Synthesis, spectral and structural characterization of three zinc(II) azide complexes with...
Transcript of Synthesis, spectral and structural characterization of three zinc(II) azide complexes with...
Synthesis, spectral and structural characterization of zinc(II) methacrylate
complexes with sparteine and a-isosparteine: The role of hydrogen bonds
and dipolar interactions in stabilizing the molecular structure
Beata Jasiewicz*, Władysław Boczon, Beata Warzajtis,
Urszula Rychlewska1**, Tomasz Rafałowicz
Faculty of Chemistry, A. Mickiewicz University, Grunwaldzka 6, 60-780 Poznan, Poland
Received 19 April 2005; accepted 19 May 2005
Available online 21 July 2005
Abstract
New complexes of zinc(II) methacrylate of the general formula [C15H26N2Zn(C4H5O2)2] where [C15H26N2] is a sparteine or
a-isosparteine have been obtained by direct synthesis using zinc salt and an appropriate alkaloid. The compounds have been characterized by
elemental analysis, mass spectrometry, IR and NMR spectroscopy as well as by X-ray methods.
q 2005 Elsevier B.V. All rights reserved.
Keywords: Sparteines; Zinc complexes; Crystal structure; IR and NMR spectroscopy
1. Introduction
(-)-Sparteine ((-)Sp) and its diastereoisomer
a-isosparteine (a-Sp) have been found extremely well-
suited as chiral bidentate ligands for many applications, e.g.
for metal complexation [1–9] and asymmetric synthesis
[10–15]. The stereochemical relationship of these two
sparteines is very simple: sparteine is the cis-trans isomer
(where cis and trans refer to the hydrogen atoms on C6 and
C11 with respect to the C7–C9 central methylene bridge),
a-isosparteine the trans–trans one (Fig. 1).
Ten years ago Haasnot claimed (on the grounds of
analysis in his TF Puckering Coordinates) that sparteine
adopts exclusively C-boat conformer a [16]. Theoretical
calculations have confirmed that the free base of sparteine
has one most favorable conformer with chair–chair trans-
quinolizidine A/B system and boat-chair trans quinolizidine
C/D system. DFT predicts a strong preference for this
conformation over the all-chair trans/cis conformation b
0022-2860/$ - see front matter q 2005 Elsevier B.V. All rights reserved.
doi:10.1016/j.molstruc.2005.05.046
* Corresponding authors. Tel.: C48 61 829 1310; fax: C48 61 865 8008.
**Tel.: C48 61 829 1268; fax: C48 61 865 8008.
E-mail addresses: [email protected] (B. Jasiewicz), urszular@
amu.edu.pl (U. Rychlewska1).
[17]. However, in the solid state, sparteine complexes
assume the conformation b [1–4]. Indeed, sparteine behaves
as an efficient chiral bidentate ligand, since flipping of
conformation a into b favors formation of two coordination
bonds in the metal complexes. The structure of
a-isosparteine diastereoisomer has been determined by the
X-ray diffraction data, proving that in the solid state
a-isosparteine monohydrate is built of four chair rings and
have both A/B and C/D ring junction trans [18]. The mono-
and di-perchlorate salts of a-isosparteine and its metal
complexes [5–8,19,20] have been shown to have the same
structure.
Cu(II) sparteine complexes have been used as model
compounds for the type I copper(II) site of blue copper
protein whereas zinc(II) complexes of sparteine are used as
diluting agents for measuring the hyperfine coupling by
EPR on powdered samples. Complexes of this kind have
been reported with a pseudo-tetrahedral metal ion
environment [21–24]. A number of organolithium com-
pounds have been found to be of remarkable value for the
enantioselective formation of carbon–carbon bonds under
the influence of (-)Sp [25]. In contrast, only a few
complexes have been obtained with a-isosparteine [8,26].
In this context, new zinc(II) complexes with a-isosparteine
and sparteine as a bidentate ligand have been synthesized.
Another aspect of our study was the examination of
Journal of Molecular Structure 753 (2005) 45–52
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Fig. 1. Conformation and atom numbering in sparteine and a-isosparteine.
B. Jasiewicz et al. / Journal of Molecular Structure 753 (2005) 45–5246
the role of steric effects imposed by a bulky sparteine and
a-isosparteine ligand and to determine the role of the
coordination of anionic ligands in the zinc complexes.
This paper reports the synthesis, IR, NMR and MS
characterization of a zinc(II) methacrylate complexes with
sparteine and a-isosparteine. Crystal structures of the
complexes have been determined by X-ray diffractometry.
2. Experimental
2.1. General techniques
The IR spectra were recorded by means of a FT-IR
Bruker 113v spectrometer (KBr pellets). The 13CNMR,1HNMR, 1H–1H COSY, 1H–13C COSY spectra were
measured on a Varian Gemini 300 spectrometer at
300 MHz and at ambient temperature, using w0.5 M
solutions in CDCl3, TMS as internal reference. ESI mass
spectra were obtained on a Waters/Micromass (Manchester,
UK) ZQ mass spectrometer. The sample solutions were
prepared in methanol.
Elemental analysis was carried out by means of a Perkin–
Elmer 2400 CHN automatic device.
Zinc methacrylate [Zn(CH2ZC(CH3)COO)2] were com-
mercial supplied by Aldrich. Sparteine was obtained from
commercial sparteine sulphate C15H26N2$H2SO4$5H2O
[27]. a-Isosparteine was obtained according to method
described previously [28].
2.2. Synthesis of complexes
The title complexes were prepared by the direct reaction
of zinc(II) methacrylate with a stoichiometric amount of a
proper alkaloid in a methanol solution. The resulting
colorless precipitate was filtered off and recrystallized
from methanol.
2.2.1. [Zn(C4H5O2)2(sparteine)] (1)
Colourless crystals. Yield: 74%. Mp 205–206 8C (with
decomposition). Anal. Calcd for C15H26N2Zn(C4H5O2)2: C,
58.79; H, 7.72; N, 5.96. Found: C, 58.65; H, 7.64; N, 6.04.
IR: gZ1644 cmK1 (CaO), 1602 cmK1 (CaC), 421 cmK1
(Zn–N). MS (ESI-mass spectra): m/z (%)Z383 (100), 385
(55), 491 (70), 495 (50).
2.2.2. [Zn(C4H5O2)2(a-isosparteine)] (2)
Colourless crystals. Yield: 74%. Mp O250 8C (with
decomposition). Anal. Calcd for C15H26N2Zn(C4H5O2)2: C,
58.79; H, 7.72; N, 5.96. Found: C, 58.81; H, 7.66; N, 5.96.
IR: gZ1644 cmK1 (CaO), 1597 cmK1 (CaC), 428 cmK1
B. Jasiewicz et al. / Journal of Molecular Structure 753 (2005) 45–52 47
(Zn–N). MS (ESI-mass spectra): m/z (%)Z383 (75), 385
(40), 465 (100), 469 (45).
2.3. Crystallographic data collection
and refinement of the structure
2.3.1. Crystal data: 1A colourless prismatic crystal having approximate
dimensions of 0.3!0.2!0.2 mm was used to measure the
intensity data with a KM4CCD kappa-geometry diffract-
ometer [29] equipped with graphite monochromated Mo Karadiation (lZ0.71073 A) at 295 K. The structure was solved
by direct methods using SHELXS86 [30] and refined by least-
squares techniques with SHELXL97 [31], to RZ0.0367 and
RwZ0.0394 for 4736 observed reflections (IO2s(I)) of 9532
independent reflections collected in the range
3.778!q!27.068 using the u scan method (index ranges:
hZK16/18, kZK14/14, lZK19/14). The intensity
data were corrected for Lp effects as well as absorption
(TminZ0.76189, TmaxZ0.84903) [32]. Anisotropic thermal
parameters were employed for non-hydrogen atoms. Methyl
hydrogens were treated as follows: one methyl hydrogen was
located from a difference Fourier map the positions of the
remaining two were calculated assuming sp3 hybridization
and standardized distances of 0.96 A. The positions of the
remaining hydrogen atoms were also calculated. All H-atoms
were refined using a riding model with isotropic temperature
factors 20% higher than the isotropic equivalent for the atom
to which the H-atom was bonded. In one of the four
methacrylate groups the distinction between methyl and
methylene substituents was not straightforward, as the two
OCaCH2 and RC–CH3 bonds were nearly equal in length.
We have therefore analyzed a distribution of valence angles
around the a carbon of the methacrylate moiety for the trans
and cis arrangement of OaC–CaC bonds using the
Cambridge Structural Data Base [33]. For the trans
conformation the mean (Oa)C–C–CH3, (Oa)C–CaCH2
and H2CaC–CH3 valence angles were, respectively,
115.7(3), 120.1(3) and 123.7(2)8. The corresponding set of
valence angles for the cis arrangement of OaC–CaC bonds
was the following: 119.1(2), 117.1(3) and 123.5(3)8. As it
follows from this comparison, the valence angle criterion
allows clear distinction between the two isomers. Therefore,
we have used this criterion to properly ascribe the methyl and
methylene functional groups within the methacrylate
moiety. It appeared that all four methacrylate groups adopted
the trans conformation. The absolute structure of the
crystals was assumed from the known absolute configuration
of (-)-sparteine and was further confirmed by the Flack
parameter which refined to a value of K0.013(6) [34].
Siemens computer graphics program [35] was used to
prepare drawings.
2.3.2. Crystal data: 2A colourless plate crystal having approximate
dimensions of 0.3!0.3!0.1 mm was used to measure
the intensity data with a KM4CCD kappa-geometry
diffractometer [29] equipped with graphite monochromated
Mo Ka radiation (lZ0.71073 A) at 295 K. The structure
was solved by direct methods using SHELXS86 [30] and
refined by least-squares techniques with SHELXL97 [31], to
RZ0.0340 and RwZ0.0469 for 1540 observed reflections
(IO2s(I)) of 2528 independent reflections collected in the
range 3.318!q! 27.068 using the u scan method (index
ranges: hZK14/14, kZK12/17, lZK19/19). The
intensity data were corrected for Lp effects as well as
absorption (TminZ0.93908, TmaxZ0.98779) [32]. Aniso-
tropic thermal parameters were employed for non-hydrogen
atoms. The positions of the hydrogen atoms were calculated
at standardized distances of 0.96 A and were refined using a
riding model with isotropic temperature factors 20%
higher than the isotropic equivalent for the atom to which
the H-atom was bonded. The absolute structure of the
crystals was assumed from the known absolute configur-
ation of (-)-a-isosparteine and was further confirmed by the
Flack parameter which refined to a value of K0.007(13)
[34]. Siemens computer graphics program [35] was used to
prepare drawings. The relevant crystal data collection and
refinement parameters are listed in Table 1. Atomic
coordinates, anisotropic displacement parameters and tables
of bond distances and angles have been deposited at the
Cambridge Crystallographic Data Centre (deposition
numbers CCDC 268904 and 268905, for sparteine and
a-isosparteine complexes, respectively).
3. Results and discussion
3.1. General aspects
The reactions of zinc(II) methacrylate with sparteine
and a-isosparteine in methanolic solution, give
complexes of the formulae LZn (C4H5O2)2 (where
LZligand). The isolated compounds are stable in air at
room temperature and exist in CDCl3 solution, as
revealed by NMR spectra.
3.2. Spectroscopic studies
The mass spectra of 1 and 2 show a signal assigned to
the protonated ions formed as a result of abstraction of a
single methacrylate group from the complex. The
complex of sparteine with zinc methacrylate (1) is less
stable than 2 under ESI conditions. The spectrum of 2
shows the molecular ion and the peak of ion
corresponding to [2–4H] of 100% intensities. These
signals are not noted in the MS spectrum of the sparteine
complex. For 1, the more abudant ion is that of
m/zZ383 formed of the molecular ion after the loss of
a single methacrylate group and one hydrogen atom. This
ion is also detected in the MS spectrum of the
a-isosparteine complex, although in less abundance.
Table 1
Selected crystal data, data collection and refinement parameters for zinc(II) methacrylate with sparteine (1) and a-isosparteine (2)
Compound (1) (2)
Chemical formula C15H26N2!Zn(C4H5O2)2 C15H26N2!Zn(C4H5O2)2
Chemical formula weight 469.91 469.91
Crystal size (mm) 0.30!0.20!0.20 0.30!0.30!0.10
Colour, habit Colourless, prismatic Colourless, plate
Crystal system Monoclinic Orthorhombic
Space group P21 C2221
a (A) 14.316(3) 11.3702(9)
b (A) 11.585(2) 13.4640(10)
c (A) 15.039(3) 15.1070(10)
b 112.88(3) 908
V (A3) 2298.0(8) 2312.7(3)
Z 4 4
Dx (Mg mK3) 1.358 1.350
No. of reflections for cell parameters 7488 2603
Absorption coefficient (mmK1) 1.099 1.092
Diffractometer Kuma KM-4CCD k-geometry Kuma KM-4CCD k-geometry
Monochromator Graphite Graphite
Data collection method u Scans u Scans
No. of measured reflections 20403 7160
No. of independent reflections 9532 2528
No. of observed reflections 4736 1540
Criterion for observed reflections IO2s(I) IO2s(I)
Rint 0.0493 0.0671
qmax (deg) 27.06 27.06
Range of h, k, l K16/h/18 K14/h/14
K14/k /14 K12/ k/17
K19 /l/14 K19/l/19
Absorption correction Empirical Empirical
Tmin, Tmax 0.76189, 0.84903 0.93908, 0.98779
Refinement on F2 F2
R[F2O2s(F2)] 0.0367 0.0340
wR(F2) 0.0467 0.0524
S 0.704 0.754
No. of reflections used in refinement 9532 2528
No. of parameters used 541 137
H-atom treatment Riding model Riding model
Weighting scheme wZ1/[s2(F2o )C(0.0031P)2] wZ1/[s2(F2
o )C(0.007P)2]
Where PZ ðF2o C2F2
c Þ=3 Where PZ ðF2o C2F2
c Þ=3
Flack parameter K0.013(6) K0.007(13)
Drmax (e AK3) 0.236 0.281
Drmin (e AK3) K0.314 K0.360
B. Jasiewicz et al. / Journal of Molecular Structure 753 (2005) 45–5248
The IR absorption in the spectra of quinolizidine and its
derivatives in the 2840–2600 cmK1 region (the so-colled
Bohlmann trans-band) is assigned to the stretching
vibrations of one or more axially oriented Ca–H bonds.
The intensity and shape of the band depend on the number
of the above bands and their steric environment in the
molecule. In the band complex covering the range
2840–2600 cmK1 in the spectrum of a-isosparteine there
are three peaks at 2793, 2758 and 2735 cmK1. The trans-
band of sparteine reveals two absorption maxima at about
2795 and 2760 cmK1 [36]. The attachment of a zinc atom to
N atoms results in the disappearance of the trans-band. The
absence of this band in the spectrum of the complexes
suggests that both of the nitrogen atoms are involved in
coordination. The spectra of 1 and 2 show a band at
approximately 440 cmK1 attributed to the metal-nitrogen
stretching frequencies. Both spectra exhibit the additionally
bands at 1644 cmK1 and near 1600 cmK1, respectively, as
expected for the g (CaO) and g (CaC).
The molecular structures of newly obtained complexes in
solution have been inferred from their 1H and 13C NMR
spectra (Table 2). For tetracyclic alkaloids, we can use quite
precise criteria of conformation being the 13C chemical
shifts of the atoms C12 and C14 (in ring D). These atoms are
exposed to the g-synclinal effects from the atoms C8 and
C17 in the chair conformers but not in the boat ones. The
less precise criterion is the 1H–1H coupling constant of the
bridgehead proton and the proton at the next carbon atom
(between the bridgehead C atom and the nitrogen atom)
from the b-side. In the alkaloids with the sparteine skeleton,
the coupling constant is denoted as J7–17b. If ring C is a
chair, J7–17b is small (less than 3 Hz in complexes), if it is
Table 2
NMR data of sparteine and a-isosparteine complexes with zinc(II)
methacrylate in CDCl3; d in ppm
Carbon
atom
Sparteine!Zn(C4H5O2)2 a-Isosparteine!Zn(C4H5O2)2
dC dH, multiplicity, J dC dH, multiplicity, J
2 59.2 1.92a 59.2 3.65; d; JZ1.12
1.92a 1.92
3 24.4 1.52a 24.0 1.60a
1.80a 1.40a
4 23.8 1.67a 24.3 1.20a
2.26a 1.70a
5 28.5 1.40 27.8 2.46a
2.18; dq; JZ12.6,
3.30, 2.70
1.42a
6 70.0 2.40 (ax) 70.0 2.42; bs (ax)
7 34.5b 1.79 34.8 1.78
8 28.3 1.50 36.8 1.88a
2.14 1.88a
9 34.8b 1.79 34.8 1.78
10 62.1 2.40; dd (ax) 57.3 2.36; m; ax
3.50 (eq) 3.75; d (eq)JZ2.66
11 59.9 3.64; bs (ax) 70.0 2.42; bs (ax)
12 24.0 1.26 27.8 2.46a
1.80 1.42a
13 23.6 1.42a 24.3 1.20a
1.85a 1.70a
14 17.8 1.35a 24.0 1.60a
1.60a 1.40a
15 52.9 3.49 59.2 3.65; d (ax)JZ1.12
3.49 1.92 (eq)
17 45.7 3.23; dd; (ax) 57.3 2.36; m (ax)
JZ12.64, 3.00 3.75; d (eq) JZ2.66
3.58; (eq) JZ2.98
–CH3 19.6 1.97; s 19.6 1.93; s
aCH2 121.7 6.00; d; JZ11.1 121.4 5.96; s
121.4 5.33; d; JZ10.2 5.30; s
C141.1 141.2
140.5
–CZO 174.3 172.4
172.8
a dH values extracted from the HET-COR spectrum.b Assignment uncertain, can be interchanged.
Table 3
Comparison of 13C effects of complexation in 1 and 2 (in relation to free
ligand) in CDCl3
Carbon atom Position (1) (2)
2 a to N1 3.2 2.0
3 b to N1 K1.2 K1.3
4 g to N1 K0.7 K0.6
5 b to N1 K0.6 K2.2
6 a to N1/g to
N16
3.7 3.7
7 b to N1 and
N16
1.8 K0.8
8 g to N1 and
N16
0.9 0.4
9 b to N1 and
N16
K1.1 K0.8
10 a to N1/g to
N16
0.3 1.5
11 a to N16/g to
N1
K4.3 3.7
12 b to N16 K10.5 K2.2
13 g to N16 K1.0 K0.6
14 b to N16 K8.0 K1.3
15 a to N16 K2.3 2.0
17 a to N16/g to
N1
K7.7 1.5
(C), upfield shift; (K), downfield shift. Complexation effects were
calculated by subtracting the chemical shifts of individual carbon atoms
of free bases from the values of the chemical shifts of the corresponding
carbon atoms in the corresponding complexes.
B. Jasiewicz et al. / Journal of Molecular Structure 753 (2005) 45–52 49
a boat, J7–17b takes a value from above 10 Hz (10.8 Hz in
sparteine [37]). The set of eight signals assigned to the
alkaloid in the 13C NMR spectrum of 2 is correctly
reproduced by the symmetric structure of a-isosparteine.
Additional signals assigned to methacrylate anion are
observed at: 19.6 ppm (–CH3), 121.4 ppm (aCH2),
141.2 ppm (quaternary carbon atom) and 172.4 ppm
(CaO).
The most distinct 13C NMR spectroscopic feature of
a-isosparteine and its complexes is the bridge carbon signal
C8, whose position is diagnostic of the conformation of the
two fused B/C rings in the a-isosparteine skeleton (chair–
chair: theor. 35.4 exp. 36.4 for free base and 36.8 for complex)
[17,38]. On the basis of a comparision of the NMR spectra of
the complex and the free base, it has been possible to calculate
the complexation effect. As expected, the 13C NMR spectrum
of 2 is similar to the spectra of a-isosparteine complexes with
zinc chloride, bromide and cyanide [26]. This fact suggests
that the nature of coordinating anions in a-isosparteine
zinc complexes does not influence the chemical shifts of the
carbon atoms. The complexation shifts of carbon atoms in
a-position to nitrogen atoms (C2, C6, C10, C11, C15 and C17)
have the positive sign and range from C1.5 to C3.7 ppm
(Table 3). The assignments of the 1H NMR signals to
particular protons has been made by two-dimensional
methods, mainly 1H–13C HETCOR and 1H–1H COSY. Only
four coupling constants were successfully determined directly
from the 1H NMR spectrum.
For sparteine, the coordinated metal rapidly shuttles
between the two nitrogen sites. We have observed large
upfield shifts of C12 (10.5 ppm), C14 (8.0 ppm) and C17
(7.7 ppm) on passing from the free base (boat ring C) to the
complex (chair ring C), as a consequence of the intervening
negative g-gauche effects in the cis-quinolizidine fragment
C/D. The others values of complexation effects range from
K4.3 to C3.7 ppm. In contrast to the a-isosparteine
complexation reaction, the complexation of sparteine does
not lead to a symmetric complex. The two chemically
inequivalent methacrylate groups give two different type
signals in the NMR. Due to severe signal overlapping,
the majority of the dH values had to be taken from
HETCOR spectra.
Fig. 2. The structure of two independent molecules of 1 and the atom numbering scheme; displacement ellipsoids are drawn at the 30% probability level and H
atoms are shown as spheres of arbitrary radii. Local CO/CH dipoles are marked with arrows.
B. Jasiewicz et al. / Journal of Molecular Structure 753 (2005) 45–5250
3.3. X-ray structural studies
The asymmetric unit of 1 contains two independent
molecules (Z0Z2), while 2 utilizes its C2 symmetry in
the crystal lattice, the Z0 value being 1⁄2. The molecules
are illustrated in Figs. 2 and 3, respectively. Selected
parameters describing geometry of the complex molecules
are listed in Table 4 and hydrogen bond parameters are given
in Table 5. Complex 1 consists of a zinc centre to which is
coordinated (-)Sp unit, while in complex 2 coordinated to the
zinc centre is a-Sp unit. Both sparteine ligands act in
Fig. 3. The molecular structure of 2 and the atom numbering scheme. The
symmetry independent part of the complex is marked by labeled atoms.
Displacement ellipsoids are drawn at 30% probability level and H atoms are
shown as spheres of arbitrary radii. Local CO/CH dipoles are marked with
arrows.
a bidentate mode, the tetrahedral arrangement of atoms
around Zn centers being supplemented by two methacrylate
groups, each acting in a monodentate fashion. In 1 the
sparteine ligand displays trans and cis configuration at the A/B
and C/D ring-junctions, respectively, and all four rings adopt
chair conformations, with the A-ring pointing towards the
metal center and the D-ring pointing away from the metal
center. In 2 the a-isosparteine skeleton displays trans/trans
configuration at the A/B and C/D ring-junctions and all four
rings adopt chair conformations with both terminal rings
(A and D) folding inwards towards the metal center. The two
independent molecules of complex 1 do not differ significantly
in geometry and conformation. However, in each molecule
there is a significant difference in the length of the two Zn–O
bonds (2.013(3) vs 1.938(3) A in the unprimed molecule, and
1.992(3) vs 1.911(3) A in the primed molecule). The two
bonds in complex 2 are symmetry related, hence no
differentiation in bond length is observed. The mean values
for the sets of longer and shorter bonds observed in 1
(2.002(15) and 1.924(19) A) can be compared with the mean
Table 4
Selected interatomic distances and valence angles for 1 and 2 complexes
(1) (1 0) (2)
Zn–N1 2.104(3) 2.095(3) Zn–N1 2.091(2)
Zn–N16 2.096(3) 2.103(3)
Zn–O1 2.013(3) 1.992(3) Zn–O1 1.920(2)
Zn–O3 1.938(3) 1.911(3)
N1/N16 2.912(4) 2.929(4) N1/N1a 2.903(4)
N1–Zn–N16 87.79(12) 88.48(12) N1–Zn–N1a 87.90(13)
O1–Zn–O3 108.88(12) 114.32(12) O1-Zn–O1a 122.82(12)
N1–Zn–O1 124.07(12) 118.25(12) N1–Zn–O1 106.72(9)
N1–Zn–O3 113.48(13) 113.99(12) N1–Zn–O1a 113.66(9)
N16–Zn–O1 94.35(12) 95.29(12)
N16–Zn–O3 127.38(12) 123.33(11)
a Atoms are generated by the two-fold symmetry axis.
Table 5
Geometry of the C–H/O intramolecular hydrogen bonds in 1 and 2
Com-
pound
D/A (A) H/A (A) D–H/A
(deg)
1 C11–H11/O1 3.213(5) 2.53 128
C15–H151/O1 3.190(5) 2.53 126
C2–H22/O2 3.141(6) 2.44 130
C3–H32/O3 3.287(6) 2.42 150
C15–H152/O4 3.196(5) 2.44 136
C25–H253/O4 2.770(6) 2.36 105
C110–H110/O1 0 3.178(5) 2.51 126
C200–H204/O1 0 2.759(5) 2.43 100
C2 0–H2 02/O20 2.138(6) 2.40 133
C3 0–H3 02/O30 3.326(5) 2.52 141
C240–H244/O3 0 2.750(5) 2.44 98
C150–H154/O4 0 3.206(5) 2.40 142
C250–H256/O4 0 2.743(5) 2.42 99
2 C5–H52/O1a 3.227(4) 2.38 148
C20–H202/O1 2.713(4) 2.37 100
C21–H213/O2 2.778(4) 2.38 104
a Atoms are generated by the two-fold symmetry axis.
B. Jasiewicz et al. / Journal of Molecular Structure 753 (2005) 45–52 51
Zn–O (carboxylate) bond length found in tetrahedral Zn
complexes [33] of 1.964(3) A. The value of 1.920(2) for the
Zn–O bond, observed in complex 2, falls into the range of
shorter bonds. Moreover, the Zn–O bond lengths in bis-acetato
(-)Sp complex [24] display the mean value of 1.948(14) A,
closer to the shorter set of bonds observed in 1. It follows from
this comparison that it is the set of longer Zn–O bonds that
constitutes an exception. The longer bonds are positioned in
front of the plane through N1–Zn–N16, with the (-)Sp skeleton
in a standard orientation, i.e. with the C8 bridging atom
pointing up, N1 to the left and N16 to the right. Interestingly,
such differentiation of bonds to two monodentate ligands of
the same type have not been observed in ZnX2 (-)Sp
complexes (XZhalogen, methyl) [21–23,39], therefore the
effect might be connected with the presence of oxygen
containing ligands and their involvement in hydrogen bond
interactions. Indeed, all methacrylate oxygen atoms are
engaged in numerous short contacts with the neighbouring
C–H groups. On the grounds of geometrical considerations,
majority of these contacts can be classified as intramolecular
C–H/O hydrogen bonds (Table 5) but those engaging the
methacrylate methyl or methylene C–H groups might also be
considered as attractive interactions between antiparallel local
dipoles formed along C–O and C–H bonds. The angles
between these dipoles (vectors) range from 163.4 to 174.0
quite close to 1808, the ideal antiparallel arrangement. Such
type of intramolecular interactions has already been observed
by us in a series of tartaric acid derivatives [40–42]. Connected
with the differentiation of Zn–O bond lengths in 1 is the
observed differentiation of the N1–Zn1–O3 and N16–Zn1–O1
tetrahedral angles which differ by nearly 208, while in complex
2 the two angles are equal, as required by symmetry. The
angular distortions from the idealized tetrahedral symmetry
around Zn in the investigated complexes are quite severe
(Table 4) and result from the difference in ligands (bidentate
sparteine isomers vs two monodentate methacrylate groups)
and from C–H/O intramolecular interactions. In complex 1
the angles around Zn range from 87.8(1)8 (bite angle) to
127.4(1)8, while in complex 2 from 87.9(1)8 (bite angle) to
122.8(1)8. Comparison of the tetrahedral environment around
Zn reveals that the ligand bite angle is not susceptible to
configurational changes connected with the cis/trans isomer-
ization at the C/D ring fusion within the sparteine skeleton.
The mean value of the N–Zn–N angle in the three molecules
(two independent molecules of 1 and one of 2) amounts to
88.1(4)8. Other ZnX2 sparteine complexes (X stands for a
monodentate ligand) of tetrahedral geometry deposited with
the Cambridge Crystallographic Data Base [33], display very
similar values for this angle with the mean of 88.5(3)8 except
for the dimethyl complex in which the N–Zn–N bite angle is
only 80.48. On the other hand, the O–Zn–O angle varies
significantly in the investigated complexes, being much
wider in the C2 symmetrical a-Sp complex 2 (122.8(1)8)
than in the (-)Sp complex 1, in which the mean of the two
observations is 111.6(2.7)8). The distribution of the values of
the X–Zn–X angle in the sparteine complexes deposited in the
CSD [33] is bimodal. When XZhalogen the angles are close to
tetrahedral (113.6(8)8), while in dimethyl- and diacetato–
ZnSp complexes they are much wider (126.8 and 128.28,
respectively). In ZnX2 a-Sp complexes (XaBr, Cl and CN)
investigated by us [26] but not yet incorporated to the CSD,
these values are close to tetrahedral, with the mean
110.9(1.9)8). The N/N intramolecular contact is, as
expected, slightly shorter in 2 2.903(4) A, than in 1, where
the average of the two distances amounts to 2.920(8) A.
However, the parameter that clearly distinguishes between
(-)Sp and a-Sp Zn (methacrylate)2 complexes seems to be the
angle between planes defined by Zn1, N1 and N16, and Zn1,
O1 and O3. In 1 this angle amounts to 70.87(11) and
75.86(12)8, while in 2 it equals to 84.64(9)8 which is much
closer to the orthogonal. This would suggest that the steric
hindrace in (-)Sp Zn (methacrylate)2 complexes is more severe
than in analogous a-Sp complex. This observation is in line
with the reported stronger complexing power of a-Sp in
comparison with (-)Sp [15,43]. Quite surprisingly, a reverse
relationship is observed in the series of Zn-sparteine
complexes with halogens (Cl, Br) [26].
The reported crystal structures consist of discrete complex
units. As a rule, a-Sp and its salts as well as its metal(II)
complexes with symmetrically coordinated ligands utilize C2
molecular symmetry in the crystal by occupying two-fold
symmetry sites in either P43212 or C2221 space groups [18],
with the exception of Cua–SpX2 complexes [5,44] which
crystallize in the space group P212121 lacking the special
position sites. Presented in this paper complex 2, which
crystallizes in the C2221 space group with four molecules in
the unit cell also mirrors this tendency. Opposite to this,
complex 1 by crystallizing with two independent molecules of
nearly the same conformation signalizes packing difficulties
caused by the presence of methacrylate moieties.
B. Jasiewicz et al. / Journal of Molecular Structure 753 (2005) 45–5252
4. Conclusion
Although, the methacrylate anion is much larger than the
earlier used halogen anion or the –CN group [26], no
differences have been observed in the complexation reaction
of a-isosparteine, all these reactions occur with high yields
and a high rate. Similarly, no differences are observed
between the complexation reactions of sparteine and
a-isosparteine with zinc methacrylate.
Two Zn (methacrylate)2 complexes with (-)-sparteine and
a-isosparteine differ significantly at both molecular and
supramolecular level. Compared to the a-isosparteine
complex, the sparteine complex displays higher distortion
from tetrahedral geometry which is contrasted with the
analogous pair of Zn dihalogen complexes, where the
tetrahedral distortion is more severe in the a-isosparteine
complex. Moreover, the sparteine complex displays signifi-
cant elongation of one of the Zn–O bonds and signalizes
difficulties in packing. The structure of the investigated
complexes seems to be stabilized by the numerous
intramolecular C–H/O bonds and local dipole–dipole
interactions. The all-chair conformation of the sparteine
and a-isosparteine backbone is universal.
Acknowledgements
This scientific work was partially financed (U.R. and
B.W.) by the Polish Committee for Scientific Research
(KBN) from the year 2003–2006 as the research project—
grant number 4T09A18525.
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