Complexes of Cu(II), Co(II) and Ni(II) with pyrazole-derived ligands. Crystal structure of {bis[3-phenyl-5-(2-pyridyl)pyrazolato, κN1:κN2]copper(II)}

Article abstract of DOI:10.1016/S0020-1693(01)00566-7

The reaction of the pyrazole derived-ligands 3-phenyl-5-(2-pyridyl)pyrazole (HL⁰) and 3-phenyl-5-(6-methyl-2-pyridyl)pyrazole (HL¹) with Cu(CH₃COO)₂, Co(CH₃COO)₂ and Ni(CH₃COO)₂ was carried out. Products were characterised by elemental analyses, conductivity measurements and infrared and electronic spectroscopy. The IR spectra of complexes display the typical absorption bands of pyrazole-derived ligands. The nature of the complexes depends on the metal, M, the ligand, HL, and the M:HL ratio: Ni(HL)₂(CH₃COO)₂, Cu(L)₂, (HL=HL⁰, HL¹), Co(L⁰)₂. In the complexes of Co(II) and Cu(II) the pyrazole is deprotonated, the band ν(N-H) was not observed in IR spectroscopy. The crystal structure of [Cu(L⁰)₂] consists of discrete centrosymmetric molecules involving a co-ordinated CuN(pz)₂N(py)₂ core with planar geometry. The anionic ligand L⁰ is not completely planar.

Full text of DOI:10.1016/S0020-1693(01)00566-7

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Inorganica Chimica Acta 324 (2001) 342–346
Note
Complexes of Cu(II), Co(II) and Ni(II) with pyrazole-derived
ligands. Crystal structure of {bis[3-phenyl-5-(2-pyridyl)pyrazolato,
kN1:kN2]copper(II)}
Josefina Pons a,*, Arafa Chadghan a, Angel Alvarez-Larena b, Joan Francesc Piniella b,
Josep Ros a
a Departament de Qu´ımica, Facultat de Cie`ncies, Unitat de Qu´ımica Inorga`nica, Uni6ersitat Auto`noma de Barcelona,
E-08193-Bellaterra-Cerdanyola, Barcelona, Spain
b Departament de Geologia, Unitat de Cristal.lografia, Uni6ersitat Auto`noma de Barcelona, E-08193-Bellaterra, Barcelona, Spain
Received 11 May 2001; accepted 4 July 2001
Abstract
The reaction of the pyrazole derived-ligands 3-phenyl-5-(2-pyridyl)pyrazole (HL0) and 3-phenyl-5-(6-methyl-2-pyridyl)pyrazole
(HL1) with Cu(CH3COO)2, Co(CH3COO)2 and Ni(CH3COO)2 was carried out. Products were characterised by elemental
analyses, conductivity measurements and infrared and electronic spectroscopy. The IR spectra of complexes display the typical
absorption bands of pyrazole-derived ligands. The nature of the complexes depends on the metal, M, the ligand, HL, and the
M:HL ratio: Ni(HL)2(CH3COO)2, Cu(L)2, (HL=HL0, HL1), Co(L0)2. In the complexes of Co(II) and Cu(II) the pyrazole is
deprotonated, the band w(N–H) was not observed in IR spectroscopy. The crystal structure of [Cu(L0)2] consists of discrete
centrosymmetric molecules involving a co-ordinated CuN(pz)2N(py)2 core with planar geometry. The anionic ligand L0 is not
completely planar. © 2001 Elsevier Science B.V. All rights reserved.
Keywords: Copper, cobalt and nickel complexes; Pyrazole complexes; Crystal structures
The 3,5-substituted pyrazolic ligands have been ex-
tensively investigated in our laboratory during the last
1. Introduction
decade [6–13], in particular the synthesis and character-
The chemistry of pyrazole and pyrazolate metal com-
isation of the ligands 3-phenyl-5-(2-pyridyl)pyrazole
plexes is quite extensive in the literature [1–5].
(HL0), 3-phenyl-5-(6-methyl-2-pyridyl) pyrazole (HL1),
The pyrazolate ligand can exhibit three co-ordination
3,5-bis(2-pyridyl)pyrazole
(HL2),
3-(6-methyl-2-
modes. It can act as a monodentate (pyrazole-N) and
exo-bidentate (pyrazole N,N%) or an endo-bidentate lig-
and [1,2]. In most cases, the pyrazolate ligand co-ordi-
nates in an exo-bidentate fashion, thus linking two
metal centres that may be identical or different.
Recent studies have described the catalytic activity of
pyrazolate complexes [2,3] under mild conditions, thus
encouraging the exploration of the pyrazolate ligand.
pyridyl)-5-(2-pyridyl)pyrazole (HL3) and 3,5-bis-2-
(6-methylpyridyl)pyrazole (HL4). These molecules have
been studied as co-ordination ligands to divalent transi-
tion metals: Co(II), Ni(II), Cu(II), Zn(II), Pd(II) and
Cd(II). Munakata et al. have also described three com-
plexes with the HL3 ligand; two of Ag(I) and one of
Cu(II) [14].
In spite of the significant results on the co-ordination
ability of pyridyl–pyrazole HL ligands, it is difficult to
predict the product of their reaction with transition
metal salts. This difficulty increases when the anion is
* Corresponding author. Fax: +34-93-581-3101.
E-mail address: josefina.pons@uab.es (J. Pons).
0020-1693/01/$ - see front matter © 2001 Elsevier Science B.V. All rights reserved.
PII: S0020-1693(01)00566-7

J. Pons et al. / Inorganica Chimica Acta 324 (2001) 342–346
343
KBr pellets in the region 4000–100 cm−1. The conduc-
tivity measures were taken with a Radiometer CDM-3
conductimeter. The electronic spectra in solution were
run on a Kontron–Uvikon 860 in different solvents
between 750 and 350 nm. The electronic spectra in solid
state (KBr pellets, diffuse reflectance) were obtained on
a Kontron–Tegimenta CH-6343 Rotkreuz AG.
Fig. 1. Pyrazole derived ligands HL0 and HL1.
2.2. Synthesis of ligands
also a co-ordinating ligand like the acetate group. Pre-
vious studies of the reactivity of HL ligands with metal
acetate salts report different results: whereas in the case
of Pd(II) a Pd2L14 compound is obtained [11], the reac-
tion of Cu(CH3COO)2 with the ligand 3-(2-pyridyl)-
pyrazole produces a tetranuclear Cu(II) complexes
[Cu4(L)6(solv)2][PF6]2 (solv=DMF or MeOH) [15,16].
In order to explore the bonding possibilities of both HL
and acetate ligands we studied the reactivity of some
transition metal acetates with pyridyl–pyrazole ligands.
Here we present the results of the reactions of Ni(II),
Cu(II) and Co(II) acetates with the HL0 and HL1
ligands.
The compounds 3-phenyl-5-(2-pyridyl)pyrazole (HL0)
and 3-phenyl-5-(6-methyl-2-pyridyl)pyrazole (HL1)
were synthesised as reported previously [10] (Fig. 1).
2.3. Synthesis of the metal complexes
2.3.1. Complexes Ni(HL)2(CH3COO)2·xH2O where
HL=HL0, x=2 (1) and HL=HL1, x=0 (2)
The appropriate ligand (0.45 mmol: HL0, 0.10 g;
HL1, 0.11 g) dissolved in ethanol (20 ml) was added to
a solution of Ni(CH3COO)2·4H2O (0.22 mmol, 0.054 g)
in ethanol (10 ml). The resulting solution was stirred at
room temperature (r.t.) for 10 h and concentrated on a
vacuum line to one-fifth of the initial volume; crys-
talline solids were obtained which were filtered off and
dried in vacuum, washed with THF and dried in vacuo.
The same products (formula and yield, Table 1) were
obtained when a 1:1 Ni:HL ratio was used.
2. Experimental
2.1. General methods
All reactions were performed out with the use of
vacuum line and Schlenk techniques. Elemental analysis
was carried out by the staff of the Chemical Analysis
Service of the Universitat Auto`noma de Barcelona on a
Carlo Erba CHNS EA-1108 apparatus. IR spectra were
obtained on a Perkin–Elmer 2000 spectrometer with
1: IR(KBr): w(N–H) 3205; w(C–H)ar 3064; w(CꢀC),
w(CꢀN) 1608, 1571; was(COO) 1593; ws(COO) 1384;
l(COO) 988; l(C–H)oop 762; was(Ni–O) 491, was(Ni–N)
422; ws(Ni–O) 310, 260; ws(Ni–N) 230 cm−1. UV–Vis
(methanol 3.92×10−3 M), u(o): 618(15), 587(21),
346(sh) nm; (DMF 2.03×10−3 M), u(o): 602(21),
Table 1
Physical and analytical data for the complexes
Compound
Colour
Yield (%)
Analysis a
C (%)
Conductivity b (V−1 cm2 mol−1
)
N (%)
H (%)
Ni(HL0)2(CH3COO)2·2H2O (1)
Ni(HL1)2(CH3COO)2 (2)
Cu(L0)2 (3)
green
35
45
87
52
50
(58.65)
58.18
(63.09)
63.40
(66.72)
66.65
(67.73)
67.49
(12.82)
12.16
(12.99)
12.78
(16.67)
16.54
(15.80)
15.48
(4.92)
4.39
(4.95)
4.90
(3.99)
4.10
(4.51)
4.30
48 c
5 d
66 c
5 d
8 d
3 e
green
brown
brown
brown
Cu(L1)2 (4)
10 d
6 e
Co(L0)2·2H2O (5)
(62.81)
62.69
(15.69)
15.07
(4.52)
3.86
6 d
6 f
a Calculated analytical values are given in parentheses.
b The reported values for 1:1 electrolyte in methanol is 80–115 V−1 cm2 mol−1, in DMF is 65–90 V−1 cm2 mol−1, in DMSO is 50–70 V−1 cm2
mol−1and, in acetonitrile the values are 120–160 V−1 cm2 mol−1, respectively [19,20].
c 10−3 M in methanol.
d 10−3 M in DMF.
e 10−3 M in DMSO.
f 10−3 M in acetonitrile.

344
J. Pons et al. / Inorganica Chimica Acta 324 (2001) 342–346
Table 2
5: IR(KBr):w(O–H) 3392; w(C–H)ar 3095; w(CꢀC),
w(CꢀN) 1613, 1548; l(C–H)oop 760; was(Co–N) 314;
ws(Co–N) 228 cm−1. UV–Vis (KBr): u=670, 400 nm.
Crystallographic data and structure refinement for 3
Compound
Cu(L0)2
C28H20CuN6
504.04
Empirical formula
Formula weight
Temperature (K)
Wavelength
Crystal system
Space group
2.4. X-ray crystal structure analyses
293(2)
0.71069
monoclinic
P21/c
Suitable crystals for X-ray diffraction experiments of
compound Cu(L0)2 5 were obtained by crystallisation
from ethanol. One crystal was mounted on an Enraf–
Nonius CAD4 diffractometer. Intensities were collected
using the ꢀ–2q scan mode to 2qmax=50°. Graphite-
monochromated Mo Ka radiation was used. The struc-
ture was solved by direct methods (SHELXS-86) [17] and
refined by full-matrix least-squares methods on F2 for
all reflections (SHELXL-97) [18]. The final R(F) and
Rw(F2) values as well as the number of parameters
refined and other details concerning the refinement of
the crystal structure are presented in Table 2. The
Unit cell dimensions
,
a (A)
13.0448(13)
5.2963(6)
16.384(3)
103.364(11)
1101.3(3)
2
1.520
0.102
0.47×0.47×0.30
1940
1.121
R(F)=0.026,
Rw(F2)=0.079
R(F)=0.030,
Rw(F2)=0.080
0.19, −0.16
,
b (A)
,
c (A)
i (°)
3
,
V (A )
Z
Dcalc (Mg m−3
)
Absorption coefficient (mm−1
Crystal size (mm)
)
Unique reflections
Goodness-of-fit on F2
Final R indices [I\2|(I)]
weight
was
w
−1=|2(Fo2)+(0.0483P)2+0.1764P
where P=(Fo2+2Fc2)/3.
R indices (all data)
Largest difference peak and hole
3. Results and discussion
−3
,
(e A
)
3.1. Synthesis and spectroscopic properties of the
complexes
569(17), 364(sh) nm. UV–Vis (KBr): u=706, 616, 570,
370 nm.
The reaction of HL0 and HL1 ligands with
M(CH3COO)2 (M=Co, Ni and Cu) salts gives differ-
ent types of complex depending on the metal, the ligand
and the metal to ligand (M:HL) ratio.
2: IR(KBr): w(N–H) 3119; w(C–H)ar 3049; w(CꢀC),
w(CꢀN) 1608, 1577; was(COO) 1615, ws(COO) 1396;
l(COO) 888; l(C–H)oop 775; was(Ni–O) 533, was(Ni–N)
434, 378; ws(Ni–O) 286; ws(Ni–N) 244 cm−1. UV–Vis
(methanol 5.22×10−3 M), u(o): 631(15), 592(19),
351(sh) nm; (DMF 2.03×10−3 M), u(o): 688(14),
658(15), 365(sh) nm. UV–Vis (KBr): u=716, 618, 592,
370 nm.
Ni(CH3COO)2 reacts with HL0 and HL1 ligands in
different M:HL ratios to produce a sole type of com-
plex: Ni(HL)2(CH3COO)2 (HL=HL0 (1) and HL1 (2)).
Cu(CH3COO)2 and HL ligands react to form the
Cu(L)2 (3, 4) complexes. The reactivity of
Co(CH3COO)2 with HL0 in a 1:2 ratio leads to a
Co(L0)2·2H2O (5) complex. Reactions at other ratios do
not give pure products. This study shows that Ni(II)
complexes contain the pyrazole derived ligand in its
neutral form whereas Cu(II) and Co(II) form com-
pounds with anionic L0 and L1 ligands. Table 1 gives
analytical and conductivity data for the complexes
synthesised.
2.3.2. Complexes ML2·xH2O where M=Cu, L=L0
and x=0 (3), M=Cu, L=L1 and x=0 (4), M=Co,
L=L0 and x=2 (5)
An amount of ligand (0.45 mmol: HL0, 0.10 g; HL1,
0.11 g) dissolved in 10 ml of ethanol, was added to a
solution of the corresponding metallic salt (0.22 mmol,
0.054
g
of Co(CH3COO)2·4H2O or 0.044
g
of
Conductivity data for complexes 1–5 in several sol-
vents show non-ionic behaviour consistent with neutral
products.
Cu(CH3COO)2·H2O) in 10 ml of ethanol. The mixture
was stirred for 20 h and the precipitate was filtered off,
washed with ethanol and ether and dried in vacuo.
3: IR(KBr):w(O–H) 3400; w(C–H)ar 3088; w(CꢀC),
w(CꢀN) 1612, 1547; l(C–H)oop 758; was(Cu–N) 420;
ws(Cu–N) 250 cm−1. UV–Vis (DMF 1.98x10−3 M),
u(o): 585(49), 366(sh) nm.
4: IR(KBr):w(O–H) 3392; w(C–H)ar 3090; w(CꢀC),
w(CꢀN) 1610, 1553; l(C–H)oop 765; was(Cu–N) 432;
ws(Cu–N) 252 cm−1. UV–Vis (DMF 1.98x10−3 M),
u(o): 612(65), 356(sh) nm.
The IR spectra of the complexes show the absorption
bands assigned to the asymmetric and symmetric
w(OCO) stretching modes and the typical bands of HL
pyrazole-derived ligands [10]. Complexes 1, 2 display
two well defined bands between 1615–1590 and 1396–
1381 cm−1, separated by Z=was(OCO)–ws(OCO)=
219–200 cm−1. These Z values suggest the presence of
unidentate acetate groups in compounds 1, 2 [21–23].
The IR spectra of complexes 1 and 2 show the w(NH)

J. Pons et al. / Inorganica Chimica Acta 324 (2001) 342–346
345
absorption at 3205 and 3119 cm−1, respectively, which
implies the neutral nature of HL ligands.
A (Cu–N20(pz)), respectively. These values are consis-
tent with those described in the literature (1.974–2.109
,
,
,
Electronic spectra of Ni(II) complexes (1 and 2) were
measured in methanol and DMF solutions and with
KBr pellets (diffuse reflectance). Both Ni(II) complexes
show two absorptions in the visible region between 688
and 569 nm (m=14–21 mol−1 cm−1 l) which are
characteristic for octahedral Ni(II) complexes [24–26].
Electronic spectra using diffuse reflectance methods
show an additional band at 716–706 nm which can be
assigned to the 3A2g“1Eg(D) transition of the d8 ion an
octahedral field [27].
Complex 5 is insoluble in methanol so we registered
its electronic spectrum using a diffuse reflectance
method. This complex displays one band at 670 nm
which is typical for octahedral Co(II) centres
[24,25,28,29].
A for Cu–N(py)) [8,14,15,37–39] and (1.929–2.088 A
for Cu–N(pz)) [8,14,15,29,40–42]. Nevertheless the
Cu–N20(pz) bond length is shorter than the Cu–N(pz)
,
distance (1.972(2) A) found in this complex. It is also
shorter than the Cu–N(pz) in the complex
[Cu(HL0)(NO3)(H2O)2] (NO3) [13] where HL0 is
neutral.
The N10–Cu–N20 bite angle of 80.95(6)° is similar
to those found in other complexes with HL0 and HL1
ligands [10–13]. The HL0 ligands are not completely
planar in this structure. The pyridyl and phenyl groups
are slightly twisted around the pyrazole ring: Thus, the
angles between aromatic rings found in the structure
are: py–pz 5.70(10)°, py–ph 9.07(10)° and pz–ph
3.68(11)°. These angles are comparable to those found
in the structure [Cu(HL0)(NO3)(H2O)2](NO3) [13].
The structure of 3 is very similar to that of the
square-planar complex PdL2 where HL=3-(2-
pyridyl)pyrazole [30]. In this case, the presence of two
hydrogen bonds was considered to stabilise the planar
configuration. In complex 3 the square-planar geometry
of Cu(II) may also be favoured by hydrogen bonds
between C15–H and N21i (the C15–H bond length has
3.2. Crystal structure of [Cu(L0)2]
Fig. 2 shows the molecular structure of compound 3
(Cu(L0)2). The crystal structure consists of discrete cen-
trosymmetric Cu(L0)2. The literature contains seventeen
structures of complexes with 5-(2-pyridyl)pyrazole lig-
and with a R=H, Me, tBu, Ph and py group bonded to
the pyrazole ring at position 3. In these structures the
pyrazole ligand can adopt three modes of co-ordina-
tion: anionic monodentante [15,16,30,31], neutral
,
been geometrically fixed in the refinement (0.93 A) and
the contact parameters between C15–H and N21 are:
H···N21i, 2.29 A; C15···N21i, 3.079(3) A; C15–
H···N21i, 142°; symmetry code (i): −x, −y, −z). It is
interesting to point out that the reaction of 3-(2-
pyridyl)pyrazole ligand with Cu(CH3COO)2 led to the
formation of [Cu4(L)6 (solv)2][PF6]2 (solv=DMF or
MeOH) complexes (the structure of which was estab-
lished by X-ray diffractometry [15,16]) in contrast to its
reaction with Pd(CH3COO)2, which gives a PdL2 com-
plex [30].
,
,
monodentate
[10,12,13]
and
exo-bidentate
[6,8,11,14,32–36].
The structure of
3
has two 3-phenyl-5-(2-
pyridyl)pyrazolato ligand in a trans disposition bonded
to a Cu(II) centre in a bidentate co-ordination mode by
the N10(py) and N20(pz) atoms. This co-ordination
mode involves a CuN4 core with distorted square pla-
nar geometry. Each anionic L0 ligand is bonded to
metal using two of its three co-ordinating nitrogen
atoms (N(py) and N(pz)). The metal–ligand bond dis-
4. Supplementary material
,
tances are 2.0450(15) A (Cu–N10(py)) and 1.9440(15)
Crystallographic data for the structural analysis have
been deposited with the Cambridge Crystallographic
Data Center, CCDC No. 162862. Copies of this infor-
mation may be obtained free of charge from The
Director, CCDC, 12 Union Road, Cambridge CB2
1EZ, UK [fax: +44-1223-336033; e-mail: deposit@
aadc.cam.ac.uk or www: http://www.ccdc.cam.ac.uk].
Acknowledgements
We thank MCYT Project BQU2000-0238 for finan-
cial support. A.C. is grateful for a grant from Ministe-
rio de Asuntos Exteriores: Agencia Espan˜ola de
Cooperacio´n Internacional (Instituto de cooperacio´n
con el mundo a´rabe).
Fig. 2. An ORTEP view of the structure [Cu(L0)2]. The displacement
ellipsoids enclose 50% probability.

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J. Pons et al. / Inorganica Chimica Acta 324 (2001) 342–346
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