New heteroscorpionate ligands with hydrogen bond donor and acceptor groups: Synthesis, characterization and reactivity with divalent Co, Zn and Ni ions

Article abstract of DOI:10.1016/j.poly.2003.11.007

Three new N₂O heteroscorpionate ligands designated L6OH, L7OH and L9OH, containing either appended hydrogen bond donating or accepting residues have been synthesized and characterized. Metal complexes of these ligands with Co(II) and Ni(II) have been characterized by X-ray crystallography. A facile decomposition pathway leading to C-N bond cleavage and isolation of metal pyrazole complexes was also identified.

Full text of DOI:10.1016/j.poly.2003.11.007

Polyhedron 23 (2004) 239–244
www.elsevier.com/locate/poly
New heteroscorpionate ligands with hydrogen bond donor
and acceptor groups: synthesis, characterization and reactivity
with divalent Co, Zn and Ni ions
*
Zahida Shirin, Carl J. Carrano
Department of Chemistry, Southwest Texas State University, San Marcos TX 78666, USA
Received 14 May 2003; accepted 5 September 2003
Abstract
Three new N2O heteroscorpionate ligands designated L6OH, L7OH and L9OH, containing either appended hydrogen bond
donating or accepting residues have been synthesized and characterized. Metal complexes of these ligands with Co(II) and Ni(II)
have been characterized by X-ray crystallography. A facile decomposition pathway leading to C–N bond cleavage and isolation of
metal pyrazole complexes was also identified.
Ó 2003 Elsevier Ltd. All rights reserved.
Keywords: Heteroscorpionate ligands; Hydrogen bond; X-ray crystallography; Divalent metals
1. Introduction
gands to connect the metal cofactor to protein. It also
controls the secondary coordination sphere (microenvi-
ronment) around the metal ion. This microenvironment
often has a significant role to play in controlling the
reactivity of the metal ion. Of the various interactions
that proteins use to modify the secondary coordination
sphere, perhaps the most important is hydrogen bond-
ing. It is used to control structure, assist in recognition
and activation of exogenous substrates or stabilize re-
active intermediates. While the use of sterically restricted
ligands to control the size and shape of metal binding
cavities is well established, it has proven more difficult,
despite its importance, to incorporate hydrogen bonding
into synthetic small molecule binding site analogs.
However, some recent successes in using hydrogen
bonding, sterically restricted, metal binding cavities
prepared by relatively simple synthetic schemes have
become evident [4–7]. Using 50-ester substituted pyra-
zoles we have also described a first generation of a
simple H-bond accepting Tp ligands that simultaneously
provides both steric bulk and hydrogen bonding groups,
which can be directed towards the center of a metal
binding cavity. The presence of strong intramolecular
H-bonding between the ligand carbonyls and water
molecules leads to the stabilization of discrete, well
Tris(pyrazolyl)borate (Tp) or ‘‘scorpionate’’ ligands
have wide application in coordination, organometallic
and bioinorganic chemistry [1]. These ligands have be-
come particularly important in the development of bi-
omimetic coordination chemistry of metalloproteins.
Despite their advantages, the tris(pyrazolyl)borate li-
gands are completely symmetric with three nitrogen
donors and many metalloproteins active site do not have
such monofunctional binding sites. Our major contri-
bution to this field has been the introduction of a family
of tripodal N2X ligands which contain all the biologi-
cally relevant donor atoms and are isostructural and
isoelectronic with Tp [2,3]. With these we have begun to
investigate how donor atom identity affects the proper-
ties of the metal center in a series of isostructural and
isoelectronic complexes, i.e., the inorganic chemists
equivalent of site-directed mutagenesis.
However in metalloproteins the structure of the active
site has a role beyond just providing the necessary li-
* Corresponding author. Tel.: +1-512-245-2156; fax: +1-512-245-
2374.
E-mail address: carrano@sciences.sdsu.edu (C.J. Carrano).
0277-5387/$ - see front matter Ó 2003 Elsevier Ltd. All rights reserved.
doi:10.1016/j.poly.2003.11.007

240
Z. Shirin, C.J. Carrano / Polyhedron 23 (2004) 239–244
characterized, divalent metal aquo complexes of the
was stirred at 50 °C for 4 days. The white precipitate
that separated from the solution was filtered, washed
with THF, and dried under vacuo. Yield: 0.58 g (63%)
Anal. Calc. for C19H22N6O3: C, 59.68; H, 5.80; N, 21.97.
Found: C, 59.51; H, 5.78; N, 21.63%. 1H NMR (CDCl3)
d 9.97 (s, 1H, OH), 7.81 (s, 2H, –NH–), 7.80 (s, 1H,
–CH–), 7.24 (t, 1H, J ¼ 7:4 Hz, ArH), 6.88 (d, 1H,
J ¼ 7:8 Hz, ArH), 6.80 (t, 1H, J ¼ 7:4 Hz, ArH), 6.75
(d, 1H, J ¼ 7:2 Hz, ArH), 6.49 (s, 2H, PzH), 2.71 (s, 3H,
NHCH3), 2.70 (s, 3H, NHCH3), 2.14 (s, 6H, Pz–CH3).
13C NMR (CDCl3) d 163.22, 156.56, 147.57, 142.66,
132.02, 129.89, 122.46, 120.33, 116.83, 108.09, 71.60,
27.11, 12.58. A second, generally minor product was
general type in [TpCO Et; MeM(L)x]þ where M ¼ Co(II),
2
Ni(II), Mn(II), Zn(II) or Cu(II), L ¼ H2O, OAcꢀ,
OHꢀ, or various amino acids, and x ¼ 2 or 3 depending
on the metal [8,9]. These complexes are both, unprece-
dented in Tp chemistry, and good structural models for
enzymes of the vicinal oxygen chelate (VOC) super-
family [10].
In this work, we describe our initial efforts to combine
hydrogen bonding capabilities with the unsymmetrical
donor set of our heteroscorpionates to produce a new
generation of such ligands.
1
also isolated and identified by H and 13C NMR as the
2. Experimental
mixed ester amide substituted complex and designated
L8OH (3).
All syntheses and crystallizations were carried out
under Ar using standard Schlenk or dry box techniques.
Solvents dichloromethane and acetonitrile were distilled
under argon over CaH2 while diethyl ether was distilled
from Na/benzophenone. 3-Methyl-5-carboxyethylpy-
razole was prepared as previously described [8]. All
other reagents and solvents were purchased from com-
mercial sources and used as received unless otherwise
noted.
L9OH (4). This ligand was synthesized as described
previously for L6OH using 3-tert-butyl-2-hydroxy-5-
methylbenzaldehyde in place of salicylaldehyde. (80%
1
Yield): H NMR (CDCl3) d 8.59 (s, 1H, OH), 7.91 (s,
1H, –CH–), 7.09 (t, 1H, J ¼ 7:9 Hz, ArH), 6.78 (d, 1H,
J ¼ 7:8 Hz, ArH), 6.74 (t, 1H, J ¼ 7:6 Hz, ArH), 6.66
(d, 1H, J ¼ 8 Hz, ArH), 6.55 (s, 2H, PzH), 4.30 (q, 4H,
J ¼ 7:2 Hz, –OCH2), 2.09 (s, 6H, Pz–CH3), 1.28 (t, 6H,
J ¼ 7:2 Hz, –CH3). 13C NMR (CDCl3) d 162.29, 154.62,
143.05, 141.90, 130.86, 128.09, 120.34, 119.71, 116.35,
109.41, 72.55, 60.93, 14.13, 11.40.
2.1. Synthesis of ligands
L6OH (1). 3-Methyl-5-carboxyethylpyrazolyl ketone
(8.78 g, 26.20 mmol) was dissolved in a minimum amount
of anhydrous DMF and placed in a 100 ml round bottom
flask which was purged and filled with argon. Salicylal-
dehyde (3.20 g, 26.20 mmol) and a catalytic amount (0.1
g) of anhydrous CoCl2 were added to the flask. The
mixture was then heated at 100 °C for 30 h under Ar.
DMF was removed under reduced pressure and the solid
mass dissolved in CH2Cl2, washed with water thrice, with
saturated sodium chloride solution and finally dried over
anhydrous MgSO4. CH2Cl2 was removed to produce a
pale yellow oil. The oil was triturated with pentane and
stirred overnight to yield a white microcrystalline solid.
This solid was collected by filtration, washed with pen-
tane and dried in vacuo. Yield: 5.4 g (50%) Anal. Calc. for
C21H24N4O5: C, 61.16; H, 5.86; N, 13.58. Found: C,
2.2. Synthesis of Co and Ni complexes
[L9OHCoBr2] ꢁ CH2Cl2 (5). A solution of L9OH
(0.20 g, 0.41 mmol) in 10 ml anhydrous MeOH was
treated with solid NaOCH3 (0.02 g, 0.41 mmol) under
Ar atmosphere. To the clear solution, solid CoBr2 (0.09
g, 0.41 mmol) was added. The mixture was stirred for 3
h and the MeOH removed under reduced pressure. The
solid mass was dissolved in CH2Cl2 and filtered. The
filtrate was concentrated and layered with hexane
whereupon blue crystals separated out. These were fil-
tered, washed and dried under vacuo. Yield: 0.20 g
(60%). Anal. Calc. (Found) for C27H37N4O6CoBr2Cl2:
C, 40.78 (40.16); H, 4.69 (4.80); N, 7.04 (7.33)%.
[(L7O)Co]2(BF4)2 ꢁ 2DMF (6). A solution of L7OH
(0.20 g, 0.52 mmol) in 10 ml anhydrous DMF was treated
with solid KH (0.02 g, 0.52 mmol) under Ar atmosphere.
After gas evolution ceased, solid Co(BF4)2 ꢁ 6H2O (0.18
g, 0.52 mmol) was added. The resulting purple solution
was stirred for 3 h and filtered to remove a small amount
of insoluble material. The filtrate was concentrated under
reduced pressure. Layering a CH3CN solution of the
complex with diethyl ether caused the separation of
purple crystals which were filtered, washed with ether and
dried under vacuo. Yield: 0.42 g (68%). Anal. Calc.
(Found) for C44H56N14O8Co2B2F8: C, 44.03 (43.79); H,
4.70 (4.75); N, 16.33 (16.26)%. 1H NMR (DMF-d5)
62.52(s), 60.69(s), 38.73(s), 36.09(s), 13.72(s), 8.08(s),
1
60.84; H, 5.83; N, 13.43%. H NMR (CDCl3) d 8.59 (s,
1H, OH), 7.91 (s, 1H, –CH–), 7.09 (t, 1H, J ¼ 7:9 Hz,
ArH), 6.78 (d, 1H, J ¼ 7:8 Hz, ArH), 6.74 (t, 1H, J ¼ 7:6
Hz, ArH), 6.66 (d, 1H, J ¼ 8 Hz, ArH), 6.55 (s, 2H,
PzH), 4.26 (q, 4H, J ¼ 7:2 Hz, –OCH2), 2.09 (s, 6H,
Pz–CH3), 1.28 (t, 6H, J ¼ 7:2 Hz, –CH3). 13C NMR
(CDCl3) d 162.29, 154.62, 143.05, 141.90, 130.86,
128.09, 120.34, 119.71, 116.35, 109.41, 72.55, 60.93,
14.13, 11.40.
L7OH (2). L6OH (1.0 g, 2.42 mmol) was dissolved in
20 ml of 2.0 M methylamine in THF. To this was added
0.02 g of tetraethylammonium cyanide and the mixture

Z. Shirin, C.J. Carrano / Polyhedron 23 (2004) 239–244
241
3.56(s), 2.87(dd, J1 ¼ 77:8 Hz, J2 ¼ 14 Hz), )5.23(s),
)24.28(s), )27.42(s).
[(L7O)Co]2Br2 ꢁ 2DMF (7). This compound was
prepared as described for [(L7O)Co]2(BF4)2 ꢁ 2DMF
using CoBr2 as the cobalt precursor (60%). Anal. Calc.
(Found) for C44H56N14O8Co2Br2: C, 44.54 (44.19); H,
4.76 (4.75); N, 16.52 (16.36)%.
least 25 reflections in the range, 20° 6 2h 6 25° used to
determine the unit cell parameters. During the data
collection, the intensities of three representative reflec-
tions were measured every 97 reflections, and any decay
observed was empirically corrected for by the software
during data processing. We thank Dr. Vincent Lynch,
Department of Chemistry University of Texas at Austin
for data collection on the CCD diffractometer. The
structures were all solved using direct methods or via the
Patterson function, completed by subsequent difference
Fourier syntheses, and refined by full-matrix least-
squares procedures on F 2. All non-hydrogen atoms were
refined with anisotropic displacement coefficients with
hydrogens treated as idealized contributions using a
riding model except were noted. All software and
sources of the scattering factors are contained in the
SHELXTL 5.0 program library (G. Sheldrick, Siemens
XRD, Madison WI). Detailed crystallographic data in-
cluding complete bond distances and angles for 1, 5, 6,
8, and 9 are on deposit at the CCDC as numbers CCDC
210363–210367.
[(L7O)Ni]2(ClO4)2 ꢁ 2DMF (8). This complex was
synthesized following the same method used for the
corresponding Co complexes, using Ni(ClO4)2 ꢁ 6H2O as
the metal precursor. X-ray quality crystals were grown
from DMF/ether, (62%). Anal. Calc. (Found) for
C44H56N14O16Ni2Cl2: C, 43.13 (43.38); H, 4.61 (4.78);
N, 16.00 (16.09)%.
[pzMe; CONHCH PyCoBr]2 ꢁ DMF (9). This complex
3
was prepared by gentle warming of a pyridine solution
of 7. Upon cooling blue–green crystals of the title
complex appeared which where characterized solely by
X-ray crystallography.
2.3. Physical methods
Elemental analyses were obtained from Quantitative
Technologies, Inc., White house, NJ. All samples were
dried in vacuo prior to analysis. The presence of solvates
3. Results and discussion
1
was corroborated by FTIR, H NMR or X-ray crys-
3.1. Ligand synthesis and characterization
tallography. 1H and 13C NMR spectra were collected on
a Varian UNITY INOVA 400 MHz NMR spectrome-
ter. Chemical shifts are reported in ppm relative to an
internal standard of TMS. The 13C quaternary carbon
peaks that are not observed are a result of either poor
solubility and/or overlapping signals. 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. Iso-
tope distribution patterns were simulated using the
program IsoPro 3.0. IR spectra were recorded as KBr
disks or in solution on a Perkin–Elmer Spectrum One
FTIR spectrometer equipped with a Dell Optiplex PC.
Electronic spectra were recorded using a Cary 50 spec-
trophotometer.
The synthesis, in multigram quantities, of the ester-
substituted heteroscorpionate ligands designated L6OH
and L9OH (Fig. 1) required only two steps. The initial
step involved treatment of two equivalents of 3-methyl-
5-carboxyethyl)pyrazole with phosgene in THF in the
presence of triethylamine as an acid scavenger to give
di(3-methyl-5-carboxyethylpyrazolyl) ketone. Reaction
of one equivalent of the ketone with an equivalent of the
appropriate salicylaldehyde, either as a solution in dry
DMF or as a melt, in the presence of 1% anhydrous
CoCl2 gave, after standard workup, the desired hetero-
scorpionate ligands. Conversion of the ester ligand
L6OH to the amide ligand L7OH used a transamidation
reaction in THF employing a large excess of methyl-
amine and tetrabutylammonium cyanide as a catalyst.
The desired product complex precipitated from solution
after 72 h of reaction at 50 °C. A generally minor con-
taminant, but which in one case was the major product,
was the unsymmetrical mixed ester-amide ligand desig-
nated L8OH. However as a reliable synthesis for this
species was not forthcoming it was not pursued further.
Attempts to prepare the corresponding 5-carboxyamido
substituted ligand from L9OH were unsuccessful.
2.4. X-ray crystallography
Crystal, data collection, and refinement parameters
for 1 and 5, 6, 8 and 9 are given in Table 1. Crystals of
all complexes were sealed in thin-walled quartz capil-
laries, mounted on either Siemens P4 diffractometer with
ꢀ
a sealed-tube Mo X-ray source (k ¼ 0:71073 A) con-
In addition to the standard methods for structure
1
trolled via PC computer (data collected at 293 K) or a
Nonius Kappa CCD diffractometer (data collected at
153 K). For the Siemens system automatic searching
(Siemens XSCANS 2.1), centering, indexing, and least-
squares routines were carried out for each crystal with at
verification (elemental analysis, H and 13C NMR etc.)
ligand L6OH was characterized by X-ray crystallogra-
phy. The structure of L6OH revealed the presence of a
unique and strongly hydrogen bonded water molecule in
the crystal lattice. The hydrogen atoms of the water

242
Z. Shirin, C.J. Carrano / Polyhedron 23 (2004) 239–244
Table 1
Summary of crystallographic data and parameters for [L6OH] ꢁ H2O (1), [L9OHCoBr2] ꢁ CH2Cl2 (5), [L7OCo]2(BF4)2 ꢁ 2DMF (6),
[L7ONi]2(ClO4)2 ꢁ 2DMF (8), [pzMe; CONHCH PyCoBr]2 ꢁ DMF (9)
3
1
5
6
8
9
Molecular formula
Formula weight
C
21H26N4O6
C25H30Br2Cl2N4O5Co C25H35BN8O5F4Co
C25H32ClN8O9Ni
682.72
293(2)
C25H33Br2N9O3Co2
785.28
293(2)
430.46
293(2)
monoclinic
P21=n
8.720(3)
20.152(2)
12.936(2)
90
756.18
293(2)
monoclinic
P21=n
673.33
293(2)
monoclinic
P21=c
Temperature (K)
Crystal system
Space group cell constants
monoclinic
P21=n
9.504(12)
12.608(2)
26.666(3)
90
triclinic
ꢁ
P1
ꢀ
a (A)
17.498(5)
11.559(2)
17.615(3)
90
9.537(2)
12.675(3)
26.620(5)
90
9.434(2)
12.329(2)
15.230(3)
70.68(8)
77.78(2)
83.55(2)
2
ꢀ
b (A)
ꢀ
c (A)
a (°)
b (°)
c (°)
Z
97.04(3)
90
111.41(2)
90
97.751(8)
90
97.477(7)
90
4
4
4
4
3
ꢀ
V (A )
2256.1(8)
0.094
3317.1(12)
3.125
3188.5(12)
0.843
3168.4(8)
0.725
1632.1(6)
3.505
Absorption coefficient
lcalc (mmꢀ1
dcal (g/cm3)
F (0 0 0)
)
1.267
912
1.514
1516
1.430
1413
0.865
880
1.598
788
Crystal dimensions (mm)
Radiation
0.5 ꢂ 0.5 ꢂ 0.6
0.6 ꢂ 0.6 ꢂ 0.3
0.6 ꢂ 0.6 ꢂ 0.5
0.6 ꢂ 0.6 ꢂ 0.6
1.0 ꢂ 0.4 ꢂ 02
Mo Ka
Mo Ka
Mo Ka
Mo Ka
Mo Ka
ꢀ
ꢀ
ꢀ
ꢀ
ꢀ
(k ¼ 0:71073 A)
0 ! 9, )21 ! 0,
)13 ! 13b
1.88)22.49
3137
(k ¼ 0:71073 A)
0 ! 18, )12 ! 0,
)18 ! 19
(k ¼ 0:71073 A)
)11 ! 0, 0 ! 15,
)31 ! 31
(k ¼ 0:71073 A)
(k ¼ 0:71073 A)
h; k; l ranges collected
)10 ! 0, )13 ! 0,
)28 ! 28
0 ! 10, )12 ! 12,
)16 ! 16
Range (°)
Number of reflections
2.06)23.03
4485
1.78)25.00
5912
3.17)26.30
4391
1.75)22.50
4464
collected
Number of unique
reflections
2916
4296
5556
4106
4158
Number of parameters
Data/parameters ratio
Refinement method
289
10.08
full-matrix
least-squares of F 2 least-squares of F 2
0.0743
0.1769
1.035
372
11.53
full-matrix
397
13.91
410
9.92
365
11.38
full-matrix
least-squares of F 2
0.0591
full-matrix
least-squares of F 2
0.0535
full-matrix
least-squares of F 2
0.0405
a
RðF Þ
0.0675
0.1741
RwðF 2Þ
0.1611
1.062
0.1378
1.065
0.0983
1.055
b
Goodness-of-fit wc
1.035
0.939 and )0.472
Largest difference peak and 0.237 and )0.288
0.539 and )0.415
0.382 and )0.769
0.906 and )0.445
3
ꢀ
hole (e A )
P
P
a R ¼ ½ jDF j= jFojꢃ.
h
i
P
P
2
b Rw
¼
wðDF Þ = wFo2
.
c Goodness-of-fit on F 2.
Fig. 1. Ligands used in this study.
molecule (Fig. 2) made a pair of bifurcated hydrogen
bonds through O1 and N1 and O2 and N2 on one ligand
molecule while the water oxygen atom was H-bonded to
the protonated phenolic group on a second. Dissolv-
ing the crystals used for X-ray diffraction in CDCl3
revealed the presence of an unexpected sharp peak

Z. Shirin, C.J. Carrano / Polyhedron 23 (2004) 239–244
243
Fig. 2. ORTEP diagram of L6OH ꢁ H2O (1), showing complete atomic
labeling and hydrogen bonding interactions between the ligand and the
water of crystallization. Thermal ellipsoids are at the 30% probability
level.
Fig. 3. ORTEP diagram of 5 showing complete atomic labeling.
Thermal ellipsoids are at the 30% probability level.
integrating for two protons at 0.055 ppm. This peak was
absent in crystals that had been dried under vacuum. If
it corresponds to the unique water seen in the X-ray
structure remains to be determined.
3.2. Metal complex chemistry
Despite our hopes that the hydrogen bond accepting
ester-substituted heteroscorpionate ligands would sta-
bilize interesting new complexes such as those we char-
acterized for the homoscorpionate Tp analogs, such
species were not forthcoming. In general the phenolate
group proved to be a poor donor for divalent metals
such as Ni, Co or Zn and the only species we could
structurally characterize even in the presence of base
designed to deprotonate the phenolate oxygen, were
protonated, tetrahedral, dihalo complexes of which 5
(Fig. 3) is a representative example. No evidence for any
hydrogen bonding interactions stabilized by the ap-
pended ester groups was evident.
Fig. 4. ORTEP diagram for the cationic portion of 6 showing the
atomic labeling for the crystallographically unique half of the molec-
ular dimer. Thermal ellipsoids are at the 30% probability level.
We next turned our attention to the amide containing
ligand L7OH. In this case treatment of a solution of the
anion of the ligand (prepared by deprotonation of the
phenol with KH in DMF) with the bromide, tetraflo-
roborate or perchlorate salts of Co(II), Ni(II) or Zn(II)
produced a series of highly crystalline, isostructural
complexes of the type shown in Fig. 4 for 6. These di-
nuclear complexes of stoichiometry M2L2 have the li-
gand functioning in an unexpected pentadentate fashion
rather than the more usual tridentate mode. In this
mode, one pyrazole nitrogen and one amide carbonyl
oxygen from each or the two ligands bind to metal with
the phenolate oxygens functioning as a bridges to a
second metal center. Each metal is thus six coordinate
In an initial attempt to grow larger crystals we un-
eventfully recrystallized both the tetrafloroborate and
perchlorate salts of the Co(II) complex from DMF/
pyridine. However upon gentle heating of the bromide
salt there was a color change from purple to greenish-
blue during which time the complex dissolved. Upon
slow cooling crystals reappeared which were different
from those of the starting complex. X-ray crystallogra-
phy showed them to be that of the dinuclear 4 + 6 de-
composition product 9 (Fig. 5) where the C–N bond
between the pyrazole and the bridgehead carbon has
been broken. In this structure one Co(II) is tetrahedrally
coordinated to two bromides and a pyrazole nitrogen
from each of two different 3-methyl-5-carboxamidopy-
razole ligands. The second Co(II) is six coordinate with
ꢀ
overall with Mꢁ ꢁ ꢁM distances on the order of 3.0 A.

244
Z. Shirin, C.J. Carrano / Polyhedron 23 (2004) 239–244
for, our exploration of their potentially rich coordina-
tion chemistry continues.
5. Supplementary information
Complete crystallographic data for compounds 1, 5,
6, 8, and 9. These data under accession numbers CCDC
210363–210367, can be obtained free of charge from The
Director, CCDC, 12 Union Road, Cambridge CB2 1EZ,
UK (fax: +44-1223-336033; E-mail: deposit@ccdc.cam.
ac.uk or www: http://www.ccdc.cam.ac.uk).
Acknowledgements
Fig. 5. ORTEP diagram for the decomposition product 9 showing
complete atomic labeling. Thermal ellipsoids are at the 30% proba-
bility level.
This work was supported in part by Grants AI-1157
from the Robert A. Welch Foundation and CHE-0202535
from the NSF. The NSF-ILI program Grant USE-
9151286 is acknowledged for partial support of the X-ray
diffraction facilities at Southwest Texas State University.
We thank Dr. Vincent Lynch, Department of Chemistry,
University of Texas at Austin for the data collection of
3–5 on the Nonius Kappa CCD diffractometer.
each of the two pyrazoles functioning as bidentate li-
gand coordinating through a second pyrazole N and the
amide carbonyl. The fifth and sixth axial coordination
sites are filled by two pyridine nitrogens from the sol-
vent. Bromide clearly plays a part in driving the
decomposition reaction as the perchlorate and tetraflo-
roborate salts do not show this behavior unless bromide
is added to the reaction mixture. No reaction takes place
(as monitored by paramagnetic NMR spectroscopy)
until the reaction mixture is heated. In the absence of
pyridine an analogous DMF adduct is obtained showing
that its presence is not required for reaction.
References
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[3] B.S. Hammes, C.J. Carrano, Inorg. Chem. 38 (1999) 4593
(references therein).
[4] Z. Shirin, B.S. Hammes, V.G. Young, A.S. Borovik, J. Am.
Chem. Soc. 122 (2000) 1836.
[5] L.M. Berreau, R.A. Allred, M.M. Makowska-Grzyska, A.M.
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4. Conclusions
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Several new heteroscorpionate ligands containing ei-
ther appended hydrogen bond donating or accepting
residues have been synthesized and characterized. Al-
though the few metal complexes that we have examined
thus far do not show the interesting intra or intermo-
lecular hydrogen bonding interactions we were looking
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