The novel ligand 4′-phenyl-3,2′:6′,3′′-terpyridine (L) and the supramolecular structure of the dinuclear complex [Zn2(μ-L)(acac)4] · H2O (acac = acetylacetonato)

Article abstract of DOI:10.1016/j.inoche.2008.09.009

The new terpyridyl ligand 4′-phenyl-3,2′:6′,3′′-terpyridine (L) reacts with Zn(acac)₂ to produce the dizinc complex [Zn₂(μ-L)(acac)₄] · H₂O (1) (acac = acetylacetonato). The analysis of the crystal structure of this zero-dimensional (0D) complex shows the existence of two Zn(acac)₂ centers bridged symmetrically by one μ-L ligand. The key role played by the acac and L ligands and the guest water molecule allows the generation of a series of intermolecular hydrogen bonds of the O-H/O, C-H/O and C-H/π type which give raise to a 3D supramolecular array. The observed C-H/π interactions are so widespread that all the π-rings present in the structure, viz., those belonging to the L ligand as well as the acetylacetonato chelate rings, participate as hydrogen bond acceptors.

Full text of DOI:10.1016/j.inoche.2008.09.009

Inorganic Chemistry Communications 11 (2008) 1388–1391
Contents lists available at ScienceDirect
Inorganic Chemistry Communications
journal homepage: www.elsevier.com/locate/inoche
The novel ligand 40-phenyl-3,20:60,300-terpyridine (L) and the supramolecular
structure of the dinuclear complex [Zn2(
l
-L)(acac)4] ꢀ H2O (acac = acetylacetonato)
a
b
b
c
d
Juan Granifo a, , Moisés Vargas , María T. Garland , Andrés Ibáñez , Rubén Gaviño , Ricardo Baggio
*
a Departamento de Ciencias Químicas, Facultad de Ingeniería, Ciencias y Administración, Universidad de La Frontera, Casilla 54-D, Temuco, Chile
b CIMAT, Facultad de Ciencias Físicas y Matemáticas, Universidad de Chile, Casilla, 653 Santiago, Chile
c Instituto de Química, Universidad Nacional Autónoma de México, Cd. Universitaria, Circuito Exterior Coyoacán, 04510 México D.F., México
d Departamento de Física, Comisión Nacional de Energía Atómica, Av. Gral Paz 1499, 1650 San Martín, Pcia. de Buenos Aires, Argentina
a r t i c l e i n f o
a b s t r a c t
The new terpyridyl ligand 40-phenyl-3,20:60,300-terpyridine (L) reacts with Zn(acac)2 to produce the dizinc
complex [Zn2(
-L)(acac)4] ꢀ H2O (1) (acac = acetylacetonato). The analysis of the crystal structure of this
zero-dimensional (0D) complex shows the existence of two Zn(acac)2 centers bridged symmetrically by
one -L ligand. The key role played by the acac and L ligands and the guest water molecule allows the
generation of a series of intermolecular hydrogen bonds of the O–H/O, C–H/O and C–H/ type which give
raise to a 3D supramolecular array. The observed C–H/ interactions are so widespread that all the
Article history:
Received 7 July 2008
Accepted 10 September 2008
Available online 16 September 2008
l
l
p
Keywords:
Polypyridine complexes
Supramolecular structure
C–H/p interaction
C–H/O interaction
p
p-
rings present in the structure, viz., those belonging to the L ligand as well as the acetylacetonato chelate
rings, participate as hydrogen bond acceptors.
Ó 2008 Elsevier B.V. All rights reserved.
Hydrogen bond
The tridentate ligand 2,20:60200-terpyridine and its derivatives
bonded to a metal have been well studied in the area of supramo-
lecular chemistry [1,2]. Recently, as an extension in the exploration
of this type of metal-binding domains, symmetric divergent and
40-functionalized terpyridine have been used in the formation of
coordination architectures [3,4]. Indeed, the scarcely reported
examples on this subject include only the 4,400 ligands 40-phenyl-
4,20:60,400-terpyridine and 40-(4000-octyloxyphenyl)-4,20-60,400-ter-
pyridine and their coordination to ZnCl2 generating polymeric 1D
helical networks, which exhibit intermolecular C–H/Cl hydrogen
bonds [3,4]. In this context, with the aim on going further in the
understanding of the bonding properties of this new class of ter-
pyridyl derivatives, we report the synthesis and characterization
of the novel 3,300 ligand 40-phenyl-3,20:60,300-terpyridine (L)
(Scheme 1) and the supramolecular structure of its reaction prod-
ing acac shows two types of interactions, one by using either its
CH and/or CH3 groups (hydrogen bond donor) and the other one
involving the
p-system of the chelate ring (as a hydrogen bond
acceptor). It was also inferred that the strength of the acac ligand
as H-bond donor depends on the acid hardness of the metal cen-
tres; complexes with soft Lewis acids metals centers have ten-
dency to produce stronger interactions than those with hard
ones. The application of these concepts to the construction of the
supramolecular assembly of the molecules of 1 allows to under-
stand the form in which the structure expands to reach a three-
dimensional array.
The ligand L was prepared in a similar way to that of its isomer
40-phenyl-4,20:60,400-terpyridine from 3-acetylpyridine and benzal-
dehyde [3], but the crude product was purified by vacuum column
chromatography over silica gel [7]. The new compound was char-
acterized by satisfactory elemental analysis, FT-IR spectrum, mass
spectrum and 1H, 13C NMR spectra [7]. The assignment of the res-
onance signals of protons was established by coupling constants
proton spectrum and 1H–1H COSY-45. The five phenyl protons
can be readily distinguished from the other for the characteristic
AA’BB’X pattern in the region 7.52–7.81 ppm. The two protons of
the central pyridine ring appear as a sharp singlet at 7.96 ppm.
Those protons of the 3-pyridyl groups show an expected low field
broad singlet at 9.39 ppm due to two H-2 protons, while the six
remaining protons of these rings H-4, H-5 and H-6 were assigned
to the chemical shifts of 8.51, 7.46 and 8.71 ppm, respectively.
The ligand L reacts with Zn(acac)2 in a methanol solution to pro-
duce light yellow crystals of 1, which are unstable when taken out
uct with Zn(acac)2 the dizinc complex [Zn2(
l
-L)(acac)4] ꢀ H2O (1).
The weak hydrogen bonds of the CH/ type have been extensively
p
studied in the past years [5]. Despite this, only recently the specific
presence of the chelating acac ligand have been introduced as an
additional factor to be considered in the analysis of the hydrogen
´
bond interactions in metal complexes. In fact, Zaric et al. [6] have
evaluated the noncovalent interactions of the C–H/ type between
p
the coordinated acac ligand and phenyl rings, on the basis of the
crystal structures from the Cambridge Structural Database and by
quantum chemical calculations. It was concluded that the chelat-
* Corresponding author. Tel.: +56 045 325434; fax: +56 045 325440.
E-mail address: jgranifo@ufro.cl (J. Granifo).
1387-7003/$ - see front matter Ó 2008 Elsevier B.V. All rights reserved.
doi:10.1016/j.inoche.2008.09.009

J. Granifo et al. / Inorganic Chemistry Communications 11 (2008) 1388–1391
1389
equatorial base. The three pyridine-based rings of the L ligand form
a nearly planar structure; each outer pyridyl group is twisted with
respect to the central one, subtending a dihedral angle of 6.46°. In
contrast, the dihedral angle between the central ring and phenyl
group amounts 44.42°.
The most conspicuous feature of the structure of 1 is its packing,
organized in a ‘‘hierarchical” disposition of interactions strengths
(or levels) leading to different types of well differentiated arrays.
Thus, in a first level we find the (strong) H-bonds generating chains
(1D structures) which run along (010); in a second level, a mixture
N
N
N
of (middle strength) non-conventional C–H/O bonds and C–H/
p
interactions which laterally join the former chains into 2D frame-
works parallel to (001); and in a third final level, a variety of
Scheme 1. The sketch of ligand L.
(weaker) C–H/p contacts which connect layers into a 3D structure.
of the mother liquor where it seems the solvated water is lost [8].
Single crystal X-ray diffraction at 123 K [9], shows that 1 consists
of a bis-monodentate L ligand bridging two {Zn(acac)2} fragments
through its 3-pyridyl N atoms, the whole assembly being halved by
a two fold axis for what only half of the group is crystallographi-
In this way, the hydrogen-bonded 16-membered ring of 1, as
shown in Fig. 1, can be considered as the basic building unit for
the 1D array. This comes from the visualization that the crystalliza-
tion water molecule plays a fundamental double role in the ‘‘first
level” interactions giving raise to this 1D substructure. First, as
mentioned above, acting as a donor for two symmetric H-bonds di-
rected towards O-acac atoms. Second, as an acceptor of the H-bond
donated by the outermost C–H group of a neighbor phenyl ring, to
produce a perfect linear C–Hꢀ ꢀ ꢀO arrangement (C121–H121ꢀ ꢀ ꢀO1W
180°) (Fig. 2). This intermolecular interaction promotes a head-to-
tail packing of the basic cyclic structures to give a clear 1D H-
bonded chain parallel to the b axis (heavy broken lines in Fig. 2).
These one-dimensional H-bonded chains are further connected
cally independent. As illustrated in Fig. 1, the resulting (
cac)2}2 branched unit is externally closed, at both sides, by a strong
H-bonded hydration water that bridges two acac atoms
l-L){Zn(a-
O
(O1Wꢀ ꢀ ꢀO12 3.045(3) Å) to configure finally a 16-membered ring.
Each Zn center has a 4 + 1 coordination sphere; four sites are pro-
vided by two different acac groups coordinated in the usual chelat-
ing form through their carbonyl O donor, the planar groups
subtending an angle of 69.9(1)° to each other. The fifth site of the
coordination polyhedron is occupied by a 3-pyridyl N atom from
the L ligand. The geometry around Zn1 is an almost perfect trigonal
bipyramid, with an apical O13–Zn1–O22 angle of 175.5(1)° and the
apical bonds deviating less than 2.6(1)° from the normal to the
into 2D structures by a combination of interchain CH/O and CH/
hydrogen bonds: two CH(pyridyl)/O(acac), one CH(pyridyl)/ (phe-
nyl ring) and one CH(pyridyl)/ (chelate-acac ring). All these four
p
p
p
‘‘second level” interactions are represented in Fig. 2 as simple bro-
ken lines and their geometric parameters are given in the legend.
One of the CH(pyridyl)/O(acac) connections, C31H31ꢀ ꢀ ꢀO23, corre-
sponds to the major component of a bifurcated hydrogen bond and
the other one to a single contact, C71H71ꢀ ꢀ ꢀO23, nevertheless the
bond distances and angles of both CH/O links [C31ꢀ ꢀ ꢀO23,
3.282 Å, 143°; C71ꢀ ꢀ ꢀO23, 3.473 Å, 161°] are within the expected
range for this class of H-bonds [10]. Similarly, the CH(pyridyl)/
p(phenyl ring) interaction in 1 agree with the results obtained
elsewhere [11] through a crystallographic database (CSD) survey
on transition metal compounds, and where the short distance
H(donor)ꢀ ꢀ ꢀC(aceptor) between aromatic groups has been used as
a parameter. More specifically, this contact correspond in 1 to
the H11ꢀ ꢀ ꢀC111 pair with a Hꢀ ꢀ ꢀC distance of 2.708 Å, which is very
similar to the observed average value (2.86 0.13) [11]. However,
it has been also settled that the C–H donor groups tend to be ori-
ented toward the centroid of the phenyl ring [11,12]. In this regard,
the C–Hꢀ ꢀ ꢀPh interaction is usually described as C–Hꢀ ꢀ ꢀCg (Cg refers
to the centroid of the phenyl ring) and in our case is designated as
C11–H11ꢀ ꢀ ꢀCg5 (Fig. 2). The last interaction in this second level set,
comes from the minor component, C31–H31ꢀ ꢀ ꢀCg1, of the above al-
luded bifurcated hydrogen bond, which involves as H-donor a 3-
pyridyl group and the p-system of the acetylacetonato chelate ring
as acceptor (Fig. 2). It has been observed that the donor/acceptor
steric effects produce a shorter linkage distance Hꢀ ꢀ ꢀcentroid(che-
late-acac ring) in square–planar complexes than those in the more
sterically crowded octahedral complexes [6]. The H31ꢀꢀꢀCg1 dis-
tance of 2.82 Å in 1 correlates well with a five-coordinated envi-
ronment around the Zn(II) cation, since is shorter than the values
found in octahedral complexes with metal(II) centers (>3.05 Å) [6].
Fig. 1. Molecular diagram of 1, with anisotropic displacement ellipsoids drawn at a
40% probability level. Independent atoms represented as labeled full ellipsoids in
full bonds. H atoms attached to carbon were removed for clarity. The heavy broken
lines represent hydrogen bonds. Selected bond lengths (Å) and bond angles (°):
Zn1–O23 1.979(2), Zn1–O12 1.987(2), Zn1–O13 2.031(2), Zn1–O22 2.044(2), Zn1–
N11 2.092(2), O23–Zn1–O12 113.07(9), O23–Zn1–O13 91.72(9), O12–Zn1–O13
89.42(9), O23–Zn1–O22 92.72(9), O12–Zn1–O22 89.47(9), O13–Zn1–O22
175.50(8), O23–Zn1–N11 113.67(9), O12–Zn1–N11 133.23(9), O13–Zn1–N11
87.60(9), O22–Zn1–N11 89.99(9), O1Wꢀ ꢀ ꢀO12 3.045(3), H1Wꢀ ꢀ ꢀO12 2.24(3),
O1W–H1Wꢀ ꢀ ꢀO12 161(4).
Finally, in a series of five C–Hꢀ ꢀ ꢀ
p contacts (our ‘‘third hierarchi-
cal level”) involving the acetylacetonato ligand, the 2D layers inter-
act with their upward/downward neighbors to form an infinite 3D
network (Fig. 3). Here, only the C33–H33ꢀ ꢀ ꢀCg3(3-pyridyl) interac-
tion presents the CH(acac) group as H-donor. The C33ꢀ ꢀ ꢀCg3 bond
length of 3.99 Å is centred within the reported range of 3.73–4.25 Å

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J. Granifo et al. / Inorganic Chemistry Communications 11 (2008) 1388–1391
Fig. 2. Packing view parallel to (001) showing first and second level interactions in 1. Chains run horizontally, parallel to [010]. H-bonds of the first level type drawn in heavy
broken lines; second level ones, in simple broken lines. All the methyl groups and those H atoms not involved in the interactions were removed for clarity. Intermolecular
hydrogen bonds (a) first level type: C121iꢀ ꢀ ꢀO1W, 3.256(8) Å, 180°; (b) second level type: C31iiꢀ ꢀ ꢀO23, 3.282(4) Å, 143°; C71iiꢀ ꢀ ꢀO23, 3.473(4) Å, 161°; C11iiiꢀ ꢀ ꢀCg5, 4.07 Å,
154°; C31iiꢀ ꢀ ꢀCg1, 3.58 Å, 140°. [Ring centroid codes: (Cg1): Zn1, O12, C22, C32, C42, O22; (Cg5): C91, C101, C111, C121, C111iv, C101iv. Symmetry codes: (i) x, ꢁ1 + y, z; (ii)
0.5 ꢁ x, ꢁ0.5 + y, 0.5 ꢁ z; (iii) 0.5 ꢁ x, 0.5 + y, 0.5 ꢁ z, (iv) 1 ꢁ x, y, 0.5 ꢁ z].
for complexes with metals of borderline Lewis acid hardness like
Zn(II) [6]. All the four remaining interactions have the CH3 group
as H-bond donor, two of them are directed towards individual
pyridyl groups (C52–H52Cꢀ ꢀ ꢀCg3; C12–H12Cꢀ ꢀ ꢀCg4) and the other
two towards individual acac-chelate rings (C13–H13Bꢀ ꢀ ꢀCg1;
C52-H52Bꢀ ꢀ ꢀCg2). The previously communicated interval of the
H(methyl)ꢀ ꢀ ꢀCg(pyridyl) distances goes from 2.2 to 4.1 Å [6]. In 1,
both values are clearly inside this wide range, 3.06 (H52Cꢀ ꢀ ꢀCg3)
and 2.91 (H12Cꢀ ꢀ ꢀCg4) Å. Very close to these values appear
those of the two H(methyl)ꢀ ꢀ ꢀCg(acac-chelate) interactions, 3.02
(H13Bꢀ ꢀ ꢀCg1) and 2.90 (H52Bꢀ ꢀ ꢀCg2) Å. This kind of interaction that
occurs between two acac moieties has not been characterized pre-
Fig. 3. Packing diagram showing the third level CH/p interactions in 1, involving
the H-donor (CH, CH3) and the -donor (chelate ring) groups of the acetylacetonato
p
ligand. Intermolecular hydrogen bonds (third level type): C33ivꢀ ꢀ ꢀCg3, 3.99 Å, 167°;
C52vꢀ ꢀ ꢀCg3, 3.76 Å, 131°; C12vꢀ ꢀ ꢀCg4, 3.78 Å, 151°; C13ivꢀ ꢀ ꢀCg1, 3.78 Å, 137°;
C52vꢀ ꢀ ꢀCg2, 3.82 Å, 160°. [Ring centroid codes: (Cg1): Zn1, O12, C22, C32, C42,
O22; (Cg2): Zn1, O13, C23, C33, C43, O23; (Cg3): N11, C11, C21, C31, C41, C51;
(Cg4): N21, C61, C71, C81, C71vi, C61vi. Symmetry codes: (iv) x, 1 ꢁ y, 0.5 + z; (v) x,
1 ꢁ y, ꢁ0.5 + z; (vi) 1 ꢁ x, y, 1/2 ꢁ z].
Fig. 4. Schematic representation of a single unit of complex 1, showing all those
noncovalent interactions in which the structure acts as an acceptor. All the methyl
groups and those H atoms not involved in the interactions were removed for clarity.
H-bonds of the first level type drawn in heavy broken lines; second level ones, in
simple broken lines; third level ones, in double broken lines.

J. Granifo et al. / Inorganic Chemistry Communications 11 (2008) 1388–1391
1391
was reduced in volume to its third part and treated with water (100 mL). The
precipitate was filtered up and redissolved in hot ethanol (40 mL). The cooled
solution gave a yellowish microcrystalline substance, which was treated again
with hot ethanol to yield a white precipitate. The crude product was purified
by vacuum column chromatography over silica gel (EtOAc/n-hexane 15%). The
viously, but its similitude with the H(methyl)ꢀ ꢀ ꢀCg(pyridyl) assem-
ble, evidenced through the comparison of their observed bond dis-
tances, induce us to assume the existence of a similar type of weak
contact. As a summary, Fig. 4 displays all the noncovalent contacts
accepted by a single unit of complex 1.
less polar product was recrystallized (dichloromethane/hexane) to give
a
white solid of L. Yield: 20%. M.p. 219–221 °C. Anal. Calcd. For C21H15N3. C:
81.53; H: 4.89; N: 13.58%. Found: C: 81.60; H: 4.99; N: 13.39 %. IR (KBr, cmꢁ1):
1607, 1550, 1405, 1023, 808, 759, 697. 1H NMR (200 MHz, CDCl3, 298 K):
d = 9.39 (br s, 2H), 8.71 (br d, 2H, J = 4.8 Hz), 8.51 (dt, 2H, J = 8.2 , 1.8 Hz), 7.96
(s, 2H), AA’BB’X system observed at 7.52–7.61 (3H) and 7.72–7.81 (2H), 7.46
(2H, dd, 8.2, 4.8 Hz). 13C-PND and 13C-DEPT NMR (50 MHz, CDCl3, 298 K):
155.3 (Cquat.), 150.8 (Cquat.), 150.2 (CH), 148.4 (CH), 138.2 (Cquat.) 134.4 (Cquat.,
CH), 129.4 (CH), 129.2 (CH), 127.1 (CH), 123.6 (CH), 117,7 (CH). HRMS (FAB+)
calcd for C21H15N3 [M + 1]+ 310.1344, found 310.1351, MS (EI+, 70 eV), for
C21H15N3 ([M]+) 309 (100%), 308 (36%), 231 (7%).
Acknowledgements
We are grateful to the Universidad de La Frontera for financial
support (Proyecto DIUFRO DI07-0114). We thank Rocio Patiño
and Erendida García for technical assistance.
[8] Synthesis of [Zn2(L)(acac)4] ꢀ H2O (1): To
a hot solution of L (7.8 mg,
Appendix A. Supplementary material
0.025 mmol) in methanol (3.0 ml) was added Zn(acac)2 (99.7 mg,
0.378 mmol). The resultant solution was cooled at room temperature in a
closed vessel and after standing for several hours a crystalline solid was
formed. After selecting suitable crystals for X-ray analysis, the rest of the
product was collected by filtration, washed with methanol and dried at room
temperature. The resulting light yellow crystals become opaque when exposed
to air, due to that the compound easily released the guest H2O molecule to
form a partially dehydrated compound. (19.0 mg, 88.9% yield). Anal. Calcd. for
C41H45N3O9Zn2: C, 57.62; H, 5.31; N, 4.92. Found: C, 58.01; H, 5.02; N, 5.03%.
[9] Crystal data were collected on a Bruker Smart CCD difractometer at 123 K
CCDC 693795 contains the supplementary crystallographic data
for 1. These data can be obtained free of charge via http://
www.ccdc.cam.ac.uk/data_request/cif, 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.
Supplementary data associated with this article can be found, in
the online version, at doi:10.1016/j.inoche.2008.09.009.
using Mo K
a radiation (k = 0.71073 Å). The structure was solved by direct
methods and refined by full-matrix least squares on F2 using the SHELXS-97
software. All non-hydrogen atoms were refined anisotropically; the water
hydrogen was found in a difference Fourier and refined with restraints; those
bound to carbon were instead idealized. The structural analysis was performed
with the help of the multipurpose PLATON program. Crystallographic data for
C41H43N3O8Zn2 ꢀ H2O (1): Mw = 854.54, monoclinic, space group C2/c, a =
16.9967(13) Å , b = 17.2414(13) Å , c = 14.2974(11) Å , Z = 2, b = 108.616(2)°,
References
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,
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ˇ ˇ
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r
[7] Synthesis of 40-phenyl-3,20:60,300-terpyridine (L): A mixture of 3-acetylpyridine
(2.42 g, 0.02 mol), benzaldehyde (1.06 g, 0.01 mol) and NaOH (1.3 g) in water
(15 mL) and ethanol (15 mL) was stirred for three days after which water
(100 mL) was added to give an amorphous white mass which was separated by
filtration, washed with plenty of water and dried in oven at 100 °C for a couple
of hours. The obtained white cake was treated with ammonium acetate (12 g)
in refluxing ethanol (80 mL) for 20 h. The resulting orange colored solution
electron density: 0.654/ꢁ0.454 eAꢁ3
.
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