Two different compounds formed from copper(II) tetrafluoridoborate and [1,2,4]triazolo[1,5-a]pyrimidine. Synthesis, spectroscopy and single-crystal structures

Article abstract of DOI:10.1007/s10870-010-9713-y

Two coordination compounds copper(II) with tetrafluoridoborate as the anion and [1,2,4]triazolo[1,5-a] pyrimidine (abbreviated as tp) as the ligand are presented, together with their crystal structure and spectroscopic properties. A light blue compound [Cu(tp)₄ H₂O)₂](BF ₄)₂ (CH3OH) (1) with a tetragonal chromophore and a dark blue compound [Cu(tp)₅](BF₄)₂(CH₃OH) (2) are formed from the same batch. Compound (2) has a quite unusual geometry for Cu(II) with just 5 tp ligands, homoleptically coordinated to the metal ion. Both compounds show interesting hydrogenbond interactions in the solid state, where coordinated water is intramolecularly bound to non-coordinated N atoms of tp (in 1), and methanol is attached to the anion (in 2). The Author(s) 2010.

Full text of DOI:10.1007/s10870-010-9713-y

J Chem Crystallogr (2010) 40:656–660
DOI 10.1007/s10870-010-9713-y
ORIGINAL PAPER
Two Different Compounds Formed from Copper(II)
tetrafluoridoborate and [1,2,4]triazolo[1,5-a]pyrimidine.
Synthesis, Spectroscopy and Single-Crystal Structures
•
Eelke D. van den Bos Ilpo Mutikainen
•
•
Urho Turpeinen Gerard A. van Albada
•
•
Jaap G. Haasnoot Jan Reedijk
Received: 10 December 2009 / Accepted: 16 January 2010 / Published online: 12 February 2010
Ó The Author(s) 2010. This article is published with open access at Springerlink.com
Abstract Two coordination compounds copper(II) with
tetrafluoridoborate as the anion and [1,2,4]triazolo[1,5-a]
pyrimidine (abbreviated as tp) as the ligand are presented,
together with their crystal structure and spectroscopic
properties. A light blue compound [Cu(tp)4(H2O)2](BF4)2
(CH3OH) (1) with a tetragonal chromophore and a dark blue
compound [Cu(tp)5](BF4)2(CH3OH) (2) are formed from the
same batch. Compound (2) has a quite unusual geometry for
Cu(II) with just 5 tp ligands, homoleptically coordinated to
the metal ion. Both compounds show interesting hydrogen-
bond interactions in the solid state, where coordinated water
is intramolecularly bound to non-coordinated N atoms of tp
(in 1), and methanol is attached to the anion (in 2).
These ligands have a fused 5-membered and 6-mem-
bered ring system and as such resemble the nucleobases
adenine and guanine of DNA (Scheme 1). A variety of
coordination compounds of metals salts with the parent
ligand and other triazoles is already known and reviewed
[1, 2]. Previous work from this laboratory has mainly been
focusing on methyl substituted tp-based ligands [2–11].
Also other research groups have been studying this type of
ligands [12–17]. Triazoles and pyrimidines may in some
cases act as bridging ligands between metals, but they may
also coordinate monodentately [18–20].
In a more recent papers we reported on transition-metal
compounds with the ligands (5,7-diethyl[1,2,4]triazolo[1,5-a]
pyrimidine), (5-methyl,7-phenyl[1,2,4]triazolo[1,5-a]pyrim-
idine) and (5,6,7-trimethyl[1,2,4]triazolo[1,5-a]pyrimidine)
[21]; [22] and (7-isobutyl-5-methyl-[1,2,4]triazolo[1,5-a]
pyrimidine) [23]. In the present study we report the X-ray
crystal structuresoftwo different copperBF4 compounds with
the ligand [1,2,4]triazolo[1,5-a]pyrimidine) (abbreviated as
tp), i.e. [Cu(tp)4(H2O)2](BF4)2(CH3OH) (1) and [Cu(tp)5]
(BF4)2(CH3OH) (2). Surprisingly with Cu(II) as the metal and
tp as the only ligand, just a few X-ray crystal structures have
been reported in the literature, i.e. with the anions NCS- and
Cl- [24], Br- [10] and ClO4- [25].
Keywords Copper Á Crystal structure Á
Triazolopyrimidine
Introduction
Triazolopyrimidines (IUPAC recommended 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.
NH2
N
O
E. D. van den Bos Á G. A. van Albada Á
J. G. Haasnoot Á J. Reedijk (&)
N
N
1
3
N
N
NH
NH2
N
7
Leiden Institute of Chemistry, Leiden University,
P.O. Box 9502, 2300 RA Leiden, The Netherlands
e-mail: reedijk@chem.leidenuniv.nl
5
4
N
N
H
N
H
N
G
N
tp
A
I. Mutikainen Á U. Turpeinen
Laboratory of Inorganic Chemistry, Department of Chemistry,
University of Helsinki, (A.I. Virtasen aukio 1),
P.O. Box 55, 00014 Helsinki, Finland
Scheme 1 The ligand [1,2,4]triazolo[1,5-a]pyrimidine (tp) and its
IUPAC recommended ring-atom numbering system, together with
adenine (A) and guanosine (G)
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J Chem Crystallogr (2010) 40:656–660
Experimental Part
657
anisotropically. Details for compound 1: The tetrafluori-
doborate anion was found to be disordered and was refined
in two positions with an SOF of 0.5. The oxygen atom of
the methanol was also found disordered and given an SOF
of 0.5. The carbon atom of the methanol molecule was
refined in two positions each with an SOF of \0.5. The
hydrogen atoms of the coordinated water molecule were
taken from a Fourier-map. The hydrogen atoms of the
methanol molecule were not located nor fixed. All other
H atoms were introduced in calculated positions and
refined with fixed geometry with respect to their carrier
atoms.
Starting Materials
Hydrated metal salts, solvents, 1,3-propane-dione and
5-amino-1,2,4-triazole were used as commercially avail-
able, without further purification.
Synthesis of the Ligand
The synthesis of the ligand tp was carried out by a known
condensation procedure [2, 26] at 160 °C, from 1,3-pro-
pane-dione and 3-amino-1,2,4-triazole. Yield was found
to be about 55%. Characterisation of the free tp ligand
was performed by elemental analysis, IR and NMR
spectroscopy.
Crystallographic data for both compounds are summa-
rized in Table 1.
Synthesis of the Coordination Compounds
Table 1 Crystallographic data for compounds 1 and 2
Synthesis of (1): A solution of 2 mmol of Cu(BF4)2Á6H2O
in 20 mL water was added to a warm aqueous solution of
2 mmol of tp. Upon standing at room temperature blue
crystals appeared after one or 2 weeks, which were col-
lected by filtration. Yields were found to be about 40%. By
inspection under the microscope two different blue col-
oured (blue or light blue and other more dark blue) crystals
were observed in the solution, which taken out of the
solution very quickly disintegrated (by loss of lattice
methanol), so that the difference of the two types could not
be distinguished any more by eye. The two different types
could not be synthesized separately, despite several
attempts by changing the solvent, the metal–ligand ratio
and the temperature.
Compound
(1)
(2)
Formula
C21H24B2CuF8N16O3 C26H24B2CuF8N20
O
Molecular weight
Crystal system
Space group
785.72
Monoclinic
C2/m
869.81
Triclinic
P-1
˚
a, (A)
19.498(2)
13.305(2)
7.217(1)
90
10.2984(5)
11.777(1)
15.522(2)
72.804(8)
82.058(8)
73.711(6)
1723.1(3)
2
˚
b, (A)
˚
c, (A)
a, (8)
b, (8)
c, (8)
110.84(1)
90
3
˚
V, (A )
1749.8(4)
2
Z
D
calc, (g cm-3
)
1.491
1.676
Physical and Analytical Methods
F(000)
l (cm-1
794
878
)
0.717
0.736
Infrared spectra of the compounds were recorded on a
PerkinElmer Paragon 1,000 FTIR spectrophotometer
equipped with a Golden Gate ATR device, using the
reflectance technique (4,000–300 cm-1, res. 4 cm-1).
Crystal size (mm)
Colour, shape
0.40 9 0.40 9 0.40 0.40 9 0.20 9 0.20
Light blue, block
3.21; 27.52
15291
Dark blue, block
2.88; 25.50
26292
h min, h max°
Total reflections
X-ray Diffraction Studies
Total unique refl.
2090 (Rint = 0.0280) 6287
(Rint = 0.0266)
524
No. of refined
parameters
145
For each coordination compound a suitable crystal was
selected from the mother liquid and quickly mounted to a
glass fibre using the oil-drop method [27]. Diffraction data
were collected on a Nonius KappaCCD diffractometer
(graphite-monochromated MoKa radiation). The structures
were solved by direct methods. The programs COLLECT
[28], SHELXS-97 [29] SHELXL-97 [29] were used for
data reduction, structure solution and structure refinement,
respectively. Refinement of F2 was performed against
all reflections. All non-hydrogen atoms were refined
b
Ra, wR2
0.0461, 0.1308
1.231
0.0416, 0.1086
1.067
SC
Min. and max.
1.086; –0.450
1.144; –0.878
3
˚
resd.dens.,e/A
a
R1 = R||Fo| - |Fc||/R|Fo|
wR2 = [R[w(F2o - F2c)2]/R[w(Fo2)2]]1/2
b
c
Goodness-of-fit S = [Rw(F2o - Fc2)2/(n - p)]1/2, where n is the
number of reflections and p the number of parameters
123

658
J Chem Crystallogr (2010) 40:656–660
Results and Discussion
Description of the X-ray Structures Crystal Structure
of [Cu(tp)4(H2O)2](BF4)2(CH3OH) (1)
An ORTEP perspective view of 1 is presented in Fig. 1.
Selected bond lengths and angles are given in Table 2. The
unit cell consists of a [Cu(tp)4(H2O)2]2? moiety, two un-
coordinating (disordered) tetrafluoridoborate anions and a
(disordered) lattice methanol molecule. A centre of sym-
metry is located at Cu, and a mirror plane is running
through the O–Cu–O axis, bisecting the N-Cu–N angle.
The Cu(II) ion has a distorted octahedral environment, of
which the basal plane is formed by four nitrogen atoms of
˚
four tp ligands with Cu–N distance 2.017(2) A. The apical
positions are formed by an oxygen atom of the water
˚
molecules with a Cu–O distance 2.472(3) A. All angles are
180°, due to the symmetry. The lattice structure is stabi-
lised by bifurcated hydrogen bonding of the water hydro-
gen atoms to the N4 of each tp ligand (OÁÁÁN distance
Fig. 2 H-bond system of (1)
˚
2.870(3) A) and to the fluorine atoms of the BF4 anion
bonds could be observed due to the severe disorder of the
methanol molecule. Details are given in Table 2.
˚
(OÁÁÁF distance 3.033(5) A). (see Fig. 2) No other hydrogen
Crystal Structure of [Cu(tp)5](BF4)2(CH3OH) (2)
An ORTEP perspective view of 2 is shown in Fig. 2. Selected
bond lengths and angles are given in Table 3. The unit cell
contains the square pyramidal [Cu(tp)5]2? moiety, two
non-coordinating tetrafluoridoborate anions and one unco-
ordinating methanol molecule. The Cu(II) ion has a square
pyramidal geometry formed by four nitrogen atoms of four
˚
tp ligands (Cu–N distances from 2.009(2) to 2.028(2) A)
and one nitrogen atom of a fifth tp ligand (Cu–N distance
˚
2.256(2) A). The largest N-Cu–N angles are 162.58(10),
168.54(10)° (Fig. 3).
The geometry of 5-coordinated compounds can be
expressed by the he structural parameter s (the structural
parameter s describes the relative amount of trigonality;
s = 0 for square pyramid and s = 1 for trigonal bipyra-
midal) [30]. In this case s = 0.10, so the geometry can be
described as distorted square pyramidal.
Fig. 1 ORTEP drawing (30% probability level) of Cu(tp)4
(H2O)2](BF4)2(CH3OH) (1). The uncoordinating tetrafluoridoborate
and methanol molecules, as well as the hydrogen atoms, are omitted
for clarity
˚
Table 2 Selected bond lengths (A) and angles (°) of (1)
Cu1–O1
2.472(3)
86.20(8)
93.80(8)
180.00
Cu1–N3
2.017(2)
O1–Cu1–N3
O1–Cu1–N3a
N3–Cu1–N3b
O1a–Cu1–N3a
O1–Cu1–O1a
N3–Cu1–N3a
N3–Cu1–N3c
180.0
88.67(10)
91.33(10)
86.20(8)
Hydrogen bonds: (bifurcated H bond)
O(1)–H(1)ÁÁÁF(11) [-x,-y,-z]
O(1)–H(1)ÁÁÁN(4) [-x,-y,-z]
D–H
HÁÁÁA
2.55(4)
DÁÁÁA
3.033(5)
D–HÁÁÁA
122(4)
0.78(4)
0.78(4)
2.17(4)
2.870(3)
150(4)
123

J Chem Crystallogr (2010) 40:656–660
659
˚
Table 3 Selected bond lengths (A) and angles (°) of (2)
Cu1–N13
2.028(2)
2.256(2)
2.009(2)
92.14(10)
162.58(10)
98.80(9)
168.54(10)
92.27(9)
D–H
Cu1–N23
Cu1–N43
2.012(2)
2.015(2)
Cu1–N33
Cu1–N53
N13–Cu1–N23
N13–Cu1–N43
N23–Cu1–N33
N23–Cu1–N53
N33–Cu1–N53
Hydrogen bonds
O(1)–H(1)ÁÁÁF(14) [1-x,-1-y,-z]
N13–Cu1–N33
N13–Cu1–N53
N23–Cu1–N43
N33–Cu1–N43
N43–Cu1–N53
HÁÁÁA
93.87(9)
90.10(9)
87.60(9)
103.39(9)
86.92(9)
DÁÁÁA
D–HÁÁÁA (°)
157
0.84
2.04
2.833(6)
Fig. 4 H-bond system in the lattice of (2)
Fig. 3 ORTEP drawing (30% probability level) of [Cu(tp)5](BF4)2
(CH3OH) (2). The uncoordinating tetrafluoridoborate and methanol
molecules, as well as the hydrogen atoms, are omitted for clarity
ascribed to the tOH of the water and methanol molecules,
hydrogen bonded to the BF4 anions.
The lattice structure is stabilised by hydrogen bonding
of the oxygen atom of the methanol molecule to the BF4
˚
Concluding Remarks
anion (OÁÁÁF distance 2.833(6) A). Such hydrogen bonding
with BF4 is relatively rare, but easily detectable with IR for
X–H groups binding to it [31]. Geometric details are given
in Table 3 (Fig. 4).
The study described above has resulted in two new Cu(II)
tetrafluoridoborate compounds with unsubstituted tp as a
ligand. The two forms crystallise from the same batch, and
despite several attempts, no conditions were found to
obtain either one or the other compound in pure form.
These two compounds appear to be the first compounds of
IR Spectroscopy
-
Cu(II) and BF4 with tp as the ligand, which have been
Due to the fact that the two different compounds were very
virtually impossible to be separated manually (see experi-
mental part), only an overall IR spectrum could be recor-
ded for characterisation (see Fig. S1). The characteristic
ligand vibrations differ only slightly from the free ligand,
as would be expected. The BF4 anion vibrations are
observed at 1051–1039 cm-1 as a split band. At around
3348 cm-1 a broad absorption is observed, which is
characterized by X-ray structures. Even with substituted tp
ligands only one case is known [22].
Compound 2 has an unusual geometry with 5 tp ligands
coordinated in an homoleptic manner, generating a five-
coordinate geometry. Five-coordinated Cu(II) compounds
are quite common, but with only a single type of a bulky
ligand, they are rarely observed.
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J Chem Crystallogr (2010) 40:656–660
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CIF files of both structures, and IR spectra of tp and the
complexes are given as supplementary material. The
files CCDC-756398 and 756399 also contain the crystal-
lographic data for 1 and 2. These data can be obtained free
of charge via http://www.ccdc.cam.ac.uk/conts/retrieving.
html, or from the Cambridge Crystallographic Data Centre,
12 Union Road, Cambridge CB2 1EZ, UK; fax: (?44)
1223-336-033; or e-mail: deposit@ccdc.cam.ac.uk. A
checkcif file for both compounds is also available.
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Acknowledgments This work was performed in the framework of
the freshmen students research project ‘‘Leren Onderzoeken 1’’
(Learning Research 1) in the BSc programme ‘‘Molecular Science
and Technology’’, a recently started concept in the joint programme
of Delft University of Technology and Leiden University.
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Open Access This article is distributed under the terms of the
Creative Commons Attribution Noncommercial License which per-
mits any noncommercial use, distribution, and reproduction in any
medium, provided the original author(s) and source are credited.
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