Two forms of a copper(II) complex of 3-phenyl-5-(2-pyridyl)-4-(4-pyridyl)- 4H-1,2,4-triazole: A six-coordinate monomer versus a five-coordinate polymer

Article abstract of DOI:10.1016/j.ica.2004.03.044

The reaction of the new bidirectional ligand 3-phenyl-5-(2-pyridyl)-4-(4- pyridyl)-4H-1,2,4-triazole (pyppt) with Cu(ClO₄)₂· 6H₂O in a 2:1 molar ratio in EtOH affords the complex [Cu ^II(pyppt)₂(ClO₄)₂]·H ₂O (1) as a microcrystalline turquoise solid. Recrystallisation of complex 1 from MeCN by vapour diffusion of Et₂O gives blue crystals of the monomeric octahedral complex [Cu^II(pyppt)₂(ClO ₄)₂]·MeCN (2). In contrast, addition of EtOH to a solution of complex 1 in MeCN followed by slow evaporation yields blue crystals of the five-coordinate polymeric complex {[Cu^II(pyppt) ₂](ClO₄)₂·EtOH}_∞ (3). The structures of both complexes have been determined by single crystal X-ray diffraction.

Full text of DOI:10.1016/j.ica.2004.03.044

Inorganica Chimica Acta 357 (2004) 3413–3417
www.elsevier.com/locate/ica
Note
Two forms of a copper(II) complex of
3-phenyl-5-(2-pyridyl)-4-(4-pyridyl)-4H-1,2,4-triazole: a
six-coordinate monomer versus a five-coordinate polymer q
*
Marco H. Klingele, Sally Brooker
Department of Chemistry, University of Otago, P.O. Box 56, Dunedin, New Zealand
Received 1 March 2004; accepted 28 March 2004
Available online 7 May 2004
Abstract
The reaction of the new bidirectional ligand 3-phenyl-5-(2-pyridyl)-4-(4-pyridyl)-4H-1,2,4-triazole (pyppt) with Cu(ClO4)2 ꢀ 6H2O
in a 2:1 molar ratio in EtOH affords the complex [CuII(pyppt)2(ClO4)2] ꢀ H2O (1) as a microcrystalline turquoise solid. Recrystal-
lisation of complex 1 from MeCN by vapour diffusion of Et2O gives blue crystals of the monomeric octahedral complex
[CuII(pyppt)2(ClO4)2] ꢀ MeCN (2). In contrast, addition of EtOH to a solution of complex 1 in MeCN followed by slow evaporation
yields blue crystals of the five-coordinate polymeric complex {[CuII(pyppt)2](ClO4)2 ꢀ EtOH}1 (3). The structures of both complexes
have been determined by single crystal X-ray diffraction.
Ó 2004 Elsevier B.V. All rights reserved.
Keywords: 1,2,4-Triazole; Bidirectional ligands; N ligands; Copper; X-Ray crystal structure
1. Introduction
binding more than one metal centre in a bridging fash-
ion. Depending on the nature of the actual ligand this
can lead to dinuclear or oligonuclear complexes as well
as coordination polymers. Hydrogen bonding or p–p
interactions can also enhance cooperativity.
In the search for switchable molecular materials with
potential applications in nano-technology Fe(II) com-
plexes incorporating 1,2,4-triazole-based ligands have
been at the centre of attention for a number of years as
many of these compounds exhibit the spin crossover
phenomenon [1]. A wide range of such ligand systems
has been synthesised and a large number of mononu-
clear, oligonuclear and polynuclear complexes has been
obtained from them, some of which show promising
properties [2–4]. The provision of suitable interaction
pathways between the individual metal centres in a spin
crossover compound is desirable as this may lead to
cooperativity, thereby increasing the abruptness of the
spin transition and the width of the hysteresis loop [5].
This can be achieved by a variety of approaches, the
simplest being the employment of ligands capable of
Within the group of potentially dinucleating 4-
substituted 3,5-di(2-pyridyl)-4H-1,2,4-triazoles [3] only
the 4-amino and the 4-(4-methylphenyl) derivatives
NH2dpt [6–9] and pmdpt [10], respectively, have gener-
ated Fe(II) spin crossover compounds so far and all of
them are mononuclear. Introduction of an N4 sub-
stituent having additional donor atoms could give access
to interlinked mono- and dinuclear units resulting in the
assembly of multi-dimensional systems with increased
cooperativity. Such a ligand, namely 4,40-(1,4-pheny-
lene)bis[3-phenyl-5-(2-pyridyl)-4H-1,2,4-triazole] (Ph2-
PBPT) (Fig. 1), has recently been incorporated into a
one-dimensional polymeric Cu(II) complex, thus con-
firming the applicability of this approach [11].
The synthesis of the two hitherto unknown ligands 3-
phenyl-5-(2-pyridyl)-4-(4-pyridyl)-4H-1,2,4-triazole (py-
ppt) and 3,5-di(2-pyridyl)-4-(4-pyridyl)-4H-1,2,4-triazole
(pydpt) was pursued [12] as they were anticipated to be
q Supplementary data associated with this article can be found, in the
online version, at doi:10.1016/j.ica.2004.03.044.
* Corresponding author. Tel.: +64-3-479-7919; fax: +64-3-479-7906.
E-mail address: sbrooker@alkali.otago.ac.nz (S. Brooker).
0020-1693/$ - see front matter Ó 2004 Elsevier B.V. All rights reserved.
doi:10.1016/j.ica.2004.03.044

3414
M.H. Klingele, S. Brooker / Inorganica Chimica Acta 357 (2004) 3413–3417
2.2. Preparation of [CuII (pyppt)2(ClO4)2] ꢀ H2O (1)
N
N
N
N
A blue solution of Cu(ClO4)2 ꢀ 6H2O (185 mg,
0.50 mmol) in EtOH (10 ml) was added dropwise to a
refluxing colourless solution of pyppt (299 mg,
1.00 mmol) in EtOH (40 ml). Halfway through the ad-
dition a solid started to precipitate from the reaction
mixture. After complete addition, the resulting blue–
green suspension was refluxed for another 1 h and was
then allowed to cool to room temperature. The precip-
itate was filtered off and washed with EtOH. Drying in
vacuo gave 436 mg (96%) of complex 1 as a turquoise
microcrystalline solid. Anal. Calc. for C36H28Cl2CuN10
O9 (879.13 g molꢁ1): C 49.18, H 3.21, N 15.93. Found: C
49.18, H 3.37, N 15.70%. IR (KBr): m/cmꢁ1 ¼ 1615,
1586, 1538, 1505, 1475, 1444, 1414, 1347, 1307, 1267,
1217, 1179, 1145, 1107, 1027, 1007, 992, 928, 841, 790,
775, 749, 728, 714, 698, 675, 650, 635, 624. ESI-MS
(pos., MeCN): m=z ¼ 300:1 [(pyppt)H]þ, 330.6 [Cu(py-
N
N
N
N
Ph2PBPT
N
N
N
N
N
N
N
N
N
N N
pyppt
pydpt
Fig. 1. Structural drawings of the related ligands 4,40-(1,4-pheny-
lene)bis[3-phenyl-5-(2-pyridyl)-4H-1,2,4-triazole] (Ph2PBPT), 3-phen-
yl-5-(2-pyridyl)-4-(4-pyridyl)-4H-1,2,4-triazole (pyppt) and 3,5-di
(2-pyridyl)-4-(4-pyridyl)-4H-1,2,4-triazole (pydpt). The arrows indicate
the bidirectionality of these ligands.
ppt)2]2þ
,
341.2 [(pyppt)(MeCN)H]þ, 403.2 [Cu(py-
ppt)(MeCN)]þ, 599.4 [(pyppt)2H]þ, 661.3 [Cu
(pyppt)2]þ, 760.3 [Cu(pyppt)2(ClO4)]þ, 825.3 [Cu2(py-
ppt)2(ClO4)]þ, 960.5 [Cu(pyppt)3]þ, 1060.5 [Cu(py-
ppt)3(ClO4)]þ, 1124.4 [Cu2(pyppt)3(ClO4)]þ. UV/VIS/
NIR (MeCN): kmax/nm (e/L molꢁ1 cmꢁ1) ¼ 244 (43200),
297 (24100), 645 (100).
ligands suitable for the preparation of complexes of
higher nuclearity, and possibly supramolecular arrays,
due to their inherent bidirectionality (Fig. 1). The pres-
ence of only one bidentate binding site in pyppt as op-
posed to two in pydpt was expected to make the behaviour
of the former ligand more predictable. Due to this, and in
light of the apparent inability of 4-aryl-substituted 3,5-
di(2-pyridyl)-4H-1,2,4-triazoles to form dinuclear com-
plexes [3], we decided to focus initially on the exploration
of the coordination chemistry of pyppt. In this paper the
results of our probe into the bidirectionality of pyppt, by
reaction with Cu(ClO4)2 ꢀ 6H2O, are presented.
2.3. Preparation of [CuII (pyppt)2(ClO4)2] ꢀ MeCN (2)
Crystals of complex 2, suitable for single crystal
X-ray structure analysis, were obtained by vapour
diffusion of Et2O into a solution of complex 1 in
MeCN.
2.4. Preparation of {[CuII (pyppt)2](ClO4)2 ꢀ EtOH}
1
(3)
2. Experimental
Crystals of complex 3, suitable for single crystal X-
ray structure analysis, were obtained by the addition of
four parts of EtOH to a solution of complex 1 in one
part of MeCN followed by slow evaporation.
2.1. General
Cu(ClO4)2 ꢀ 6H2O was purchased from Aldrich and
used as received. 3-Phenyl-5-(2-pyridyl)-4-(4-pyridyl)-
4H-1,2,4-triazole (pyppt) was prepared as described
elsewhere [12]. The elemental analysis was carried out by
the Campbell Microanalytical Laboratory at the Uni-
versity of Otago. The infrared spectrum was recorded
over the range 4000–400 cmꢁ1 on a Perkin–Elmer
Spectrum BX FT-IR spectrophotometer. The ESI mass
spectrum was run on a MicroMass LCT mass spec-
trometer at the University of Canterbury. The UV/VIS/
NIR spectrum was recorded over the range 200–1400
nm on a Varian Cary 500 Scan UV/VIS/NIR spectro-
photometer.
2.5. X-Ray crystallography
Data were collected on Bruker SMART CCD area
detectors using grahite-monochromated Mo Ka radia-
ꢀ
tion k ¼ 0:71073 A). The structures were solved by di-
rect methods with SHELXS-97 [13,14] and refined against
F 2 using all data by full-matrix least-squares techniques
using SHELXL-97 [15]. All non-hydrogen atoms were
refined anisotropically. Hydrogen atoms were placed at
calculated positions and refined using a riding model
with thermal parameters 1.2 times the equivalent iso-
tropic thermal parameters of the atom to which they
were bonded.
Caution: While no problems were encountered in the
course of this work, ClO4ꢁ salts are potentially explosive
and should be handled with appropriate care!

M.H. Klingele, S. Brooker / Inorganica Chimica Acta 357 (2004) 3413–3417
3415
Table 1
Crystallographic data for [CuII(pyppt)2(ClO4)2] ꢀ MeCN (2) and
3. Results and discussion
{[CuII(pyppt)2](ClO4)2 ꢀ EtOH}1 (3)
When pyppt was reacted with Cu(ClO4)2 ꢀ 6H2O in a
2:1 molar ratio in EtOH a microcrystalline turquoise
solid precipitated from the reaction mixture which gave
an elemental analysis consistent with the formulation
[CuII(pyppt)2(ClO4)2] ꢀ H2O (1). In the IR spectrum of
2
3
Empirical formula
Formula weight
C38H29Cl2CuN11O8
902.16
C38H32Cl2CuN10O9
907.18
(g molꢁ1
)
Crystal system
Space group
Unit cell dimensions
triclinic
ꢁ
monoclinic
Pn
ꢁ
complex 1 the ClO4 m4 absorption was split into two
P1
equal intensity bands at 635 and 624 cmꢁ1, possibly due
to coordination of these ions to the metal centre [16] as
was later observed for complex 2. The ESI-MS was in
agreement with the proposed structure with no indica-
tion that the nitrogen donor of the 4-pyridyl group was
involved in any coordination. In order to establish the
molecular structure of complex 1 by X-ray diffraction a
number of recrystallisation methods to grow single
crystals were tried. Two of them were successful and
afforded suitable crystals. The ones obtained by vapour
diffusion of Et2O into a solution of the initial solid in
MeCN were found to have the composition [CuII(py-
ppt)2(ClO4)2] ꢀ MeCN (2) which confirmed the structural
assignment of complex 1. Unexpectedly, the crystals
obtained by slow evaporation of a solution of complex 1
in MeCN/EtOH were markedly different from those of
complex 2 and were identified as the EtOH-solvated
polymeric form {[CuII(pyppt)2](ClO4)2 ꢀ EtOH}1 (3)
(Table 1).
ꢀ
a (A)
8.2376(1)
10.0040(1)
12.9597(2)
79.722(1)
86.483(1)
83.524(1)
1043.22(2)
1
10.983(4)
13.875(5)
12.709(4)
90
ꢀ
b (A)
ꢀ
c (A)
a (°)
b (°)
c (°)
97.823(5)
90
3
ꢀ
V (A )
1918.8(11)
2
1.570
Z
qcalc (g cmꢁ3
l (mmꢁ1
T (K)
)
1.436
0.716
)
0.780
200(2)
461
blue prism
168(2)
930
blue plate
F ð000Þ
Crystal colour and
shape
Crystal size (mm3)
0.46 ꢂ 0.26 ꢂ 0.20
1.60/27.11
ꢁ10 ! 10
ꢁ12 ! 12
0 ! 16
0.60 ꢂ 0.18 ꢂ 0.06
2.18/26.42
ꢁ12 ! 13
ꢁ17 ! 17
ꢁ15 ! 15
24173
h
h
k
l
min=hmax (°)
Reflections collected 4506
Data/restraints/
parameter
4506/0/287
6362/2/542
The molecular structure of complex 2 is shown in
Fig. 2. The Cu2þ ion is octahedrally N4O2 coordinated
with two pyppt molecules occupying the equatorial
Goodness-of-fit
R1=wR2½I > 2rðIÞÞꢃ
R1=wR2 (all data)
Absolute structure
factor
1.103
0.0529/0.1618
0.0661/0.1720
1.022
0.0390/0.0810
0.0526/0.0852
)0.002(11)
ꢁ
positions and two ClO4 ions bound axially. For
mononuclear octahedral complexes of 4-substituted
3,5-di(2-pyridyl)-4H-1,2,4-triazoles with a metal-to-li-
gand ratio of 1:2 this trans-ðN0; N1Þ2 coordination
mode is the one most commonly observed and it is
usually accompanied by longer Cu–Npyr than Cu–Ntrz
distances [3]. This is also true for complex 2 with the
Maximum peak/hole 0.899/)0.583
0.559/)0.447
ꢁ3
ꢀ
(e A
)
Fig. 3 shows a section of the zig–zag chain of the five-
coordinate EtOH-solvated form {[CuII(pyppt)2]-
(ClO4)2 ꢀ EtOH}1 (3). The shortest distance between
ꢀ
respective distances being 2.045(2) and 1.989(2) A. In
related complexes of 4-amino-3,5-di(2-pyridyl)-4H-
1,2,4-triazole (NH2dpt) the Cu–Npyr and Cu–Ntrz dis-
tances are in the range of 2.027(3)–2.046(5) and
ꢀ
two Cu(II) centres in complex 3 [9.746(2) A] is within the
chain, with the corresponding Cu–Cu–Cu angle being
106.57(2)°. The N5 coordination sphere about the Cu2þ
ion is distorted square–pyramidal with the degree of
trigonality defined by the parameter s ¼ 0:24 [27]. Two
of the basal positions are occupied by N(1) and N(2) of
the bidentate pyridine–triazole moiety of one pyppt
molecule whose symmetry equivalent provides the third
basal donor atom in the form of its 4-pyridyl nitrogen
atom N(6A). The remaining basal donor atom N(8) is
provided by the triazole ring of the second pyppt mol-
ecule while its pyridine nitrogen atom N(7) occupies the
apical position. The nitrogen atom of the 4-pyridyl
group of this ligand molecule forms a hydrogen bond to
the hydroxyl hydrogen atom of the EtOH solvate
ꢀ
1.968(3)–1.987(5) A, respectively [17,18]. To the best of
our knowledge complex 2 is the first example of any
metal complex of a ligand featuring the bidentatꢁe
pyridine–triazole moiety to have coordinated ClO4
ꢀ
ions. The Cu–O distance of 2.466(3) A is relatively
shortꢁcompared to other CuN4O2 systems with axial
ClO4 coordination where distances in the range of
ꢀ
2.50–2.75 A are usually observed [19,20], although both
shorter [21–23] and longer distances [24–26] have also
been reported. There is only a 5.9(2)° deviation from
planarity within the pyridine–triazole moiety while the
phenyl and the 4-pyridyl groups are tilted by 19.6(2)°
and 84.5(1)°, respectively, relative to the triazole mean
plane. The shortest Cuꢀ ꢀ ꢀCu distance, between two
ꢀ
[N(12)ꢀ ꢀ ꢀO(41) 2.82 A]. Once again, the Cu–Npyr dis-
ꢀ
tances are all longer than the Cu–Ntrz distances. As
molecules, is 8.2376(1) A.

3416
M.H. Klingele, S. Brooker / Inorganica Chimica Acta 357 (2004) 3413–3417
Fig. 2. View of the molecular structure of [CuII(pyppt)2(ClO4)2] ꢀ MeCN (2). Hydrogen atoms have been omitted for clarity. The MeCN solvate is not
ꢀ
shown. Selected distances (A): Cu(1)–N(1) 2.045(2), Cu(1)–N(2) 1.989(2), Cu(1)–O(11) 2.466(3). Selected angles (°): N(1)–Cu(1)–N(2) 80.46(9), N(1)–
Cu(1)–O(11) 92.12(11), N(1)–Cu(1)–N(2A) 99.54(9), N(1)–Cu(1)–O(11A) 87.88(11), N(2)–Cu(1)–O(11) 89.07(11), N(2)–Cu(1)–O(11A) 90.93(11).
Symmetry operation used to generate equivalent atoms: (a) ꢁx þ 2; ꢁy; ꢁz.
Fig. 3. View of a section of the zig–zag chain of {[CuII(pyppt)2](ClO4)2 ꢀ EtOH}1 (3). Hydrogen atoms, except for the hydrogen atom of the EtOH
solvate involved in the hydrogen bonding, have been omitted for clarity. The ClOꢁ4 ions are not shown. Selected distances (A): Cu(1)–N(1) 2.053(3),
ꢀ
Cu(1)–N(2) 1.960(3), Cu(1)–N(7) 2.227(3), Cu(1)–N(8) 2.001(3), Cu(1)–N(6A) 2.060(3). Selected angles (°): N(1)–Cu(1)–N(2) 79.35(12), N(1)–Cu(1)–
N(7) 104.64(12), N(1)–Cu(1)–N(8) 95.12(12), N(1)–Cu(1)–N(6A) 159.10(12), N(2)–Cu(1)–N(7) 101.12(12), N(2)–Cu(1)–N(8) 173.77(13), N(2)–
Cu(1)–N(6A) 92.95(12), N(7)–Cu(1)–N(8) 77.36(12), N(7)–Cu(1)–N(6A) 95.86(12), N(8)–Cu(1)–N(6A) 93.22(12). Symmetry operations used to
generate equivalent atoms: (a) x ꢁ 0:5; ꢁy þ 1; z ꢁ 0:5; (b) x ꢁ 1; y; z ꢁ 1; (c) x ꢁ 1:5; ꢁy þ 1; z ꢁ 1:5; (d) x ꢁ 2; y; z ꢁ 2; (e) x ꢁ 2:5; ꢁy þ 1; z ꢁ 2:5.
could be expected from the fact that N(7) is the apical
donor, the Cu(1)–N(7) distance is considerably longer
ꢀ
[2.227(3) A] than the other two Cu–Npyr distances
ꢀ
[2.053(3) and 2.060(3) A] and, of the two Cu–Ntrz dis-
ꢀ
tances, the Cu(1)–N(8) distance [2.001(3) A] is some-
The pyridine–triazole moieties of the two pyppt mole-
cules are not completely flat but show slight deviations
from planarity [6.3(2)° and 9.9(2)°, respectively]. Both
the phenyl and the 4-pyridyl groups of the two ligand
molecules are inclined relative to the triazole mean
plane, by 28.5(1)° and 43.8(1)° for the phenyl groups
ꢀ
what longer than the Cu(1)–N(2) distance [1.960(3) A].

M.H. Klingele, S. Brooker / Inorganica Chimica Acta 357 (2004) 3413–3417
3417
and 70.2(1)° and 74.4(1)° for the 4-pyridyl groups,
respectively.
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with a number of grants including a University of Otago
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Prof. G.R. Clark (University of Auckland) are thanked
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