Communications
unprecedented. Lai and co-workers[15] observed a similar
acetonitrile at 0.725 V in a cyclic-voltammetry cell. The
CuII complex could be stabilized for a short time by quench-
ing the solution at 77 K. The ESR spectrum of 12 shows gII(av)
at 2.54 with A(av) = 190 G and g?(av) at 2.09 with A?(av)
= 67.50 G. The green-colored CuII complex is reduced again
to the orange-colored CuI complex within half an hour when
left to stand in solution.
reduction of a CuII ion when treated with a quinquedentate
macrocycle, and they suggested that the autoreduction
occurred because of the electron-donating properties of the
ligand or the geometry of the complex formed.
Single crystals of 10 were isolated as orange needles from
a solution in acetonitrile/ether for X-ray diffraction studies.[16]
The structure confirms the novel coordination of the CuI
center to all four nitrogen atoms and to the two mercury
atoms to give a distorted octahedral geometry (Figure 1). The
The electronic absorption spectrum of 9 in acetonitrile
solution exhibits a strong absorption band at 292 nm (e =
6400mꢀ1 cmꢀ1). Complex 10 shows a low-energy band at
410 nm (e = 800mꢀ1 cmꢀ1) and a strong peak at 292 nm in the
same solvent. The band at 410 nm is attributed to a metal-to-
ligand charge transfer. CuI complexes 10 and 11 were found to
be luminescent at room temperature and also at 77 K both in
acetonitrile solution and in the solid state. The acetonitrile
solution of 10 shows a very weak emission at lmax = 445 nm.
Upon cooling to 77 K and in the solid state, the emission
spectrum becomes more intense. Upon excitation at lmax
= 450 nm in the solid state, the emission spectra exhibited a
sharp band at lmax = 485 nm, along with weaker bands at 530
and 545 nm. Detailed photophysical studies are in progress.
Successful trapping of a CuI ion in a mercuramacrocycle
demonstrates that a metallamacrocycle can be used to entrap
suitably sized metal ions with metal–metal interactions in a
preorganized system. This approach can be extended to
prepare various mixed-metal systems, in particular those with
d10···d10 interactions, with interesting structural and lumines-
cent properties.
Figure 1. PLATON view of compound 10 that shows the dimerization
of compound 10 through a Hg···Hg intermolecular homometallic
d10···d10 interaction and Hg···Cu d10···d10 heterometallic interactions.
Hydrogen atoms and anions are omitted for clarity. Selected bond
lengths [ꢁ] and angles [8]: Cu1–Hg1 2.921(7), Cu1–Hg2 2.919(7), Hg2–
Hg2# 3.203(4), Hg1-Cu1-Hg2 177.88(3), Cu1-Hg2-Hg2# 154.40(17),
C11-Hg1-C12 177.80(18), C27-Hg2-C28 177.21(18), Hg2-Cu1-N1
69.70(12), Hg2-Cu1-N4 71.03(10), Cu1-Hg2-Hg2# 154.40(17).
Received: November 1, 2004
Published online: February 3, 2005
Keywords: copper · heterometallic complexes · mercury ·
.
metallacycles · metal–metal interactions
Cu···Hg interatomic distances (Cu1–Hg1 2.921 ꢀ and Cu1–
Hg2 2.919 ꢀ) are shorter than the sum of the van der Waals
radii of the copper and mercury atoms (rvwd = 1.40 and 1.75 ꢀ,
respectively).[17] However, this Cu···Hg distance is longer than
the Cu···Hg distance found in the polymetallic mesocycle
[1] a) M. Newcomb, J. H. Homer, M. T. Blanda, J. Am. Chem. Soc.
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[Hg{Fe[Si(OMe)3](CO)3(m-dppm)}2Cu]+ [18] Further inspec-
.
tion of the crystal packing revealed that two cations of 10
are linked by a Hg···Hg intermolecular interaction of 3.20 ꢀ
to give a chain of six d10 ions. The Hg···Hg distance is longer
than the Hg···Hg distance in metallic mercury (3 ꢀ)[19] but
much shorter than those observed in other structures with
Hg···Hg interactions[5b,c,d,g,20] and the calculated value for the
perpendicular HgMe2 dimer (3.50 ꢀ).[17b] However, this
distance in 10 is slightly longer than that observed for
bis(trimethylsilyl)mercury.[21] The important feature of this
molecule is the presence of two types of d10···d10 metallophilic
interaction: a homometallic HgII···HgII interaction and a
heterometallic HgII···CuI interaction.
Complexes 10 and 11 show a well-defined reversible redox
wave with E1/2 values of 0.55 and 0.57 V versus the saturated
calomel electrode (SCE) and DE values of 0.078 and 0.080 V
with Ipc/Ipa values of 1.06 and 1.03, respectively. The green-
colored solution of the CuII complex 12 could be generated by
coulometric oxidation of the orange-colored solution of 10 in
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