Supramolecular Assemblies in Silver Complexes: Phase Transitions and the Role of the Halogen Bond

Article abstract of DOI:10.1021/acs.inorgchem.0c00256

Weak interactions (hydrogen bonds, halogen bonds, CH···πand π-πstacking) can play a significant role in the formation of supramolecular assemblies with desired structural features. In this contribution, we report a systematic investigation on how a haloge

Full text of DOI:10.1021/acs.inorgchem.0c00256

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Article
Supramolecular Assemblies in Silver Complexes: Phase Transitions
and the Role of the Halogen Bond
Giulia Bonfant, Matteo Melegari, Davide Balestri, Francesco Mezzadri, Vittoria Marzaroli,
̀
Irene Bassanetti, and Luciano Marchio*
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ABSTRACT: Weak interactions (hydrogen bonds, halogen bonds,
CH···π and π−π stacking) can play a significant role in the
formation of supramolecular assemblies with desired structural
features. In this contribution, we report a systematic investigation
on how a halogen bond (XB) can modulate the structural
arrangement of silver supramolecular complexes. The complexes
are composed of X-phenyl(bispyrazolyl)methane (X = Br, I) and I-
alkynophenyl(bispyrazolyl)methane ligands functionalized in meta
(L3Br, L3I) and para (L4Br, L4I, L4CCI) positions on a phenyl ring with
the purpose of providing different directionalities of the X function
with respect to the N,N coordination system. The obtained
[Ag(L)2]+ moieties show remarkable geometric similarities, and the
L4Br, L4I, and L4CCI ligands exhibit the most conserved types of supramolecular arrangement that are sustained by XB. The increased
σ-hole in L4CCI with respect to L4I leads to an occurrence of short (and strong) XB interactions with the anions. [Ag(L4I)2]PF6 and
[Ag(L4I)2]CF3SO3 are characterized by the presence of three different phases, and the single-crystal evolution from phase-1 (a
honeycomb structure with large 1D cavities) to phase-3 (solventless) occurs by a stepwise decrease in the crystallization solvent
content, which promotes an increase in XB interactions in the lattice. The present paper aims to provide useful tools for the selection
of appropriate components for the use of coordination compounds to build supramolecular systems based on the halogen bond.
hydrogen bond (HB) dimers,26−28 which represent a route for
expanding the dimensionality of these architectures.
INTRODUCTION
■
There is extreme variability in the 1D, 2D, and 3D structural
In the present work, we wish to investigate the formation of
architectures that can be built by combining metal centers and
supramolecular architectures formed by silver bis(pyrazolyl)-
ligands with various functional groups.1−4 In many cases, these
methane complexes functionalized with halogen atoms such as
architectures are characterized by properties that depend on
bromine and iodine (L3Br, L3I, L4Br, L4I, L4CCI, Schemes 1 and
structural cavities that can encapsulate additional components
2). The rationale behind the present work is to generate
such as solvent molecules, counterions, and small mole-
supramolecular architectures by exploring different types of
cules.3,5−7 Furthermore, these architectures have applications
covalent and noncovalent interactions, particularly halogen
in luminescent materials8,9 and magnetic materials.10,11 The
bonds.29 The halogen bond is a weak interaction that has been
presence of metal centers is also a source of potential reactivity
extensively investigated in recent decades,30−35 and it occurs
toward the interaction and activation of small molecular
due to the presence of a partial positive charge (σ hole, Cl < Br
guests,12,13 and the formation of channels favors transport to
< I) on the opposite side of the σ bond.36,37 Halogen bond
and from the reactive metal centers. Moreover, structural
interactions have been used to sustain the formation of
organization in a solid state may result in a close proximity of
multidimensional networks based on coordination compounds
specific molecular components, which can be made to react by
as repetitive units.38−43 To compare the influence of halogen
external stimuli, such as UV light, to form covalent bonds that
atoms on the structural outcome, we investigate a parent
are otherwise difficult to obtain.14−16 In many cases, the ligand
is characterized by bridging functionalities; hence it is capable
of linking two, or more, metal centers in an extended network.
Received: January 24, 2020
However, multidimensional architectures can be built by
combining coordination compound assemblies, which may be
connected due to weak interactions,17,18 such as hydrogen
bonds,9,19−21 halogen bonds,22,23 and π−π stackings.24,25 For
example, dimerization of carboxylic functional groups form
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adopts coordination geometries that vary from linear to
tetrahedral.44−65 Due to the lack of electronic stabilization (d10
metal ion), these geometries are usually distorted, and the
metal adapts to the steric requirements of the ligands. Thus,
two different counteranions are used to provide different
systems that can potentially act as halogen bond acceptors
Scheme 1. (a) Previously Reported Supramolecular
Architecture Based on a Ag−S Coordination and (b) an
Example of a Molecular Crystal Obtained by Exploiting
Halogen Bonds and Other Weak Interactions, As Reported
in This Work
−
−
(fluorine in PF6 or fluorine and oxygen in CF3SO3 ) as well
as having different coordination capabilities toward a metal
center. Halogen bonds are present in all the structures
obtained with the halogenated ligands, and in two cases,
when crystallizing [Ag(L4I)2]PF6 and [Ag(L4I)2]CF3SO3 in
tetrahydrofuran/hexane (THF/Hx), we identify three phases,
which differ by their solvent content. Phase-1 is characterized
by a honeycomb structure with large 1D channels (diameter of
30 Å), and phase-1 evolves into phase-2 after a spontaneous
loss of most of the solvent. Phase-2 presents smaller 1D
channels that confine THF molecules, and the evolution from
phase-2 to a solventless phase-3 can be promoted by a thermal
treatment at 120 °C. The phase-1 to phase-3 transitions are
investigated by thermal methods and powder X-ray diffraction.
The single-crystal X-ray structures allow the role of the weak
interactions in the formation of these supramolecular arrange-
ments to be established. Overall, the analysis of the structural
arrangements wishes to provide useful hints for the selection of
the appropriate components in the formation of supra-
molecular systems based on coordination compounds as
repetitive units.
Scheme 2. (a) Bis-pyrazolyl Ligands Used in the Present
Study and (b) a Summary of the Complexes Synthesized in
This Work
RESULTS AND DISCUSSION
■
The Ag+ complexes are prepared by mixing AgPF6 and
AgCF3SO3 with different ligand (L) systems in a 1/2 ratio. The
choice of the two different counteranions is made by
considering their different symmetries and potential inter-
actions with metal centers. In particular, the highly symmetric
−
PF6 anion exhibits little coordination capability toward Ag+.
−
In contrast, the CF3SO3 anion has a more pronounced
tendency to interact with a metal center, usually as an O-
monodentate.49−52 Both anions, having a net negative charge,
can also act as nucleophilic sites for interactions involving
positively charged molecular fragments, such as the σ-holes
present in halogen atoms or electrophilic CH groups.
The coordination geometries of all of the complexes
reported in the present work are depicted in Figures S26−
S58. In the structures, the metal appears to be in a distorted
tetrahedral environment, but it is difficult to assign a definitive
metal geometry to these four-coordinated silver complexes.
Hence, it is perhaps useful to employ a τ4 index that takes into
account all the possible distortions from the square-planar to
the tetrahedral geometries.66,67 In all complexes, the τ4 and τ4′
geometry indices are in the ranges 0.70−0.61 and 0.65−0.46,
respectively, which are in line with a seesaw geometry (Table
S10). More specifically, two of the four Ag−N coordinative
interactions are longer (range 2.34−2.49 Å), and two are
shorter (2.21−2.31 Å, Tables S7−S9). As a general
observation, in all the reported systems, the metal environment
is quite conserved. Hence, we may assume that [Ag(L)2]+ is a
preorganized synthon, with a relatively fixed orientation of
phenyl rings attached to a bis-pyrazole moiety. Consequently,
the different functionalization of the aromatic ring, with respect
to the 3 (meta) and 4 (para) positions, is what dictates the
orientations of the halogen atoms (Figure 1). When the
halogen atoms are in the 4 position, the conformation of the
phenyl ring has little influence on the directionality of the C−X
phenylbis(pyrazolyl)methane ligand that is devoid of halogen
atoms. However, we increase the XB donor potential of these
ligands with an alkyno group interposed by an iodine and a
phenyl ring. The resulting ligand (L4CCI) is characterized by a
large positive charge in the σ-hole, which is potentially capable
of forming strong XB interactions.
The complex building units are prepared by reacting the
ligands with silver salts (AgPF6 and AgCF3SO3). Silver usually
B
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be pointed out how the presence of the halogen atom at
position 4 gives rise to two crystal packing motifs involving the
anions. In the first one, one halogen atom acts as an XB donor
toward the anion, and it simultaneously acts as an XB acceptor
toward a second halogen atom (Figure 2h). In the second
motif, the anion bridges between two XB donor moieties
(Figure 2i,l).68 The following discussion will focus on the
solid-state properties of the silver complexes with the L4I and
L4CCI ligands (9−12; see Scheme 2), which are the systems
characterized by preorganized orientations of the two halogen
atoms within the [Ag(L)2]+ moiety. The presence of the alkyne
group in L4CCI is devised to increase the XB donor properties
of the ligand with respect to L4I while preserving the same
spatial orientation of the halogen.30
SOLVENT ROLE AND PHASE TRANSITIONS
■
The 9−12 complexes are crystallized in different solvent
mixtures since it was previously shown that the solvent can
have an important role in selecting the type of weak interaction
that occurs between two multifunctional molecular counter-
parts.69 In our case, the choice of solvent is limited by
solubility issues related to the [Ag(L)2]+/anion complexes,
which can dissolve in chlorinated solvents (DCM, DCE) or
more polar solvents (acetone, THF, methanol). The
crystallizing conditions make use of hexane as an antisolvent.
The crystalline material for [Ag(L4I)2]PF6 (9) and [Ag(L4I)2]-
CF3SO3 (10) in the form of different solvates is recovered
from the following crystallization conditions: dichloroethane/
hexane (DCE/Hx), dichloromethane/hexane (DCM/Hx), and
THF/Hx.
Figure 1. Schematic representation of the multiple experimental
orientations, which can be experienced by the halogen atoms after the
formation of the Ag complex. The indicated values refer to the
observed angles between the C-halogen vector (color codes: C, gray;
N, blue; Br, light brown; P, orange; I, purple; Ag, yellow).
vector. In contrast, functionalization of the 3 position leads to
different arrangements of the two C−X vectors located on the
two ligands. In Figure 2, we report an overview of the
intermolecular interaction exchanged between the halogen
atoms and the surrounding molecules. More specifically, it can
More interesting results are obtained from the THF/Hx
crystallizing condition, since three different phases can be
observed, and the evolution from phase-1 to phase-3 occurs
upon decreasing the solvent content. 9-phase-1 and 10-phase-1
are characterized by long prismatic crystals (Figure 3 and
Figure 4), which are stable in the presence of the mother liquor
or when protected by a low temperature environment (less
than 200 K). The single-crystal X-ray characterization of these
systems shows that they are isostructural, forming large 1D
hexagonal cavities filled with solvent molecules (10-phase-1
will be described here). When proceeding from the molecular
unit to the crystal packing, it can be instructive to analyze the
hierarchical construction of the lattice based on the weak XB,
CH···F, CH···O, and CH···π interactions. In particular, three
molecular units in the inner core are arranged around a PF6− or
−
CF3SO3 anion (P18/S18) by means of CH···F or CH···O
interactions. Interestingly, toward the periphery of the trimer,
the inner iodine atoms of the molecular unit (I6) are directing
the σ-hole toward the negative corona of the outermost iodine
atom (I3). Even though the halogen−halogen intermolecular
distance is particularly long (∼4.5 Å), the geometry of the
interaction is preserved, since the C−I6···I3 angle is
approximately 160° and close to the theoretical value of
180°. The supramolecular trimers are then piled one over the
other by means of CH···F and CH···O interactions mediated
by anions bridging different stacking levels along the c-axis
(Figure 3b). The expansion of the columnar stacking of trimers
along the ab crystallographic plane is promoted by the anion
(P17/S17) that links together two adjacent complex molecules
by means of CH···F interactions (Figure 3c). The final
supramolecular arrangement results in the formation of a
honeycomb structure characterized by hexagonal 1D cavities
that are parallel to the crystallographic c-axis. Even though the
Figure 2. Summary of the XB interactions exchanged by the halogen
atoms in the reported structures. The inset describes a simplified
representation of XB between two halides and one anion (color codes,
C, gray; N, blue; O, red; H, white; F, green; S, yellow; Br, light brown;
P, orange; I, purple).
C
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data collection is performed at low temperature, it is possible
to identify only some THF molecules in these cavities during
crystallization, which are close to the surface of the hexagonal
channel. One of these THF molecules exchanges an XB with
the I3 atom, which points toward the interior of the cavity
(I3···O 1s 3.24 Å, see Figure 2f). It is not possible to identify a
reasonable structural model of the solvent into the remaining
part of the large 1D cavity, and the Squeeze program is used to
determine the residual and diffuse electron density. By taking
into account only the complex molecular entity [Ag(L4I)2]-
CF3SO3, which is the building unit of the hexagonal
framework, the cavity volume corresponds to 7300 Å3/cell
(56% of the unit cell volume), and the 1D cavity diameter is
approximately 30 Å (Figure 3d). When the prismatic needle-
like crystals of 10-phase-1 are taken out of the mother liquor,
they rapidly change phase and convert into 10-phase-2 (Figure
4A−D, a video of the single-crystal phase transition is available
as a web enhanced object). The time span of the conversion
process usually takes significantly less than a minute, and it can
be partially hampered by immersing the crystals into viscous
matrixes, but the conversion eventually goes to completeness.
The 10-phase-2 crystals exhibit a plate-like morphology, and
according to the single-crystal X-ray analysis, they contain one
THF molecule per [Ag(L4I)2]CF3SO3 complex (Figure 5).
−
The complex molecules and the CF3SO3 anions delimit a
small channel-like cavity (∼5 Å diameter) hosting the THF
molecules. All of the iodine atoms are engaged in XBs with the
oxygen or fluorine atoms of the anion, and the I···F interaction
distances (3.27 and 3.38 Å) are significantly longer than the I···
O interaction distances (2.97 and 2.99 Å). 9-phase-2 is
isomorphous with 10-phase-2, as reported in the Supporting
Information (Table S1 and Figure S44). 10-phase-2 is stable
for several weeks at room temperature; however, when the
plate-like crystals are heated above 130 °C, they convert into
10-phase-3, as reported in Figure 4E,F (a video of the SC to
SC phase transition is available as a web enhanced object).
After the thermal treatment, the crystals were partially
fractured, but a small sample could be used for the single-
crystal X-ray data collection (see Figure 5f). The structural
analysis revealed that the system has experienced a significant
spatial reorganization resulting in a more compact structure
with negligible residual voids; hence, 10-phase-3 can be
considered the completely desolvated phase. Only I3
exchanges an XB with an oxygen atom of the anion (3.14 Å;
see Figure 2g), whereas the second iodine atom I6 interacts
with a methyl group by virtue of its negatively charged corona
surrounding the σ-hole. Interestingly, 10-phase-3 exhibits a
different structural organization than 9-phase-3. The latter
phase is also closely packed and forms without a solvent.
Nevertheless, in this case, both iodine atoms act as XB donors,
in line with one of the structural motifs involving the halogen
atoms reported in Figure 2h. In fact, I3 simultaneously acts as
an XB donor (toward the anion, I6···F17, 3.221 Å) and an
acceptor (toward I6, I3···I6, 3.646 Å). 9-phase-3 can be
obtained after a thermal treatment at 130 °C of 9-phase-2, but
interestingly, it can also be obtained by direct crystallization
from a DCM/Hx mixture (Figure 6).
Figure 3. Crystal structure of 10-phase-1 crystallized in THF/Hx. (a)
Supramolecular trimer. (b) Trimeric units piled along the c-axis. (c)
Expansion of the trimeric unit in the ab crystallographic plane. (d)
Crystal packing highlighting the 1D channels.
Figure 4. (A)−(D) Polarized microscopy images collected at different
points in time showing the phase transition from 10-phase-1
(needles) to 10-phase-2 (plates) at RT. (E,F) Hot-stage microscopy
images showing the phase transition from 10-phase-2 to 10-phase-3.
POWDER X-RAY DIFFRACTION
■
Powder X-ray diffraction is performed for compounds 9 and 10
to confirm the phase composition in the bulk and to monitor
the conversion between the three phases. For both
compounds, phase-1 is the most difficult to characterize
D
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Figure 6. Schematic representation of the phase transitions and the
solvates of 9 and 10 described in this work.
for several days; however, it is interesting to note that the
solvent content of phase-2 is not constant over time. In fact,
the SC-XRD data collection of a freshly mounted crystal shows
one THF molecule per complex molecular entity, whereas after
the crystal is left for 24 h at room temperature and in the
absence of the crystallizing solvent, the solvent content
decreases to 0.25 per complex molecule (compare Figure
5b,d). This observation is in line with the presence of the
narrow channels that characterize phase-2 and that contain the
THF molecules, which weakly interact with complex cations
and anions. The relatively small size of the channels implies
that the removal of the solvent can be tolerated without the
system undergoing structural reorganization. Phase-2 of the
two compounds is isostructural, but after the thermal
treatment, they give rise to two different phase-3’s (Figures
7g and S21).
Figure 5. Views of the intermolecular interactions (a) and crystal
packing (c) for 10-phase-2 (THF molecules in a space-filling model).
Single-crystal to single-crystal phase transition from 10-phase-2 to 10-
phase-3 due to the loss of solvent and thermal treatment (b, d, f).
Representation of the interactions (dashed bonds) exchanged by the
anions and the complex molecules for 9-phase-3 (e). The insets in (b)
and (d) describe the decrease in the residual electron density
associated with the THF molecules.
THERMAL ANALYSIS
■
As pointed out in the PXRD section, the transformation from
hexagonal phase-1 to phase-2 for both systems is very rapid
once they are removed from the mother liquor (THF/Hx),
and it occurs in a time span of a few seconds. Hence, the
thermal experiments monitor the events occurring between
phase-2 and phase-3. The hexagonal prims of 10-phase-1 are
dried prior to performing the experiments to remove the
solvent wetting the crystals. The DSC profile shows the
presence of an exothermic peak at 113 °C with a shoulder at
the beginning of the event (Figure 7B). The exothermic peak is
associated with the phase-2 to phase-3 conversion, whereas a
minor endothermic event can be associated with the residual
THF desorption within the channels of 10-phase-2. There are
no other events occurring when decreasing the temperature to
room temperature (RT) and then increasing the temperature
above 200 °C. The TGA profile of 10-phase-2 shows no
appreciable weight loss at approximately 120 °C, but the
compound undergoes decomposition at 221 °C.
experimentally since the long prismatic crystals are very
unstable once removed from the mother liquor (THF/Hx).
Wet crystals are placed onto the sample holder and covered
with a protective film as described in the experimental section
(General Methods in Supporting Information). The crystals
are not ground to prevent phase transformations; hence, the
data collection is affected by significant preferential orientation.
Figure 7 shows the comparison between the experimental
PXRD of 10-phase-1 with the calculated patterns derived by
SC-XRD.70 There is good agreement between the predicted
and experimental diffractograms, which is particularly true for
the peak positions, while the relative intensities are affected by
the cited strong preferential orientation and sample roughness.
The conversion of phase-1 into phase-2 is very fast, and it went
to completion in approximately 30 s after the removal of the
film and the evaporation of the solvent. The rapid evolution
from phase-1 to phase-2 implies that the investigation based on
the thermal analysis (DSC and TGA; see below) exclusively
involves phase-2 even when starting from the long prismatic
crystals of phase-1. The plate-like crystals of phase-2 are stable
For 9, we grew plate-like crystals corresponding to 9-phase-
2, which were then used for the thermal experiments (Figure
S17). In the DSC scan, there is an endothermic peak at 111 °C
associated with the loss of the solvent into the small channels,
and concomitantly, the systems experience a structural
E
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(CF3SO3) (12) are reported in Figure 8. In both compounds,
the anions bridge two complex cations by means of an XB with
Figure 8. Halogen bond interactions for 11·THF (a) and 12 (c).
Schematic representations of the supramolecular chains in 11·THF
(b) and 12 (d).
the peripheral iodine atoms, in agreement with the second
motif described above for the XB reported in this work (see
Figure 2l). In particular, in 12, CF3SO3− acts as an XB acceptor
toward two opposite iodine atoms (I3···O1T, 2.844 Å; I6···
−
F2TB, 3.059 Å); in 11·THF, PF6 engages two cis-fluorine
atoms into an XB formation with symmetry-related iodine
atoms (I3···F24B, 2.987 Å; I3···F24A, 2.960 Å). The result is
the formation of supramolecular chains in both cases, even
though they each express a different structural packing. In fact,
in 12, the chains are more interwoven, leaving no residual void
for the presence of solvent during crystallization. In contrast, in
11·THF, the chains delimit channel-like cavities filled with
disordered THF molecules during crystallization. Obviously, in
11·THF and 12, the presence of the PhCCI group with
respect to the PhI moiety in 9 increases the dimension of
the supramolecular synthon, which is represented by the
[Ag(L)2]+ complex cation. However, by comparing the
structures of 11·THF, 12, and 9/10-phase-1, it is evident
that increasing the length of the XB donor moiety does not
produce systems characterized by large channels as in the 9/
10-phase-1.
Figure 7. (A) Overlap between the simulated and experimental
PXRD of 10: 10-phase-1 (a,b), 10-phase-2 (c,d), 10-phase-3 (f,g).
(B) DSC and (C) TGA traces for 10-phase-2.
reorganization to the more stable 9-phase-3. There are no
other events taking place when decreasing the temperature to
RT and then increasing the temperature above 200 °C. At 264
°C, the system undergoes decomposition. The loss of solvent
at 111 °C is confirmed by a 5% weight loss, in agreement with
1 molecule of THF per [Ag(L4I)2]PF6 (6% theoretical), Figure
S18.
CONCLUSIONS
■
The ligands described here are characterized by two functions,
one that can bind a metal center (N,N system) and the other
that can form directional supramolecular interactions (halogen
atoms). The assemblies generated with Ag+ result in an almost
invariant molecular geometry, with the cation in a well-defined,
even though distorted, tetrahedral environment. The reason for
such behavior can be ascribed to the presence of the moderate
steric hindrance provided by the methyl groups attached to the
pyrazole rings. Consequently, when the two ligands are bound
to the metal center, they are interlocked to minimize steric
A LONGER SYNTHON: [Ag(L4CCI)2]+
■
As pointed out earlier in the discussion, the presence of an
iodoalkyne functional group confers to the ligand a greater
propensity to act as an XB donor with respect to the L4I ligand,
with L4CCI having a more pronounced σ-hole and negative
corona on the halogen atom. The molecular structures of
[Ag(L4CCI)2](PF6)·THF (11·THF) and [Ag(L4CCI)2]-
F
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repulsion. The result is a preorganized XB donor directionality,
which exclusively depends on the position of the halogen
functionalization on the phenyl ring. When comparing all of
ASSOCIATED CONTENT
■
sı
* Supporting Information
The Supporting Information is available free of charge at
https://pubs.acs.org/doi/10.1021/acs.inorgchem.0c00256.
the reported structures, it appears that with L4X and L4CCI
,
there are two repetitive structural motifs. The first one is
Xδ+···−δXδ+···Anion, with the central halogen atoms acting
simultaneously as XB donors and acceptors, and the second
corresponds to Xδ+···Anion···+δX, with the anion forming a
bridge between the two XB donors (see Figure 2).
Synthesis of the ligands and complexes, NMR spectra,
single-crystal structures, optical microscope images,
crystallographic tables, geometric parameters, τ4 indices,
thermal analyses (DSC and TGA), and powder X-ray
diffraction spectra (PDF)
The [Ag(L4I)2]PF6/CF3SO3 systems crystallized from THF/
Hx are characterized by the presence of three phases. The
conversion from phase-1 to phase-3 occurs by a stepwise
decrease in the solvent content and by a reinforcement of the
XB interactions among the molecular components. 9/10-
phase-1 presents a supramolecular structure with a large
columnar cavity filled with solvent molecules, and we have not
investigated the various methodologies that are suitable to
activate porous materials that are characterized by large cavities
occupied with solvent−guest molecules. These methods are
usually applied to metal organic frameworks,71 in which the
weakest type of interaction is the metal−ligand coordination
bond, which is significantly stronger than the XB or other weak
interactions found in the reported structures.
we
* Web-Enhanced Features
Single-crystal to single-crystal phase transitions 10-phase-1/10-
phase-2/10-phase-3 in an MPEG format are available in the
HTML version of the paper.
Accession Codes
CCDC 1902455−1902465 and 1968843−1968848 contain
the supplementary crystallographic data for this paper. These
data can be obtained free of charge via www.ccdc.cam.ac.uk/
data_request/cif, or by emailing data_request@ccdc.cam.ac.
uk, or by contacting The Cambridge Crystallographic Data
Centre, 12 Union Road, Cambridge CB2 1EZ, UK; fax: +44
1223 336033.
Even though the PhBr and PhI moieties may be
considered moderately good XB donors, the XB donor
potential of these ligands can be increased by introducing
additional electron withdrawing groups on the aromatic
fragment, hence increasing the positive charge of the σ-
hole.30 L4CCI was therefore devised to increase the strength of
the XB interactions. A summary of the normalized
distances72−74 pertaining to the XBs described here is provided
in Figure 9. Generally, it is clear that shorter interactions are
AUTHOR INFORMATION
■
Corresponding Author
̀
Luciano Marchio − Dipartimento di Scienze Chimiche, della
̀
Vita e della Sostenibilita Ambientale (Chemistry Unit),
̀
Universita di Parma 43124 Parma, Italy; orcid.org/0000-
0002-0025-1104; Email: luciano.marchio@unipr.it
Authors
Giulia Bonfant − Dipartimento di Scienze Chimiche, della Vita e
̀
̀
della Sostenibilita Ambientale (Chemistry Unit), Universita di
Parma 43124 Parma, Italy; orcid.org/0000-0001-5108-
8354
Matteo Melegari − Dipartimento di Scienze Chimiche, della
̀
Vita e della Sostenibilita Ambientale (Chemistry Unit),
̀
Universita di Parma 43124 Parma, Italy
Figure 9. Plot of the normalized distance R for the XB interactions. A
value of 1 corresponds to an XB donor−acceptor distance equal to the
sum of the v.d.W. radii.
Davide Balestri − Dipartimento di Scienze Chimiche, della Vita
̀
̀
e della Sostenibilita Ambientale (Chemistry Unit), Universita di
Parma 43124 Parma, Italy; orcid.org/0000-0003-3493-
9115
Francesco Mezzadri − Dipartimento di Scienze Chimiche, della
̀
Vita e della Sostenibilita Ambientale (Chemistry Unit),
−
experienced with the oxygen atom of the CF3SO3 anion and
̀
Universita di Parma 43124 Parma, Italy; orcid.org/0000-
iodine compared to those of the other interactions. This
observation is also in agreement with the propensity of
CF3SO3 to act as an O-monodentate ligand toward a metal
0001-9505-1457
Vittoria Marzaroli − Dipartimento di Scienze Chimiche, della
−
̀
Vita e della Sostenibilita Ambientale (Chemistry Unit),
−
̀
Universita di Parma 43124 Parma, Italy; orcid.org/0000-
center when compared to PF6 . It is also evident that there is a
0003-1781-2622
significant decrease in the XB distance along the Br < I < C
CI series. This observation is consistent with a more
pronounced σ-hole on L4CCI with respect to L4I. As a result,
more robust interactions can potentially be formed with this
ligand, and the high directionality of the XB allows for
significant control over the supramolecular arrangements. The
studied systems provide insight into the choice of molecular
components for the construction of supramolecular assemblies
comprising coordination entities as building units.
Irene Bassanetti − Dipartimento di Scienze Chimiche, della Vita
̀
̀
e della Sostenibilita Ambientale (Chemistry Unit), Universita di
Parma 43124 Parma, Italy; orcid.org/0000-0003-0618-
5440
Complete contact information is available at:
https://pubs.acs.org/10.1021/acs.inorgchem.0c00256
Notes
The authors declare no competing financial interest.
G
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Article
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ACKNOWLEDGMENTS
■
This work benefited from the equipment and framework of the
COMP-HUB Initiative, funded by the “Departments of
Excellence” program of the Italian Ministry for Education,
University and Research (MIUR, 2018-2022). Chiesi Farm-
aceutici SpA is acknowledged for the support of the D8
Venture X-ray equipment. The COST action CM1402
“Crystallize” is acknowledged for networking support.
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