Dimeric metallacycles and coordination polymers: Zn(II), Cd(II) and Hg(II) complexes of two positional isomers of a flexible N,O-hybrid bispyrazole derived ligand

Article abstract of DOI:10.1016/j.ica.2020.119549

Reaction of MCl₂ (M = Zn(II), Cd(II) and Hg(II)) with two flexible N,O-hybrid arene-linked, bispyrazole derivative ligands (1,2-bis([4-(3,5-dimethyl-1H-pyrazol-1-yl)-2-oxabutyl]benzene (L1) and 1,4-bis([4-(3,5-dimethyl-1H-pyrazol-1-yl)-2-oxabut

Full text of DOI:10.1016/j.ica.2020.119549

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Research paper
Dimeric metallacycles and coordination polymers: Zn(II), Cd(II) and Hg(II)
complexes of two positional isomers of a flexible N,O-hybrid bispyrazole de-
rived ligand
Joan Soldevila-Sanmartín, Miguel Guerrero, Duane Choquesillo-Lazarte, José
Giner Planas, Josefina Pons
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S0020-1693(20)30072-4
https://doi.org/10.1016/j.ica.2020.119549
ICA 119549
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Inorganica Chimica Acta
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Please cite this article as: J. Soldevila-Sanmartín, M. Guerrero, D. Choquesillo-Lazarte, J. Giner Planas, J. Pons,
Dimeric metallacycles and coordination polymers: Zn(II), Cd(II) and Hg(II) complexes of two positional isomers
of a flexible N,O-hybrid bispyrazole derived ligand, Inorganica Chimica Acta (2020), doi: https://doi.org/10.1016/
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Dimeric metallacycles and coordination polymers: Zn(II),
Cd(II) and Hg(II) complexes of two positional isomers of a
flexible N,O-hybrid bispyrazole derived ligand.
Joan Soldevila-Sanmartína, Miguel Guerreroa, Duane Choquesillo-Lazarteb, José Giner
Planasc, Josefina Ponsa,*.
a
Departament de Química, Universitat Autònoma de Barcelona, 08913-Bellaterra,
Barcelona, Spain.
b
Laboratorio de Estudios Cristalógraficos, IACT (CSIC-Universidad de Granada),
Avda. de las Palmeras 4, Armilla, 18100 Granada, Spain.
c
Institut de Ciència de Materials de Barcelona (ICMAB-CSIC), Campus UAB, 08913-
Bellaterra, Barcelona, Spain.
* Corresponding Author
E-mail address: josefina.pons@uab.cat (J. Pons)
1

Abstract
Reaction of MCl2 (M = Zn(II), Cd(II) and Hg(II)) with two flexible N,O-hybrid
arene-linked, bispyrazole derivative ligands (1,2-bis([4-(3,5-dimethyl-1H-pyrazol-1-yl)-
2-oxabutyl]benzene (L1) and 1,4-bis([4-(3,5-dimethyl-1H-pyrazol-1-yl)-2-
oxabutyl]benzene (L2)) in EtOH yields six new compounds. All compounds have been
characterized by analytical and spectroscopic techniques. Their crystal structures have
been elucidated by single-crystal X-ray diffraction. Compounds containing L1 are
isostructural dimeric metallacycles of general formula [M(L1)Cl2]2 (M= Zn(II) (1), Cd(II)
(2) and Hg(II) (3)), L1 bearing a NN’-bridged coordination mode. Those containing L2,
are coordination polymers of general formula {[M(L2)Cl2]·1/2solvent}n (M = Zn(II),
solvent = H2O (4); M = Cd(II) (5) or Hg(II) (6), solvent = EtOH), L2 showing two
different coordination modes depending on the metal: NN’-bridged in 4 and NON’-
chelated and bridged in 5 and 6. Their molecular and extended structures are discussed,
with a special focus on the coordination modes and conformations of L1 and L2. Finally,
their photoluminescence properties have been analyzed.
Keywords: Coordination Polymers / d10 Metals / Metallacycles / N,O-ligands / Pyrazole
ligands
2

1. Introduction
Since the late eighties, the discovery of Metal-Organic Frameworks (MOFs) and
porous coordination polymers (PCPs) opened the gate for a whole new field of research
in coordination chemistry, and arguably one of the most researched topics of today. Since
these days, interest in this field has skyrocketed, leading to the systematization of the
principles of ligand design and molecular architecture [1-4]. In the first stages, the
research was focused on the synthesis of said materials using rigid organic ligands and
their properties in gas absorption and storage. The field evolved towards the search of
different applications [5], due to the infinite customization properties that the combination
of inorganic (nodes) and organic moieties (linkers) allow. Thus, ligand design became the
driving force of many coordination chemists’ research. As of today, no longer rigid
linkers are considered of interest, but also flexible ones which could lead to stimuli-
responsive materials [5-7].
In recent times, N-donor ligands appear as great candidates for the synthesis of
functional coordination polymers due to their greater resistance to hydrolysis. Among
them, azoles appear as better candidates over pyridines due to their stronger and
directional N-metal bond. Thus, ligand design of new linkers containing azoles is thriving
[8,9]. Among them, pyrazole derivative ligands are of great interest, as they can be easily
functionalized via modification of the parent pyrazole and possess interesting applications
in the fields of catalysis [10-12], sensing [13], medicine [14], magnetism [15], and optics
[16].
Conformational freedom of the ligand does also have a great impact on the final
topology of the coordination polymers. As demonstrated by a plethora of different works,
the presence of a flexible moiety, or weak spot, between the N-pyrazole coordinating sites
greatly increases the possibility of obtaining interesting networks, promotes different
types of self-assembly and even enhances the functionality of the new compounds. This
has spurred the synthesis of new polypyrazole ligands in the last decades [17-23]. Besides,
the inclusion of new functional groups bearing heteroatoms in di-, tri- or tetrapyrazole
ligands could also further increase the variability of coordination modes and promote
fascinating interactions such as hemilability or selective coordination [24-26].
Previously, our group has synthesized and studied the coordination behavior of
several N,X-hybrid bispyrazole ligands (X = N, O and S) containing functional groups
3

such as amines [27,28], thioethers [29,30], or sulfoxides/sulfones [31]. Furthermore,
several bispyrazole ligands bearing ether functional groups have been previously
synthesized [32] and their reactivity against different metal centers studied. For instance,
an extensive research on the reactivity of the N,O-hybrid bispyrazole, diether ligand 1,8-
bis(3,5-dimethyl-1H-pyrazol-1-yl)-3,6-dioxaoctane (bpdo) against different Zn(II),
Cd(II), Hg(II), Pd(II), Pt(II) and Ni(II) salts was conducted, showing that the use of
different metal centers resulted in coordination compounds with a wide diversity of
nuclearity, coordination geometries and modes [33,34]. Moreover, the reactivity of the
title compounds 1,2-bis([4-(3,5-dimethyl-1H-pyrazol-1-yl)-2-oxabutyl]benzene (L1) and
1,4-bis([4-(3,5-dimethyl-1H-pyrazol-1-yl)-2-oxabutyl]benzene (L2) against Pd(II) was
carried out (Scheme 1) [35]. In the resulting Pd(II) coordination compounds only syn
conformations were observed, despite the fact that bispyrazolyl ligands can adopt syn or
anti conformations. In the light of these results, new metal centers which allow different
coordination geometries such as Zn(II), Cd(II) and Hg(II) were chosen to study their
reactivity against L1 and L2.
Scheme 1. a. Schematic representation of the synthesis of L1 and L2. b. Previously Synthesized
compounds containing L1 and L2.
In this contribution, we present the synthesis, characterization and X-ray crystal
structures of six new compounds: three of general formula [M(L1)Cl2]2 (M= Zn(II) (1),
Cd(II) (2) and Hg(II) (3)), and three of general formula {[M(L2)Cl2]·1/2solvent}n (M =
Zn(II), solvent = H2O (4); M = Cd(II) (5) or Hg(II) (6), solvent = EtOH). The molecular
4

and supramolecular structures of these compounds are discussed, with a special focus on
the different coordination modes and conformations of L1 and L2. Finally, their behavior
in solution has been studied via NMR and photoluminescence measurements.
2. Results and Discussion
2.1 Synthesis and characterization of the complexes
The reaction of L1 and L2 with MCl2 (M = Zn(II), Cd(II) and Hg(II)) in absolute
ethanol (EtOH) in a 1M/1L ratio yields compounds 1-6. Phase purity of the samples has
been confirmed by powder X-ray diffraction (PXRD) (S.I.: Figures S1-S6). All
1
compounds have been characterized by elemental analysis (EA), FTIR-ATR, H,
13C{1H}, HSQC, DOSY NMR and UV-Vis spectroscopies. This data is provided in the
experimental section and in the Supporting Information (S.I.). Finally, their
photoluminescence properties are studied.
For compounds 1-6 it has been possible to obtain crystals suitable for single-
crystal X-ray diffraction. In them, L1 and L2 show extremely different coordination
behavior. Compounds 1-3 are dimers with general formula [M(L1)Cl2]2 (M= Zn(II) (1),
Cd(II) (2) and Hg(II) (3)). These compounds are isostructural, showing a M2L2
metallacyclic ring motif of thirty-four members. Compounds 4-6 are polymers with
general formula {[M(L2)Cl2]·1/2solvent}n (M = Zn(II), solvent = H2O (4); M = Cd(II)
(5) or Hg(II) (6), solvent = EtOH). Despite compounds 4-6 sharing a similar chemical
composition, the metal center in 4 is tetracoordinate, whereas in isostructural compounds
5 and 6 is pentacoordinate due the coordination of an oxygen atom from L2. Furthermore,
in 4 the presence of occluded H2O molecules can be seen, while in 5 and 6 the occluded
solvent is EtOH (Scheme 2). For all of them, elemental analyses (EA) agree with the
elucidated crystal structures.
5

Scheme 2. Synthetic reactions carried out in this work. Compounds are shown with their
numbering scheme. Compounds 4-6 occluded solvents have been removed for clarity.
The FTIR-ATR spectra of the six compounds in the range of 4000-500 cm-1
confirms the coordination of the organic ligand to the metal center. The most
characteristic bands of the IR spectra are those attributable to the [ν(C=C)ar/ν(C=N)ar]
(1554-1547 cm-1) and [δ(C=C)ar/δ(C=N)ar] (1424-1420 cm-1) of the pyrazolyl group [36].
Other characteristic bands are attributable to the [ν(C-O-C)] (1105-1099 cm-1) of the ether
groups [36]. Moreover, for compounds 4-6, the presence of solvent molecules allows
further identification of some bands. Compound 4 shows a broad band between 3600-
3200 cm-1 attributable to [ν(O-H)] of H2O molecules. For compounds 5 and 6, bands at
3496 cm-1 and 3515 cm-1 are attributed to [ν(O-H)] of EtOH molecules (S.I.: Figures S7-
S12 and experimental section).
2.2 Crystal and Extended Structures of compounds 1-3.
For isostructural compounds 1-3, two L1 molecules act as a NN’-bridged ligand
in a syn configuration, coordinating to two metal centers forming a closed-loop. Hence, a
M2L2 type metallacyclic motif of thirty-four members is obtained (Figure 1 and S.I:
Figure 13).
6

Figure 1. Compound 1 showing all its non-hydrogen atoms and their corresponding numbering
scheme.
The metal centers have the same distorted tetrahedral (τ4 = 0.88 to 0.92 [37])
[M(NPz)2Cl2] core (M = Zn(II) (1), Cd(II) (2) Hg(II) (3)), with angles ranging from
98.52(15)° to 122.45(6)°. A search in the CCDC database [38] reveals that this core is
present in up to sixty-one reported crystal structures containing Zn(II), four containing
Hg(II) and none containing Cd(II). Of them, only one is a Zn(II) metallacycle [20].
Similar macrocyclic architectures are reported with monopyrazolyl [39] and
tetrapyrazolyl derivative ligands [40,41]. Remarkably, coordination compounds of the
bis(dipyrazolyl) analogue of L1 containing Ag(I) are mononuclear metallacycles [42], in
stark contrast to the dimeric metallacycles reported in this work. Selected bond lengths
and bond angles are reported on Table 1. All these values agree with similar compounds
reported in the literature [20,33,34,43].
7

Table 1. Selected bond lengths and angles for compounds 1-3
1
2
3
Bond lengths (Å)
Zn(1)-Cl(1)
Zn(1)-Cl(2)
Zn(1)-N(1)
Zn(1)-N(28)#1
Zn(1)···Zn(1)#1
2.2485(7)
2.2563(7)
2.062(2)
2.035(2)
9.3697(6)
Cd(1)-Cl(1)
Cd(1)-Cl(2)
Cd(1)-N(1)
Cd(1)-N(3)#1
Cd(1)···Cd(1)#1
2.4277(12)
2.4236(12)
2.258(4)
2.234(4)
9.5206(7)
Hg(1)-Cl(1)
Hg(1)-Cl(2)
Hg(1)-N(1)
Hg(1)-N(3)#1
Hg(1)···Hg(1)#1
2.4216(16)
2.4403(16)
2.270(6)
2.331(6)
9.6636(5)
Bond angles (°)
Cl(1)-Zn(1)-Cl(2)
N(28)#1-Zn(1)-Cl(1) 115.23(7)
N(28)#1-Zn(1)-Cl(2) 104.59(6)
N(1)-Zn(1)-Cl(2)
N(1)-Zn(1)-Cl(1)
N(1)-Zn(1)-N(28)#1 109.23(8)
113.09(2)
Cl(1)-Cd(1)-Cl(2)
N(1)-Cd(1)-Cl(1)
N(1)-Cd(1)-Cl(2)
N(1)-Cd(1)-N(3)#1
N(3)#1-Cd(1)-Cl(1)
N(3)#1-Cd(1)-Cl(2)
116.75(4)
Cl(1)-Hg(1)-Cl(2)
N(1)-Hg(1)-Cl(1)
N(1)-Hg(1)-Cl(2)
N(1)-Hg(1)-N(3)#1
N(3)#1-Hg(1)-Cl(1)
N(3)#1-Hg(1)-Cl(2)
122.45(6)
114.16(16)
102.93(15)
107.8(2)
98.52 (15)
110.47(15)
112.48(11)
100.31(11)
109.88(15)
104.50(10)
113.04(12)
114.57(6)
100.45(6)
#1: -x+1, -y+1, -z+1
The metallacyclic ring can be defined by its intramolecular M···M distance, the
distance between two methyl groups and the distance between the centroids of pyrazolyl
rings (S.I.: Figure S14). Compounds 1-3 show intramolecular C-H···π interactions
between the methyl groups and the phenyl rings (Table 2). The angle between the mean
planes of L1 pyrazolyl rings in the same ligand is 89.13° (1), 87.78° (2) and 87.11° (3),
whereas phenyl rings are parallel to each other in all three compounds. This metallacycle
highly reminds of the previously reported [Pd(L2)Cl2]2 compound [35]. However, in this
compound the ring is not folded, which allows for the above-mentioned compound to be
nanoporous.
As isostructural compounds, the extended structures of 1-3 are alike. They could
be described as a close-packing of M2L2 rings, where each ring is connected to six other
rings via hydrogen interactions, forming a three-dimensional lattice. This supramolecular
arrangement is held together by interactions between pyrazolyl moieties and both phenyl
rings and ether chains. Furthermore, interactions involving chlorine atoms and pyrazolyl
moieties are also key in sustaining the supramolecular network (Figure 2 and S.I.: Figure
S15). Relevant interactions for all compounds are summarized on Table 2.
8

Table 2. Selected intra- and intermolecular interactions for compounds 1-3
D-H···A (Å)
D-H (Å)
H-D···A (Å)
>D-H···A (°)
130.21
1
Intramolecular
C27-H27C···Cg1
Intermolecular
C17-H17···N22
C18-H18A···Cg2
C20-H20B···Cg2
C5-H5···Cl2
3.180
0.980
3.885
2.691
2.868
3.532
2.961
3.048
0.950
0.990
0.990
0.950
0.980
3.519
3.839
4.297
3.861
4.011
145.91
167.08
135.71
158.72
167.61
C27-H27B···Cl2
2
Intramolecular
C22-H22A···Cg3
Intermolecular
C3-H3···Cl1
C5-H5A···Cg3
C14-H14···N4
C15-H15B···Cg4
C16-H16A···Cg4
C22-H22B···Cl2
3
3.354
0.979
4.039
128.71
2.809
2.797
2.717
2.865
3.430
2.849
0.950
0.979
0.949
0.991
0.990
0.980
3.716
3.662
3.549
3.824
4.205
3.823
159.91
147.56
146.72
163.28
136.64
172.48
Intramolecular
C5-H5B···Cg5
Intermolecular
C5-H5A···Cl1
C20-H20···Cl2
C8-H8A···Cg6
C7-H7B···Cg6
3.338
0.979
4.004
126.92
2.841
2.789
2.883
3.487
0.980
0.951
0.991
0.990
3.818
3.692
3.843
4.251
179.63
159.11
163.54
135.64
Cg1 = C12-C13-C14-C15-C16-C17; Cg2 = N1-N2-C3-C5-C6; Cg3 = C9-C10-C11-C12-C13-C14;
Cg4 = N1-N2-C1-C3-C4; Cg5 = C9-C10-C11-C12-C13-C14; Cg6 = N3-N4-C18-C20-C21
Figure 2. Detail of the non-bonding interactions in 1, showing only hydrogen atoms involved in
the interactions. View along c axis.
9

Intermolecular interactions of compounds 1-3 have been also studied by Hirshfeld
surface analysis, using CrystalExplorer 2.1 software [44-46]. Surfaces have been
calculated using an isovalue of 0.5 e au-3. The normalized contact distance (dnorm) surface
mapping shows red spots where relevant intramolecular interactions occur. For 1, in the
dnorm surface mapping red spots can be seen over hydrogen atoms of the ether chains and
phenyl rings, as well as over both pyrazolyl moieties, confirming their role in its
supramolecular structure (Figure 3a). However, the biggest red spots in 2 and 3 (and thus
the strongest intermolecular interactions) correspond to the ones involving chlorine
atoms. Interactions involving phenyl, methyl and pyrazolyl moieties are also identified
(Figure 3b and 3c). Additional mapping surfaces have also been calculated (S.I.: Figure
S16).
Figure 3. Hirshfeld surface mapped with dnorm of a. 1, b. 2, c. 3. Surface transparency has been
enabled and relevant atoms labelled.
The fingertip plots of compounds 1-3 (S.I.: Figures S17-19) show an overall
rounded shape, lacking defined spikes, which suggest weak directional intramolecular
interactions. Their decomposition show that the majority of the Hirshfeld surface (55.5-
58.6%) is dominated by H···H interactions, which can be attributed to dispersive London
10

forces [47]. Concerning C-H···C contacts (11.0-11.6%), they appear as “wings” instead
of spikes, showing its C-H···π character [48] while C-H···N contacts (3.6-3.9%) appear
as more defined spikes. Lastly, it is remarkable the high percentage of interactions
involving C-H···Cl contacts (22.7-24.5%). These last ones appear as sharp peaks, thus
being the strongest directional supramolecular interactions.
2.3 Crystal and Extended Structure of 4.
Compound 4 has a [Zn(NPz)2Cl2] core, comprising two chlorine atoms and two
different pyrazolyl nitrogen atoms provided by L2 (Figure 4a). The coordination structure
of the Zn(II) is a slightly distorted tetrahedron (τ4 = 0.90 [37]), with angles ranging from
102.99(13)° to 117.18(9)°. As stated before, this Zn(II) core is reported in sixty-one
crystal structures [38], only eight of them having a polymeric structure (13%). However,
coordination compounds containing the bis(dipyrazolyl) analogue of L2 and Ag(I) are
also known to have polymeric structures [49]. Selected bond lengths and angles are shown
on Table 3. All values agree with similar compounds reported in the literature
[33,34,50,51].
Figure 4. a. Compound 4, showing all its non-hydrogen atoms and their corresponding numbering
scheme. b. Representation of the infinite 1D polymeric chain, showing relevant intra-chain
distances.
11

Table 3. Selected bond lengths and angles for compounds 4-6
4
5
6
Bond lengths (Å)
Zn(1)-Cl(1)
Zn(1)-Cl(2)
Zn(1)-N(1)
Zn(1)-N(3)#1
Zn(1)···Zn(1)#1
2.2313(11)
2.2623(11)
2.036(3)
2.050(3)
12.461(2)
Cd(1)-Cl(1)
Cd(1)-Cl(2)
Cd(1)-N(1)
Cd(1)-N(3)#1
Cd(1)-O(1)
Cd(1)···Cd(1)#1
2.4286(11)
2.4312(9)
2.248(3)
2.361(3)
2.743(3)
9.4935(4)
Hg(1)-Cl(1)
Hg(1)-Cl(2)
Hg(1)-N(1)
Hg(1)-N(3)#1
Hg(1)-O(1)
2.399(2)
2.391(2)
2.313(5)
2.498(5)
2.987(4)
9.610(1)
Hg(1)···Hg(1)#1
Bond angles (°)
Cl(1)-Zn(1)-Cl(2)
N(3)#1-Zn(1)-Cl(2)
N(3)#1-Zn(1)-Cl(1)
N(1)-Zn(1)-Cl(2)
N(1)-Zn(1)-Cl(1)
N(1)-Zn(1)-N(3)#1
108.41(4)
105.89(9)
116.28(9)
117.18(9)
106.45(10)
102.99(13)
Cl(1)-Cd(1)-Cl(2)
N(1)-Cd(1)-Cl(1)
N(1)-Cd(1)-Cl(2)
N(1)-Cd(1)-N(3)#1
N(3)#1-Cd(1)-Cl(1)
N(3)#1-Cd(1)-Cl(2)
Cl(1)-Cd(1)-O(1)
Cl(2)-Cd(1)-O(1)
N(1)-Cd(1)-O(1)
N(3)#1-Cd(1)-O(1)
120.81(4)
117.00(9)
113.67(9)
96.51(11)
95.02(9)
107.74(8)
84.63(7)
85.29(7)
70.3(1)
Cl(1)-Hg(1)-Cl(2)
N(1)-Hg(1)-Cl(1)
N(1)-Hg(1)-Cl(2)
N(1)-Hg(1)-N(3)#1
N(3)#1-Hg(1)-Cl(1)
N(3)#1-Hg(1)-Cl(2)
Cl(1)-Hg(1)-O(1)
Cl(2)-Hg(1)-O(1)
N(1)-Hg(1)-O(1)
N(3)#1-Hg(1)-O(1)
131.16(9)
109.22(15)
112.12(16)
96.75(18)
107.25(14)
92.68(15)
84.35(9)
89.2(1)
66.4(2)
162.3(1)
164.71(1)
#1: x, y+1, z+1/2
#1 -x+1/2, y-1/2, -z+3/2
In this polymer, adjacent Zn(II) atoms are connected by L2 via a NN’-bridged
mode in an anti conformation, resulting in an infinite helical-chain along the c axis. The
distance between repeating units is 23.742(9) Å, and between adjacent Zn(II) atoms is
12.461(2) Å (Figure 4b). This M···M distance is larger than the ones found in related
compounds [Zn(bpdo)Cl2]n (bpdo
=
1,8-bis(3,5-dimethyl-1H-pyrazol-1-yl)-3,6-
dioxaoctane, 9.523 Å [33]) and [Zn(bpmx)Cl2]n (bpmx = α,α-bis(pyrazolyl)-m-xylene,
7.976 Å [52]). The dihedral angle between the mean planes of the pyrazolyl rings in the
centrosymmetric L2 ligands is 68.82°, which shows its twisting around the benzene rings.
The extended structure of compound 4 could be described as a dense three-
dimensional thread of parallel chains. In this thread, the occluded H2O molecules play a
key role, as they bind one left-handed and one right-handed helical-chain thanks to a
double symmetrical O3-H3A···Cl2 interaction, forming a supramolecular chain parallel
to the c axis. These double helical-chains are stacked together thanks to another set of
distinct interactions. They involve the hydrogen of the pyrazolyl ring and chlorine
moieties (C20-H20···Cl2) and the methyl and chlorine moieties (C2-H2B···Cl1). Lastly,
a C-H···C interaction between the methyl groups and the phenyl rings also reinforces the
3D structure (C5-H5B···C12) (Figure 5). Relevant H-bond interactions are summarized
on Table 4.
12

Figure 5. Detail of the H-bond interactions in 4, showing only hydrogen atoms involved in the
interactions. View along b axis.
Table 4. Selected intermolecular interactions for 4
D-H···A (Å) D-H (Å) H-D···A (Å) >D-H···A (°)
4
O3-H3A···Cl2
C5-H5B···C12
C2-H2B···Cl1
C20-H20···Cl2
2.587
2.755
2.847
2.849
0.983
0.980
0.980
0.950
3.531
3.727
3.794
3.755
161.08
171.85
162.76
159.77
The H2O molecules occupy cavities defined by these sets of double helical-chains.
These non-connected cavities have a volume of 91.22 Å3 (1.9 % of unit cell), calculated
defining a prove radius of 1.2 Å (Figure 6).
13

Figure 6. Voids (91.22Å3) representation in 4.
2.4 Crystal and Extended Structure of 5 and 6.
Isostructural compounds 5 and 6 have a [M(NPz)2OCl2] core (M = Cd(II) (5),
Hg(II) (6)) which results from the coordination of one ether group to the metal center
(Figure 7 and S.I. Figure S20). Their coordination structure is a distorted trigonal
bipyramid (τ = 0.73 (5), 0.52 (6) [53]). In them, the basal plane comprises two chlorine
atoms and the nitrogen of the pyrazolyl closest to the coordinating oxygen, forming a six-
membered ring. The apical positions are occupied by an oxygen atom and the nitrogen of
the other pyrazolyl group. Remarkably, crystal structures with a [M(NPz)2OCl2] core (M
= Cd(II), Hg(II)) have been not reported [38]. Other reported structures including similar
bispyrazolyl ligands show that Cd(II) tends to form either dimers or polymers through
double chlorine bridges [54-56]. Regarding Hg(II), reported crystal structures containing
bispyrazolyl ligands show great morphological variability, as monomers [57,58], dimers
[58],tetramers [43], polymers [59] or even more complicated architectures [60] have been
reported. Selected bond lengths and bond angles are shown on Table 3. All values are in
agreement with other reported Cd(II) [32,33,54-56] and Hg(II) compounds [57,58].
14

Figure 7. Polymer 5 showing all its non-hydrogen atoms and their corresponding numbering
scheme.
In compounds 5 and 6, L2 acts as a NON’-chelated and bridged ligand in an anti
configuration, resulting in an infinite helical-chain along the b axis. The distance between
repeating units is 12.999(6) (5)/13.094(9) (6) Å, and between adjacent metal centers is
9.4935(4) (5)/9.610(1) (6) Å. These distances are shorter than in 4 (23.742(9) Å and
12.461(2) Å, respectively) due to the coordination of one ether group of L2 (Figure 8).
Pyrazole rings of different ligands coordinate to the same metal center are almost
perpendicular in this conformation, being 83.49° (5)/83.76° (6) the dihedral angles
between their mean planes. Phenyl rings of two consecutive bridging ligands are also
perpendicular, as the dihedral angle between their mean planes is 84.78° (5)/84.15° (6).
A similar coordination behavior has been observed for the related monomer
[Cd(bpdo)Cl2] [33], as both oxygen atoms of the two ether groups are bonded to the metal
center, resulting in a NOON’-chelated coordination mode. Probably, the steric hindrance
of the phenyl group in L2 prevents both the coordination of the second ether group and
the chelation of the ligand, resulting in the formation of a polymer.
15

Figure 8. Representation of the infinite 1D polymeric chain for 5, showing relevant intra-chain
distances.
For both compounds, each chain is surrounded by six other parallel chains,
resulting in a dense thread of alternating left-handed and right-handed polymeric chains
(Figure 9 and S.I.: Figure S21). As in 4, the main supramolecular interactions are related
to the disordered solvent, which occupies non-connected cavities for a total volume of
227.28 / 229.75 Å3 (8.6%/8.5% of unit cell for 5/6), calculated defining a prove radius of
1.2 Å (S.I.: Figure S22). This volume is notably bigger than in 4 (91.22 Å3, 1.9% of the
unit cell), as the occluded solvent is H2O in 4, whereas in 5 and 6 the solvent is EtOH.
Because of the disorder present in this occluded solvent, its structural role cannot be
determined precisely. Secondary C-H···Cl and C-H···π interactions involving methyl,
chlorine and phenyl moieties also appear in the supramolecular structure.
16

Figure 9. Supramolecular structure of 5 and 6. View along b axis. Occluded solvent molecules
have been removed for clarity.
2.5 Conformations and bonding modes of L1 and L2 in the complexes
In a previous work by our group, complexes obtained with L2 and Pd(II) were
either monomeric or dimeric [35], having a syn conformation. In this work, L2 adopts a
different anti conformation in all compounds (4-6), leading to the formation of polymeric
helical-chains. On the other hand, L1 proves much less flexible adopting syn
conformations in all the reported compounds (1-3).
In Table 5 the behavior of L1 and L2 is summarized according to θ (angular tilt
between the coordinating N and the centroid of the phenyl ring),
(dihedral angle
흓
between pyrazolyl rings of the same ligand), d (M···M distance), conformation and
coordination mode (Figure 10).
For 1-3, θ,
and d have similar values, as L1 has the same NN’-bridged
흓
coordination mode and syn conformation. In the case of 4-6, the different coordination
modes are reflected in several parameters. First, NN’-bridged and NN’-chelated
coordination modes result in different θ values, which are sensibly lower for NN’-chelated
[Pd(L2)Cl2] [35] (31.16°) than for NN’-bridged compounds 4 and [Pd(L2)Cl2]2 [35]
17

(105.10° and 110.66°). Second, the NON’-chelated and bridged coordination mode in 5
and 6 results in θ values between NN’-bridged and NN’-chelated (82.50° and 82.94°).
Last, in NN’-bridged compounds 4 and [Pd(L2)Cl2]2 [35] the d values are higher
(12.461(2) Å and 11.499(8) Å) than in the NON’-chelated and bridged compounds 5 and
6 (9.4935(6) Å and 9.610(1) Å).
Figure 10. Illustration of the geometrical θ,
and d parameters for compound 4 (complete
흓
structure not shown).
The syn or anti disposition governs the formation of polymers or
monomers/dimers for these flexible bispyrazolyl ligands. In the case of syn
conformations, M2L2 metallacycles and monomers are obtained, whereas for anti
conformations, polymers are obtained. For L2, the compounds with syn conformations
[Pd(L2)Cl ] [35] and [Pd(L2)Cl ] [35] show low values (10.53° and 10.58°) when
흓
2
2 2
compared to values for anti conformation in compounds 4-6 (68.82°-83.49°). On the
흓
contrary, for L1, values in 1-3 (87.11°-89.13°), are comparable to those in 4-6, but a
흓
syn conformation is observed.
When 1-6 compounds are compared, syn or anti conformation is reflected in θ
parameter: higher values (82.50°-105.10°) result in anti (4-6) while syn (1-3) is obtained
with lower values (76.58°-77.03°). According to this data, the turning point is at θ ≈ 80°.
Nevertheless, the use of Pd(II) as metal center severely disrupts this pattern. This can be
18

attributable to spatial constraints induced to L2 by Pd(II) square planar coordination
structure. Further details about the selected distances and angles are provided on Table 5.
Table 5. Coordination modes of L1 and L2
흓
Compounds
1 (work)
θ (°)
76.58
76.67
77.03
105.10
82.50
82.94
31.16
110.66
d (Å)
Conformation
Coordination Mode
(°)
89.13
87.78
87.11
68.82
83.48
83.49
10.63
10.58
9.3697(6)
9.5206(7)
9.6636(5)
12.461(2)
9.4935(4)
9.610(1)
-
2 (work)
syn
NN’-bridged
3 (work)
4 (work)
anti
5 (work)
Distorted anti
NON’-chelated and bridged
6 (work)
[Pd(L2)Cl2] [35]
[Pd(L2)Cl2]2 [35]
syn
syn
NN’-chelated
NN’-bridged
11.499(8)
θ: Angle between coordinating nitrogen atoms and the phenyl rings’ centroid.
흓
: Dihedral angles between pyrazolyl planes.
d: Metal····Metal distance.
2.6 NMR Studies
NMR spectra of compounds 1-6 were recorded in CDCl3 at r.t. The NMR signals
were assigned by 1H, 13C{1H} and HSQC NMR experiments (S.I.: Figures S23-S41). For
all of them, 1H NMR spectra show the coordination of the ligands to the metal center as
an upfield displacement on the 1-H-pyrazolyl proton signal (5.79-5.97 ppm (1-6) vs. 5.77
(L1) and 5.76 (L2) ppm). In the 1H NMR spectra the phenyl protons appear mostly as a
singlet (7.15-7.25 ppm) for 1-3, whereas for 4-6 where they appear as a multiplet (7.24-
7.26 ppm). The protons of the -OCH2Ph- fragment appear as singlets (4.40-4.53 ppm) and
the protons of the -OCH2CH2Pz- appear as triplets (4.17-4.67 ppm and 3.71-3.84 ppm)
with J = 5.2-5.7 Hz. For Zn(II) complexes (1 and 4) these protons appear as broad bands.
Regarding the 13C{1H} NMR spectra, there is an upfield displacement in the 1-H-
pyrazolyl carbon signal (106.1-107.0 ppm in 1-3, 105.6-107.0 ppm in 4-6) respect to the
free ligand (104.9 ppm in free L1 and 105.1 ppm in free L2) due to coordination of the
metal center. The carbon signals of the -OCH2Ph- fragments also show an upfield
displacement in 1-3 (73.1-73.8 ppm) respect to free L1 (70.7 ppm). However, in
compounds 4-6, the same carbon signals show a downfield displacement (69.9-71.8 ppm)
19

respect to non-coordinated L2 ligand (73.2 ppm). Further NMR details are provided in
the experimental section.
We further investigated whether compounds 4-6 remained as polymers in solution
or revert to different species by DOSY-NMR spectroscopy [61], which is a powerful tool
for studying the behaviour of coordination compounds in solution [62,63]. DOSY-NMR
spectra of 4-6 (Figure 11 and S.I.: Figures S42 and S43) were carried out in CDCl3 at 298
K. DOSY-NMR of 1 was also carried out for comparation purposes (S.I.: Figure S44).
The spectra of 1 shows a single diffusion peak at D = 6.83·10-10 m2s-1. For both polymers
4 and 6, also single diffusion peaks appear at D = 16.3·10-10 m2s-1 (4) and D = 8.95·10-10
m2s-1 (6). These higher diffusion coefficient values mean that the hydrodynamic radius of
4 and 6 in solution are smaller than 1. If compound 1 maintains a dimeric structure in
solution, those smaller species in 4 and 6 could be attributed to monomers. For 5, a more
sophisticated spectrum is obtained. Although there is severe line broadening, two main
peaks are identified at D = 14.1·10-10 m2s-1 and D = 6.59·10-10 m2s-1 suggesting a dynamic
equilibrium between monomeric and dimeric species. However, integration of the
diffusion peaks show that the equilibrium is heavily tilted towards the monomeric species,
as it is fifty-two times more abundant than the dimeric one.
20

Figure 11. DOSY NMR spectrum of 5 (400 MHz, CDCl3). Note the minor diffusion peak at D
= 6.59·10-10 m2s-1, highlighted with a black arrow.
We attempted to estimate the molecular weight (MW) of the species in solution
using the model proposed by Evans et al. in Equation (1) [64]. In this equation, MW and
MW stand for the solute and solvent MW respectively, for the viscosity parameter, K
ƞ
S
B
for the Boltzmann constant and NA for the Avogadro number. The parameter α is defined
as the cubic root of the molecular weight of the solvent divided by the molecular weight
of the solute. Lastly, ρeff is an empirical parameter whose value has been optimized for
CDCl3 at 647 Kg m-3 [64]. Further optimization is required for calculations in CDCl3,
establishing an effective MWS value of 83 g mol-1 [64]. Deviations from the ideal
behavior are expected when heavy atoms are present [64,65].
ퟑ휶
ퟐ
ퟏ
푲푩푻
+
(
)
ퟏ + 휶
푴푾풔
푴푾
ퟑ
푫 =
,
풘풉풆풓풆 휶 =
(1)
ퟑ푴푾
ퟒ흅흆풆풇풇푵푨
ퟔ흅ƞퟑ
For compound 1 an estimated MW of 917 g mol-1 is obtained (1037.54 g mol-1),
which suggests the conservation of its dimeric structure in solution. For 5, the diffusion
peak at D = 6.59·10-10 m2s-1 results in an estimated MW of 995 g mol-1 (1177.7 g mol-1
21

for dimeric 5), suggesting a dimeric species, whereas for 6 its only diffusion peak results
in an estimated MW of 510 g mol-1, suggesting a monomeric species (677.02 g·mol-1 for
monomeric 6). This model, however, severely underestimated the MW of lighter,
monomeric species of 4 and 5. In any case, this data supports the reversion of polymeric
compounds 4-6 to monomeric and dimeric species in solution.
2.7 Photoluminescence Properties
The fluorescence emission spectra were carried out with an excitation wavelength
of 260 nm and recorded between 270-600 nm. The L1 and L2 and coordination
compounds 1-6 show emission bands in the range of 282-286 nm (Figure 12). Regarding
compounds 1-3, hyperchromicity is detected for 3, while in 1 and 2, the intensity value is
lower than for free L1. None of them does show a bathochromic shift. For compounds 4-
6, however, both bathochromic (ʎmax: 286 nm for 4-6, 282 nm for free L2) and
hyperchromic shifts are detected in all cases (S.I.: Figures S45 and S46). There is a similar
enhancement of the fluorescence intensity for 4 and 5, whereas for 6 this enhancement is
stronger. In both families, Hg(II) compounds (3 and 6) show the strongest fluorescence
enhancement effect, especially in compound 6.
Figure 12. a. Fluorescence spectra of L1 (4.87·10-4 M) and 1-3 (1.26·10-4-1.38·10-4 M) recorded
in a CH3CN solution at r.t. b. Fluorescence spectra of L2 (5.02·10-4 M) and 4-6 (1.21·10-4-1.32·10-
4 M) recorded in a CH3CN solution at r.t.
3. Conclusions
The reactions of L1 and L2 with Zn(II), Cd(II) and Hg(II) salts afforded six new
coordination compounds. Compounds 1-3 are isostructural metallacyclic dimers where
L1 shows NN’-bridged coordination mode with a syn conformation. Compounds 4-6 are
22

coordination polymers where L2 shows two different coordination modes depending on
the metal: NN’-bridged in compound 4 or NON’-chelated and bridged in isostructural 5
and 6 compounds. In all of them L2 displays an anti conformation. The coordination of
one ether group causes the NON’-chelated and bridged coordination mode. Thus, para-
substitution (L1) results in a domination of the metallacyclic motif, while ortho-
substitution (L2) results in a domination of the linear polymeric motif.
The present results show that these family of bispyrazole ligands are highly
flexible and provide new Zn(II) (1 and 4), Cd(II) (2 and 5) and Hg(II) (3 and 6) complexes
with a variety of coordination modes (NON’-chelate and bridged) and conformations
(anti).
The behavior of compounds 1-6 in solution was studied via NMR and
photoluminescence measurements. Moreover, DOSY NMR spectra of compounds 1 and
4-6 were also recorded, showing the presence of monomeric species for 4 and 6,
monomeric and dimeric (52:1 ratio) for 5 and dimeric for 1. Finally, regarding the
photoluminescent properties, all polymeric compounds (4-6) display
a
photoluminescence enhancement respect to free L2. However, for dimeric metallacycles
(1-3) only compound 3 displays a photoluminescence enhancement respect to free L1.
Furthermore, Hg(II) compounds (3 and 6) show the highest fluorescence enhancement.
These results could be promoted by the lengthening of the conjugation and enhancement
of the rigidity of the coordinated ligand in these complexes [66,67].
The aim of this work was to test the versatility of these bispyrazole ligands. In
previous results, L1 and L2 ligands showed only one coordination mode in their Pd(II)
compounds [32]. Therefore, in order to gain further insight on the influence of substituent
position in this system, compounds bearing coordinative flexible metal cations were
synthesized. This has been evinced as the resulting topological motifs (metallacyclic or
polymeric) depend on the substituent position. Moreover, the flexibility of these ligands
has been demonstrated as they show new coordination modes and conformations. The
knowledge gained on the coordination behaviour of these bispyrazole ligands could be
exported to the design and fine-tuning of coordination compounds with new architectures.
23

4. Experimental Section
4.1 Materials and General Details
Metal(II) chloride (Metal = zinc(II), cadmium(II) and mercury(II)), absolute
ethanol (EtOH) and diethyl ether (Et2O) were purchased from Sigma-Aldrich and used
without further purification. Spectroscopic grade acetonitrile (CH3CN) was purchased
from ROMIL-SpS and used without further purification. Deuterated chloroform (CDCl3)
was purchased from Eurisotop and used without further purification. All reactions and
manipulations were carried out in air. Powder X-ray patterns (PXRD) were measured
with a Siemens D5000 apparatus (with 40 kW and 45 mA using Cu kα radiation with ʎ =
1.5406 Å). Patterns were recorded from 2θ = 5° to 40° with a step scan of 0.02° counting
for 1s at each step. 1H NMR, 13C{1H} NMR, HSQC and DOSY spectra were recorded on
an NMR-FT Bruker 400 MHz NMR spectrometer in CDCl3 solutions at 298 K. All
chemical shifts (δ) are given in ppm relative to TMS as internal standard. FTIR-ATR
spectra were recorded on a high-resolution spectrometer FT-IR Perkin Elmer Spectrum
One equipped with a universal attenuated total reflectance (ATR) accessory with a
diamond window in the range 4000-500 cm-1. The electronic spectra were run on a Varian
Cary 500 spectrophotometer, using spectroscopic grade CH3CN, in a normal quartz cell
having a path length of 10 mm in the range of 200-800 nm, with concentrations between
1.05·10-4-1.34·10-4 M at room temperature (r.t.). The fluorescence emission and
excitation spectra were recorded in a Varian Cary Eclipse Fluorescence Spectrometer at
r.t., equipped with a quartz cell having a path length of 10 mm. The samples were excited
at 260 nm and the emission was recorded in the range of 270-600 nm in spectroscopic
grade CH3CN (4.87·10-4 M for L1, 5.02·10-4 M for L2 and 1.21·10-4-1.38·10-4 M for 1-
6). The dilution effects of the obtained data were corrected using Origin Pro 8 software
[68]. Ligands L1 and L2 were synthesized according to the procedure reported in the
literature [32,35]. Elemental analyses (C, H, N) were carried out on a Thermo Scientific
Flash 2000 CHNS Analyser.
4.2. Synthesis of the complexes [M(L1)Cl2]2 [M = Zn(II) (1), Cd(II) (2), Hg(II) (3)].
An absolute EtOH (20 mL) solution of MCl2 (0.690 mmol: 0.094 g (1); 0.127 g
(2); 0.187 g (3)), was added dropwise to a solution of L1 (0.692 mmol, 0.265 g,) in
absolute EtOH (20 mL). The resulting solutions were stirred for 48 h at r.t. After that
24

period, the solutions were concentrated under vacuum until white solids precipitated. The
resulting solids were filtered off, washed with 5 mL of cold Et2O and dried under vacuum.
Suitable crystals for X-ray diffraction were obtained by letting an EtOH solution of the
white powder crystallize at r.t. for sixteen (1), nineteen (2) or twenty (3) days.
1. Yield: 74.1% (0.265 g). 1H NMR (CDCl3, 400 MHz, ppm): δ = 7.26 (overlapped
with CDCl3, br, 4H, Ph), 5.97 (s, 2H, CH(Pz)), 4.72 (br, 4H, OCH2Ph), 4.53 (s, 4H,
NPzCH2CH2O), 3.84 (br, 4H, NPzCH2CH2O), 2.34 (s, 6H, CH3(Pz)), 2.29 (s, 6H,
CH3(Pz)). 13C{1H} NMR (CDCl3, 100.6 MHz, ppm): δ = 150.4, 143.5 (Pz-C), 136.3 (Ph-
CH2O), 128.8 (Ph-H), 107.1 (CH(Pz)), 73.8 (Ph-CH2O), 69.2 (NPzCH2CH2O), 47.8
(NPzCH2CH2O), 13.4, 11.6 (CH3(Pz)). FTIR-ATR (wavenumber, cm-1): 2935-2859(m)
[ν(C-H)al], 1551(s) [ν(C=C)ar/ν(C=N)ar], 1479(w), 1457(w), 1455(m), 1424(m)
[δ(C=C)ar/δ(C=N)ar], 1375(w), 1371(w), 1345(m), 1306(m), 1266(w), 1254(w), 1209(m),
1099(s) [ν(C-O-C)], 1067(m), 1033(s) [δ(C-H)ip], 873(w), 843(m), 816(s) [δ(C-H)oop],
772(s) [δ(C-H)oop], 650(w), 631(s). UV-Vis: (CH3CN, 1.07·10-4 M) ʎmax (Ɛ (M-1cm-1)) =
221 nm (3.42·104). Fluorescence (CH3CN): ʎex = 260 nm, ʎem = 283 nm. Elemental
analysis calc. (%) for C44H60Zn2Cl4N8O4 (1037.54): C 50.93; H 5.83; N 10.80. Found: C
50.74; H 5.85; N 10.71.
2. Yield: 73.6% (0.287 g). 1H NMR (CDCl3, 400 MHz, ppm): δ = 7.16 (s, 4H, Ph),
5.79 (s, 2H, CH(Pz)), 4.47 (s, 4H, OCH2Ph), 4.17 (t, 4H, 3J = 5.8 Hz, NPzCH2CH2O), 3.78
(t, 4H, 3J = 5.7 Hz, NPzCH2CH2O), 2.24 (s, 6H, CH3(Pz)), 2.22 (s, 6H, CH3(Pz)). 13C{1H}
NMR (CDCl3, 100.6 MHz, ppm): δ = 147.8, 140.3 (Pz-C), 137.6 (Ph-CH2O), 127.7 (Ph-
H), 106.1 (CH(Pz)), 73.1 (Ph-CH2O), 69.4 (NPzCH2CH2O), 48.7 (NPzCH2CH2O), 13.7,
11.4 (CH3(Pz)). FTIR-ATR (wavenumber, cm-1): 3188(w) [ν(C-H)ar], 2951-2850(s) [ν(C-
H)al], 1547(s) [ν(C=C)ar/ν(C=N)ar], 1496(w), 1465(s), 1440(w), 1423(s)
[δ(C=C)ar/δ(C=N)ar], 1397(w), 1387(w), 1376(m), 1373(m), 1357(w), 1307(m), 1267(w),
1254(w), 1207(m), 1162(w), 1112(m), 1105(s) [ν(C-O-C)], 1065(m), 1043(m) [δ(C-H)ip],
1013(m), 982(w), 870(m), 836(m), 816(s) [δ(C-H)oop], 762(s) [δ(C-H)oop], 649(w),
628(m). UV-Vis: (CH3CN, 1.17·10-4 M) ʎmax (Ɛ (M-1cm-1)) = 219 nm (1.40·104).
Fluorescence (CH3CN): ʎex = 260 nm, ʎem = 282 nm. Elemental analysis calc. (%) for
C44H60Cd2Cl4N8O4 (1131.60): C 46.70; H 5.34; N 9.90. Found: C 46.55; H 5.20; N 9.60.
1
3. Yield: 61.7% (0.275 g). H NMR (CDCl3, 400 MHz, ppm): δ = 7.15 (s, 4H,
3
Ph), 5.90 (s, 2H, CH(Pz)), 4.47 (s, 4H, OCH2Ph), 4.33 (t, 4H, J = 5.26 Hz,
NPzCH2CH2O), 3.79 (t, 4H, 3J = 5.33 Hz, NPzCH2CH2O), 2.31 (s, 6H, CH3(Pz)), 2.27 (s,
25

6H, CH3(Pz)). 13C{1H} NMR (CDCl3, 100.6 MHz, ppm): δ = 147.7, 141.2 (Pz-C), 137.3
(Ph-CH2O), 128.1 (Ph-H), 107.0 (CH(Pz)), 73.1 (Ph-CH2O), 68.8 (NPzCH2CH2O), 48.7
(NPzCH2CH2O), 13.3, 11.4 (CH3(Pz)). FTIR-ATR (wavenumber, cm-1): 3117(w) [ν(C-
H)ar], 2961-2860(s) [ν(C-H)al], 1547(s) [ν(C=C)ar/ν(C=N)ar], 1494(w), 1463(m), 1423(m)
[δ(C=C)ar/δ(C=N)ar], 1387(w), 1376(m), 1347(w), 1307(m), 1266(m), 1207(m), 1122(s),
1105(s) [ν(C-O-C)], 1065(m), 1040(m) [δ(C-H)ip], 1014(m), 870(w), 821(m), 816(s)
[δ(C-H)oop], 763(w), 630(m), 533(m). UV-Vis: (CH3CN, 1.05·10-4 M) ʎmax (Ɛ (M-1cm-1))
= 219 nm (2.45·104). Fluorescence (CH3CN): ʎex = 260 nm, ʎem = 286 nm. Elemental
analysis calc. (%) for C44H60Hg2Cl4N8O4 (1307.98): C 40.40; H 4.62; N 8.57. Found: C
40.27; H 4.54; N 8.30.
4.3 Synthesis of {[Zn(L2)Cl2]·1/2H2O}n (4) and {[M(L2)Cl2]·1/2EtOH}n [M = Cd(II) (5),
Hg(II) (6)].
An absolute EtOH (20 mL) solution of MCl2 (0.934 mmol: 0.127g (1); 0.171 g
(2); 0.254 g (3)) was added dropwise to a solution of L2 (0.357 g, 0.934 mmol) in absolute
EtOH (20 mL). The resulting solutions were stirred for 48 h. at r.t. After that period, the
solutions were concentrated until white precipitates appeared, which were filtered off,
washed with 5 mL of cold Et2O and dried under vacuum. Suitable crystals for X-ray
diffraction were obtained by letting an EtOH solution of the white powder crystallize at
r.t. for twelve (4), twenty-five (5) or eleven days in the fridge for 6.
1
4. Yield: 92.9% (0.458 g). H NMR (CDCl3, 400 MHz, ppm): δ = 7.25 (s, 4H,
Ph), 5.95 (s, 2H, CH(Pz)), 4.67 (t, 4H, 3J = 5.6 Hz, NPzCH2CH2O), 4.40 (s, 4H, OCH2Ph),
3.84 (br, 4H, NPzCH2CH2O), 2.32 (s, 6H, CH3(Pz)), 2.25 (s, 6H, CH3(Pz)). 13C{1H} NMR
(CDCl3, 100.6 MHz, ppm): δ = 150.1, 144.0 (Pz-C), 136.1 (Ph-CH2O), 128.2, 128.1 (Ph-
H), 107.4 (CH(Pz)), 69.9 (Ph-CH2O), 68.7 (NPzCH2CH2O), 48.5 (NPzCH2CH2O), 13.7,
11.7 (CH3(Pz)). FTIR-ATR (wavenumber, cm-1): 3600-3200(br) [ν(O-H], 3125(w) [ν(C-
H)ar], 2954-2855(s) [ν(C-H)al], 1554(m) [ν(C=C)ar/ν(C=N)ar], 1470(w), 1440(m),
1420(m) [δ(C=C)ar/δ(C=N)ar], 1385(w), 1374(m), 1353(m), 1314(w), 1286(w), 1261(w),
1220(w), 1218(w), 1189(w), 1168(w), 1148(w), 1124(s), 1105(s) [ν(C-O-C)], 1065(m),
1050(s) [δ(C-H)ip], 1014(w), 876(w), 816(m), 786(s) [δ(C-H)oop], 758(s) [δ(C-H)oop],
656(m), 634(m). UV-Vis: (CH3CN, 1.26·10-4 M) ʎmax (Ɛ (M-1cm-1)) = 218 nm (1.84·104).
Fluorescence (CH3CN): ʎex = 260 nm, ʎem = 286 nm. Elemental analysis calc. (%) for
C44H62Zn2Cl4N8O5 (1055.55): C 50.06; H 5.92; N 10.62. Found: C 49.96; H 5.64; N
10.33.
26

1
5. Yield: 88.3% (0.486 g). H NMR (CDCl3, 400 MHz, ppm): δ = 7.22 (m, 4H,
Ph), 5.85 (s, 2H, CH(Pz)), 4.40 (s, 4H, OCH2Ph), 4.32 (br, 4H, NPzCH2CH2O), 3.75 (t,
4H, 3J = 5.6 Hz, NPzCH2CH2O), 2.32 (s, 6H, CH3(Pz)), 2.23 (s, 6H, CH3(Pz)). 13C{1H}
NMR (CDCl3, 100.6 MHz, ppm): δ = 148.6, 148.2 (Pz-C), 136.2 (Ph-CH2O), 128.8,
128.0 (Ph-H), 105.6 (CH(Pz)), 71.8 (Ph-CH2O), 69.3 (NPzCH2CH2O), 48.6
(NPzCH2CH2O), 13.6, 11.4 (CH3(Pz)). FTIR-ATR (wavenumber, cm-1): 3496(br) [ν(O-
H)], 2965-2866(m) [ν(C-H)al], 1550(s) [ν(C=C)ar/ν(C=N)ar], 1468(w), 1444(m), 1422(m)
[δ(C=C)ar/δ(C=N)ar], 1374(s), 1356(w), 1315(w), 1300(w), 1281(w), 1256(w), 1209(w),
1184(w), 1123(s), 1101(s) [ν(C-O-C)], 1069(m), 1036(s) [δ(C-H)ip], 1019(m), 993(w),
838(w), 811(w), 791(m) [δ(C-H)oop], 751(s) [δ(C-H)oop], 631(m). UV-Vis: (CH3CN,
1.05·10-4 M) ʎmax (Ɛ (M-1cm-1)) = 219 nm (1.52·104). Fluorescence (CH3CN): ʎex = 260
nm, ʎem = 286 nm. Elemental analysis calc. (%) for C23H33CdCl2N4O2.5 (588.83): C 46.91;
H 5.65; N 9.52. Found: C 46.87; H 5.61; N 9.22.
1
6. Yield: 24.5% (0.155 g). H NMR (CDCl3, 400 MHz, ppm): δ = 7.24 (m, 4H,
Ph), 5.86 (s, 2H, CH(Pz)), 4.46 (s, 4H, OCH2Ph), 4.33 (t, 4H, 3J = 5.3 Hz, NPzCH2CH2O),
3
3.71 (t, 4H, J = 5.4 Hz, NPzCH2CH2O), 2.29 (s, 6H, CH3(Pz)), 2.20 (s, 6H, CH3(Pz)).
13C{1H} NMR (CDCl3, 100.6 MHz, ppm): δ = 142.4, 141.5 (Pz-C), 136.0 (Ph-CH2O),
129.3, 128.3 (Ph-H), 106.2 (CH(Pz)), 71.3 (Ph-CH2O), 69.3 (NPzCH2CH2O), 48.4
(NPzCH2CH2O), 13.6, 11.5 (CH3(Pz)). FTIR-ATR (wavenumber, cm-1): 3515(br) [ν(O-
H)], 2925-2863(m) [ν(C-H)al], 1550(s) [ν(C=C)ar/ν(C=N)ar], 1489(w), 1469(w), 1442(s),
1420(m) [δ(C=C)ar/δ(C=N)ar], 1375(s), 1356(m), 1281(m), 1255(w), 1216(w), 1209(w),
1184(w), 1123(s), 1101(s) [ν(C-O-C)], 1068(m), 1027(s) [δ(C-H)ip], 1022(m), 984(w),
874(w), 843(w), 805(m) [δ(C-H)oop], 752(s) [δ(C-H)oop], 658(w), 631(m). UV-Vis:
(CH3CN, 1.34·10-4 M) ʎmax (Ɛ (M-1cm-1)) = 219 nm (1.66·104). Fluorescence (CH3CN):
ʎex =260 nm, ʎem = 286 nm. Elemental analysis calc. (%) for C23H33HgCl2N4O2.5 (677.02):
C 40.80; H 4.98; N 8.27. Found: C 40.70; H 4.76; N 8.05.
4.4 Crystallographic Data
The crystallographic data of complexes 1-3 and 4-6 are gathered in Tables 6 and
7, respectively. Suitable crystals for X-ray elucidation were obtained by recrystallization
of the compounds in EtOH. Measured crystals were prepared under inert conditions,
immersed in perfluoropolyether as protecting oil for manipulation. Suitable crystals were
mounted on MiTeGen Micromounts and used for data collection. Crystallographic data
for 1−3 was collected at 100 K at XALOC beamline at ALBA synchrotron (λ = 0.72931
27

Å). Crystallographic data for compounds 4−6 was collected with a Bruker D8 Venture
diffractometer (λ = 1.54178 (4); λ = 0.71073 (5, 6). Data was processed with APEX2
program [69] and corrected for absorption using SADABS [70]. The structures were
solved by direct methods and subsequently refined by correction of F2 against all
reflections [71] and Olex2 as the graphical interface [72]. All non-hydrogen atoms were
refined with anisotropic thermal parameters by full-matrix least-squares calculations on
F2. All hydrogen atoms were located in difference Fourier maps and included as fixed
contributions riding on attached atoms with isotropic thermal displacement parameter 1.2
or 1.5 (O−H) times those of the respective atom. The contribution of the disordered
solvent molecules to the diffraction pattern could not be rigorously included in the model
and were consequently removed with the SQUEEZE routine of PLATON [73] (0.5
molecules of EtOH for 5 and 6). This contribution has been included in the empirical
formula to give the correct calculated density, absorption coefficient and molecular
weight. Details of the structure determination and refinement of compounds are
summarized in Tables 6 and 7. 5 was treated as a two-component non-merohedral twin;
the exact twin matrix identified by the integration program was found to be −1 0 −0.5 0
−1 0 0 0 1. The structure of 5 was solved using direct methods with only the non-
overlapping reflections of component 1. The structure was refined using the HKLF 5
routine with all reflections of component 1 (including the overlapping ones), resulting in
a BASF value of 0.317. Complete information about crystal structure and molecular
geometry is available in CIF format as Supporting Information. CCDC 1954385-1954390
(1-6) contain the supplementary data for this paper. Molecular graphics were generated
using MERCURY software [74,75] with POV-Ray package [76]. Colour codes for all
molecular graphics are: grey (C), red (O), light-blue (N), white (H), green (Cl), blue-grey
(Zn), bone (Cd) and light-grey (Hg).
28

Table 6. Crystallographic data for compounds 1-3
Formula
C44H60Hg2Cl4N8O4 (3)
C44H60Zn2Cl4N8O4 (1)
C44H60Cd2Cl4N8O4 (2)
Formula Weight
Temperature (K)
Wavelength (Å)
System, space group
a (Å)
1037.54
100(2)
0.72932
1131.60
100(2)
0.72929
1307.98
100(2)
0.72931
Monoclinic, P21/n
9.5030(4)
19.1113(9)
13.3218(6)
90
Monoclinic, P21/n
9.5328(8)
19.3000(16)
13.5436(11)
90
Monoclinic P21/n
9.5573(4)
b (Å)
c (Å)
α (º)
19.2939(7)
13.5592(5)
90
β (º)
γ (º)
96.203(2)
90
97.179(2)
90
97.3560(10)
90
U (Å 3) / Z
Dcalc (g cm-3) / μ (mm-1)
F(000)
2405.27(19) / 2
1.433 / 1.353
1080
0.12x0.1x0.1
-11≤h≤11,
-22≤k≤22,
-15≤l≤15
2472.3(4) / 2
1.520 / 1.196
1152
0.11x0.1x0.1
-11≤h≤11,
-23≤k≤23,
-16≤l≤16
2479.71(17) / 2
1.752 / 6.872
1280
0.1x0.1x0.08
-11≤h≤11,
-22≤k≤22,
-16≤l≤16
Crystal size (mm3)
hkl ranges
θ Range (°)
Reflections
collected/unique/ [Rint]
1.920 to 25.773
2.461 to 25.812
1.894 to 25.728
42758/ 4370 /
0.0719
17476 / 4097 / 0.0516
19112 / 4111 / 0.0646
Completeness to θ (%)
95.9
93.2
99.6
Semi-empirical from
equivalents
0.0189 and 0.0048
Semi-empirical from
equivalents
0.0922 and 0.0385
Semi-empirical from
equivalents
0.0961 to 0.0280
Absorption correction
Max. and min. trans.
Data/restrains/
parameters
Goodness-of-fit on F2
Final R indices [I>2σ
(I)]
4097 / 0 / 284
4111 / 0 / 284
4370 / 0 / 285
1.064
1.074
1.174
R1= 0.0457
wR2= 0.1320
R1= 0.0466
wR2= 0.1344
R1= 0.0672
wR2= 0.1866
R1= 0.0688
wR2= 0.1906
R1= 0.0695
wR2= 0.1714
R1= 0.0707
wR2= 0.1738
R indices (all data)
Largest diff. peak and
hole (e Å-3)
1.134 and -0.723
1.108 and -0.889
2.049 and -4.641
29