Synthesis, spectral and structural characterization of three zinc(II) azide complexes with aminopyrazine

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

www.elsevier.com/locate/molstruc

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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