Cooperative hydrogen-bonded chain in molecular ionic complex of

5,50-dibromo-2,20-biphenol with 7-methyl-1,5,7-

triazabicyclo[4.4.0]dec-5-ene hydrofluoride

Grzegorz Wojciechowski, Małgorzata Ratajczak-Sitarz, Andrzej Katrusiak,Bogumil Brzezinski*

Faculty of Chemistry, Adam Mickiewicz University, ul Grunwaldzka 6, 60-780 Poznan, Poland

Received 11 February 2002; accepted 8 March 2002

Abstract

A complex of 5,50-dibromo-2,20-biphenol (DBBPh) with 7-methyl-1,5,7-triazabicyclo[4.4.0]dec-5-ene (MTBD) hydro-

fluoride has been studied using X-ray diffraction, FT-IR, and 1H NMR spectroscopy. The formula unit of the crystal structure

consists of a MTBDHþ cation, a fluoride anion, and one neutral molecule of 5,50-dibromo-2,20-biphenol. In the solid state the

F2 anion is an acceptor in two very short O–H· · ·F2 intermolecular hydrogen bonds of 2.487 and 2.390 A involving the

hydroxyl groups. One oxygen atom of these groups forms also an Nþ–H· · ·O intermolecular hydrogen bond of 2.775 A with

the MTBDHþ cation. In chloroform and acetonitrile, the structures of the complexes are comparable with those studied

previously for 5,50-dibromo-2,20-biphenol with MTBD, because the hydrogen fluoride goes into the gas phase during the

solution process. q 2002 Elsevier Science B.V. All rights reserved.

Keywords: 5,50-Dibromo-2,20-biphenol; Fluoride; MTBD; Intermolecular hydrogen bond; X-ray structure; FT-IR; 1H NMR spectroscopy

1. Introduction

Pursuing our interest in the interactions between

phenols and strong N-bases in biological systems, we

have reported the preparation and spectroscopic studies

of 5,50-dibromo-3-diethylaminomethyl-2,20-biphenol

and other 5,50-derivativates of 3-diethylaminomethyl-

2,20-biphenol as well as X-ray studies of 5,50-dibromo-

3-diethylaminomethyl-2,20-biphenol and complexes of

5,50-dibromo-2,20-biphenol with 7-methyl-1,5,7-triaza-

bicyclo[4.4.0]dec-5-ene (MTBD) [1–10]. Recently,

we have also found that MTBD hydrohalides form

complexes with 5,50-dibromo-2,20-biphenol and there-

fore X-ray diffraction, FT-IR and 1H NMR studies of

5,50-dibromo-2,20-biphenol and MTBD hydrochloride

in solutions and in the crystal were undertaken [11]. As

a continuation of these studies, we report here the

structure of the complex formed between 5,50-dibromo-

2,20-biphenol molecule and MTBD hydrofluoride in the

crystal and in solution, elucidated by X-ray crystal-

lography as well as FT-IR and 1H NMR spectroscopic

methods.

2. Experimental

7-Methyl-1,5,7-triazabicyclo[4.4.0]dec-5-ene

0022-2860/02/$ - see front matter q 2002 Elsevier Science B.V. All rights reserved.

PII: S0 02 2 -2 86 0 (0 2) 00 1 22 -9

Journal of Molecular Structure 613 (2002) 83–90

www.elsevier.com/locate/molstruc

* Corresponding author. Tel.: þ48-61-8291330; fax: þ48-61-

865-8008.

E-mail address: bbrzez@main.amu.edu.pl (B. Brzezinski).

(MTBD) and 2,20-biphenol were commercial products

from Fluka and were used without any purification.

2.1. Synthesis

5,50-Dibromo-2,20-biphenol was synthesised fol-

lowing a method described in Refs. [12,13]. Colour-

less crystals of the 1:1 complex of 5,50-dibromo-2,20-

biphenol with MTBD hydrofluoride were obtained by

crystallisation from ethanol solution of a 1:1 weight

ratio of the 5,50-dibromo-2,20-biphenol with MTBD

hydrofluoride.

2.2. X-ray measurements

The crystals have the form of thick needles, usually

of few twinned crystallites. The crystals are unstable

at normal conditions (see Section 4), but no decay of

the bare sample crystal cooled down to 90 K was

observed. The unit cell parameters at room tempera-

ture (see Table 1) were measured for the crystal

enclosed in quartz capillary. The diffraction data have

been collected on a Kuma KM-4 CCD diffractometer,

equipped with an Oxford Cryostream low-tempera-

ture attachment. The structure has been solved by

direct methods [14] and refined by full-matrix least-

squares on F 2 [15], the hydroxyl H atoms and the

proton at N(05) were located from difference Fourier

maps and refined with isotropic temperature factors,

all the other H-atoms were calculated from the

molecular geometry and their Uiso related to the

thermal vibrations of their carriers. The crystal data

and details of the X-ray analysis are given in Table 1,

the fractional atomic coordinates are listed in Table 2.

The crystallographic-information-file has been

deposited with the Cambridge Crystallographic Data-

base Centre as a supplementary publication no. CCDC

178811.

2.3. Spectroscopic measurements

The IR spectra of the complex were recorded in

KBr pellets (1.5/200 mg) as well as in chloroform

and acetonitrile at 300 K on a Bruker IFS 113v

spectrometer (DTGS detector, resolution of

2 cm21). For the solution measurements, a cell

with Si windows and a wedge-shaped layer was

used to avoid interferences (mean layer thickness:

0.176 mm and the concentration of the samples

0.1 mol dm23).

The 1H NMR measurements in CDCl3 and CD3CN

were carried out at the operating frequency

300.075 MHz; flip angle, pw ¼ 458; spectral width,

sw ¼ 4500 Hz; acquisition time, at ¼ 2:0 s; relax-

ation delay, d1 ¼ 1:0 s; T ¼ 293:0 K and using TMS

as the internal standard. No window function or zero

filing was used. Digital resolution ¼ 0.2 Hz per point.

3. Results and discussion

The molecules used for the synthesis of the

complex with the atoms numbering are given on

Scheme 1.

3.1. X-ray crystallography

The 1:1 complex formed between 5,50-dibromo-

2,20-biphenol molecule (DBBPh) and MTBD

Table 1

Crystal data and structure refinement

Empirical formula C20H24N3O2Br2F

Formula weight 517.24

Temperature 90 K, 295 K

Wavelength 0.71073 A

Crystal system, space group Orthorhombic, Pna21

Unit cell dimensions

a 21.155(1) A, 20.908(5) A

b 9.405(1) A, 9.751(3) A

c 10.370(1) A, 10.349(3) A

Volume 2063.2(3) A3, 2110.0(9) A3

Z, calculated density 4, 1.665 g cm23

Absorption coefficient 3.959 mm21

Fð000Þ 1040

Crystal size 0.15 £ 0.23 £ 0.28 mm

u range for data collection 3.50–29.888

Limiting indices 227 # h # 22, 210 # k # 12,

213 # l # 14

Reflections collected/unique 19602/5266 RðintÞ ¼ 0:1225

Completeness to u ¼ 29:88 92.4%

Refinement method Full-matrix least-squares on F 2

Data/restraints/parameters 5266/1/265

Goodness-of-fit on F 2 1.011

Final R indices ½I . 2sðIÞ� R1 ¼ 0:0507; wR2 ¼ 0:0824

R indices (all data) R1 ¼ 0:0794; wR2 ¼ 0:0900

Absolute structure parameter 20.005(12)

Largest diff. peak and hole 0.603 and 20.697 eA23

G. Wojciechowski et al. / Journal of Molecular Structure 613 (2002) 83–9084

hydrofluoride, as formed in the crystalline state, and

the numbering of the atoms are given in Fig. 1. The

geometry of the DBBPh molecule and MTBDHþ

cation is described in Tables 3 and 4. The asymmetric

unit consists of a protonated MTBD molecule

(MTBDHþ), a fluoride anion, and a neutral molecule

of 5,50-dibromo-2,20-biphenol (DBBPh). The DBBPh

molecules and F2 anions are consecutively hydrogen-

bonded into chains along crystal [0 1 2 1] direction.

Table 2

Atomic coordinates ( £ 104) and equivalent isotropic displacement

parameters ( £ 103, A2) Ueq is defined as one third of the trace of the

orthogonalised Uij tensor

x y z Ueq

Br(1) 5463(1) 2220(1) 23728(1) 24(1)

Br(10) 4532(1) 4869(1) 2500(1) 23(1)

O(10) 6693(2) 838(4) 1462(4) 22(1)

C(10) 5926(3) 2453(5) 691(4) 15(1)

C(20) 6215(2) 1741(5) 1728(4) 15(1)

C(30) 5988(2) 1971(5) 2981(5) 17(1)

C(40) 5496(2) 2881(5) 3207(4) 18(1)

C(50) 5215(2) 3598(5) 2198(4) 16(1)

C(60) 5431(2) 3377(5) 934(4) 15(1)

C(1) 6146(2) 2196(5) 2673(4) 13(1)

C(2) 6673(2) 2846(5) 21179(4) 15(1)

O(1) 7010(2) 3741(4) 2443(3) 18(1)

C(3) 6852(2) 2572(4) 22465(5) 18(1)

C(4) 6495(2) 1651(5) 23212(5) 18(1)

C(5) 5963(2) 1029(4) 22718(4) 13(1)

C(6) 5792(2) 1266(5) 21441(4) 17(1)

F(1) 7145(2) 21(3) 3541(3) 36(1)

N(01) 6356(2) 6789(4) 3224(4) 24(1)

C(02) 5906(3) 7730(6) 2542(7) 34(2)

C(03) 5850(3) 7363(6) 1129(6) 31(2)

C(04) 6484(3) 7031(7) 611(5) 33(1)

N(05) 6766(2) 5872(4) 1340(4) 22(1)

C(06) 6710(2) 5827(5) 2636(5) 18(1)

N(07) 7008(2) 4828(4) 3306(4) 23(1)

C(08) 6898(3) 4738(6) 4699(4) 28(1)

C(09) 6871(3) 6172(6) 5260(5) 32(1)

C(10) 6374(3) 7027(6) 4627(5) 32(1)

C(11) 7484(3) 3872(5) 2744(5) 29(1)

Scheme 1.

Table 3

Bond length (A) and angles (8)

5,50-Dibromo-2,20-biphenol Ring 1 Ring 10

Br(1)–C(5) 1.895(4) 1.902(5)

O(1)–C(2) 1.341(5) 1.349(5)

C(1)–C(6) 1.399(6) 1.383(7)

C(1)–C(2) 1.376(6) 1.406(6)

C(2)–C(3) 1.411(6) 1.401(7)

C(3)–C(4) 1.386(6) 1.368(7)

C(4)–C(5) 1.368(6) 1.379(6)

C(5)–C(6) 1.391(6) 1.404(6)

C(10)–C(1) 1.509(6)

C(4)–C(5)–Br(1) 121.1(3) 120.7(3)

C(6)–C(5)–Br(1) 118.8(4) 119.6(3)

O(1)–C(2)–C(1) 119.5(4) 118.0(4)

O(1)–C(2)–C(3) 120.7(4) 122.9(4)

C(1)–C(2)–C(3) 119.8(4) 119.1(4)

C(2)–C(3)–C(4) 119.7(4) 121.0(5)

C(3)–C(4)–C(5) 120.4(4) 120.2(4)

C(4)–C(5)–C(6) 120.1(4) 119.7(4)

C(5)–C(6)–C(1) 120.2(4) 120.7(4)

C(6)–C(1)–C(2) 119.7(4) 119.2(4)

C(6)–C(1)–C(10) 117.9(4) 120.4(4)

C(2)–C(1)–C(10) 122.4(5) 120.4(4)

MTBDHþ

N(07)–C(06) 1.328(6)

N(07)–C(08) 1.465(6)

N(07)–C(11) 1.471(6)

C(10)–N(01) 1.473(6)

C(10)–C(09) 1.478(8)

C(09)–C(08) 1.471(7)

C(06)–N(01) 1.323(6)

C(06)–N(05) 1.349(6)

N(05)–C(04) 1.455(7)

C(04)–C(03) 1.479(9)

C(03)–C(02) 1.510(7)

C(02)–N(01) 1.479(7)

C(06)–N(07)–C(08) 118.8(4)

C(06)–N(07)–C(11) 123.4(4)

C(08)–N(07)–C(11) 117.6(4)

N(01)–C(10)–C(09) 112.0(5)

C(08)–C(09)–C(10) 110.6(5)

N(07)–C(08)–C(09) 110.1(4)

N(01)–C(06)–N(07) 120.7(5)

N(01)–C(06)–N(05) 119.2(4)

N(07)–C(06)–N(05) 120.1(4)

C(06)–N(05)–C(04) 120.3(4)

N(05)–C(04)–C(03) 109.9(5)

C(04)–C(03)–C(02) 109.3(6)

N(01)–C(02)–C(03) 112.2(5)

C(06)–N(01)–C(10) 123.0(5)

C(06)–N(01)–C(02) 123.6(4)

C(10)–N(01)–C(02) 113.4(5)

G. Wojciechowski et al. / Journal of Molecular Structure 613 (2002) 83–90 85

These hydrogen bonds involve the hydroxyl groups of

DBBPh, and their dimensions are listed in Table 5.

One of the hydroxyl groups, O(1), is additionally

hydrogen bonded to the MTBDHþ cation, involving

the protonated N(05), as shown in Fig. 1. This O(1)–

H(1)- -F2 hydrogen bond is significantly longer than

the other –O(10)–H(10)- -F2 (see Table 5). Thus the

difference between the two OH· · ·F hydrogen bonds is

justified by the different other interactions of the

hydroxyl groups (Fig. 2). The conformation of the

DBBPh molecule is described by the torsion angle

about the C(1)–C(10) bond, of 79.4(1)8. This is a soft

parameter, which was equal to 33.6(1)8 in the DBBPh

anion where the hydroxyl groups are hydrogen

bonded, or 59.3(0)8 in the neutral DBBPh molecule

[10]; this torsion angle in complex of DBBPh with

MTBD hydrochloride is equal to 67.3(1)8 [11], in 2,20-

biphenol monohydrate is equal to 67.6(1)8 [16].

3.2. Spectroscopic measurements

Fig. 3(a)–(c) compares the IR spectra of the 1:1

complex of MTBD hydrofluoride with 5,50-dibromo-

2,20-biphenol in the solid, chloroform and acetonitrile,

respectively. In Table 6, the 1H NMR data of this

complex in chloroform and acetonitrile are summar-

ised. For comparison the 1H NMR data of 5,50-

dibromo-2,20-biphenol and MTBD and protonated

MTBD are also given.

The spectrum of the polycrystalline solid complex

in KBr pellet (Fig. 3(a)) features an intense band in the

3300–3000 cm21 range corresponding to the proton

vibrations in relatively weak hydrogen bonds formed

between Nþ–H (protonated MTBD) groups and OH

group in the 2 position. The protonation of the MTBD

molecule is corroborated by the two bands corre-

sponding to the n(CN) vibrations (1624 and

1600 cm21) [6–9]. The position of this band demon-

strate that the Nþ–H· · ·OH intermolecular hydrogen

bond is very asymmetrical.

Apart from the Nþ–H· · ·OH intermolecular hydro-

gen bond in the crystal structure, there are two types

of OH· · ·F2 short intermolecular hydrogen bonds.

The protonic stretching vibrations in the very short

Fig. 1. Two formula units of complex of 5,50-dibromo-2,20-biphenol with 7-methyl-1,5,7-triazabicyclo[4.4.0]dec-5-ene hydrofluoride

illustrating the H-bonding scheme in this crystal. The DBBPh molecules are –OH- -F2- -HO– hydrogen bonded via the F2 anion forming

chains along crystal direction ½01�1�: This chain is indicated by solid covalent bonds and solid dashed lines for the H-bonds in this drawing.

Additional ‘side’ H-bonds are formed to the MTBDHþ cations, for clarity both the cations and their H-bonds has been drawn by thin lines.

G. Wojciechowski et al. / Journal of Molecular Structure 613 (2002) 83–9086

OH· · ·F2 hydrogen bond (2.390) are shown as broad

intense band in the 2000–1000 cm21 range with a

maximum at about 1400 cm21 and some Evans

windows at ca. 1600 and 1500–1300 cm21. For

such short and almost linear hydrogen bond should

be expected an intense absorption with a maximum

ca. 1000 cm21 or below these wavenumbers. The only

explanation for this spectral feature is the strong

asymmetry of this hydrogen bond (Table 5). The

longer OH· · ·F2 hydrogen bond (2.487) is reflected as

continuous absorption in the region 3300–1000 cm21

showing band-like structures with maxima at 2480

and 2170 cm21. The continuous absorption in the

spectrum demonstrates that within the complex a fast

fluctuation of the proton in the OH· · ·F2 hydrogen

bond occurs. Thus, this hydrogen bond shows the so-

called Zundel’s polarizability [17,18], although the

asymmetric structure is predominant in the crystal at

lower temperature.

The spectra of the complex dissolved in chloro-

form and acetonitrile are shown in Fig. 3(b) and (c),

respectively. Both spectra of the solutions are

dramatically different than that recorded in the solid

state. The comparison of these spectra with the

respective spectra of 1:1 complexes formed between

5,50-dibromo-2,20-biphenol (DBBPh) and MTBD,

studied earlier [19], demonstrate clearly that during

the solution process the following reaction occurs:

DBBPh–MTBD–HþF2 ! DBBPh2 –MTBD–Hþ

þ HF"

The 1H NMR spectra of the chloroform and

acetonitrile solutions of the complex confirm this

conclusion because they are identical with that formed

between 5,50-dibromo-2,20-biphenol and MTBD of

1:1 stoichiometry.

4. Conclusions

5,50-Dibromo-2,20-biphenol forms with MTBD

fluoride a complex including DBBPh molecule,

protonated MTBD molecule and fluoride. The crystals

of the complex are stable at low temperatures;

however, at room conditions they slowly decay,

possibly due to the slow adsorption of water and

crystal dissolution. The spectrum of the complex in

the solid reflects very well the structure determined by

X-ray method. In chloroform and acetonitrile sol-

utions, this complex dissociated and the hydrogen

fluoride evaporated. In the chloroform and acetonitrile

solutions, respective 1:1 complexes of 5,50-dibromo-

2,20-biphenolate with protonated MTBD molecule

were found. These hydrogen-bonded systems show

great proton polarizability as demonstrated by the

continuous absorption in the FT-IR spectra.

Table 4

Selected torsion angles (8)

C(60)–C(10)–C(20)–O(10) 179.5(4)

C(1)–C(10)–C(20)–O(10) 0.4(7)

C(1)–C(10)–C(20)–C(30) 2178.2(5)

O(10)–C(20)–C(30)–C(40) 2179.0(4)

C(30)–C(40)–C(50)–Br(10) 2179.9(4)

C(1)–C(10)–C(60)–C(50) 178.6(4)

Br(10)–C(50)–C(60)–C(10) 2179.7(4)

C(60)–C(10)–C(1)–C(2) 100.5(6)

C(20)–C(10)–C(1)–C(2) 280.4(6)

C(60)–C(10)–C(1)–C(6) 279.0(6)

C(20)–C(10)–C(1)–C(6) 100.1(6)

C(6)–C(1)–C(2)–O(1) 179.7(4)

C(10)–C(1)–C(2)–O(1) 0.2(7)

C(10)–C(1)–C(2)–C(3) 2179.5(4)

O(1)–C(2)–C(3)–C(4) 2179.5(4)

C(3)–C(4)–C(5)–Br(1) 179.5(3)

Br(1)–C(5)–C(6)–C(1) 2179.2(3)

C(10)–C(1)–C(6)–C(5) 177.9(4)

N(01)–C(10)–C(09)–C(08) 240.4(6)

C(06)–N(07)–C(08)–C(09) 240.4(7)

C(11)–N(07)–C(08)–C(09) 134.7(5)

C(10)–C(09)–C(08)–N(07) 57.1(6)

C(08)–N(07)–C(06)–N(01) 4.8(7)

C(11)–N(07)–C(06)–N(01) 2170.0(4)

C(08)–N(07)–C(06)–N(05) 2175.2(4)

C(11)–N(07)–C(06)–N(05) 10.0(7)

N(01)–C(06)–N(05)–C(04) 5.1(7)

N(07)–C(06)–N(05)–C(04) 2174.9(5)

C(06)–N(05)–C(04)–C(03) 241.5(7)

N(05)–C(04)–C(03)–C(02) 57.4(6)

C(04)–C(03)–C(02)–N(01) 240.9(7)

N(07)–C(06)–N(01)–C(10) 13.7(7)

N(05)–C(06)–N(01)–C(10) 2166.3(4)

N(07)–C(06)–N(01)–C(02) 2166.4(5)

N(05)–C(06)–N(01)–C(02) 13.6(7)

C(09)–C(10)–N(01)–C(06) 5.5(7)

C(09)–C(10)–N(01)–C(02) 2174.4(5)

C(03)–C(02)–N(01)–C(06) 5.8(8)

C(03)–C(02)–N(01)–C(10) 2174.2(5)

G. Wojciechowski et al. / Journal of Molecular Structure 613 (2002) 83–90 87

Table 5

Geometry of the hydrogen bonds (A and 8)

D–H· · ·A d(D–H) d(H· · ·A) d(D· · ·A) /(DHA)

O(10)–H(10)· · ·F(1) 0.71(8) 1.80(8) 2.487(5) 162(9)

O(1)–H(1)· · ·F(1)a 0.89(9) 1.51(9) 2.390(4) 170(9)

N(05)–H(05)· · ·O(1) 0.97(5) 1.87(5) 2.775(5) 153(4)

a Symmetry code: 1.5 2 x, 0.5 þ y, 20.5 þ z.

Fig. 2. Autostereogram [20] of the crystal packing of complex of 5,50-dibromo-2,20-biphenol with 7-methyl-1,5,7-triazabicyclo[4.4.0]dec-5-ene

hydrofluoride viewed along [z ].

Table 61H NMR chemical shifts (ppm) and coupling constants (Hz) of the complex of MTBD hydrofluoride with 5,50-dibromo-2,20-biphenol (3). For

comparison the data of 5,50-dibromo-2,20-biphenol (1) and protonated MTBD (2) are shown

Compound Solvent OH H-3(30) H-4(40) H-6(60) J 3,4(30 ,40) J 4,6(40 ,60) MTBD Nþ–H

1 CD3CN 4.62s 6.86 d 7.31 q 7.28 d 8.2 2.5 –

2 CD3CN – – – – – – 6.45 s

3 CDCl3 12.54 bs 7.18 d 7.30 q 7.36 d 8.8 2.5 9.31 s

3 CD3CN 14.30 bs 7.12 d 7.35 q 7.37 d 8.8 2.5 6.53 s

bs: Broad singled; d: doublet; q: quartet.

G. Wojciechowski et al. / Journal of Molecular Structure 613 (2002) 83–9088

Acknowledgments

Financial support from the State Committee for

Scientific Research (KBN), grant 3 T09A 01817, is

gratefully acknowledged. G. Wojciechowski thanks

Foundation of Polish Science for fellowship.

References

[1] B. Brzezinski, P. Radziejewski, J. Olejnik, G. Zundel, J. Mol.

Struct. 323 (1994) 71.

[2] B. Brzezinski, P. Radziejewski, A. Rabold, G. Zundel, J. Mol.

Struct. 355 (1995) 185.

[3] B. Brzezinski, H. Urjasz, G. Zundel, F. Bartl, J. Mol. Struct.

355 (1995) 185.

[4] B. Brzezinski, H. Urjasz, G. Wojciechowski, G. Zundel,

J. Mol. Struct. (1998) 470.

[5] E. Bartoszak-Adamska, G. Wojciechowski, M. Jaskolski, B.

Brzezinski, J. Mol. Struct. 525 (2000) 253.

[6] B. Brzezinski, P. Radziejewski, G. Zundel, J. Chem. Soc.,

Faraday Trans. 91 (1995) 3141.

[7] B. Brzezinski, G. Zundel, J. Mol. Struct. 380 (1996) 195.

[8] G. Wojciechowski, G. Schroeder, G. Zundel, B. Brzezinski,

J. Phys. Chem. A 104 (2000) 7469.

[9] B. Brzezinski, G. Wojciechowski, F. Bartl, G. Zundel, J. Mol.

Struct. 554 (2000) 245.

[10] G. Wojciechowski, A. Katrusiak, B. Brzezinski, J. Mol. Struct.

604 (2002) 279.

[11] E. Bartoszak-Adamska, G. Wojciechowski, M. Jaskolski, B.

Brzezinski, J. Mol. Struct. 595 (2001) 21.

[12] B. Brzezinski, P. Radziejewski, A. Rabold, G. Zundel, J. Mol.

Struct. 355 (1995) 185.

[13] O. Diels, A. Bibergeil, Chem. Ber. 35 (1902) 309.

[14] G. Sheldrick, SHELXS-97, Program for crystal structure

solution, University of Goettingen, 1997.

[15] G. Sheldrick, SHELXL-97, Program for crystal structure

refinement, University of Goettingen, 1997.

Fig. 3. FT-IR spectra of 3:2 complex in (a) KBr pellet, (b) chloroform, and (c) acetonitrile.

G. Wojciechowski et al. / Journal of Molecular Structure 613 (2002) 83–90 89

[16] X.-M. Chen, G.-B. Luo, M.-L. Tong, Z.-Y. Zhou, Acta

Crystallogr. C52 (1996) 1727–1729.

[17] G. Zundel, in: P. Schuster, G. Zundel, C. Sandorfy (Eds.), The

Hydrogen Bond—Recent Developments in Theory and

Experiments, vol. II, North Holland, Amsterdam, 1976, pp.

687, Chapter 15.

[18] D. Borgis, G. Tarjus, H. Azzouz, J. Chem. Phys. 97 (1992)

1390.

[19] G. Wojciechowski, B. Brzezinski, J. Mol. Struct. 607 (2002)

111.

[20] A. Katrusiak, J. Mol. Graph. Model. 19 (2001) 363–367. see

also p. 398.

G. Wojciechowski et al. / Journal of Molecular Structure 613 (2002) 83–9090