distances of 1 are (Cu· · ·Cu)avg = 2.76 A and ∠(Cu–S–Cu)avg = 76◦
˚
Synthesis
while 2 (or 3) has ∠(Cu–S–Cu)avg = 103.75◦ and (Cu· · ·Cu)avg
=
Preparation of 1. Solid CuCl (0.99 g, 10 mmol) was added
to a solution of Na2(mnt) 11 (1.86 g, 10 mmol) in 80 mL H2O
and the mixture was stirred for 1/2 h to dissolve the solid.
Excess of Bu4NBr was added to the solution to precipitate a
yellow solid (1), which was collected by filtration, washed with
H2O, isopropanol and finally by diethyl ether. Diffraction quality
crystals were obtained by vapor diffusion of diethyl ether into an
acetonitrile solution of the crude product. Yield: 2.72 g (78%).
Anal. calc. (found): C, 53.78 (53.73); N, 9.41 (9.38); H, 8.07 (8.08);
S, 14.34 (14.37). IR (KBr, cm−1): 2225 m(C≡N). UV-Vis, k/nm
(e/M−1 cm−1): 377 (36600). 13C NMR (CD3CN, d, ppm); 126.35
˚
3.47 A. So, breaking of metal–sulfur bonds with the formation of
newer bonds may take place in such conversion. The copper ion
normally prefers a trigonal planar geometry. So the newly formed
metal–ligand coordinated bonds may drag the sulfur atoms away
from their earlier positions. As a result, the two enantiomers may
re-organize with square bases. These further adopt an offset face-
to-face arrangement to form the cubic complex 3 (and 2) as shown
in Fig. 4. So in the first step, the conversion from 1 to the larger
complex (2 or 3) may occur either with the intermediate formation
of a hexanuclear form by the combination of two enantiomers or
with the formation of a tetranuclear intermediate by the addition
of a metal ion to 1 (Fig. 6). For the reverse reaction, the newly
capped metal ion may be easily released from the larger complex by
the interaction with a halide to form an intermediate {Cu6(mnt)6}
moiety which may dissociate to form 1. The Cu· · ·Cu distance
=
(–CN), 121.40 (–C C–), 59.69 (–aCH2), 24.61 (–bCH2), 20.51
(–cCH2) and 13.95 (–dCH3). Mp 160–162 ◦C.
Preparation of 2. Solid CuCl (0.099 g, 1 mmol) was added
to 25 mL of acetonitrile containing 1.34 g (1 mmol) of 1 and the
resultant solution was stirred for 10–15 min. The resultant solution
was filtered and to this yellow solution H2O was added dropwise to
start hazy nucleation for crystallization. It was left as such at 0 ◦C
and on standing overnight, yellow crystalline 2 was precipitated
out. This was isolated by filtration, and washed with isopropanol
and diethyl ether. Yield: 1.05 g (68%). IR spectral data are identical
with earlier reported data.5 UV-Vis, k/nm (e/M−1 cm−1): 377
(32928). Mp 195–198 ◦C. Crystals of 2 showed lattice parameters
identical to those of the complex synthesized by another method.5
˚
in 1 is in◦the range 2.66–2.83 A, with ∠Cu–S–Cu angles of ca.
72.8–77.8 , suggesting a relatively weak Cu· · ·Cu interaction.10
The Cu· · ·Cu distance of the hexanuclear core, {Cu6(mnt)6}, in 3
˚
is 3.09–3.83 A and the resultant bond angle at the bridging sulfur
is 88.1–116.9◦, suggesting ready dissociation of such a species to
yield 1.
Conclusion
In summary, we have shown that a trinuclear complex 1 can
function as a sulfur donor ligand in two enantiomeric forms to
chelate a CuI or AgI ion to form an octanuclear complex 2 or 3.
The introduced CuI or AgI ions in 2 or 3 can readily be removed by
halide ion leaching, reverting these back to the starting trinuclear
complex 1.
Preparation of 3. Solid AgCl (0.144 g, 1 mmol) was added
to 25 mL of acetonitrile containing 1.34 g (1 mmol) of 1 and
the resultant mixture was stirred until all solid was dissolved.
The yellow solution was filtered and H2O was added dropwise
to the filtrate to make it cloudy, i.e. to the point of incipient
crystallization, and was stored at 0 ◦C overnight. Orange crystals
of 3 were separated out, which were isolated by filtration followed
by washing with isopropanol and diethyl ether. Yield: 1.08 g (75%).
Anal. calc. (found): C, 43.85 (43.88); N, 9.30 (9.28); H, 5.98 (5.95);
S, 15.95 (15.97). IR (KBr, cm−1): 2225 m(C≡N). UV-Vis, k/nm
(e/M−1 cm−1): 377 (32135). 13C NMR (CD3CN, d, ppm); 127.39
Experimental
General
=
(–CN), 119.44 (–C C–), 59.69 (–aCH2), 24.55 (–bCH2), 20.50
All starting materials were purchased from commercial sources
and were used without further purification. Solvents were freshly
distilled over appropriate drying reagents. Na2(mnt) was prepared
as described in the literature.11 All reactions were carried out under
an argon atmosphere using the standard Schlenk technique unless
otherwise stated. Cyclic voltammetry was performed using an
Epsilon EC-20 with a scan rate of 100 mV s−1. The electrolytic
cell used was a conventional three-compartment cell, in which a
GCE working electrode, a Pt auxiliary electrode, and a Ag/AgCl
reference electrode were employed. The CV measurements were
performed at room temperature using 0.2 M (nBu4N)(ClO4)
as the supporting electrolyte and CH3CN as a solvent. The
ferrocenium/ferrocene couple was used as the internal standard
(E0 = 0.53 V). Electronic absorption spectra were measured with
use of a USB2000 UV-Visible spectrometer. 13C NMR spectra were
recorded on JEOL JNM-LA 400 FT-NMR machine. IR spectra
were recorded by KBr pellet in the range 400–4000 cm−1 on a
Bruker Vertex 70, FT-IR spectrophotometer. Elemental analyses
for carbon, hydrogen, nitrogen and sulfur analysis were carried
out with a Perkin–Elmer 2400 microanalyser.
(–cCH2) and 13.92 (–dCH3). Mp 175–178 ◦C.
Data collection and analysis. Suitable diffraction quality crys-
tals of 1, 2 and 3 were obtained from the crystallization procedures
described in each synthesis.† The crystals used in the analyses were
glued to a glass fiber and mounted on a Bruker SMART APEX
diffractometer. The instrument was equipped with a CCD area
detector and data were collected using graphite-monochromated
˚
Mo Ka radiation (k = 0.71069 A) at low temperature (100 K). All
empirical absorption corrections were applied using the SADABS
program. Cell constants were obtained from the least-squares
refinement of three-dimensional centroids through the use of CCD
recording of narrow x rotation frames, completing almost all-
reciprocal space in the stated h range. The cell parameters of
complex 2 have been found to be identical to those of the known
compound reported earlier.5 All data were collected with SMART
5.628 (Bruker, 2003), and were integrated with the Bruker SAINT
program. The structure was solved using SIR97 and refined using
SHELXL-97.12 The respective space groups of these compounds
This journal is
The Royal Society of Chemistry 2008
Dalton Trans., 2008, 1003–1008 | 1007
©
Maiti, Biplab K.
