A novel hybrid terpyridine-pyrimidine ligand and the supramolecular structures of two of its complexes with Zn(II) and acetylacetonato: The underlying role of non-covalent π?π contacts and C-H?X(O, N, π) hydrogen bonds

Article abstract of DOI:10.1016/j.molstruc.2014.01.053

The novel 4′-[4-(pyrimidin-5-yl)phenyl]-4,4′:6′,2″- terpyridine (L1) ligand reacts with Zn(acac)₂ (acac = acetylacetonato) to give the monomeric complex [Zn(acac)₂(L1) ₂] (1) and the coordination polymer [Zn(acac)₂(μ-L1)] _n (2). The structure of 1 consists of a Zn(II) cation sitting on an inversion centre, surrounded by a slightly elongated octahedral environment, defined by two trans N(4-pyridyl) atoms from a pair of mondentate L1 ligands, and four O atoms from two chelating acac anions. The polymeric structure of 2 presents a similar though non-symmetric Zn(acac)₂ unit, since the two coordinated N atoms come from two different donor moieties of L1: the 4-pyridyl and the pyrimidinyl. Both compounds present weak C-H?N contacts generating 2D aromatic structures, complemented by π?π contacts plane-stacking giving raise to 3D structures and further stabilized by C-H?O and C-H?π interactions.

Full text of DOI:10.1016/j.molstruc.2014.01.053

Journal of Molecular Structure 1063 (2014) 102–108
Contents lists available at ScienceDirect
Journal of Molecular Structure
journal homepage: www.elsevier.com/locate/molstruc
A novel hybrid terpyridine–pyrimidine ligand and the supramolecular
structures of two of its complexes with Zn(II) and acetylacetonato: The
underlying role of non-covalent
hydrogen bonds
pꢀ ꢀ ꢀp
contacts and C–Hꢀ ꢀ ꢀX(O, N,
p)
b
Juan Granifo a, , Rubén Gaviño , Eleonora Freire c,d, Ricardo Baggio c
⇑
a Departamento de Ciencias Químicas y Recursos Naturales, Facultad de Ingeniería y Ciencias, 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
g r a p h i c a l a b s t r a c t
h i g h l i g h t s
ꢁ
A novel hybrid terpyridine–
pyrimidine ligand (L1) was
synthesized.
ꢁ
ꢁ
The reaction of L1 with Zn(acac)2
gives simultaneously 1 and 2.
1 and 2 present C–Hꢀ ꢀ ꢀN bonds
generating planar 2D aromatic
structures.
ꢁ
The spacings between the 2D arrays
strongly suggests a
among them.
pꢀ ꢀ ꢀp linkage
a r t i c l e i n f o
a b s t r a c t
The novel 40-[4-(pyrimidin-5-yl)phenyl]-4,40:60,200-terpyridine (L1) ligand reacts with Zn(acac)2
(acac = acetylacetonato) to give the monomeric complex [Zn(acac)2(L1)2] (1) and the coordination poly-
mer [Zn(acac)2(l-L1)]n (2). The structure of 1 consists of a Zn(II) cation sitting on an inversion centre, sur-
rounded by a slightly elongated octahedral environment, defined by two trans N(4-pyridyl) atoms from a
pair of mondentate L1 ligands, and four O atoms from two chelating acac anions. The polymeric structure
of 2 presents a similar though non-symmetric Zn(acac)2 unit, since the two coordinated N atoms come
from two different donor moieties of L1: the 4-pyridyl and the pyrimidinyl. Both compounds present
Article history:
Received 4 December 2013
Received in revised form 13 January 2014
Accepted 14 January 2014
Available online 29 January 2014
Keywords:
40-[4-(pyrimidin-5-yl)phenyl]-4,20:60,400-
terpyridine
weak C–Hꢀ ꢀ ꢀN contacts generating 2D aromatic structures, complemented by
p p contacts plane-stack-
ꢀ ꢀ ꢀ
ing giving raise to 3D structures and further stabilized by C–Hꢀ ꢀ ꢀO and C–Hꢀ ꢀ ꢀ
p
interactions.
Zinc(II) complexes
Ó 2014 Elsevier B.V. All rights reserved.
p
ꢀ ꢀ ꢀ
p
Stacking
hydrogen bonds
C–Hꢀ ꢀ ꢀ
p
Coordination polymer
1. Introduction
derivatives has been centered mainly in its action as chelating
ligands [1–3], i. e., where they present a convergent disposition
of its N,N0,N00 donor atoms to link the metal atoms. More recently,
as a further exploration in this type of metal-binding domains, the
divergent 4,400 isomers and pyridyl-substituted in the 40-position
have been used [4–11]. Indeed, to the best of our knowledge, in
The large number of studies of the coordination chemistry of
the tridentate ligand 2,20;60,600-terpyridine and its 40-substituted
⇑
Corresponding author. Tel.: +56 045 2325434.
E-mail address: juan.granifo@ufrontera.cl (J. Granifo).
http://dx.doi.org/10.1016/j.molstruc.2014.01.053
0022-2860/Ó 2014 Elsevier B.V. All rights reserved.

J. Granifo et al. / Journal of Molecular Structure 1063 (2014) 102–108
103
to afford the related L1 ligand (Scheme 1). It was expected that
the inclusion of a N-donor substituent like the pyrimidine moiety
can act not only as a metal coordination site, but also to enable
the diversification of the types of non-covalent interactions pres-
ent, such as hydrogen bonding,
p–p stacking, etc. Under these
expectations, the coordinating properties of L1 were tested by
reacting it with Zn(acac)2 to afford simultaneously the molecular
complex 1, with L1 as a monodentate N-pyridyl donor ligand,
and the polymer 2, with L1 as an asymmetric-bidentate bridging
ligand employing N atoms from the pyridyl and pyrimidinyl
fragments.
2. Experimental
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. An 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.
Scheme 1. The sketches of the ligands L and L1. For L1 the numbering of carbon
atoms (hydrogen atoms where correspond) is indicated.
all the reported examples only the 40-(4-pyridyl)-40,20:60,400-terpyr-
idine ligand (L, Scheme 1) has been tested. The divergent nature of
L has allowed to connect metal centers acting either as bidentate-
bridging (using the 4,400pyridyl groups to give infinite chain struc-
tures [4–6] or a 3D network structure [7]) or as tridentate (using
the three external 4-pyridyl groups to engage 3D structural motifs
[8] or molecular capsules [9,10]). In addition, a polymeric Cu(II)
compound with a protonated HL+ ligand has been reported [11]
as well as two coordination polymers containing a chloro derivate
of L [9]. It is relevant to mention here that the coordination poly-
2.1. Synthesis of 40-[4-(pyrimidin-5-yl)phenyl]-4,20:60,400-terpyridine
(L1)
L1 was prepared by using the one-pot method of Hanan and
Wang [12]. 4-Acetylpyridine (0.61 g, 5.0 mmol) was added to a
solution of 4-(pyrimidin-5-yl)benzaldehyde (0.46 g, 2.5 mmol) in
EtOH (20 mL). After stirring for 0.25 h, KOH pellets (0.28 g,
5.0 mmol) were added. The resulting solution was stirred at room
temperature over a period of 6 h, then an excess of aqueous NH3
(8.6 mL, 25%, 115 mmol) was added and stirring was continued
for further 24 h. The solid was filtered off and washed with water
(5 ꢂ 10 mL) and with ethanol (3 ꢂ 10 mL). The product was dis-
solved in CHCl3 (20 mL) and the addition of methanol (60 mL)
mer [Co(acac)2(l-L)]n [4] is the sole example where the acac and
L ligands coexist, with the last one presenting a symmetric nature
to form the bridge by using the pyridyl-nitrogen atoms N and N00.
In this work, as an extension of the studies of bonding and
supramolecular properties of the 4,400 divergent terpyridine-based
ligands, we decided to replace in L its pyridyl portion localized in
the 40-position by another containing the pyrimidinyl fragment
Table 1
Crystal data and refinement parameters for 1 and 2.
Compound
1
2
Crystal data
Chemical formula
Mr
Crystal system, space group
Temperature (K)
a, b, c (Å)
C
60H48N10O4Zn
C35H31N5O4Zn
651.02
1038.45
Triclinic, P ꢃ 1
295
Triclinic, P ꢃ 1
295
11.0116 (4), 11.3556 (6), 11.4396 (4)
10.8123 (3), 11.1869 (4), 14.1734 (5)
a
, b,
c
(°)
115.612 (4), 91.818 (3), 104.204 (4)
1234.82 (11)
1
66.837 (2), 88.609 (3), 77.171 (3)
1533.02 (10)
2
V (Å3)
Z
Radiation type
Mo K
0.56
a
Mo K
0.85
a
l
(mmꢃ1
)
Crystal size (mm)
0.32 ꢂ 0.24 ꢂ 0.08
0.36 ꢂ 0.12 ꢂ 0.10
Data collection
Diffractometer
Oxford Diffraction Gemini CCD S Ultra
diffractometer
Oxford Diffraction Gemini CCD S Ultra
diffractometer
Absorption correction
Multi-scan CrysAlis PRO, Oxford Diffraction (2009) Multi-scan CrysAlis PRO, Oxford Diffraction (2009)
Tmin, Tmax
0.85, 0.96
0.88, 0.92
No. of measured, independent and observed [I > 2
r
(I)]
14711, 5743, 4901
36853, 7399, 6242
reflections
Rint
0.025
0.679
0.027
0.679
(sinh/k)max (Åꢃ1
)
Refinement
R[F2 > 2
r
(F2)], wR(F2), S
0.037, 0.098, 1.04
0.031, 0.081, 1.04
No. of reflections
No. of parameters
No. of restraints
H-atom treatment
5743
342
0
7399
410
0
H-atom parameters constrained
0.25, ꢃ0.26
H-atom parameters constrained
0.24, ꢃ0.28
D
imax
,
D
imin (e Åꢃ3
)

104
J. Granifo et al. / Journal of Molecular Structure 1063 (2014) 102–108
Table 2
was obtained for analysis of the bulk sample and the spectroscopic
measurements evidence the mixture of the two compounds.
Selected bond lengths (Å) and bond angles (°) for 1 and 2.
(a) Compound 1
Zn1–O12
Zn1–O22
2.0623 (12)
2.0806 (13)
Zn1–N11
2.2505 (13)
90.78 (5)
2.3. X-ray crystallography
O12–Zn1–O22
O22–Zn1–N11
89.18 (5)
89.31 (5)
O12–Zn1–N11
Crystal Data were collected on a Oxford Gemini CCD S Ultra dif-
fractometer at room temperature using Mo
Ka radiation
(b) Compound 2
Zn1–O13
Zn1–O12
(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 [13,14]. 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 [15].
Data collection and refinement parameters are summarized in
Table 1, while selected bond lengths and angles are presented in
Table 2. The molecular representations shown in the figures were
generated using XP in the SHELXTL package [14] and MERCURY
[16]. Crystallographic data (excluding structure factors) for the
structures in this paper have been deposited with the Cambridge
Crystallographic Data Centre as supplementary publication No.
CCDC 970229-970230. 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).
2.0294 (11)
2.0375 (11)
2.0532 (12)
Zn1–O22
Zn1–N11
Zn1–N41i
2.0596 (12)
2.2182 (12)
2.3860 (13)
Zn1–O23
O13–Zn1–O12
O13–Zn1–O23
O12–Zn1–O23
O13–Zn1–O22
O12–Zn1–O22
O23–Zn1–O22
O13–Zn1–N11
O12–Zn1–N11
174.44 (4)
89.69 (5)
89.53 (5)
90.88 (5)
89.52 (5)
176.04 (4)
92.42 (5)
93.11 (5)
O23–Zn1–N11
O22–Zn1–N11
O13–Zn1–N41i
O12–Zn1–N41i
O23–Zn1–N41i
O22–Zn1–N41i
N11–Zn1–N41i
91.86 (5)
92.04 (5)
86.76 (5)
87.72 (5)
89.23 (5)
86.89 (5)
178.64 (5)
Symmetry code: (i) x ꢃ 1, y, z + 1.
afforded a crystalline solid, which was washed with methanol
(3 ꢂ 10 mL) (yield: 0.42 g, 43%). Analysis calculated for C25H17N5:
C 77.50, H 4.42, N 18.08%; found: C 77.40, H 4.38, N 18.15%. 13C-
PND and 13C-DEPT NMR (75 MHz, CDCl3, 298 K): d = 158.0 (CH),
155.6 (Cquat), 154.9 (CH), 150.7 (CH), 150.1 (Cquat), 145.9 (Cquat),
138.7 (Cquat), 135.6 (Cquat), 133.4 (Cquat), 128.3 (CH), 127.9 (CH),
121.2(CH), 118.8(CH). 1H NMR (300 MHz, CDCl3, 298 K): d = 9.25 (s,
1H), 9.02 (s, 2H), 8.79 (AA0, 4H, J = 4.5 Hz), 8.07 (BB0, 4H, J = 4.5 Hz),
8.06 (s, 2H), 7.90 (AA0, 2H, 8.1 Hz), 7.78 (BB0, 2H, 8.1 Hz). IR (KBr,
cmꢃ1): 2848, 1594, 1535, 1389, 1129, 997, 810.
3. Results and discussion
3.1. The NMR spectra of L1 (performed through Correlation
Spectroscopy (COSY), Distortionless Enhancement of Polarisation
Transfer (DEPT) and Proton Noise Decoupled (PND))
The NMR results in CDCl3 solution of the L1 ligand are in good
agreement with the expected molecular structure (Scheme 1 and
Section 2.1). Thus, the 13C NMR spectrum shows 13 signals exclu-
sively for sp2 carbon atoms, the carbon multiplicity was deter-
mined by 13C-DEPT experiment: six signals are due to quaternary
carbons 155.6 (C6/C10), 150.1 (C8), 145.9 (C3/C13), 138.7 (C16),
135.6 (C19), 133.4 (C22) and seven due to CH carbons 158.0
(C24), 154.9 (C23/C25), 150.7 (C1/C5/C11/C15), 128.3 (C18/C20),
127.9 (C17/C21), 121.2 (C2/C4/C12/C14) and 118.8 (C7/C9). Simi-
2.2. Synthesis of [Zn(acac)2(L1)2] (1) and [Zn(acac)2(l-L1)]n (2)
To a hot solution (using an oil bath at 57–60 °C) of L1 (7.6 mg,
0.020 mmol) in MeOH (6.0 mL) contained in a closed volumetric
flask (10 mL) was added an excess of Zn(acac)2 (65.0 mg,
0.25 mmol). The resultant solution was heated in the oil bath for
15 h. A mixture of needle-like and block-like colorless crystals
were obtained after the removal of the hot solvent, washing with
MeOH (4 ꢂ 4 mL) and diethyl ether (2 ꢂ 4 mL) and dried in the
air. From the final product (8.2 mg), crystals suitable for single
crystal X-ray analysis were separated by hand. Scarse material
larly, the 1H NMR is characterized for
a low field singlet
(9.25 ppm) and a second singlet (9.02 ppm) due to the pyrimidine
protons H24 and H23/25, respectively. The four phenyl protons can
Fig. 1. Molecular diagram of 1, with 40% displacement ellipsoids, showing atom and ring labeling. Full (empty) bonds and atoms denote the independent (symmetry related)
part of the structure. In broken bonds the intramolecular C–Hꢀ ꢀ ꢀO hydrogen bonds. Symmetry code: (i) ꢃx + 1, ꢃy + 1, ꢃz + 1.

J. Granifo et al. / Journal of Molecular Structure 1063 (2014) 102–108
105
Table 3
Table 4
Relevant hydrogen-bonds (Å, °) found in 1 and 2.
pꢀ ꢀ ꢀp contacts in 1 and 2 (Å, °).
D–Hꢀ ꢀ ꢀA
D–H
Hꢀ ꢀ ꢀA
Dꢀ ꢀ ꢀA
D–Hꢀ ꢀ ꢀA
Group 1ꢀ ꢀ ꢀGroup 2
ccd (Å)
da (°)
ipd (Å)
(a) Compound 1
(a) Compound 1
Cg1ꢀ ꢀ ꢀCg4vi
C11–H11ꢀ ꢀ ꢀO12
0.93
0.93
0.93
0.93
0.93
0.93
0.96
2.50
2.53
2.70
2.72
2.61
2.72
3.28
3.104 (2)
3.114 (2)
3.569 (3)
3.601 (3)
3.393 (4)
3.641 (4)
3.900 (4)
123
121
156
159
142
170
124
3.629 (2)
4.057 (2)
3.946 (2)
2.12 (14)
9.12 (19)
8.89 (18)
3.565 (11)
3.59 (18)
3.66 (6)
C51–H51ꢀ ꢀ ꢀO12i
C21–H21ꢀ ꢀ ꢀN31ii
C251–H251ꢀ ꢀ ꢀN51iii
C231–H231ꢀ ꢀ ꢀO22iv
C181–H181ꢀ ꢀ ꢀO22iv
C52–H52Bꢀ ꢀ ꢀCg5v
Cg1ꢀ ꢀ ꢀCg3vii
Cg3ꢀ ꢀ ꢀCg4viii
(b) Compound 2
Cg2ꢀ ꢀ ꢀCg2vii
Cg3ꢀ ꢀ ꢀCg4viii
Cg4ꢀ ꢀ ꢀCg5ix
3.8631 (10)
3.8633 (12)
3.9643 (11)
0
3.6262 (7)
3.4 (3)
3.5 (4)
20.92 (9)
29.29 (9)
(b) Compound 2
Symmetry codes: (vi) x, 1 + y, 1 + z, (vii) ꢃx, ꢃy, ꢃz; (viii) ꢃx, ꢃy, ꢃ1 – z. Ring code:
Cg1: N11,C11 ? C51; Cg3: N31, C111 ? C151, Cg4: N41, N51, C221 ? C251.
Symmetry codes: (vii) 1 ꢃ x, 2 ꢃ y, ꢃz; (viii) ꢃ1 + x, y, z;(ix) 2 ꢃ x, 1 ꢃ y, ꢃz; Ring
code: Cg2, N21,C61 ? C101, Cg3, N31,C111 ? C151; Cg4, N41,N51, C221 ? C251;
Cg5, C161 ? C211.ccd: center-to-center distance; da: dihedral angle between rings;
ipd: interplanar distance, or (mean) distance from one plane to the neighboring
centroid.
C51–H51ꢀ ꢀ ꢀO13
0.93
0.93
0.93
0.93
0.93
0.93
0.93
0.93
0.96
2.49
2.48
2.64
2.64
2.69
2.48
2.68
2.80
3.12
3.102 (2)
3.083 (2)
3.210 (3)
3.203 (2)
3.371 (2)
3.382 (2)
3.603 (2)
3.446 (2)
3.842 (3)
124
122
120
119
131
163
172
128
133
C231–H231ꢀ ꢀ ꢀO12ii
C11–H11ꢀ ꢀ ꢀO12
C241–H241ꢀ ꢀ ꢀO13ii
C21–H21ꢀ ꢀ ꢀN31iii
C41–H41ꢀ ꢀ ꢀꢀO22iv
C211–H211ꢀ ꢀ ꢀO22iv
C141–H141ꢀ ꢀ ꢀCg5v
C52–H52Cꢀ ꢀ ꢀCg3vi
3.2. Coordination geometry, bonding and non-covalent contacts in the
monomeric complex 1
Symmetry codes: (i) ꢃx + 1, ꢃy + 1, ꢃz + 1; (ii) x + 1, y, z; (iii) ꢃx, ꢃy ꢃ 1, ꢃz ꢃ 2; (iv)
x, y ꢃ 1, z ꢃ 1; (v) ꢃx + 1, ꢃy + 1, ꢃz. Ring code: Cg5, C161 ? C211.
Symmetry codes: (ii) x + 1, y, z ꢃ 1; (iii) ꢃx, ꢃy + 2, ꢃz; (iv) ꢃx + 1, ꢃy + 1, ꢃz + 1; (v)
ꢃx + 1, ꢃy + 2, ꢃz; (vi) x, y ꢃ 1, z + 1. Ring code: Cg2, N21,C61 ? C101; Cg5,
C161 ? C211.
The single-crystal X-ray structure of 1 (Fig. 1 and Table 2) re-
veals a monomeric species with a sixfold coordinated Zn cation
on an inversion centre, bound to a monodentate L1 ligand, through
a 4-pyridyl N atom, a chelating-bidentate acac-j2O,O0 anion,
through both O atoms, and their two centrosymmetric images.
The environment of Zn1 is an octahedron, with the two chelating
acac ligands defining the ZnO4 base (Zn–O range: 2.0623 (12)–
2.0806 (13) Å) and both coordinated N(4-pyridyl) atoms occupying
the apical sites, with slightly elongated bonds of Zn–N: 2.2505
(13) Å. Angular deformations, in turn, are quite small (cis-angles
be readily distinguished by the characteristic AA0BB0 pattern for
H17/H21 (7.90 ppm) and H18/H20 (7.78 ppm). The two protons
of the central pyridine ring H7/H9 appear as a singlet (8.06 ppm).
The eight protons of the two 4-pyridyl rings in and positions show
an AA0BB0 pattern for H1/H5/H11/H15 (8.79 ppm) and for H2/H4/
H12/H14 (8.07 pm).
Fig. 2. Packing diagram of 1. (a): The 2D substructure formed by the intermolecular C–Hꢀ ꢀ ꢀN hydrogen bonds. One central monomeric unit is presented surrounded by the
neighboring species. (b) CH(methyl)/ (Cg5) hydrogen bond.
p

106
J. Granifo et al. / Journal of Molecular Structure 1063 (2014) 102–108
C161ꢀ ꢀ ꢀC221 axis. Finally, acac moieties do not present any signif-
icant deviation from commonly accepted values both in distances
as in angles.
In 1 there are many non-covalent interactions of varied type
and strength, which are presented in Table 3a (H-bonding) and
Table 4a (
p p interactions). For the sake of simplicity, in what fol-
ꢀ ꢀ ꢀ
lows we shall use a shorthand notation, viz., ‘‘Tn(m)’’ to denote
‘‘Table n (mth entry)’’.
The packing of structure 1 is characterized by the presence of a
2D substructure based on intramolecular C–Hꢀ ꢀ ꢀO (Fig. 1) and
intermolecular C–Hꢀ ꢀ ꢀN (Fig. 2a) hydrogen bonds. The intramolec-
ular C–Hꢀ ꢀ ꢀO contacts involve H atoms from the coordinated 4-pyr-
idyl groups and the O atoms from the acac, T3a(1,2) (Fig. 1),
generating a S(5) ring (A in Fig. 3a; for a survey on Graph Set
nomenclature of H-bonding loops, see Etter [17] and Bernstein
et al. [18]), which serve to further stabilize the coordination poly-
hedra. Regarding intermolecular C–Hꢀ ꢀ ꢀN interactions, they are
weak but they give rise anyway to a well defined structure, and
comprise the N atom of the non-coordinated 4-pyridyl group,
T3a(3), and only one N atom of the pyrimidinyl group, T3a(4).
The motifs that include the two different C–Hꢀ ꢀ ꢀN contacts are
shown in Fig. 3a, and by using the graph notation we find three dif-
ferent types of rings, R22 (6) (B in Fig. 3a), R44 (58) (C) and R66 (32) (D).
Therefore, the resultant of all non-covalent interactions indicated
above define a planar 2D array of aromatic rings parallel to
ꢀ
(032), characterized by a number of H-bonding rings of quite dif-
ferent size and shape. This 2D array build up a parallel stacking of
ꢀ
planes (Fig. 3b), with interplanar spacings of 3.59 Å (the d(032
spacing)), which strongly suggests
a
p p linkage between
ꢀ ꢀ ꢀ
planes. Under this premise, the observed array should perhaps
be described as an overall interaction of delocalized electronic den-
sity clouds distributed along the aromatic system, better than de-
Fig. 3. Packing diagram of 1. (a) The hydrogen bonded 2D substructure defined the
intramolecular C–Hꢀ ꢀ ꢀO motifs (rings A) and by intermolecular C–Hꢀ ꢀ ꢀN motifs
(rings B–D). For ring definitions, see text. (b) The stacking of planes, as described in
the text.
fined in terms of individual
p p interactions, with a large
ꢀ ꢀ ꢀ
dispersion of inter-centroid distances and slippages (nonetheless
reported in T4a(1,2,3). Further support for this argument can be
found in the extreme planarity of this 2D substructure (RMS devi-
ations from the planes defined by C and N atoms: 0.15 Å), difficult
to sustain without some sort of extended interaction. Additional
support to this tentative proposal could be found attempting
theoretical studies, e.g., as those obtained for some zinc-organic
complexes [19–22], by using quantum chemical methods of the
density functional theory and of the electron density topological
analysis.
range: O–Zn–O: 90 0.82 (5)°, O–Zn–N: 90 0.69 (5)°; trans-an-
gles being exactly 180° due to symmetry constraints). Also due
to these symmetry limitations the basal plane is perfectly planar,
with the apical bond being almost perpendicular to the plane, at
179.0 (2)°. The L1 ligand, in turn, presents an essentially planar
substructure made up of the four N-containing groups:
rings 1 ? 4 (See Fig. 1 for ring labeling) adopt a collective flattened
disposition, with a mean deviation from the L.S. plane of 0.0637 Å,
and a maximum departure of 0.141 (2) Å for C111. The central
phenyl ring 5, however, protrudes significantly from this pla-
In addition to the generalized
is also sustained by some localized C–Hꢀ ꢀ ꢀO (T3a(5,6)) and C–Hꢀ ꢀ ꢀ
(T3a(7)) interactions, which also provide some clues for the already
pꢀ ꢀ ꢀ
p bonds, interplanar cohesion
p
nar geometry, through
a rotation of 26.8 (2)° around the
Fig. 4. Molecular diagram of 2, with 40% displacement ellipsoids, showing atom and ring labeling. Full(empty) bonds and atoms denote the independent (symmetry related)
part of the structure. In broken bonds the intramolecular C–Hꢀ ꢀ ꢀO bonds. Symmetry code: (i) x ꢃ 1, y, z + 1.

J. Granifo et al. / Journal of Molecular Structure 1063 (2014) 102–108
107
ꢀ
Fig. 5. Packing diagram of 2. (a): The 2D substructure formed by the intermolecular C–Hꢀ ꢀ ꢀN hydrogen bonds. A and B are strands of inversion related [101] chains. (b): The
CH(methyl)/ (Cg3) hydrogen bond.
p
Fig. 6. Packing diagram of 2. (a): The band substructure defined by C–Hꢀ ꢀ ꢀN bonds. For ring definitions, see text. (b): The stacking of planes, as described in the text.
mentioned rotational deviation of the phenyl ring 5 out of the
overall mean plane. More specifically, there are two interactions
engaged in the torsion: one is a CH(phenyl)/O(acac) connection,
C181H181ꢀ ꢀ ꢀO22, and the remaining one have the acac-CH3 group
as H-bond donor directed towards the phenyl ring (C52–
H52Bꢀ ꢀ ꢀCg5; Fig. 2b) [23]. Even if these interactions are particularly
3.3. Coordination geometry and bonding in the coordination polymer 2
The polymeric structure 2 (Fig. 4 and Table 2) is compared here
with the already described structure 1. In this regard, it exhibits a
sixfold coordinated Zn cation, but now laying on a general position
and bound to two bidentate bridging L1 ligands related by a [ꢃ110]
translation. In each trans 4 + 2 environment of the Zn centres, the
basal plane is defined by two (now independent) j2O,O0 chelat-
ing-bidentate acac anions and the axial positions are, in this case,
occupied by two asymmetric N atoms: one from a 4-pyridyl group
weak (Hꢀ ꢀ ꢀO and Hꢀ ꢀ ꢀ
p distances are beyond commonly accepted
values for relevant contacts) the rotational barrier for these move-
ments are sufficiently low as to make the effect of these interac-
tions noticeable.

108
J. Granifo et al. / Journal of Molecular Structure 1063 (2014) 102–108
and the other one from a pyrimidinyl group. The environment of
the Zn atom in 2 is less regular than its counterpart in 1, due to
the lack of symmetry, though it preserves the same general trend
(basal Zn–O range: 2.0294 (11)–2.0596 (12) Å; apical Zn–N range:
2.2182 (12)–2.3860 (13) Å. Angular deformations are also larger,
(cis-angles range: O–Zn–O: 90 0.88 (5)°, O–Zn–N: 90 3.24
(5)°; trans-angles: O–Zn–O: 174.44 (4), 176.04 (4)°, N–Zn–N:
178.64 (5)°). The basal plane is very nearly planar, with a mean
deviation of 0.014 (2) Å for all oxygen atoms and leaving the cat-
ion 0.085 (4) Å aside. Apical bonds deviate little from the plane
normal (0.4 and 1.3°, respectively). The structure of the L1 ligand
in 2 is significantly more deformed than in 1 through rotations of
many of its constitutive rings: only rings 2 and 4 remain roughly
in a plane (mean deviation from the L.S. plane of 0.069 (3) Å, and
a maximum departure of 0.125 (2) Å for C251). The remaining
three rings depart significantly from this basic framework through
rotations around the single C–C bonds (viz., ring 1, by 14.8 Å, ring 3
by 24.1 Å and ring 5 by 25.1 Å). Similarly to 1, acac ligands in 2
show the standard values both in distances as in angles.
on the other hand, in the coordinated pyridyl group this kind of
interactions are insignificant.
4. Conclusions
The new hybrid terpyridine–pyrimidine ligand L1 was synthe-
tized and then characterized through spectroscopic methods. The
coordinating properties of L1 were tested by reacting with
Zn(acac)2 to give unexpectedly a mixture of the mononuclear com-
plex 1 and the coordination polymer 2. The hybrid ligand acting
monodentaly uses the N atom from an exo-pyridyl group, but
when acting as a bidentate-bridging ligand it uses two different
N-donors: an exo-pyridyl group in alliance with a pyrimidinyl
one. The N atom of the central pyridine ring in L1 does not partic-
ipate in the binding to the metal centers. The supramolecular
structures of 1 and 2 can be understood considering the key role
of the non-covalent C–HꢀꢀꢀN interactions that produce 2D substruc-
tures, which in combination with the
the abundant aromatic rings, develops the 3D arrangement. These
p
ꢀ ꢀ ꢀ
p contacts provided by
The type of non-covalent interactions in 2 (Tables 3b and 4b and
Figs. 4, 5a and b, 6a and b) are similar to those in 1. Thus, in 2 the
intramolecular C–Hꢀ ꢀ ꢀO contacts are present, T3b(1,2,3,4) (Fig. 4),
but in this case by using hydrogen atoms of the coordinated pyri-
dyl and pyrimidinyl groups to contact the acac oxygens atoms,
displaying a S(5) motif (A in Fig. 6a). Likewise, the intermolecular
C–Hꢀ ꢀ ꢀN interactions appear defining a planar 2D array (Fig. 5a),
but instead of the two contacts of 1 here there is only one that in-
volves the N atom of the uncoordinated 4-pyridyl group, T3b(5),
and its effect is to link pairs of neighboring, inversion related
synthons act in conjunction with several CH/O and CH/
bonds to assemble the crystal packing.
p hydrogen
Acknowledgements
The authors acknowledge the Universidad de La Frontera (Proy-
ecto DIUFRO DI13-0101) and ANPCyT (Project No. PME 2006-
01113) for the purchase of the Oxford Gemini CCD diffractometer.
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ˇ ˇ
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