Synthesis and characterization of copper(II) complexes of nonfacially coordinating heteroscorpionate ligands (4-carboxyphenyl)bis(3,5- dimethylpyrazolyl)methane and (3-carboxyphenyl)bis(3,5-dimethylpyrazolyl)methane

Article abstract of DOI:10.1021/ic062226u

Complexes of Cu(II) derived from two new nonfacially coordinating heteroscorpionate ligands, (4-carboxyphenyl)-bis(3,5-dimethylpyrazolyl)methane (L4c) and (3-carboxyphenyl)bis(3,5-dimethylpyrazolyl)methane (L3c), have been synthesized and characterized by

Full text of DOI:10.1021/ic062226u

Inorg. Chem. 2007, 46, 1751−1759
Synthesis and Characterization of Copper(II) Complexes of Nonfacially
Coordinating Heteroscorpionate Ligands
(4-Carboxyphenyl)bis(3,5-dimethylpyrazolyl)methane and
(3-Carboxyphenyl)bis(3,5-dimethylpyrazolyl)methane
Guillermo A. Santillan and Carl J. Carrano*
Department of Chemistry and Biochemistry, San Diego State UniVersity,
San Diego, California 92182-1030
Received November 22, 2006
Complexes of Cu(II) derived from two new nonfacially coordinating heteroscorpionate ligands, (4-carboxyphenyl)-
bis(3,5-dimethylpyrazolyl)methane (L4c) and (3-carboxyphenyl)bis(3,5-dimethylpyrazolyl)methane (L3c), have been
synthesized and characterized by X-ray diffraction, ESI-MS, IR, and UV−vis spectroscopy, electrochemistry, and
magnetic susceptibility. The use of these new complexes as building blocks for the construction of supramolecular
architectures is discussed.
Introduction
rational design of such systems is through molecular self-
assembly of simple building blocks and linkers.13-16 Poly-
topic organic carboxylates and nitrogen heterocycles have
been widely used as bridging motifs in the development of
these metallosupramolecular complexes.17-18 On the other
hand nitrogen-, oxygen-, and sulfur-based multidentate
scorpionate and heteroscorpionate ligands have been used
almost exclusively as nonbridging, facially coordinating
ligands designed to enforce mononuclearity.19,20 Recently,
however new bispyrazolyl derivatives and other scorpionate
ligands have been developed to generate metallosupramo-
lecular complexes.21-25
The development of coordination polymers or metal-
organic frameworks (MOF) is of great current interest
because of their potential applications in a variety of different
areas including molecular magnetism,1-3 electronic conduc-
tivity,4 host-guest chemistry,5-8 sensors,9 and optical de-
vices.10 These materials are constructed of metal centers
connected through organic ligands that can lead to extended
multidimensional topologies.11,12 One approach for the
* To whom correspondence should be addressed. E-mail:
carrano@sciences.sdsu.edu.
(1) Caneschi, A.; Gatteschi, D.; Lalioti, N.; Sengregorio, C. Angew. Chem.,
Int. Ed. 2001, 40, 1760-1763.
(2) Clerac, R.; Miyasaka, H.; Yamashita, M.; Coulon, C. J. Am. Chem.
Soc. 2002, 124, 12837-12844.
(13) Caulder, D. L.; Raymond, K. N. Acc. Chem. Res. 1999, 32 (11), 975-
982.
(3) Ichikawa, S.; Kimura, S.; Mori, H.; Yoshida, G.; Tajima, H. Inorg.
Chem. 2006, 45, 7575-7577.
(14) Cotton, F. A.; Lin, C.; Murillo, C. A. Acc. Chem. Res. 2001, 34, 759-
771.
(4) Kitagawa, H.; Onodera, N.; Sonoyama, T.; Yamamoto, M.; Fukawa,
T.; Mitani, T.; Seto, M.; Maeda, Y. J. Am. Chem. Soc. 1999, 121,
10068-10080.
(15) Seidel, S. R.; Stang, P. J. Acc. Chem. Res. 2002, 35, 972-983.
(16) Linton, B.; Hamilton, A. D. Chem. ReV. 1997, 97, 1669-1680.
(17) Steel, P. J. Acc. Chem. Res. 2005, 38, 243-250.
(18) Eddaoudi, M.; Moler, D. B.; Li, H.; Chen, B.; Reineke, T. M.;
O’Keeffe, M.; Yaghi, O. M. Acc. Chem. Res. 2001, 34, 319-330.
(19) Trofimenko, S. Scorpionates: The Coordination Chemistry of Poly-
pyrazolylborate Ligands; Imperial College Press: London, 1999.
(20) Otero, A.; Antin˜olo, J. F. B.; Tejeda, J.; Lara-Sa´nchez, A. Dalton Trans.
2004, 1499-1510.
(21) Calhorda, M. J.; Costa, P. J.; Crespo, O.; Gimeno, C.; Jones, P. G.;
Laguna, A.; Naranjo, N.; Quintal, S.; Shi, Y.; Villacampa, M. D.
Dalton Trans. 2006, 4104-4113.
(22) Reger, D. L.; Semeniuc, R. F.; Gardinier, J. R.; O’Neal, J.; Reinecke,
B.; Smith, M. D. Inorg. Chem. 2006, 45, 4337-4339.
(23) Reger, D. L.; Semeniuc, R. F.; Little, C. A.; Smith, M. D. Inorg. Chem.
2006, 45, 7758-7769.
(5) Albrecht, M.; Janser, I.; Burk, S.; Weis, P. Dalton Trans. 2006, 2875-
2880.
(6) Seeber, G.; Tiedemann, B.; Raymond, K. N. Top. Curr. Chem. 2006,
265, 147-183.
(7) Leung, D. H.; Bergman, R. G.; Raymond, K. N. J. Am. Chem. Soc.
2006, 128, 9781-9797.
(8) Yeh, R. M.; Raymond, K. N. Inorg. Chem. 2006, 45, 1130-1139.
(9) Wuerthner, F.; You, C.; Saha-Moeller, C.; Chantu, R. Chem. Soc. ReV.
2004, 33, 133-146.
(10) Evans, O. R.; Lin, W. Acc. Chem. Res. 2002, 35, 511-522.
(11) Holliday, B. J.; Mirkin, C. A. Angew. Chem., Int. Ed. 2001, 40, 2022-
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10.1021/ic062226u CCC: $37.00
Published on Web 02/08/2007
© 2007 American Chemical Society
Inorganic Chemistry, Vol. 46, No. 5, 2007 1751

Santillan and Carrano
1
Yield: 71%. H NMR (500 MHz, d-chloroform): δ 2.18 (s, 6H,
CH3), 2.238 (s, 6H, CH3), 5.912 (s, 2H, PzH), 7.017 (d, 2H, J )
7.8 Hz, ArH), 7.753 (s, 1H, CH), 7.946 (d, 2H, J ) 7.7 Hz, ArH).
13C (CDCl3): δ 168.99, 148.71, 141.40, 140.97, 130.64, 130.31,
127.22, 107.34, 73.92, 13.47, 11.56. FT-IR (KBr) ν /cm-1: ν(OH)
3448 (br, carboxylate), 2920, ν(CdO) 1690 (carboxylic
acid), ν
1560 (s, pyrazolyl), ν(C-O) 1257, ν(Ar) 753. mp:
(CdN)
173(1) °C.
(3-Carboxyphenyl)bis(3, 5-dimethylpyrazolyl)methane, L3c.
This ligand was synthesized in a manner similar to that described
for L4c using 3-carboxybenzaldehyde in place of the 4-carboxy-
benzaldehyde. The white solid began to precipitate at pH 4.6.
Yield: 65%. 1H NMR (500 MHz, ((CD3)2SO): δ 2.08 (s, 6H, CH3),
2.12 (s, 6H, CH3), 5.92 (s, 2H, PzH), 7.23 (d, 2H, J ) 7.8 Hz,
ArH), 7.50 (t, 1H, J ) 7.7 Hz, ArH), 7.66 (s, 1H, ArH), 7.92 (d,
2H, J ) 7.7 Hz, ArH). 13C NMR: δ 166.97, 147.01, 140.24, 137.31,
131.75, 130.77, 129.07, 128.51, 128.27, 106.40, 71.78, 13.45, 10.94.
FT-IR (KBr) ν/cm-1: 3448, 2920, 1690, 1560, 1257, 753. mp:
206(1)°C.
Copper Complexes. Cu2(L4c)2(H2O)2(ClO4)2 (1). A methanol
solution (10 mL) of ligand L4c (120 mg, 0.370 mmol) was added
to an aqueous solution (10 mL) of Cu(ClO4)2‚6H2O (137 mg 0.370
mmol) at room temperature, and the mixture was stirred for 2 h.
The resulting green precipitate was collected by filtration, washed
with methanol and water, and dried under vacuum for 2 h. Yield:
166 mg (0.164 mmol, 89%). Anal. Calcd (Found) for [Cu2(L4c)2-
(H2O)2(ClO4)2]‚2H2O, C36H46Cl2Cu2N8O16: C, 41.38 (41.45); H,
4.44 (4.06); N, 10.72 (11.32). IR (KBr) ν/cm-1: 3415, 1558, 1487,
1436, 1109, 862, 769, 625. λmax(CH3CN): 734 nm. µeff: 2.84 µB
(solid, 295 K). ESI-MS: m/z: 774, 873.
Single crystals suitable for X-ray analysis were prepared by the
careful diffusion of a methanol solution of L4c containing sodium
methoxide into an aqueous solution of Cu(ClO4)2‚6H2O.
Cu2(L4c)2Cl2 (2). This complex was prepared in a manner
analogous to that of 1 using CuCl2 in place of the perchlorate.
Yield: 425 mg (0.5 mmol 73%). Anal. Calcd (Found) for
[Cu2(L4c)2Cl2]‚3H2O, C36H44Cl2Cu2N8O7: C, 48.11 (48.07); H, 4.93
(4.55); N, 12.47 (12.98). IR (KBr) ν/cm-1: 3448, 1560, 1502, 1436,
1253, 858, 835, 766, 714. µeff: 2.75 µB. ESI-MS: m/z (acetoni-
trile): 775, 810.
Here we redesign several heteroscorpionate ligands and
explore their potential use as diatopic bridging units for the
development of new supramolecular assemblies. To ac-
complish this, we have altered the position of the X
functional group on the aromatic ring in the N2X heteroscor-
pionate ligands so that they can no longer function as facially
coordinating tridentate tripods but instead allow bridging
interactions between metal nuclei. These new heteroscorpi-
onates can thus be expected to function as binucleating
ligands.26 It is hoped that these binuclear blocks can, when
combined with various linkers, produce unique and control-
lable supramolecular architectures. This paper is the first of
a series of reports in which the full details of our work be
presented. We report herein the preparation, synthesis, and
characterization of five potential copper-containing building
blocks and evaluate their ability to produce higher-order
structures.
Experimental Section
Single crystals suitable for X-ray analysis were prepared by the
careful diffusion of a methanol solution of L4c containing sodium
methoxide into aqueous solution of CuCl2.
Materials. All chemicals and solvents used during the syntheses
were reagent grade. Bis(3,5-dimethylpyrazolyl)ketone was prepared
according to the procedure described by Peterson et al.27 Caution:
Perchlorate salts are dangerous (especially if they are dry) and
should be handled with care.
Ligand Synthesis. (4-Carboxyphenyl)bis(3,5-dimethylpyra-
zolyl)methane (L4c). Bis(3,5-dimethylpyrazolyl)ketone (2.4 g, 11
mmol) was placed in a 100 cm3 round-bottomed flask. 4-Carboxy-
benzaldehyde (1.62 g, 10.8 mmol), CoCl2 (20 mg), and triethy-
lamine (4 mL) were then added. The mixture was heated to 120
°C for 4 h with vigorous stirring, during which the mixture turned
deep purple and evolved CO2. The flask was then allowed to cool
to room temperature. The solid was taken up in water and filtered.
The filtrate was neutralized with 6 M hydrochloric acid. At
approximately pH 5.4, a white solid began to precipitate. This solid
was collected by filtration, washed with water, and dried in vacuum.
Cu(L4c)acac(H2O) (3). A methanol solution (10 mL) of Cu-
(acac)2 (570 mg 2.17 mmol) was added to a methanol solution (10
mL) of ligand L4c (706 mg, 2.17 mmol). The resulting dark green
solution was allowed to stand, and crystals were obtained by slow
evaporation. These were collected by filtration, washed with water
and ether, and dried under vacuum for 1 h. Yield: 625 mg (1.24
mmol, 57%). Anal. Calcd (Found) for [Cu(L4c)acac(H2O)]‚2H2O,
C23H32CuN4O7: C, 51.15 (50.70); H, 5.97 (5.45); N, 10.37(10.55).
IR (KBr) ν/cm-1: 3416, 1592, 1552, 1519, 1373, 825, 770, 715.
λmax (CH3CN, ꢀ): 730 nm (63.0 M-1 cm-1). µeff: 1.68 µB (solid
295 K).
Cu(L4c)Cl2 (4). An acetonitrile solution (10 mL) of CuCl2 (69.6
mg 0.52 mmol) was added to acetonitrile solution (10 mL) of ligand
L4c (168 mg, 0.52 mmol) at room temperature, and the mxture
was stirred for 1 h. The resulting light green solution was
precipitated with diethyl ether. The bright yellow precipitate was
collected by filtration, washed with ether, and dried under vacuum
for 1 h. Yield: 122 mg (0.265 mmol, 51%). Anal. Calcd (Found)
for [Cu(L4c)Cl2]H2O, C18H22CuN4O3Cl2: C, 45.34 (45.00); H, 4.65
(4.64); N, 11.75 (12.06). IR (KBr) ν/cm-1: 3448, 1717, 1560, 1459,
(24) Reger, D. L.; Semeniuc, R. F.; Pettinari, C.; Luna-Giles, F.; Smith,
M. D. Cryst. Growth Des. 2006, 6, 1068-1070.
(25) Ward, M. D.; McCleverty, J. A.; Jeffery, J. C. Coord. Chem. ReV.
2001, 222, 251-272.
(26) Gavrilova, A. L.; Bosnich, B. Chem. ReV. 2004, 104, 349-384.
(27) The K. I.; Peterson, L. K. Can. J. Chem. 1973, 51, 422.
1752 Inorganic Chemistry, Vol. 46, No. 5, 2007

Cu(II) Complexes of Heteroscorpionate Ligands
1259, 1108, 873, 814, 756. λmax (CH3CN, ꢀ) 453 nm (785 M-1
cm-1). µeff: 1.73 µB (solid 295 K).
Single crystals suitable for X-ray analysis were prepared by the
careful diffusion of diethyl ether into an acetonitrile solution of
the complex.
Cu2(L3c)2(H2O)4(ClO4)2 (5). A methanol solution (10 mL) of
ligand L3c (510 mg, 1.57 mmol) was added to an aqueous solution
(10 mL) of Cu(ClO4)2‚6H2O (582 mg, 1.57 mmol) at room
temperature, and the mixture was stirred for 3 days. The resulting
blue precipitate was collected by filtration, washed with methanol
and water, and dried under vacuum for 2 h. Yield: 509 mg (0.48
mmol, 62%). Anal. Calcd (Found) for [Cu2(L3c)2(H2O)4(ClO4)2]‚H2O,
C36H52Cl2Cu2N8O19: C, 39.35 (39.30); H, 458 (4.83); N, 10.20
(10.34). IR (KBr) ν/cm-1: 3425, 1561, 1467, 1396, 1120, 1090,
762, 695, 636. λmax(CH3CN, ꢀ) 736 nm (176 M-1 cm-1). µeff: 2.49
µB (solid, 295 K). ESI-MS (acetonitrile): m/z 775, 873.
Figure 1. ORTEP diagram with 40% thermal ellipsoids of ligand L4c
showing complete atomic labeling.
Single crystals suitable for X-ray analysis were prepared by the
careful diffusion of a methanol solution of L3c into a sodium
methoxide-containing aqueous solution of Cu(ClO4)2‚6H2O.
Physical Methods. Elemental analyses were performed on all
compounds by Numega, San Diego, CA. All samples were dried
in vacuo prior to analysis. 1H and 13C NMR spectra were collected
on Varian 200, 300, or 500 MHz NMR spectrometers. Chemical
shifts are reported in parts per million relative to an internal standard
of TMS. IR spectra were recorded as KBr disks on a ThermoNicolet
Nexus 670 FT-IR spectrometer and are reported in wavenumbers.
Cyclic voltammetric experiments were conducted using a BAS
Epsilon (Bioanalytical Systems Inc., West Lafayette, IN) voltam-
metric analyzer. All experiments were done under nitrogen at
ambient temperature in solutions with 0.1 M tetrabutylammonium
hexafluorophosphate as the supporting electrolyte. Cyclic voltam-
mograms (CV) were obtained using a three-electrode system
consisting of glassy carbon or Pt working, platinum wire auxiliary,
and SCE reference electrodes. The ferrocinium/ferrocene couple
was used to monitor the reference electrode and was observed at
+0.442 V with ∆Ep ) 75 mV and ipc/ipa ) 1.0 in acetonitrile under
these conditions. IR compensation was applied before each CV was
recorded. Electronic spectra were recorded using a Cary 50 UV-
vis spectrophotometer. Room-temperature magnetic susceptibility
measurements of the metal complexes were determined using a
MSB-1 magnetic susceptibility balance manufactured by Johnson
Matthey and calibrated with mercury(II) tetrathiocyanatocobaltate-
(II) (Xg ) 16.44(8) × 10-6 cm3 g-1). Diamagnetic corrections were
taken from those reported by O’Connor.28 Solution studies were
carried out in Wilmad coaxial NMR tubes in either acetonitrile or
methanol with TMS as the internal standard. Electrospray mass
spectra (ESI-MS) were recorded on a Finnigan LCQ ion-trap mass
spectrometer equipped with an ESI source (Finnigan MAT, San
Jose, CA). A gateway PC with Navigator software version 1.2
(Finnigan Corp., 1995-1997) was used for data acquisition and
plotting. Isotope distribution patterns were simulated using the
program IsoPro 3.0.
Figure 2. ORTEP diagram with 40% thermal ellipsoids of ligand L3c
showing complete atomic labeling.
F2. All non-hydrogen atoms were refined with anisotropic displace-
ment coefficients and treated as idealized contributions using a
riding model except where noted. All software and sources of the
scattering factors are contained in the SHELXTL 5.0 program
library (G. Sheldrick, Siemens XRD, Madison, WI).
Results and Discussion
Synthesis and Characterization. Using our standard
synthetic methodology, we placed the carboxyl donor group
in a phenyl-substituted heteroscorpionate in a para or meta
position and thus converted the ligand from a facially
coordinating tripodal one favoring mononuclear complexes
into one capable of bridging interactions. The structures of
these two new ligands have been determined by X-ray
crystallography and are shown in Figures 1 and 2. The
reaction of the p-carboxylate ligand designated L4c in MeOH
with aqueous solutions of the divalent metal Cu(II) leads to
a head-to-tail 2M:2L dimer as the primary species as
characterized by X-ray crystallography (vide infra). With
copper perchlorate, the aquo complex is isolated, while the
corresponding chloro derivative ensues starting with CuCl2.
Synthesis in nonaqueous solvents (methanol or acetonitrile)
starting from CuCl2 or Cu(acac)2 as the metal source leads
to mononuclear complexes 3 and 4. In these cases, the
carboxylate group of the heteroscorpionate remains unco-
ordinated, while the metal retains one or more of the anionic
X-ray Crystallography. Crystals of ligand L4c and L3c and
complexes 1-5 were mounted either in capillaries for room-
temperature data collection or with nylon loops and paratone oil
(Hampton Research) and were placed in the cold stream for low-
temperature collection on a Bruker X8 APEX CCD diffractometer.
The structures were solved using direct methods or via the Patterson
function, completed by subsequent difference Fourier syntheses,
and refined by full-matrix least-squares procedures on
(28) O’Connor, C. J. Prog. Inorg. Chem. 1982, 29, 203.
Inorganic Chemistry, Vol. 46, No. 5, 2007 1753

Santillan and Carrano
Figure 3. ORTEP diagram with 40% thermal ellipsoids of the cationic
portion of [(L4c)2Cu2 (H2O)2](ClO4)2 showing complete atomic labeling.
ligands present in the starting material. These reactions are
summarized in the following graphic
Figure 4. Crystal packing diagram for [(L4c)2Cu2(H2O)2](ClO4)2 as seen
along the crystallographic c axis. Hydrogen bonds are shown as dotted lines.
Figure 5. ORTEP diagram with 40% thermal ellipsoids of [(L4c)2Cu2-
Cl2] showing complete atomic labeling.
65.27°. The Cu atom sits 0.38 Å out of the mean N1, N3,
O1, O3 plane. Because the complex is cationic, there is a
slightly disordered perchlorate in the lattice that functions
as a counterion and is involved in the hydrogen-bonding
interactions that lead to extended structures in the crystal
(Figure 4). The complex packs in extended columns because
of H-bonding interactions between the ligand water mol-
ecules and the carboxylate groups on succesive dimeric units.
H-bonding intereactions between the perchlorate ions and
the water molecules serves to link the columns together.
The corresponding dinuclear complex Cu2(L4c)2Cl2 (2)
(Figure 5), prepared from CuCl2 as a starting material, is
extremely similar. Each copper is again pentacoordinate but
with a chloride rather than a water as the axial ligand. In
addition, the Cu is significantly further out of the basal plane,
(0.45 vs 0.38 Å) than in the aquo complex. Otherwise, the
bond lengths and angles are similar with the only notable
difference being the 2.354 Å Cu-Cl distance that is
expectedly larger than the Cu-Owater distance. While there
is no counterion in the lattice, a disordered methanol of
crystallization is present whose H-bonding interactions drive
the extended network seen in the crystal packing (data not
shown).
With the m-substituted ligand L3c, substantial changes in
coordination about the copper ensue. In this case, sterics
dictate that the carboxylate group coordinate in a unidentate
rather than bidentate mode in the 2M:2L complexes so that
the still pentacoordinate copper responds by picking up a
second water molecule to complete the coordination sphere
giving rise to a diaquo species.
Solid-State Chemistry. An ORTEP drawing of the
cationic part of Cu2(L4c)2(H2O)2(ClO4)2 (1) is shown in
Figure 3. The crystal structure reveals that the molecular
entity possesses a crystallographic inversion center making
only one-half of the dimer unique. In this complex, the two
copper atoms are both five coordinate and can be described
as having a distorted square pyramidal geometry, where the
two nitrogen and two carboxylate oxygen donors of the
chelating L4c ligands occupy the four positions of the basal
plane, while one H2O molecule is 2.202(2) Å away in the
apical position. The intramolecular Cu-Cu distance is large
(7.762 Å). The carboxylate groups are bound to the coppers
in a regular bidentate mode with very similar Cu-O bonds
of 2.013 and 2.035 Å. The average Npz-Cu(1)-O(3) angle
is 104°; both the Npz-Cu(1)-O bond angles in the basal plane
therefore deviate significantly from 90°. The N(3)-Cu(1)-
N(1) angle is 90.59°, while the bidentate binding mode of
the carboxylate constrains the O1-Cu(1)-O(3) angle to
On the other hand using methanol as a solvent, without
any deliberately added water, and Cu(acac)2 as a copper
source, we isolate the mononuclear complex Cu(L4c)acac-
(H2O) (3) shown in Figure 6 which crystallizes in space
1754 Inorganic Chemistry, Vol. 46, No. 5, 2007

Cu(II) Complexes of Heteroscorpionate Ligands
Figure 8. ORTEP diagram with 40% thermal ellipsoids of the cationic
portion of [(L3c)2Cu2 (H2O)2](ClO4)2 showing complete atomic labeling.
Figure 6. ORTEP diagram with 40% thermal ellipsoids of [(L4c)Cu(acac)-
H2O] showing complete atomic labeling.
carboxyl group lead to a zigzag extended network in the solid
state (data not shown).
When the m-substituted ligand, L3c, is used, a new
dinuclear 2M:2L complex, Cu2(L3c)2(H2O)4(ClO4)2 (5), is
produced using copper perchlorate as the metal source. Here,
the dinuclear unit does not possesses a crystallographic
inversion center, and there are substantial changes in
coordination about the copper as compared to the analogous
complexes 1 and 2. In 5, steric considerations dictate that
the carboxylate group coordinate in a unidentate rather than
bidentate fashion (Cu-Ocarboxylate distances of 1.96 and 3.27
Å) so that the still pentacoordinate copper responds by
picking up an additional water molecule to complete the
coordination sphere (Figure 8). The geometry around each
copper can still be described as distorted square pyramidal
with one molecule of H2O, two pyrazole nitrogens, and one
carboxylate oxygen donor of the chelating L3c ligands
occupying the four positions in the basal plane, while a
second H2O molecule sits in the apical position. The
intramolecular Cu-Cu distance is near 6.8 Å, about an
angstrom closer together than in the analogous para-
carboxylate ligand complexes. The perchlorate ions and water
molecules contribute H-bonding interactions that lead to a
different packing and extended network structure than that
seen for the complexes of L4c, as shown in Figure 9. Here
the dinuclear units are stacked in columns held together by
H-bonding between the water molecules and Cu ligands;
π-π stacking interactions also appear to be important. The
resulting 1-D columns are in turn H-bonded via the perchlo-
rate ions and lattice water molecules which interact with each
other and the water ligands on the copper to produce an
extended array.
Figure 7. ORTEP diagram with 40% thermal ellipsoids of [(L4c)CuCl2]‚
MeOH showing complete atomic labeling.
group C2/c. Structurally, the copper is again pentacoordinate
in a square pyramidal geometry with the two pyrazole
nitrogens and the two acetylacetonate oxygens now making
up the basal plane with a water molecule occupying the axial
position. Since there are no counterions in the structure,
charge considerations indicate that either the coordinated
“water” is actually a hydroxide or that the carboxylate group,
which is uncoordinated, is deprotonated. The average 2.27
Å Cu-O distance clearly indicates a coordinated water and
not a hydroxide ion; hence the carboxylate must be depro-
tonated and (surprisingly) uncoordinated. Other bond lengths
and angles within the structure are unexceptional except that
the Cu is closer to the basal plane (0.25 Å) than in the other
two structures. A series of water molecules in the lattice
provides hydrogen bond interactions that lead to extended
structures within the crystal (data not shown).
The coordination environment around the copper in Cu-
(L4c)Cl2 (4) is considerably different than the pseudosquare
pyramidal geometry seen in 1-3 (Figure 7). Thus, in 4, the
Cu is only four coordinate and is best described as distorted
tetrahedral where the largest angular deviations from ideal
are found for N1-Cu-Cl2 and N3-Cu-Cl1, which are near
132°. The remaining angles are all below the idealized 109°
and average ∼99°. The twist angle between the Cl1-Cu1-
Cl2 and N1-Cu1-N3 planes at 63.6° is much closer to the
90° angle expected of a tetrahedron, as compared to the 0°
angle for the alternate square planar description. H-bonding
between the lattice methanol, the chloride, and the protonated
Solution Chemistry. Although complexes 1, 2, and 5 are
clearly dimeric in the solid state, the question is do such
structures persist in solution? The positive-ion mode ESI
mass spectrum in acetonitrile solution is shown for [Cu2-
(L4c)2(H2O)4](ClO4)2 in Figure 10. The highest-mass cluster
corresponds to the cation [Cu2(L4c)2(H2O)4(ClO4)]+, as
expected if the complex remains dinuclear. The calculated
isotope pattern is also in agreement with this formulation.
A second intense mass cluster occurs with a nominal mass
of 775 amu which corresponds to [Cu2(L4c)2]+, a dinuclear
species, where presumably one of the Cu ions has been
reduced from Cu(II) to Cu(I) during the ionization process.
Inorganic Chemistry, Vol. 46, No. 5, 2007 1755

Santillan and Carrano
Figure 9. Crystal packing diagram for [(L3c)2Cu2(H2O)2](ClO4)2 as seen along the crystallographic a axis. Hydrogen bonds are shown as dotted lines.
Figure 10. Positive-ion ESI-MS of [(L4c)2Cu2(H2O)2](ClO4)2 in acetonitrile. The upper frame shows the peak clusters associated with the [(L4c)2Cu2-
(ClO4)]+ ion (right) and the [(L4c)2Cu2]+ ion (left). The lower frames show the calculated isotope distribution pattern expected for the fragments proposed.
The situation is different in methanol however (Figure 11)
where the primary mass cluster at 711 amu corresponds to
[Cu(L4c)2]+ indicating that the dimer has dissociated with
loss of Cu to produce a mononuclear complex. Similar
behavior is seen for 2 and 5. That the apparent reductive
events are the results of the electrospray ionization process
and not indicative of the generic solution chemistry is shown
by the magnetic susceptibility and electrochemistry results
presented below.
Magnetic Measurements. Magnetic measurements gave
values of near 2.8 µB for all the dimers in the solid state.
This corresponds to moments near 1.79 µB/Cu indicative of
simple nonmagnetically interacting d9 Cu(II) ions. This is
expected given the very long >6 Å through-space distance
1756 Inorganic Chemistry, Vol. 46, No. 5, 2007

Cu(II) Complexes of Heteroscorpionate Ligands
Figure 11. Positive-ion ESI-MS of [(L4c)2Cu2(H2O)2](ClO4)2 in methanol. The left panel shows the peak cluster associated with the [(L4c)2Cu]+ ion,
while the right panel shows the calculated isotope distribution pattern expected for the fragment proposed.
oxidative wave near +0.6 V. Given the very long Cu-Cu
distance and their non-interacting nature, this corresponds
to a simple Cu(II)/Cu(I) couple on each copper. The change
of the bridging ligand from L3c to L4c has little effect on
the reduction potential but substantially reduces the revers-
ibility of the couple suggesting that the latter complexes are
more prone to dissociation in solution. Replacement of the
axial water by a chloride has the expected effect of reducing
the reduction potential by about 100 mV. The cyclic
voltammogram of the mononuclear complex Cu(L4c)acac-
(H2O) looks very similar to that of the corresponding dimer,
[Cu2(L4c)2(H2O)4(ClO4)]+, suggesting that the former may
rearrange in solution to the latter. The electrochemical
behavior of the mononuclear, pseudotetrahedral Cu(L4c)-
Cl2 is very different as a quasireversible oxidative (Cu(II)/
Figure 12. Cyclic voltammogram of [(L3c)2Cu2(H2O)2](ClO4)2 in aceto-
Cu(III)), rather than reductive, wave is observed at +0.500
V with ∆Ep ) 0.110 V.
nitrile at a scan rate of 100 mV s-1
.
between copper ions in the complexes. Virtually identical
values are seen in solution as determined by the Evans
method in either acetonitrile or methanol indicating that these
complexes remain in the Cu(II) oxidation state in solution,
but this unfortunately conveys no information about their
nuclearity.
Electrochemical Properties. The electrochemical behav-
ior of all the complexes were examined by cyclic voltam-
metry between 1.5 and -1.5V. The results are presented in
Figure 12 and Table 4. The CV of 5 is representative of the
dimers and shows a quasireversible wave at E1/2 ) -0.850
V (∆Ep ) 0.231 V, υ ) 0.1 V s-1) and an irreversible
Conclusions
We have shown, by using our previously reported synthetic
strategy, that we can transform heteroscorpionate ligands
from tripodal-coordinating, mononuclear-favoring ligands
into ones capable of bridging and producing dinuclear
species. The dinuclear species appear to persist in solution
in less polar solvents (e.g., acetonitrile) but to rearrange in
more polar ones (e.g., methanol). Changing the position of
the X group in these N2X ligands produces subtle changes
in the coordination environment around the copper in the
dimers. Replacement of the labile water or halide ligands
Inorganic Chemistry, Vol. 46, No. 5, 2007 1757

Santillan and Carrano
Table 1. Summary of Crystallographic Data and Parameters for L4c,
L3c, [(L4c)2Cu2(H2O)2](ClO4)2 (1), [(L4c)2Cu2(H2O)Cl2] (2),
[(L4c)Cu(acac)(H2O)] (3), [(L4c)CuCl2]‚MeOH (4), and [(L3c)2Cu2
(H2O)2](ClO4)2 (5)
Table 2. Selected Bond Lengths (Å) and Angles (deg) for
[Cu2(L4c)2(H2O)2](ClO4)2, Cu2(L4c)2Cl2, and [Cu2(L3c)2(H2O)4](ClO4)2
1
2
5
Cu(1)-O(1)
Cu(1)-O(2)
Cu(1)-O(3)
Cu(1)-O(4)
Cu(1)-N(1)
Cu(1)-N(3)
Cu(1)-Cl(1)
Cu(2)-N(5)
Cu(2)-N(7)
Cu(2)-O(6)
Cu(2)-O(7)
2.013(2)
2.035(2)
2.202(2)
2.037(6)
2.051(7)
L4c
L3c
1
2
1.9589(19)
2.196(2)
1.9672(19)
2.018(2)
molecular
formula
fw
temp (K)
cryst syst
C18H22N4O2
C18H19N4O2 C18H21N4O17
-
C18.5H19N4O2.5
ClCu
-
ClCu
326.40
298(2)
monoclinic
323.37
200(2)
monoclinic
P21/c
504.38
298(2)
436.37
1.989(3)
1.986(2)
1.992(8)
1.983(7)
2.354(3)
200(2)
2.0056(19)
monoclinic
P21/c
monoclinic
P21/c
space group P21/c
cell constants
2.013(2)
1.9959(18)
1.961(2)
2.215(2)
a (Å)
10.1408(3)
12.7148(8)
9.6352(7)
13.8772(10) 10.0016(5)
9.2908(5)
22.7790(12)
9.300(3)
15.852(5)
13.942(6)
90
107.607(10)
90
b (Å)
10.8961(3)
16.3592(4)
90
c (Å)
R (deg)
â (deg)
γ (deg)
90
90
105.9460(10) 90.574
102.100(2)
N(1)-Cu(1)-O(1)
N(1)-Cu(1)-O(2)
N(1)-Cu(1)-O(3)
N(1)-Cu(1)-O(4)
N(1)-Cu(1)-Cl(1)
N(3)-Cu(1)-N(1)
N(3)-Cu(1)-O(1)
N(3)-Cu(1)-O(2)
N(3)-Cu(1)-O(3)
N(3)-Cu(1)-O(4)
N(3)-Cu(1)-Cl(1)
O(1)-Cu(1)-O(2)
O(1)-Cu(1)-O(3)
O(1)-Cu(1)-Cl(1)
O(2)-Cu(1)-O(3)
O(2)-Cu(1)-O(4)
O(2)-Cu(1)-Cl(1)
O(3)-Cu(1)-O(4)
96.47(10)
156.58(10)
104.11(10)
97.5(3)
150.9(3)
90
90
4
90
4
167.53(9)
93.67(9)
92.54(9)
Z
4
4
V (Å3)
1738.06(8)
0.084
1700.0(2)
0.085
2069.66(19)
1.234
1959.0(13)
1.275
abs coeff,
µ
µ
calcd (mm-1
)
104.6(2)
90.4(3)
150.5(3)
96.7(3)
calcd (g/cm3) 1.247
1.263
684
1.619
1036
1.480
896
90.59(10)
152.17(10)
99.46(9)
88.64(9)
F(000)
cryst
dimensions
(mm)
radiation
696
0.3 × 0.2 ×
0.2 × 0.3 × 0.4 × 0.4 ×
0.1 × 0.2 ×
87.55(8)
95.91(8)
169.09(9)
0.3
0.1
0.2
0.1
104.09(10)
Mo KR
Mo KR
Mo KR
Mo KR
(λ )0.71073 Å) (λ )0.7107 Å) (λ )0.71073 Å) (λ ) 0.71073 Å)
104.0(2)
63.7(3)
h,k,l
-13 f 13,
-14 f 14,
-20 f 15
-13 f 13,
-10 f 9,
-14 f 13
2.57-22.41
20 576
-12 f 11,
-28 f 30,
-11 f 13
2.27-28.95
21 847
-11 f 10,
-17 f 18,
-16 f 16
2.57-25.05
14 850
65.27(9)
100.23(10)
101.4(2)
31.3(3)
θ range (deg) 2.13-27.54
reflns
collected
unique reflns 3948
params
18 016
93.94(9)
98.53(9)
89.00(8)
2193
217
5299
332
15.96
3456
253
13.66
100.93(19)
221
94.84(9)
data/params 17.86
ratio
10.10
R(F)a
0.0572
0.1709
1.031
0.0534
0.1688
1.034
0.494 and
-0.331
0.0476
0.1259
1.003
0.0873
0.1781
0.985
Table 3. Selected Bond Distances (Å) and Angles (deg) for
(L4c)Cu(acac)(H2O) and (L4c)CuCl2
Rw(F2)b
GOFc
largest diff 0.389 and
0.480 and
-0.353
1.942 and
-0.603
3
4
peak and
-0.524
hole (e/Å3)
Cu(1)-N(1)
Cu(1)-N(3)
Cu(1)-O(5)
Cu(1)-O(4)
Cu(1)-O(3)
Cu(1)-Cl(1)
Cu(1)-Cl(2)
2.047(3)
2.010(3)
1.914(3)
1.913(3)
2.272(3)
2.009(4)
1.969(4)
3
4
5
molecular formula
fw
C23H28N4O8Cu C19H20Cl2CuN4O3 C37H46N8O20Cl2Cu2
552.03
298(2)
monoclinic
C2/c
486.83
240(2)
monoclinic
P21/n
1120.80
200(2)
monoclinic
P21/c
2.2000(2)
2.215(2)
temp (K)
cryst syst
space group
cell constants
a (Å)
b (Å)
c (Å)
R (deg)
â (deg)
O(3)-Cu(1)-O(4)
O(3)-Cu(1)-O(5)
O(3)-Cu(1)-N(3)
O(3)-Cu(1)-N(1)
O(4)-Cu(1)-N(3)
O(4)-Cu(1)-N(1)
O(4)-Cu(1)-O(5)
N(3)-Cu(1)-O(5)
N(3)-Cu(1)-N(1)
N(1)-Cu(1)-O(5)
N(1)-Cu(1)-Cl(1)
N(1)-Cu(1)-Cl(2)
N(3)-Cu(1)-Cl(1)
N(3)-Cu(1)-Cl(2)
Cl(1)-Cu(1)-Cl(2)
94.75(12)
100.48(14)
96.90(12)
96.13(12)
168.11(12)
88.66(12)
92.91(13)
87.28(12)
87.78(11)
163.12(13)
24.4844(7)
10.9463(3)
19.7862(5)
90
103.899(2)
90
11.635(3)
14.149(3)
12.908(3)
90
93.928(10)
90
16.8155(8)
15.5036(7)
18.9048(8)
90
100.917(2)
90
γ (deg)
Z
8
4
4
V (Å3)
5147.7(2)
0.901
2120.2(8)
1.310
4839.3(4)
1.073
91.72(16)
abs coeff,
µ
µ
calcd (mm-1
)
105.04(13)
136.14(13)
131.96(13)
99.31(12)
98.57(6)
calcd (g/cm3)
1.425
2296
1.525
996
1.538
2304
F(000)
cryst dimensions 0.6 × 0.4 × 0.2 0.3 × 0.1 × 0.05 0.5 × 0.5 × 0.4
(mm)
radiation
Mo KR
Mo KR
Mo KR
(λ ) 0.71073 Å) (λ ) 0.71073 Å) (λ ) 0.71073 Å)
Table 4. Electrochemical Properties of [Cu2(L4c)2(H2O)2]2+
,
h,k,l
-30 f 30,
-13 f 13,
-24 f 24
2.21-26.67
51 021
5419
329
-12 f 12,
-11 f 14,
-13 f 13
2.70-21.77
18 306
2490
266
9.36
0.0392
0.0929
1.016
-26 f 26,
-24 f 24,
-27 f 29
2.30-34.32
118 048
20 214
Cu2(L4c)2Cl2 Cu(L4c)acac(H2O), Cu(L4c)Cl2 and [Cu2(L3c)2(H2O)4]2+
complex
E1/2 (V)
∆Ep (mV)
ic/ia
θ range (deg)
reflns collected
unique reflns
params
(1) [Cu2(L4c)2(H2O)2]2+
(2) Cu2(L4c)2Cl2
-0.895
-0.787
-0.840
+0.500
-0.853
326
340
347
124
247
0.80
0.76
0.56
0.95
1.0
678
29.81
0.0586
0.1746
(3) Cu(L4c)acac(H2O)
(4) Cu(L4c)Cl2
data/params ratio 16.47
R(F)a
0.0548
0.1606
1.033
(5) [Cu2(L3c)2(H2O)4]2+
Rw(F2)b
GOFc
1.076
largest diff peak
0.730 and
0.389 and
1.312 and
on the metal with another diatopic ligand such as terephthalic
acid or 4,4′-bipyridine should allow for the linkage of these
dinuclear building blocks into larger multidimensional
and hole (e/Å3)
-0.728
-0.430
-1.143
a R ) [∑|∆F|/∑|Fo|]. b Rw )[∑w(∆F)2/∑wFo ]. c Goodness of fit on F2.
1758 Inorganic Chemistry, Vol. 46, No. 5, 2007
2

Cu(II) Complexes of Heteroscorpionate Ligands
structures of different geometries. Indeed, we have shown
that the labile water or halide ligands on various metal dimers
can be substituted by various exogenous carboxylates. These
results will be presented in the future.
of the X-ray diffraction facilities at San Diego State
University.
Supporting Information Available: Additional crystallographic
data (CIF files) for ligands L4c and L3c and complexes 1-5. This
material is available free of charge via the Internet at http://
pubs.acs.org.
Acknowledgment. This work was supported in part by
NSF Grant CHE-0313865. The NSF-MRI program Grant
CHE-0320848 is also gratefully acknowledged for support
IC062226U
Inorganic Chemistry, Vol. 46, No. 5, 2007 1759