Bimetallic reactivity. On the use of oxadiazoles as binucleating ligands

Article abstract of DOI:10.1021/ic0012773

Two (1,3,4)-oxadiazole ligands have been prepared. In one case the oxadiazole ring is flanked by two o-aniline groups, and in the other case it is an extension of the first where the amines are condensed with 2-picolyl groups. A monometallic copper(II) complex of the former has been prepared, and its crystal structure was determined. A number of bimetallic copper(II), cobalt(II,), and nickel(II) complexes of the di-deprotonated latter ligand were prepared and isolated. The crystal structure of the cobalt(II) complex bearing two acetate bridges is reported. The work demonstrates that the seldom-employed oxadiazole ring can be used effectively for generating bimetallic complexes.

Full text of DOI:10.1021/ic0012773

1386
Inorg. Chem. 2001, 40, 1386-1390
Bimetallic Reactivity. On the Use of Oxadiazoles as Binucleating Ligands
Christopher Incarvito and Arnold L. Rheingold*
Department of Chemistry and Biochemistry, University of Delaware, Newark, Delaware 19716
C. Jin Qin, Anna L. Gavrilova, and B. Bosnich*
Department of Chemistry, The University of Chicago, 5735 South Ellis Avenue, Chicago, Illinois 60637
ReceiVed September 29, 2000
Two (1,3,4)-oxadiazole ligands have been prepared. In one case the oxadiazole ring is flanked by two o-aniline
groups, and in the other case it is an extension of the first where the amines are condensed with 2-picolyl groups.
A monometallic copper(II) complex of the former has been prepared, and its crystal structure was determined. A
number of bimetallic copper(II), cobalt(II), and nickel(II) complexes of the di-deprotonated latter ligand were
prepared and isolated. The crystal structure of the cobalt(II) complex bearing two acetate bridges is reported. The
work demonstrates that the seldom-employed oxadiazole ring can be used effectively for generating bimetallic
complexes.
Introduction
the binucleating ligand. It appeared that properly constructed
ligands bearing azole or azolate bridges would provide the least
strained systems.
We considered the three bridging azole or azolate ligands 4,
5, and 6. The bridging fragments 4 and 5 have been used
Generally, bimetallic complexes are formed by bridging
ligands. The bridging ligands can consist of one atom, X, or
two atoms, Y-Y, and with these combinations, four-, five-, or
six-membered metallo-ring systems can be formed. Such rings
are shown as 1, 2, and 3, where the bridges may or may not be
part of a complex binucleating ligand. The four-membered rings,
1, are strained because the internal bond angles are different
from those associated with the constituent atoms. The five- and
six-membered rings, 2 and 3, respectively, engender less strain
because the atoms are allowed to adopt more closely their natural
bond angles. These considerations bear on the construction of
binucleating ligands because if the bridging ligand is part of
the binucleating ligand structure, the strain of the bridge ring
will usually be transmitted to other parts of the complexed
ligand. Because the systems 2 and 3 are less strained, the two
sites of the binucleating ligand complex will be less prone to
transmit the effect of changes at one site to the other. Such strain
factors are germane to the question of designing systems where
the task of the metals is to act cooperatively. As we have
demonstrated1 in some bimetallic systems, oxidation of one
metal leads to the deactivation of the other to oxidation
principally because of mechanical coupling,1 a conformational
strain effect that couples the two sites. To obviate this mutual
deactivation, we sought bimetallic complexes where mechanical
coupling between the sites would be minimized. A properly
designed system bearing the ring bridge, 2, presented such a
prospect. The nature of the Y-Y bridge, however, is important
in decoupling the two metal sites when this bridge is part of
extensively2 for the syntheses of multimetallic complexes. The
(1,3,4)-oxadiazole, 6, bridge has received much less attention.
We are aware of only three reports of attempts to use oxadiazole
as a binucleating ligand.3-5 In all cases, the ligand was 7, but
in every case only monometallic complexes were isolated and
attempts to prepare bimetallic species failed. Molecular models
indicate that the five-membered chelate rings that are formed
(1) (a) Bosnich, B. Inorg. Chem. 1999, 38, 2554. (b) Fraser, C.; Johnston,
L.; Rheingold, A. L.; Haggerty, B. S.; Williams, C. K.; Whelan, J.;
Bosnich, B. Inorg. Chem. 1992, 31, 1835. (c) Fraser, C.; Ostrander,
R.; Rheingold, A. L.; White, C.; Bosnich, B. Inorg. Chem. 1994, 33,
324. (d) Fraser, C.; Bosnich, B. Inorg. Chem. 1994, 33, 338. (e)
McCollum, D. G.; Hall, L.; White, C.; Ostrander, R.; Rheingold, A.
L.; Whelan, J.; Bosnich, B. Inorg. Chem. 1994, 33, 924. (f) McCollum,
D. G.; Fraser, C.; Ostrander, R.; Rheingold, A. L.; Bosnich, B. Inorg.
Chem. 1994, 33, 2383. (g) McCollum, D. G.; Yap, G. P. A.; Liable-
Sands, L.; Rheingold, A. L.; Bosnich, B. Inorg. Chem. 1997, 36, 2230.
(h) McCollum, D. G.; Yap, G. P. A.; Rheingold, A. L.; Bosnich, B.
J. Am. Chem. Soc. 1996, 118, 1365.
(2) Steel, P. J. Coord. Chem. ReV. 1990, 106, 227.
(3) Wignacourt, J. P.; Sueur, S.; Lagrenee, M. Acta Crystallogr. 1990,
C46, 394.
(4) Lagrenee, M.; Sueur, S.; Wignacourt, J. P.; Mernari, B.; Boukhari,
A. J. Chim. Phys. 1991, 88, 2075.
(5) Scott, J. D.; Puddephat, R. J. Organometallics 1986, 5, 2522.
10.1021/ic0012773 CCC: $20.00 © 2001 American Chemical Society
Published on Web 02/15/2001

Oxadiazoles as Binucleating Ligands
Inorganic Chemistry, Vol. 40, No. 6, 2001 1387
acid (0.75 g, 6 mmol) in dry pyridine (5 mL) was added triphenyl
phosphite (1.1 mL, 4 mmol).7 The mixture was kept at 50 °C for 15 h
and was then refluxed for 1 h. More triphenyl phosphite (0.55 mL, 2
mmol) was added, and the refluxing was continued for 3 more hours.
The solvent was removed in vacuo. The white residue was suspended
in benzene and filtered. It was washed successively with cold benzene,
water, ether, and pentane. It was dried under vacuum to afford a pure
product as a white crystalline solid (0.68 g, 74%). It can be recrystallized
by vapor diffusion of ether into chloroform solution. Mp, 249-251
°C. Selected IR bands (mineral oil, cm-1): 1683, 1584, 1538, 1441,
by 7 are strained and that six-membered chelate rings are
required for strain-free coordination. Consequently, the systems
reported here contain adjacent six-membered chelate rings.
Experimental Section
General Procedures and Methods. All reagents were obtained from
commercial suppliers and used without further purification. Infrared
spectra were recorded on a Nicolet 20SXB FTIR spectrometer using
Nujol mulls on NaCl disks for solid samples. Electronic absorption
spectra were obtained with a Perkin-Elmer Lambda 6 UV/vis spectro-
photometer. Elemental analyses were performed by Desert Analytics
Laboratory, Arizona. Magnetic susceptibilities were measured at 25
°C on powdered samples using a Johnson Matthey magnetic suscep-
tibility balance. Conductance measurements were made at 25 °C in
dry acetonitrile using 1.0 × 10-3 M samples and a YSI Scientific model
1
1303, 744. H NMR (400 MHz, CDCl3): δ ) 12.86 (s, 2H), 9.06 (d,
2H, J ) 8.5 Hz), 8.84 (d, 2H, J ) 4.7 Hz), 8.34 (d, 2H, J ) 7.8 Hz),
8.17 (d, 2H, J ) 7.9 Hz), 7.94 (t, 2H, J ) 7.7 Hz), 7.64 (dd, 2H, J )
7.9 Hz, J ) 8.5 Hz), 7.55 (dd, 2H, J ) 4.7 Hz, J ) 7.6 Hz), 7.29 (t,
2H, J ) 7.6 Hz). 13C NMR (400 MHz, C6D6): δ ) 163.85, 162.84,
150.38, 148.36, 138.03, 137.46, 133.01, 128.28, 126.49, 123.64, 122.89,
121.33, 111.44 Hz. Anal. Calcd for C26H18N6O3: C, 67.53; H, 3.92;
N, 18.17. Found: C, 67.60; H, 3.69; N, 18.18.
1
35 conductance meter. H NMR and 13C NMR spectra were recorded
on either a Bruker DRX400 or a DMX500 Fourier transform spec-
trometer. Chemical shifts (δ) are given in ppm, coupling constants (J)
in hertz. All of the aromatic signals show long-range coupling that
ranges from J ) 1.0 to J ) 1.7 Hz. Consequently, the quoted coupling
constants are difficult to determine precisely. Melting points are
uncorrected. Acetonitrile was dried over CaH2, THF was dried over
potassium/benzophenone ketyl, and ethyl ether was dried over sodium/
benzophenone ketyl.
N,N-Bis(2-aminobenzoyl)hydrazine (8). 8 was prepared by modi-
fication of the literature procedure.6 To a suspension of isatoic anhydride
(16.13 g, 0.1 mol) in absolute ethanol (80 mL) at 25 °C was added
hydrazine monohydrate (2.43 mL, 0.05 mol) dropwise over 5 min. The
mixture was brought to reflux and was refluxed for 1 h during which
time the solid dissolved and a new precipitate formed. The mixture
was slowly cooled to room temperature, then was kept at 5 °C for 1 h.
Pale-gray crystals were collected and washed with cold ethanol, ether,
and pentane. They were recrystallized from hot DMF-water to afford
pure product as a light-brown solid (7.2 g, 53% yield). 1H NMR (400
MHz, DMSO-d6): δ ) 10.04 (s, 2H), 7.60 (d, 2H, J ) 7.4 Hz), 7.18
(t, 2H, J ) 7.7 Hz), 6.73 (d, 2H, J ) 7.9 Hz), 6.51 (t, 2H, J ) 7.5 Hz),
6.43 (s, 4H).
[Cu(oxan)Cl2]‚DMF (11). To a solution of oxan (300 mg, 1.19
mmol) in DMF (3 mL) was added a solution of copper chloride hydrate
(289 mg) in DMF (5 mL). The dark brown-green solution was stirred
for 18 h. Then ethanol (3 mL) was added followed by ether (15 mL).
Dark-green crystals started forming. The mixture was kept at 5 °C for
3 h. The green solid was filtered, washed with ether, and dried in air
(506 mg, 93% yield). It was dissolved in DMF (5 mL) and vapor-
diffused with acetonitrile over 4 days. Dark blocks suitable for X-ray
crystallography were formed. They were washed with ether and dried
under vacuum (320 mg, 59%). Selected IR bands (mineral oil, cm-1):
3452, 3348, 3147, 1653, 1620, 1540, 1319, 1257. Absorption spectrum
[λmax in nm (ꢀ in L mol-1cm-1), DMF solution]: 275 (12 140), 367
(21 480), 402 (sh, 386). Anal. Calcd for C17H19N5OCuCl2: C, 44.40;
H, 4.17; N, 15.23; Cl, 15.42. Found: C, 44.46; H, 4.26; N, 15.17; Cl,
14.69.
[Cu(oxanpy)Cu(µ-O)] (12). OxanpyH2 (10) (0.46 g, 1 mmol) was
dissolved in DMF (30 mL) with heating to 80 °C. The solution was
cooled to room temperature. DBU (1,8-diazabicyclo[5.4.0]undec-7-ene)
(0.55 mL, 3.5 mmol) was added followed by water (0.36 mL, 20 mmol)
and DMF (10 mL). To this clear solution was added a solution of copper
trifluoromethanesulfonate (0.73 g, 2 mmol) in DMF (5 mL). The clear
dark-green solution became turbid within 3 min. The mixture was heated
at 90 °C for 1 h. A light-brown suspension was formed after 30 min of
heating. It was cooled to room temperature. The solid was collected
and was washed with DMF (9 mL), ether (15 mL), and hexane (15
mL) and was dried under vacuum. Brownish-green powder was obtained
(0.54 g, 90% yield). Selected IR bands (mineral oil, cm-1): 1580, 1565,
1533, 1346. Anal. Calcd for C26H16N6O4Cu2: C, 51.74; H, 2.67; N,
13.92. Found: C, 51.45; H, 2.68; N, 13.71.
2,2′-(1,3,4)Oxadiazole-2,5-diyl-bis-aniline (oxan, 9). 9 was prepared
by a modification of the literature procedure.6 A mixture of 8 (7.2 g,
[Cu(oxanpy)Cu(µ-OH)]BF4 (13). To a suspension of oxanpyH2
(0.23 g, 0.5 mmol) in DMF (8 mL) was added DBU (164 µL, 1.05
mmol) followed by a solution of Cu(BF4)2 (334 mg, 77%, 1.0 mmol)
in DMF (2 mL). A green solution formed and became turbid after 4
min of stirring. After the mixture was stirred for 3 h, acetone (20 mL)
was added and the suspension was stirred further for 30 min. The solid
was collected and washed successively with acetone (15 mL), methanol
(2 mL), acetone (5 mL), ether, and finally hexane. It was dried under
vacuum to afford a greenish powder (0.29 g). It was recrystallized by
slow vapor diffusion of acetone into DMF solution. The product was
obtained as a yellowish-green crystalline solid (70 mg, 20%). Selected
IR bands (mineral oil, cm-1): 1620, 1601, 1576, 1547, 1338, 756.
Absorption spectrum [λmax in nm (ꢀ in L mol-1cm-1), DMF solution]:
267 (51 450), 289 (36 000 sh), 366 (35 200), 579 (254). Anal. Calcd
for C26H17N6O4BF4Cu2: C, 45.17; H, 2.48; N, 12.16. Found: C, 45.24;
H, 2.71; N, 12.36.
26.64 mmol) and polyphosphoric acid (18.5 mL) was heated to 160
°C. A light-brown thick solution was formed in 30 min. It was kept at
160 °C for 2 h, then was slowly cooled to 50 °C. Then 100 mL of an
ice-water mixture was carefully added to the solution. A yellow
precipitate formed immediately. It was collected via filtration and
washed with water. The filtrate was adjusted with 15% NaOH solution
to pH 5. The precipitated solid was collected, washed with water,
combined with the main crop, and recrystallized from hot DMF-water.
Light-brown needles of 9 were obtained. These were washed with water
and dried under vacuum (5.7 g, 85%). Mp, 228-230 °C. Lit. mp, 228-
230 °C. Selected IR bands (mineral oil, cm-1): 3463, 3429, 3376, 3334,
1
1619, 1534, 1496, 1316, 1257, 1158, 740, 707. H NMR (400 MHz,
DMSO-d6): δ ) 7.86 (d, 2H, J ) 7.9 Hz), 7.27 (t, 2H, J ) 7.6 Hz),
6.91 (d, 2H, J ) 8.3 Hz), 6.77 (s, 4H), 6.70 (t, 2H, J ) 7.5 Hz).13C
NMR (400 MHz, DMSO-d6): δ ) 162.33, 147.82, 132.46, 127.86,
115.87, 115.60, 103.98 Hz.
N,N-Dipicolylamide-2,2′-(1,3,4)oxadiazole-2,5-diyl-bis-aniline
(oxanpyH2, 10). To a suspension of oxan (0.5 g, 2 mmol) and picolinic
[Co(oxanpy)Co(µ-OAc)2]‚CH2Cl2 (14). To a suspension of oxan-
pyH2 (0.27 g, 0.6 mmol) in deaerated DMF (10 mL), DBU (196 µL,
1.26 mmol) was added. The reaction mixture was flushed with N2 for
10 min before solid cobalt acetate tetrahydrate (0.306 g, 1.23 mmol)
(7) Barnes, D. J.; Chapman, R. L.; Vagg, R. S.; Watton, E. C. J. Chem.
Eng. Data 1978, 23, 349.
(6) Nagahara, K.; Takada, A. Chem. Pharm. Bull. 1977, 25, 2713.

1388 Inorganic Chemistry, Vol. 40, No. 6, 2001
Incarvito et al.
was added in one portion. An orange solution formed and became turbid
within minutes. It was stirred for 3 h at room temperature. The yellow
solid was collected under N2, washed with deaerated DMF (8 mL) and
ether (6 mL), and dried under vacuum. A yellow-orange powder (310
mg) was obtained. It was recrystallized by slow vapor diffusion of ether
(deaerated) into CH2Cl2 solution (deaerated, 25 mL). Two types of
crystals formed, brown blocks and yellow needles. The blocks (260
mg, 55%) were manually separated from the needles. Both the blocks
and needles were analyzed. The blocks, which contain CH2Cl2 of
crystallization, were used for X-ray diffraction. The needles do not
contain any solvent of crystallization. Selected IR bands (needles,
mineral oil, cm-1): 1620, 1601, 1576, 1547, 1338, 756. Absorption
spectrum [needles, λmax in nm (ꢀ in L mol-1cm-1), deaerated CH2Cl2
solution]: 284 (68 100), 384 (18 167), 504 (106 sh), 640 (30). Anal.
Calcd for C31H24N6O7Cl2Co2 (blocks): C, 47.65; H, 3.10; N, 10.76.
Found: C, 47.37; H, 3.71; N, 10.65. Anal. Calcd for C30H22N6O7Co2
(needles): C, 51.73; H, 3.19; N, 12.07. Found: C, 51.60; H, 3.08; N,
11.94.
Scheme 1. Synthesis of oxan and oxanpyH2
Table 1. Physical Properties of oxan and oxanpy Complexes
solid-state
magnetic conductivity,
[Ni(oxanpy)Ni(µ-OAc)2]‚2DMF (15). A solution of nickel acetate
tetrahydrate (118 mg, 0.47 mmol) in dry DMF (3 mL) was added to a
stirred suspension of oxanpyH2 (100 mg, 0.216 mmol) in dry DMF (1
mL). A clear dark-green solution formed and was stirred for 3 h at
room temperature. Then ether (30 mL) was slowly added. Greenish-
brown crystals started forming. The mixture was kept at 5 °C for 3 h.
The solid was collected, washed with ether, and dried in air (160 mg,
88%). It was recrystallized by slow vapor diffusion of ether into a DMF
solution. Greenish-brown crystals were collected, washed with DMF,
and were dried in vacuo (113 mg, 62% yield). Selected IR bands
(mineral oil, cm-1): 1677, 1614, 1587, 1547, 1330, 1258, 1226, 1166,
755. Absorption spectrum [λmax in nm (ꢀ in L mol-1cm-1), DMF
solution]: 263 (66 230), 377 (18 620), 575 (58), 816 (34). Anal. Calcd
for C36H36N8O9Ni2: C, 51.38; H, 4.27; N, 13.17. Found: C, 51.37; H,
4.28; N, 13.31.
Crystallographic Structural Determination. Crystal, data collec-
tion, and refinement parameters are given in Table 2. Suitable crystals
for data collection were selected and mounted with epoxy cement on
the tip of a fine glass fiber. All data were collected at 173(2) K with
a Siemens P4/CCD diffractometer with graphite-monochromated Mo
KR X-radiation (λ ) 0.710 73 Å).
The systematic absences in the diffraction data for 14 are uniquely
consistent with the reported space group, and the centrosymmetric
option for 11 was verified by the results of refinement. Structure 14
was solved using direct methods and structure 11 by the heavy-atom
Patterson method. Both structures were completed by subsequent
difference Fourier syntheses and refined by full-matrix least-squares
procedures. Structure 14 cocrystallized with one molecule of methylene
chloride per dicobalt complex. Structure 11 cocrystallized with dimeth-
ylformamide, which resides in proximity to the coordinated amine group
(O(2)-N(1) ) 2.79(4) Å). The four amine protons of 11 were located
from the electron difference map and allowed to refine. All non-
hydrogen atoms were refined with anisotropic displacement coefficients.
Hydrogen atoms, with the exception of the amine protons of 14, were
treated as idealized contributions.
moment Ω-1 mol-1 cm2
complex
color
(µB)25°C
(solvent)
[Cu(oxan)Cl2]‚DMF
[Cu(oxanpy)Cu(µ-O)]
dark-brown
brown-green
1.73
2.14
1.66
5.96
4.51
27 (DMF)
insoluble
67 (DMF)
3 (CH2Cl2)
2 (DMF)
[Cu(oxanpy)Cu(µ-OH)]BF4 olive-green
[Co(oxanpy)Co(µ-OAc)2] yellow
[Ni(oxanpy)Ni(µ-OAc)2]
green-brown
in the presence of triphenyl phosphite gave oxanpy(H)2 as a
white crystalline solid.
Complexes. Some of the complexes that were prepared with
the oxan and oxanpy ligands are listed in Table 1, together with
some of their physical properties. An outline of the preparation
of the complexes is shown in Scheme 2. The oxan ligand with
varying equivalents of CuCl2 in DMF formed a dark-brown
solution. Addition of ethanol followed by diethyl ether always
precipitated the monometallic complex irrespective of the
equivalents of CuCl2 that were present. The formation of the
monometallic complex is consistent with the results reported
for the ligand 7. Whether the isolation of the monometallic
complex of oxan is a reflection of the instability of the bimetallic
species or is merely a consequence of solubility has not been
pursued. The solid-state magnetic moment is representative of
an S ) 1/2 system, but the conductivity in DMF solution suggests
some dissociation of the chloro ligands.
The Cu2+, Co2+, and Ni2+ complexes formed by the oxanpy
ligand are bimetallic (Table 1). The oxo-bridged complex, [Cu-
(oxanpy)Cu(µ-O)], is insoluble in all solvents, protic and aprotic,
that were tried, and as a result, preparation of the soluble
hydroxo-bridged complex [Cu(oxanpy)Cu(µ-OH)]BF4 requires
some care. The latter was prepared by the addition of 2 equiv
of DBU (1,8-diazabicyclo[5.4.0]undec-7-ene) to deprotonate the
ligand. Addition of more than 2 equiv of DBU led to the
precipitation of the µ-oxo complex. Even when the µ-hydroxy
complex is allowed to stand in methanol solution at 25 °C, the
µ-O complex begins to slowly precipitate from solution. The
µ-OH complex is stable in aprotic solvents such as acetone or
DMF. Curiously, addition of acid to a methanol suspension of
the insoluble µ-O complex does not result in the detectable
formation of the µ-OH complex.
All software and sources of the scattering factors are contained in
the SHELXTL (version 5.1) program library (G. Sheldrick, Siemens
XRD, Madison, WI).
Results
Ligand Synthesis. The two ligands investigated here are 9
and 10. Two aspects of these ligands are noteworthy. First, the
oxadiazoles bear aromatic substituents, which provide stability
to the oxadiazole ring that otherwise is prone to nucleophic
attack at the imine carbon atoms. Second, the chelate rings
associated with the bridging ligand are six-membered, the least
strained ring. The syntheses of the two ligands 9 and 10 followed
modifications of known procedures (Scheme 1). Isatoic anhy-
dride was reacted with hydrazine hydrate in ethanol to give 8,
which after recrystallization was converted to the oxadiazole
ligand oxan, 9.6 Reaction of 9 with picolinic acid in dry pyridine
Both of these complexes have magnetic moments lower than
the expected spin-only values, indicating antiferromagnetic
coupling. The µ-OH complex in DMF displays a molar
conductivity consistent with a 1:1 electrolyte.8 The analogous
Co2+ and Ni2+ complexes were prepared from the metal acetates.
Both are nonelectrolytes and have magnetic moments lower than
(8) Geary, W. J. Coord. Chem. ReV. 1971, 7, 81.

Oxadiazoles as Binucleating Ligands
Inorganic Chemistry, Vol. 40, No. 6, 2001 1389
Scheme 2
Table 2. Crystallographic Data for
[Co(oxanpy)Co(µ-OAc)2]‚CH2Cl2 (14) and [Cu(oxan)Cl2]‚DMF (11)
the expected spin-only values for high-spin complexes. The
conductivity indicates that the acetate ions are coordinated to
the metals. The cobalt complex is sensitive to dioxygen in
solution but is moderately stable in the solid state in air. None
of the complexes gave reversible cyclic voltammetry waves
under a variety of conditions.
Crystal Structures. Crystal structures of the [Cu(oxan)Cl2]‚
DMF and [Co(oxanpy)Co(µ-OAc)2]‚CH2Cl2 were determined.
Crystallographic data for these complexes are provided in Table
2, and selected bond lengths and angles are listed in Tables 3
and 4. The Cu2+ (Cu(1)) in [Cu(oxan)Cl2]‚DMF (Figure 1) is
square planar, as expected, but the bond length of Cu(1)-Cl-
(1) is longer than that of Cu(1)-Cl(2). The dimethylformamide
(DMF) solvate forms a hydrogen bond with one of the protons
of the neighboring nitrogen atoms (N(1)). The other amine
nitrogen atom (N(4)) is oriented so that one of its hydrogen
atoms may form a hydrogen bond to N(3) of the oxadiazole
group.
The [Co(oxanpy)Co(µ-OAc)2] complex forms two types of
crystals when crystallized from CH2Cl2/ether: yellow needles
and brown blocks. The latter is a CH2Cl2 solvate, for which the
structure is reported, and the former is devoid of solvate. The
crystal structure is shown in Figure 2 where the Co2+ ions are
in a distorted trigonal bipyramidal geometry. The oxadiazole
and pyridine nitrogen atoms represent the axial positions of the
trigonal bipyramid. The metal-metal distance, Co(1)-Co(2),
is 3.781 Å. The other bond lengths and angles are unexceptional.
14
11
formula
fw
C31H24Cl2Co2N6O7
781.32
C17H19Cl2CuN5O2
459.81
space group
a, Å
b, Å
P21/c
P1h
10.8054(10)
18.5327(17)
15.7320(15)
10.4222(3)
10.4310(4)
11.3251(4)
75.014(2)
63.130(2)
61.121(2)
960.41(6)
2, 1
c, Å
R, deg
â, deg
96.575(2)
γ, deg
V, Å3
3129.7(5)
4, 1
Z, Z_
cryst color, habit
D(calcd), g cm-3
µ(Mo KR), cm-1
temp, K
dark-red block
1.658
12.90
dark-green block
1.590
14.38
173(2)
173(2)
diffractometer
λ (Mo KR), Å
R(F),a %
R(wF2),a %
Siemens P4/CCD
0.710 73
4.37
Siemens P4/CCD
0.710 73
3.33
13.53
13.32
2
2
a Quantity minimized ) R(wF2) ) ∑[w(Fo - Fc2)2]/∑[(wFo )2]1/2
;
2
R ) ∑∆/∑(Fo), ∆ ) (Fo - Fc); w ) 1/[σ2(Fo ) + (aP)2 + bP], P )
[2Fc2 + max(Fo,0)]/3.
acetate, hydroxide, and oxo supporting bridges between the two
metals. One of the possible problems with using oxadiazole rings
is the possible hydrolysis of the ring to give 169 under basic
conditions:
Discussion
This work illustrates that the oxadiazole fragment can be used
for the formation of bimetallic complexes, which can incorporate
(9) Lagrenee, M.; Sueur, S.; Wignacourt, J. P. Acta Crystallogr. 1991,
C47, 1158.

1390 Inorganic Chemistry, Vol. 40, No. 6, 2001
Incarvito et al.
Table 3. Selected Bond Lengths and Angles for
[Cu(oxan)Cl2]‚DMF
Bond Lengths (Å)
Cu(1)-N(1)
Cu(1)-N(2)
2.0056(16)
2.0167(15)
Cu(1)-Cl(2)
Cu(1)-Cl(1)
2.2304(5)
2.3184(4)
Angles (deg)
86.96(6) N(1)-Cu(1)-Cl(1)
N(1)-Cu(1)-N(2)
88.69(5)
N(1)-Cu(1)-Cl(2) 173.36(5) N(2)-Cu(1)-Cl(1) 150.94(5)
N(2)-Cu(1)-Cl(2)
94.02(4) Cl(2)-Cu(1)-Cl(1)
93.583(17)
Table 4. Selected Bond Lengths and Angles for
[Co(oxanpy)Co(µ-OAc)2]‚CH2Cl2
Bond Lengths (Å)
Co(1)-O(1)
Co(1)-O(3)
Co(1)-N(1)
Co(1)-N(3)
Co(1)-N(5)
1.989(2)
2.015(2)
2.041(2)
2.048(2)
2.075(2)
Co(2)-O(4)
Co(2)-O(2)
Co(2)-N(2)
Co(2)-N(4)
Co(2)-N(6)
1.990(2)
2.009(2)
2.032(3)
2.038(2)
2.068(3)
Angles (deg)
Figure 2. ORTEP diagram of [Co(oxanpy)Co(µ-OAc)2]‚CH2Cl2 (14).
Thermal ellipsoids are at 30% probability, and the lattice solvent
molecule is omitted for clarity.
O(1)-Co(1)-O(3) 110.98(10) O(4)-Co(2)-O(2) 118.82(10)
O(1)-Co(1)-N(1)
O(3)-Co(1)-N(1)
96.28(9)
93.52(9)
O(1)-Co(1)-N(3) 125.29(9)
O(3)-Co(1)-N(3) 123.19(9)
O(4)-Co(2)-N(2)
O(2)-Co(2)-N(2)
95.26(10)
91.17(9)
O(4)-Co(2)-N(4) 128.84(10)
O(2)-Co(2)-N(4) 111.95(9)
bridging systems, 4 and 5, the oxan, 9, fragment is simple to
prepare and to elaborate. The pyrazole bridging group 17, related
to oxan, carries with it synthetic difficulties when elaboration
from the amino groups is attempted. It is known10 that aldehydes
and acyl chlorides give the products 18 and 19.
N(1)-Co(1)-N(3)
O(1)-Co(1)-N(5)
O(3)-Co(1)-N(5)
87.95(9)
90.37(9)
91.98(9)
N(2)-Co(2)-N(4)
O(4)-Co(2)-N(6)
O(2)-Co(2)-N(6)
89.43(10)
92.64(10)
89.16(9)
N(1)-Co(1)-N(5) 169.23(10) N(2)-Co(2)-N(6) 170.79(10)
N(3)-Co(1)-N(5) 81.30(9) N(4)-Co(2)-N(6) 81.92(10)
Metal-Metal Separation (Å)
Co(1)-Co(2)
3.781
Both of the products 18 and 19 are stable, and hence, the
elaboration, such as in the preparation of oxanpyH2, 10, is not
possible with 17. Aside from the synthetic difficulties in
preparing 17, the reaction 17 f 19 was the other reason that
led us to explore the coordination chemistry of oxadiazoles. We
will report on the complexes of a more elaborate oxadiazole
binucleating ligand shortly.
Figure 1. ORTEP diagram of [Cu(oxan)Cl2]‚DMF (11). Thermal
ellipsoids are at 30% probability.
Acknowledgment. The work was supported by grants from
the PRF, NSF, and NIH.
Supporting Information Available: Detailed crystallographic data
for all structures including tables of atomic coordinates, bond lengths,
bond angles, anisotropic displacements, and hydrogen atom param-
eters. This material is available free of charge via the Internet at
http://pubs.acs.org.
During the course of this work, no such problems were
encountered, although the complexes were not subjected to
strong alkali. It appears, therefore, that the present oxadiazoles
are stable to the normal conditions under which coordination
chemistry is performed. Compared to the other 2-nitrogen
IC0012773
(10) deStevens, G.; Blatter, H. M. Angew. Chem., Int. Ed. Engl. 1962, 1,
159.