Dicopper(I,I) and delocalized mixed-valent dicopper(I,II) complexes of a sterically hindered carboxylate ligand

Article abstract of DOI:10.1039/b301154b

Admixture of the lithium salt of the bulky ligand 2,6-dimesitylbenzoate [ArCO₂]^- with [Cu(CH₃CN)₄]O ₃SCF₃ yielded the dicopper(I,I) complex [(ArCO ₂)₂Cu₂(THF)₂)] (1), which upon oxidation with AgX (X = SbF₆^- or ClO₄ ^-) in THF afforded the mixed-valent complexes [(ArCO ₂)₂Cu₂(THF)₂]SbF₆ (2) and [(ArCO₂)₂Cu₂(THF)₃]ClO₄ (3), respectively. Fully delocalized mixed-valent (Cu^1.5Cu ^1.5) formulations for 2 and 3 were determined on the basis of X-ray crystallography and UV-vis, resonance Raman, ¹H NMR, and EPR spectroscopy. Notably, solvent dependent UV-vis spectra suggest that THF and/or counter ion coordination influence the intermetal bonding interactions in the mixed-valent cores. The Royal Society of Chemistry 2003.

Full text of DOI:10.1039/b301154b

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Dicopper(I,I) and delocalized mixed-valent dicopper(I,II) complexes
of a sterically hindered carboxylate ligand
John R. Hagadorn, Theresa I. Zahn, Lawrence Que, Jr.* and William B. Tolman*
Department of Chemistry, Center for Metals in Biocatalysis, University of Minnesota,
207 Pleasant St. SE, Minneapolis, MN 55455, USA. E-mail: que@chem.umn.edu.
E-mail: tolman@chem.umn.edu; Fax: 612 624 7029; Tel: 612 625 0389, 4061
Received 29th January 2003, Accepted 17th March 2003
First published as an Advance Article on the web 28th March 2003
Admixture of the lithium salt of the bulky ligand 2,6-dimesitylbenzoate [ArCO2]Ϫ with [Cu(CH3CN)4]O3SCF3
yielded the dicopper(,) complex [(ArCO2)2Cu2(THF)2)] (1), which upon oxidation with AgX (X = SbF6Ϫ or ClO4
in THF afforded the mixed-valent complexes [(ArCO2)2Cu2(THF)2]SbF6 (2) and [(ArCO2)2Cu2(THF)3]ClO4 (3),
respectively. Fully delocalized mixed-valent (Cu1.5Cu1.5) formulations for 2 and 3 were determined on the basis of
Ϫ
)
X-ray crystallography and UV-vis, resonance Raman, 1H NMR, and EPR spectroscopy. Notably, solvent dependent
UV-vis spectra suggest that THF and/or counter ion coordination influence the intermetal bonding interactions in
the mixed-valent cores.
and resonance Raman spectral properties, the examples of such
Introduction
compounds we have prepared exhibit interesting 1H NMR
Since the discovery1 of the novel mixed-valent bis(thiolato)-
spectral properties and solvent-dependent electronic absorption
spectral features that implicate subtle effects of solvent and/or
counter ion coordination on the Cu–Cu interaction.
dicopper “CuA” electron transfer biosite in which an unpaired
electron is fully delocalized between the two metal ions (i.e.,
class III mixed valent behavior),2 interest has focused on under-
standing its unique structural, spectroscopic, and functional
properties.3 As a means toward these ends, Cu1.5Cu1.5 com-
pounds have been targeted for synthesis and in-depth character-
ization.4–10 A key challenge in designing such species is
enforcing full delocalization in a mixed-valent dicopper com-
plex, which more typically adopts an unsymmetric structure
with the unpaired electron localized to a significant extent on
one site (class I or II).11 Most of the ligands used successfully
so far to access fully delocalized mixed valent complexes
sequester the copper ions in a symmetrical environment that
also inhibits intermolecular reactions (e.g., disproportionation).
For example, class III Cu1.5Cu1.5 complexes were prepared using
the XDK ligand system (Fig. 1(a)),7 in which the effects of
steric hindrance and preorganization of the ligating carboxylate
groups combine to stabilize the mixed valent core (as well
as other biologically relevant dimetal species)12 sufficiently
for structural and spectroscopic characterization. In a comple-
mentary approach, sterically hindered benzoate ligands
(Fig. 1(b)) have been used in order to prepare coordinatively
unsaturated and reactive iron complexes that model key aspects
of metalloprotein active sites.13 A dicopper(,) complex
bridged by a bulky benzoate was reported recently.14 Here, we
show that such ligands also may be used to construct di-
copper(,) complexes and class III mixed valent species derived
therefrom. Although similar to other delocalized mixed-valent
dicopper complexes with respect to their structures and EPR
Results and discussion
Syntheses and structures
Treatment of [ArCO2]Li(Et2O)0.5(CH3CN)0.5 with 1 equiv.
[Cu(CH3CN)4]O3SCF3 yielded [(ArCO2)2Cu2(THF)2)] (1) as
colorless crystals in moderate yield (Scheme 1). As shown by
X-ray crystallography (Fig. 2, Table 1), 1 adopts a discrete
molecular structure that features inversion symmetry, a short
Cu–Cu separation of 2.524(1) Å, and three-coordinate Cu()
ions in a T-shaped geometry. The overall structure contrasts
with the oligo- or poly-meric topologies typical for Cu() com-
plexes of simple carboxylates (e.g. acetate or benzoate),15 but is
similar to that of a class of dicopper(,) compounds prepared
using XDK derivatives.16 Thus, higher aggregate formation is
Ϫ
effectively inhibited by the bulk of the ArCO2 ligand, albeit
through steric influences that differ from those factors that
control complex nuclearity and structure in the preorganized
XDK system. The high symmetry of the solid state structure of
Fig. 1 (a) XDK ligand system (R = Me, Pr, Bn). (b) Sterically hindered
carboxylates (R = Me, RЈ = H or Me).
Scheme 1 Synthesis of complexes.
D a l t o n T r a n s . , 2 0 0 3 , 1 7 9 0 – 1 7 9 4
T h i s j o u r n a l i s © T h e R o y a l S o c i e t y o f C h e m i s t r y 2 0 0 3
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Table 1 Selected bond distances (Å) and angles (Њ) for the X-ray
structures of 1 and 3a
ates and THF solvate molecules. Both Cu sites are square
pyramidal, with the axial positions occupied by a weakly
bonded ClO4Ϫ (Cu2–O8 2.501(4) Å) or a THF molecule (Cu1–
O6 2.146(4) Å). The Cu–Cu distance (2.3947(8) Å) is signifi-
cantly shorter than that of 1 (by >0.12 Å) and is comparable to
the shortest value reported for a delocalized mixed valence
dicopper complex (2.3876(12) Å).6 Since Cu–Cu bonding has
been implicated for other mixed-valence species with similar, or
even slightly longer metal–metal distances, an analogous inter-
metal bonding interaction is indicated. This conclusion is
supported by spectroscopic data for both 2 and 3, as described
below. A preliminary X-ray crystal structure was acquired for 2,
but a full structure solution was not possible due to the quality
of the data.‡ Nonetheless, a molecular topology analogous to
that of 3 was discernible, the only notable difference being the
absence of an axial THF solvate molecule on one Cu ion and
1
Cu1–Cu1A
Cu1–Cu1A
Cu1–O3
2.524(1)
2.524(1)
2.247(3)
Cu1–O1
Cu1–O2A
1.919(3)
1.920(3)
O1–Cu1–O3
O3–Cu1–O2A
94.0(1)
95.7(1)
O1–Cu1–O2A
170.3(1)
3
Cu1–Cu2
Cu1–O1
Cu1–O3
Cu1–O5
Cu2–O8
2.3947(8)
1.901(3)
1.894(3)
2.055(3)
2.501(4)
Cu1–O6
Cu2–O2
Cu2–O4
Cu2–O7
2.146(4)
1.882(3)
1.881(3)
2.022(4)
Ϫ
the presence of SbF6 weakly bonding to the axial position of
the other.
O3–Cu1–O1
O1–Cu1–O5
O1–Cu1–O6
O4–Cu2–O2
O2–Cu2–O7
164.1(2)
89.5(1)
95.3(2)
167.2(2)
93.6(2)
O3–Cu1–O5
O3–Cu1–O6
O5–Cu1–O6
O4–Cu2–O7
92.4(2)
100.4(2)
92.4(2)
91.6(2)
a Estimated standard deviations are indicated in parentheses. Symmetry
transformations used to generate equivalent atoms for 1 are Ϫx ϩ 1,
Ϫy ϩ 2, Ϫz ϩ 1.
Fig. 3 Representations of the X-ray structure of 3, with all non-
hydrogen atoms shown as 50% ellipsoids and the carboxylate
substituents omitted for clarity.
Spectroscopic features
The EPR spectra of 2 and 3 exhibit a rhombic signal with
extensive hyperfine features, including a clearly discernible
seven-line pattern at low field due to coupling to two I = 3/2
Cu ions (shown for 2 in Fig. 4, bottom; 1 : 1 THF–toluene,
X-band, 2 K). The following g values and hyperfine parameters
were determined via spectral simulation (Fig. 4, top): g1 = 2.027,
g2 = 2.159, g3 = 2.309, ACu = 22.5 G, ACu = 63.0 G, ACu
=
1
2
3
132.9 G. The signals confirm class III mixed valence form-
ulations for 2 and 3, and are similar to those exhibited for other
reported examples of such species.4,6–8
1
The H NMR spectrum of crystals of 2 in CDCl3 (Fig. 5)
reveals six broadened and slightly shifted features in the
Fig. 2 Representation of the X-ray crystal structure of 1, with all non-
hydrogen atoms shown as 50% ellipsoids.
1 is retained in solution, as evinced by the single set of peaks for
1
the carboxylate ligand and coordinated THF in its H NMR
spectrum.
Dropwise addition of THF solutions of AgX (1 equiv.,
X = SbF6Ϫ or ClO4Ϫ) to a colorless THF solution of 1 immedi-
ately yielded air-sensitive violet solutions and a dark precipitate
(presumably, Ag0) (Scheme 1). After filtration, purple
crystalline products were formed by the addition of pentane
and cooling to Ϫ30 ЊC. The products were identified as
[(ArCO2)2Cu2(THF)2]SbF6 (2) and [(ArCO2)2Cu2(THF)3]ClO4
(3) as described below.† Upon exposure to vacuum, the crystals
Ϫ
of the SbF6 salt became gray, and loss of coordinated THF
was confirmed by elemental analysis. Interestingly, exposure of
the gray solid to THF vapor resulted in conversion back to
purple material, a process that may be repeated many times
Ϫ
without apparent decomposition. Crystals of the ClO4 salt 3
suitable for an X-ray diffraction study were grown from a
THF-pentane mixture (Fig. 3). The structure shows a dicopper
core comprising Cu ions supported by a pair of µ-1,3-carboxyl-
Fig. 4 X-Band EPR spectrum (bottom) and simulation (top) of 2 in
1 : 1 THF–toluene, 2 K.
‡ Unit cell information: C62H74ClCu2O11, M = 1157.74, orthorhombic,
Pbcn, a = 19.007(1) Å, b = 24.185(1) Å, c = 25.356(2) Å, V = 11656(1)
Å3, Z = 8.
† Cyclic voltammograms of 2 measured in THF (0.5 M Bu4NPF6,
Pt electrode) showed an irreversible oxidation at ϩ0.076 V vs. Fc–Fcϩ.
D a l t o n T r a n s . , 2 0 0 3 , 1 7 9 0 – 1 7 9 4
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Fig. 5 1H NMR spectrum of 2 (CDCl3, 300 MHz, room temp.).
0–10 ppm range. The simplicity of the spectrum, comparable to
that of its precursor 1, indicates that the equivalence of the
carboxylate ligands is maintained upon one-electron oxidation,
consistent with the valence delocalized description of the com-
plex. Given the relative sharpness of the NMR features, the
valence delocalized dicopper(,) center in 2 has an electronic
relaxation time (T 1e) much shorter than that typical of a mono-
nuclear Cu() center (∼10Ϫ9 s), as noted previously for the bio-
logical CuA site.17,18 Assignment of the six observed signals can
be made upon consideration of relative peak areas, linewidths,
and metal–proton distances (δ (ppm): 9.5 (2H, m-H); 7.8 (4H,
THF β-H); 3.6 (4H, mЈ-H); 2.9 (6H, pЈ-Me); 1.7 (1H, p-H); 1.5
(12H, oЈ-Me)). Only the α-THF protons are not observed,
which is not surprising considering their proximity to the
paramagnetic metal center.
As noted above, the color of solid 2 is affected by the absence
or presence of THF; crystalline 2 is gray under vacuum, purple
in the presence of excess THF vapor, and red when crystallized
from toluene (two THF molecules coordinated). In addition,
UV-vis spectra of 2 and 3 in solution are influenced by the
nature of the solvent (cf. data for 2 shown in Fig. 6). Solu-
tions of 2 in THF are purple, with intense bands at λmax = 379
(ε = 2400 MϪ1 cmϪ1), 534 (1300) and 941 (1000) nm (Fig. 6, solid
line). These bands shift appreciably for 2 dissolved in toluene
(red, dot–dash line) or CH2Cl2 (green–brown, dotted line), with
Fig. 7 Electronic absorption spectra acquired during the titration of 2
in CH2Cl2 with THF (up to 30% v/v).
The combined observations for solid 2 and for 2 and 3 in
solution suggest that THF coordination and/or solvent polarity
variation dramatically influence the absorption spectral
features of these mixed valence complexes. The large solvent
dependence of the λmax of the low energy feature is most signifi-
cant, since this feature is probably due to a Ψ
Ψ* transition
of the mixed valence system. By analogy to previous studies of
class III mixed valence dicopper compounds that feature short
intermetal separations (<2.5 Å),3,4,6–8 substantial metal–metal
bonding/antibonding character for the wave functions involved
in this transition is likely for 2 and 3. Thus, it may be concluded
that the Cu1.5Cu1.5 bonding interactions in 2 and 3 are per-
turbed by binding of THF molecules and/or altering counter
ion coordination through solvent polarity changes. To our
knowledge, these solvent effects are unique in mixed valence
dicopper systems, although related influences of axial solvent
coordination on metal–metal bonding interactions have been
reported recently for Rh2(O2CR)4 paddlewheel complexes.19
The apparent solvent dependent variation of the Cu–Cu
interaction in 2 was further investigated through EPR and reson-
ance Raman spectroscopy experiments, but with mixed results.
Thus, while solutions of 2 in THF–toluene or CH2Cl2–toluene
mixtures were purple and green–brown, respectively, at room
temperature, both were violet when frozen, and EPR spectra
acquired at 15 K for both samples were identical. In another
attempt to probe the metal–metal interaction in 2, we obtained
a resonance Raman spectrum of a frozen THF solution using
514.5 nm laser excitation (Fig. 8). A strongly enhanced band
appears at 244 cmϪ1, with weaker features at 182, 482 and
738 cmϪ1. The positions of the latter two bands are close to
values predicted for overtones of the primary 244 cmϪ1 peak
(488 and 732 cmϪ1). We tentatively assign the primary band
as a vibration with significant Cu–Cu stretching character, by
analogy to assignments of similar bands reported in the range
241–289 cmϪ1 for Cu1.5Cu1.5 cryptate complexes.20,21 While a
previous study demonstrated extreme sensitivity of this Cu–Cu
the low energy feature changing the most (941
788
736 nm). For 3, the low energy absorption shifts from 911 nm
(THF) to 753 nm (CH2Cl2).
Fig. 6 Electronic absorption spectra of 2 at 25 ЊC in THF (solid),
toluene (dot–dash), and CH2Cl2 (dotted).
Conversion of the spectral features for 2 in CH2Cl2 upon
titration with THF is shown in Fig. 7. The dependence of the
spectrum on the concentration of THF indicates a complex
equilibrium in which the initial molecule (0% THF) converts to
a different species (30% THF), with no isosbestic points appar-
ent when all spectra are overlayed. Upon closer inspection,
there is an isosbestic point at ∼650 nm at low THF con-
centrations (<3%) and at ∼600 nm at higher concentrations
(4–30%). The involvement of an intermediate(s) in the conver-
sion of the species in CH2Cl2 to the one in THF is implicated by
these data, but the nature of this intermediate(s) is not known
at present.
Fig. 8 Resonance Raman spectrum of 2 in THF (77 K, λex = 514.5
nm). Asterisks (*) label peaks arising from the solvent.
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mode to solvent (leading to the conclusion that ligand conform-
ational isomerism underlies the mode shifts),21 spectra of 2 in
frozen CH2Cl2 or toluene were the same as that in THF.
Attempts to obtain spectra at room temperature have not yet
been successful. Thus, while we have been able to identify a
Cu–Cu vibrational mode by Raman spectroscopy, we have been
unable to corroborate by this method the conclusion derived
from UV-vis data that the Cu–Cu interaction is perturbed by
changing the solvent.
forming a colorless suspension. After ca. 20 h, CH2Cl2 (80 mL)
was added and the mixture was filtered. The solvent was
removed from the filtrate under vacuum and the residue was
crystallized from a mixture of THF (25 mL) and HMDSO (25
mL) to yield the product as colorless crystals (0.250 g, 32%). 1H
NMR (CDCl3, 300 MHz): δ 7.37 (t, J = 7.8 Hz, 1H, p-C6H3),
7.00 (d, J = 7.8 Hz, 2H, m-C6H3), 6.85 (s, 4H, m-Mes), 3.73 (m,
4H, THF), 2.33 (s, 6H, p-CH3), 1.92 (s, 12H, o-CH3), 1.85 (m,
4H, THF). Anal. Calc. for C58H66O6Cu2: C, 70.64, H, 6.75.
Found: C, 71.14; H, 6.84%.
Conclusions
Preparation of [(ArCO2)2Cu2(THF)2)]SbF6 (2)
We have described a dicopper() complex of a carboxylate
ligand, employing self assembly methods and taking advantage
of its steric bulk to prevent oligomerization. One-electron
oxidation affords a dicopper(,) complex, the spectroscopic
properties of which clearly demonstrate Class III mixed-valent
behavior analogous to that found for other dicopper complexes
with Cu–Cu distances of less than 2.5 Å. The unusually large
solvent dependence we have observed in the absorption features
of its electronic spectrum suggests that the metal–metal inter-
actions that give rise to the valence delocalized behavior
can significantly be perturbed by solvent and/or counter ion
binding. Unfortunately, further study of this phenomenon
with spectroscopic techniques that can provide more detailed
molecular insight such as ESR and Raman may be precluded by
the apparent conversion of all forms into spectroscopically
indistinguishable species below 77 K.
To a solution of 1 (0.200 g, 0.216 mmol) in THF (10 mL) was
added dropwise a solution of AgSbF6 (0.074 g, 0.216 mmol) in
THF (4 mL), forming a deep purple solution. The reaction
mixture was filtered and concentrated to 5 mL. Upon addition
of pentane (12 mL) crystals started to form, and crystallization
was continued by allowing the mixture to stand for ca. 24 h at
Ϫ30 ЊC. The deep purple crystals were collected, washed with
pentane and dried under reduced pressure, after which the
purple crystals became gray (0.147 g, 56%). Crystallization from
toluene at Ϫ20 ЊC gave red crystals with two toluene solvate
molecules that were suitable for X-ray diffraction studies. Addi-
tion of CH3CN to a solution of 2 in THF resulted in the form-
ation of a precipitate and a blue solution, interpreted as the
1
disproportionation of the compound to Cu(0) and Cu(). H
NMR (D8-THF, 300 MHz): δ 9.58 (∆w1/2 = 115 Hz, 2H,
m-C6H3), 7.83 (∆w1/2 = 87 Hz, 4H, m-Mes), 2.97 (∆w1/2 = 41 Hz,
6H, p-CH3), 1.52 (∆w1/2 = 150 Hz, 12H, o-CH3), Ϫ0.86 (∆w1/2
≈
Experimental
400 Hz, 1H, p-C6H3), 1.92 (s, 12H), 1.85 (m, 4H). UV-vis (THF)
[λmax/nm (ε/MϪ1 cmϪ1)]: 379 (2400), 543 (1300), 941 (1000);
(toluene): 382 (1700), 509 (800), 788 (900). (CH2Cl2): 410
(2500), 491 (1600), 736 (1400), 805sh (1300). Anal. Calc. for
C58H66O6Cu2F6Sb: C, 57.01, H. 5.44. Found: 56.25; H, 5.63%.
General
Standard Schlenk-line and glovebox techniques were used for
the handling of all compounds. Tetrahydrofuran (THF), pen-
tane and toluene were distilled from Na/benzophenone ketyl,
and CH3CN, hexamethyldisiloxane (HMDSO) and CH2Cl2
were distilled from CaH2 under nitrogen. CDCl3 was vacuum
Preparation of [(ArCO2)2Cu2(THF)3)]ClO4 (3)
1
To a solution of 1 (0.247 g, 0.268 mmol) in THF (10 mL) was
added dropwise a solution of AgClO4 (0.055 g, 0.268 mmol) in
THF (3 mL), forming a deep purple solution. The reaction
mixture was filtered and concentrated to 5 mL. Addition of
pentane (15 mL) and cooling to Ϫ20 ЊC afforded the product as
deep purple needle-like crystals (0.089 g, 33%). UV-vis (THF)
[λmax/nm (ε/MϪ1 cmϪ1)]: 325 (2700), 367 (2100), 535 (1000),
911 (790); (CH2Cl2): 392 (2000), 501 (1200), 753 (1000). Anal.
Calc. for C62H74O11Cu2Cl: C, 64.32; H, 6.44. Found: C, 63.40;
H, 6.23%.
transferred from CaH2. Chemical shifts for H NMR spectra
are given relative to residual protium in the deuterated solvents.
X-Band EPR spectra were recorded using a Bruker E-500 spec-
trophotometer with the temperature (2–20 K) regulated by an
Oxford Instruments EPR-10 liquid-helium cryostat. Spectra
were recorded with a modulation amplitude of 10 G and a
modulation frequency of 100 kHz. Spin quantification was
performed by comparison to a 1 mM sample of [LHAmMe
-
CuCl]ClO4.22 Resonance Raman spectra were collected on an
Acton 506 spectrometer using a Princeton Instruments LN/
CCD-1100-PB/UVAR detector and ST-1385 controller inter-
faced with Winspec software. A Spectra-Physics 2030-15 argon
ion laser was used to give the excitation wavelength at 457.9 and
514.5 nm; laser power was ca. 50 mW at the sample. The spectra
were obtained at ca. 77 K using a 135Њ backscattering geometry;
solutions of samples were frozen onto a gold-plated copper
cold finger in thermal contact with a Dewar flask containing
liquid nitrogen. Spectra in pixel units were converted to fre-
quency units by a quadratic fit of pixels to several peaks in the
known spectrum of indene. Spectra were generally recorded
with slits set for a band-pass of 4 cmϪ1. Elemental analyses were
determined by Atlantic Microlab, Inc. Single crystal X-ray
diffraction data were collected using a Siemens SMART
X-Ray crystal structure determinations
Crystal data, data collection, and refinement parameters for 1
and 3 are listed in Table 2.
A crystal of appropriate size was mounted on a quartz fiber
using hydrocarbon oil, transferred to a Siemens SMART dif-
fractometer/CCD area detector, centered in the beam (Mo-Kα;
λ = 0.71073 Å; graphite monochromator), and cooled to
Ϫ100 ЊC by a liquid-nitrogen low-temperature apparatus. Pre-
liminary orientation matrix and cell constants were determined
by collection of 60 10-s frames, followed by spot integration
and least-squares refinement. A hemisphere of data was
collected using 0.3Њ ␼ scans. The raw data were integrated (xy
spot spread = 1.60Њ, z spot spread = 0.60Њ) and the unit cell
parameters refined using SAINT.25 Absorption corrections
were applied using SADABS.26 The data were corrected for
Lorentz and polarization effects, but no correction for crystal
decay was applied. Structure solutions and refinements were
performed (SHELXTL-Plus V5.027) on F 2. All non-hydrogen
atoms were refined anisotropically. Hydrogen atoms were
placed in idealized positions and refined as riding atoms with
relative isotropic displacement parameters.
23
diffractometer. The compounds [Cu(CH3CN)4]O3SCF3 and
[ArCO2]Li(Et2O)0.5(CH3CN)0.5 were prepared according to
reported procedures. All other chemicals were purchased from
Aldrich and used as received.
24
Preparation of [(ArCO2)2Cu2(THF)2)] (1)
Toluene (40 mL) and CH3CN (10 mL) were added to a flask
charged with solid [Cu(CH3CN)4]O3SCF3 (0.638 g, 1.69 mmol)
and [ArCO2]Li(Et2O)0.5(CH3CN)0.5 (0.723 g, 1.69 mmol),
D a l t o n T r a n s . , 2 0 0 3 , 1 7 9 0 – 1 7 9 4
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Table 2 Crystal data, data collection, and refinement parameters for
complexes 1 and 3a
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Al-Obaidi, J. J. McGarvey, J. Nelson and A. J. Thomson,
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6293.
1
3
Formula
M
Crystal system
Space group
C58H66Cu2O6
986.19
Monoclinic
P21/c
C62H74ClCu2O11
1157.74
Orthorhombic
Pbcn
a/Å
b/Å
c/Å
8.5214(3)
24.6971(9)
11.8867(4)
91.626(1)
2500.6(2)
2
19.007(1)
24.185(1)
25.356(2)
90
11656(1)
8
β/Њ
V/Å3
Z
Dc/g cmϪ3
1.310
0.901
1.320
0.834
µ/mmϪ1
Reflns. measured
Unique reflns. obs.
11898
4343
67759
13335
Rint
0.0559
0/298
0.0639
0.1058
0.0561
40/763
0.0793
0.1587
Restraints/params.
R1b
wR2b
GOF
1.127
0.407, Ϫ0.354
1.173
0.981, Ϫ0.730
Largest diff. peak, hole/e ÅϪ3
a All structures determined at 173 K, Mo-Kα radiation, refinement
10 X.-M. Zhang, M.-L. Tong and X.-M. Chen, Angew. Chem., Int. Ed.,
2002, 41, 1029.
11 M. Dunaj-Jurco, G. Ondrejovic, M. Melnik and J. Garaj,
Coord. Chem. Rev., 1988, 83, 1.
based on F 2. b For I > 2σ(I ), R1 = Σ||Fo| Ϫ |Fc||/Σ|Fo|, and wR2 =
2
2
[Σ[w(Fo2 Ϫ Fc2)2]/Σ[w(Fo )2]]1/2, where w = 1/σ2(Fo ) ϩ (aP)2 ϩ bP.
12 D. D. LeCloux, A. M. Barrios, T. J. Mizoguchi and S. J. Lippard,
J. Am. Chem. Soc., 1998, 120, 9001.
13 (a) L. Que, Jr. and W. B. Tolman, J. Chem. Soc., Dalton Trans., 2002,
653 and references therein; (b) D. Lee and S. J. Lippard,
Inorg. Chem., 2002, 41, 827; (c) E. Y. Tshuva, D. Lee, W. Bu and
S. J. Lippard, J. Am. Chem. Soc., 2002, 124, 2416.
For 3, the perchlorate anion was found to be disordered over
two positions. The first (half occupancy) perchlorate (Cl1, O8,
O9, O10, O11) is located near a crystallographic inversion
center and is shared between two (inversion) related [(ArCO2)2-
Cu2(THF)3]ϩ units. The second (half occupancy) perchlorate
(Cl2, O12, O13, O14, O15) is also located near an inversion
center, but it is not coordinated to a metal center. It was neces-
sary to restrain the Cl–O and the “1,3” O–O distances to obtain
a reasonable refinement.
14 D. Maspoch, D. Ruiz-Molina, K. Wurst, C. Rovira and J. Veciana,
Chem. Commun., 2002, 2958.
15 (a) M. G. B. Drew, D. A. Edwards and R. Richards, J. Chem. Soc.,
Chem. Commun., 1973, 124; (b) M. G. B. Drew, D. A. Edwards and
R. Richards, J. Chem. Soc., Dalton Trans., 1977, 299.
16 D. D. LeCloux and S. J. Lippard, Inorg. Chem., 1997, 36, 4035.
17 C. Luchinat, A. Soriano, K. Djinovic-Carugo, M. Saraste,
B. G. Malmström and I. Bertini, J. Am. Chem. Soc., 1997, 119,
11023.
CCDC reference numbers 202090 and 202089.
See http://www.rsc.org/suppdata/dt/b3/b301154b/ for crystal-
lographic data in CIF or other electronic format.
18 R. C. Holz, M. L. Alvarez, W. G. Zumft and D. M. Dooley,
Biochemistry, 1999, 38, 11164.
19 F. A. Cotton, E. A. Hillard and C. A. Murillo, J. Am. Chem. Soc.,
2002, 124, 5658.
Acknowledgements
20 A. A. Obaidi, G. Baranovic, J. Coyle, C. G. Coates, J. J. McGarvey,
V. McKee and J. Nelson, Inorg. Chem., 1998, 37, 3567.
21 V. M. Miskowski, S. Franzen, A. P. Shreve, M. R. Ondrias, S. E. W.
Williams, M. E. Barr and W. H. Woodruff, Inorg. Chem., 1999, 38,
2546.
22 L. M. Berreau, J. A. Halfen, V. G. Young, Jr. and W. B. Tolman,
Inorg. Chem., 1998, 37, 1091.
We thank the NIH (F32-GM19374 to J. R. H. and GM38767
to L. Q.) and the University of Minnesota Undergraduate
Research Opportunities and Lando Undergraduate Research
Programs (T. I. Z.) for financial support of this research. We
also thank Anne M. Reynolds and Victor G. Young, Jr., for
assistance with X-ray crystallographic data analysis.
23 (a) G. J. Kubas, Inorg. Synth., 1979, 19, 90; (b) G. J. Kubas,
Inorg. Synth., 1990, 28, 68.
24 (a) J. R. Hagadorn, L. Que, Jr. and W. B. Tolman, J. Am. Chem. Soc.,
1998, 120, 13531; (b) J. R. Hagadorn, L. Que, Jr. and W. B. Tolman,
Inorg. Chem., 2000, 39, 6086.
25 SAINT, Bruker Analytical X-ray Systems, Madison, WI, 1999.
26 SADABS: An empirical correction for absorption anisotropy,
R. Blessing, Acta Crystallogr., Sect. A, 1995, 51, 33.
27 G. M. Sheldrick, SHELXTL-Plus V5.0, Program for refinement of
crystal structures, University of Göttingen, Germany, 1997.
References and notes
1 P. M. H. Kroneck, W. A. Antholine, J. Riester and W. G. Zumft,
FEBS Lett., 1988, 242, 70.
2 M. B. Robin and P. Day, Adv. Inorg. Chem. Radiochem., 1967, 10,
247.
3 Selected recent references: (a) F. Neese, R. Kappl, J. Hüttermann,
W. G. Zumft and P. M. H. Kroneck, J. Biol. Inorg. Chem., 1998, 3,
D a l t o n T r a n s . , 2 0 0 3 , 1 7 9 0 – 1 7 9 4
1794