Coordination behaviour of new dipyridylpyrazole ligands towards ZnCl 2 and PdCl2 fragments. Crystalline structural characterization and multinuclear NMR studies as evidence of linkage and conformational isomers

Article abstract of DOI:10.1039/c3ra45821k

A series of novel N,N,N-donor pyrazole based ligands of the type pypz ^R(n)py (R(n) = C₆H₄OC_nH _2n+1, n = 1, 12-18) (1-5) bearing two pyridine substituents at the 1- and 3-positions and an alkyloxyphenyl group at the 5-position have been prepared and characterized. The X-ray structure of pypz^R(1)py is presented. Coordination of those ligands to MCl₂ fragments (M = Zn, Pd) gives rise to complexes of the type [MCl₂(pypz^R(n)py)] (M = Zn, Pd; R(n) = C₆H₄OC_nH_2n+1; n = 1, 12-18) (6-15) which were characterized and studied in the solid state and in solution. In these compounds the ligands were highly versatile as they were metal coordinated in a N,N-bidentate, N,N,N-tridentate fashion or N,N-bidentate fashion with an additional interaction via the third active nitrogen, this different behaviour depending on the metal fragment as well as on the state (solid or in solution) in which the complexes are. The X-ray structures of [ZnCl₂(pypz^R(1)py)] (6) and [PdCl₂(pypz ^R(1)py)] (11) have also been determined showing distorted trigonal bipyramid and square-planar geometries at the zinc and palladium centres, respectively. In both cases the coordination environment has been confirmed by ¹³C-and ¹⁵N-NMR studies in solid state. In particular, two binuclear M-M stereoisomers "Z"- and "U"-shaped may be established for the Pd derivative. The ¹H and ¹³C-NMR studies in CDCl₃ solution of (6) and (11) indicate the presence of monomeric species which exhibit the same or different bidentate coordination of the ligand, respectively, than that observed in solid state. However, DMSO-d⁶ causes a total dissociation of the ligand in Zn derivatives, while for the related Pd complexes two monomeric linkage isomers (N2,N1′PdCl2 and N2,N1′′PdCl2) were detected.

Full text of DOI:10.1039/c3ra45821k

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PAPER
Coordination behaviour of new dipyridylpyrazole
ligands towards ZnCl2 and PdCl2 fragments.
Crystalline structural characterization and
multinuclear NMR studies as evidence of linkage
and conformational isomers†‡
Cite this: RSC Adv., 2014, 4, 9383
a
a
a
Lorena Soria, Paloma Ovejero, Mercedes Cano, Jose Vicente Heras,§a
*
´
M. Rosario Torres,b Rosa Claramuntc and Pilar Cornagoc
A series of novel N,N,N-donor pyrazole based ligands of the type pypzR(n)py (R(n) ¼ C6H4OCnH2n+1, n ¼ 1, 12–
18) (1–5) bearing two pyridine substituents at the 1- and 3-positions and an alkyloxyphenyl group at the
5-position have been prepared and characterized. The X-ray structure of pypzR(1)py is presented.
Coordination of those ligands to MCl2 fragments (M ¼ Zn, Pd) gives rise to complexes of the type
[MCl2(pypzR(n)py)] (M ¼ Zn, Pd; R(n) ¼ C6H4OCnH2n+1; n ¼ 1, 12–18) (6–15) which were characterized and
studied in the solid state and in solution. In these compounds the ligands were highly versatile as they were
metal coordinated in a N,N-bidentate, N,N,N-tridentate fashion or N,N-bidentate fashion with an additional
interaction via the third active nitrogen, this different behaviour depending on the metal fragment as well as
on the state (solid or in solution) in which the complexes are. The X-ray structures of [ZnCl2(pypzR(1)py)] (6)
and [PdCl2(pypzR(1)py)] (11) have also been determined showing distorted trigonal bipyramid and square-
planar geometries at the zinc and palladium centres, respectively. In both cases the coordination
environment has been confirmed by 13C-and 15N-NMR studies in solid state. In particular, two binuclear
M–M stereoisomers “Z”- and “U”-shaped may be established for the Pd derivative. The 1H and 13C-NMR
studies in CDCl3 solution of (6) and (11) indicate the presence of monomeric species which exhibit the
same or different bidentate coordination of the ligand, respectively, than that observed in solid state.
However, DMSO-d6 causes a total dissociation of the ligand in Zn derivatives, while for the related Pd
complexes two monomeric linkage isomers (N2,N10PdCl2 and N2,N100PdCl2) were detected.
Received 14th October 2013
Accepted 20th January 2014
DOI: 10.1039/c3ra45821k
www.rsc.org/advances
In particular in our research group, many metallomesogens
containing mesogenic or promesogenic pyrazole type ligands
have been prepared.3–6 In addition, we have found that the
Introduction
The interest of the current research on metallomesogens is
directed to explore new systems with optimized LC properties.1,2
In this context, factors such as coordination geometry, the
nature of the metal fragments or the characteristics of the
ligands have been investigated in many metal derivatives.
introduction of a polar group like pyridine on the molecular
periphery appears to be determinant to achieve and/or to
improve the mesomorphic properties of the metal complexes.7
So it was interesting to note that Ag(I) and Pd(II) metal-
lomesogens with pyridylpyrazole type ligands pypzR(n) and
HpzR(n)py (R(n) ¼ C6H4OCnH2n+1, n ¼ 1, 12–18)3–6 exhibited lower
melting points and a wider mesophase range than the related
ones with ligands not containing pyridine groups.4,7 On the
other hand dipyridylpyrazole ligands have been recently proved
as candidates to stabilize polymeric structures through strong
chelation.8–14 Therefore they could play a signicant role as
inducers of LC behaviour. On these basis we propose to explore
the potential ability of new related long-chained ligands to
generate metallomesogens.
a
´
´
´
Departamento de Quımica Inorganica I, Facultad de Ciencias Quımicas, Universidad
Complutense, 28040 Madrid, Spain. E-mail: mmcano@quim.ucm.es; Fax: +34 91 394
4352; Tel: +34 91 394 4340
bCAI de Difraccion de Rayos-X, Facultad de Ciencias Quımicas, Universidad
´
´
Complutense, 28040 Madrid, Spain. E-mail: mrtorres@quim.ucm.es; Tel: +34 91
394 4284
c
´
´
Departamento de Quımica Organica, Facultad de Ciencias, UNED, 28040, Madrid,
Spain. E-mail: rclaramunt@ccia.uned.es
´
´
† Dedicated to the memory of Prof.Dr Jose Vicente Heras Castello.
‡ Electronic supplementary information (ESI) available. CCDC 948534 (1), 948535
(6) and 948536 (11). For ESI and crystallographic data in CIF or other electronic
format see DOI: 10.1039/c3ra45821k
The present paper reports the synthesis and characterisation
of a new versatile class of alkyloxyphenyl-substituted dipyr-
idylpyrazoles pypzR(n)py (R(n) ¼ C6H4OCnH2n+1, n ¼ 1, 12–18)
§ Deceased on 26th April, 2013.
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12.5 kHz for 15N, a 1024 ꢁ 256 data set, a relaxation delay of 1 s
and a 7 ms delay for the using zero lling in the F1 domain, and
a sine-bell window function in both dimensions was applied
prior to Fourier transformation.
For the rest of compounds 1H-NMR spectra were performed
at room temperature on a Bruker DPX-300 spectrophotometer
(NMR Service of Complutense University) from solutions in
DMSO-d6 or CDCl3. 1H Chemical shis (d) are listed relative to
Me4Si using the signal of the deuterated solvent as reference
(2.50 and 7.26 ppm, respectively), and coupling constants J are
in hertz. Multiplicities are indicated as s (singlet), d (doublet), t
(triplet), dd (doublet of doublets), ddd (double doublet of
doublets) and m (multiplet). The 1H chemical shis and
coupling constants are accurate to ꢂ0.01 ppm and ꢂ0.3 Hz,
respectively.
Fig. 1 Schematic representation and numbering of the atoms for
pypzR(n)py ligands.
(1–5) (Fig. 1) as well as the study of their metal complexes of the
type [MCl2(pypzR(n)py)] (M ¼ Zn, Pd, R(n) ¼ C6H4OCnH2n+1, n ¼ 1, Solid state
Solid-state 13C (100.73 MHz) and 15N (40.60 MHz) CPMAS NMR
12–18) (6–15) (Table 2). A careful structural analysis of the
coordination compounds will be achieved in order to establish
structure/properties relationship.
spectra of 1, 6 and 11 have been obtained on a Bruker WB 400
spectrometer at 300 K using a 4 mm DVT probehead. Samples
were carefully packed in a 4 mm diameter cylindrical zirconia
rotor with Kel-F end-caps. Operating conditions involved 3.2 ms
90ꢃ 1H pulses and decoupling eld strength of 78.1 kHz by
TPPM sequence. 13C spectra were originally referenced to a
glycine sample and then the chemical shis were recalculated
to the Me4Si [for the carbonyl atom d (glycine) ¼ 176.1 ppm].
Similarly, 15N spectra were initially referenced to 15NNH4Cl and
then recalculated to nitromethane, using the relationship d
15NNitromethane ¼ d 15NNH4Cl – 338.1. Typical acquisition
parameters for 13C CPMAS were: spectral width, 40 kHz; recycle
delay, 5 s; acquisition time, 30 ms; contact time, 2 ms; and spin
rate, 12 kHz. In order to distinguish protonated and unproto-
nated carbon atoms, the NQS (Non-Quaternary Suppression)
experiment by conventional cross-polarization was recorded;
before the acquisition the decoupler is switched off for a very
short time of 25 ms. Typical parameters for the 15N CPMAS were:
spectral width, 40 kHz; recycle delay, 5 s, acquisition time, 35
ms; contact time, 7 ms; and spin rate, 6 kHz. Fig. 1 recovers the
nomenclature used in the NMR assignments.
Experimental
Materials and physical measurements
All commercial reagents were used as supplied. Elemental
analysis for carbon, hydrogen and nitrogen were carried out by
the Microanalytical Service of Complutense University. IR
spectra were recorded on a FTIR Thermo Nicolet 200 spectro-
photometer in solid state, with samples as KBr pellets, in the
4000–400 cmꢀ1 region.
Solution NMR spectra
Solution NMR spectra of 1, 6 and 11 were recorded on a Bruker
DRX 400 (9.4 T; 400.13 MHz for 1H, 100.62 MHz for 13C and
40.56 MHz for 15N) spectrometer tted with a 5 mm inverse
detection H–X probe and equipped with a z-gradient coil at 300
K. 1H and 13C NMR chemical shis (d in ppm) are referenced to
Me4Si; for 15N NMR, nitromethane (0.00) was used as an
external standard. Typical parameters for 1H NMR spectra were:
spectral width 3100 Hz and pulse width 7.5 ms at an attenuation
level of 0 dB. Typical parameters for 13C NMR spectra were:
spectral width 21 kHz, pulse width 10.6 ms at an attenuation
level of ꢀ6 dB and relaxation delay 2 s. 2D (1H–13C) gs-HMQC
and, (1H–13C) gs-HMBC were acquired and processed using
standard Bruker NMR soware and in non-phase-sensitive
Phase studies were carried out by optical microscopy using
an Olympus BX50 microscope equipped with a Linkam THMS
600 heating stage. The temperatures were assigned on the basis
of optic observations with polarised light.
Compounds 1,3-bis-(2-pyridyl)-5-(4-n-alkyloxyphenyl)pyrazole
[pypzR(n)py] (R(n) ¼ C6H4OCnH2n+1, n ¼ 1, 12–18) (1–5)
mode. Selected parameters for (1H–13C) gs-HMQC and gs-
1
HMBC spectra were spectral width 3100 Hz for H and 25 kHz To a solution of 6.1 mmol of the corresponding b-diketone
for 13C, 1024 ꢁ 256 data set, number of scans 2 (gs-HMQC) or 4 (synthesised according to the previously described methods)15
(gs-HMBC) and relaxation delay 1 s. The FIDs were processed in 200 mL of absolute ethanol were added 2 mL of HCl (35%)
using zero lling in the F1 domain and a sine-bell window and 9.5 mmol of NH2NHpy (97%). The reaction mixture was
function in both dimensions was applied prior to Fourier stirred for 72 h at reux temperature. Once it was cooled to
transformation. In the gs-HMQC experiments GARP modula- room temperature, 50 mL of a saturated Na2CO3 aqueous
tion of 13C was used for decoupling. 15N NMR spectra were solution was added until neutral pH was reached, being
acquired using 2D inverse proton detected heteronuclear shi observed, at this point, the plentiful appearance of a brown
correlation spectroscopy. Typical parameters for the gs-HMBC precipitate, which was ltered off and washed with 50 mL of
1
(1H–13C) spectra were: a spectral width of 3100 Hz for H and CH2Cl2. The solution was extracted with CH2Cl2 (2 ꢁ 50 mL) and
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the organic layers were washed with water (2 ꢁ 50 mL) and nitrogen atmosphere (Scheme 1). The mixture was stirred for 24
dryed over anhydrous MgSO4. The solvent of the resulting h at room temperature, leading to the precipitation of a beige
brown/orange solution was removed under the reduced pres- solid, which was ltered off, washed with n-hexane (10 mL) and
sure of a rotatory evaporator until the formation of an oily dried in vacuo (0.05 hPa).
product which was dissolved with 15 mL of diethyl ether. The
nal solid was formed by slow evaporation of the solvent at found: C, 50.6; H, 3.6; N, 12.1%. C20H16N4OZnCl2 requires C,
room temperature.
51.7; H, 3.5; N, 12.1%. nmax(KBr)/cmꢀ1: 1608 n(C]C + C]N),
[pypzR(1)py]$H2O (1). Yellow solid (60%). Elemental analysis: 789 g(CH)py. dH (see Results and discussion section).
found: C, 69.9; H, 5.4; N, 15.9%. C20H16N4O requires C, 69.4; H,
[ZnCl2(pypzR(12)py)] (7). Beige solid (49%). Elemental analy-
[ZnCl2(pypzR(1)py)] (6). Beige solid (8%). Elemental analysis:
5.2; N, 16.2%. nmax(KBr)/cmꢀ1: 1614 n(C]C + C]N), 782 sis: found: C, 59.5; H, 6.0; N, 9.3%. C31H38N4OZnCl2 requires C,
g(CH)py. dH (see Results and discussion section).
60.2; H, 6.2; N, 9.0%. nmax(KBr)/cmꢀ1: 1607 n(C]C + C]N), 786
[pypzR(12)py] (2). Dark brown solid (73%). Elemental analysis: g(CH)py. dH (300 MHz, CDCl3, Me4Si)/ppm: 0.87 (t, J 6.0, 3H,
found: C, 75.9; H, 7.6; N, 12.4%. C31H38N4O requires C, 77.1; H, CH3), 1.27 (m, 18H, CH2), 1.84 (m, 2H, CH2), 4.05 (t, 3J 6.0, 2H,
7.9; N, 11.6%. nmax(KBr)/cmꢀ1: 1614 n(C]C + C]N), 786 g(CH)py. OCH2), 6.93 (s, 1H, H4), 6.97 (d, 3J 9.0, 1H, H30), 7.06 (d, 3J 9.0,
dH (300 MHz, DMSO-d6, Me4Si)/ppm: 0.85 (t, 3J 6.8, 3H, CH3), 1.24 2H, Hm), 7.39 (m, 1H, H50), 7.41 (d, 3J 9.0, 2H, Ho), 7.57 (dd, 3J ¼
3
(m, 18H, CH2), 1.68 (m, 2H, CH2), 3.95 (t, 3J 6.4, 2H, OCH2), 6.88 7.5, J ¼ 5.3, 1H, H500), 7.67 (ddd, J ¼ 3J¼ 8.1, J 1.8, 1H, H40),
3
3
4
(d, 3J 8.8, 2H, Hm), 7.13 (s, 1H, H4), 7.19 (d, 3J 8.8, 2H, Ho), 7.39 7.99 (d, 3J 9.0, 1H, H300), 7.98 (ddd, 3J ¼ 3J ¼ 7.8, 4J 1.4, 1H, H400),
(ddd, 3J 7.4, 3J 4.8, 4J 1.1, 1H, H50), 7.46 (ddd, 3J 7.4, 3J 4.9,4J 1.0, 8.78 (d, J 4.5, 1H, H60), 8.87 (d, J 5.1, 1H, H600).
3
3
1H, H500), 7.73 (d, 3J 7.6, 1H, H300), 7.88 (ddd, 3J ¼ 3J ¼ 7.6, 4J 1.8,
[ZnCl2(pypzR(14)py)] (8). Beige solid (66%). Elemental anal-
1H, H40), 8.04 (dd, 3J ¼ 3J ¼ 7.1, 1H, H400), 8.05 (d, 3J 7.7, 1H, H30), ysis: found: C, 61.9; H, 6.9; N, 9.1%. C33H42N4OZnCl2 requires
8.38 (dd, 3J 4.9, 4J 1.1, 1H, H600), 8.65 (d, 3J 4.4, 1H, H60).
C, 61.3; H, 6.5; N, 8.7%. nmax(KBr)/cmꢀ1: 1609 n(C]C + C]N),
[pypzR(14)py] (3). Brown solid (77%). Elemental analysis: 790 g(CH)py. dH (300 MHz, CDCl3, Me4Si)/ppm: 0.87 (t, J 6.0,
found: C, 76.8; H, 8.1; N, 10.8%. C33H42N4O requires C, 77.6, H, 3H, CH3), 1.27 (m, 22H, CH2), 1.84 (m, 2H, CH2), 4.00 (t, 3J 6.0,
8.3; N, 10.9%. nmax(KBr)/cmꢀ1: 1614 n(C]C + C]N), 788 g(CH)py. 2H, OCH2), 6.87 (s, 1H, H4), 6.93 (d, 3J 9.0, 1H, H30), 7.01 (d, 3J
dH (300 MHz, DMSO-d6, Me4Si)/ppm: 0.84 (t, 3J 6.9, 3H, CH3), 1.23 9.0, 2H, Hm), 7.35 (m, 1H, H50), 7.39 (d, 3J 9.0, 2H, Ho), 7.50 (dd,
3
(m, 22H, CH2), 1.68 (m, 2H, CH2), 3.95 (t, 3J 6.4, 2H, OCH2), 6.88 3J ¼ 7.6, J ¼ 5.0, 1H, H500), 7.63 (ddd, J ¼ 3J¼ 8.0, J 1.8, 1H,
3
3
4
(d, 3J 8.8, 2H, Hm), 7.13 (s, 1H, H4), 7.19 (d, 3J 8.8, 2H, Ho), 7.38 H40), 7.97 (d, 3J 9.0, 1H, H300), 8.01 (ddd, 3J ¼ 3J ¼ 7.5, 4J 1.0, 1H,
(ddd, 3J 7.6, 3J 5.3,4J 1.1, 1H, H50), 7.46 (ddd, 3J 7.4, 3J 4.8,4J 0.9, H400), 8.74 (d, J 4.6, 1H, H60), 8.86 (d, J 5.0, 1H, H600).
3
3
1H, H500), 7.72 (d, 3J 8.0, 1H, H300), 7.72 (ddd, 3J ¼ 3J ¼ 7.7, 4J 1.8,
[ZnCl2(pypzR(16)py)] (9). Beige solid (72%). Elemental anal-
1H, H40), 8.03 (dd, 3J ¼ 3J ¼ 7.7, 1H, H400), 8.05 (d, 3J 7.8, 1H, H30), ysis: found: C, 62.9; H, 7.2; N, 8.6%. C35H46N4OZnCl2 requires
8.38 (dd, 3J 4.9, 4J 1.1, 1H, H600), 8.64 (d, 3J 4.0, 1H, H60).
C, 62.3; H, 6.9; N, 8.3%. nmax(KBr)/cmꢀ1: 1609 n(C]C + C]N),
[pypzR(16)py] (4). Dark brown solid (81%). Elemental analysis: 791 g(CH)py. dH (300 MHz, CDCl3, Me4Si)/ppm: 0.88 (t, J 6.0,
found: C, 77.8; H, 8.4; N, 9.9%. C35H46N4O requires C, 78.0; H, 3H, CH3), 1.27 (m, 26H, CH2), 1.85 (m, 2H, CH2), 4.00 (t, 3J 6.0,
8.6; N, 10.4%. nmax(KBr)/cmꢀ1: 1613 n(C]C + C]N), 786 g(CH)py. 2H, OCH2), 6.91 (s, 1H, H4), 6.96 (d, 3J 9.0, 1H, H30), 7.00 (d, 3J
dH (300 MHz, DMSO-d6, Me4Si)/ppm: 0.84 (t, 3J 6.9, 3H, CH3), 1.23 9.0, 2H, Hm), 7.38 (m, 1H, H50), 7.42 (d, 3J 9.0, 2H, Ho), 7.55 (dd,
3
(m, 26H, CH2), 1.69 (m, 2H, CH2), 3.95 (t, 3J 6.4, 2H, OCH2), 6.89 3J ¼ 7.4, J ¼ 5.3, 1H, H500), 7.66 (ddd, J ¼ 3J¼ 8.3, J 1.5, 1H,
3
3
4
(d, 3J 8.8, 2H, Hm), 7.15 (s, 1H, H4), 7.19 (d, 3J 8.8, 2H, Ho), 7.42 H40), 7.96 (d, 3J 9.0, 1H, H300), 8.00 (ddd, 3J ¼ 3J ¼ 7.5, 4J 1.3, 1H,
(ddd, 3J ¼ 7.5, 3J 5.0, 4J 1.1, 1H, H50), 7.46 (ddd, 3J ¼ 7.4, 3J 4.9, 4J H400), 8.77 (d, J 4.3, 1H, H60), 8.86 (d, J 5.2, 1H, H600).
3
3
0.9, 1H, H500), 7.73 (d, 3J 8.0, 1H, H300), 7.92 (ddd, 3J ¼ 3J ¼ 7.6, 4J
1.7, 1H, H40), 8.06 (dd, 3J ¼ 3J ¼ 7.8, 1H, H400), 8.07 (d, 3J 7.8, 1H,
H30), 8.39 (dd, 3J 4.8, 4J 1.1, 1H, H600), 8.66 (d, 3J 4.2, 1H, H60).
[pypzR(18)py] (5). Dark brown solid (83%). Elemental analysis:
found:C, 78.1; H, 8.7; N, 9.6%. C37H50N4O requires: C, 78.4; H,
8.7; N, 9.9%. nmax(KBr)/cmꢀ1: 1614 n(C]C + C]N), 787 g(CH)py.
3
dH (300 MHz, DMSO-d6, Me4Si)/ppm: 0.84 (t, J 6.8, 3H, CH3),
1.23 (m, 30H, CH2), 1.69 (m, 2H, CH2), 3.95 (t, 3J 6.5, 2H, OCH2),
6.88 (d, 3J 8.8, 2H, Hm), 7.13 (s, 1H, H4), 7.19 (d, 3J 8.8, 2H, Ho),
7.38 (dd, 3J 6.9, 3J 5.8, 1H, H50), 7.46 (dd, 3J 7.0, 3J 5.0, 1H, H500),
3
3
4
7.72 (d, J 8.0, 1H, H300), 7.88 (ddd, J ¼ 7.7, J 1.8, 1H, H40),
8.03(dd, 3J ¼ 3J ¼ 6.9, 1H, H400), 8.05 (d, 3J 7.8, 1H, H30), 8.38 (d,
3J 4.2, 1H, H600), 8.64 (d, J 4.2, 1H, H60).
3
Complexes [ZnCl2(pypzR(n)py)]; R(n) ¼ (C6H4OCnH2n+1, n ¼ 1,
12–18) (6–10)
To a solution of the corresponding pypzR(n)py in 20 mL of
Scheme 1 Schematic synthesis of pypzR(n)py and [MCl2(pypzR(n)py)]
absolute ethanol was added ZnCl2 in a 1 : 1 molar ratio, under (M ¼ Zn, Pd).
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3J 6.0, 3H, CH3), 1.26 (m, 18H, CH2), 1.73 (m, 2H, CH2), 3.90 (t, 3J
6.0, 2H, OCH2), 6.78 (d, 3J 9.0, 2H, Hm), 6.93 (s, 1H, H4), 7.12 (d,
3J 9.0, 2H, Ho), 7.32 (d, 3J 9.0, 1H, H300), 7.43 (m, 1H, H50), 7.45
(m, 1H, H500), 7.74 (ddd, 3J ¼ 3J ¼ 7.8, 4J 1.5, 1H, H40), 7.84 (d, 3J
9.0, 1H, H30), 8.04 (dd, 3J 7.5, 3J 7.2, 1H, H400), 8.61 (dd, 3J 4.8, 4J
[ZnCl2(pypzR(18)py)] (10). Beige solid (49%). Elemental anal-
ysis: found: C, 63.8; H, 7.7; N, 8.5%. C37H50N4OZnCl2 requires
C, 63.2; H, 7.2; N, 8.0%. nmax(KBr)/cmꢀ1: 1609 n(C]C + C]N),
3
790 g(CH)py. dH (300 MHz, CDCl3, Me4Si)/ppm: 0.87 (t, J 6.0,
3H, CH3), 1.27 (m, 30H, CH2), 1.84 (m, 2H, CH2), 4.05 (t, 3J 6.0,
2H, OCH2), 6.93 (s, 1H, H4), 6.97 (d, 3J 9.0, 1H, H30), 7.06 (d, 3J
9.0, 2H, Hm), 7.39 (m, 1H, H50), 7.41 (d, 3J 9.0, 2H, Ho), 7.57 (dd,
3
1.2, 1H, H600), 9.25 (d, J 5.7, 1H, H60).
[PdCl2(pypzR(14)py)] (13). Yellow solid (50%). Elemental
analysis: found: C, 56.9; H, 5.9; N, 8.2%. C33H42N4OPdCl2
requires C, 57.5; H, 6.2; N, 8.1%. nmax(KBr)/cmꢀ1: 1612 n(C]C +
C]N), 790 g(CH)py. dH (300 MHz, CDCl3, Me4Si)/ppm: 0.87 (t, 3J
6.0, 3H, CH3), 1.27 (m, 22H, CH2), 1.73 (m, 2H, CH2), 3.89 (t, 3J
6.0, 2H, OCH2), 6.79 (d, 3J 9.0, 2H, Hm), 6.93 (s, 1H, H4), 7.12 (d,
3J 9.0, 2H, Ho), 7.31 (d, 3J 9.0, 1H, H300), 7.43 (m, 1H, H50), 7.44
(m, 1H, H500), 7.74 (ddd, 3J ¼ 3J ¼ 7.8, 4J 1.5, 1H, H40), 7.85 (d, 3J
9.0, 1H, H30), 8.06 (dd, 3J 7.5, 3J 7.2, 1H, H400), 8.62 (dd, 3J 4.5, 4J
3
3
4
3J ¼ 7.6, J ¼ 5.3, 1H, H500), 7.68 (ddd, J ¼ 3J¼ 8.0, J 1.7, 1H,
H40), 7.99 (d, 3J 9.0, 1H, H300), 8.04 (ddd, 3J ¼ 3J ¼ 7.7, 4J 1.3, 1H,
3
3
H400), 8.78 (d, J 4.6, 1H, H60), 8.87 (d, J 5.0, 1H, H600).
Complexes [PdCl2(pypzR(n)py)]; R(n) ¼ (C6H4OCnH2n+1
n ¼ 1,12–18) (11–15)
,
To a solution of the corresponding pypzR(n)py in 20 mL of dicloro-
methane was added PdCl2(C7H5N)2 in a 1 : 1 molar ratio, under
nitrogen atmosphere (Scheme 1). The mixture was stirred for 24 h
at room temperature. The nal mixture was vacuum concentrated
yielding to the precipitation of a solid, which was ltered off,
washed with n-hexane (10 mL) and dried in vacuo (0.05 hPa).
[PdCl2(pypzR(1)py)] (11). Yellow solid (54%). Elemental
analysis: found: C, 47.0; H, 3.2; N, 11.0%. C20H16N4OPdCl2
requires C, 47.5; H, 3.2; N, 11.1%. nmax(KBr)/cmꢀ1: 1609 n(C]C
+ C]N), 786 g(CH)py. dH (see Results and discussion section).
[PdCl2(pypzR(12)py)] (12). Yellow solid (30%). Elemental
analysis: found: C, 55.9; H, 5.4; N, 8.1%. C31H38N4OPdCl2
requires C, 56.4; H, 5.8; N, 8.5%. nmax(KBr)/cmꢀ1: 1612 n(C]C +
C]N), 789 g(CH)py. dH (300 MHz, CDCl3, Me4Si)/ppm: 0.87 (t,
3
1.5, 1H, H600), 9.30 (d, J 6.0, 1H, H60).
[PdCl2(pypzR(16)py)] (14). Light yellow solid (98%). Elemental
analysis: found: C, 58.3; H, 6.1; N, 8.0%. C35H46N4OPdCl2
requires C, 58.7; H, 6.5; N, 7.8%. nmax(KBr)/cmꢀ1: 1609 n(C]C +
C]N), 779 g(CH)py. dH (300 MHz, CDCl3, Me4Si)/ppm: 0.87 (t, 3J
6.0, 3H, CH3), 1.26 (m, 26H, CH2), 1.75 (m, 2H, CH2), 3.90 (t, 3J
6.0, 2H, OCH2), 6.78 (d, 3J 9.0, 2H, Hm), 6.94 (s, 1H, H4), 7.12 (d,
3J 9.0, 2H, Ho), 7.32 (d, 3J 9.0, 1H, H300), 7.44 (m, 1H, H50), 7.46
(m, 1H, H500), 7.75 (ddd, 3J ¼ 3J ¼ 7.8, 4J 1.5, 1H, H40), 7.86 (d, 3J
9.0, 1H, H30), 8.05 (dd, 3J ¼ 3J ¼ 7.5, 1H, H400), 8.61 (dd, 3J 3.9, 4J
3
0.9, 1H, H600), 9.28 (d, J 5.7, 1H, H60).
[PdCl2(pypzR(18)py)] (15). Light yellow solid (49%). Elemental
analysis: found: C, 59.8; H, 6.5; N, 7.1%. C37H50N4OPdCl2
Table 1 Crystal and refinement data for 1$H2O, 6 and 11$CH2Cl2
1$H2O
6
11$CH2Cl2
Empirical formula
Formula weight
Crystal system
Space group
[C20H18N4O2]
346.38
Monoclinic
P21/n
6.0659(7)
15.261(2)
[C20H16Cl2N4OZn]
464.64
Monoclinic
P21/c
13.105(3)
21.483(5)
8.078(2)
90
[C21H16Cl4N4OPd]
588.58
Monoclinic
C2/c
11.693(2)
13.833(2)
28.947(3)
90
˚
a/A
˚
b/A
˚
c/A
19.086(2)
a/ꢃ
b/ꢃ
g/ꢃ
90ꢃ
98.971(2)ꢃ
103.413(4)
90
2212.1(9)
96.969(3)
90
4647.6(7)
90ꢃ
3
˚
V/A
1745.2(4)
Z
4
4
8
T/K
293(2)
296(2)
296(2)
F(000)
728
1.318
0.088
944
1.395
1.368
2336
1.682
1.280
rc/g cmꢀ3
m/mmꢀ1
Scan technique
Data collected
q range/ꢃ
u and 4
u and 4
u and 4
(ꢀ7, ꢀ18, ꢀ21) to (6, 18, 21)
(ꢀ15, ꢀ24, ꢀ9) to (15, 25, 9)
(ꢀ14, ꢀ17, ꢀ33) to (12, 17, 36)
1.72 to 25.00
13202
1.60 to 25.00
16529
1.42 to 27.00
20530
Reections collected
Independent reections
Completeness to maximum q/%
Data/restraints/parameters
Observed reections [I > 2s(I)]
Ra
3033 (Rint ¼ 0.1215)
3876 (Rint ¼ 0.1271)
5082 (Rint ¼ 0.0741)
98.9
99.4
100.0
3033/0/236
1116
0.0674
3876/0/253
1322
0.0822
5082/3/269
2766
0.0513
b
RwF
0.1876
0.2039
0.1487
S[|Fo| ꢀ |Fc|]/S|Fo|. b {S[w(Fo ꢀ Fc2)2]/S[w(Fo2)2]}1/2
.
a
2
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requires C, 59.7; H, 6.8; N, 7.5%. nmax(KBr)/cmꢀ1: 1609 n(C]C +
C]N), 781 g(CH)py. dH (300 MHz, CDCl3, Me4Si)/ppm: 0.86 (t, 3J
6.0, 3H, CH3), 1.25 (m, 30H, CH2), 1.74 (m, 2H, CH2), 3.90 (t, 3J
6.0, 2H, OCH2), 6.79 (d, 3J 9.0, 2H, Hm), 6.91 (s, 1H, H4), 7.14 (d,
3J 9.0, 2H, Ho), 7.32 (d, 3J 9.0, 1H, H300), 7.44 (m, 1H, H50), 7.46
(m, 1H, H500), 7.76 (ddd, 3J ¼ 3J ¼ 7.5, 4J ¼ 1.8, 1H, H40), 7.82 (d,
3J 9.0, 1H, H30), 8.04 (ddd, 3J ¼ 3J ¼ 7.8, 4J ¼ 1.5, 1H, H400), 8.62
Table 2 Formulation and numbering of the compounds
Compounda
pypzR(n)py
n
Number
1
1
2
3
4
5
6
7
8
12
14
16
18
1
12
14
16
18
1
3
3
4
(dd, J 4.8, 4J 0.9, 1H, H600), 9.30 (dd, J 5.7, J 0.6, 1H, H60).
The new compounds were stable solids soluble in common
organic solvents such as CHCl3, CH2Cl2 or acetone, between
others.
[ZnCl2(pypzR(n)py)]
[PdCl2(pypzR(n)py)]
9
10
11
12
13
14
15
X-Ray data collection and structure renement
12
14
16
18
Data collection for all compounds was carried out at room
temperature on a Bruker Smart CCD diffractometer using
graphite-monochromated Mo-Ka radiation (l ¼ 0.71073 A)
˚
a
R(n) ¼ OC6H4CnH2n+1
.
operating at 50 kV and 35 mA. In all cases, data were collected
over a hemisphere of the reciprocal space by combination of
three exposure sets. Each exposure was of 10 s for (1) and (6) and
20 s for (11) covered 0.3ꢃ in u. The cell parameters were deter-
mined and rened by a least-squares t of all reections. The
rst 100 frames were recollected at the end of the data collection
to monitor crystal decay, and no appreciable decay was
observed. A summary of the fundamental crystal and rene-
ment data is given in Table 1.
The complexes [MCl2(pypzR(n)py)] (M ¼ Zn, Pd; R(n) ¼
C6H4OCnH2n+1, n ¼ 1, 12–18) (1–15) were obtained by reaction of
the corresponding ligands with ZnCl2 or PdCl2(C7H5N)2 as
described in Scheme 1. The elemental analysis of the
compounds agrees with the proposed molecular formula
[MCl2(pypzR(n)py)].
Details for the synthesis of all ligands and complexes are
given in the Experimental section. The molecular representa-
tions of Scheme 1 are made on the basis of the crystalline
structures of pypzR(1)py$H2O (1$H2O), [ZnCl2(pypzR(1)py)] (6) and
[PdCl2(pypzR(1)py)]$CH2Cl2 (11$CH2Cl2) (see Crystal structures
section and ESI‡).
The structures were solved by direct methods and rened by
full-matrix least-square procedures on F2 (SHELXL-97).16 All
non-hydrogen atoms were rened anisotropically.
All hydrogen atoms were included in their calculated posi-
tions and rened riding on the respective carbon atoms, except
for compound (1) where the hydrogen atoms of the water
molecule were located in a Fourier synthesis and xed.
For compound (6), aer rening, the presence of solvent
residual electron density was detected as disordered atomic
groups located in the void regions, and centered in sites among
the molecule. The solvent molecule could not be modeled
properly in none of the crystals, due to the poor spectra quality.
The program SQUEEZE, a part of the PLATON17 package of
crystallographic soware, was used to calculate the solvent
disordered area and remove its contribution to the overall
intensity data. An improvement was observed in all renement
parameters and residuals when this procedure was applied.
Spectroscopic studies
All the ligands and complexes were characterized by spectro-
scopic techniques (IR, and 1H-, 13C- and 15N-NMR in solution as
well as in the solid state), and in all cases the results agree with
the proposed molecular formulations (see Experimental
section).
IR spectra
The IR spectra in the 4000–400 cmꢀ1 region in the solid state of
the ligands and complexes show the characteristic bands of
pyridine and pyrazole rings. In the complexes, those are scarcely
modied with respect to the free ligands.
Results and discussion
Synthetic procedures
1H- and 13C-NMR spectra
All the new compounds (1–5, 6–10, 11–15) described in this
work are schematically presented in Table 2 including the The H-NMR and 13C-NMR spectra of [MCl2(pypzR(n)py)] (M ¼
1
numbering used for their identication.
Zn, Pd; R(n) ¼ C6H4OCnH2n+1; n ¼ 1) were recorded in solutions
The new dipyridylpyrazole ligands pypzR(n)py (R(n)
¼
of CDCl3 and DMSO-d6 (HMQC and HMBC) and in the solid
C6H4OCnH2n+1, n ¼ 1, 12–18) (1–5) were prepared by condensa- state (CPMAS) (Tables 3 and 4).
tion of the corresponding 1-(4-n-alkyloxyphenyl)3-pyridyl)
The main feature from the 1H-NMR spectra is related to the
propane-1,3-diones with 2-hydrazinopyridine. b-pyridinediketone chemical shi values of the H6 protons from the two pyridine
precursors were generated through a two-step process involving groups (H60 and H600) which allow to indicate the presence
alkylation of 4-hydroxyacetophenone followed by a Claisen of both N-coordinated and N-uncoordinated pyridine
condensation with ethyl picolinate (Scheme 1).
substituent.
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Paper
Table 3 1H-NMR chemical shifts (in ppm) and some coupling constants (in Hz) in solution for 1, 6 and 11a
L
L
PdCl2L
ZnCl2L
ZnCl2L
PdCl2L
DMSO-d6 7.3 ꢁ 10ꢀ3
M
DMSO-d6
CDCl3
CDCl3
Nuclei
8.8 10ꢀ2
M
CDCl3
(49%)
(8%)
2.0 ꢁ 10ꢀ2
M
8.8 ꢁ 10ꢀ2
M
DMSO-d6
H-4
7.14 (s)
8.05 (d)
7.15 (s)
8.16 (d)
3J ¼ 9.0
7.76 (m)
7.52 (s)
8.30
7.70 (s)
8.03
6.91 (s)
6.96 (s)
7.14 (s)
H-30
7.81 (d)
3J ¼ 8.7
7.76 (ddd)
6.97 (d)
3J ¼ 8.5
7.67 (ddd)
8.05 (d)
3J ¼ 7.5
7.89 (ddd)
3J ¼ 3J ¼ 7.5
4J ¼ 1.7
7.38 (ddd)
3J ¼ 7.5
3J ¼ 4.5
4J ¼ 1.1
8.65 (d)
3J ¼ 8.0
H-40
7.92
7.69
8.07
7.75
7.89 (ddd)
3J ¼ 3J ¼ 7.7
4J ¼ 1.7
3J ¼ 3J ¼ 7.8
3J ¼ 3J ¼ 7.8
4J ¼ 1.8
4J ¼ 1.6
H-50
7.26 (m)
7.44* (m)
7.37 (m)
7.38 (ddd)
3J ¼ 6.6
3J ¼ 3J ¼ 6.3
4J ¼ 2.2
3J ¼ 4.8
H-60
8.67 (d)
3J ¼ 6.0
7.50 (d)
3J ¼ 9.0
9.00
8.95
9.32 (d)
3J ¼ 5.7
7.32 (d)
3J ¼ 7.8
8.74 (d)
3J ¼ 4.2
7.81 (d)
3J ¼ 7.8
8.65
3J ¼ 4.5
7.73 (dd)
3J ¼ 7.7
3J ¼ 8.0
8.04 (m)
3J ¼ 5.1
7.24
3J ¼ 5.6
7.71
3J ¼ 4.3
7.73 (d)
3J ¼ 8.0
H-300
H-400
H-500
7.76 (m)
8.30
7.55
8.23
7.70
8.04 (ddd)
3J ¼ 3J ¼ 7.8
4J ¼ 1.5
7.97 (ddd)
3J ¼ 3J ¼ 7.5
4J ¼ 1.2
8.04
3J ¼ 3J ¼ 7.7
4J ¼ 1.8
7.46 (ddd)
3J ¼ 6.7
3J ¼ 5.0
7.46 (ddd)
3J ¼ 7.2
3J ¼ 4.9
4J ¼ 0.8
8.39 (dd)
3J ¼ 4.9
4J ¼ 1.1
7.22 (d)
3J ¼ 8.8
6.91 (d)
3J ¼ 8.8
3.77 (s)
7.26 (m)
7.47* (m)
7.54 (ddd)
3J ¼ 3J ¼ 6.3
4J ¼ 1.6
H-600
8.46 (d)
8.51
8.87
8.62 (dd)
3J ¼ 5.1
4J ¼ 1.0
7.16 (d)
3J ¼ 9.0
6.81 (d)
3J ¼ 9.0
3.79 (s)
8.82 (d)
8.39 (dd)
3J ¼ 4.8
4J ¼ 1.1
7.22 (d)
3J ¼ 8.8
6.91 (d)
3J ¼ 8.8
3.77 (s)
3J ¼ 6.0
3J ¼ 3.7
3J ¼ 5.9
3J ¼ 4.8
H-ortho
H-meta
7.25 (d)
3J ¼ 9.0
6.85 (d)
3J ¼ 9.0
3.82 (s)
7.19
7.10
7.40 (d)
3J ¼ 8.7
7.04 (d)
3J ¼ 8.7
3.91 (s)
3J ¼ 8.6
6.90
3J ¼ 8.8
6.86
3J ¼ 8.6
3.73 (s)
3J ¼ 8.6
3.84
OCH3
a
* These signals may be reverse.
As the ligands exhibit three potential coordinating positions, solution nding out that only the signals corresponding to the
we have determined the manner in which the different posi- free N,N,N-ligands (n ¼ 1, 12–18) (1–5) were observed, indicating
tions are involved towards each metal fragment.
that the solvent originates decomposition. However the 1H-NMR
The 1H-NMR spectra in CDCl3 solution of Zn derivatives (6– and 13C-NMR spectra of [PdCl2(pypzR(1)py)] exhibited duplicity of
10) exhibited a similar pattern which can be related to a type of all signals in agreement with the presence of the two proposed
complexes with a molecular structure analogous to that of linkage isomers A and B (Fig. 2) which were found in a 49–8%
[ZnCl2(pypzR(1)py)] (6) complex, whose crystalline structure has relationship respectively. In addition, new signals from the free
been solved by us and described in the present paper (Fig. 8). In ligand (found in a 43% relationship) were also present, indicating
these cases H600 are the most shied ones with respect to those again certain dissociation from the starting complexes (Table 5).
of the free ligand. Similarly, all Pd complexes (11–15) in CDCl3
Inuence of variables like chain length, time and tempera-
solution exhibit a similar pattern, involving the protons of the ture on the isomeric mixture of Pd complexes was followed by
coordinated pyridine group. However, in Pd complexes the H60 1H-NMR experiments. So it was observed that the A/B isomers
and H600 chemical shi coordination effects are reversed when ratio increased with the chain length, being in all cases the
comparing to those found in Zn complexes, so suggesting a highest concentration for A (Table 5).
different coordinating mode. The crystalline structure of (11),
On the other hand, by comparison of 1H-NMR results of
which is also solved in this work (Fig. 9), indicated a bidentate freshly prepared samples with those obtained seven days later,
coordination around the Pd centre. Therefore, on the basis of a an increase of the free ligand concentration and therefore a
bidentate coordination of the ligand around the metal frag- decrease of both linkage isomers was observed (Table 5). This
ment, two isomers N2,N10-(isomer A) (Fig. 2(a)) or N2,N100- result can be explained by considering the existence of an initial
(isomer B) (Fig. 2(b)) can be proposed.
equilibrium between both A and B isomers and the free ligand
To shed some light to this proposal we recorded the 1H-NMR (Scheme 2) which evolves over time to the decomposition of the
spectra of [ZnCl2(pypzR(n)py)] (6–10) complexes in DMSO-d6 less stable isomer B, releasing free ligand.
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Table 4 13C-NMR chemical shifts (in ppm) and some coupling constants (in Hz) in solution and solid state for 1, 6 and 11
L
L
PdCl2L
ZnCl2L
ZnCl2L
CPMAS
PdCl2L
DMSO-d6
(49%)
Nuclei
DMSO-d6
CPMAS
(8%)
CPMAS
CDCl3
C-3
C-4
151.4
152.1
106.1
149.6
106.2
152.1
104.9
150.0
100.2 (weak)
103.1
147.8
153.4
147.3
146.4
107.8
105.7
107.6
1J ¼ 178.7
1J ¼ 181.5
C-5
144.2
145.0
150.4
146.0
149.8
146.0
151.0
147.3
144.7
144.7
C-20
150.6
147.3
3J ¼ 9.0
113.6
C-30
C-40
C-50
119.3 (br)
120.2
136.7
124.4
122.5
140.7
125.1
119.0
141.9
124.8
124.3
139.2
124.3
113.6
140.1
124.3
1J ¼ 169.7
3J ¼ 7.2
139.7
136.4
1J ¼ 166.3
1J ¼ 165.6
3J ¼ 6.4
124.0
126.4
1J ¼ 159.7
2J ¼ 7.3
148.9
1J ¼ 167.9
2J ¼ 2J ¼ 6.8
149.4
C-60
149.5
153.1
120.2
149.1
149.6
120.2
152.2
150.4
118.9
141.3
150.0
124.3
148.3
143.1
123.6
1J ¼ 175.8
151.7
C-200
C-300
145.1
3J ¼ 8.4
121.0
119.1
1J ¼ 165.9
3J ¼ 6.6
138.6
1J ¼ 166.3
3J ¼ 7.2
139.4
C-400
C-500
139.8
123.9
138.2
125.5
140.1
124.4
137.8 (Weak)
136.9 (Weak)
138.2
127.8
1J ¼ 165.5
3J ¼ 6.5
123.0
1J ¼ 166.4
3J ¼ 6.0
126.1
124.3
1J ¼ 166.3
2J ¼ 2J ¼ 7.4
147.7
1J ¼ 167.5
2J ¼ 2J ¼ 6.8
149.8
C-600
148.8
121.6
128.0
148.1
119.7
152.1
123.0
129.8
141.3
118.9
151.9
118.8
1J ¼ 179.7
122.0
C-ipso
C-ortho
120.0
3J ¼ 3J ¼ 6.8
129.2
3J ¼ 3J ¼ 8.0
130.6
129.8
129.4
129.6
127.1 (Weak)
132.5
129.1
1J ¼ 159.8
3J ¼ 7.3
113.2
1J ¼ 161.0
3J ¼ 7.5
115.0
C-meta
109.4
113.6
113.5
113.9
113.3
114.8
116.1
111.7
1J ¼ 160.8
3J ¼ 4.6
158.7
1J ¼ 161.5
3J ¼ 4.5
161.6
C-para
OCH3
159.8
55.6
159.6
54.7
159.6
54.7
160.7
54.9
56.6
162.6
57.4
54.6
55.5
1J ¼ 144.6
1J ¼ 144.4
Finally the variable temperature spectra of [PdCl2(pypzR(1)py)](11)
registered between 25 and 95 ꢃC (Fig. 3) allow to establish at
65 ꢃC the coalescence of the signals of both isomers, this
result being clearly observed in the H6 and aromatic protons
signals.
On the other hand in solid state, the 13C-NMR data of 11
(Table 4) suggest the presence of two types of compounds on the
basis of the duplicity of several of their C signals. This result was
surprising, specially if we consider that the crystalline structure
of the mentioned metal derivative shows the presence of a sole
compound which exhibit a dimeric structure through a Pd–Pd
interaction, in which each metal centre has the ligand N2,N100-
coordinated in a square-planar environment. The aliphatic
chains of each moiety are trans- oriented so giving rise to a
Fig. 2 Possible linkage isomers for [MCl2(pypzR(1)py)] (M ¼ Zn, Pd).
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Table
Evolution of the isomers ratio of [PdCl2(pypzR(n)py)]
Paper
5
complexes by increasing the chain length and time
Samples instantaneously registered in DMSO-d6
n
[ ]/M
% Isomer A
% Isomer B
% Ligand
1
7.3 ꢁ 10ꢀ3
1.5 ꢁ 10ꢀ2
1.6 ꢁ 10ꢀ2
1.6 ꢁ 10ꢀ2
49
55
63
68
8
13
11
11
43
32
25
21
12
14
16
Fig.
4
“Z”
–
(a) and “U”
–
(b) shaped binuclear isomers of
[PdCl2(pypzR(1)py)].
Samples registered aer 7 days in DMSO-d6
1
7.3 ꢁ 10ꢀ3
1.5 ꢁ 10ꢀ2
1.6 ꢁ 10ꢀ2
1.6 ꢁ 10ꢀ2
41
46
51
57
3
6
7
9
56
48
42
34
12
14
16
isomer B (Fig. 2(b)), which evolves to the N2,N10-coordination
observed for isomer A (Fig. 2(a)). By contrast, coordinating
solvents like DMSO-d6 induce substantial changes of the elec-
tronic density of the metal centre, allowing the formation of two
different linkage isomers through a suggested ve-coordinated
intermediate [PdCl2(pypzR(1)py)(DMSO)].
15N-NMR spectra
In order to conrm the above proposal as well as to deduce the
coordinating form of the ligands in Zn and Pd complexes,
15N-NMR studies of pypzR(1)py (1), [ZnCl2(pypzR(1)py)] (6) and
[PdCl2(pypzR(1)py)] (11) as representative examples of each
family were registered in CDCl3, DMSO-d6 and in the solid state
(Table 6).
The Pd complex in DMSO-d6 exhibits two signal pairs at
ꢀ163.2 (N1) and ꢀ154.7 (N100) ppm, and at ꢀ170.9 (N1) and
ꢀ169.7 (N10) corresponding to the linkage isomer A and isomer
B respectively. The two N1 signals guarantee the presence of
both isomers. Signals from N2 were not detected.
Scheme 2 Proposed equilibrium between A and B linkage isomers
and the free ligand on DMSO-d6 solution.
In addition, for the Pd complex, it was remarkable that the
largest coordination chemical shis (Dd ¼ dcomplex ꢀ dligand) were
found for the pyridinic N100 or N10 nitrogens involved in the
coordination (DdN10 ¼ ꢀ93.5 for A and DdN100 ¼ ꢀ75.1 for B).
By contrast, the complex [ZnCl2(pypzR(1)py)] (which decom-
poses in DMSO-d6) exhibits in CDCl3 a single signal from N1 at
ꢀ171.3 ppm in agreement with the presence of a sole species.
The remaining d signals at ꢀ132.7, ꢀ105.8, and ꢀ106.3 ppm are
assigned to N2,N10 and N100 atoms respectively (Table 6). The
Fig. 3 Evolution of 1H-NMR proton signals of [PdCl2(pypzR(1)py)] by
increasing temperature.
Table 6 15N-NMR chemical shifts (in ppm) in solution and solid state
for 1, 6 and 11
L
L
PdCl2L ZnCl2L ZnCl2L
PdCl2L
head-to-tail or “Z”-shaped molecular conguration (Fig. 4(a)).
However, a related head-to-head (or “U”-shaped) structure
(Fig. 4(b)), probably less favourable to crystallize, should not be
avoided.18–21 On this consideration the presence of both
“U”-shaped and “Z”-shaped binuclear stereoisomers in the solid
state agree with 15N-NMR results, as it will be described later.
This proposal was also supported by 1H-NMR results
obtained in CDCl3 solution. So the metal–metal breaking, either
of “Z” or “U” dimers, by non coordinating solvents as CDCl3,
should yield to the same monomeric form N2,N100-coordinated
DMSO-d6
Nuclei DMSO-d6 CPMAS (49%) (8%)
CPMAS CDCl3 CPMAS
N-1
N-2
N-10
ꢀ162.4
ꢀ104.8
ꢀ76.2
ꢀ164.7 ꢀ170.9 ꢀ163.2 ꢀ162.7 ꢀ171.3 ꢀ172.0
a
a
a
ꢀ83.4
ꢀ159.7 ꢀ132.7 ꢀ132.0
ꢀ62.0 ꢀ105.8 ꢀ100.1
ꢀ65.0
ꢀ81.0 ꢀ169.7
a
N-100
ꢀ79.6
ꢀ67.8
ꢀ154.7 ꢀ159.7 ꢀ106.3 ꢀ107.8
a
Not detected values.
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coordination chemical shis of all N signals were almost pyridine groups are arranged at the 1-and 3-positions of the
equivalent of ca 28 ppm, this fact, suggesting a similar inter- pyrazole ring with their respective nitrogen atoms N10 and N100
action between the Zn centre and each of the three coordinating at trans-position respect to the N2 of the pyrazole ring in order
nitrogens of the N,N,N-ligand.
to minimize the interelectronic repulsions. The four rings are
In the solid state the Pd complex [PdCl2(pypzR(1)py)] exhibited twisted each other with dihedral angles between 15.7(2)y
two N10 signals at ꢀ62.0 and ꢀ65.0 ppm in agreement with the 57.9(2)ꢃ respectively (Table S2†).
presence of two “Z” and “U”-shaped binuclear stereoisomers
The water molecule is bonded to the pyrazole ring through
above mentioned. These d values were close to those of the free hydrogen bonds involving the N2 atom of the pyrazolic group
ꢃ
ligand so suggesting that the N10 was not involved in the coor- (d(N2/O2)) ¼ 3.038 (5) A, p(O2–H2A/N2) ¼ 159.8 .
˚
dination to the metal centre.
Each asymmetric unit is linked to the neighbouring one
However, the d values of N2 and N100 are ꢀ76.3 and through coulombic interactions between the O atom of one water
ꢀ91.9 ppm shied respect to the free ligand, supporting their molecule and the N10 of the pyridine at the 1-position (d ¼ (O2/
0
˚
participation in the coordination. The X-ray structure of N1 ) ¼ 2.991(5) A) (symmetry code: 1 + x, y, z), giving rise to chains
[PdCl2(pypzR(1)py)] (11) conrms the foregoing features.
along the a axis (Fig. 6(a)). Furthermore, the adjacent chains are
Similar deductions can be reached for [ZnCl2(pypzR(1)py)] (6) bonded through weak C–H/O interactions (d(O1–C15) ¼ 3.39(1)
ꢃ
˚
derivative.
A) with an angle (C15–H15/O1) ¼ 152.9 (symmetry code:ꢀx ꢀ
In summary the 15N-NMR studies allow to conrm that the 1, ꢀy + 1/2, z + 1/2) generating a double chain (Fig. 6(b)).
Pd derivative [PdCl2(pypzR(1)py)] (11) presents two binuclear
Additionally, p/p lateral interactions and C–H/N hydrogen
stereoisomers in the solid state in which the ligand was N2,N100- bonds give rise to the formation of a 3D framework (Fig. 7).
coordinated. In DMSO-d6 solution, duplicity of signals for N1
and single signals for N10 and N100 agree with the presence of
Crystal structures of [ZnCl2(pypzR(1)py)] (6) and [PdCl2-
two linkage isomers.
(pypzR (1)py)]$CH2Cl2 (11$CH2Cl2)
By contrast, only one species was found for [ZnCl2(pypzR(1)py)]
Suitable crystals of compounds 6 and 11 were obtained by
diffusion of hexane into a dichloromethane solution. Fig. 8 and
9 illustrate the perspective view of both compounds and Tables
7 and 8 list selected bond distances and angles for them. Both
complexes (6 and 11) crystallise in the monoclinic system, space
(6) both in the solid state and in solution. In the rst case a
bidentate N2,N100-coordination of the ligand was produced while,
in the later, the three N atoms are interacting with the metal centre.
Crystal structures
Crystal structure of [pypzR(1)py]. H2O (1$H2O). Crystals of
enough quality to be analyzed by X-ray diffraction analysis were
grown for the ligand pypzR(n)py with n ¼ 1. For long chained
ligands all attempts of crystallization were proved to be
unsuccessful.
A single crystal of the pyrazole [(pypzR(1)py)]$H2O (1$H2O),
was obtained by slow evaporation from a dichloromethane
solution at room temperature. The compound crystallizes in
monoclinic system, space group P21/n, with one molecule per
asymmetric unit along with one water molecule (Table 1).
Table S1‡ lists the typical selected bond lengths and angles
and the molecular structure is illustrated in Fig. 5.
The bond distances in the pyrazole, pyridine and benzene
rings evidence a delocalized p system having this fact already
been observed in related pyridine pyrazole ligands.7,22 The two
Fig. 6 Molecular chain (a) and double chain (b) along the a axis.
Fig. 5 ORTEP plot of [(pypzR(1)py)]$H2O (1$H2O) with 20% probability. Fig. 7 3D framework through the a axis.
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dihedral angles between the ZnN2C5C6N100 (6) and
PdN2C3C6N100 (11) metallocycles and the pyrazole and pyridine
planes (value 1–3ꢃ). By contrast, the dihedral angles between the
phenyl and the pyridine (at the 1-position of the pyrazole ring)
of 46.3(1)ꢃ for (6) and 70.1(1)ꢃ for (11) avoid the overall planarity
of the molecule (Fig. 10(a) and (b)).
The Zn(II) center is ve-coordinated by three N atoms from
the two pyridine rings, the pyrazole ring and two chlorine
˚
atoms, with Zn–Cl1 and Zn–Cl2 distances of 2.205(3) A and
˚
2.209(3) A respectively, and the Zn–N distances in the range of
Fig. 8 ORTEP plot of [ZnCl2(pypzR(1)py)] (6) with 20% probability.
1.997(8)–2.601(8) A, being the Zn–N2 (1.997(8) A) the shortest
one. The geometry around the Zn(II) center could be considered
as distorted trigonal bipyramidal with the basal plane described
by the pyrazolic nitrogen and the 2 chlorine atoms while the
axial sites are occupied by the pyridinic nitrogens (p(Cl2–Zn–
Cl1) ¼ 118.4(1)ꢃ; p(N100–Zn–N10) ¼ 140.6 (3)ꢃ).
˚
˚
The palladium derivative (11) exhibits a square-planar
coordination produced by 2-cis located chlorine ligands and two
nitrogen atoms of the N,N,N-ligand giving rise to two short
distances Pd–N2 of 2.044(5) and Pd–N100 of 2.046(5) A and one
˚
0
˚
longer Pd–N1 of 4.057(5) A. Additionally, a Pd–Pd interaction of
˚
3.55(1) A between metallic centers of neighbouring molecules
give rise to the formation of dimers. The molecular dimer
adopts a “Z”-shaped conformation in which the pirazolic
substituents of each monomer are trans-oriented. The uncoor-
dinated pyridine and phenyl ring planes of each monomer are
twisted with an angle of 70.1(1)ꢃ (Fig. 11).
Fig. 9 ORTEP plot of [PdCl2(pypzR(1)py)]$CH2Cl2 (11$CH2Cl2) with 20%
probability. The dichloromethane molecule have been omitted for
clarity.
The methoxy groups are almost perpendicular to their
respective phenyl plane with their two arms pointing in oppo-
site directions.
The molecular geometry of this compound can be consid-
ered similar to that reported by us for the dimer complex
[Ag(HpzR(14)py)2]2[NO3]2.7
Table 7 Selected bond distances (A˚) and angles (ꢃ) for (6)
Zn – N2
Zn–N100
Zn–Cl1
Zn–Cl2
Zn/N10
1.997(8)
2.263(9)
2.205(3)
2.209(3)
2.62(2)
N2–Zn–N100
N2–Zn–Cl1
N2–Zn–Cl2
N20–0Zn–N10
N1 – Zn–Cl1
N100–Zn–Cl2
N100–Zn–N10
N10–Zn–Cl1
N10–Zn–Cl2
Cl2–Zn–Cl1
74.0(3)
117.7(2)
122.7(2)
67.3(3)
106.8(2)
100.2(2)
140.6(3)
97.5(2)
94.7(2)
118.4(1)
Table 8 Selected bond distances (A˚) and angles (ꢃ) for 11$CH2Cl2
Pd–N2
2.044(5)
2.046(5)
2.282(2)
2.285(2)
4.057(2)
N2–Pd–N100
N2–Pd–Cl2
N100–Pd–Cl2
N2–Pd–Cl1
Cl2–Pd–Cl1
79.4(2)
98.4(1)
177.3(1)
172.6(1)
88.76(6)
Pd–N100
Pd–Cl2
Pd–Cl1
Pd/N10
Fig. 10 View of the complexes (a) [ZnCl2(pypzR(1)py)] (6) and (b)
[PdCl2(pypzR(1)py)] (11) showing the lack of planarity.
group P21/c and C2/c respectively, the second one as dichloro-
methane solvate (Table 1). Both of them present one molecule
in the asymmetric unit.
In both structures (6) and (11) the pypzR(1)py ligand presents
the pyridine rings at the 1- and 3-positions of the pyrazole core.
The planes between the pyrazole ring and the coordinated
pyridyl group at the 3-position are twisted at 6.4 (1) and 2.2 (1)ꢃ
for compound (6) and (11) respectively giving rise to an almost
Fig. 11 Dimers of [PdCl2(pypzR(1)py)] (11) defined by Pd–Pd
planar molecular fragment. This fact is conrmed by the interactions.
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Although several crystalline structures of Pd-complexes
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Table 9 Melting points of the compounds
with a cis-PdCl2(L2) core (L2 ¼ pyridylpyrazole type ligands)
have been described in the literature,23–27 from the best of
our knowledge this is the rst one of Pd–pyridyl-
pirazole complexes exhibiting metal–metal interactions in a
dimer.
Compounda
pypzR(n)py
n
Melting point (ꢃC)
12
14
16
18
12
14
16
18
12
14
16
18
70
77
78
90
On the other hand, in (6) the monomeric unities are
arranged generating 1D double chains through weak non
[ZnCl2(pypzR(n)py)]
[PdCl2(pypzR(n)py)]
184
161
156
155
198
199
182
196
˚
conventional hydrogen-bonding interactions C–H/O of ꢄ3.4 A
˚
and C–H/Cl of ꢄ3.5 A. These double chains are packed along
the (1 0 1) direction (Fig. 12(a) and 13(a)).
a
R(n) ¼ OC6H4CnH2n+1
.
˚
In the case of (11) weak C–H/Cl interactions of ꢄ3.6 A
between dimeric unities give rise to 1D chains which are crossed
in the (1 0 1) and (ꢀ1 1 0) (Figs. 12(b) and 13(b)). New interac-
tions between chains are not observed.
Thermal studies
The results obtained from POM observations and DSC studies
of compounds 1–15 indicate that neither the pypzR(n)py ligands
nor their Pd or Zn complexes are liquid crystalline compounds.
The melting temperatures increased with the chain length for
ligands and Pd derivatives, as expected, being the opposite
variation observed for the Zn derivatives (Table 9).
The structural features related with the remarkable distor-
tion of the planarity found in the compounds 1, 6 and 11 with n
¼ 1 determines a bulky whole molecular core which is also
present in the related compounds containing longer chains
substituents (2–5, 7–10, 12–15). Then we believe that this
molecular core involve an inadequate width-to-length molec-
ular ratio which appears to be responsible for the non
achievement of the supramolecular ordering of the mesophases
in agreement with the observed non mesomorphic behaviour of
all the investigated compounds.
Fig. 12 (a) 1D chains parallel to the (1 0 1) direction for [ZnCl2(pypzR(1)py)]
(6) and (b) crossed in the (1 0 1) and (ꢀ1 1 0) for [PdCl2(pypzR(1)py)] (11).
Conclusions
All ligands and complexes were not LC materials as deduced
from their thermal behaviour, this result being associated to
their inadequate molecular shape to reach the required
ordering at the LC state.
The Zn complexes [ZnCl2(pypzR(n)py)] are mononuclear
species according to the X-ray structure of [ZnCl2(pypzR(1)py)] (6).
The ligand is coordinated to the metal centre through N2 and
N100 atoms and interacts with the third one (N10) giving rise to a
distorted trigonal bipyramidal geometry.
However, in CDCl3 solution, the three N atoms of the
revealed species interact with the metal in a similar fashion.
The Pd derivatives [PdCl2(pypzR(n)py)] were found as two “Z”-
and “U”- shaped binuclear stereoisomers. In those, the biden-
Fig. 13 Packings of (a) [ZnCl2(pypzR(1)py)] (6) and (b) [PdCl2(pypzR(1)py)] (11). tate N2,N100-coordination with the third nitrogen (N10) pointing
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out, preserve the square planar environment at each Pd centre,
allowing a Pd–Pd interaction between neighboring molecules to
produce dimers. In the solid state the “Z”-shape was found in
the crystalline structure of [PdCl2(pypzR(1)py)]$CH2Cl2
(11$CH2Cl2) while 13C- and 15N-NMR data evidenced the pres-
ence of the two forms.
6 P. Ovejero, M. J. Mayoral, M. Cano, J. A. Campo, J. V. Heras,
´
´
P. Fernandez-Tobar, M. Valien, E. Pinilla and M. R. Torres,
Mol. Cryst. Liq. Cryst., 2008, 481, 34.
7 P. Ovejero, E. Asensio, J. A. Campo, J. V. Heras, M. Cano,
˜
´
M. R. Torres, C. Nunez and C. Lodeiro, Dalton Trans., 2013,
42, 2107.
´
In CDCl3 solution the metal–metal interaction is broken
yielding to a square planar molecular species which maintain
the bidentate N2,N10-coordination.
8 J. Casabo, J. Pons, K. S. Siddiqi, F. Teixidor, E. Molins and
C. Miravitlles, J. Chem. Soc., Dalton Trans., 1989, 1401.
9 J. Pons, X. Lopez, J. Casabo, F. Teixidor, A. Caubet, J. Rius
´
´
An equilibrium between N2,N100- and N2,N10-coordinated
and C. Miravitlles, Inorg. Chim. Acta, 1992, 195, 61.
species was proposed in DMSO-d6 solution, so indicating the 10 J. Pons Picart, F. J. Sanchez, J. Casabo, J. Rius, A. Alvarez-
´
´
´
inuence of the coordinating solvent to produce linkage isomers
(probably through ve-coordinated intermediate species).
Larena and J. Ros, Inorg. Chem. Commun., 2002, 5, 130.
´
´
´
11 J. Pons, F. J. Sanchez, J. Casabo, A. Alvarez-Larena,
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Acknowledgements
´
Thanks are given to Ministerio de Economıa y Competitividad
(MINECO) of Spain for nancial support (CTQ2010-16122 and
´
15 M. J. Mayoral, P. Cornago, R. M. Claramunt and M. Cano,
New J. Chem., 2011, 35, 1020.
16 G. M. Sheldrick, SHELX97, Program for Renement of Crystal
CTQ2011-25172). L. S. thanks the Ministerio de Educacion,
Cultura y Deporte (Spain) for the predoctoral scholarship from
the FPU program.
¨
¨
Structure, University of Gottingen, Gottingen, Germany,
1997.
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