface area and ion-pair and
packing interactions are expected in the solid state along
with the above-mentioned weak H-bonding. The flexible
structure of the anion maps the hydrophobic surface area
of the cation in an attempt to maximize the anion/cation
surface area interactions. Such a driving force is not ex-
pected to be directional like H-bonding, although some ori-
entational effects are expected to occur. Some distortion of
the cation may reflect packing interactions with the anion.
These forces are individually weak but collectively they dic-
tate a discrete supramolecular entity in the solid state.
Elastic Host-Framework
Figure 10. Various tetramer conformations found in 1 (first row),
2 (second row), 3 (third row), and 4 (fourth row); first column:
bottom view of the host framework (space-filling model) with one
cation (frame-wire model, disordered tetramethyl cation) showing
the cavity size and shape; the red arrows show the area of cavity;
second column: frame-wire model representing the core structure
of the tetramers; the corresponding bond lengths and angles are
obtained by considering Cu ions as the vertex of the quadrilaterals.
Color code: C: black; N: blue; S: yellow; Cu: cyan; H: green.
A significant variation is observed in the core structures
with a change in the cations. Figure 10 shows the structural
variations in the tetramer found in complexes 1–5. As stated
earlier, cations such as Me4N+, Me3EtN+, Me2Et2N+,
MeEt3N+, or Et4N+ each occupy the interior of the corre-
sponding partly opened host cavity with another cation
present on the opposite side. The changes of the S···S sepa-
ration should be reflected in the change in cavity size of
these complexes. The cavity size, in other words the opening
of the umbrella, gradually increases on going from Me4N+
The overall shape of the macrocyclic entity could be hy-
to Et4N+, and we have calculated the area of the quadrilat- pothetically considered to start with the four coplanar cop-
eral (4S areaquad.) formed by connecting the midpoints of per ions situated at the corners of a quadrilateral. We also
the sulfur atoms in structures 1, 2, 3, and 5 (20.98, 27.00, calculated the area of the quadrilateral (4Cu-areaquad.
)
29.68, and 40.36 Å2, respectively). The size of the cavity de- formed by connecting the midpoints of the copper atoms in
pends on the nature of the cation, as the largest cation pro- 1, 2, 3, and 5 (8.85, 10.56, 11.41, and 14.93 Å2, respec-
duces the maximum value of areaquad.. Thus, there is a tively). Thus, there is a 68.70% increase in areaquad. in 5
Eur. J. Inorg. Chem. 2008, 2407–2420
© 2008 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
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2415

B. K. Maiti, K. Pal, S. Sarkar
FULL PAPER
compared to that in 1. This numerical comparison of the
The µ2-S bridge behaves like a hinge on a door, therefore
area of these complexes is guided by three principal param- the Cu–S distance does not contribute to the structural
eters, which can be explained by considering the reference variability. It is important to recognize that it is only within
geometry shown in Figure 11.
the elastic limit of the host frame that various guests can
find suitable linkers for an adaptable overall geometry. The
size and shape of the frameworks are governed by the cat-
ion,[30] therefore the cation plays a decisive role in deciding
the structure in the solid state. A 2D projection view (the
four terminal H-atoms from four arms point vertically in
the virtual 4S-plane) of the cation taken from the 3D geom-
etry is shown in Figure 12 to clarify the situation.
Figure 11. Representation of the geometric parameters: ψ denotes
the angle between the Cu(mnt) and Cu4 planes, θ denotes the angle
(ЄCu–S–Cu) at the S atom which bridges two Cu(mnt) units, and
d denotes the arm length (alkyl chain) of the cation; the other parts
are transparent for clarity.
The three parameters are: (1) the {Cu(mnt)} planes are
inclined at an angle (ψ) with the Cu4 plane; (2) the angle
(θ) at the S atom which is linked to two {Cu(mnt)} units;
and (3) the length (d) of the arms of the cation. These pa-
rameters are related as d is proportional to θ and to 1/ψ.
The angle θ ranges from 76.8° to 126.6° (Table 2) and is
greatly affected even by a partial change in the arms of
the cation. This gives rise to appreciable variations in the
intramolecular Cu···Cu separation, which ranges from
2.753 to 3.952 Å. The four methyl arms of the cation in 1
push the edge of the tetramer in different directions by H-
bonding to make two pairs of Cu–S–Cu angles (88.3° and
80.4°), which reflect the corresponding Cu···Cu separations
of 2.875 and 3.087 Å, respectively. In 2, where one of the
four arms of the cation increases in length from Me to Et,
one of the Cu–S–Cu angles increases to 125.2° (the other
three angles are 110.3°, 79.7°, and 76.8°), which means that
the maximum Cu···Cu separation increases to 3.905 Å (the
other three distances are 3.641, 2.856, and 2.753 Å). In the
Figure 12. Projection view of four terminal H-atoms from four
arms of the cation and four µ-S atoms of the host framework in
the 2D plane (virtual 4S plane, taken from 3D geometry). The blue-
print of the size and shape of the cation and length of the carbon
chain (arm) are shown by solid lines: (a) disordered tetramethylam-
monium cation (almost rectangular), (b) trimethylethylammonium
cation (parallelogram), (c) diethyldimethylammonium cation (close
to rectangular), (d) tetraethylammonium cation (perfect square).
The overall dimension and shape of the cation can there-
molecular tetramer of 3, two of the Cu–S–Cu angles are fore be extracted by considering the four coplanar H-atoms
large (126.6° and 124.5°) and the remaining two angles are to be at the corners of a hypothetical quadrilateral. The
small (77.4° and 77.5°) due to the presence of two Et and blueprint of Me4N+ is a distorted square geometry (due to
two Me arms in the cation. As a result, the Cu···Cu separa- the special position disorder of the N-atom in lattice) with
tions are 3.952, 3.919, 2.782, and 2.784 Å. The four Cu–S– dimensions of 3.203ϫ2.675 Å2 and angles that deviate
Cu angles in 5 are the same (122°) and so are the Cu···Cu slightly from 90° (94.1° and 85.9°). Et4N+ resembles a per-
separations (3.865 Å). This is due to the presence of four fect square with dimensions of 4.701ϫ4.701 Å2 and all the
equivalent Et arms in the cation.
angles being 90°, whereas Me2Et2N+ resembles a rectangle
Table 2. Structural parameters of 1–5.
Complexes
d[a] [Å]
θ (ЄCu–S–Cu) [°]
ψ [°]
Cu···Cu [Å]
1
2
3
5
4 Me
88.3 and 80.4
65.1 and 59.9
2.875 and 3.087
3 Me and Et
2 Me and 2 Et
4 Et
110.3, 125.2, 79.7 and 76.8
126.6, 124.5, 77.4 and 77.5
122
62.9, 55.3, 57.7 and 41.4
56.8, 47.6, 58.5 and 39.9
36.4
3.641, 3.905, 2.846 and 2.753
3.952, 3.919, 2.784 and 2.782
3.865
[a] Substituents in the tetraalkylammonium cation.
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Plasticity in [(R4–xR1x)4N]4[Cu4{S2C2(CN)2}4]
samples (dissolved in acetonitrile) were introduced into the ESI
source with a syringe pump at the rate of 5 µL per minute; the ESI
capillary voltage was set to 3.5 or 2.5 kV and the cone voltage was
40 V. Theoretical isotope ratio calculations were performed using
the program ISOPRO3.[20] Far-infrared spectra were recorded for
CsI pellets in the range 200–400 cm–1 and IR spectra were recorded
for KBr pellets in the range 400–4000 cm–1 with a Bruker Vertex
70 FT-IR spectrophotometer. Elemental analyses for carbon, hy-
drogen, nitrogen and sulfur analysis were determined with a Per-
kin–Elmer 2400 microanalyser.
with sides of 3.815, 3.906, 3.857, and 3.764 Å and angles of
66.3°, 112.5°, 66.3° and 114.8°, and Me3EtN+ resembles a
parallelogram with sides of 3.821, 2.834, 2.741, and 3.229 Å
and angles of 96.2°, 85.9°, 113.3°, and 64.6°. The 4S-base
of the host and the 4H base of the guest are oriented face-
to-face with a rotation angle of close to 90°. These sizes
and shapes of the host framework are in agreement with
expectations based on the size[31] and shape of the cations,
therefore the structural design information[32] stored in a
cation is transferred to the host framework through H-
bonding to yield a specific supramolecular entity. This work
unambiguously proves that how a discrete {Cu4S4} frame-
work responds to the inclusion of a guest depends on the
General Procedure for the Synthesis of Complexes 1–5: Solid CuCl
(0.99 g, 10 mmol) was added to a solution of Na2(mnt) (1.86 g,
10 mmol) in 80 mL of H2O and the mixture was stirred for 30 min
to dissolve the solid. An excess of the corresponding tetraalkylam-
nature of the guest. More interestingly, and contrary to monium salt [Me4NBr (1), Me3EtNI (2), Me2Et2NBr (3),
MeEt3NBr (4), and Et4NBr (5)] was added to the solution to pre-
cipitate a yellow solid, which was collected by filtration, washed
with H2O and 2-propanol, and finally with diethyl ether. Diffrac-
tion-quality crystals were obtained by diffusion of diethyl ether
vapor into an acetonitrile solution of the crude product.
common host-guest assemblies, the present framework
demonstrates elasticity by shrinking and expanding to ac-
commodate guests of varying sizes and shapes.
[Me4N]4[Cu4(mnt)4] (1): Orange crystals, m.p. 232–234 °C, yield
2.28 g (82%). C32H48Cu4N12S8 (1111.6): calcd. C 34.55, H 4.32, N
15.11, S 23.03; found C 34.50, H 4.29, N 15.12, S 22.97. IR (KBr):
ν = 2190 cm–1 [ν(CϵN)]. FT far-IR (CsI): ν = 280 cm–1 [ν(Cu–S)].
Conclusions
This work illustrates the power of a guest cation to deter-
mine the final shape of some supramolecular species in the
solid state. The host anion is relaxed in solution and be-
haves like melted plastic, i.e., free from any rigid shape. The
guest molds the shape of the cavity of the melted elastic
host due to its size and shape and the host then solidifies
during the crystallization process and assumes a rigid plas-
tic shape. The molecular structural design information that
is stored in the cation is therefore transferred to the host
framework through H-bonding to yield a specific supramo-
lecular entity. The combined UV/Vis, NMR, CV, and ESI-
MS results confirm that all these designed structures are
lost in solution, which means that guest encapsulation and
guest exchange become possible by taking advantage of the
plasticity in the solid state and the elasticity in solution.
˜
˜
UV/Vis: λ (ε) = 377 nm (46195 –1 cm–1), 266 (36275). ESI-MS: m/z
1035.81 [Me4N]3[Cu4(mnt)4]–. 13C NMR ([D6]DMSO): δ = 124.67
(CN), 120.12 (C=C), 59.48 ppm (CH3).
[Me3EtN]4[Cu4(mnt)4] (2): Orange crystals, m.p. 220–222 °C, yield
2.39 g (82%). C36H56Cu4N12S8 (1167.7): calcd. C 36.99, H 4.79, N
14.39, S 21.93; found C 36.97, H 4.74, N 14.32, S 21.95. IR (KBr):
ν = 2190 cm–1 ν(CϵN). FT-far-IR (CsI): 279 cm–1 [ν(Cu–S)]. UV/
˜
Vis: λ (ε) =377 nm (46185 –1 cm–1), 266 (36257). ESI-MS: m/z
1077.94 [Me3EtN]3[Cu4(mnt)4]–. 13C NMR ([D6]DMSO): δ =
124.67 (CN), 120.12 (C=C), 60.94 (α-CH2), 51.73 (CH3), 8.16 ppm
(β-CH3).
[Me2Et2N]4[Cu4(mnt)4] (3): Orange crystals, m.p. 201–203 °C, yield
2.54 g (83%). C40H64Cu4N12S8 (1223.8): calcd. C 39.23, H 5.23, N
13.73, S 20.92; found C 38.99, H 5.21, N 13.75, S 20.94. IR (KBr):
ν = 2190 cm–1 [ν(CϵN)]. FT-far-IR (CsI): ν = 276 cm–1 [ν(Cu–S)].
˜
˜
UV/Vis: λ (ε) =377 nm (46177 –1 cm–1), 266 (36263). ESI-MS: m/z
1119.87 [Me2Et2N]3[Cu4(mnt)4]–. 13C NMR ([D6]DMSO): δ =
124.67 (CN), 120.12 (C=C), 58.04 (α-CH2), 48.99 (CH3), 7.83 ppm
(β-CH3).
Experimental Section
Materials: All manipulations were carried out under argon using
Schlenk-line techniques. Na2(mnt) was prepared by the literature
method,[33] as was diethyldimethylammonium bromide.[34] Freshly
prepared[35] CuCl was used in the synthesis. Ethyltrimethylammo-
nium iodide, tetramethylammonium bromide, triethylmethylammo-
nium bromide, and tetraethylammonium bromide were purchased
from Aldrich and used without further purification.
[MeEt3N]4[Cu4(mnt)4] (4): Yellowish orange crystals, m.p. 189–
191 °C, yield 2.72 g (85%). C44H72Cu4N12S8 (1279.9): calcd. C
41.25, H 5.62, N 13.13, S 20.00; found C 41.28, H 5.58, N 13.10,
S 19.98. IR (KBr): ν = 2190 cm–1 [ν(CϵN)]. FT-far-IR (CsI): ν =
˜
˜
278 cm–1 [ν(Cu–S)]. UV/Vis: λ (ε) =377 nm (46159 –1 cm–1), 266
(36235). ESI-MS: m/z 1161.84 [MeEt3N]3[Cu4(mnt)4]–. 13C NMR
([D6]DMSO): δ = 124.67 (CN), 120.12 (C=C), 53.71 (α-CH2), 50.33
(CH3), 11.34 ppm (β-CH3).
Physical Measurements: Cyclic voltammetry (CV) and differential
pulse polarography (DPP) were performed with an Epsilon EC-
20 machine. The electrolytic cell used was a conventional three-
compartment cell with a GCE working electrode, a Pt auxiliary
electrode, and an Ag/AgCl reference electrode. The CV measure-
ments were performed at room temperature using 0.1  KPF6 as
the supporting electrolyte in CH3CN at a scan rate of 100 mVs–1.
The ferrocenium/ferrocene couple was used as the internal standard
(E0 = 0.53 V under these conditions). Electronic absorption spectra
were measured with the help of a USB2000 UV/Vis Spectrometer.
13C NMR spectra were recorded with a JEOL JNM-LA 400 FT-
NMR machine. The negative mode ESI mass spectra were recorded
with a Waters Micromass Q TOF Premier Mass Spectrometer. The
[Et4N]4[Cu4(mnt)4] (5): Yellow crystals, m.p. 178–180 °C, yield
2.84 g (85%). C48H80Cu4N12S8 (1335.9): calcd. C 43.11, H 5.99, N
12.57, S 19.16; found C 43.09, H 5.98, N 12.55, S 19.13. IR (KBr):
ν = 2190 cm–1 [ν(CϵN)]. FT-far-IR (CsI): ν = 279 cm–1 [ν(Cu–S)].
˜
˜
UV/Vis: λ (ε) =377 nm (46195 –1 cm–1), 266 (36245). ESI-MS: m/z
1203.99 [Et4N]3[Cu4(mnt)4]–. 13C NMR ([D6]DMSO): δ = 124.67
(CN), 120.12 (C=C), 51.49 (α-CH2), 7.15 ppm (β-CH3).
Preparation of [Et4N][Cu(mnt)(PPh3)] (6): Compound 5 (0.34 g,
0.25 mmol) and PPh3 (0.27 g, 1.2 mmol) were added to 40 mL of
dichloromethane and the mixture stirred for about 5 min to give a
Eur. J. Inorg. Chem. 2008, 2407–2420
© 2008 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
www.eurjic.org
2417

B. K. Maiti, K. Pal, S. Sarkar
FULL PAPER
Table 3. Crystallographic data and refinement details for complexes 1–3, 5, and 6.
Compounds
1
2
3
5
6
Empirical formula
Formula weight
Temperature [K]
Crystal system
C32H48Cu4N12S8 C36H56Cu4N12S8 C40H64Cu4N12S8 C48H80Cu4N12S8 C30H35CuN3PS2
1111.58
100(2)
monoclinic
C2/c
1167.69
100(2)
1223.79
100(2)
monoclinic
P21/c
1335.88
100(2)
tetragonal
P4/n
596.27
100(2)
monoclinic
P21/n
triclinic
¯
Space group
P1
a [Å]
b [Å]
c [Å]
α [°]
13.379(5)
27.810(5)
13.075(5)
90
94.773(5)
90
4848(3)
4
1.523
13.279(5)
14.144(5)
15.524(5)
64.226(5)
87.667(5)
82.496(5)
2602.7(16)
2
14.730(5)
28.028(5)
13.408(5)
90
97.053(5)
90
5494(3)
4
1.480
14.158(5)
14.158(5)
15.044(5)
90
90
90
3015.6(18)
2
1.471
11.648(5)
11.579(5)
22.173(5)
90
94.679(5)
90
2980.6(19)
4
1.329
β [°]
γ [°]
Volume [Å3]
Z
Dc [Mgm–3]
1.490
1.969
µ [mm–1]
2.113
1.872
1.712
0.950
F(000)
θ range [°]
2272
1200
2528
1392
1248
2.14–28.32
6004(16172)
1.159
2.11–28.32
12419(17494)
1.048
2.07–28.34
13580(36819)
1.040
1.98–28.33
3761(19978)
1.295
1.99–28.31
7359(19617)
1.023
Independent reflections (collected)
Goodness-of-fit on F2
Final R indices [I Ͼ 2σ(I)] R1,[a] (wR2)[b] 0.0437 (0.0890)
0.0878 (0.1912)
0.0864 (0.1925)
0.0768 (0.1633)
0.0460 (0.1037)
[%]
2
2 2
[a] R1 = ∑||Fo| – |Fc||/∑|Fo|. [b] wR2 = {∑[w(Fo – Fc ) ]/∑[w(Fo2)2]}1/2
.
clear, light yellow solution. Addition of petroleum ether afforded 6
as a pale-yellow crystalline product, which was collected by fil-
tration and washed with petroleum ether. Single crystals suitable
for X-ray structure analysis were grown by slow diffusion of petro-
leum ether into a dichloromethane solution, yield 0.54 g (90%),
m.p. 159–161 °C. C30H35CuN3PS2 (596.27): calcd. C 60.38, N 7.04,
H 5.87, S 10.73; found C 60.40, N 7.00, H 5.89, S 10.71. IR (KBr):
ν = 2190 cm–1 [ν(CϵN)]. FT-far-IR (CsI): ν = 277 cm–1 [ν(Cu–S)].
CCDC-668698 (for 5), -668699 (for 2), -668700 (for 1), -668701 (for
6), -668702 (for 3) contain the supplementary crystallographic data
for this paper. These data can be obtained free of charge from The
Cambridge Crystallographic Data Center via www.ccdc.cam.ac.uk/
data_request/cif.
Supporting Information (see also the footnote on the first page of
this article): UV/Vis spectra of [Et4N]4[Cu4(mnt)4], [Et4N]
4[Cu8(mnt)6], and [Et4N]2[CuII(mnt)2] (Figure S1); CV of [Et4N]
4[Cu4(mnt)4] at platinum and glassy carbon disc electrodes in the
scan range 50–400 mVs–1 (Figure S2); CV (repetitive scan) of
[Et4N]4[Cu4(mnt)4] (Figure S3); theoretical and experimental (ESI-
MS) isotopic distribution patterns of the parent ion peak for
[Me4N]3[Cu4(mnt)4]– (Figure S4), [Me4EtN]3[Cu4(mnt)4]– (Figure
S5), [Me2Et2N]3[Cu4(mnt)4]– (Figure S6), [MeEt3N]3[Cu4(mnt)4]–
(Figure S7); theoretical and experimental (ESI-MS) isotopic distri-
bution patterns of the ion peak for [Et4N]2[Cu3(mnt)3]– (Figure S8),
[Et4N][Cu2(mnt)2]– (Figure S9), [Cu(mnt)]– (Figure S10); XRD
pattern of [Et4N]4[Cu4(mnt)4] (Figure S11); far-FT-IR spectra of
1–6 (Figure S12).
˜
˜
UV/Vis:
λ
(ε) =372 nm (11305 –1 cm–1). ESI-MS: m/z 465
[Cu(mnt)PPh3]–. 13C NMR ([D6]DMSO, δ): δ = 133.48 (1-Ph),
130.60 (o-CH of Ph), 129.11 (m,p-CH of Ph), 125.21 (CN), 120.86
(C=C), 51.55 (α-CH2), 7.16 ppm (β-CH3).
X-ray Crystallographic Data Collection and Refinement of Struc-
tures: Single crystals of 1–6 suitable for X-ray diffraction measure-
ments were obtained by slow diffusion of diethyl ether vapor into
a solution of the respective complex in acetonitrile X-ray data were
collected on a Bruker SMART APEX CCD-based X-ray dif-
fractometer equipped with a CCD area detector. Data were col-
lected using graphite-monochromated Mo-Kα radiation (λ
=
0.71069 Å) at low temperature (100 K). All empirical absorption
corrections were applied using the SADABS program.[36] Cell con-
stants were obtained from the least-squares refinement of three-
dimensional centroids through the use of CCD recording of narrow
ω rotation frames, completing almost all-reciprocal space in the
stated θ range. All data were collected with SMART 5.628 (Bruker,
2003), and were integrated with the Bruker SAINT[37] program.
Each structure was solved using SIR-97 and refined using
SHELXL-97.[38] The space group of each compound was deter-
mined based on the lack of systematic absences and intensity statis-
tics. Full-matrix least-squares/difference and Fourier cycles were
performed to locate the remaining non-hydrogen atoms. All non-
hydrogen atoms were refined with anisotropic displacement param-
eters. Some carbon atoms of the ethyl groups of the cations were
disordered for 2, 3, and 5; these atoms were refined with the free
part instruction in SHELXL-97. Additional crystallographic calcu-
lations were performed with the PLATON[39] program suite. Fur-
ther details of the crystallographic data and refinement parameters
are provided in Table 3.
Acknowledgments
B. K. M. and K. P. gratefully acknowledge senior doctoral fellow-
ships from the UGC and the CSIR, New Delhi, respectively, and
S. S. thanks the DST, New Delhi, for a research grant.
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2419

B. K. Maiti, K. Pal, S. Sarkar
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Received: January 25, 2008
Published Online: April 15, 2008
2420
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