The new sulphur-containing ligand 4′-(4-methylthiophenyl)-3,2′: 6′,3″-terpyridine (L1) and the supramolecular structure of the dinuclear complex [Zn2(μ-L1)(acac)4] (acac = acetylacetonato): The key role of non-covalent S?O contacts a

Article abstract of DOI:10.1016/j.molstruc.2011.10.038

The new terpyridyl ligand 4′-(4-methylthiophenyl)-3,2′: 6′,3″-terpyridine (L1) combines with Zn(acac)₂ to form the dizinc complex [Zn₂(μ-L1)(acac)₄] (1) (acac = acetylacetonato). The single crystal structure of 1 shows the

Full text of DOI:10.1016/j.molstruc.2011.10.038

Journal of Molecular Structure 1006 (2011) 684–691
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Journal of Molecular Structure
journal homepage: www.elsevier.com/locate/molstruc
The new sulphur-containing ligand 40-(4-methylthiophenyl)-3,20:60,300-terpyridine
(L1) and the supramolecular structure of the dinuclear complex [Zn2(l-L1)(acac)4]
(acac = acetylacetonato): The key role of non-covalent Sꢀ ꢀ ꢀO contacts and C–Hꢀ ꢀ ꢀS
hydrogen bonds
b
Juan Granifo a, , Rubén Gaviño , Eleonora Freire c,d,1, Ricardo Baggio c
⇑
a Departamento de Ciencias Químicas y Recursos Naturales, Facultad de Ingeniería, Ciencias y Administración, Universidad de La Frontera, Casilla 54-D, Temuco, Chile
b Instituto de Química, Universidad Nacional Autónoma de México, Cd. Universitaria, Circuito Exterior Coyoacán, 04510 México, DF, Mexico
c Departamento de Física, Comisión Nacional de Energía Atómica, Av. Gral Paz 1499, 1650 San Martín, Pcia. de Buenos Aires, Argentina
d Escuela de Ciencia y Tecnología, Universidad Nacional de San Martín, 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-(4-methylthiophenyl)-3,20:60,300-terpyridine (L1) combines with Zn(acac)2 to
form the dizinc complex [Zn2(l-L1)(acac)4] (1) (acac = acetylacetonato). The single crystal structure of 1
shows the existence of two different Zn(acac)2 centres bridged by the L1 ligand through its two 3-pyridyl-
nitrogen atoms. The acac and L1 ligands allow the generation of a series of intra- and intermolecular
Article history:
Received 21 August 2011
Received in revised form 19 October 2011
Accepted 20 October 2011
Available online 28 October 2011
hydrogen bonds of the C–Hꢀ ꢀ ꢀN, C–Hꢀ ꢀ ꢀO and C–Hꢀ ꢀ ꢀ
p type. In addition, the presence of the CH3–S group
in L1 plays a crucial role by providing the non-covalent Sꢀ ꢀ ꢀO, Sꢀ ꢀ ꢀH and H(CH3)ꢀ ꢀ ꢀO contacts, which per-
mit to describe fully this unusual supramolecular network. The NMR spectra of 1 in CDCl3 solution con-
firm the presence of the two zinc atoms joined by the bridging L1 ligand, but, differently to the solid state,
their environments are identical.
Keywords:
Sꢀ ꢀ ꢀO interactions
C–Hꢀ ꢀ ꢀS hydrogen bonds
Zinc(II) complexes
Acetylacetonate
40-(4-Methylthiophenyl)-3,20:60,300-
terpyridine
Ó 2011 Elsevier B.V. All rights reserved.
1. Introduction
using a series of intermolecular hydrogen bonds: either conven-
tional (of the O–H/O type) or non-conventional (C–H/O and CH/
p
The study of the coordination chemistry of 2,20:60,200-terpyridine
and its derivatives has been ascribed more widely to its action as
chelating ligands, i.e., where they present a convergent disposition
of its N-pyridyl donor atoms to link the metal centres [1,2]. In con-
trast, terpyridine-based ligands with the divergent mode able to
bridge at least two metal centres are scarse; a few recent examples
can be found mainly for functionalized 4,20:60,400-terpyridines [3].
In this regard and only in two recent works, 3,300 divergent and 40-
functionalized terpyridines [40-phenyl-3,20:60,300-terpyridine (L2,
Scheme 1) and 40-(4-pyridyl)-3,20:60,300-terpyridine] involving the
N 3-pyridyl atoms as linkers have been used [4]. More specifically,
the reported examples that include one of these ligands are a
coordination polymer [4b] and a dinuclear compound [4a]. This last
complex, which incorporates the L2 ligand, was formulated as
[5,6]) including those CH/ arising between the coordinated acac li-
p
´
´
gand and phenyl rings, recently proposed by Zaric et al. [7]. Zaric
et al. demonstrated that the chelating acac shows two types of inter-
actions, 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). With the aim on going further in
the study of the bonding and supramolecular properties of this kind
of systems, we replaced the L2 ligand, with its phenyl ring, by the
related L1 ligand, with
(Scheme 1). The result of the reaction of L1 with Zn(acac)2 was the
new dizinc complex [Zn2( -L1)(acac)4] (1) with the sulphur atom
a 4-methylthiophenyl group instead
l
of the 4-methylthio substituent non-coordinated, but instead it
appears involved in the singular non-covalent Sꢀ ꢀ ꢀO and Sꢀ ꢀ ꢀH
interactions.
[Zn2(
l
-L2)(acac)4]ꢀH2O (acac = acetylacetonato) (2). The supramo-
lecular structure of 2 was described on the basis of the key role
2. Results and discussion
played by the acac and L2 ligands and the guest water molecule by
2.1. Synthesis
⇑
Corresponding author.
E-mail address: jgranifo@ufro.cl (J. Granifo).
Member of CONICET.
The L1 ligand was prepared via the one-step general method by
mixing 3-acetylpyridine, 4-(methylthio)benzaldehyde and NH3 in
1
0022-2860/$ - see front matter Ó 2011 Elsevier B.V. All rights reserved.
doi:10.1016/j.molstruc.2011.10.038

J. Granifo et al. / Journal of Molecular Structure 1006 (2011) 684–691
685
Scheme 1. The sketches of the ligands L1 and L2. For L1 the numbering of carbon
atoms (hydrogen atoms where correspond) is indicated.
a EtOH solution. The newly synthesized ligand was characterized by
elemental analysis, 1H, 13C and 2D NMR experiments, mass spec-
trometry and IR spectroscopy. Complex 1 was prepared by the reac-
tion of an excess of Zn(acac)2 with L1 in a hot acetonitrile solution,
from which colourless blocks suitable for single crystal X-ray analy-
sis were obtained.
Fig. 1. Molecular diagram of 1, with anisotropic displacement ellipsoids drawn at a
40% probability level. The disordered PhSCH3 end shown in full/broken lines. H
atoms removed, for clarity.
2.2. The NMR spectra of L1 (performed through COSY, DEPT, PND)
The NMR results in CDCl3 solution of the L1 molecule are in good
agreement with the expected molecular structure (Scheme 1 and
Section 5.1). Thus, the 13C NMR spectrum shows one solitary methyl
group (15.13 (C22) ppm) and the corresponding signals of the aro-
matic region: four due to quaternary carbons [134.00 (C16 superim-
posed with C4/C12), 140.76 (C19), 149.69 (C8), 155.00 (C6/C10) ppm]
and seven due to CH carbons [116.83 (C7/C9), 123.38 (C2/C14),
126.34 (C17/C21), 127.10 (C18/C20), 134.22 (C3/C13), 148.13 (C1/
C15), 149.95 (C5/C11) ppm]. Similarly, the 1H NMR is characterized
for a high field singlet (2.48 ppm) due to the three protons of the thio-
methyl group. The four phenyl protons can be readily distinguished
from the other for the characteristic AA0BB0 pattern of H18/H20
(7.30 ppm) and H17/H21 (7.57 ppm). The two protons of the central
pyridine ring H7/H9 appear as a sharp singlet (7.79 ppm). Those four
protons of the 3-pyridyl groups next to the electronegative N atoms,
H5/H11 (9.29 ppm) and H1/H15 (8.63 ppm), together with the two
H3/H13 (8.39 ppm) protons, show the largest displacement towards
low field. The two remaining protons H2/H14 (7.36 ppm) of the 3-
pyridyl rings appear in a predictable manner as a multiplet.
Table 1
Selected bond lengths (Å) and bond angles (°) for 1.
Bond distances
Zn1–O1A
Zn1–O1B
Zn1–O2A
Zn1–O2B
Zn1–N1
Zn2–O1C
Zn2–O1D
Zn2–O2C
Zn2–O2D
Zn2–N3
1.948(3)
1.986(3)
2.009(4)
2.061(4)
2.091(2)
2.010(3)
1.941(3)
2.055(4)
2.067(4)
2.099(3)
Bond angles
O1A–Zn1–O1B
O1A–Zn1–O2A
O1B–Zn1–O2A
O1A–Zn1–O2B
O1B–Zn1–O2B
O2A–Zn1–O2B
O1A–Zn1–N1
O1B–Zn1–N1
O2A–Zn1–N1
O2B–Zn1–N1
O1C–Zn2–O1D
O1C–Zn2–O2C
O1D–Zn2–O2C
O1C–Zn2–O2D
O1D–Zn2–O2D
O2C–Zn2–O2D
O1C–Zn2–N3
O1D–Zn2–N3
O2C–Zn2–N3
O2D–Zn2–N3
119.19(14)
90.15(14)
92.95(15)
88.97(14)
89.54(15)
177.49(14)
112.84(12)
127.96(13)
87.36(13)
90.81(12)
119.57(14)
91.43(14)
91.31(14)
90.15(15)
89.09(16)
177.91(13)
113.27(12)
127.15(13)
88.64(13)
89.49(14)
2.3. Coordination geometry and bonding in 1
The crystal and molecular structure of 1 was determined by sin-
gle crystal X-ray diffraction at 273 K and it consists of a bis-
monodentate L1 ligand bridging the Zn1 and Zn2 atoms from two
different {Zn(acac)2} fragments, through its 3-pyridyl N atoms
(Fig. 1 and Table 1). Even if crystallizing in the non-centrosymmetric
space group Cc, the molecular assembly presents a strongly-pseudo
twofold rotation axis in a way that the whole symmetry ends up
mimicking the C2/c space group; the whole molecular body abides
to this pseudo operation, while the terminal PhSCH3 group, which
would not possible respond to this C2 operation, appears disordered
into two almost equally populated halves (occupancies: higher,
0.532; lower, 0.468), thus complying with the pseudosymmetry.
Refinement in the centrosymmetric space group, however, resulted
in much higher R indices, for what a constrained refinement in Cc
was preferred, and it is the one herein reported.
planar groups subtending to each other angles of 61.6/60.2° for
Zn1/Zn2, respectively. The fifth site of the coordination polyhedron
is occupied by a 3-pyridyl N atom from the L1 ligand. The geometry
around each Zn atom is an almost perfect trigonal bipyramid, with
apical O2A–Zn1–O2B/O2C–Zn2–O2D angles of 177.5/177.9° and
the apical bonds deviating by less than 1.9/0.9° from the normal
Each Zn centre (Zn1/Zn2) has a NO4 coordination sphere; four
sites are provided by two different acac groups coordinated in
the usual chelating form through their carbonyl O donor, the

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J. Granifo et al. / Journal of Molecular Structure 1006 (2011) 684–691
to the equatorial base. The pyridine-based rings of the L1 ligand
depart somewhat from a nearly planar structure; each outer pyri-
dyl group is twisted with respect to the central one, subtending
dihedral angles of 10.9/10.0° to this ring and 15.3° to each other.
The two disordered images of the terminal phenyl groups appear
almost at 180° from one another, and form dihedral angles of
39.0/44.4° to the central pyridyl ring.
2.4. Solid state weak interactions in 1
Compound 1 is very similar to its recently published dinuclear
[Zn2(l
-L2)(acac)4]ꢀH2O (2) analogue (L2 = 40-phenyl-3,20:60,300-ter-
pyridine, Scheme 1) [4a]. The similarities between 1 and 2 reflect
also in the packing disposition although 1 lacks the hydration
water molecule, which is responsible in 2 of the generation of
strongly coupled hydrogen bonded units into a 1D chain along b
(Scheme 2). Notably, in 1 the water site is occupied by the –SCH3
group, which fulfils the function of accomplishing a 1D chain of
non-covalent intermolecular interactions. Both one-dimensional
structures present similar, though differently connected, inter-
linked CH/O and CH/p contacts to go then into a 2D array. These
planar structures are further linked by a large number of CH/
p con-
tacts in a final 3D network.
Fig. 2. Nꢀ ꢀ ꢀH and Oꢀ ꢀ ꢀH intramolecular hydrogen bonding in 1 (only the higher
2.4.1. Intramolecular interactions in 1
occupancy conformer is shown).
Fig. 2 shows the intramolecular interactions present in 1. The
three pyridine-based rings are internally connected by two hydrogen
bonds involving the bifurcated N lone pairs on the central terpyridine
ring and the H atoms of the lateral 3-pyridyl groups, H5ꢀ ꢀ ꢀN2
[C5ꢀ ꢀ ꢀN2, 2.836 Å, 103°] and H11ꢀ ꢀ ꢀꢀN2 [C11ꢀ ꢀ ꢀꢀN2, 2.833 Å, 100°],
something which has been observed in a number of similar systems
[8]. This 2D structure is further connected to the apical acac oxygen
atoms through four CH(3-pyridyl)ꢀ ꢀ ꢀO contacts H1ꢀ ꢀ ꢀO2B
[C1ꢀ ꢀ ꢀO2B, 3.022 Å, 117°], H5ꢀ ꢀ ꢀꢀO2A [C5ꢀ ꢀ ꢀO2A, 3.037 Å, 108°],
H11ꢀ ꢀ ꢀꢀO2C [C11ꢀ ꢀ ꢀO2C, 2.992 Å, 109°] and H15ꢀ ꢀ ꢀO2D [C15ꢀ ꢀ ꢀO2D,
3.022 Å, 117°], whose geometric parameters arecompatible with this
type of links [6].
Scheme 3. Directionality of nucleophiles and electrophiles towards the sulphur
atom in non-covalent Sꢀ ꢀ ꢀX interactions. (For interpretation of the references to
colour in this artwork, the reader is referred to the web version of this article.)
2.4.2. 1D supramolecular structure of 1: relevance of the Sꢀ ꢀ ꢀO and
Sꢀ ꢀ ꢀH interactions
the highest occupied molecular orbital (HOMO). Type II are nucleo-
philes that approach the sulphur backwards with directions close to
those of the S–C bonds, providing electrons to the antibonding low-
est unoccupiedmolecularorbital (LUMO)of theS–C bonds. Later, the
specific intermolecular Sꢀ ꢀ ꢀO and Sꢀ ꢀ ꢀH distances were evaluated by
Iwaoka et al. [10] and van den Berg and Seddon [11] through
comprehensive data base studies, which showed that the highest
The directional tendency of the Sꢀ ꢀ ꢀX interactions including the
Sꢀ ꢀ ꢀH and Sꢀ ꢀ ꢀO for the divalent sulphur atom have been evaluated
by Rosenfield et al. [9]. The interactions were characterized by two
types of surrounding environments for the sulphur atom relative
to the C–S–C plane (Scheme 3). Type I are electrophiles which tend
to interact over and under the plane with the sulphur lone-pair of
Scheme 2. The 1D chain running along b in the complex 2.

J. Granifo et al. / Journal of Molecular Structure 1006 (2011) 684–691
687
Fig. 3. Non-covalent interactions (1D supramolecular structure) in the higher occupancy conformation of 1: blue dotted lines involve the sulphur atom; green broken lines
involve the thiomethyl H-atoms. (For interpretation of the references to colour in this figure legend, the reader is referred to the web version of this article.)
Fig. 4. Non-covalent interactions (1D supramolecular structure) in the lower occupancy conformation of 1: blue dotted lines involve the sulphur atom; green broken lines
involve the thiomethyl H-atoms. (For interpretation of the references to colour in this figure legend, the reader is referred to the web version of this article.)
incidence values were centred at 3.82 and 3.21 Å, respectively. In 1
the two orientations due to the disordered PhSCH3 groups display
similar Sꢀ ꢀ ꢀO and Sꢀ ꢀ ꢀH interactions (Figs. 3 and 4). Thus, the Sꢀ ꢀ ꢀO
distances are very close (S1ꢀ ꢀ ꢀO1B, 3.651 Å; S10ꢀ ꢀ ꢀO1D, 3.710 Å),
but a little shorter than the expected value (3.82 Å) for this kind of
interactions [10]. The geometry of these contacts resembles Type
II interaction ones: the O atoms are located close to the plane of
the C–S–C unit and the interaction can be conceived as the donation
of lone pair electrons located on the oxygen atoms towards the
empty rꢁ orbital of the S–C bonds. Likewise, the geometry of the
interaction between the C–H (acac-methyl) with the sulphur atom
can be assigned as a Type I contact, where the role of the sulphur
atom is to act as an electron donor. Sꢀ ꢀ ꢀH distances are almost equal
(S1ꢀ ꢀ ꢀH1BC, 2.769 Å; S10ꢀ ꢀ ꢀH1DA, 2.779 Å) and significantly shorter
than the ‘‘highest incidence’’ value (3.21 Å) [11]. A similar coexis-
tence of the interactions of Type I (C–Hꢀ ꢀ ꢀS) and Type II (Sꢀ ꢀ ꢀO) has
been reported previously for an aromatic disulphide [12].
In addition to the above sulphur-based interactions, two
C–H(thiomethyl)ꢀ ꢀ ꢀO(acac) hydrogen bonds are present in both dis-
ordered structures to reinforce the 1D chains (Figs. 3 and 4). The
Cꢀ ꢀ ꢀO bond distances and angles of these CH/O links [higher occu-
pancy conformer: C22ꢀ ꢀ ꢀO2C, 3.899 Å, 161°; C22ꢀ ꢀ ꢀO1D, 3.602 Å,

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J. Granifo et al. / Journal of Molecular Structure 1006 (2011) 684–691
132°; lower occupancy conformer: C220ꢀ ꢀ ꢀO2C, 3.434 Å, 153°;
C220ꢀ ꢀ ꢀO1B, 3.387 Å, 140°] show features tobe expectedwhen weak-
er C–H donor species are involved, such as CH3 groups [6]. In this
particular case, in support of this H-donor capacity of the methyl
groups, solution NMR studies [13] have evidenced that they are en-
gaged in intermolecular interactions when linked to divalent sul-
phur atoms, i.e., the acidity of the methyl protons is increased by
this kind of link.
the bond distances and mainly the magnitude of the angles
(>130°) of all these CH/O connections [C7ꢀ ꢀ ꢀO1C, 3.628 Å, 161°;
C7ꢀ ꢀ ꢀO2D, 3.560 Å, 136°; C9ꢀ ꢀ ꢀO1A, 3.606 Å, 163°; C9ꢀ ꢀ ꢀO2B,
3.470 Å, 134°; C3ꢀ ꢀ ꢀO1C, 3.206 Å, 135°; C13ꢀ ꢀ ꢀO1A, 3.208 Å, 137°]
allow to infer the existence of this type of interactions [6]. The fol-
lowing two interactions are of the CH(pyridyl)/p(phenyl ring) type,
now including the system of the disordered phenyl rings (two
p
interactions on each disordered ring). These interactions in 1 agree
with the correlations established previously by Nishio et al. [5], by
using as a parameter the short distance H(donor)ꢀ ꢀ ꢀC(acceptor)
when the interacting groups are aromatic (average value
2.90 0.13 Å). More specifically, in 1 these contacts correspond
to H1ꢀ ꢀ ꢀC20 (H1ꢀ ꢀ ꢀC200) and H15ꢀ ꢀ ꢀC18 (H15ꢀ ꢀ ꢀC180) with a Hꢀ ꢀ ꢀC
distances of 2.794 (3.026) and 2.941 (2.872) Å, respectively
(Fig. 5). The two final synthons that complete the 2D structure
2.4.3. 2D supramolecular structure of 1: based on CH/O and CH/
p
hydrogen bonds
The above one-dimensional H-bonded chains are then put to-
gether side by side generating 2D structures through an assembly
of CH/O and CH/
p
hydrogen bonds: six CH(pyridyl)/O(acac), two
(chelate-acac
CH(pyridyl)/ (phenyl ring) and two CH(pyridyl)/
p
p
are unusual: they include the acetylacetonate ligand in CH/
p
ring) (Fig. 5). Four of the CH(pyridyl)/O(acac) contacts, envisaged
as significant since their Cꢀ ꢀ ꢀO distances are in the range 3.470–
3.628 Å [6b], are provided by two bifurcated CH donor groups
(C7H7 and C9H9). The two remaining CH(pyridyl)/O(acac) connec-
tions, with short Cꢀ ꢀ ꢀO distances (3.206 and 3.208 Å), are also car-
ried out by bifurcated hydrogen bonds, but only via their mayor
components (C3H3ꢀ ꢀ ꢀO1C and C13H13ꢀ ꢀ ꢀO1A). In spite of this,
interactions, CH(pyridyl)/ (chelate-acac ring), which have been
p
´
revealed recently by Zaric et al. [7]. In this particular case, the
H-donor groups CH(pyridyl) correspond to the above mentioned
bifurcated H-bonds (C3–H3 and C13–H13) via their minor compo-
nents, which interact with the
p electrons of the acetylacetonato
chelate rings (Fig. 5). In this situation, the Hꢀ ꢀ ꢀCg(centroid of the
Fig. 5. Non-covalent interactions (2D supramolecular structure) in the higher occupancy conformation of 1.

J. Granifo et al. / Journal of Molecular Structure 1006 (2011) 684–691
689
acetylacetonate ring) distances are used to define the linkages. The
H3ꢀ ꢀ ꢀCg8 and H13ꢀ ꢀ ꢀCg5 distances of 2.785 and 2.871 Å in 1 corre-
late well with the expected range (2.45–3.44 Å) for complexes con-
taining borderline Lewis acid metals such as the Zn(II) cation [7].
differences in non-covalent interactions in both structures readily
explain some differences found in cell parameters. For example,
when comparing 2 with 1 a cell contraction along b is observed
(17.2414(13) Å in 2 vs. 16.8640(5) Å in 1) as well as an expansion
along a and c (16.9967(13) and 14.2974(11) Å vs. 17.7602(7) and
14.5089(5) Å). Here, the most significant difference occurs along
a (0.7635 Å). This effect can be attributed, in part, to the strong
Oꢀ ꢀ ꢀH interactions of the water molecule that bridge the two
Zn(acac)2 fragments in 2 getting them closer (Scheme 2). As an
experimental support to this argument are the distances between
the Zn(II) centres which reside in the (001) plane: the one in 2
(6.7509(7) Å) is revealingly shorter than that in 1 (7.1077(4) Å).
So, the expansion of 1 in the (001) plane indeed could be under-
stood as a contraction of 2 in this plane.
2.4.4. 3D supramolecular structure of 1: based on CH/p hydrogen
bonds
To form the final 3D structure the above described 2D layers are
stacked involving the acetylacetonate ligand either as H-donor and/
or H-acceptor in CH/pinteractions (Figs. 6 and 7). It is possible to ob-
serve ten of this kind of contacts which can be classified in two clas-
ses. The first class include the acetylacetonate ligand (CH and CH3) as
H-donor in six interactions with the terpyridine-base pyridyl groups
as H-acceptors (Fig. 6). Inside this class, the CH groups are involved
in four contacts [H3Dꢀ ꢀ ꢀCg3, 3.229 Å; H3Cꢀ ꢀ ꢀCg3, 3.356 Å;
H3Aꢀ ꢀ ꢀCg1, 3.320 Å; H3Bꢀ ꢀ ꢀCg1, 3.315 Å] and the CH3 groups in
two contacts [H1BBꢀ ꢀ ꢀCg2, 2.932 Å; H1DCꢀ ꢀ ꢀCg2, 3.126 Å], with
Hꢀ ꢀ ꢀCg bond lengths clearly centred within the observed ranges for
complexes with metal-ion of borderline hardness, 2.84–3.45 Å and
3. Structure of 1 in solution. A nuclear magnetic resonance
study
The diamagnetic compound 1 is soluble in CHCl3 where it was
characterized by mono- and two dimensional NMR (1H and 13C) at
room temperature (Section 5.2). The analysis of the results evi-
denced that the complex 1 has the Zn1/Zn2 metal centres in mag-
netically equivalent environments. Consequently, the asymmetric
molecular structure in the solid state switches to a symmetric one
in solution. In this way, the 13C spectrum show a pattern similar
to that of the free ligand L1 (Sections 2.2 and 5.2) with three addi-
tional signals provide by the four equivalent chelating acac
ligands [28.26 ppm (8 C, methyl groups); 100.01 ppm (4 C, methine
groups); 193.67 ppm (8 C, acetyl groups)]. Likewise, the proton
spectrum contains the signals corresponding to ligand L1 (atom
numbering in Scheme 1) symmetrically coordinated [2.57 ppm
(S–CH3); 7.40 ppm (H18/H20); 7.57 ppm (H2/H14); 7.66 ppm
(H17/H21); 7.94 ppm (H7/H9); 8.65 ppm (H1/H15); 8.68 ppm (H3/
H13); 9.32 ppm (H5/H11)] plus two singlets supplied by the
acetylacetonate ligands [2.04 ppm (methyl groups, 24 H);
5.40 ppm (methine groups, 4 H)].
2.7–3.5 Å, respectively [7]. In the second class of CH/p interactions
appear four equivalent links that involve exclusively the acetyl-
acetonato ligands (Fig. 7). More specifically, the CH3 groups act as
H-donors and the chelate rings as H-acceptors [H5ACꢀ ꢀ ꢀCg5,
3.390 Å; H5CCꢀ ꢀ ꢀCg8, 3.142 Å; H5DCꢀ ꢀ ꢀCg7, 3.170; H5BCꢀ ꢀ ꢀCg6,
3.272 Å]. In a previous work [4a], the range of the distances in what
occur these H(CH3)ꢀ ꢀ ꢀCg(acac-chelate) interactions have been con-
sidered similar to those of the H(CH3)ꢀ ꢀ ꢀCg(pyridyl) interactions.
Therefore, since these interaction in 1 (3.142–3.339 Å) fall inside
of the expected range as indicated above (2.7–3.5 Å) [7], it seems
acceptable to postulate the presence of this kind of weak
interactions.
2.4.5. The cell size
As already stated, compounds 1 and 2 present similar structures
with the sole difference that the –SCH3 group plays in 1 the role of
an intermolecular bridge which the water molecule fulfils in 2. But
as a result the molecules are differently connected through their
non-covalent bonds. An interesting observation is that these clear
An additional feature emerges by comparing the proton signals
of the coordinated L1 with respect to when it is free. The proton
Fig. 6. CH/p hydrogen bonds (3D supramolecular structure) in the stacking of 1 involving the acac CH and CH3 groups as H-donor towards the three pyridyl rings (only the
higher occupancy conformer is shown).

690
J. Granifo et al. / Journal of Molecular Structure 1006 (2011) 684–691
Fig. 7. CH/
p
hydrogen bonds (3D supramolecular structure) in 1 implicating only the acac ligand: the CH3 groups act as H-donors and the chelate rings as H-acceptors (only
the higher occupancy conformer is shown).
with Zn(acac)2 to give the dinuclear complex 1, where L1 acts as a
bridging ligand only via its 3-pyridyl nitrogen atoms. The N atom
of the central pyridine ring and the S atom of the thiomethyl unit
of L1 do not participate in the binding to the metal centres. The
supramolecular structure of 1 can be understood by using the
non-covalent interactions in which the thiomethyl group plays a
key role through the unusual Sꢀ ꢀ ꢀO and Sꢀ ꢀ ꢀH contacts. These syn-
Table 2
Crystal data and refinement parameters of 1.
Empirical formula
Mw
Crystal system
Space group
C42H45N3O8SZn2
882.61
Monoclinic
Cc
a = 17.7602(7) Å, b = 16.8640(5) Å,
c = 14.5089(5) Å, b = 106.571(4) °
4165.0(3) Å3
Unit cell dimensions
thons act in conjunction with the abundant CH/O and CH/
gen bonds to stabilize the crystal packing.
p hydro-
V
Z
4
Calculated density
Absorption coefficient (
Reflections (measured/
unique/observed)
Rint
Data/parameters
R1, wR2 [I > 2
R1, wR2 (all data)
1.408 Mg/m3
l)
1.256 mmꢄ1
5. Experimental
45,146/10,070/6986
0.023
10,070/542
R1 = 0.0274, wR2 = 0.0680
R1 = 0.0484, wR2 = 0.0726
The solvents were purchased from commercial sources and
used without further purification. The compound Zn(acac)2 was
obtained from Aldrich. Infrared spectra were recorded using KBr
plates on a Bruker Tensor 27 FT-IR spectrometer. A Exeter Analyt-
ical CE-440 elemental analyser was used for microanalysis (C, H,
N). 1H and 13C NMR spectra were recorded on a Bruker Avance
300 MHz NMR instrument. Mass spectra were recorded on a JEOL
JEM-AX505HA spectrometer by electronic impact (EI) of lower res-
olution at 70 eV.
r
(I)]
signals belonging to L1 are all clearly shifted downfield upon coor-
dination (
dH ꢂ 0.09–0.29 ppm) with the exception of those four
of 3-pyridyl H atoms adjacent to the coordinated N atoms (H5/
H11,
D
D
dH ꢂ 0.03 ppm; H1/H15,
D
dH ꢂ 0.02 ppm) which do not
5.1. Synthesis of 40-(4-methylthiophenyl)-3,20:60,300-terpyridine (L1)
show significant changes. This is contrary to that expected when
coordination occurs [14], the loss of electron density upon coordi-
nation to a metal usually results in shifts to lower field of the adja-
cent protons of the coordinated pyridyl nitrogen atoms. An
explanation to this finding is that the shielding would come from
The procedure of synthesis is similar to that of Hanan and Wang
[15]. 3-Acetylpyridine (2.42 g, 20 mmol) was added to a solution of
4-(methylthio)benzaldehyde (1.54 g, 10 mmol) in EtOH (50 mL).
KOH pellets (1.12 g, 20 mmol) were then added to the solution fol-
lowed by aqueous NH3 (29 mL, 25 mmol). The resulting solution
was stirred at room temperature for 4 h. The solid was collected
by filtration and washed with H2O (5 ꢃ 10 mL) and MeOH
(3 ꢃ 10 mL). Recrystallization from CH2Cl2–MeOH afforded white
solid L1. Yield: 1.0 g, 28%. M.p. 183–185°C. Anal. Calcd for
the magnetic anisotropy of the
in the neighbourhood of these protons [14].
p system of the chelating acac rings
4. Conclusions
The novel terpyridine-based and potentially bridging ligand L1
was synthesized and then characterized through spectroscopic
methods. The coordinating properties of L1 were tested by reacting
C
22H17N3S: C, 74.34; H, 4.82; N, 11.82; S, 9.02. Found: C, 74.37; H,
4.98; N, 11.45; S, 9.20. IR (KBr, cmꢄ1): 3036, 2917, 1905, 1600,

J. Granifo et al. / Journal of Molecular Structure 1006 (2011) 684–691
691
1384, 808, 703 (Fig. S1). 1H NMR (200 MHz, CDCl3, 298 K): d = 9.29
(br d, 2H, J = 1.6 Hz), 8.63 (dd, 2H, J = 4.7, 1.2 Hz), 8.39 (dt, 2H,
J = 8.1, 1.7 Hz), 7.79 (s, 2H), AA0BB0 system observed at 7.57 (d, 2H,
8.6 Hz) and 7.30 (d, 2H, J = 8.6 Hz), 7.36 (dd, 2H, J = 7.9, 4.7), 2.48
(s, 3H) (Fig. S2). 13C-PND and 13C-DEPT NMR (50 MHz, CDCl3,
298 K): 155.00 (2C, Cquat.), 149.95 (2C, CH), 149.69 (1C, Cquat.),
148.13 (2C, CH), 140.76 (1C, Cquat.), 134.22 (2C, CH), 134.00 (3C,
Crystallographic Data Centre as supplementary publication No.
CCDC 838813. Copies of the data can be obtained, free of charge,
on application to CCDC, 12 Union Road, Cambridge CB2 1EZ, UK,
(fax: +44 1223 336033 or e-mail: deposit@ccdc.cam.ac.uk).
Acknowledgements
C
quat.), 127.10 (2C, CH), 126.34 (2C, CH), 123.38 (2C, CH), 116.83
The authors acknowledge the Universidad de La Frontera (Proy-
ecto DIUFRO No. DI11-0026) for financial support. We also
acknowledge the ANPCyT (Project No. PME 01113) for the purchase
of the CCD diffractometer and the Spanish Research Council (CSIC)
for providing a free-of charge license to the Cambridge Structural
Database (Allen, 2002).
(2C, CH), 15.13 (1C, CH3) (Fig. S3). HRMS (FAB+) Calcd for
C
C
22H17N3S [M + 1]+ 356.1221, found 356.1219, MS (EI+, 70 eV) for
22H17N3S ([M]+) 355 (100%), 354 (16.7%), 339 (7.2%), 308 (6.3%),
340 (5.7%) (Fig. S4).
5.2. Synthesis of [Zn2(l-L1)(acac)4] (1)
Appendix A. Supplementary material
To a hot solution (using an oil bath at 64–68 °C) of L1 (30.0 mg,
0.084 mmol) in MeCN (15 mL) contained in a closed volumetric flask
(25 mL) was added an excess of Zn(acac)2 (442.8 mg, 1.680 mmol).
The resultant solution was heated in the oil bath for 26 h. Block-like
colourless crystals (suitable for single crystal X-ray analysis) were
obtained after the removal of the hot solvent, washing with MeCN
(5 ꢃ 5 mL) and diethyl ether (2 ꢃ 4 mL). Yield: 60 mg, 80.5%. Anal.
Calcd for C42H45N3O8SZn2: C, 57.15; H, 5.14; N, 4.76; S, 3.63. Found:
C, 57.38, H, 5.32, N: 4.54, S: 3.78. IR (KBr, cmꢄ1): 3078, 2915, 1582,
1514, 1383, 1014, 817, 406 (Fig. S5). 1H NMR (300 MHz, CDCl3,
298 K): d = 9.32 (2H, dd, J = 1.8, 1.5 Hz), 8.68 (2H, dt, J = 8.1,
1.8 Hz), 8.65 (2H, dd, J = 5.1, 1.5 Hz), 7.94 (2H, s), 7.66 (2H, d,
J = 6.9 Hz) 7.57 (2H, dd, J = 8.1, 5.1 Hz), 7.40 (2H, d, J = 6.9 Hz), 5.40
(4H, s), 2.57 (3H, s), 2.04 (24H, s) (Fig. S6). 13C-PND and 13C-DEPT-
135 NMR (75 MHz, CDCl3, 298 K): 193.67 (8C, Cquat.), 154.27 (2C,
Supplementary data associated with this article can be found, in
the online version, at doi:10.1016/j.molstruc.2011.10.038.
References
[1] E.C. Constable, Chem. Soc. Rev. 36 (2007) 246–253.
[2] I. Eryazici, Ch.N. Moorefield, G.R. Newkome, Chem. Rev. 108 (2008) 1834–
1895.
[3] (a) L. Hou, D. Li, Inorg. Chem. Commun. 8 (2005) 190;
(b) X.-Z. Li, M. Li, Z. Li, J.-Z. Hou, X.-C. Huang, D. Li, Angew. Chem. Int. Ed. 47
(2008) 6371;
(c) E.C. Constable, G. Zhang, C.E. Housecroft, M. Neuburger, J.A. Zampese,
CrystEngComm 11 (2009) 2279;
(d) E.C. Constable, G. Zhang, E. Coronado, C.E. Housecroft, M. Neuburger,
CrystEngComm 12 (2010) 2139.
[4] (a) J. Granifo, M. Vargas, M.T. Garland, A. Ibañez, R. Gaviño, R. Baggio, Inorg.
Chem. Commun. 11 (2008) 1388;
(b) C. Liu, Y.-B. Ding, X.-H. Shi, D. Zhang, M.-H. Hu, Y.-G. Yin, D. Li, Cryst.
Growth Des. 9 (2009) 1275.
[5] H. Suezawa, T. Yoshida, Y. Umezawa, S. Tsuboyama, M. Nishio, Eur. J. Inorg.
Chem. (2002) 3148.
[6] (a) T. Steiner, Angew. Chem. Int. Ed. 41 (2002) 48;
(b) G.R. Desiraju, Acc. Chem. Res. 29 (1996) 441;
T. Steiner, Chem. Commun. (1997) 727.
Cquat.), 150.49 (1C, Cquat.), 149.47 (2C, CH), 147.82 (2C, CH), 141.48
(1C, Cquat.), 136.64 (2C, CH), 135.43 (2C, Cquat.), 133.85 (1C, Cquat.),
127.23 (2C, CH), 126.63 (2C, CH), 124.52 (2C, CH), 117.48 (2C, CH),
100.01 (4C, CH), 28.26 (8C, CH3), 15.31 (1C, CH3) (Fig. S7).
5.3. X-ray crystallography
ˇ ˇ
´
´
´
´
[7] M.K. Milcic, V.B. Medakovic, D.N. Sredojevic, N.O. Juranic, S.D. Zaric, Inorg.
Chem. 45 (2006) 4755.
Crystal data were collected on a Oxford Gemini CCD S Ultra dif-
[8] E. Medlycott, G.S. Hanan, Chem. Soc. Rev. 34 (2005) 133.
[9] R.E. Rosenfield Jr., R. Patthasarathy, J.D. Dunitz, J. Am. Chem. Soc. 99 (1977)
4860.
[10] M. Iwaoka, S. Takemoto, S. Tomoda, J. Am. Chem. Soc. 124 (2002) 10613.
[11] J.-A. van den Berg, K.R. Seddon, Cryst. Growth Des. 3 (2003) 643.
[12] A. Esparza-Ruiz, A. Pena-Hueso, J. Hernandez-Diaz, A. Flores-Parra, R.
Contreras, Cryst. Growth Des. 7 (2007) 2031.
[13] R. Dubey, A.K. Tewari, K. Ravikumar, B. Sriddhar, Bull. Korean Chem. Soc. 31
(2010) 1326.
[14] C. Bazzicalupi, A. Bencini, A. Bianchi, A. Danesi, E. Faggi, C. Giorgi, S. Santarelli,
B. Valtancoli, Coord. Chem. Rev. 252 (2008) 1052.
fractometer at room temperature using Mo
Ka 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 soft-
ware [16]. All non-hydrogen atoms were refined anisotropically.
Hydrogen atoms were found in a difference Fourier but further ide-
alized. The structural analysis was performed with the help of the
multipurpose PLATON program [17].
Data collection and refinement parameters are summarized in
Table 2. The molecular representations shown in the figures were
generated using XP in the SHELXTL package [16] and VESTA [18].
Crystallographic data (excluding structure factors) for the struc-
tures in this paper have been deposited with the Cambridge
[15] G.R. Hanan, J. Wang, Synlett 8 (2005) 1251.
[16] G.M. Sheldrick, Acta Crystallogr., A 64 (2008) 112–122.
[17] A.L. Spek, PLATON, A Multipurpose Crystallographic Tool, Utrecht University,
Utrecht, The Netherlands, 2005.
[18] K. Momma, F. Izumi, J. Appl. Crystallogr. 41 (2008) 653–658.