ORIGINAL PAPER

Synthesis, crystal structure, and characterization of a newnon-centrosymmetric organic–inorganic hybrid material:[C6H16N2]2(BiBr6)NO3

Manel Essid1 • Thierry Roisnel2 • Mohamed Rzaigui1 • Houda Marouani1

Received: 18 January 2015 / Accepted: 27 April 2015

� Springer-Verlag Wien 2015

Abstract A novel organic–inorganic hybrid material,

[C6H16N2]2(BiBr6)NO3, was synthesized, and its structure

was determined by means of single crystal X-ray diffraction

studies at room temperature in the non-centrosymmet-

ric orthorhombic space group P21212 with the

following parameters: a = 17.629(5) A, b = 20.279(5) A,

c = 7.319(5) A, and Z = 4. The crystal lattice is composed

of discrete hexabromobismuthates and nitrate anions sur-

rounded by trans-2,5-dimethylpiperazine-1,4-diium cations

linked via simple and bifurcated N–H���Br(O) and weak

C–H���Br(O) hydrogen bonds to form three-dimensional

network. The vibrational spectrum has been measured at

room temperature by FT-IR spectroscopy (4000–400 cm-1)

on polycrystalline samples, shows the presence of organic

cation and nitrate anion. The number of 13C CP-MAS NMR

lines is in full agreement with the crystallographic data.

Graphical abstract

Keywords Crystal structure � Hydrogen bonds �IR spectroscopy � NMR spectroscopy

Introduction

In recent years, the non-linear optical (NLO) materials have

attracted considerable interest because of their new scien-

tific phenomena and potential applications in photonic

technologies. The development of photonic and optoelec-

tronic technologies rely heavily on the growth of NLO

materials with high non-linear optical responses and the

development of novel and more efficient materials [1–6].

As an important class of low-dimensional hybrid materials,

organic–inorganic perovskite-like family of the type Rx-

MyXz (where R is protonated amine, M is a metal, and X is a

halide) has received considerable interest in the past dec-

ades. In this case, the structures of halogenobismuthates(III)

with organic cations, a new group of ferroic crystals, are

best described as molecular-ionic, organic inorganic hybrid

materials. They consist of organic cations within anionic

inorganic frameworks. Differences in the size, symmetry,

and ability to form hydrogen bonds of the various possible

& Manel Essid

essid.manel@gmail.com

1 Laboratoire de Chimie des Materiaux, Faculte des Sciences

de Bizerte, Universite de Carthage, 7021 Zarzouna, Tunisie

2 Centre de Diffractometrie X, UMR 6226 CNRS, Unite

Sciences Chimiques de Rennes, Universite de Rennes I, 263

Avenue du General Leclerc, 35042 Rennes, France

123

Monatsh Chem

DOI 10.1007/s00706-015-1485-9

organic cations, together with the many different possible

metal–halogen atom configurations, provide a rich family of

compounds. Furthermore, the architecture of the metal

halide can be tuned at the molecular level so as to produce

unusual electronic properties. Their structures are charac-

terized by MX6 octahedral sharing corners, edges, or faces

forming naturally zero (0D)-, one (1D)-, two (2D)-, or three

(3D)-dimensional semiconductor networks according to the

organic cation by N–H���X hydrogen bonds and covalent

interactions [7–17]. The cavities between inorganic moi-

eties are filled by organic cations to anionic framework

through hydrogen bonds and/or electrostatic interactions.

Piperazine and its derivatives are a strong basic amine able

to form a dication, in which all N–H bonds are generally

active in hydrogen bond formation. They are found in

biologically active compounds across a number of different

therapeutic areas such as antifungal, antibacterial, anti-

malarial, antipsychotic, antidepressant, and antitumor

activity against colon, prostate, breast, lung, and leukemia

tumors [18].

Considering the attractive properties and attributes of

halogenobismuthates(III) and the new promising oppor-

tunities they may open with regard to the development

of useful organic–inorganic hybrid materials, the present

study reports the synthesis and structural characteriza-

tion of the organic–inorganic hybrid material,

[C6H16N2]2(BiBr6)NO3, which crystallizes in chiral

space group and could be a good candidate for non-

linear optical applications. This compound is character-

ized by X-ray diffraction, infrared, and CP-MAS NMR

spectroscopies.

Results and discussion

Crystal structure

The X-ray analysis shows that the title compound crystal-

lizes in the non-centrosymmetric orthorhombic space

group P21212 with four formula units cell (Z = 4). Refin-

ing the structure in the chiral space group P21212 gives a

value of -0.032 for the Flack parameter [19]. This value

shows that the handedness of the crystal axes is right and

corresponds to the correct absolute structure. The non-

centrosymmetrical space group has been frequently ob-

served in bismuth halide chemistry. We mention in

particular the (C5H14N2)BiCl5 [20], which exhibits very

similar chiral space group than that of present compound.

The asymmetric unit contains one hexabromobismuthate

[BiBr6]3-, two independent nitrate (NO3-) anions halves,

and two crystallographically independent trans-2,5-

dimethylpiperazine-1,4-diium cations (A, B) as shown in

Fig. 1. The nitrogen atoms of nitrate anions are located in

special position. The spaces between the inorganic entities

are filled by organic cations (A, B) assuring their connection

by means of the N–H���Br (O) and C–H���Br (O) hydrogen

bonds, forming a three-dimensional network (Fig. 2).

The [BiBr6]3- unit possesses a configuration of distorted

octahedron, so that the central bismuth(III) ion is sur-

rounded by six bromine atoms. The Bi–Br bond lengths

vary from 2.7929(19) to 2.9242(14) A. These values are

much shorter than the sum of Van der Waals radii of Bi and

Br (4.7 A) according to Pauling [21]. The bond-valence

sum (BVS) calculation of the Bi cation, using the

Fig. 1 Chemically partly

complemented view of the

[C6H16N2]2(BiBr6)NO3

compound showing the atom

numbering scheme.

Displacement ellipsoids are

drawn at the 50 % probability

level. Symmetry codes: (1)

-x ? 1, -y, z; (2) -x, -y, z

M. Essid et al.

123

parameters given by Brown [22], gave value of 3.02 va-

lence units. These results confirm primary the presumed

oxidation state of Bi(III) and secondary the stereochemical

activity of Bi lone electron pair.

The [BiBr6]3- anions are connected to the first organic

cation (A) through N–H���Br and C–H���Br hydrogen bonds

to form a layer parallel to the (a, c) plane (Fig. 3). While

the second organic cations (B) are connected to the bro-

mine atoms by N–H���Br and C–H���Br hydrogen bonds to

build a chain extending along the b-axis (Fig. 4). The

isolated nitrate anions play an important role in cohesion of

the structure so they are located in the gaps between the

octahedra of bismuth and diprotonated organic cations. In

fact, the presence of those anions as a part of an anionic

sublattice in the family of organic–inorganic hybrids was

also found in other structure such as, e.g., (C10H18N8-

S2)2[BiCl6]NO3�2H2O [23].

The total negative charge (-4) on the framework is bal-

anced by the presence of two independent fully protonated

[C6H16N2]4? molecules situated in the space delimited by the

anionic sublattice ([BiBr6]3-). The first cation (A) spreads

along the b-axis, while the second cation (B) develops along

the a-axis. They adopt both an almost ideally puckered chair

conformation with the side methyl groups in the equatorial

position. Therefore, the puckering parameters [24] for (A) are

Q = 0.58 A, U = -133�, and h = 0� and for (B) are

Q = 0.55 A, U = -132�, and h = 0�. The N–C and C–C

bond lengths vary from 1.469(16) to 1.541(18) A and angles

C–C–C, N–C–C, and C–N–C are between 109.2(11) and

113.8(9)� (Table 1). These values are in agreement with those

reported in other trans-2,5-dimethylpiperazine-1,4-diium

salts such as [C6H16N2](NO3)2 [25].

The various hydrogen bond parameters are summarized

in Table 2. All of these hydrogen bonds, N–H���Br(O) and

C–H���Br(O) give rise to a three-dimensional network in

the structure and to stability.

IR spectroscopy

The IR spectrum of crystalline [C6H16N2]2(BiBr6)NO3 is

shown in Fig. 5. The most representative and characteristic

vibrational modes of this compound can be compared to

those of similar complexes associated to the same cation

and to the literature [26, 27]. Heterocyclic compounds

Fig. 2 Projection along the c-axis of the atomic arrangement of

[C6H16N2]2(BiBr6)NO3. The hydrogen bonds are shown as dashed

lines

Fig. 3 Projection of [C6H16N2]2(BiBr6)NO3 structure along [010] direction showing a layer of [BiBr6]3- and cations (A). The hydrogen bonds

are shown as dashed lines

Synthesis, crystal structure, and characterization…

123

containing an N–H group exhibit N–H stretching absorp-

tion in the region from 3000 to 2800 cm-1 overlap with

stretching vibrations of C–H groups.

The bending vibrations of N–H and C–H bonds were

located in the 1598–1400 cm-1 spectral region. The in-

frared bands observed at 1365 cm-1 are assigned to

stretching vibration of NO3. The bands related to the

stretching mode of the C–N and C–C groups are located in

the range 1280–1045 cm-1. Finally, the very weak bands

observed between 942 and 440 cm-1 were attributed to

bending modes of C–N–H, CCN, NO3, CNC, and c(CCH).

Nuclear magnetic resonance analysis

The 13C CP-MAS NMR spectrum of the title compound

is shown in Fig. 6. The 13C NMR spectrum of [C6H16-

N2]2(BiBr6)NO3 exhibits four signals situated at 17.40,

18.64, 19.87, and 22.17 ppm corresponding to four

methyl groups substituent of piperazine-1,4-diium cation.

This result, which proves that the asymmetric unit should

contain two organic molecules, is also in good agreement

with the crystallographic data. The eight carbon atoms in

the two piperazinium rings resonate as two lines (47.90

and 51.76 ppm) showing that the peaks of some ring

carbon atoms overlap because these atoms have a similar

chemical environment.

Conclusion

A promising non-linear optical single crystal of [C6H16-

N2]2(BiBr6)NO3 was synthesized from aqueous solution by

slow evaporation technique at room temperature. The

orthorhombic structure and the corresponding lattice pa-

rameters were confirmed using single crystal and powder

Table 1 Selected bond distances/A and angles/� for

[C6H16N2]2BiBr6NO3

Bi–Br1 2.7929(19) C10–C9 1.494(18)

Bi–Br5 2.8168(14) N6–O32 1.220(11)

Bi–Br2 2.8239(14) C7–C11 1.494(19)

Bi–Br3 2.8909(18) C7–C8 1.515(16)

Bi–Br6 2.9136(14) N6–O32 1.220(11)

Bi—Br4 2.9242(14) C2–C1 1.538(17)

O4–N6 1.27(2) C3–C4 1.532(18)

N3—C7 1.485(16) C3–C6 1.541(18)

N3–C10 1.507(17) C5–C1 1.535(17)

N5–O2 1.229(11) N1–C4 1.485(16)

N5–O21 1.229(11) N1–C1 1.511(15)

N5–O1 1.24(2) N4–C8 1.482(15)

O3–N6 1.220(11) N4–C9 1.517(16)

N2–C2 1.469(16) C12–C9 1.522(18)

N2–C3 1.477(14)

Br1–Bi–Br5 91.83(5) C11–C7–C8 111.0(10)

Br1–Bi–Br2 91.55(5) N2–C2–C1 108.9(10)

Br5–Bi–Br2 89.45(4) N1–C1–C5 110.7(10)

Br1–Bi–Br3 174.95(4) N1–C1–C2 109.1(10)

Br5–Bi–Br3 87.83(4) C5–C1–C2 109.1(11)

Br2–Bi–Br3 93.49(5) N1–C1–C5 110.7(10)

Br1–Bi–Br6 88.92(5) N2–C3–C4 108.1(10)

Br5–Bi–Br6 178.57(4) N2–C3–C6 112.0(9)

Br2–Bi–Br6 89.31(4) C4–C3–C6 108.3(11)

Br3–Bi–Br6 91.53(5) N1–C4–C3 110.2(11)

Br1–Bi–Br4 88.37(4) N2–C3–C4 108.1(10)

Br5–Bi–Br4 95.72(4) N2–C3–C6 112.0(9)

Br2–Bi–Br4 174.83(4) C4–C3–C6 108.3(11)

Br3–Bi–Br4 86.65(5) C4–N1–C1 112.1(9)

Br6–Bi–Br4 85.52(4) N4–C8–C7 110.7(9)

C7–N3–C10 113.1(9) C8–N4–C9 113.8(9)

O2–N5–O21 122.1(15) C9–C10–N3 111.6(10)

O2–N5–O1 119.0(8) C10–C9–N4 109.2(11)

O2i–N5–O1 119.0(8) C10–C9–C12 113.7(11)

C2–N2–C3 114.1(9) N4–C9–C12 109.3(10)

O3–N6–O32 124.1(16) N3–C7–C11 110.0(10)

O3–N6–O4 117.9(8) N3–C7–C8 110.7(10)

O32–N6–O4 117.9(8)

Symmetry codes: (1) -x ? 1, -y, z; (2) -x, -y, z

Fig. 4 Arrangement of chain anions [BiBr6]3-and cations (B) in

[C6H16N2]2(BiBr6)NO3 along the [100] direction. The hydrogen

bonds are shown as dashed lines

M. Essid et al.

123

XRD analyses. The crystal structure consists of one bro-

mobismuthate [BiBr6]3-, two independent nitrate (NO3-)

anions halves, and two crystallographically independent

trans-2,5-dimethylpiperazine-1,4-diium cation linked via

simple and bifurcated N–H���Br (O) and C–H���Br (O) hy-

drogen bonds, forming a three-dimensional network. The

presence of functional groups was established by FT-IR

studies. Molecular structure of the grown crystal was

studied by 13C NMR spectroscopy and shows a good

agreement between the number of 13C CP-MAS lines and

the crystallographic data.

Experimental

All reagents were from commercial sources and used

without further purification: HBr (48 %), Bi(NO3)3�5H2O,

trans-2,5-dimethylpiperazine (98 %).

The powder diffraction patterns were obtained using a

D8 Advance Bruker powder diffractometer with CuKa(k = 1.5418 A) radiation. The infrared spectrum of [C6-

H16N2]2(BiBr6)NO3 was measured at room temperature in

the frequency range 4000–400 cm-1 using a Perkin Elmer-

type FT-IR 1000 spectrometer. The solid-state 13C MAS

NMR spectrum was recorded at room temperature on a

Bruker AC 300 spectrometer. The 13C frequency was

75.48 MHz. The spectrum was acquired with the use of

cross-polarization for protons with 5 ms contact time. A

powdered sample was packed in a 4-mm-diameter rotor

and set to rotate at a speed of up to 10 kHz in a Doty MAS

probe head. The chemical shifts were referenced with re-

spect to tetramethylsilane.

Bis(trans-2,5-dimethylpiperazine-1,4-diium) hexabromo-

bismuthate(III) nitrate (C12H32BiBr6N5O3)

Crystals of [C6H16N2]2(BiBr6)NO3 were obtained by dis-

solving in concentrated solution of HBr (48 %) a

stoichiometric mixture of bismuth(III) nitrate pentahydrate

and trans-2,5-dimethylpiperazine. The resulting aqueous

solution was then kept at room temperature. After several

weeks of slow evaporation at room temperature, yellow

prismatic-shaped single crystals of [C6H16N2]2(BiBr6)NO3

were obtained. Yield: 75 %; 13C NMR (75 MHz, CP-MAS):

d = 19.87 (C5), 22.17 (C6), 18.64 (C11), 17.40 (C12), 47.90,

51.76 (C1, C2, C3, C4, C7, C8, C9, C10) ppm; FT-IR

(KBr): = 3000–2800 (mN–H, C–H), 1598-1400 (dN–H, C–H),

1365 (mNO3), 1280–1045 (mC–N, C–C) cm-1. The PXRD

pattern of synthesized product is in good agreement with the

calculated pattern from the single crystal data, indicating the

phase purity of the sample (Fig. 7). The slight differences in

the intensity of reflection values could be due to the slight

changes in the cell dimensions.

X-ray analysis

The X-ray data collection was carried out on a Bruker

APEXII CCD diffractometer using Mo Ka radiation

(0.71073 A) at 150 K. An empirical multi-scan [28] ab-

sorption correction was applied. The positional parameters

for the heavy atoms were obtained from a three-dimen-

sional Patterson map, while the non-hydrogen atoms were

found from successive difference Fourier maps. The

structure was refined by full-matrix least squares using

anisotropic temperature factors for all non-hydrogen atoms.

All the hydrogen atoms positions were calculated. The

Fig. 5 IR absorption spectrum of [C6H16N2]2(BiBr6)NO3

Table 2 Hydrogen bond distances/A and angles/� for

[C6H16N2]2BiBr6NO3

D–H���A D–H H���A D���A D–H���A

N1–H1A���Br22 0.90 2.44 3.327(11) 167

N1–H1B���Br53 0.90 2.54 3.314(11) 144

N2–H2A���Br41 0.90 2.53 3.300(10) 144

N2–H2B���Br64 0.90 2.46 3.353(10) 170

N3–H3A���O2 0.90 2.16 2.871(14) 135

N3–H3A���O1 0.90 2.26 3.099(10) 155

N3–H3B���Br42 0.90 2.42 3.318(11) 173

N4–H4A���O3 0.90 2.14 2.826(14) 133

N4—H4A���O4 0.90 2.22 2.998(9) 144

N4–H4B���Br6 0.90 2.45 3.340(10) 171

C2–H2C���Br34 0.97 2.79 3.560(11) 137

C4–H4D���Br32 0.97 2.86 3.664(13) 141

C6–H6B���O3 0.96 2.55 3.437(18) 154

C7–H7���Br2 0.98 2.84 3.628(12) 138

C9–H9���Br52 0.98 2.89 3.672(13) 137

Symmetry codes: (1) -x, -y, z; (2) -x ? 1/2, y - 1/2, -z ? 1; (3)

-x ? 1/2, y - 1/2, -z; (4) -x, -y, z - 1

Synthesis, crystal structure, and characterization…

123

calculations were performed with the SHELXS-97 and

SHELXL-97 [29] programs. The experimental details of

the structure determination for the studied compound are

presented in Table 3. Complete crystallographic data for

the structural analysis have been deposited with the Cam-

bridge Crystallographic Data Centre; CCDC reference

number 1042317. These data can be obtained free of

charge via http://www.ccdc.cam.ac.uk/conts/retrieving.

html (or from the Cambridge Crystallographic Data

Fig. 7 Experimental (black line) and calculated (red line) powder

X-ray diffraction patterns of [C6H16N2]2(BiBr6)NO3

Fig. 6 13C CP-MAS NMR

spectrum of

[C6H16N2]2(BiBr6)NO3

Table 3 Crystal data and structure refinement details for

[C6H16N2]2BiBr6NO3

Crystal data

Chemical formula (C6H16N2)2BiBr6NO3

Mr 982.87

Crystal system, space group Orthorhombic, P21212

Temperature/K 150

a, b, c/A 17.629(5), 20.279(5), 7.319(5)

V/A3 2617(2)

Z 4

Radiation type Mo Ka

l/mm-1 15.92

Crystal size/mm 0.45 9 0.26 9 0.17

Data collection

Diffractometer APEXII, Bruker-AXS diffractometer

Absorption correction Multi-scan (SADABS; Bruker, 2006)

Tmin, Tmax 0.006, 0.067

No. of measured,

independent and observed

[I[ 2r(I)] reflections

22944, 5977, 4790

Rint 0.085

(sin h/k)max/A-1 0.649

Refinement

R[F2[ 2r(F2)], wR(F2), S 0.051, 0.129, 1.03

No. of reflections 5977

No. of parameters 250

H-atom treatment H-atom parameters constrained

Dqmax, Dqmin/e A-3 2.60, -1.06

Absolute structure parameter -0.032(13)

M. Essid et al.

123

Centre, 12 Union Road, Cambridge CB2 1EZ, UK; e-mail:

deposit@ccdc.cam.uk.

Acknowledgments This work is supported by the Tunisian National

Ministry of Higher Education and Scientific Research.

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