The chelating ligand 1,3-bis(pyrazol-1′-yl)propane (Bpp) enforces a tetrahedral geometry in both CuII and CuI species

Article abstract of DOI:10.1002/ejic.200390093

The ligand 1,3-bis(pyrazol-1′-yl)propane (bpp) has been prepared by reacting 1,3-dichloropropane with two equivalents of pyrazole. After reaction of bpp with copper(II) tetrafluoroborate, three different compounds were obtained, two with Cu^II and one with Cu^I as cation, depending on the preparative method. The formation of single crystals of these compounds was only observed when 1-(3-chloropropyl)pyrazole (ppc) was present in the solution. The single-crystal X-ray structures of [Cu(bpp)₂](BF₄)₂ and [Cu(bpp)₂](BF₄) show that bpp acts as a didentate chelating ligand to form an uncommon eight-atom chelate ring with the copper ion. Two polymorphs of the Cu^II complex were characterized. In each of them, the metal atoms possess a distorted tetrahedral geometry. In the copper(I) complex the metal center is present in a less-distorted tetrahedral coordination sphere. The spectroscopic properties of the compounds are in agreement with the structural data. Cyclic voltammetry measurements showed a redox wave at 0.92 V vs. Ag/AgCl. Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2003.

Full text of DOI:10.1002/ejic.200390093

FULL PAPER
The Chelating Ligand 1,3-Bis(pyrazol-1Ј-yl)propane (Bpp) Enforces a
Tetrahedral Geometry in Both CuII and CuI Species
Kristel Flinzner,[a] Arno F. Stassen,[a] Allison M. Mills,[b] Anthony L. Spek,[b]
Jaap G. Haasnoot,*[a] and Jan Reedijk[a]
Keywords: N ligands / Copper / Crystal structures / Cyclic voltammetry
The ligand 1,3-bis(pyrazol-1Ј-yl)propane (bpp) has been pre-
pared by reacting 1,3-dichloropropane with two equivalents
mon eight-atom chelate ring with the copper ion. Two poly-
morphs of the CuII complex were characterized. In each of
of pyrazole. After reaction of bpp with copper(II) tetrafluoro- them, the metal atoms possess a distorted tetrahedral geo-
borate, three different compounds were obtained, two with metry. In the copper( ) complex the metal center is present in
CuII and one with CuI as cation, depending on the preparat- a less-distorted tetrahedral coordination sphere. The spectro-
I
ive method. The formation of single crystals of these com-
pounds was only observed when 1-(3-chloropropyl)pyrazole
(ppc) was present in the solution. The single-crystal X-ray
structures of [Cu(bpp)2](BF4)2 and [Cu(bpp)2](BF4) show that
bpp acts as a didentate chelating ligand to form an uncom-
scopic properties of the compounds are in agreement with
the structural data. Cyclic voltammetry measurements
showed a redox wave at 0.92 V vs. Ag/AgCl.
( Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim,
Germany, 2003)
Introduction
CuII ions in coordination complexes display several geo-
metries; (distorted) octahedral,[17Ϫ19] distorted trigonal bi-
Didentate ligands may either form chelates or bridges be- pyramidal,[10] square pyramidal,[11] (distorted) square-
tween two different metal ions depending on the number of planar[8,20] and (distorted) tetrahedral[4,5] complexes have
atoms between the donor atoms. However, they frequently been observed. However, because of the influence of the
form chelates, coordinating to one metal ion in a chelate JahnϪTeller effect square-planar-based geometries are usu-
ring.[1] Chelate rings of different sizes have been the subject ally preferred[1] by four-coordinate CuII. Steric constraints
of intensive research in the past. For instance, five- to thir- are known to generate tetrahedral geometries. Coordination
teen-membered rings are formed with 2,2Ј-bipyridine,[2] complexes of CuII and CuI sharing the same molecular for-
bis(2-benzimidazolyl)ethanes,[3,4] bis(2-benzimidazolyl)pro- mula and (distorted) tetrahedral geometry are therefore
panes[3,5,6] 1,3-bis(pyrazol-1Ј-yl)propane and derivatives[7] very rare. The previously reported[21] CuII and CuI com-
and
1,8-bis(3,5-dimethyl-1-pyrazolyl)-3,6-dithiaoctane.[8] pounds formed with the ligand 2,2Ј-bis(2-imidazolyl)bi-
Five-membered chelate rings are generally the most stable.[9] phenyl are examples of such complexes.
In this paper, CuII and CuI complexes with 1,3-bis(pyr-
azol-1Ј-yl)propane (bpp) that display similar (distorted) tet-
rahedral geometries are described. In these complexes, the
bpp ligands act as didentate chelating ligands to form un-
common eight-atom chelate rings. In earlier work[7] metal
complexes with the general formula [M(bpp)X2] (M ϭ
Cu2ϩ, Zn2ϩ or Co2ϩ and X ϭ ClϪ or NO3Ϫ) have been re-
ported.
The complexes described in this paper are the first con-
taining two bpp ligands coordinated to one metal center.
The best single crystals were grown from solutions of 1,3-
bis(pyrazol-1Ј-yl)propane and CuII tetrafluoroborate, in
which an excess of 1-(3-chloropropyl)pyrazole (ppc) was
also present.
The metal ion used also influences the stability of a com-
plex. Although CuI is very unstable in protic solutions with
respect to disproportionation [2 Cuϩ(aq) Ǟ Cu2ϩ(aq) ϩ
Cu0(s)],[1] the CuI ion can be stabilized by coordination with
ligands having a π-acceptor character.
Generally, CuI ions in coordination complexes have a
(distorted) tetrahedral geometry. A few examples are com-
plexes formed with bipyridine derivatives,[10] thiocyanate,[11]
adiponitriles,[12] pyridines[13,14] and indole-containing li-
gands.[15] In rare cases, CuI can have other coordination
environments, including linear,[1] trigonal,[1] and trigonal
pyramidal.[16]
[a]
Leiden Institute of Chemistry, Gorlaeus Laboratories, Leiden
University
Two red polymorphic forms of the compound
[Cu(bpp)2](BF4)2 were obtained: orthorhombic α-
[Cu(bpp)2](BF4)2 (1) crystallized from ethanol, and triclinic
β-[Cu(bpp)2](BF4)2 (2) crystallized from methanol. In addi-
P. O. Box 9502, 2300 RA Leiden, The Netherlands
Bijvoet Center for Biomolecular Research, Vakgroep Kristal-
[b]
en Structuurchemie, Utrecht University
Padualaan 8, 3584 CH Utrecht, The Netherlands
E-mail: haasnoot@chem.leidenuniv.nl
Eur. J. Inorg. Chem. 2003, 671Ϫ677  2003 WILEY-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim 1434Ϫ1948/03/0204Ϫ0671 $ 20.00ϩ.50/0
671

K. Flinzner, A. F. Stassen, A. M. Mills, A. L. Spek, J. G. Haasnoot, J. Reedijk
FULL PAPER
tion, the light yellow CuI complex [Cu(bpp)2](BF4) (3) was polymorphs. In 1, all of the cations are parallel with their
isolated. This complex also formed from CuII tetrafluoro- three C2-axes aligned with the three cell axes, as required
borate, upon standing, by auto-reduction.
by the orthorhombic symmetry (Figure 4). In the triclinic
The X-ray crystal structures of the two forms of polymorph 2, the cations centered by Cu(2) and Cu(3) are
[Cu(bpp)2](BF4)2 and [Cu(bpp)2](BF4) will be presented nearly parallel and together with the BF4Ϫ anions they form
and discussed. Furthermore, the spectroscopic properties of two-column-wide layers within which the packing is similar
[Cu(bpp)2](BF4), and spectroscopic and magnetic proper- to that in 1. Columns of Cu(1)-centered cations, rotated by
ties of [Cu(bpp)2](BF4)2 will be presented. Finally, the re- approximately 60° (about [100]) with respect to the other
sults of cyclic voltammetry measurements performed with cations, fit efficiently between these layers (Figure 5). The
[Cu(bpp)2](BF4)2 will be discussed.
higher calculated density of 2 (1.590 g cmϪ3) in comparison
to that of 1 (1.563 g cmϪ3) reflects its more compact pack-
ing.
Results and Discussion
˚
Table 1. Selected bond lengths (A) and bond angles (°) in α-
[Cu(bpp)2](BF4)2 (1) and [Cu(bpp)2](BF4) (3)
General Complex Synthesis
α-[Cu(bpp)2](BF4)2
Bond lengths (A)
[Cu(bpp)2](BF4)
Bond lengths (A)
When crystallization attempts were performed with the
ligand ppc, complexes containing the ligand bpp, which was
present as a contamination in ppc, were isolated instead.
These experiments were repeated using different Cu:bpp ra-
tios and ppc in a large excess. In each case, independent of
the Cu:bpp ratio, complexes in which Cu and bpp are pre-
sent in a 1:2 ratio were formed. When crystallizations were
performed without ppc, red solids formed which were
shown by elemental analysis also to possess a Cu:bpp ratio
˚
˚
Cu(1)ϪN(2)
1.948(3)
Cu(1)ϪN(2)
2.0344(15)
2.0207(15)
2.0246(15)
2.0458(15)
Cu(1)ϪN(4)
Cu(1)ϪN(6)
Cu(1)ϪN(8)
Bond angles (°)
Bond angles (°)
N(2)ϪCu(1)ϪN(2)a 107.71(13) N(2)ϪCu(1)ϪN(4) 113.00(6)
of 1:2, as for the complexes formed in the presence of ppc. N(2)ϪCu(1)ϪN(2)b 127.20(13) N(2)ϪCu(1)ϪN(6) 106.91(6)
N(2)ϪCu(1)ϪN(2)c
95.23(13) N(2)ϪCu(1)ϪN(8) 103.33(6)
N(4)ϪCu(1)ϪN(6) 114.18(6)
N(4)ϪCu(1)ϪN(8) 107.65(6)
N(6)ϪCu(1)ϪN(8) 111.26(6)
However, no single crystals could be obtained when ppc
was not present in the solution. A possible reason for this
is that ppc keeps the bpp complexes in solution longer, thus
allowing slower crystallization and therefore the growth of
high-quality single crystals. This theory is supported by the
fact that the copper() complex [Cu(bpp)2](BF4) does not
form at all without the presence of ppc. Because the com-
plex does not spend enough time in solution, formation by
slow auto-reduction does not take place.
˚
Table 2. Selected bond lengths (A) and bond angles (°) in β-
[Cu(bpp)2](BF4)2 (2)
˚
Bond lengths (A)
Bond angles (°)
Residue 1
Molecular Structures of α-[Cu(bpp)2](BF4)2 (1) and β-
[Cu(bpp)2](BF4)2 (2)
Cu(1)ϪN(2)
1.973(3)
1.982(3)
1.975(3)
1.981(3)
N(2)ϪCu(1)ϪN(4)
N(6)ϪCu(1)ϪN(8)
N(2)ϪCu(1)ϪN(8)
N(4)ϪCu(1)ϪN(6)
N(2)ϪCu(1)ϪN(6)
N(4)ϪCu(1)ϪN(8)
Residue 2
N(10)ϪCu(2)ϪN(12)
N(14)ϪCu(2)ϪN(16)
N(10)ϪCu(2)ϪN(14)
N(12)ϪCu(2)ϪN(16)
N(10)ϪCu(2)ϪN(16)
N(12)ϪCu(2)ϪN(14)
Residue 3
N(18)ϪCu(3)ϪN(20)
N(22)ϪCu(3)ϪN(24)
N(18)ϪCu(3)ϪN(22)
N(20)ϪCu(3)ϪN(24)
N(18)ϪCu(3)ϪN(24)
N(20)ϪCu(3)ϪN(22)
104.49(11)
104.32(10)
135.66(10)
135.65(11)
91.34(10)
92.80(10)
Cu(1)ϪN(4)
Cu(1)ϪN(6)
Cu(1)ϪN(8)
The CuII complex [Cu(bpp)2](BF4)2 crystallizes in two
polymorphs: orthorhombic α-[Cu(bpp)2](BF4)2 (1), formed
in ethanol, and triclinic β-[Cu(bpp)2](BF4)2 (2), formed in
methanol. The formation of 1 and 2 in different solvents is
probably caused by a solvent effect. The presence of both
polymorphs in the preparations is unlikely because several
crystals were used for structure determination and each
time only one polymorph was observed. Selected geometric
parameters for 1 and 2 are listed in Table 1 and 2, respect-
ively. The asymmetric unit of 1 contains one unique quarter
of a cation with D2 symmetry (Figure 1). In 2, three inde-
pendent cations are present in the asymmetric unit, all of
which adopt similar conformations with approximate
(noncrystallographic) D2 symmetry (Figure 2). The cations
in both structures are oriented such that one of their
(pseudo) C2-axes is parallel to a short a axis [1: a ϭ
Cu(2)ϪN(10)
Cu(2)ϪN(12)
Cu(2)ϪN(14)
Cu(2)ϪN(16)
1.961(3)
1.957(3)
1.967(3)
1.963(3)
105.58(11)
105.08(11)
134.25(11)
130.34(11)
93.96(10)
93.16(11)
Cu(3)ϪN(18)
Cu(3)ϪN(20)
Cu(3)ϪN(22)
Cu(3)ϪN(24)
1.959(2)
1.966(3)
1.963(3)
1.967(3)
105.76(10)
105.61(11)
130.47(10)
132.15(11)
94.24(10)
93.71(10)
˚
˚
7.9532(1) A; 2: a ϭ 7.9557(15) A]. Translation-related cat-
As shown in Figure 1 and 2, the CuII ions in both struc-
ions are stacked into columns along the [100] direction tures are each coordinated to two didentate bpp ligands via
˚
(Figure 3). These columns, separated by the (disordered) the N2 atoms of the pyrazole rings [1: CuϪN 1.948(3) A;
Ϫ
˚
BF4 anions, are arranged in different patterns in the two 2: CuϪN 1.957(3)Ϫ1.982(3) A], forming eight-membered
672
Eur. J. Inorg. Chem. 2003, 671Ϫ677

1,3-Bis(pyrazol-1Ј-yl)propane (Bpp) Enforces Tetrahedral Geometry
FULL PAPER
Figure 1. PLATON/POVRAY representation[27,28] of the molecular
structure of the cation in α-[Cu(bpp)2](BF4)2 (1); hydrogen atoms
and counterions have been omitted for clarity
Figure 4. PLATON/POVRAY representation[27,28] of the crystal
packing of α-[Cu(bpp)2](BF4)2 (1), seen in a view down the a axis
chelate rings. The coordination geometry at the metal cen-
ters is distorted tetrahedral. Although the ligand bite angles
are close to 109° [1: NϪCuϪN 107.71(13)°; 2: NϪCuϪN
104.32(10)Ϫ105.76(10)°], the other NϪCuϪN angles devi-
ate by up to 18° (1) or 27° (2) from the ideal tetrahedral
value. The dihedral angles between the NϪCuϪN planes
of the chelate rings in each complex cation [1: 66.8(2)°; 2:
57.05(15)Ϫ62.30(15)°] also indicate a flattening of the
CuN4 tetrahedrons for which a value of 90° would be ex-
pected.
Molecular Structure of [Cu(bpp)2](BF4) (3)
In the crystal structure of the CuI complex
[Cu(bpp)2](BF4) (3), the asymmetric unit contains one inde-
Figure 2. PLATON/POVRAY representation[27,28] of the molecular
structure of the three independent cations in β-[Cu(bpp)2](BF4)2
(2); hydrogen atoms and counterions have been omitted for clarity
Figure 3. PLATON/POVRAY representation[27,28] of translation-related cations stacked into columns parallel to the a axis, in α-
[Cu(bpp)2](BF4)2 (1) and β-[Cu(bpp)2](BF4)2 (2)
Eur. J. Inorg. Chem. 2003, 671Ϫ677
673

K. Flinzner, A. F. Stassen, A. M. Mills, A. L. Spek, J. G. Haasnoot, J. Reedijk
FULL PAPER
Spectroscopic and Magnetic Properties
Ligand field spectra have been recorded for both
[Cu(bpp)2](BF4)2 and [Cu(bpp)2](BF4) in the solid state.
The spectrum of α-[Cu(bpp)2](BF4)2 (1) consists of broad
signals at 39.2 ϫ 103 cmϪ1 and 22.7 ϫ 103 cmϪ1, which
are attributed to LMCT transitions. In the spectrum of β-
[Cu(bpp)2](BF4)2 (2), these signals are present at 40.2 ϫ 103
cmϪ1 and 21.5 ϫ 103 cmϪ1. Furthermore, in the spectrum
of 1 a weak signal is present at 14.5 ϫ 103 cmϪ1, in the
normal range for d-d transitions in slightly distorted tetra-
hedrally coordinated CuII complexes.[7,22] This signal is not
visible in the spectrum of 2, where the LMCT transition
dominates.
The diffuse reflectance spectrum of [Cu(bpp)2](BF4) con-
sists of one broad signal at 37.9 ϫ 103 cmϪ1, with a shoul-
der at 25.0 ϫ 103 cmϪ1, which is ascribed to MLCT trans-
itions. No d-d transition signals are present, as is expected
for CuI.
The X-band EPR spectra of a polycrystalline powder of
α-[Cu(bpp)2](BF4)2 (1) were recorded at room temperature
and 77 K. The resolution did not improve upon cooling to
77 K. The spectra show an axial S ϭ 1/2 signal with g
Figure 5. PLATON/POVRAY representation[27,28] of the crystal
packing of β-[Cu(bpp)2](BF4)2 (2), seen in a view down the a axis
values that are normal for CuII in a slightly distorted tetra-
hedral environment: gЌ ϭ 2.11, g// ϭ 2.32 and A//
ϭ
13.0 mT.[7] The spectrum of α-[Cu(bpp)2](BF4)2 in a frozen
solution of ethanol was also recorded. This spectrum shows
g values that are similar to the g values of the powder spec-
tra, which indicates that the complex is stable in solution.
The same spectra were recorded for β-[Cu(bpp)2](BF4)2 (2).
These spectra show an axial S ϭ 1/2 signal with gЌ ϭ 2.13,
g// ϭ 2.38 and A// ϭ 12.0 mT.
Magnetic susceptibility measurements were also per-
formed on [Cu(bpp)2](BF4)2 to detect any possible magnetic
exchange. A plot of χϪ1 vs. T fits a straight line through
zero, with a value of the Curie constant C of 0.44
cm3·K·molϪ1, which corresponds to a µeff of 1.88.
pendent cation possessing (noncrystallographic) S4-based
symmetry, as shown in Figure 6. The relevant geometric
parameters for 3 are given in Table 1. The CuI ion of 3 is
coordinated to two bpp ligands, but at CuϪN distances of
˚
2.0207(15)Ϫ2.0458(15) A which, as expected, are longer
than those found in the CuII complex. Similar CuIϪN
II
˚
˚
[2.029(6)Ϫ2.053(6) A] and Cu ϪN [1.941(9)Ϫ1.977(8) A]
bond lengths have been reported for the nearly tetrahedral
complexes [CuL2](ClO4) and [CuL2](ClO4)2 [L ϭ 2,2Ј-bis(2-
imidazolyl)biphenyl].[21] In 3, The Cu-centered coordination
environment is
a slightly distorted tetrahedron; the
NϪCuϪN angles range from 103.33(6)Ϫ114.18(6)°, and
the dihedral angle between the NϪCuϪN planes of the che-
late rings is 89.58(9)°.
Cyclic Voltammetry
The cyclic voltammogram of [Cu(bpp)2](BF4)2 (Figure 7)
shows an irreversible wave at 0.92 V vs. Ag/AgCl, ascribed
to the couple CuII/CuI (Epc at 0.83 V, Epa at 1.01 V). At
scan rates between 30Ϫ80 mV/s, Ipc/Ipa ϭ 1 and Ip/v1/2 is
independent of v, but at higher and lower scan rates this
reversibility is lost. In the CuII and CuI complexes with the
ligand 2,2Ј-bis(2-imidazolyl)biphenyl mentioned above,[21]
the CuII/CuI reduction wave occurs at 0.08 V vs. SCE
(Ϫ0.052 V vs. Ag/AgCl) in acetonitrile.[23] Upon com-
parison, the reduction of [Cu(bpp)2]2ϩ to [Cu(bpp)2]ϩ takes
place at an unusually high potential, confirming the high
stability of the CuI complex [Cu(bpp)2](BF4), and also ex-
plaining the easy reduction of the CuII species in ethanol
solution. Such a stabilisation of CuI by π-donor ligands
such as azoles is well known. After reduction of CuI to
Cu(0) at Epc ϭ Ϫ0.55 V, a stripping peak appears at Epa
ϭ
Ϫ0.28 V, as a result of the deposition of Cu(0) on the elec-
trode surface. The CuII/CuI reduction wave becomes less
prominent at scan rates higher and lower than 60 mV/s.
Figure 6. PLATON/POVRAY representation[27,28] of the molecular
structure of the cation in [Cu(bpp)2](BF4) (3); hydrogen atoms and
counterions have been omitted for clarity
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Eur. J. Inorg. Chem. 2003, 671Ϫ677

1,3-Bis(pyrazol-1Ј-yl)propane (Bpp) Enforces Tetrahedral Geometry
FULL PAPER
Figure 7. Cyclic voltammogram of [Cu(bpp)2](BF4)2, in acetonitrile (10Ϫ3 ) at a scan rate of 60 mV/s
RE2x electron spin resonance spectrometer using DPPH (g ϭ
2.0036) as a standard. FTIR spectra were obtained with a
PerkinϪElmer Paragon 1000 FTIR spectrophotometer equipped
with a Golden Gate ATR device, using the diffuse reflectance tech-
nique (4000Ϫ300 cmϪ1, res. 4 cmϪ1). Magnetic susceptibility meas-
urements (2Ϫ300 K) were carried out using a Quantum Design
MPMS-5 5T SQUID magnetometer (measurements carried out at
1000 Gauss). Data were corrected for the magnetization of the
Conclusion
The ligand 1,3-bis(pyrazol-1Ј-yl)propane (bpp) has been
synthesized from 1,3-dichloropropane and pyrazole. At-
tempts to obtain coordination complexes of bpp with both
CuII and CuI succeeded. The complexes that were obtained
are the first to contain copper ions surrounded by two —
rather than only one — bpp ligands forming eight-atom sample holder and for the sample diamagnetism, which was estim-
ated from the Pascal constants.[24] Cyclic voltammetry measure-
ments were performed with an Autolab PGSTAT 10 cyclic voltam-
meter, using a Pt working electrode, a Pt auxiliary electrode and a
Ag/AgCl reference electrode in acetonitrile (10Ϫ3 ), with tetrabu-
tylammonium hexafluorophosphate as electrolyte, at a scan rate of
chelate rings with the metal ion.[7] The best single crystals
were grown from solutions of 1,3-bis(pyrazol-1Ј-yl)propane
and CuII tetrafluoroborate, in which an excess of 1-(3-chloro-
propyl)pyrazole (ppc) was also present. A possible reason
for this behavior is that the complexes stay in solution
longer when ppc is present. The slower crystal growth yields
higher quality single crystals. All attempts to obtain crystal-
line CuII complexes with only ppc were unsuccessful. The
CuII ions in the two polymorphs of the [Cu(bpp)2](BF4)2
complex are surrounded by a distorted tetrahedral coor-
dination environment. This is remarkable because CuII has
a strong preference for a square-planar geometry when it is
surrounded by four monodentate ligands or two didentate
ligands.[1] Tetrahedral geometries are much more common
for CuI than for CuII. When the CuII complexes were found
to be stable in a distorted tetrahedral geometry, it was ex-
pected that a tetrahedral CuI complex should also be stable,
as is indeed the case. However, this complex was not ex-
pected to form from a CuII solution. The large redox poten-
tial for the copper ion in the complexes (0.92 V vs. Ag/
AgCl) indicates the stability of the CuI complex.
60 mV/s. C, H,
N determinations were performed with a
PerkinϪElmer 2400 Series II analyzer.
Synthesis of the Ligands
1,3-Bis(pyrazol-1Ј-yl)propane (bpp; Figure 8) was prepared by
adding 0.2 mol (13.6 g) of pyrazole and 0.4 mol (45.2 g) of 1,3-
dichloropropane dissolved in 80 mL of toluene to a solution of 0.1
mol (4 g) of sodium hydroxide in 80 mL of water. After addition
of 0.2 g of tetrabutylammonium bromide to increase the rate of
charge transfer between the layers, the solution was refluxed at 100
°C for four days. The two layers were separated and the water layer
was extracted with dichloromethane. All organic layers were com-
bined, then dried with magnesium sulfate, and filtered. After evap-
oration of the solvents, the product was obtained as a yellow oil.
The yield was 17% (2.99 g). 1H NMR (300 MHz, [D6]DMSO): δ ϭ
7.70(d, a), 6.23 (dd, b), 7.44 (d, c), 4.07 (t, d), 2.17 (q, e).
Experimental Section
General Remarks
1H NMR spectra were obtained with a Bruker 300 MHz spectro-
meter. X-band powder EPR spectra were obtained with a Jeol
Figure 8. The ligand bpp
Eur. J. Inorg. Chem. 2003, 671Ϫ677
675

K. Flinzner, A. F. Stassen, A. M. Mills, A. L. Spek, J. G. Haasnoot, J. Reedijk
Table 3. Crystallographic data for α-[Cu(bpp)2](BF4)2, β-[Cu(bpp)2](BF4)2 and [Cu(bpp)2](BF4)
FULL PAPER
α-[Cu(bpp)2](BF4)2
β-[Cu(bpp)2](BF4)2
[Cu(bpp)2](BF4)
Formula
C18H24B2CuF8N8
589.61
Orthorhombic
Fddd (No. 70)
7.9532(1)
17.0680(3)
36.9087(8)
C18H24B2CuF8N8
589.61
C18H24BF4CuN8
502.80
Monoclinic
P21/c (No. 14)
9.6773(2)
23.9139(4)
9.5287(1)
Molecular weight
Crystal system
Space group
Triclinic
¯
P1 (No. 2)
˚
a (A)
7.9557(15)
20.485(4)
23.835(4)
74.406(16)
81.178(15)
89.381(14)
3695.3(12)
6
˚
b (A)
˚
c (A)
α (°)
β (°)
γ (°)
90.4560(10)
3
˚
V (A )
5010.18(15)
8
1.563
0.955
2205.08(6)
4
1.515
1.047
Z
Dcalc (g·cmϪ3
)
1.590
0.972
1794
µ (Mo-Kα) (mmϪ1
F(000)
)
2392
1032
Crystal size (mm)
T (K)
λ (A)
θ range (°)
Data collected
Data unique
0.06 ϫ 0.12 ϫ 0.21
150
Mo-Kα 0.71073
2.2 to 27.5
14882
0.09 ϫ 0.30 ϫ 0.45
150
Mo-Kα 0.71073
1.5 to 27.5
44203
0.09 ϫ 0.15 ϫ 0.30
150
Mo-Kα 0.71073
1.7 to 26.0
15999
4243
˚
1448
16786
Data observed [I Ͼ 2σ(I)]
Rint
No. of parameters
No. of restraints
R(F), [I Ͼ 2σ(I)]
ωR(F2)
1167
0.046
123
84
0.0548
0.1470
1.03
12647
0.051
1160
566
0.0466
0.1041
1.08
Ϫ0.52, 0.70
3624
0.032
289
0
0.0280
0.0706
1.04
S
Ϫ3
˚
∆ρmin, ∆ρmax (e·A
)
Ϫ0.41, 0.88
Ϫ0.35, 0.25
1-(3-Chloropropyl)pyrazole (ppc) was prepared using the same pro-
cedure, but in this case only 0.1 mol (6.8 g) of pyrazole was added
to the reaction mixture.
X-ray Crystallographic Study: Intensity data for each of the struc-
tures were collected on a Nonius KappaCCD diffractometer with
˚
rotating anode (Mo-Kα, λ ϭ 0.71073 A) at 150 K. Correction for
absorption was considered unnecessary in all cases. The structures
were solved by automated Patterson methods using DIRDIF99,[25]
and refined on F2 by least-squares procedures using SHELXL-
97.[26] Structure validation and molecular graphics preparation
were performed with the PLATON package.[27]
Synthesis of the Complexes
α-[Cu(bpp)2](BF4)2 (1): This complex was obtained by adding a so-
lution of 1.0 mmol (0.31 g) of Cu(BF4)2·4H2O in 8 mL of ethanol
to a solution of 1.0 mmol (0.15 g) of ppc and 0.1 mmol (0.02 g) of
bpp in 8 mL ethanol. The compound crystallized from the green
solution as red plates that were isolated by filtration and dried for
several hours in air. C18H24B2CuF8N8 (589.6): calcd. C 36.7, H 4.1,
N 19.0; found C 36.7, H 4.3, N 19.0.
Ϫ
The BF4 anion in 1, and four of the six independent anions in 2,
are disordered over two sets of atomic positions. All non-hydrogen
atoms were refined with anisotropic displacement parameters, but
the displacement parameters of the disordered atoms, as well as the
ligand alkyl C atoms in complex 1, were restrained to be approxim-
ately isotropic. Hydrogen atoms were constrained to idealized geo-
metries and allowed to ride on their carrier atoms with an isotropic
displacement parameter related to the equivalent displacement
β-[Cu(bpp)2](BF4)2 (2): This complex was obtained by adding a so-
lution of 1.0 mmol (0.31 g) of Cu(BF4)2·4H2O in 3 mL of methanol
to a solution of 1.0 mmol (0.15 g) of ppc and 0.1 mmol (0.02 g) of
bpp in 3 mL of methanol. The compound crystallized from the
green solution as red plates that were isolated by filtration and
dried for several hours in air. C18H24B2CuF8N8 (589.6): calcd. C
36.7, H 4.1, N 19.0; found C 36.5, H 4.0, N 18.5.
Ϫ
parameter of their carrier atoms. The BF4 anions were restrained
to approximately tetrahedral geometries. Crystal data and further
details of the data collections are given in Table 3.
CCDC-184550 (1), -184551 (2), and -184552 (3) contain the supple-
mentary crystallographic data for this paper. These data can be ob-
tained free of charge at www.ccdc.cam.ac.uk/conts/retrieving.html
(or from the CCDC, 12 Union Road, Cambridge CB2 1EZ, UK;
Fax: (internat.) ϩ44-1223/336-033; E-mail: deposit@ccdc.cam.ac.uk).
[Cu(bpp)2](BF4) (3): This complex was obtained by adding a solu-
tion of 1.0 mmol (0.31 g) of Cu(BF4)2·4H2O in 12 mL of ethanol
to a solution of 10.5 mmol (2.16 g) of ppc and 3.0 mmol (0.54 g)
of bpp in 12 mL of ethanol. The resulting solution was heated to
boiling and immediately filtered. After two weeks, colorless blocks
crystallized from the green solution and these were isolated by fil-
Acknowledgments
tration, then dried for several hours in air. C18H24BCuF4N8 (502.8): The work described in this paper has been supported by the Leiden
calcd. C 43.0, H 4.8, N 22.3; found C 42.7, H 5.0, N 22.5.
University Study Group WFMO and has been performed under
676
Eur. J. Inorg. Chem. 2003, 671Ϫ677

1,3-Bis(pyrazol-1Ј-yl)propane (Bpp) Enforces Tetrahedral Geometry
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677