Synthesis and characterisation of tetrazole compounds: 3 Series of new ligands representing versatile building blocks for iron(II) spin-crossover compounds

Article abstract of DOI:10.1016/j.molstruc.2004.07.036

New tetrazole compounds were synthesized and characterised by NMR and FTIR spectroscopy as well as by single crystal X-ray diffraction. We present in this paper mono- and ditetrazoles, which represent a versatile class of building blocks for the formation of mononuclear iron(II) complexes with monotetrazoles as terminal ligands as well as iron(II) coordination polymers with ditetrazoles as bridging ligands. Especially, the series of α,ω-bis[tetrazol-1- yl]-alkanes open the field of fascinating supramolecular structures with spin transition properties.

Full text of DOI:10.1016/j.molstruc.2004.07.036

Journal of Molecular Structure 733 (2005) 41–52
www.elsevier.com/locate/molstruc
Synthesis and characterisation of tetrazole compounds: 3 series
of new ligands representing versatile building blocks
for iron(II) spin-crossover compounds
a,b
a,
a
c
*
C. Matthias Grunert , Peter Weinberger , Johannes Schweifer , Christina Hampel ,
Arno F. Stassena,d, Kurt Mereitere, Wolfgang Linerta
aInstitute of Applied Synthetic Chemistry, Vienna University of Technology, Getreidemarkt 9/163-AC, Vienna A-1060, Austria
bInstitute for Inorganic and Analytical Chemistry, Johannes-Gutenberg University Mainz, Staudingerweg 9, Mainz D-55099, Germany
c
¨
Gesellschaft zur Forderung von Medizin-, Bio- und Umwelttechnologien e.V., Merseburger Str. 371, Halle/Saale D-06132, Germany
dKavli Institute of Nanoscience Delft, Delft University of Technology, Lorentzweg 1, 2628 CJ Delft, The Netherlands
eInstitute of Chemical Technologies and Analytics, Vienna University of Technology, Getreidemarkt 9/164-SC, Vienna A-1060, Austria
Received 13 May 2004; revised 26 July 2004; accepted 27 July 2004
Available online 11 September 2004
Abstract
New tetrazole compounds were synthesized and characterised by NMR and FTIR spectroscopy as well as by single crystal X-ray diffraction.
We present in this paper mono- and ditetrazoles, which represent a versatile class of building blocks for the formation of mononuclear iron(II)
complexes with monotetrazoles as terminal ligands as well as iron(II) coordination polymers with ditetrazoles as bridging ligands. Especially,
the series of a,u-bis[tetrazol-1-yl]-alkanes open the field of fascinating supramolecular structures with spin transition properties.
q 2004 Elsevier B.V. All rights reserved.
Keywords: Tetrazole; Crystal structure; FTIR spectroscopy; NMR spectroscopy
1. Introduction
or hysteresis effects we want to present in this paper the
synthesis and characterisation of three sets of ligands.
These above mentioned spin transition properties depend
not only on the intrinsic electronic and steric features of the
ligand used, but on the subtle interplay of stabilizing
interactions between the ligands forming the structural
backbone of the compound and the counteranions and
maybe solvates within the crystal lattice. In the quest to
reveal the influence of these parameters we want to alter
only one of them within each of the three series of otherwise
rather similar ligands.
Since Franke et al. [1] synthesized N1-substituted
tetrazoles as ligands of iron(II) spin-crossover compounds
in the beginning of the 1980s a lot of homologous alkyl-
substituted ligands have been prepared [1,2]. It was with this
class of compounds that a systematic investigation of effects
influencing the spin transition behaviour has been per-
formed. Gu¨tlich et al. [3] described the pressure dependency
as well as the LIESST effect for [Fe(ptz)6](BF4)2 with ptzZ
1-propyl-1H-tetrazole giving a new boost to investigations
in the field of spin-crossover compounds. To contribute to
the elucidation of the different factors governing the spin
transition behaviour in terms of the spin transition
temperature T1/2, the abruptness of the spin transition
Aiming for an insight into the effect of variation of
terminal substituents of the alkyl side-chain of the tetrazole
moiety we synthesized 1-ethyltetrazoles teeX (XZF, Cl, Br
and I). Due to this variation, we are able to fine-tune the
electronic influence on the coordinating N4 of the tetrazole
ring thus yielding a 100 K up-shift of T1/2 upon varying
from F/I [4,5].
* Corresponding author. Tel.: C158-80115352; fax: C158-80116299.
E-mail addresses: weinberg@mail.zserv.tuwien.ac.at (P. Weinberger),
wlinert@mail.zserv.tuwien.ac.at (W. Linert).
In recent years, a few bridging bis-tetrazoles have been
prepared consisting of a rather short aliphatic chain-type
0022-2860/$ - see front matter q 2004 Elsevier B.V. All rights reserved.
doi:10.1016/j.molstruc.2004.07.036

42
C.M. Grunert et al. / Journal of Molecular Structure 733 (2005) 41–52
linker between the tetrazole moieties, e.g. 1,2-bis(tetrazole-
1-yl)ethane (btze) [6,7], 1,2-bis(tetrazole-1-yl)propane
(btzp) [8] and 1,4-bis(tetrazole-1-yl)butane (btzb) [9].
With these ligands iron(II) spin-crossover coordination
polymers have been obtained forming 1D chains (btze and
btzp) or 3D networks (btzb) [10]. Based on recent
achievements [11], we report the synthesis of homologous
a,u-bis(tetrazole-1-yl)alkanes (nditz) with longer even-
numbered alkyl spacers (hexane/dodecane) to enable the
formation of manifold interlocked 3D networks. Further-
more, it might be interesting to gain insight into flexible
connected iron(II) spin-crossover centers forming new
materials like folia and/or coatings with desired features.
As progress in the design of technical applications like
optical display devices [12] were made with powdered
microcrystalline iron(II) triazole compounds [13], a ductile
material would open new perspectives for the applicability
of such materials.
The structures were then solved with direct methods using
SHELXS97 [17] followed by structure refinements on F2
with program SHELXL97 [17]. Non-hydrogen atoms were
refined anisotropically. Hydrogen atoms were inserted in
calculated positions and refined with the riding model.
Crystallographic details are given in Table 1. Selected
bond lengths and angles are presented in Table 2. CCDC
244395-244404 contains the supplementary crystallo-
graphic data for this paper. These data can be obtained
free of charge via www.ccdc.cam.ac.uk/data_request/cif,
by emailing data_request@ccdc.cam.ac.uk, or by contact-
ing The Cambridge Crystallographic Data Centre, 12,
Union Road, Cambridge CB2 1EZ, UK; fax:C44-1223-
336033.
Chemicals. NaN3 (99%), triethylorthoformate (99%),
glacial acetic acid (99%), a,u-diaminoalkane (O98%) and
NaOH (97%) were obtained from Aldrich. All other
chemicals were standard reagent grade and used as
supplied.
For the third set of ligands aromatic substituents instead
of the alkyl side chain have been chosen. Unfortunately,
these aryl-substituted tetrazoles turned out not to coordinate
to iron(II) but to copper(II) successfully. Due to their
Jahn-Teller distortion these compounds structurally deviate
from iron(II) analogues [14], but may be interesting
because of other magnetic interactions, e.g. ferromagnetic
behaviour [15].
3. Results and discussion
3.1. Synthesis and characterisation
A general synthesis of 1-substituted tetrazoles is
described by Franke et al. [1]. Some modifications
were made to obtain the teei [13] and aromatic
substituted tetrazoles. Furthermore, especially for the
bis-tetrazole compounds the synthetic pathway was
optimized in order to obtain good quality products in
sufficient yields.
2. Experimental
General procedures and spectroscopy. Elemental ana-
lyses (C, H and N) were performed by the Mikroanaly-
tisches Laboratorium, Institute for Physical Chemistry,
¨
Vienna University, Wahringerstrasse 42, Vienna A-1090,
1
3.1.1. 2-(1-haloethyl)-tetrazoles (teeX)
Austria. H-NMR and 13C-NMR in deuterated d6-DMSO
teeCl. The synthesis was described by Stassen et al. [5].
But as their NMR analysis was made in DMSO, measure-
ments in CDCl3 are presented here for the reason of
comparison of all presented compounds (Fig. 1).
1H-NMR (250.13 MHz, d1 CDCl3) d [ppm]: 8.78 (s, 1H,
or d1-CDCl3 were measured using a Bruker 250 FS FT-
NMR spectrometer. Proton NMR chemical shifts are
reported in ppm versus TMS. Mid-range FTIR spectra of
the compounds were recorded as KBr-pellets within the
range 4400–450 cmK1 using a Perkin–Elmer 16PC FTIR
spectrometer. Pellets were obtained by pressing the
powdered mixture of the samples in KBr in vacuo using
a hydraulic press applying a pressure of 10.000 kg/cm2 for
5 min. Far FTIR spectra were recorded within the range
600–200 cmK1 on a Perkin–Elmer System 2000 far FTIR
spectrometer in a polyethylene matrix.
3
3
Ha); 4.81 (t, JZ5.4 Hz, 2H, Hb); 3.95 (t, JZ5.5 Hz, 2H,
Hc); 13C-NMR (62.86 MHz, d1 CDCl3) d [ppm]: 144.0 (Ca);
50.5 (Cb); 42.5 (Cc).
teeF, teeBr, teeI. The syntheses of these compounds were
described by Stassen et al. [5]. teeF is a liquid at room
temperature. Purification was done via complexation with
CuBr2 and re-extraction of the compound in chloroform. For
the synthesis of teeI a Finkelstein reaction was used. Data of
elemental analysis and NMR in DMSO can also be found in
the reference given above; NMR data in CDCl3 are given
below.
teeF. The NMR spectra show distinct 19F–1H and
19F–13C spin coupling.
1H-NMR (250.13 MHz, d1 CDCl3) d [ppm]: 8.88/8.86
(s, 1H, Ha); 4.81 (m, 2H, Hc); 4.66 (m, 2H, Hb).
13C-NMR (62.86 MHz, d1 CDCl3) d [ppm]: 144.1 (Ca);
82.6/79.9 (Cc); 49.2/48.9 (Cb).
Crystallographic studies. Single crystals of all
measured compounds were glued to glass fibers and
transferred to a Bruker SMART diffractometer (graphite
monochromated Mo Ka radiation from a sealed X-ray
˚
tube, lZ0.71073 A, platform 3-circle goniometer, CCD
area detector) and intensity data were collected at room or
at low temperature. After raw data extraction with
program SAINT, absorption and related effects were
corrected with program SADABS (multi-scan method) and
data analysis was carried out with program XPREP [16].

C.M. Grunert et al. / Journal of Molecular Structure 733 (2005) 41–52
43
Table 1
Details for the crystal structure determinations of compounds teeX (XZCl, Br, I), nditz (nZ6,8,10,12), pytz, and naphtz
teeCl
TeeBr
teeI
6ditz
8ditz
10ditz
12ditz
pytz
naphtz
Formula
fw
C3H5ClN4
132.56
P21/n
C3H5BrN4
177.02
P21/n
C3H5IN4
224.01
P21
C8H14N8
222.27
P21/n
C10H18N8
250.32
P21/c
C12H22N8
278.38
C2/c
C14H26N8
306.43
P21/c
C6H5N5
147.15
P21/c
C11H8N4
196.21
P21/c
Space group
(no. 14)
6.711(3)
13.808(5)
6.892(3)
117.26(1)
567.7(4)
4
(no. 14)
6.681(3)
13.653(6)
6.960(4)
115.84(2)
571.4(5)
4
(no. 4)
5.3868(5)
7.1815(7)
8.7660(8)
96.872(2)
336.7(1)
2
(no. 14)
4.621(1)
17.927(3)
7.387(1)
106.988(3)
575.4(2)
2
(no. 14)
9.562(2)
5.448(1)
12.610(2)
94.838(3)
654.6(2)
2
(no. 15)
28.425(5)
5.366(1)
10.473(2)
110.154(3)
1499.5(4)
4
(no. 14)
15.254(3)
5.461(1)
10.303(2)
107.253(4)
819.6(3)
2
(no. 14)
3.811(2)
14.867(7)
11.887(6)
91.45(2)
673.3(6)
4
(no. 14)
4.525(3)
11.323(7)
18.469(9)
91.96(2)
945.7(10)
4
˚
a (A)
˚
b (A)
˚
c (A)
b (deg)
3
˚
V (A )
Z
rcalc (g cmK3
)
1.551
2.058
2.210
1.283
1.270
1.233
1.242
1.452
1.378
T (K)
296(2)
296(2)
296(2)
4.661
297(2)
0.090
183(2)
0.086
123(2)
123(2)
297(2)
0.101
297(2)
0.089
m (mmK1
(Mo Ka)
F(000)
)
0.559
7.082
0.082
0.082
272
30
344
208
236
27
268
600
332
304
408
qmax (deg)
30
25
30
30
30
30
25
No. of rflns meads 6020
No. of unique rflns 1623
4255
1633
1156
3434
1193
1120
3490
1244
944
8520
1866
1637
9138
2034
1757
5787
2314
1891
4667
1862
1239
4120
1459
1182
No. of rflns IO
2s(I)
1294
No. of params
R1 (IO2s(I))a
R1 (all data)
wR2 (all data)
Diff. Four. peaks
75
75
74
74
83
92
100
121
137
0.0286
0.0338
0.0747
0.0285
0.0431
0.0661
0.0336
0.0356
0.0921
0.0396
0.0529
0.1151
0.0343
0.0396
0.0984
0.0403
0.0463
0.1082
0.0374
0.0495
0.1056
0.0424
0.0679
0.1288
0.0477
0.0570
0.1332
K0.25/0.22 K0.71/0.71 K0.79/0.53 K0.12/0.14 K0.20/0.33 K0.18/0.43 K0.21/0.29 K0.19/0.19 K0.14/0.18
K3
˚
min/max (e A
)
a
2
2
1=2
R1 ZSjjFojKjFcjj=SjFoj; wR2 Z½SðwðFo2 KFc2Þ Þ=SðwðFo2Þ ÞŠ
.
1
teeBr. H-NMR (250.13 MHz, d1 CDCl3) d [ppm]: 8.84
teeI. 1H-NMR (250.13 MHz, d1 CDCl3) d [ppm]: 8.79 (s,
3
3
3
3
(s, 1H, Ha); 4.89 (t, JZ5.8 Hz, 2H, Hb); 3.78 (t, JZ
5.7 Hz, 2H, Hc).
13C-NMR (62.86 MHz, d1 CDCl3) d [ppm]: 143.9 (Ca);
50.3 (Cb); 29.5 (Cc).
1H, Ha); 4.84 (t, JZ6.6 Hz, 2H, Hb); 3.59 (t, JZ6.6 Hz,
2H, Hc).
13C-NMR (62.86 MHz, d1 CDCl3) d [ppm]: 143.4 (Ca);
50.9 (Cb); 0.359 (Cc).
Table 2
Selected bond lengths and angles (A and deg) of compounds teeX (XZCl, Br, I), nditz(nZ6,8,10,12), pytz, and naphtz
˚
teeCl
1.336(1)
teeBr
1.320(3)
teeI
6ditz
8ditz
1.346(1)
10ditz
1.347(1)
12ditz
1.346(1)
pytz
naphtz
1.356(2)
N1–N2
1.296(10)
1.318(9)
1.341(2)
1.295(2)
1.351(2)
1.310(2)
1.321(2)
1.472(2)
1.517(2)
1.529(2)
1.519(3)
1.345(2)
1.289(2)
1.354(2)
1.296(2)
1.334(2)
1.430(2)
1.379(2)
1.369(2)
1.376(2)
1.378(2)
1.335(2)
1.323(2)
N2–N3
1.291(1)
1.346(2)
1.309(2)
1.321(1)
1.454(1)
1.499(2)
1.789(1)
1.274(3)
1.340(3)
1.286(3)
1.309(3)
1.440(3)
1.478(3)
1.920(3)
1.301(1)
1.356(1)
1.318(1)
1.334(1)
1.467(1)
1.522(1)
1.527(1)
1.523(1)
1.527(2)
1.295(1)
1.358(1)
1.319(1)
1.336(1)
1.459(1)
1.522(1)
1.522(1)
1.526(1)
1.524(1)
1.526(2)
1.300(1)
1.361(1)
1.317(1)
1.337(1)
1.462(1)
1.522(1)
1.524(1)
1.526(1)
1.524(1)
1.528(1)
1.523(2)
1.295(2)
1.357(2)
1.302(2)
1.344(2)
1.438(2)
1.412(2)
1.362(3)
1.425(3)
1.424(2)
1.412(2)
1.372(2)
N3–N4
1.358(10)
1.310(12)
1.334(9)
N4–C1
C1–N1
N1–C2
1.493(10)
1.441(12)
2.164(10)
C2–C3
C3–X/C4
C4–C40/C5
C5–C50/C6
C6–C60/C7/N5
C7–C70/N5–C2
N1–C1–N4
C1–N1–C2
N2–N1–C2
C1–N1–N2
N1–N2–N3
N2–N3–N4
N3–N4–C1
C1–N1–C2–C3
N1–C2–C3–X/C4
109.8(1)
109.8(2)
106.4(6)
109.7(1)
109.4(1)
109.1(1)
109.2(1)
109.9(1)
110.0(2)
131.1(1)
121.3(1)
107.6(1)
106.8(1)
110.6(1)
105.2(1)
K85.4(1)
68.5(1)
131.2(2)
121.1(2)
107.7(2)
106.9(2)
110.3(2)
105.3(2)
K87.8(3)
69.2(2)
121.8(7)
130.1(6)
108.1(6)
111.3(6)
103.9(6)
110.3(5)
K59.4(7)
K179.9(6)
130.4(1)
121.8(1)
130.3(1)
121.7(1)
108.0(1)
106.4(1)
110.8(1)
105.4(1)
K93.5(1)
177.8(1)
130.7(1)
121.1(1)
130.6(1)
121.2(1)
108.2(1)
106.4(1)
110.9(1)
105.3(1)
K98.6(1)
K168.9(1)
130.4(1)
122.0(1)
131.5(2)
121.6(1)
106.9(1)
106.6(2)
110.9(2)
105.6(2)
11.9(3)
107.9(1)
108.2(1)
107.6(1)
106.6(1)
106.3(1)
106.0(1)
110.6(1)
111.2(1)
111.3(1)
105.3(1)
105.2(1)
105.2(1)
K107.9(1)
K179.8(1)
K102.8(1)
K179.3(1)
K178.4(1)
K179.2(1)
179.1(2)

44
C.M. Grunert et al. / Journal of Molecular Structure 733 (2005) 41–52
separated, washed with NaHCO3 solution and dried with
Na2SO4. The ether was removed and the product re-
crystallized in ethanol. Yields and melting points were: pytz,
1
20%, 125–126.5 8C; naphtz, 10%, 114–115.5 8C. The H-
and the 13C-NMR data are listed as follows:
Fig. 1. 2-(1-haloethyl)-tetrazole (teeX) with XZF, Cl, Br, I.
1
Pytz. H-NMR (250.13 MHz, CDCl3, 293 K) dH [ppm]:
9.53 (s, 1H, Ha); 8.53 (m, 3JfeZ5.2 Hz, 4JfdZ1.7 Hz, 5JfcZ
3.1.2. a,u-bis(tetrazol-1-yl)-alkane (nditz)
3
4
0.9 Hz 1H, Hf); 8.06 (m, JcdZ8.2 Hz, JceZ1.2 Hz 4H,
Hc); 7.98 (m, 3Jdc,deZ7.3 Hz, 4Jdb,dfZ1.8 Hz, 1H, Hd); 7.44
(m, 1H, He); 13C-NMR (62.86 MHz, CDCl3 293 K) d [ppm]:
149.7 (Ca); 140.7 (Cf); 140.4 (Cc); 125.5 (Cd); 115.0 (Ce).
The synthesis of 2ditz and 4ditz was already described in
Schweifer et al. [6] and Koningsbruggen et al. [9],
respectively. For nditz with nZ6, 8, 10 and 12, the
respective a,u-diaminoalkane, sodium azide, and triethyl
orthoformate in molar ratios of 0.15: 0.3: 0.3 were heated to
90 8C in 150 ml of acetic acid for 4 h. After adding another
0.05 mol of sodium azide and 0.3 mol of triethyl orthofor-
mate the reaction solution was stirred at 90 8C for further
12 h. For a last time, 0.05 mol of sodium azide and 0.3 mol
of triethyl orthoformate were added and the reaction was
kept stirring at 90 8C for additional 24 h. Most of the solvent
was removed using a rotavapor. The residue was neutralized
to pHZ8–9 using conc. Na2CO3. The raw product crystal-
lised in water and was re-crystallised from ethanol. The
product was dried in vacuum over P2O5. Yields and melting
points were: 6ditz, 33%, 108–109 8C; 8ditz, 40%, 101–
102 8C, 10ditz, 25%, 105.5–107.5 8C; 12ditz, 30%, 109–
110 8C.
Naphtz. 1H-NMR (250.13 MHz, CDCl3, 293 K) dH
4
[ppm]: 9.13 (s, 1H, Ha); 8.18 (d, JckZ2.0 Hz 1H, Hc);
3
8.06 (d, JjkZ8.5 Hz, 1H, Hj); 7.98 (m, 1H, Hk); 7.94 (m,
1H, He); 7.81 (m, 3JhgZ9.0 Hz, 4JhfZ1.2 Hz, 1H, Hh) 7.65
(m, 1H, Hf); 7.61 (m, 1H, Hg).
1
The H- and the 13C-NMR data are listed as follows:
6ditz. 1H-NMR (300 MHz, d1 CDCl3) d [ppm]: 8.61
3
3
(s, 2H, Ha); 4.44 (t, JZ7.1 Hz, 4H, Hb); 1.97 (m, JZ
7.0 Hz, 4H, Hc); 1.39 (m, 4H, JZ3.7 Hz, Hd); 13C-NMR
3
(62.86 MHz, d1 CDCl3) d [ppm]: 143.2 (Ca); 48.7 (Cb); 30.2
(Cc); 26.3 (Cd).
13C-NMR (62.86 MHz, CDCl3 293 K) d [ppm]: 141.3
(Ca); 134.0 (Cd); 133.7 (Cj); 131.8 (Cb); 131.3 (Cg), 129.0,
128.7, 128.6, 128.5 (Cf,h,i,k).
8ditz. H-NMR (250.13 MHz, d1 CDCl3) d [ppm]: 8,61
1
3
3
(s, 2H, Ha); 4,42 (t, JZ7.1 Hz, 4H, Hb); 1.93 (m, JZ
7.1 Hz, 4H, Hc); 1.33 (m, 4H, Hd); 1.31 (m, 4H, He), 13C-
NMR (62.86 MHz, d1 CDCl3) d [ppm]: 143.1 (Ca); 49.0
(Cb); 26.7 (Cc); 30.3 (Cd); 29.1 (Ce).
3.2. Crystal structures of teeCl, teeBr and teeI
Of the four 2-(1-haloethyl)tetrazoles teeX, the F com-
pound is liquid at room temperature, the Cl and Br
compounds are isostructural and crystallize in monoclinic
lattices of space group symmetry P21/n with each four
molecules in the unit cell and with cell dimensions given in
Table 1, whereas the I-compound adopts a different lattice,
also monoclinic but with space group symmetry P21 and only
two molecules per unit cell. The molecular structures of
teeCl (teeBr not shown because it is analogous to teeCl) and
teeI are shown in Fig. 2 (vide infra). teeCl and teeBr exhibit
1
10ditz. H-NMR (300 MHz, d1 CDCl3) d [ppm]: 8,63
3
3
(s, 2H, Ha); 4,42 (t, JZ7.2 Hz, 4H, Hb); 1.93 (m, JZ
7.0 Hz, 4H, Hc); 1.29 (m, 4H, Hd); 1.26 (m, 8H, He,f); 13C-
NMR (70 MHz, d1 CDCl3) d [ppm]: 143.1 (Ca); 49.0 (Cb);
26.8 (Cc); 30.4 (Cd); 29.65 (Ce); 29.32 (Cf).
1
12ditz. H-NMR (300 MHz, d1 CDCl3) d [ppm]: 8,63
3
3
(s, 2H, Ha); 4,42 (t, JZ7.2 Hz, 4H, Hb); 1.92 (m, JZ
7.0 Hz, 4H, Hc); 1.28 (m, 8H, Hd,e); 1.21 (m, 8H, Hf,g);
13C-NMR (70 MHz, d1 CDCl3) d [ppm]: 143.1 (Ca); 49.0
(Cb); 26.8 (Cc); 30.4 (Cd); 29.8 (Ce); 29.8 (Cf); 29.3 (Cg).
3.1.3. Aryltetrazoles (aryltz)
0.05 mol of 1-aminopyridin or b-naphthylamine and
equimolar amounts of triethyl orthoester and of sodium
azide together with 300 ml of acetic acid were heated to
100 8C for 1 week. Subsequently the acetic acid was
removed under reduced pressure. The raw product was
dissolved in diethyl ether and aq. NaHCO3 solution, the
insoluble fraction was filtered off. The ether phase was
Fig. 2. The thermal ellipsoid plots (20% electron density ellipsoids) of teeCl
(teeBr is isostructural)—left—and teeI—right—show the significant
difference in the orientation of the halogen.

C.M. Grunert et al. / Journal of Molecular Structure 733 (2005) 41–52
45
transition at lower temperatures, but this aspect was outside
the scope of the present work.
3.3. Crystal structures of a,u-bis(tetrazol-1-yl)alkanes
(nditz)
In this section we discuss molecular and lattice
structures of the new compounds 6ditz through 12ditz.
The crystal structures of 2ditz and 4ditz previously
reported by Schweifer et al. [6,7] and Koningsbruggen
et al. [9] are also included in order to complement
the picture of the whole series of nditz with even n
between 2 and 12. All these compounds crystallize in
centrosymmetric monoclinic lattices of space group type
P21/c/P21/n, except for 10ditz which crystallizes in space
group C2/c. The molecular structures of 2ditz through
12ditz (nZeven) are depicted in Fig. 4 and salient
geometric data of 6ditz through 12ditz are given in
Table 2. It can be seen from Fig. 4 that all even-spaced
ditetrazolyl-alkanes adopt Ci as the common molecular
symmetry. Except for 4ditz, they all adopt trans-config-
ured alkyl chains representing the most stable configur-
ation in case of the free molecules. In case of the longer
alkyl chains, some distortive influence of the lattice
environment of the molecules can be noticed, however.
A good example for this is 12ditz which shows in a view
parallel to its alkyl carbon atom main plane a notable
S-shaped distortion stemming from packing (see below).
Only 4ditz shows a different conformation with gauche-
geometry of the N1–C–C–C moiety (N1–C2–C3–C30Z
65.18 where C30 is the Ci symmetric equivalent of C3).
The bond lengths and bond angles in all molecules show
Fig. 3. Packing diagrams of teeCl showing the pair-wise C–H/Cl
interactions (top) and of teeI showing intralayer I/N interactions as well as
the interlayer slipped p-stacking of the tetrazole rings (bottom).
a gauche-conformation of the haloethyl group whereas in
teeI it is trans. The torsion angles C1–N1–C2–C3 for teeCl
and teeBr are close to 908 (K85.4 and K87.88 for Cl and Br),
whereas in the I-compound it is lower (K59.48). Bond
lengths and angles in all three compounds are normal and
will be in part discussed below. Representative packing
diagrams of teeCl and teeI are shown in Fig. 3. The solid state
structures of teeCl and the isostructural teeBr do not show
any mutual p-stacking of the tetrazole moieties, but are
governed by weak intermolecular C–H/N and C–H/Cl/Br
interactions. Most significant among them are pairs of
angular C(1)–H(1)/N interactions, which link a pair of
teeCl/Br molecules via a centre of inversion (H(1)–N(4)Z
˚
usual values, i.e. C–CZ1.52–1.53 A in the alkyl chains,
˚
C–NZ1.46–1.47 A between tetrazole ring and alkyl
˚
chain, C–NZ1.31–1.34 A in the tetrazole rings, and N–
˚
NZ1.29–1.36 A in the tetrazole rings. The most reliable
geometric data of the tetrazole rings stem from 8ditz,
10ditz and 12ditz, which have been measured at low
temperatures. The ring mean bond lengths of these three
˚
˚
compounds are: N1–N2Z1.346 A, N2–N3Z1.300 A, N3–
˚
˚
˚
N4Z1.358 A, N4–C1Z1.318 A and C1–N1Z1.336 A.
These data point to a cyclodiene-like structure of the
ring, which can be observed in a related fashion also for
the other compounds listed in Table 2. The orientation of
the tetrazole rings relative to the alkyl chains is roughly
perpendicular to the mean plane of the alkyl C-atom
planes, but varies from compound to compound, as may
be seen from the torsion angles /C1–N1–C2–C3/Z93.5–
107.98 of 6ditz to 12ditz.
˚
˚
2.64 A for teeCl and 2.66 A for teeBr) whereas other pairs of
molecules are linked via pairs of C(3)–H(3B)/Cl/Br
˚
˚
interactions (H/ClZ2.89 A; H/BrZ2.95 A). Further
interactions between C–H and N/Cl/Br are present but
exhibit longer H–X distances. The solid state structure of teeI
is distinctly different from the Cl/Br compounds and shows a
pronounced layering parallel to (010) (Fig. 3, bottom).
Within these layers iodine is in close end-on contact with two
˚
˚
nitrogen atoms, I/N(3)Z3.43 A and I/N(4)Z3.58 A.
Coherence between the layers is provided by some p-
stacking interactions between the tetrazole rings. It should be
pointed out here that solid teeI is thermally quite active at
room temperature and showed large thermal displacement
parameters and significant diffuse scattering as well. It can be
speculated therefore that this compound is prone to a phase
Despite this uniformity in molecular geometries (except
for 4ditz) and space group symmetries (monoclinic P21/c or
P21/n except 10ditz), there are surprising differences in the
packing of the molecules in their crystal lattices. This stems
in part from the different types of intermolecular inter-
actions for the moieties of the ditetrazolylalkanes, namely
p-stacking between tetrazole rings, hydrogen bond-like

46
C.M. Grunert et al. / Journal of Molecular Structure 733 (2005) 41–52
Fig. 4. Thermal ellipsoid plots of 2ditz, 4ditz, 6ditz, 8ditz, 10ditz and 12ditz (from top to bottom).
C–H/N interactions between more acidic CH groups
(tetrazole C–H and a–CH2 groups) as donors and tetrazole
N atoms as acceptors, and alkyl–alkyl-chain van-der-Waals
interactions.
chains [also parallel to (010) at yw0, 1/2) with no prominent
mutualinteractions]. Inorder to achieve areasonable packing
density for the alkyl part of the structure, the butyl groups
have to be kinked (gauche instead of anti-conformation at
The structure of 2ditz, which has the lowest ratio alkyl-
chain to tetrazole, can be described as being built up from
layers of molecules parallel to (001) with internal coherence
by p-stacking between pairs of parallel tetrazole rings
supplemented by intra-layer C1–H1/N4 interactions
˚
(H/NZ2.73 A). These layers are then mutually linked
primarily by C1–H1/N3 and C2–H2/N4 interactions
˚
(H/NZ2.60 A), as shown in Fig. 5.
The outstanding molecular conformation of 4ditz can be
regarded as the result of a clear-cut differentiation of the
structure in layers parallel to (010) of p-stacked tetrazole
rings [layers at yw1/4, 3/4; ring orientation approximately
parallel to (001); mutually linked by in-layer C1–H1/N3
Fig. 5. Packing diagram of 2ditz showing the characteristic intra-layer
interactions and p-stacking of the tetrazole rings.
˚
interactions of H1/N3Z2.48 A] and in layers of butyl

C.M. Grunert et al. / Journal of Molecular Structure 733 (2005) 41–52
47
p-stacking. However, there are significant amounts of short
˚
C–C distances of approx. 4 A between neighbouring hexyl-
chains suggesting van-der-Waals interactions which con-
ꢀ
tribute to the coherence of the structure in ð101Þ direction
and perpendicular to the corrugated sheets.
The structure of 8ditz consists of flat layers of molecules
ꢀ
which are oriented parallel to ð101Þ and show intra-layer
interactions between C1–H1 and the nitrogen atoms N3
˚
and N4 (H1–N3Z2.56 A effective along the b-axis,
˚
Fig. 6. Packing diagram of 4ditz showing the p-stacked tetrazole rings
forming layers along the a-axis being mutually linked by in-layer
C1–H1/N3 interactions (alkyl hydrogen omitted for clarity).
and H1–N4Z2.72 A inclined to b) along the short b-axis
(Fig. 8). Within one layer all 8ditz molecules are oriented
parallel to each other whereas those of adjacent layers are
cross bedded. This arrangement enables alkyl–alkyl chain
interactions between molecules of the same layer with C–C
C2–C3), which helps to explain the uncommon conformation
of 4ditz in solid state (cf. Figs. 4 and 6).
˚
distances between 4.35 and 4.65 A. Weak and slipped
In contrast to the structures of 2ditz and 4ditz with their
dominant tetrazole ring p-stacking, the structure of 6ditz
shows much poorer p-stacking (Fig. 7). This structure
consists of corrugated sheets of molecules arranged in a
herring bone fashion and linked by C1–H1/N3 and
C2–H2A/N4 intra-layer interactions. These corrugated
sheets are oriented parallel to (101) and are stacked in a way
which concentrates tetrazole rings in one and alkyl chains in
another part of the structure. Mutual overlap of tetrazole
rings in stacking direction is poor (Fig. 7) and so is
p-stacking tetrazole interactions are limited because each
tetrazole ring faces only on one side nearby tetrazole rings
whereas on the opposite side it is exposed to alkyl chains.
The structure is reinforced by short inter-layer C2–H2A/
˚
N4 interactions (H2A–N4–2.62 A).
The structure of 10ditz differs from the other nditz
compounds by adopting different space group symmetry
(Table 1). It is built up from slightly corrugated layers of
ꢀ
molecules that ore oriented parallel to ð301Þ; as shown in
Fig. 9. In each layer the 10ditz molecules form parallel to
Fig. 7. The corrugated sheet structure of 6ditz roughly seen perpendicular (8a) and parallel (8b) to the sheets. Alkyl hydrogen atoms were omitted for clarity.
Fig. 8a shows on the left half three superimposed sheets and on the right half a single sheet with C1–H1/N3 intra-layer interactions.
Fig. 8. Packing of 8ditz crystalline state in a view (a) parallel to the b-axis and (b) perpendicular to the cross-bedded layers of the octyl-chains. Alkyl hydrogen
omitted for clarity. 9b shows one layer with three 8ditz ribbons under-laid by one layer with two 8ditz ribbons.

48
C.M. Grunert et al. / Journal of Molecular Structure 733 (2005) 41–52
Fig. 9. Packing diagrams of 10ditz showing the layered structure (a) and the cross-bedded herring-bone motif (b) (alkyl hydrogens omitted for clarity).
˚
the b-axis ribbons of molecules with parallel orientation, but
perpendicular to the b-axis the ribbons produce a herring
bone-like alternation (note the difference to 8ditz where the
molecules of one layer are all aligned parallel to each other).
Subsequent layers show cross-bedding again as in 8ditz.
Intralayer interactions in 10ditz comprise again C–H/N
alkyl–alkyl-chain contacts (e.g. C3–C4Z4.73 A, C4–C6Z
˚
˚
˚
4.18 A, C6–C6AZ4.03 A and C5–C7Z3.90 A). Perpen-
dicular to the layers the molecules adopt a cross-bedding,
but with a different symmetry than in 10ditz. Again the
tetrazole rings show only strongly slipped p-stacking on
one side whereas their second side is exposed to the alkyl
chains.
˚
bonds, namely C1–H1/N4 (H1–N4Z2.54 A) and
˚
C1–H1/N3 (H1–N3Z2.63 A), and alkyl–alkyl chain
van-der-Waals interactions with C–C-distances of approx.
3.4. Crystal structures of two aryltetrazoles
˚
4.4 A. p-stacking interaction between tetrazoles are poor
(cf. Fig. 9b).
The structure of 12ditz consists of slightly corrugated
In comparison to the alkyl tetrazoles, the two investi-
gated aryltetrazoles, pytz and naphtz, behave differently.
Both form essentially flat molecules in order to maximize
hybridization (Figs. 11 and 12). Bond lengths in their
tetrazole moieties do not differ significantly from those in
the alkyl series (Table 2). In pytz, the pyridine nitrogen is
syn-oriented to the tetrazole C–H group which is favourable
because of the special vicinity of the tetrazole H
and the pyridine N lone-pair. Therefore, the molecule is
almost perfectly flat. In naphtz, however, there is a short
ꢀ
layers of molecules parallel to the ð101Þ (Fig. 10). Within
these layers the basic arrangement of the molecules and
their interactions corresponds to that of 10ditz, i.e. parallel
to the b-axis ribbons of molecules aligned parallel to each
other, but perpendicular to the b-axis a herring bone
arrangement of the ribbons. Tetrazole–tetrazole inter-
actions within one layer correspond in principle to those
of 10ditz. Remarkably, the molecules adopt a notable
S-like shape (Fig. 10b) to achieve close van-der-Waals
˚
H1–H3 contact of 2.36 A for X-ray H-positions which
Fig. 10. Packing diagrams of 12ditz in views parallel and perpendicular to the 12ditz layers. Alkyl hydrogen atoms omitted for clarity. In Fig. 10b, a layer of 4C
5C4 molecules is under-laid by a layer of 3C3 molecules. Note the cross-bedded herring-bone motif and the notable S-like distortion of the dodecyl chains.

C.M. Grunert et al. / Journal of Molecular Structure 733 (2005) 41–52
49
molecule, c.f. Fig. 12) and the stacking distance is only
˚
3.3 A. In adjacent rods the molecules are mutually inclined
offering the possibility of C–H–p interactions which are a
characteristic feature of aromatic hydrocarbons, e.g.
naphthalene [18]. Moreover, a significant C3–H3/N3
˚
interaction (H3–N3Z2.71 A) contributes to the lateral
cohesion of the structure.
3.5. Infrared spectroscopy
Mid-range FTIR spectra of all the compounds as KBr
pellets have been recorded within the range of 4400–
450 cmK1 at room temperature. For the interpretation of the
spectra, the observed data have been compared with general
tables in the book of Hesse et al. [19], several publication of
similar tetrazole compounds [11,20–25] as well as with the
educt spectra. Table 3 gives an overview of the obtained IR
data, which is the basis for the following discussion dealing
with changes within a series of ligands (teeX, nditz, and
aryltz) and the comparison of the different ligand series as a
whole.
Fig. 11. Molecular structure (top) and perspective packing diagrams
(bottom) of pytz. View directions of the packing diagrams are along b
(bottom left) and slightly inclined to a (bottom right).
enforces an inclination of 11.9(1)8 of the tetrazole ring
relative to the naphthyl moiety. The crystal packing in pytz
is characterized by the association of Ci related pairs of
molecules linked via pairs of weak intermolecular C1–H1–
N5 interactions. Controlled obviously by further C–H–
The most significant changes within one of these series
are found for the different halo-ethyl tetrazoles. A trend
towards a decrease in energy with increasing size of the
halogen substituent can be observed for the N1–Calkyl
˚
Ntetrazole interactions (C4–H4/N3, H4–N3Z2.64 A;
˚
C5–H5/N3, H5–N3Z2.63 A) these pairs form almost
ꢀ
perfect layers parallel to ð102Þ of the unit cell (Fig. 11)
stretching vibration (nN –Calkyl) at about 1355 cmK1, a
1
which are mutually p-stacked with layer–layer separations
˚
of approximately 3.45 A. This situation is notably different
stretching of the Ctz–N1 bond, which influences an in-plane
Ctz–H deformation (dC –H) at about 1100 cmK1 and an in-
tz
from naphtz (Fig. 12). There the molecules are p-stacked in
rods parallel to the a-axis with a distinct slip between
neighbouring molecules (first benzene ring of the naphthyl
moiety is above the tetrazole ring of an under-lying
molecule and below the second benzene ring of an opposite
plane ring vibration (dring2), which shifts from teeF at
963 cmK1 to teeI at 900 cmK1. The opposite effect is
observed for an in-plane ring vibration (dring1) around
1260 cmK1 as well as for the C–H2 deformations (dC–H2 and
gH2C–CH2). For the dC–H2 vibration the H–C–H angle
changes, whereas for gH2C–CH2 the C–H2 groups change
their position with respect to each other having their H–C–H
angle fixed.
Generally, the energy changes within the series of a,u-
bis(tetrazol-1-yl)-alkanes are not that significant with the
only exemption of the nN –Calkyl, for which the energy
1
increases with the enlargement of the molecule, which is in
contrast to the tendency found for the teeX compounds. Due
to the formation of a conjugated p-system involving the
whole molecule for both aryl substituted tetrazole com-
pounds significant changes in energies are observed, e.g. for
nN2ZN3 and nN –Caryl with shifts of 29 and 16 cmK1
,
1
respectively. The comparison of both investigated series of
tetrazole ligands yields quite a distinguishable image.
The C–H stretching vibration of the tetrazole ring (nC–H
)
is one of the most characteristic bands of a tetrazole moiety.
The sharp band at a high energy position well above
3100 cmK1 does not show any band overlapping in all of
our investigated compounds (except for both aryltz).
Generally speaking, the comparison within all series
revealed a rather typical absorption frequency of approx.
3120 cmK1. For the teeX series this band features an
up shift of about 20 cmK1 towards higher energies varying
Fig. 12. Molecular structure (top) and perspective packing diagram
(bottom) of naphtz (naphthyl H atoms omitted). Note the inclination of
11.9(1)8 of the tetrazole ring relative to the naphthyl moiety.

Table 3
Prominent mid IR bands of all three series of substituted tetrazole ligands
Compound
teeF
teeCl
teeBr
teeI
2ditz
4ditz
6ditz
8ditz
10ditz
12ditz
pytz
naphtz
n(C–H)19–21
3138s
3142s
3136s
3142s
3121vs
3025m,
2978w
3117vs
2962m,
2945w,
2925w,
2869vw
3115s
3117s
3119s
3116s
3120m
3127m
n(C–H)13 (of aliphatic C–H2 and
3003w,
3031m,
3009w,
2974m,
2908m
1618w,
1598m
1574w
1486s
3040m,
3005m,
2976m,
2952w
1601m
3027m,
2999w,
2961w
2952m,
2919m,
2855w
2935vs,
2904m,
2864w
2937vs,
2917vs,
2849s
2942s,
2916vs,
2849s
3098w,
3067vw,
3038vw
3072vw,
3055vw
C–H3 groups or in case of pytz und 2972m,
naphtz aromatic C–H of the
naphthalene and pyridine)
n(CaC)18 aromatic
2909w
n(CaN)18 aromatic
n(N2aN3)20–23 {Cg(C5–N1)C
n(Calkyl–N1)}
1487s
1481s
1485s
1480s
1492s
1492s
1485m
1482m
1482m
1468vs
1393m
1484m
1364w
d(C–H2)18
1429m,
1434m
1435m,
1423m
1432m,
1419m
1443m,
1425m
1444s
1428s
1450s,
1422m
1462s,
1447m,
1428m
1471m,
1455w,
1435m
1470s,
1458w,
1335m,
1424m
1382m
1470vs,
1450w,
1437m,
1424m
1376w
18
n(N1–Calkyl
n(C–F)18,24
)
1363m
1263m
1246m
1174vs
1107s
1358m
1355am
1353m
1324m
1359m
1374m
1371m
d(ring1)19–21
1255m
1176vs
1101s
1075sh
1041m
971s
1265s
1174vs
1098s
1090sh
1033m
968s
1263m
1172vs
1096s
1089w
1042w
970s
1253s
1243m
1173vs
1126w
1107vs
1033w,
1007w
1264m
1176vs
1126s
1251m
1170vs
1115s
1268w
1169vs
1111vs
1097s
1260w
1167vs
1110s
1213s
1210m
1183w
1091vs
n(CaN4), n(N1–N2)21
n(Ctz–N1), d(Ctz–H)21
n(C–C)18
1170vs
1121s
1179m
1091vs
1097vs
1021m
1097vs
1047w,
1026w,
1015w
1096s
1097s
n(N3–N4)19–21Cn(N1–N2)21
1041s
973sh
1045w,
1032w
1064w,
1028m
1075w,
1033w
1042w,
1008m,
1001w
951m
1039m,
1017w,
1006w
960w
d(ring2)20,21 in-plane bending
{d(NCN), d(NNN)}
g(Ctz–H)20,21
963m
947m
930m
900m
965s
970s,
925m
886m
791s
964s 909sh 970s
968m
969s
880sh
858s
914s
875s
914m
888sh
909s
770s
897s
896s
904m
745m,
740sh
908m
726w,
746m,
732w
893w
883m
g(H2C–CH2)18
892s, 872s 881s
751s,
736sn
755w,
740m,
728w
g(aromatic)18
g(ring3)121 out-of-plane
g(ring4)20,21 out-of-plane
784s
760s, 753s
714w
722m
679s
721m
677s,
667vs
461s
720m
673vs
717w
660vs
722m
691w,
671m
723m
720m
720w
670s
720m
672s,
677m
719s
717m
657m,
620m
670s, 647s 666vs,
647w
672s,
667m
665m,
634m
n(C–Cl)24
Frequencies in cmK1; n, stretching; d, deformation or in-plane vibration of the ring; g, out-of-plane; vs, very strong; s, strong; m, medium; w, weak; vw, very weak; sh, shoulder, b, broad.

C.M. Grunert et al. / Journal of Molecular Structure 733 (2005) 41–52
51
Fig. 13. Graphical comparison of several prominent IR bands.
XZF/I. Exactly the opposite trend is observed for the
nC –N1 and the dC –H vibration, which downshifts from
of the tetrazole rings plays an influential role for the nditz
compounds with rather short alkyl-spacer. Nevertheless, the
one important contribution for the stabilization of this class
of compounds comes from a C1–H1/N4 or N3 interaction
of neighbouring molecules thus governing the mutual
orientation of the molecule as a whole. A second interaction
of hydrogen of the a-CH2 groups towards nitrogen of this
neighbouring assists in the formation of molecular layers.
Especially, the nditz compounds of intermediate length
(nZ4, 6) favour corrugated layers whereas with larger chain
lengths flat layers are formed. These layers themselves can
stack differently featuring cross-bedded herring-bone
motifs when seen perpendicular to the layers with varying
cross-angles between the molecular orientations of neigh-
bouring layers, which is quite usual for long chained
n-alkanes [26].
tz
tz
1107/1096 cmK1 for teeX (XZF/I). No significant
changes are experienced by a lot of in-plane and out-of-
plane vibrations, e.g. nN2ZN3, nN1–N2 and gring3, especially.
A graphical representation of the most prominent
vibrational features is given in Fig. 13.
4. Conclusions
The comparison of the three sets of ligands elucidates the
kind of factors governing and influencing their crystal
packing in order to stabilize the solid-state structures. In the
teeX compounds the geometric factor (i.e. the size of
the substituent) becomes dominating only for the I, whereas
the electronic interactions between the halogen and the
acidic H of a neighbouring molecule dominates for the other
teeX compounds.
Finally, the two aryl-substituted tetrazoles are dominated
by p–p, C–H/N, and for naphtz also by C–H/p
interactions.
Based on these three sets of tetrazole compounds, we
aim to broaden the number of useful ligands to make
series of maybe structurally related iron(II) spin-cross-
over compounds. A systematic study of the factors
governing the spin-transition behaviour of these com-
pounds can only be performed having a reasonably big
set of samples at hand, which differ only in very specific
features (i.e. halogen substituent, chain length of the
spacer, etc.). This holds for instance for the comparison
More surprising each of the nditz (nZ2–12) compounds
exhibit a rather different packing scheme despite of the fact
the molecules seem to look so similar. This is due to several
influencing factors stabilizing their mutual orientation, their
build-up of layers and the stacking of the layers. Due to
steric reasons, the pure alkyl–alkyl van-der-Waals inter-
action is small only in the short side chain tetrazoles but
becomes decisive for the structures in the longer nditz
compounds (8ditz–12ditz). In contrast to that the p-stacking

52
C.M. Grunert et al. / Journal of Molecular Structure 733 (2005) 41–52
of mononuclear iron(II) complexes of the halogen-
substituted compounds 2-(1-haloethyl)-tetrazole (teeX)
with XZF, Cl, Br and I [5]. One major outcome of
this comparative study was the up-shift of the spin-
transition temperature T1/2 of approx. 100 K within this
series from F/I. This tremendous up-shift is at least to
some extent due to both an electronic and steric effect of
the increasing size of the halo-substituent. Although these
effects are of importance, it is still too early to make
them fully responsible for the observed differences in the
spin transition behaviour.
and Optical Spin State Switching’ (TOSS) supported by the
European Community under the contract number ERB-
FMRX-CT98-0199 as well as the EU-COST action D14
project 0011/01.
References
[1] P.L. Franke, J.G. Haasnoot, A.P. Zuur, Inorg. Chim. Acta 59 (1982) 5.
[2] Th. Buchen, P. Gu¨tlich, Chem. Phys. Lett. 220 (1994) 262.
[3] P. Gu¨tlich, A. Hauser, H. Spiering, Angew. Chem. Int. Ed. Engl. 1994;
2024.
Another interesting fact is the significant conformational
difference between the pure ligands 2ditz and 4ditz in
comparison to their Fe(II) complexes, i.e. the chain-type
[Fe(2ditz)3](BF4)2 [5] and the 3D network [Fe(4ditz)3]
(PF6)2 [11]. Obviously, the rotational flexibility of the C–C
bond(s) of the alkyl spacer of 2ditz and 4ditz facilitates their
conformational reorientation upon coordination. Therefore,
the Ci symmetric 2ditz with the two tetrazole rings in
trans-configuration is forced into a bent syn-configuration
featuring a N1–C2–C20–N10 torsion angle of roughly K358.
In contrast to this shows the pure 4ditz a kinked butyl-spacer
in gauche-orientation due to the N1–C2–C3–C30 torsion
angle of approximately 658, whereas a trans-conformation
is adopted in the 3D three-fold intercalated [Fe(4ditz)3]
(PF6)2. These drastic structural differences suggest maybe
the existence of at least two categories of bridging ligands
within the family of nditz. The very short 2ditz and its
derivatives [5,8] enforcing chain-type structures whereas
the medium-sized 4ditz–6ditz seem to facilitate the
formation of 3D networks [9,11]. As the role of the anion
(despite of its size) as well as solvate molecules for the
stabilization of a certain crystal structure and their influence
on the spin transition behaviour is still under investigation
this postulate needs to be verified and work is in progress to
achieve this goal. If the categorisation of the pure nditz
ligands as mentioned above holds for the Fe(II) complexes,
too, a somehow new structural situation may be faced for
the longer 8ditz–12ditz complexes.
[4] E. Dova, A.F. Stassen, R.A.J. Driessen, Ed Sonneveld, K. Goubitz,
R. Peschar, J.G. Haasnoot, J. Reedijk, H. Schenk, Acta Crystallogr.
B57 (2001) 531.
[5] A.F. Stassen, M. Grunert, E. Dova, H. Schenk, G. Wiesinger,
M. Mu¨ller, P. Weinberger, W. Linert, J.G. Haasnoot, J. Reedijk, Eur.
J. Inorg. Chem. 2003; 2273–2282.
[6] J. Schweifer, P. Weinberger, K. Mereiter, M. Boca Reicl,
G. Wiesinger, G. Hilscher, P.J. van Koningsbruggen, H. Kooijman,
M. Grunert, W. Linert, Inorg. Chim. Acta 339 (2002) 297.
[7] J. Schweifer, Diploma Thesis at the Vienna University of Technology,
Institute of Applied Synthetic Chemistry, 2002.
`
[8] P.J. van Koningsbruggen, Y. Garcia, O. Kahn, L. Fournes,
H. Kooijman, A.L. Spek, J.G. Haasnoot, J. Moscovici,
K. Provost, A. Michalowicz, F. Renz, P. Gu¨tlich, Inorg. Chem.
39 (2000) 1891.
[9] P.J.V. Koningsbruggen, Y. Garcia, H. Kooijman, A.L. Spek,
J.G. Haasnoot, O. Kahn, J. Linares, E. Codjovi, F. Varret, J. Chem.
Soc. Dalton Trans. 2001; 466.
[10] P.J. van Koningsbruggen, M. Grunert, P. Weinberger, Monatsh.
Chem. 134 (2003) 183.
[11] M. Grunert, J. Schweifer, P. Weinberger, W. Linert, K. Mereiter,
G. Hilscher, M. Mu¨ller, G. Wiesinger, P.J. van Koningsbruggen,
Inorg. Chem. 43 (1) (2004) 155–165.
[12] O. Kahn, C.J. Martinez, Science 279 (1998) 44.
[13] M. Verelst, L. Sommier, P. Lecante, A. Mosset, O. Kahn, Chem.
Mater. 10 (4) (1998) 980.
[14] Y. Garcia, P.J. van Koningsbruggen, G. Bravic, P. Guionneau,
D. Chasseau, G.C. Cascarano, L. Moscovici, K. Lambert,
A. Michalowicz, O. Kahn, Inorg. Chem. 36 (1997) 6357.
[15] A. Stassen, M. Grunert, A. Mills, A. Spek, J.G. Haasnoot, J. Reedijk,
W. Linert, Dalton Trans. 2003; 3628–3633.
[16] Bruker, Programs SMART, version 5.054; SAINT, version 6.2.9; SADABS
version 2.03; XPREP, version 5.1; SHELXTL, version 5.1, Bruker AXS
Inc., Madison, WI, 2001.
Therefore, the synthesis of the a,u-bis(tetrazol-1-yl)alk-
anes with longer alkyl spacer may not only enable the self-
assembly of 3D manifold intercalating iron(II) compounds
in analogy to the recently published supramolecular 3D
three-fold intercalating [m-tris(1,4-bis(tetrazol-1-yl)butane-
N4,N40)iron(II)] bis(hexafluorophosphate) [11], but will
open the fascinating new field of supramolecular spin-
crossover compounds.
[17] G.M. Sheldrick, Programs SHELXS97 and SHELXL97, University of
¨
Gottingen, Germany, 1997.
[18] B.K. Vainshtein, V.M. Fridkin, V.L. Indenbom, Structure of Crystals,
second ed., Springer, Berlin, 1995.
[19] M. Hesse, H. Meyer, B. Zeeh, Spektroskopische Methoden in der
Organischen Chemie, Auflage 5, Thieme, Stuttgart, 1995.
[20] E. Lieber, D.R. Levering, L.J. Patterson, Anal. Chem. 11 (1951) 1594.
´
[21] F. Billes, H. Endredi, G. Keresztury, Theochemistry 2000; 183.
ˆ
[22] S.C.S. Bugalho, E.M.S. Mac¸oas, M.L.S. Cristiano, R. Fausto, Phys.
Chem. 2001; 3541.
[23] R.D. Holm, P.L. Donnelly, J. Inorg. Nucl. Chem. 1966; 1887.
[24] E.O.J. John, R.D. Willet, B. Scott, R.L. Kirchmeier, J.M. Shreeve,
Inorg. Chem. 1989; 893.
Acknowledgements
[25] K. Nakamoto, Infrared and Raman Spectra of Inorganic and
Coordination Compounds, fourth ed., Wiley, London, 1986 ISBN 0-
471-01066-9.
Thanks for financial support are due to the ‘Fonds zur
¨
Forderung der wissenschaftlichen Forschung in Osterreich’
¨
(Project 15874-N03), the ‘Hochschuljubilaumsstiftung der
¨
[26] T.C.W. Mak, G.-D. Zhou, Crystallography in Modern Chemistry,
ISBN 0-471-54702-6, Wiley, London, 1992 pp. 750–756 and
references therein (Chapter 5.1).
Stadt Wien’ (Project H1010/2003), the Training and
Mobility of Researchers Network (TMR) project ‘Thermal