Coordination chemistry of substituted [1,2,4]triazolo[1,5-a]pyrimidines with first-row transition-metal ions: Synthesis, spectroscopy and single-crystal structure analysis

Article abstract of DOI:10.1016/j.ica.2008.02.020

A number of new coordination compounds with transition-metal salts and triazole-based heterocyclic ligands is described. The ligands used are disubstituted [1,2,4]triazolo[1,5-a]pyrimidines, with as substituents: ethyl, methyl and phenyl, and in addition

Full text of DOI:10.1016/j.ica.2008.02.020

Available online at www.sciencedirect.com
Inorganica Chimica Acta 362 (2009) 861–868
www.elsevier.com/locate/ica
Coordination chemistry of substituted
[1,2,4]triazolo[1,5-a]pyrimidines with first-row transition-metal
ions: Synthesis, spectroscopy and single-crystal structure analysis
Jeral M. Balkaran a, Stein C.P. van Bezouw a, John van Bruchem a, Joeri Verasdonck a,
Peter C. Verkerk a, Anne Geert Volbeda a, Ilpo Mutikainen b, Urho Turpeinen b,
Gerard A. van Albada a, Patrick Gamez a, Jaap G. Haasnoot a, Jan Reedijk a,*
a Leiden Institute of Chemistry, Leiden University, P.O. Box 9502, 2300 RA Leiden, The Netherlands
b Laboratory of Inorganic Chemistry, Department of Chemistry, P.O. Box 55 (A.I. Virtasen aukio 1), 00014 University of Helsinki, Finland
Received 4 December 2007; received in revised form 30 January 2008; accepted 6 February 2008
Available online 15 February 2008
Dedicated to Professor Bernhard Lippert to celebrate his contribution to chemistry.
Abstract
A number of new coordination compounds with transition-metal salts and triazole-based heterocyclic ligands is described. The
ligands used are disubstituted [1,2,4]triazolo[1,5-a]pyrimidines, with as substituents: ethyl, methyl and phenyl, and in addition a 2-
methylthio-dimethyl ligand was used (sdmtp). To determine the structures of the coordination compounds in a number of cases 3D crys-
tal structure determinations have been carried out, i.e. for [Fe(NCS)2(detp)3(H2O)], [Co(NCS)2(sdmtp)2(H2O)], [ZnBr2(fmtp)2],
[Ni(NCS)2(detp)3(CH3OH)] and [Fe(NCS)2(fmtp)2(H2O)2](fmtp). The latter compound is quite unusual as it contains an uncoordinated
fmtp ligand in the crystal lattice with special packing features. The ligands and the coordination compounds have been further charac-
terized by NMR, IR and LF spectra, as well as by C, H, N element analyses. The coordination around the metal varies from 4 (Zn), via 5
(Co) to 6 (for Ni and Fe).
Ó 2008 Elsevier B.V. All rights reserved.
Keywords: Iron; Cobalt; Zinc; Nickel; Cadmium; Triazolopyrimidine
1. Introduction
[1,2]. Previous work from this laboratory has mainly been
focusing on symmetric, and methyl substituted tp-based
ligands [2–13] Also other groups have been studying this
type of ligands [14–19]. In general triazoles and pyrimidines
can act as bridges between metals, but also coordinate
monodentately [20–22]. The steric effects of substituents
in these ligands are interesting and have not been explored
in great detail, especially substituents at position 2 are
hardly known, and also 2 different substituents at positions
5 and 7 are not known. So we have set up a systematic
study towards the steric effects of substituents by studying
a variety of reactions with transition-metal(II) salts. The
results of this work are described below, for the following
3 ligands (Scheme 2). In the case of the ligand fmtp it is
Triazolopyrimidines (traditional IUPAC name: [1,2,
4]triazolo[1,5-a]pyrimidines) are versatile ligands as they
have several nitrogen atoms with accessible lone pairs to
bind to Lewis acids like metal ions (see the structure in
Scheme 1, with the current IUPAC ring numbering).
These ligands contain 6–5 condensed rings and therefore
resemble the nucleobases adenine and guanine, of the nat-
ural DNA. A variety of complexes of metals salts with this
ligand and other triazoles is already known and reviewed
*
Corresponding author.
E-mail address: reedijk@chem.leidenuniv.nl (J. Reedijk).
0020-1693/$ - see front matter Ó 2008 Elsevier B.V. All rights reserved.
doi:10.1016/j.ica.2008.02.020

862
J.M. Balkaran et al. / Inorganica Chimica Acta 362 (2009) 861–868
N
7
1
N
6
5
8
2
3
4
N
N
Scheme 1. The unsubstituted ligand tp and its IUPAC ring-numbering system.
A solution of the metal salt in (0.01 mol) water was
added to a warm aqueous solution of the ligand (0.01–
0.04 mmol). Upon cooling to room temperature crystals
of the desired compound appeared, which were collected
by filtration. In some cases acetonitrile/water or pure ace-
tonitrile were used as solvent. To prepare the thiocyanate
compounds a metathesis reaction was used, starting from
the metal nitrate and ammonium thiocyanate (1:2). Yields
were found to be between 30% and 60%.
N
2
3
7
N
1
N
6
5
7
8
1
N
2
3
N
N
7
6
5
N
1
8
6
5
4
2
8
S
N
3
N
4
4
N
N
N
Scheme 2. The ligands fmtp, sdmtp and detp as used in this study.
not known a priori how the substituents are distributed
over the 5 and 7 positions, just like in e.g. 3(5)-methyl pyr-
azole [23] and an X-ray structure of a metal coordination
compound would help to discriminate. Therefore, a selec-
tion of 5 different compounds was made for which suitable
single crystals were isolated and this study has been supple-
mented with some other compounds for which structures
will be proposed based on spectral analogies with the
known compounds.
2.4. Physical and analytical methods
Infrared spectra of all compounds were recorded on a
Perkin–Elmer Paragon 1000 FTIR spectrophotometer
equipped with a Golden Gate ATR device, using the reflec-
tance technique (4000–300 cmꢀ1, res. 4 cmꢀ1). NMR spec-
tra were recorded on a Bruker instrument at 300 MHz,
with the use of dmso as a solvent.
C, H, N determinations were performed on a Perkin–
Elmer 2400 Series II analyzer. Ligand field spectra in the
300–2000 nm range were obtained on a Perkin–Elmer
Lambda900 spectrophotometer using the diffuse reflectance
technique, with MgO as a reference.
2. Experimental
2.1. Starting materials
Hydrated metal salts, solvents, diketones and 5-amino-
1,2,4-triazole were used as commercially available, without
further purification. The intermediate 3-methylthio-5-
amino-1,2,4-triazole was obtained from Aldrich.
2.5. X-ray diffraction studies
A suitable crystal for a coordination compound was
selected from the mother liquid and mounted to a glass
fibre using the oil-drop method. Diffraction data were col-
lected on a Nonius KappaCCD diffractometer (graphite-
monochromated Mo Ka radiation). The structures were
solved by direct methods. The programs COLLECT [25],
SHELXS-97 [26], SHELXL-97 [27] were used for data reduction,
structure solution and structure refinement, respectively.
Refinement of F2 was done against all reflections. All
non-hydrogen atoms were refined anisotropically. The
water H atoms in compounds 1, 3 and 4 and the methanol
H atom in compound 2 were picked from a difference Fou-
rier map and refined isotropically. All other H atoms were
introduced in calculated positions and refined with fixed
geometry with respect to their carrier atoms. Crystallo-
graphic data of the compounds are summarized in Table 1.
2.2. Synthesis of the ligands
The synthesis of the ligands was carried out by a long-
known condensation procedure [2,24] at 160 °C, from a
diketone and an amino-triazole schematically given below
in Scheme 3, followed by recrystallization from ethanol.
Yields were between 30% and 70% depending on the
ligand. Characterization was done by IR and NMR
spectroscopy.
2.3. Synthesis of the coordination compounds
The coordination compounds were prepared by the fol-
lowing general recipes:
3. Results and discussion
R''
R'
3.1. General observations and spectral analyses
N
R
R'
R''
N
N
+
N
N
2H2O
+
O
O
N
H
NH2
With many metal salts when applied in solution with
one of the ligand solid products were formed often crystal-
line, and reproducible, irrespective of the used metal to
ligand ratio. The so-obtained unique products are listed
R
N
Scheme 3. Synthesis scheme of substituted triazolopyrimidines; R,
R0 = Me, Ph, R00 = H, Me.

J.M. Balkaran et al. / Inorganica Chimica Acta 362 (2009) 861–868
863
Table 1
Crystal and refinement data for 5 new compounds (number and working code)
Compound
1
2
3
4
5
Molecular formula
Molecular weight
T (K)
C29H38FeN14OS2
718.7
173(2)
monoclinic
P21/c
8.874(1)
20.126(3)
19.973(3)
90.0
101.44(3)
90.0
3496.3(9)
4
C30H40N14NiOS2
735.59
173(2)
orthorhombic
Pbca
C18H22CoN10OS4 C50H44FeN18O2S2 C24H20Br2N8Zn
581.63
173(2)
monoclinic
C2/c
1049.0
173(2)
orthorhombic
Fdd2
645.67
173(2)
monoclinic
P21
Crystal system
Space group
˚
a (A)
18.251(3)
17.341(3)
22.515(4)
90.0
90.0
90.0
13.237(2)
22.048(4)
9.241(2)
90.0
22.909(5)
57.095(11)
7.4460(15)
90.0
9.747.(2)
18.735(4)
14.223(3)
90.0
˚
b (A)
˚
c (A)
a (°)
b (°)
c (°)
107.34(3)
90.0
90.0
90.0
97.56(3)
90.0
3
˚
V (A )
7126(2)
8
2574.4(9)
4
9739(3)
8
2574.7(9)
4
Z
F(000)
1504
1.365
0.597
3088
1.371
0.709
1196
1.501
1.023
4352
1.431
0.458
1280
1.666
4.087
Dcalc (Mg mꢀ3
)
l (mmꢀ1
)
Crystal size (mm)
Colour, shape
h Range (°)
Number of reflections collected
Number of independent reflections (Rint
Number of reflections parameters
Sc (Goodness of fit)
0.20 ꢁ 0.20 ꢁ 0.10 0.10 ꢁ 0.06 ꢁ 0.06 0.25 ꢁ 0.25 ꢁ 0.15 0.30 ꢁ 0.20 ꢁ 0.10 0.35 ꢁ 0.15 ꢁ 0.15
yellow, plate
2.31–27.51
44521
blue, needle
3.10–27.53
84051
purple, prism
3.21–27.53
16815
yellow, prism
3.36–25.90
30534
colourless, prism
2.89–27.52
33174
)
7778 (0.0662)
436
8161 (0.1065)
444
2919 (0.0510)
162
4650 (0.0525)
335
11201 (0.0486)
633
1.059
1.028
1.028
1.036
1.040
Final R indices [I > 2r(I)]
R1 = 0.0483,
wR2 = 0.0771
R1 = 0.1297,
wR2 = 0.0988
R1 = 0.0495,
wR2 = 0.0804
R1 = 0.1411,
wR2 = 0.1039
R1 = 0.0357,
wR2 = 0.0677
R1 = 0.0716,
wR2 = 0.0787
R1 = 0.0295,
wR2 = 0.0603
R1 = 0.0439,
wR2 = 0.0652
R1 = 0.0386,
wR2 = 0.0531
R1 = 0.0883,
wR2 = 0.0631
R indices (all data)
Largest difference in minimum and maximum
ꢀ0.447 and 0.395 ꢀ0.406 and 0.404 ꢀ0.293 and 0.340 ꢀ0.269 and 0.190 ꢀ0.553 and 0.498
ꢀ3
˚
(e A
)
P
P
P
2
2 1=2
R ¼ kF oj ꢀ jF ck= jF ok; Rw ¼ ½ wfjF okF cjg =wjF oj ꢂ
.
P
Goodness-of-fit S ¼ ½ wðF 2o ꢀ F c2Þ =ðn ꢀ pÞꢂ1=2, where n is the number of reflections and p the number of parameters.
2
c
in Table 2, with their composition and some spectral char-
acteristics. They were all characterized by C, H, N analysis,
which were found sufficient to prove the composition. All
compounds have been characterized by common physical
methods, i.e. infrared spectroscopy, ligand field spectros-
copy, and for the Zn and Cd compounds by NMR. In five
cases an X-ray structure determination was carried out to
obtain molecular structure details (vide infra). These com-
pounds will be numbered 1–5. The Table is complemented
by 4 other, related compounds, for which a structure is pro-
posed based on spectroscopy.
Some comments on their spectral data are given below.
NMR spectra of the Zn and Cd complexes were recorded
in dmso and compared with the respective free ligands.
The effect of coordination on the ring vibrations is rather
small, as deduced from the small shifts in the proton signals
of the ligand. Also in the IR spectra of these and the other
compounds the changes in the ring structure are small, as
deduced from the small shifts in vibrations. The IR absorp-
tion bands for the anions in the complexes illustrate their
presence and indicate coordination for the nitrate and for
the thiocyanate-N.
Table 2
New coordination compound obtained with the ligands detp, fmtp, sdmtp and some selected properties
Compound
Colour
IR, NCS stretch and other data Number of the compound LF spectral maxima in 103 cmꢀ1
[Fe(NCS)2(detp)3(H2O)]
[Ni(NCS)2(detp)3(CH3OH)]
[Co(NCS)2(detp)2](H2O)
[Co(NCS)2(sdmtp)2(H2O)]
[Fe(NCS)2(fmtp)2(H2O)](fmtp) orange-
yellow
yellow
blue
deep blue
purple
2082 and 2057
2101, 2073
2062
2069
2081
1
2
6
3
4
9.8 (d–d) octahedral
9.4, 16.0, 26.1 (d–d) octahedral
7.7 (br), 16.1, 20.2 sh (d–d): tetrahedral
5.5, 11.0, 17.3 (d–d, 5 coord)
9.8 (d–d) octahedral
[Co(NO3)2(fmtp)(H2O)4]
[ZnBr2(fmtp)2]
[CdI2(fmtp)2]
[CdBr2(fmtp)]
a
orange
white
white
white
nitrate visible: 1423, 1299 cmꢀ1
a
7
5
8
9
8.5, 18.0 (sh), 21.0 (d–d) octahedral
colourless
colourless
colourless
a
These 2 compounds display identical IR above 300 cmꢀ1
.

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J.M. Balkaran et al. / Inorganica Chimica Acta 362 (2009) 861–868
The ligand field spectra of the Fe, Co and Ni com-
Table 3. The iron(II) centre is in a octahedral coordina-
tion environment formed by three detp ligands, two N-
coordinated thiocyanate anions and one water molecule.
The basal plane of the [FeN5O] octahedron includes two
cis NCSꢀ anions exhibiting normal Fe–NNCS bond
lengths for HS FeII species [32,33]. The other basal posi-
tions are occupied by the nitrogen N21 of a detp ligand
and a water molecule at typical distances for this type of
pounds are illustrative for their structure; also a few spectra
of compounds are listed for which no crystal structure
determinations have been carried out. The crystal field
parameters for the octahedral Fe, Co and Ni compounds,
as deduced from the LF maxima given in Table 2, are as
expected for such chromophores [28–30] and will not be
discussed in detail. For the five-coordinate Co(II) com-
pound, 3, the maxima at are indeed characteristic for such
trigonal bipyramidal-based compounds [31]. In the two
cases of Co compound for which no 3D structure is avail-
able, an octahedrally coordinated Co(II) is clearly visible
for the fmtp complex, although the LF maximum cannot
discriminate between a water and a nitrate oxygen donor.
The IR spectrum suggests that the two nitrates are both
monodentate coordinated. The LF spectrum of [Co(N-
CS)2(detp)2(H2O)] strongly resembles a tetrahedral Co(II)
with 4 relatively strong N-donor ligand, this would imply
that the water is non-coordinated. In fact the water band
in the IR spectrum is rather broad, suggesting the presence
of lattice water.
Table 3
˚
Selected bond lengths (A) and Angles (°) in compounds 1–5
Compound 1
Bond distance
Fe1–N1
Fe1–O1
Fe1–N31
2.141(2)
2.203(2)
2.220(2)
Fe1–N4
Fe1–N21
Fe1–11
2.116(3)
2.218(2)
2.219(2)
Bond angle
N1–Fe1–N4
O1–Fe1–N21
N11–Fe1–N31
93.02(10)
87.45(8)
176.67(9)
N4–Fe1–O1
N21–Fe1–N1
89.61(9)
89.89(10)
Compound 2
Bond distance
Ni1–N1
Ni1–N11
Ni1–N21
From the two Cd compounds, the compound 9 is iso-
morphous with the zinc bromide compound 5. The mono-
adduct of the cadmium bromide has an unknown structure,
but the IR spectra suggest a bonding of the ligand via the
N3, just as in the other compounds.
2.070(3)
2.121(2)
2.138(2)
Ni1–N4
Ni1–O7
Ni1–N31
2.060(3)
2.113(2)
2.135(2)
Bond angle
N1–Ni1–N4
O7–Ni1–N11
N21–Ni1–N31
91.22(10)
87.38(9)
178.78(9)
N4–Ni1–O7
N11–Ni1–N1
89.07(10)
90.64(10)
3.2. Description of the X-ray structures
3.2.1. [Fe(NCS)2(detp)3(H2O)] (1)
Compound 3
Bond distance
Co1–N1
Compound 1 crystallizes in the P21/c monoclinic space
group. An ORTEP perspective view of 1 is shown in
Fig. 1. Selected bond lengths and angles are given in
1.982(2)
2.254(2)
Co1–O1
1.972(3)
Co1–N11
Bond angle
N1–Co1–N1a
O1–Co1–N1
119.61(9)
120.20(7)
N1a–Co1–O1
N11–Co1–N11a
120.20(7)
170.35(7)
Compound 4
Bond distance
Fe1–N1
2.126(2)
2.151(2)
Fe1–N11
2.233(2)
Fe1–O1
Bond angle
N1–Fe1–N11
N1–Fe1–N1a
N1–Fe1–O1a
N11–Fe1–N11a
87.57(6)
94.11(8)
173.45(7)
175.70(6)
N1–Fe1–O1
N1–Fe1–N11a
O1–Fe–O1a
88.11(8)
95.37(6)
90.35(8)
Compound 5
Bond distance
Zn1–Br1
Zn1–N11
Zn2–Br3
2.375(1)
2.040(3)
2.389(1)
2.047(3)
Zn1–Br2
Zn1–N31
Zn2–Br4
Zn2–N71
2.396(1)
2.039(4)
2.389(1)
2.068(4)
Zn2–N51
Bond angle
Br1–Zn1–Br2
Br1–Zn1–N31
Br2–Zn1–N31
Br3–Zn2–Br4
Br3–Zn2–N71
Br4–Zn2–N71
118.01(4)
102.29(9)
100.25(9)
115.59(4)
102.83(9)
102.49(10)
Br1–Zn1–N11
Br2–Zn1–N11
N11–Zn1–N31
Br3–Zn2–N51
Br4–Zn2–N51
N51–Zn2–N71
111.32(10)
112.67(9)
111.04(15)
108.42(12)
114.38(12)
112.48(15)
Fig. 1. ORTEP drawing (30% probability level) of [Fe(NCS)2(detp)3
(H2O)] (1). Hydrogen atoms are omitted for clarity.

J.M. Balkaran et al. / Inorganica Chimica Acta 362 (2009) 861–868
865
coordination geometry (Table 3) [34]. The basal angles
vary between 87.45(8)° and 93.02(10)° (Table 3), reflect-
ing an almost perfect octahedral geometry. The coordi-
nated water molecule is hydrogen bonded to the
nitrogen atoms N18 and N28 of two detp ligands (intra-
and Ni–OMeOH bond lengths are in normal ranges for this
type of NiN5O chromophore [35]. The basal angles deviate
by a maximum of 2.62° from the ideal angle of 90° for a
perfect octahedron (see Table 3). The methanol hydrogen
atom H7A forms a strong hydrogen bond with the detp
nitrogen atom N18 (intramolecular H bonds: N18ꢃ ꢃ ꢃ
˚
molecular H bonds: N18ꢃ ꢃ ꢃO1 = 2.916(3) A and N18ꢃ ꢃ ꢃ
˚
˚
H1–O1 = 152(3)°; N28ꢃ ꢃ ꢃO1 = 2.834(3) A and N28ꢃ ꢃ ꢃ
O7 = 2.722(3) A and N18ꢃ ꢃ ꢃH7A–O7 = 152(3)°). The crys-
H2–O1 = 146(3)°). The crystal packing of 1 reveals that
two iron(II) units self-assemble through C–Hꢃ ꢃ ꢃp con-
tacts and p–p interactions (Fig. S1). The face-to-face
tal packing of 2 (Fig. S2) displays similarities with that of 1.
Molecules of 2 are associated by means of C–Hꢃ ꢃ ꢃp bond-
˚
ing interactions (C–Hꢃ ꢃ ꢃring centroid = 2.83 A; Fig. S2A).
˚
p–p stacks are separated by a distance of about 3.7 A
However, in this case, the detp ligands are not p–p stacked
(Fig. S2B), most likely owing to steric constraints induced
by the methanolic methyl groups. Indeed, the rings that are
p–p stacked in 1 (Fig. S1A) are now apart from each other
as is evidenced in Fig. S2C. As a result, an infinite supra-
molecular 1D chain is generated by the self-assembly of
complexes 2 through C–H/p contacts (Fig. S2D), instead
of dimers like in 1 (Fig. S1B).
(Fig. S1A). The hydrogen atom H11G (from an ethyl
substituent of a coordinated detp ligand) is in close
˚
contact (C–Hꢃ ꢃ ꢃring centroid = 2.74 A) with the triazole
ring of a detp ligand belonging to an adjacent iron(II)
complex (Fig. S1B). The supramolecular dimer is
generated by two C–Hꢃ ꢃ ꢃp and one p–p bonding
interactions.
3.2.2. [Ni(NCS)2(detp)3(CH3OH)] (2)
3.2.3. [Co(NCS)2(sdmtp)2(H2O)] (3)
Compound 2 crystallizes in the orthorhombic Pbca
space group. An ORTEP perspective view of 2 is shown in
Fig. 2. The mononuclear unit consists of a NiII ion coordi-
nated by two thiocyanate nitrogen atoms (N1 and N4),
three monodentate detp ligands (N11, N21 and N31) and
one methanol molecule (O7) in an octahedral environment
comparable to the one of 1. Actually, the main difference
between 1 and 2 is that 1 has a water molecule coordinated
to the metal centre while 2 exhibits a methanol molecule at
this position (see Figs. 1 and 2). The Ni–NNCS, Ni–Ndetp
Compound 3 crystallizes in the monoclinic C2/c space
group. An ORTEP perspective view of complex 3 is depicted
in Fig. 3. Selected bond lengths and angles are given in
Table 3. The CoII ion is in a distorted trigonal bipyramidal
coordination environment (s5 = 0.84; s5 = 0 for a square
pyramidal geometry and s5 = 1 for a trigonal bipyramidal
geometry) [36], formed by two crystallographically equiva-
lent thiocyanate anions (nitrogen atoms N1 and N1a) and
one water molecule (oxygen atom O1) in the trigonal
plane, and by two symmetry-related sdmtp ligands (nitro-
gen atoms N11 and N11a) at the apical positions. The
Fig. 3. ORTEP drawing (30% probability level) of [Co(NCS)2-
(sdmtp)2(H2O)] (3). Hydrogen atoms are omitted for clarity. Symmetry
operation: (a) 1 ꢀ x, y, ꢀ1/2 ꢀ z.
Fig. 2. ORTEP drawing (30% probability level) of [Ni(NCS)2(detp)3
(CH3OH)] (2). Hydrogen atoms are omitted for clarity.

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J.M. Balkaran et al. / Inorganica Chimica Acta 362 (2009) 861–868
Co–NNCS, Co–Nsdmtp and Co–Owater are in the expected
ranges [37]. The basal angles range between 119.61(9)°
and 120.20(7)°, very close to the ideal value of 120°. The
small distortion of the trigonal bipyramid is reflected by
the axial angle N11–Co–N11a of 170.35(7)°. This distor-
tion is obviously related to the very strong hydrogen bond-
ing interactions between the sdmtp ligands and the
bisligand complexes and free fmtp ligands generates a 1D
supramolecular chain which is further stabilized by
SNCSꢃ ꢃ ꢃOwater contacts (Fig. S5B; S3ꢃ ꢃ ꢃO1 = 3.272(2) A).
˚
3.2.5. [ZnBr2(fmtp)2] (5)
Compound 5 crystallizes in the monoclinic P21 space
group. An ORTEP perspective view of 5 is shown in Fig. 5.
Selected bond lengths and angles are given in Table 3.
The crystal lattice of 5 is constituted of two slightly differ-
ent zinc(II) coordination compounds. Both Zn1 and Zn2
are in almost perfect tetrahedral environments (s4 = 0.92
for Zn1 and s4 = 0.92 for Zn2; s4 = 0 for a square planar
˚
coordinated water molecule (N18ꢃ ꢃ ꢃO1 = 2.664(2) A and
N18ꢃ ꢃ ꢃH1a–O1 = 152(3)°). Consequently, the angle N11–
Co–N11a, involving the H bonded sdmtp ligands deviates
from the ideal value by as much as 9.65° (see Fig. S3).
The crystal packing of 3 reveals the presence of 1D supra-
molecular infinite chains assembled via p–p interactions
between sdmtp ligands belonging to neighbouring cobalt
˚
complexes (p–p contacts of 3.381 A; Fig. S3).
3.2.4. [Fe(NCS)2(fmtp)2(H2O)2](fmtp) (4)
Compound 4 crystallizes in the Fdd2 orthorhombic
space group. An ORTEP perspective view of 4 is shown in
Fig. 4. Selected bond lengths and angles are given in Table
3. The iron(II) centre is in an almost perfect octahedral
coordination environment. The basal plane of the octahe-
dron is formed by two crystallographically related N-coor-
dinating thiocyanates anions (N1 and N1a) and two water
molecules (O1 and O1a). The axial positions of the
[FeN4O2] octahedron are occupied by nitrogen atoms
(N11 and N11a) of two crystallographically equivalent
fmtp ligands. The Fe–NNCS distances are within the normal
range for HS FeII species (Fe–N1 = 2.126(2) A) [38,39].
˚
The Fe–Nfmtp and Fe–O bond lengths are typical for this
type of coordination geometry [40]. The basal angles are
close to the ideal value of 90°, varying from 88.11(8)° to
94.11(8)° (Table 3). Interestingly, each coordinated fmtp
ligand is interacting with two non-coordinated fmtp
ligands through p–p contacts (Fig. S4) with centroidꢃ ꢃ ꢃcen-
˚
troid distances of 3.549(1) A (Cg1ꢃ ꢃ ꢃCg2; Fig. S4A) and
Fig. 5. ORTEP drawing (30% probability level) of [ZnBr2(fmtp)2] (5).
Hydrogen atoms are omitted for clarity.
˚
3.706(2) A (Cg3ꢃ ꢃ ꢃCg4; Fig. S4A). The assembly between
Fig. 4. ORTEP drawing (30% probability level) of [Fe(NCS)2(fmtp)2(H2O)2](fmtp) (4). Hydrogen atoms are omitted for clarity. Symmetry operation: (a)
ꢀx, ꢀy, z.

J.M. Balkaran et al. / Inorganica Chimica Acta 362 (2009) 861–868
867
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geometry and s4 = 1 for a tetrahedral geometry) [41],
formed by two bromide anions and to monodentate fmtp
ligands. The Cu–N and Cu–Br bond distances are in typical
ranges for this type of [ZnN2Br2] tetrahedron [42,43]. The
angles vary from 100.25(9)° to 118.01(4)° for Zn1 and from
102.49(10)° to 115.59(4)° for Zn2. The crystal packing of 5
shows the presence of p–p interactions between the hetero-
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uents of two adjacent Zn units (Cg1ꢃ ꢃ ꢃCg2 = 3.483(3) A
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and Cg3ꢃ ꢃ ꢃCg4 = 3.481(2) A Fig. S6).
4. Concluding remarks
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The study described above on the coordination behav-
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coordinate in all cases via N3. The ligands are versatile in
their behaviour towards different metals and anions, result-
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hydrogen bonding from the solvent and to the anions.
Which compounds are formed as described above is diffi-
cult to predict beforehand, and appears to depend strongly
on the used metal and the selected anion.
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Acknowledgements
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This work was performed in the framework of freshmen
students research project ‘‘Leren Onderzoeken 1” (Learn-
ing Research 1) in the BSc programme ‘‘Molecular Science
and Technology” a new concept in the joint programme of
Delft University of Technology and Leiden University. The
present undergraduate student co-authors, i.e. Jeral M.
Balkaran, Stein C.P. van Bezouw, John van Bruchem, Joeri
Verasdonck, Peter C. Verkerk, and Anne Geert Volbeda,
have performed this project in a team of 6 freshmen
students.
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Appendix A. Supplementary material
CCDC 669962, 669963, 669964, 669965 and 669966
contain the supplementary crystallographic data for 1, 3,
4, 2 and 5. These data can be obtained free of charge from
The Cambridge Crystallographic Data Centre via
www.ccdc.cam.ac.uk/data_request/cif. Figures with pack-
ing diagrams for the 5 compounds are available. Supple-
mentary data associated with this article can be found, in
the online version, at doi:10.1016/j.ica.2008.02.020.
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