Zn(II) and Cd(II) monomer, dimer and polymer compounds coordinated by benzoic acid and 4-acetylpyridine: Synthesis and crystal structures

Article abstract of DOI:10.1016/j.ica.2020.119561

Reaction of MO (MO = Metal oxide, M = Zn(II) or Cd(II)) with benzoic acid (HBz) in H₂O/MeOH mixture as solvent yields two benzoate compounds: [Zn(μ-Bz)₂]_n (1) and [Cd(Bz)₂(H₂O)₃] (2). In addition, the reaction between M(MeCO₂)₂ (M = Zn(II) or Cd(II)) with HBz and 4-acetylpyridine (4-Acpy) in a 1:2:4 M ratio and in MeOH solution, leads to the formation of [Zn(μ-Bz)₂(4-Acpy)]₂ (3) and [Cd(μ-Bz)₂(4-Acpy)₂]₂ (4). These four compounds have been fully characterized by analytical and spectroscopic techniques. Besides, their crystal structures have been elucidated revealing a 1D coordination polymer (1), a monomer (2), a paddle-wheel (3) and a dimer (4). In 1, the Zn(II) ion is four-coordinated in a tetrahedral geometry while in 3 is penta-coordinated in a square-pyramidal geometry. By contrast, compounds 2 and 4 exhibit seven-coordinated Cd(II) ions in a pentagonal-bipyramidal geometry. In these set of compounds, the benzoate ligand presents different coordination modes such as bidentate bridged (μ₂-η¹:η¹) (1 and 3), chelate (μ₁-η²) (2) and both bridged and chelate (μ₂-η²:η¹) (4). Besides, their extended structures have been analyzed. Finally, the UV–Vis and fluorescence spectra of all the compounds have been recorded as well as their quantum yields calculated.

Full text of DOI:10.1016/j.ica.2020.119561

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Research paper
Zn(II) and Cd(II) monomer, dimer and polymer compounds coordinated by
benzoic acid and 4-acetylpyridine: Synthesis and crystal structures
Laura Moreno-Gómez, Francisco Sánchez-Férez, Teresa Calvet, Mercè Font-
Bardia, Josefina Pons
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DOI:
Reference:
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https://doi.org/10.1016/j.ica.2020.119561
ICA 119561
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28 February 2020
Please cite this article as: L. Moreno-Gómez, F. Sánchez-Férez, T. Calvet, M. Font-Bardia, J. Pons, Zn(II) and
Cd(II) monomer, dimer and polymer compounds coordinated by benzoic acid and 4-acetylpyridine: Synthesis and
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Zn(II) and Cd(II) monomer, dimer and polymer compounds
coordinated by benzoic acid and 4-acetylpyridine: Synthesis and
crystal structures
Laura Moreno-Gómez,a Francisco Sánchez-Férez,a Teresa Calvet,b Mercè Font-Bardia,c
and Josefina Pons,a,*
aDepartament de Química, Universitat Autònoma de Barcelona, 08193-Bellaterra,
Barcelona, Spain
bMineralogia, Petrologia i Geologia Aplicada, Universitat de Barcelona, Martí i
Franquès s/n, 08028-Barcelona, Spain.
cUnitat de Difracció de Raig-X, Centres Científics i Tecnològics de la Universitat de
Barcelona (CCiTUB), Universitat de Barcelona, Solé i Sabarís, 1-3, 08028-Barcelona,
Spain.
1

Abstract
Reaction of MO (MO = Metal oxide, M = Zn(II) or Cd(II)) with benzoic acid
(HBz) in H2O/MeOH mixture as solvent yields two benzoate compounds: [Zn(µ-Bz)2]n
(1) and [Cd(Bz)2(H2O)3] (2). In addition, the reaction between M(MeCO2)2 (M = Zn(II)
or Cd(II)) with HBz and 4-acetylpyridine (4-Acpy) in a 1:2:4 molar ratio and in MeOH
solution, leads to the formation of [Zn(µ-Bz)2(4-Acpy)]2 (3) and [Cd(µ-Bz)2(4-Acpy)2]2
(4). These four compounds have been fully characterized by analytical and
spectroscopic techniques. Besides, their crystal structures have been elucidated
revealing a 1D coordination polymer (1), a monomer (2), a paddle-wheel (3) and a
dimer (4). In 1, the Zn(II) ion is four-coordinated in a tetrahedral geometry while in 3 is
penta-coordinated in a square-pyramidal geometry. By contrast, compounds 2 and 4
exhibit seven-coordinated Cd(II) ions in a pentagonal-bipyramidal geometry. In these
set of compounds, the benzoate ligand presents different coordination modes such as
bidentate bridged (µ2-η1:η1) (1 and 3), chelate (µ1-η2) (2) and both bridged and chelate
(µ2-η2:η1) (4). Besides, their extended structures have been analyzed. Finally, the UV-
Vis and fluorescence spectra of all the compounds have been recorded as well as their
quantum yields calculated.
Zn(II), Cd(II); benzoic acid; 4-acetylpyridine ligand; X-ray crystal structures; quantum
yield
2

Introduction
During the last decades two new classes of metal-organic materials (MOMs),
supramolecular coordination compounds (SCCs) and coordination polymers (CPs) have
emerged in the field of coordination chemistry. They have attracted a huge interest not
only for their structural versatility but also for their hierarchical assembly and their
applications in many fields including catalysis [1], chemical separation [2] or sensing
[3].
The arrangement of these compounds is mainly based on the geometry of the
metal center and the nature of the ligands, which direct the formation of the primary
structural motif. From there, the growth of the crystal structure could be driven through
intermolecular interactions, such as hydrogen bonds or π-π stacking, into SCCs [4] or
via coordination bonds resulting in CPs [5]. Remarkable is the effect of additional
factors as metal:ligand ratio, counterions or solvent occluded molecules, in the final
structural inception. The main characteristic of SCCs is the capability of outperforming
CPs in their industrial applications due to the enhanced host-guest interactions and wet-
processability [6].
Carboxylic acids have been widely used in coordination chemistry as
multifunctional ligands due to their large variety of coordination modes, yielding mono-
, di-, tri- polynuclear and polymeric coordination complexes [7]. Simple aromatic
monocarboxylate anions are ubiquitous and versatile ligands in coordination chemistry.
Therefore, benzoic acid has attracted notable interest because either allows the synthesis
of SCCs or CPs [8] and even more important their synthesis in water as solvent, the
greenest and most abundant of all solvents [9].
As aforementioned, the geometry of the metal atom is one of the structural
determining forces in these systems. In particular, M(II) ions with d10 electronic
3

configuration confer a wide range of coordination numbers and geometries [10]. In
addition, Zn(II) carboxylate complexes are relevant in biological systems [11], as
[Zn(aspirinate)2(H2O)2] which presents anti-convulsing activity [12]. Besides, Cd(II)
carboxylates are interesting for their photochemical and photocatalytic properties [13],
as well as their structural versatility [14].
The synthesis of metal complexes by mixed ligand approach, combining
carboxylate and heterocyclic N-donor ligands has enabled the obtainment of different
physical, chemical and biological properties [15]. In addition, the reversible
arrangement of the coordination bonds during the formation of the d10 metal complexes
evolves into highly ordered structures [16].
Previously, our group have reported the preparation of Zn(II) and Cd(II)
compounds either via direct reaction of carboxylic acids (1,3-benzodioxole-5-carboxylic
(HPip); 3,5-dihydroxybenzoic (3,5-HDHB) or 3,5-dimethoxybenzoic (3,5-H(MeO)2Bz))
or by mixed ligand strategy, combining these acids with different pyridine derivatives.
The reaction of M(MeCO2)2 (M=Zn(II) or Cd(II)) with HPip and 3- or 4-phenylpyridine
resulted in two Zn(II) paddle-wheels and two Cd(II) dimers [17]. Unlike these previous
results, the reaction between ZnO and 3,5-HDHB yielded a coordination polymer
[Zn(µ-3,5-DHB)2(H2O)2]n, which in presence of isonicotinamide (Isn), 4-acetylpyridine
(4-Acpy) and 3-methylpyrazole (3-Mepz) generated monomeric complexes [18]. The
role of 4,4’-bipyridine (4,4’-bpy) as linker via its reaction against Zn(MeCO2)2 , 3,5-
HDB or 3,5-H(MeO)2Bz was also studied [19].
Recently, we have assayed the reaction between M(MeCO2)2 (M = Zn(II), Cd(II)
or Hg(II)) and HPip. While Zn(II) lead to a monomeric complex, Cd(II) and Hg(II)
drove the formation of three coordination polymers with different nuclearity and
4

different coordination modes of the Pip ligand. In addition, their phosphorescence
properties were recorded and their corresponding quantum yields calculated [20].
As a continuation of this study, in this paper we present the reaction of MO (M =
Zn(II), Cd(II)) with HBz, which formed complexes [Zn(µ-Bz)2]n (1) and
[Cd(Bz)2(H2O)3] (2). Compound 1 is a coordination polymer while 2 presents a
monomeric structure. Within this frame, the addition of 4-Acpy drove the formation of
a paddle-wheel compound [Zn(µ-Bz)2(4-Acpy)]2 (3) and a dimeric compound [Cd(µ-
Bz)2(4-Acpy)2]2 (4). In these structures, the Bz ligand showed different coordination
modes: chelate, bridged or both, and the incorporation of the 4-Acpy increased the
coordination number, nuclearity and dimensionality of the resulting products (Scheme
1). Their molecular and supramolecular structures have been analyzed mainly
associating via intermolecular hydrogen bond, π-π stacking and C-H···O interactions. In
addition, their UV-Vis and fluorescence spectra have been recorded and the
corresponding quantum yields calculated.
Scheme 1. Outline of the synthesis of the complexes 1-4.
5

Results and discussion
2.1. Synthesis and general characterization
Complexes 1 and 2 were obtained by direct reaction of benzoic acid (HBz) with
ZnO or CdO, in a 1:2 molar ratio. Reactions were performed refluxing a solution of
H2O/methanol (35/10) mL for 1 h (1) or 24 h (2). Complexes 3 and 4 were obtained by
mixing Zn(MeCO2)2·2H2O or Cd(MeCO2)2·2H2O with HBz and 4-Acpy ligands in a
1:2:4 molar ratio. These reactions were carried out for 3 h (3) or 13 h (4) in MeOH
solution at reflux conditions.
Compounds 1-4 were characterized by powder X-Ray diffraction (PXRD),
1
elemental analysis (EA), FTIR-ATR and H NMR spectroscopies and single crystal X-
ray diffraction method. In addition, their UV-Vis and phosphorescence spectra have
been recorded and their quantum yields calculated. It should be noted that the structure
of compound 1 was previously elucidated [8]. Nevertheless, we thought it appropriate to
analyze and compare its supramolecular interactions, which were not previously
studied.
Phase purity of the bulk samples was confirmed by PXRD. EA of all the
compounds are in accordance with the proposed formula. FTIR-ATR spectra of
compounds 1-4 display the characteristic bands of the Bz ligand. Besides, 3 and 4 also
present bands attributable to the 4-Acpy ligand. The carboxylate bands of 1-4 appear
between 1595 and 1501 cm-1 for νas(CO2) and between 1493 and 1391 cm-1 for νs(CO2)
(SI: Figures S5-S8). For 1-4, their Δ values (νas(CO2) - νs(CO2)) have been calculated:
170 (1), 110 (2), 176 (3), and 102, 156 (4) cm-1. These values indicate a bidentate
bridging coordination mode (µ2-η1:η1) of the carboxylate groups in 1 and 3 and a
bidentate chelate coordination mode (µ1-η2) in 2. Finally, compound 4 presents two
6

values of Δ, inasmuch as the Bz ligand simultaneously has two coordination modes:
bidentate bridged and chelate (µ2-η2:η1) [21].
Compound 2 also exhibits a broad band in the range 3419-3229 cm-1, which
corresponds to ν(O-H) from water molecules coordinated to the Cd(II). For all the
compounds, additional bands attributable to the aromatic groups ν(C=C)/ν(C=N),
δ(C=C)/δ(C=N), δ(C-H)ip and δ(C-H)oop are also observed [22]. The FTIR-ATR spectral
data thus, clearly lend support to the structures determined by the single crystal X-ray
diffraction method.
1H NMR spectra of the complexes 1-4 were recorded in DMSO-d6 for 1, D2O for
2, and CDCl3 for 3 and 4, due to their different solubility. All the spectra show the
signals belonging from Bz (1, 2) or Bz and 4-Acpy (3, 4) (SI: Figures S9-S12). The 1H
NMR spectra of all the compounds present three signals between 8.16 and 7.31 ppm
assigned to the aromatic protons of the Bz ligand while those of the 4-Acpy appear at
8.89 ppm and 7.79 ppm (3) and at 8.90 ppm and 7.69 ppm (4). Moreover, the 4-Acpy
present two signals at 2.65 (3) and 2.57 (4) ppm assigned to the CH3 group [22]. The
chemical shifts of ortho-benzoate and ortho-pyridyl groups are consistent with the
presence of O2C-coordinated and N-coordinated benzoate and pyridyl linkers,
respectively.
2.2.Crystal and extended structure of compound 1
The crystal structure of compound 1 was previously reported [8]. Although the
syntheses were performed starting from Zn(CO3) [8.a] or ZnCl2 [8.d] in this work has
been performed with ZnO. Three of them ([8.a, 8.b and 8.d]) were elucidated at a
different temperature (in this paper at 100K while the reported structures around 295K)
exhibiting variation in the intermolecular interactions (vide infra) as previously reported
in our group [23]. The last structure [8.c] was not studied and presented as a CSD
7

communication. The intermolecular interactions of these complexes were not studied
and thus, the determination of the crystal structure allows the better comparison of the
intermolecular interactions that hold together these structures.
Compound 1 has a polymeric zig-zag chain structure with a [ZnO4] core
composed by four benzoate ligands in a bridging (syn-syn and syn-anti) coordination
mode (Figure 1). The Zn(II) ions exhibit a slightly distorted tetrahedral geometry, τ4 =
0.86 (Zn(1)) and 0.94 (Zn(2)) [24], with angles ranging from 98.58(10)° to 121.87(10)°
(Table 1).
Figure 1. Molecular structure representation of compound 1. Hydrogen atoms are omitted for clarity.
Compared to the reported structures [8], those determined at 295K [8.b] and
296K [8.d], present differences in the values of the Zn-O lengths and O-Zn-O angles
(Zn(2)-O(2)#2, 1.954(2) and O(3)-Zn(1)-O(8)#1, 103.09(10) (present work) ;Zn(2)-
O(8), 1.9792 and O(7)-Zn(1)-O(5) 112.26 [8.b]; Zn(1)-O(8)#1, 1.954(2) (present work);
Zn(1)-O(8), 1.917(2) [8.d]). In compound 1, the intermolecular interactions expand the
structure forming 2D layers parallel to the bc plane (Figure 2a). This association is
determined by weak C-H··· π interactions [25, 26] (C(20)···Cg(1), 4.251 Å (work);
C(4)···Cg(1), 5.044 Å [8.b]; C(25)···Cg(1), 5.026 Å [8.d]) between the meta-protons of
the syn-anti Bz linkers and the syn-syn aromatic benzoate rings with the concomitant
torsion of the syn-anti Bz rings (Table 1) (Figure 2b).
8

Table 1. Selected bond lengths (Å), bond angles (°) and intermolecular interactions for 1.
Bond length (Å)
Zn(1)-O(5)
Zn(1)-O(3)
Zn(1)-O(1)
Zn(1)-O(8)#1
1.938(2)
1.938(2)
1.938(2)
1.954(2)
Zn(2)-O(6)
Zn(2)-O(7)
Zn(2)-O(4)#2
Zn(2)-O(2)#2
1.939(2)
1.940(2)
1.949(2)
1.954(2)
Bond angles (°)
O(5)-Zn(1)-O(3)
O(5)-Zn(1)-O(1)
O(3)-Zn(1)-O(1)
O(5)-Zn(1)-O(8)#1
O(3)-Zn(1)-O(8)#1
O(1)-Zn(1)-O(8)#1
105.99(10)
98.66(9)
116.59(10)
109.62(10)
103.09(10)
121.87(10)
O(6)-Zn(2)-O(7)
108.34(10)
111.96(10)
113.99(10)
98.58(10)
109.68(11)
113.17(10)
O(6)-Zn(2)-O(4)#2
O(7)-Zn(2)-O(4)#2
O(6)-Zn(2)-O(2)#2
O(7)-Zn(2)-O(2)#2
O(4)#2-Zn(2)-O(2)#2
Intermolecular interactions
D-H···A
C(20)-H(20)···Cg(1) 0.950
D-H (Å)
H···A (Å)
3.481
D···A (Å)
4.251
> D-H···A (°)
139.88
#1 -x+1,y-1/2,-z+1/2 #2 -x+1,y+1/2,-z+1/2
Cg1 (C(23) C(24) C(25) C(26) C(27) C(28))
Although the structure elucidated at 100K [8.c] has a similar bond length and
angles, the intermolecular C-H···π interaction also differs from our structure (C(20)-
H(20)···Cg(1), 3.481 Å, C(20)···Cg(1), 4.251, 139.88º (present work); C(25)-
H(25)···Cg(1), 4.712 Å, C(25)···Cg(1), 5.017 Å, 103.30º [8.c]).
Figure 2. (a) Perpendicular view of the 2D layer generated by 1 along the bc plane. (b) c axis expansion
via C-H···π interaction.
9

2.3. Crystal and extended structure of compound 2
Compound 2 belongs to the orthorhombic Pbca space group. It has a monomeric
structure with a [CdO7] core composed by two bidentate chelate benzoate ligands and
three water molecules (Figure 3a). The Cd(II) ion exhibits a slightly distorted
pentagonal-bipyramidal geometry [27] (Figures 3b and 3c) in which the equatorial plane
is set by two Bz ligands and one H2O molecule (ranging from 54.10(7) to 90.75(7)°)
while the remaining two H2O molecules hold the axial positions. Bond lengths and
angles are provided in Table 2.
The pentagonal-bipyramidal is the most common geometry of hepta-coordinated
metals, which in turn are less common than six- or eight-coordinated. This fact is due to
a less effective packing arrangement caused by electronic repulsion and steric effects
between ligands [28].
Figure 3. (a) Molecular structure representation of compound 2. Front (b) and upper (c) view of the Cd(II)
centers geometry.
In this case, the asymmetric chelated benzoate ligands enable this hepta-
coordination. Similar Cd(II) polymeric compounds reported in the literature showed Cd-
10

O bond lengths and angles ranging between 2.277(6) and 2.487(5) Å and between
53.7(2) and 176.1(2)°, respectively [29].
In compound 2, the supramolecular expansion is promoted by hydrogen bond
interactions between the coordinated water molecules and the carboxylate oxygen atoms
of the Bz ligands (Figure 4a) [30]. The equatorial water molecules exhibit hydrogen
bond interactions along the b axis by only one proton (Figure 4b) while the axial water
molecules present hydrogen bond interactions along the ab plane via both hydrogen
atoms (Figures 4c).
All these set of interactions hold together the monomeric units forming 2D
layers parallel to the ab plane. Bond lengths and angles related to hydrogen bond
interactions are listed in Table 2.
Figure 4. (a) Perpendicular view of the 2D layer generated by 2 along the ab plane. (b) Perpendicular
view of the a axis and (c) b axis expansion via hydrogen bond interactions (highlighted in blue and green)
through the axial and equatorial water molecules, respectively.
11

Table 2. Selected bond lengths (Å), bond angles (°) and intermolecular interactions for 2.
Bond length (Å)
Cd-O(1)
Cd-O(2)
Cd-O(3)
Cd-O(4)
2.3741(19)
2.4670(19)
2.383(2)
Cd-O(5)
Cd-O(6)
Cd-O(7)
2.277(2)
2.323(2)
2.257(2)
2.334(2)
Bond angles (°)
O(7)-Cd-O(5)
O(7)-Cd-O(6)
O(5)-Cd-O(6)
O(7)-Cd-O(4)
O(5)-Cd-O(4)
O(6)-Cd-O(4)
O(7)-Cd-O(1)
O(5)-Cd-O(1)
O(6)-Cd-O(1)
O(4)-Cd-O(1)
O(7)-Cd-O(3)
173.38(8)
91.90(8)
92.52(8)
93.34(8)
87.06(8)
134.52(7)
94.69(8)
81.08(7)
81.61(7)
142.61(7)
89.22(8)
O(5)-Cd-O(3)
O(6)-Cd-O(3)
O(4)-Cd-O(3)
O(1)-Cd-O(3)
O(7)-Cd-O(2)
O(5)-Cd-O(2)
O(6)-Cd-O(2)
O(4)-Cd-O(2)
O(1)-Cd-O(2)
O(3)-Cd-O(2)
96.46(8)
79.03(7)
55.94(7)
160.36(7)
83.73(8)
89.65(7)
134.73(7)
90.75(7)
54.10(7)
145.53(7)
Intermolecular interactions
D-H···A
D-H (Å)
0.766(5)
H···A (Å)
D···A (Å)
2.777(3)
2.748(3)
2.658(3)
2.783(3)
2.797(3)
> D-H···A (°)
170.77(4)
162.92(3)
163.69(4)
171.45(3)
177.92(3)
O(5)-H(5B)···O(1)
O(7)-H(7A)···O(2)
O(5)-H(5A)···O(4)
O(7)-H(7B)···O(1)
O(6)-H(6A)···O(2)
2.018(5)
1.973(2)
1.848(4)
1.990(2)
1.996(2)
0.800(2)
0.833(4)
0.799(2)
0.801(2)
2.4. Crystal and extended structure of compound 3
Compound 3 belongs to the monoclinic C2/c space group. There are two
crystallographically independent dimeric units with similar bond lengths and angles
present in the unit cell (Molecule A and B) (Figure 5).
Figure 5. Molecular structure representation of compound 3 showing the two crystallographically
independent units comprised in the unit cell (A left, B right). Hydrogen atoms are omitted for clarity.
12

Both display a dimeric paddle-wheel like structure with a [ZnO4N] core. The
dimeric units are composed by four bidentate bridging benzoate ligands in a syn-syn
disposition, which join the two Zn(II) centers and two monodentate 4-Acpy ligands.
These Zn(II) ions exhibit a slightly distorted square-pyramidal geometry (τ = 0.01-0.06)
[31] with an elongation (0.355-0.398 Å) from the basal plane towards the axial position.
Table 3. Selected bond lengths (Å), bond angles (°) and intermolecular interactions for 3.
Molecule A
Bond length (Å)
Zn(1A)-O(5A)
Zn(1A)-N(1A)
Zn(1A)-O(3A)
2.015(2)
2.032(4)
2.046(2)
Zn(2A)-N(2A)
Zn(2A)-O(6A)
Zn(2A)-O(4A)
2.015(4)
2.037(3)
2.046(3)
Bond angles (°)
O(5A)-Zn(1A)-O(5A)#1
O(5A)-Zn(1A)-N(1A)
O(5A)-Zn(1A)-O(3A)#1
O(5A)-Zn(1A)-O(3A)
N(1A)-Zn(1A)-O(3A)
O(3A)#1-Zn(1A)-O(3A)
N(2A)-Zn(2A)-O(6A)
155.81(15)
102.10(8)
87.87(11)
87.74(11)
100.52(7)
158.95(15)
99.23(8)
O(6A)#1-Zn(2A)-O(6A)
N(2A)-Zn(2A)-O(4A)#1
O(6A)-Zn(2A)-O(4A)#1
N(2A)-Zn(2A)-O(4A)
O(6A)-Zn(2A)-O(4A)
O(4A)#1-Zn(2A)-O(4A)
O(6A)#1-Zn(2A)-O(6A)
161.53(15)
101.04(8)
88.36(11)
101.04(8)
88.12(11)
157.92(16)
161.53(15)
Molecule B
Bond length (Å)
Zn(1B)-O(9B)
Zn(1B)-N(1B)
Zn(1B)-O(5B)
Zn(1B)-O(7B)
Zn(1B)-O(3B)
2.005(3)
2.012(3)
2.041(3)
2.052(3)
2.054(3)
Zn(2B)-O(4B)
Zn(2B)-N(2B)
Zn(2B)-O(8B)
Zn(2B)-O(10B)
Zn(2B)-O(6B)
2.012(3)
2.027(3)
2.031(3)
2.067(3)
2.080(3)
Bond angles (°)
O(9B)-Zn(1B)-N(1B)
O(9B)-Zn(1B)-O(5B)
N(1B)-Zn(1B)-O(5B)
O(9B)-Zn(1B)-O(7B)
N(1B)-Zn(1B)-O(7B)
O(5B)-Zn(1B)-O(7B)
O(9B)-Zn(1B)-O(3B)
N(1B)-Zn(1B)-O(3B)
O(5B)-Zn(1B)-O(3B)
O(7B)-Zn(1B)-O(3B)
98.25(13)
160.04(14)
101.60(13)
86.68(14)
99.05(12)
88.19(15)
89.48(13)
101.81(12)
88.47(14)
159.12(13)
O(4B)-Zn(2B)-N(2B)
O(4B)-Zn(2B)-O(8B)
N(2B)-Zn(2B)-O(8B)
O(4B)-Zn(2B)-O(10B)
N(2B)-Zn(2B)-O(10B)
O(8B)-Zn(2B)-O(10B)
O(4B)-Zn(2B)-O(6B)
N(2B)-Zn(2B)-O(6B)
O(8B)-Zn(2B)-O(6B)
O(10B)-Zn(2B)-O(6B)
98.95(12)
161.29(12)
99.74(12)
87.07(12)
100.35(12)
90.38(13)
87.62(11)
100.82(12)
88.08(12)
158.73(13)
Intermolecular interactions
D-H···A
D-H (Å)
H···A (Å)
D···A (Å)
3.669
> D-H···A (°)
Cg(1)···Cg(2)
3.689
Cg(3)···Cg(4)
0.950
0.950
2.777
2.777
3.698
163.33
138.80
C(40)-H(40)···Cg(5)
C(32)-H(32)···O(2)
#1 -x+2,y,-z+3/2
3.547(5)
The basal plane is formed by four oxygen atoms from the Bz ligands with bond
angles between 86.68(14)-90.38(13)° (Table 3), while the 4-Acpy ligand holds the
13

apical position. Other reported Zn(II) paddle-wheel benzoates containing different
heterocyclic nitrogen donors showed similar bond lengths (2.018-2.083 Å) and bond
angles (between 86.47-159.36°): [Zn2(py)2(Bz)4] (py = pyridine) [32] and
[Zn2(Bz)4(2,5-Me2pyz)]n (2,5-Me2pyz = 2,5-dimethylpyrazine) [11].
The paddle-wheel units in 3 are hold together via weak π-π, C-H···π and C-
H···O interactions. Bz ligands stack with the 4-Acpy ligands by π-π interactions at
3.669 Å (Cg1-Cg2). In addition, they also drive π-π (3.689 Å, Cg3-Cg4) and a C-H··· π
(3.698 Å) interactions with other Bz ligands from neighboring paddle-wheels through
their Hpara protons (Table 3). Finally, Bz ligand also promotes weak C-H···O
interactions between the Hmeta and the carbonyl group of the 4-Acpy (2.777 Å). Planar
π-π interactions expands along the c axis while C-H··· π and C-H···O interactions
expands it along a and b axis, respectively, forming a 3D supramolecular structure
(Figure 6).
Figure 6. Supramolecular expansion of compound 3. Blue (4-Acpy) and red (Bz) centroids implied in the
intermolecular interactions are highlighted.
14

2.5. Crystal and extended structure of compound 4
Compound 4 belongs to the tetragonal P41212 space group. It has a dimeric
structure with four benzoate ligands and four 4-Acpy ligands. Each cadmium atom
adopts a [CdO5N2] core (Figure 7a). The dimeric unit is composed by two bidentate
benzoate ligands exhibiting both chelate and bridged coordination modes. One of the
carboxylate oxygen atoms is bonded to the Cd(II) center while the other acts as ditopic
linker joining both Cd(II) ions.
Figure 7. (a) Molecular structure representation of compound 4. Front (b) and upper (c) view of the Cd(II)
centers geometry.
These metal centers exhibit a slightly distorted pentagonal-bipyramidal
geometry [27] and all the benzoate ligands are arranged in the equatorial plane, with
equatorial angles between 52.98(7)-92.87(7)° (Table 4). The four 4-Acpy ligands hold
the axial positions (Figures 7b and 7c). There are similar Cd(II) compounds with
comparable bond lengths (2.314(4) - 2.520(5) Å) and bond angles (52.98 to 173.74°)
[27].
15

These dimeric units are held together forming a 3D net via weak C-H···O and C-
H···π interactions (Figure 8). Lengths and angles related to these interactions are shown
in Table 4.
Table 4. Selected bond lengths (Å), bond angles (°) and intermolecular interactions for 4.
Bond length (Å)
Cd(1)-O(1)
Cd(1)-O(3)
Cd(1)-N(2)
Cd(1)-N(1)
2.291(2)
2.315(2)
2.331(3)
2.338(3)
Cd(1)-O(4)#1
Cd(1)-O(2)
Cd(1)-O(4)
2.344(2)
2.5149(19)
2.577(2)
Bond angles (°)
O(1)-Cd(1)-O(3)
O(1)-Cd(1)-N(2)
O(3)-Cd(1)-N(2)
O(1)-Cd(1)-N(1)
O(3)-Cd(1)-N(1)
N(2)-Cd(1)-N(1)
O(1)-Cd(1)-O(4)#1
O(3)-Cd(1)-O(4)#1
N(2)-Cd(1)-O(4)#1
N(1)-Cd(1)-O(4)#1
O(1)-Cd(1)-O(2)
84.89(8)
95.47(11)
93.65(10)
92.58(11)
95.87(10)
168.04(9)
147.17(7)
127.91(7)
84.81(9)
83.63(9)
54.34(7)
O(3)-Cd(1)-O(2)
N(2)-Cd(1)-O(2)
N(1)-Cd(1)-O(2)
O(4)#1-Cd(1)-O(2)
O(1)-Cd(1)-O(4)
O(3)-Cd(1)-O(4)
N(2)-Cd(1)-O(4)
N(1)-Cd(1)-O(4)
O(4)#1-Cd(1)-O(4)
O(2)-Cd(1)-O(4)
139.22(7)
90.01(9)
87.51(9)
92.87(7)
137.85(7)
52.98(7)
89.33(9)
90.63(9)
74.93(7)
167.79(6)
Intermolecular interactions
D-H···A
C(13)-H(13)···O(3)
C(7)-H(7)···Cg(1)
C(16)-H(16)···Cg(2) 0.950
C(25)-H(25)···Cg(2) 0.950
D-H (Å)
0.950
0.950
H···A (Å)
D···A (Å)
3.338(4)
3.974
4.231
3.794
> D-H···A (°)
141.56
112.35
137.77
152.76
2.541
3.514
3.479
2.925
#1 y,x,-z+1
Cg1 (C(9) C(10) C(11) C(12) C(13) C(14)); Cg2 (C(2) C(3) C(4) C(5) C(6) C(7))
Figure 8. Perpendicular view of the ab expansion of compound 4 (left). In detail of c axis expansion
(right).
16

2.6.UV-Vis and photoluminescence experiments
The UV-Vis and fluorescence spectra of complexes 1, 3 and 4 have been
performed in MeOH solution while the spectra of 2 in H2O. All the experiments have
been recorded between 190 and 320 nm at 298 K. The UV-Vis measurements of L-
tyrosine, HBz and 4-Acpy ligands, and complexes 1-4, have been carried out with a
concentration ranging from 1·10-9 to 1·10-4 M to ensure their no aggregation (S.I.: Fig.
S13-S14).
L-tyrosine used as reference also displayed three λmax at 193, 222 and 275 nm.
The HBz as well as the 4-Acpy ligand presents three absorption peaks (λmax) at 202,
224, 271 nm and 203, 220, 278 nm, respectively. Compounds 1-4 present λmax bands
centered around 200, 222 and 270 nm. Considering the conjugation of the aromatic
rings present in both ligands as well as the lone pairs of the nitrogen and oxygen atoms,
there are several potential transitions in these complexes, rising from π-π*, n-π* and n-
σ* [33]. The absorbance of the complexes at 270 nm increase 2<3<1<4, in that order
(Figure 9).
Figure 9. UV-Vis absorption spectra of L-tyrosine, 4-Acpy and HBz ligands and complexes 1-4 recorded
between 190 and 320 nm.
17

The emission spectra of L-tyrosine, HBz and 4-Acpy ligands and complexes 1-4,
have been measured at 298 K. All the experiments have been performed with an λexc of
270 nm and recording between 280 and 470 nm. The concentrations used were 9.75·10-6
M (L-tyrosine) for the standard, 1.68·10-7 M (HBz) and 1.68·10-7 M (4-Acpy) for the
ligands, and 8.11·10-8 M (1), 1.10·10-7 M (2), 6.46·10-8 M (3) and 4.16·10-6 M (4) for
the complexes. Their emission spectra have been depicted in Figure 10.
Figure 10. Emission spectra of L-tyrosine, 4-Acpy and HBz ligands and complexes 1-4 excited at 270 nm
and recorded between 280 and 470 nm.
Fluorescence quantum yield (φs) is defined as the ratio of the number of photons
emitted to the number of photons absorbed and describes how a fluorophore converts
the excitation light into fluorescence [34]. The relative fluorescence quantum yield is
calculated relating the quantum yield value of the desired compound and comparing
with a reference (standard) [35].
The quantum yields of compounds 1-4 have been calculated using equation 1,
2
ɳ
φs = φr (OD ) (I ) (ɳ )
(eq. 1)
I
ref
s
s
OD
s
ref
ref
18

where φref and φs, are the quantum yields of the reference and the sample, respectively. I
is the area under the curve for the emission spectra, OD is the optical density (or
absorbance), and ɳ is the refractive index of the solvent. L-tyrosine has been used as a
standard (φref = 0.14) [36]. The values of Aref and Iref for L-tyrosine as well as for
compound 2 have been recorded using Milli-Q water as solvent (nref = 1.3325) [37]. The
values of As and Is of HBz and 4-Acpy ligands and compounds 1, 3 and 4 have been
measured using MeOH as solvent (ns = 1.3314) [37] at r.t. The values of relative
quantum yields obtained for compounds 1-4 are 0.034 (1), 0.012 (2), 0.021 (3) and
0.026 (4) (Table 5).
Table 5. Fluorescence data for quantum yield calculations (φs).
Sample
λabs (nm)
λem
(nm)
Solvent Refractive
index [36]
Absorba
nce (a.u.)
Area
Quantum
yield
L-tyrosine
4-Acpy
HBz
1
2
3
4
193, 222, 275
203, 222, 278
202, 224, 271
203, 225, 270
192, 223, 269
201, 222, 272
202, 222, 277
314
350
330
334
349
332
318
Water
MeOH
MeOH
MeOH
Water
MeOH
MeOH
1.3325
1.3314
1.3314
1.3314
1.3325
1.3314
1.3314
0.030
0.054
0.041
0.049
0.043
0.048
0.049
21525.7
14097.3
4602.45
8572.74
2622.32
5286.73
6545.58
0.14 [37]
0.051
0.022
0.034
0.012
0.021
0.026
The complexation of the HBz ligand to the metal center resulted in a
bathochromic shift in 2 while compound 4 shows a hyperchromic shift respect to both
HBz and 4-Acpy ligands. Photoluminescence in 1 is probably favored by the increased
rigidity of the ligand in the polymeric array, with concomitant decrease of radiation, the
minor decay process of the intraligand (π-π*) excited state and the reduced energy loss
driven by the intramolecular or intermolecular interactions of the organic linker [39].
Compared to 1, the incorporation of the 4-Acpy ligand caused a decay in the emission
probably driven by the less structural rigidity of the dimeric array (3). In presence of
HBz ligand, the Cd(II) center formed a monomeric array (2) which could easily transfer
the absorbed energy to other relaxation processes. Finally, as opposed to the Zn(II)
19

complexes, the addition of the 4-Acpy to the Cd(II) center resulted in a more rigid
structure and its consequent increase in quantum yield.
Conclusions
In this paper, we present the reactivity of HBz against MO or M(MeCO2)2 and 4-
Acpy (M = Zn(II) or Cd(II)). The study of their coordination has revealed the formation
of compounds with different nuclearity and dimensionality, from monomers to
polymers (1-4). These compounds presented a great variety of coordination numbers:
four (1), five (3) and seven (2 and 4), and different coordination modes of the
carboxylate groups (bidentate chelate, bridged or both). Their coordination numbers
increase with the size of metal (1 and 2) or (3 and 4) and also increase with the presence
of the 4-Acpy (1 and 3) or (2 and 4). The higher coordination number in 2 and 4 is
reasonably understood by the large ionic radius of the Cd(II) centers. Although in 2 the
water coordination facilitated the increase of coordination number, it should be noted
that in the case of compound 4, the chelate and bridging coordination mode of the Bz
ligands enable this seven-coordination. Thus, the structural differences of complexes 1-
4 are determined by both the metal size and the incorporation of the 4-Acpy ligand.
The structural analysis evinced that complexes 1 and 2 form 2D layers while 3
and 4 form 3D network supported by hydrogen bonds (2) and weak interactions: C-
H···π (1, 2, 4), π-π and C-H···O (3, 4). In addition, the luminescence properties of all
the complexes and the ligands have been analyzed and their quantum yields calculated
(1>4 >3>2).
20

Experimental Section
4.1 Materials and general details
Zinc(II) oxide nanopowder (ZnO), cadmium(II) oxide (CdO), zinc(II) acetate
dihydrate (Zn(OAc)2·2H2O), cadmium(II) acetate dihydrate (Cd(OAc)2·2H2O), benzoic
acid (HBz), 4-acetylpiridine (4-Acpy) and methanol (MeOH) were purchased from
Sigma-Aldrich and deuterated dimethyl sulfoxide (DMSO-d6), deuterated chloroform
(CDCl3) and deuterated water (D2O) were purchased from Eurisotop. All products were
used without further purification. All the reactions were carried out at reflux conditions,
in MeOH for compounds 1 and 3 and in MeOH/H2O for compounds 2 and 4. Powder X-
ray diffraction (PXRD) patterns were measured with Siemens D5000 apparatus (with 40
kW and 45 mA using CuKα radiation with λ = 1.5406 Å. All of them were recorded
from 2ϴ = 5º to 30º with a step scan of 0.02º counting 1s at each step. Elemental
analyses (C, H, N) were carried out on a Thermo Scientific Flash 2000 CHNS Analyzer.
FTIR-ATR spectra were recorded on a Tensor 27 (Bruker) spectrometer, equipped with
an attenuated total reflectance (ATR) accessory model MKII Golden Gate with diamond
1
window in the range 4000-500 cm-1. H NMR spectra were recorded on an NMR-FT
Bruker 360 MHz and 400 MHz spectrometers in DMSO-d6 solution for compound 1, in
D2O solution for compound 3 and in CDCl3 solution for compounds 2 and 4. All
chemical shifts (δ) are given in ppm relative to TMS as internal standard. The electronic
spectra in MeOH (1, 3 and 4) or H2O (2) solution (from ~1·10-9 M to ~1·10-4 M) were
run on a Agilent HP 8453 UV-Vis spectrophotometer with a quartz cell having path
length of 1 cm in the range of 195-320 nm. Fluorescence measurements were carried
out with a PerkinElmer LS 55 50 Hz fluorescence spectrometer using a 1cm quartz cell,
in MeOH (1, 3 and 4) or H2O (2) solution. The samples were excited at 270 nm and the
emission spectra were recorded between 285 and 450 nm at 297 K. The data obtained
21

were corrected for the dilution effects by means of the Origin Pro 8 software. FTIR-
1
ATR and H-NMR spectra were generated using Origin Pro 8.6 and MestReNova
programs.
4.2 Synthesis of the compound [Zn(µ-Bz)2]n (1)
A H2O suspension (35 mL) of ZnO (151 mg, 1.86 mmol) was added dropwise to
a MeOH solution (10 mL) of HBz (451 mg, 3.69 mmol) and stirred for 15 h at room
temperature (r.t.). Then, the solution was stirred under reflux conditions for 1 h and a
white powder precipitated. The resulting solid was filtered, washed with 10 mL cold
MeOH and dried under vacuum. Mother liquors were concentrated until half of the
volume and colorless crystals were obtained after 1 h.
Yield: 131 mg (23%). Anal. Calc. for C28H20O8Zn2 (615.18 gmol-1): C, 54.66; H,
3.28. Found: C, 54.54; H, 3.14%. ATR-FTIR (wavenumber, cm-1): 3061(w), 3030(w)
[ν(CH)]ar, 1575(m) [νas(COO)], 1551-1527(br) [ν(C=C), ν(C=N)]ar, 1405(s) [νs(COO)],
1
1026(m) [δip(C–H)], 712(s), 675(s) [δoop(C–H)]. H-NMR: (400 MHz, DMSO-d6
3
4
solution, Me4Si, 298 K) δ: 7.95 [2H, m, ortho-HBz], 7.49 [1H, tt, J = 7.3 Hz, J = 1.8
Hz, para-HBz], 7.41 [2H, m, meta-HBz] ppm. (UV−Vis: (MeOH, 8.11×10−8 M) λmax
=
203 nm; 225 nm; 270 nm.
4.3 Synthesis of the compound [Cd(Bz)2(H2O)3] (2)
A H2O suspension (35 mL) of CdO (150 mg, 1.17 mmol) was added dropwise to
a MeOH solution (10 mL) of HBz (286 mg, 2.34 mmol) and stirred for 2 h at r.t. Then,
the solution was stirred under reflux conditions for 3 h. The resulting colorless solution
was vacuumed until a white powder precipitated. The solid obtained was filtered and
washed with 10 mL of cold MeOH. After six days, colorless crystals were obtained via
recrystallization of compound 2 in H2O solution.
22

Yield: 58.4 mg (57%). Anal. Calc. for C14H16O7Cd (408.67 gmol-1): C, 41.14; H,
3.95. Found: C, 40.84; H, 3.91%. ATR-FTIR (wavenumber, cm-1): 3419-3229(br)
[ν(OH)]water, 3087(w), 3054(w), 3030(w) [ν(CH)]ar, 1501(m) [νas(COO)], 1391(s)
1
[νs(COO)], 1024(m) [δip(C–H)], 712(s), 679(s) [δoop(C–H)]. H-NMR: (250 MHz, D2O
solution, Me4Si, 298 K) δ: 7.87 [2H, br, ortho-HBz], 7.54 [1H, br, para-HBz], 7.47 [2H,
br, meta-HBz] ppm. (UV−Vis: (H2O, 1.1×10−7 M) λmax = 192 nm; 223 nm; 269 nm.
4.4 Synthesis of the compound [Zn(µ-Bz)2(4-Acpy)]2 (3)
A MeOH solution (10 mL) of HBz (111 mg, 0.911 mmol) with 4-Acpy (219 mg,
1.81 mmol) was added dropwise to a MeOH solution (6 mL) of Zn(OAc)2·2H2O (99.7
mg, 0.454 mmol) and stirred for 2 days at r.t. Then, the solution was stirred under reflux
conditions for 24 h. The resulting white suspension was cooled down and concentrated
until half of the volume. Suitable crystals were grown from the mother liquors in 1 h.
Crystals were filtered and washed with 10 mL of cold MeOH.
Yield: 366 mg (77%). Anal. Calc. for C42H34N2O10Zn2 (857.45 gmol-1): C,
58.43; H, 4.00; N, 3.27. Found: C, 58.72; H, 3.84; N, 3.05%. ATR-FTIR (wavenumber,
cm-1): 3055(w), 3008(w) [ν(CH)]ar, 2920(w) [ν(CH)]al, 1703(m) [ν(C=O)]4-Acpy
,
1574(m) [νas(COO)], 1553(w) [ν(C=C), ν(C=N)]ar, 1398(s) [νs(COO)], 1359(m)
1
[δ(C=C), δ(C=N)]ar, 1024(w) [δip(C–H)], 718(s), 677(s) [δoop(C–H)]. H-NMR: (400
MHz, CDCl3 solution, Me4Si, 298 K) δ: 8.89 [2H, br, ortho-H4-Acpy], 8.16 [4H, br,
ortho-HBz], 7.79 [2H, br, meta-H4-Acpy], 7.51 [2H, br, para-HBz], 7.40 [4H, br, meta-
HBz], 2.65 [3H, s, CH3] ppm. (UV−Vis: (MeOH, 6.5×10−8 M) λmax = 201 nm; 222 nm;
272 nm.
4.5 Synthesis of of the compound [Cd(µ-Bz)2(4-Acpy)2]2 (4)
23

A MeOH solution (10 mL) of HBz (91.3 mg, 0.748 mmol) with 4-Acpy (186
mg, 1.54 mmol) was added dropwise to a MeOH solution (6 mL) of Cd(OAc)2·2H2O
(101 mg, 0.377 mmol) and stirred for 18 h at r.t. Then, the solution was stirred under
reflux conditions for 13 h. The resulting yellowish solution was concentrated until half
of the volume and kept on fridge. After 15 h suitable yellow crystals were obtained.
Crystals were filtered and washed with 10 mL of cold MeOH.
Yield: 126 mg (57%). Anal. Calc. for C56H48N4O12Cd2 (1193.78 gmol-1): C,
56.34; H, 4.05; N, 4.69. Found: C, 56.07; H, 3.94; N, 4.48%. ATR-FTIR (wavenumber,
cm-1): 3073(w), 3043(w), 3000(w) [ν(CH)]ar, 2981(w) [ν(CH)]al, 1695(m) [ν(C=O)]4-
Acpy, 1595(m), 1548(m) [νas(COO)], 1533(m) [ν(C=C), ν(C=N)]ar, 1493(w), 1392(s)
[νs(COO)], 1362(s) [δ(C=C), δ(C=N)]ar, 1014(m) [δip(C–H)], 727(s), 715(s), 681(m)
1
[δoop(C–H)]. H-NMR: (400 MHz, CDCl3 solution, Me4Si, 298 K) δ: 8.90 [2H, br,
3
3
ortho-H4-Acpy], 7.97 [2H, d, J = 7.6 Hz, ortho-HBz], 7.69 [2H, d, J = 4.7 Hz meta-H4-
Acpy], 7.31 [1H, t, 3J=7.3 Hz, para-HBz], 7.16 [2H, t, 3J = 7.5 Hz, meta-HBz], 2.57 [3H, s,
CH3] ppm. (UV−Vis: (MeOH, 4.2×10−6 M) λmax = 202 nm; 222 nm; 277 nm.
4.6 X-ray crystallography
Colorless (1-3) and yellow (4) prism-like specimens were used for the X-ray
crystallographic analysis. The X-ray intensity data were measured on a D8 Venture
system equipped with a multilayer mono-chromate and a Mo microfocus (λ = 0.71073
Å). For 1-4, the frames were integrated with the Bruker SAINT Software package using
a narrow-frame algorithm. For 1, the integration of the data using a monoclinic unit cell
yielded a total of 35296 reflections to a maximum θ angle of 27.11° (0.78 Å resolution),
of which 5564 were independent (average redundancy 6.344, completeness = 99.8%,
Rint = 8.42%, Rsig = 5.00%) and 4248 (76.35%) were greater than 2σ(|F|2). The calculated
minimum and maximum transmission coefficients (based on crystal size) are 0.6464
24

and 0.7455. For 2, the integration of the data using an orthorhombic unit cell yielded a
total of 42047 reflections to a maximum θ angle of 38.60° (0.57 Å resolution), of which
8656 were independent (average redundancy 4.858, completeness = 99.7%, Rint
=
6.88%, Rsig = 6.10%) and 5632 (65.06%) were greater than 2σ(|F|2). The calculated
minimum and maximum transmission coefficients (based on crystal size) are 0.5894
and 0.7476. For 3, the integration of the data using a monoclinic unit cell yielded a total
of 187379 reflections to a maximum θ angle of 28.38° (0.75 Å resolution), of
which 13991 were independent (average redundancy 13.393, completeness = 99.0%,
Rint = 9.68%, Rsig = 4.30%) and 9146 (65.37%) were greater than 2σ(|F|2). The
calculated minimum and maximum transmission coefficients (based on crystal size)
are 0.5421 and 0.7457. For 4, the integration of the data using a tetragonal unit cell
yielded a total of 77802 reflections to a maximum θ angle of 30.06° (0.71 Å resolution),
of which 7209 were independent (average redundancy 10.792, completeness = 99.5%,
Rint = 4.63%, Rsig = 2.54%) and 6808 (94.44%) were greater than 2σ(|F|2). The
calculated minimum and maximum transmission coefficients (based on crystal size)
are 0.3241 and 0.7460.
The structures were solved and refined using the Bruker SHELXTL Software,
package and refined using SHELX (version-2018/3) [39]. For 1, the final anisotropic
full-matrix least-squares refinement on |F|2 with 343 variables converged at R1 = 4.16%,
for the observed data and wR2 = 8.52% for all data. For 2, the final anisotropic full-
matrix least-squares refinement on |F|2 with 219 variables converged at R1 = 4.82%, for
the observed data and wR2 = 10.63% for all data. For 3, the final anisotropic full-matrix
least-squares refinement on |F|2 with 762 variables converged at R1 = 4.92%, for the
observed data and wR2 = 14.78% for all data. For 4, the final anisotropic full-matrix
least-squares refinement on |F|2 with 337 variables converged at R1 = 2.66%, for the
25

observed data and wR2 = 5.86% for all data. For 1-4, the final cell constants and volume,
are based upon the refinement of the XYZ-centroids of reflections above 20 σ(I). Data
were corrected for absorption effects using the multi-scan method (SADABS). Crystal
data and relevant details of structure refinement for compounds 1-4, are reported in
Table 6.
Table 6. Crystallographic data for 1-4.
1
2
3
4
Empirical formula
Formula weight
T (K)
C28H20O8Zn2
615.18
100(2)
C14H16O7Cd
408.67
100(2)
C42H34N2O10Zn2
857.45
100(2)
C56H48N4O12Cd2
1193.78
100(2)
Wavelength (Å)
System, space group
0.71073
0.71073
0.71073
Monoclinic, C2/c Tetragonal,
P41212
0.71073
Monoclinic, P21/c Orthorhombic,
Pbca
Unit cell dimensions
a (Å)
b (Å)
c (Å)
α (°)
10.8064(4)
12.6391(4)
18.8322(8)
90
9.6838(6)
10.2466(6)
30.956(2)
90
17.307(3)
24.801(4)
27.504(5)
90
13.3285(5)
13.3285(5)
27.8077(11)
90
β (°)
γ (°)
V (Å3)
100.670(2)
90
2527.69(16)
90
90
3071.6(3)
107.284
90
11273(3)
90
90
4940.0(4)
Z
4
8
12
4
Dcalc (mg/m3)
μ (mm-1)
1.617
1.949
1248
1.767
1.453
1632
1.516
1.340
5280
1.605
0.931
2416
F(0 0 0)
Crystal size (mm)
0.109x0.104x0.0
62
0.161x0.145x0.1
06
0.248x0.220x0.1
92
0.208x0.112x0.0
78
hkl ranges
-13 ≤ h ≤ 13
-16 ≤ k ≤ 16
-24 ≤ l ≤ 24
2.505 to 27.109
-14 ≤ h ≤ 16
-17 ≤ k ≤ 17
-54 ≤ l ≤ 53
2.481 to 38.596
-23 ≤ h ≤ 22
-33 ≤ k ≤ 33
-36 ≤ l ≤ 36
2.259 to 28.384
-18 ≤ h ≤ 18
-18 ≤ k ≤ 18
-39 ≤ l ≤ 37
2.282 to 30.057
2θ range (°)
Reflections
35296/5564/
[Rint=0.0842]
42047/8656/
[Rint=0.0688]
187379/13991/
[Rint=0.0968]
77802/7209/
[Rint=0.0463]
collected/unique/[Rint]
Completeness to θ
Absorption correction
99.9%
99.9%
99.3%
99.4%
Semi-empirical
from equivalents
0.7455 and
Semi-empirical
from equivalents
0.7476 and
Semi-empirical
from equivalents
0.7457 and
Semi-empirical
from equivalents
0.7460 and
Max. and min.
transmission
0.6464
0.5894
0.5421
0.3241
Refinement method
Full-matrix least- Full-matrix least- Full-matrix least- Full-matrix least-
squares on |F|2
squares on |F|2
8656 / 6 / 219
squares on |F|2
squares on |F|2
7209 / 2 / 337
Data/restrains/paramet 5564 / 0 / 343
13991 / 19 / 762
ers
Goodness of fit on |F|2 1.057
1.084
1.073
1.114
Final R indices
[I > 2σ(I)]
R1 = 0.0416,
wR2 = 0.0779
R1 = 0.0482,
wR2 = 0.0826
R1 = 0.0492,
wR2 = 0.1100
R1 = 0.0266,
wR2 = 0.0539
R indices (all data)
R1 = 0.0670,
wR2 = 0.0852
R1 = 0.0954,
wR2 = 0.1063
R1 = 0.0919,
wR2 = 0.1478
R1 = 0.0322,
wR2 = 0.0586
26

Extinction coefficient
Largest diff. peak and
hole (e.Å-3)
n/a
0.00115(11)
2.525 and -1.783
n/a
0.0042(2)
0.591 and -0.861
0.731 and -0.642
0.994 and -1.477
Molecular graphics were generated using Mercury 4.1.2 software [40] with
POV-Ray package [41]. Color codes for all molecular graphics: Grey (C), white (H),
red (O), light blue (N), blue (Zn), yellow (Cd). Crystal structures and molecular
geometry are available in .cif format.
Conflicts of interest
There are no conflicts to declare.
Acknowledgements
This work was financed by CB615921 project, the Spanish National Plan of
Research MAT2015-65756R, and 2017SGR1687 project from the Generalitat de
Catalunya. The authors also acknowledge “Fundació La Caixa” for CB616406
endowment. F. S. acknowledges the PIF pre-doctoral fellowship from the Universitat
Autònoma de Barcelona.
Appendix A. Supplementary data
CCDC-1972796-1972799 contains the supplementary crystallographic data for 1-4.
These
data
can
be
obtained
free
or
of
from
charge
via
http://www.ccdc.cam.ac.uk/conts/retrieving.html,
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.
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