Isothiocyanate Sulfur Atom as an Acceptor Site for Halogen-Bonded Cocrystallization of Werner Ni(II) Coordination Compounds and Perfluorinated Iodobenzenes

We explore the halogen bond acceptor potential of the isothiocyanate sulfur atom in the synthesis of cocrystals involving metal–organic building blocks by using Werner Ni(II) coordination compounds whose pendant isothiocyanate group enables halogen bonding. A series of 14 cocrystals involving octahedral Ni(L)4(NCS)2 coordination compounds (L = pyridine or 4-methylpyridine) has been prepared by both crystallization from solution and liquid-assisted grinding. The effectiveness of this strategy is demonstrated by the assembly of a large family of cocrystals involving five perfluorinated iodobenzenes. For both coordination compounds, we generally obtained one cocrystal with each donor; in one case, we obtained an additional two stoichiomorphs, and in another, we obtained three additional solvates. Single-crystal X-ray diffraction experiments revealed that building units in all cocrystals are connected via S···I halogen bonds involving the donor iodine atom and the isothiocyanate sulfur atom, which is an acceptor of two and, in some cases, even three halogen bonds. Consequently, both coordination compounds act as multitopic acceptors that can form multiple halogen bonds leading to the formation of one-, two-, and three-dimensional halogen-bonded architectures. The relative shortenings of S···I distances are from 7 to 15%, while the S···I–C angles are in the range from 160 to 180°.


■ INTRODUCTION
−26 Coordination compounds can also provide a wide range of different geometries that are not available to simple organic molecules and can be easily modified by changing the metal center 27−30 or by changing the ligands attached to the metal, 31,32 thus enabling halogen bonds between the coordination compound and halogen bond donor molecules.In the literature, few approaches for the synthesis of halogen-bonded metal−organic cocrystals have been presented. 33The halogen bond acceptor functionality on the coordination compound can be introduced as an additional functional group on the periphery of the ligand (i.e., the pyridine nitrogen atom, the carbonyl or morpholinyl oxygen atom) 11,[30][31][32]34,35 or by using monovalent, inorganic anions, like halides or pseudohalides.36−39 Halide ligands, especially chloride ligands, show great acceptor ability in different coordination compounds, even when competing with other acceptor groups containing oxygen or nitrogen atoms. 40,41 Onthe other hand, pseudohalide ligands have hardly been recognized as halogen bond acceptors, with most research done on cyanide coordination compounds.43−45 Furthermore, for both metal−organic and organic solids, the sulfur atom is significantly less studied as an acceptor species relative to the oxygen or nitrogen atom.According to available structural data in the Cambridge Structural Database (CSD), 46 there are a total of 6880 data sets for the [S, I−X] motif (X being any atom and with an unspecified charge on S), and it was found that the S•••I halogen bond is present in 811 data sets.A subset of these data corresponds to multicomponent crystals containing perhalogenated iodobenzenes (PHB) with 256 data sets, which is 17% of a total of 1627 data sets for structures with perhalogenated iodobenzenes. Of those, 127 data sets correspond to structures with a charged sulfur atom. Futhermore, for the [C�S, I−X] motif, there are 1053 data sets, of which 96 correspond to the [C�S, I PHB ] motif.It was found that the C�S•••I PHB halogen bond is present in 94 data sets (98%, which represents the propensity of a particular acceptor species).When we narrowed the search to isothiocyanate sulfur as a halogen bond acceptor, it was found that the NCS•••I halogen bond, including both neutral and charged sulfur atoms, is present in 167 data sets.Of those, only 28 correspond to structures with the M−NCS•••I halogen bond motif (M being any metal atom) and only one structure is a multicomponent crystal that contains a perhalogenated halogen bond donor (1,4-diiodotetrafluorobenzene).42,47 In this work, we decided to explore the potential of the isothiocyanate ligand bonded to the metal atom as a reliable halogen bond acceptor species to form cocrystals containing metal−organic building blocks and perfluorinated iodobenzenes.As coordination compounds, we selected Werner coordination compounds that are mostly known for displaying inclusion phenomena.48−50 In general, these Werner coordination compounds are of the MX 2 L 4 general formula, where M is a divalent metal cation, typically Ni(II), Co(II), Fe(II), Cu(II), or Mn(II), X is an anionic ligand (NCS − , CN − , NO 3 − , and NCO − ), and L is a substituted pyridine or α-arylalkylamine. 51 Th remarkable chlathration ability of this type of complexes was first reported in 1957, 52 and since then, many studies have been done on this type of coordination compounds.53−56 The most interesting feature of these compounds is the rotational freedom of the metal-N(pyridine) bond.For the substituted pyridine ligands, there is additional torsional flexibility at the substituent, which allows the coordination compound to adjust its shape to accommodate different guest molecules of varying shapes and sizes.This property can also be used for the separation of similar guest molecules (isomers), depending on the selectivity of Werner clathrates toward the components of a mixture and whether or not guest uptake/removal is reversible.,60 Through modification of the pyridine ligand type within the metal coordination sphere, this type of coordination compound can exhibit different inclusion properties. Foinstance, coordination compound 2 exhibits only one type of clathrate due to the easy formation of a close-packed nonclathrate α-phase because it lacks substituents on the pyridine ring.Compound 1 is known to exist in two different polymorphic modifications: a microporous (β-form) phase that can change into a different type of clathrate when it interacts with guest molecules, and a densely packed, nonporous phase (α-form).61 Recently, this coordination compound has been studied in terms of shape-memory effects, since it possesses a porous polymorph.Through p-xylene vapor sorption studies, it was confirmed that compound 1 possesses properties of shapememory material (SMM), meaning that it transforms to a new polymorphic morphology in response to an external stimulus and reverts to its original phase when subjected to a different external stimulus.62 As there has been no systematic research on this type of halogen bond acceptor, in this work, the selected coordination compounds 1 and 2 were cocrystallized with different halogen bond donors, perfluorinated iodobenzenes: 1,2-diiodotetrafluorobenzene (12tfib), 1,3-diiodotetrafluorobenzene (13tfib), 1,4-diiodotetrafluorobenzene (14tfib), 1,3,5-trifluoro-2,4,6triiodobenzene (135tfib), and iodopentafluorobenzene (ipfb) (Scheme 1).

■ RESULTS AND DISCUSSION
Our screen for cocrystal synthesis was based on mechanochemical liquid-assisted grinding (LAG).As a means to explore the reactivity of solid reactants and the stoichiometric ratio, we first performed LAG of the reactants in stoichiometric ratios of 1:1 and 1:2 (coordination compound to halogen bond donor), respectively, and in the presence of a small amount of methanol or acetone.Grinding experiments were conducted in a Retsch MM200 mill using stainless steel jars under normal laboratory conditions (temperature ca. 25 °C, 40−60% relative humidity).Mechanochemical experiments were accompanied by crystallization from the solution in order to obtain bulk products and single crystals.Crystallization experiments were performed by dissolving a reactant mixture in an appropriate solvent with heating, followed by letting the solvent or solvent mixture cool down and evaporate at room temperature.The obtained products were characterized by thermogravimetric analysis (TGA), powder analysis (PXRD), and single-crystal Xray diffraction (SCXRD) (see the Supporting Information).A total of 14 new cocrystals were synthesized and characterized.For both coordination compounds, we obtained one cocrystal with each donor; in the case of the (1) 2 (14tfib) cocrystal, we additionally prepared three solvates (with acetone, nitromethane, and acetonitrile), and for compounds 1 and ipfb, we isolated two stoichiomorphs.Molecular and crystal structure determination by SCXRD of the prepared solids revealed that in all cocrystals, metal−organic acceptors and halogen bond donors are connected via S•••I halogen bonds involving a donor iodine atom and an isothiocyanate sulfur atom.Analysis of halogen bond parameters for each cocrystal confirmed the formation of halogen bonds, as the relative shortenings of S•••I distances are from 7 to 14.7%, while the S•••I−C angles are in the range from 160 to 180°(Table 1).It was shown that the Crystal Growth & Design isothiocyanate sulfur atom participates as an acceptor of at least two and, in some cases, three halogen bonds.Therefore, as both coordination compounds 1 and 2 contain two isothiocyanate groups, they act as multitopic acceptors that can form multiple halogen bonds in all prepared cocrystals (up to five in the cocrystal of compound 1 with 135tfib).
The possibility of forming multiple halogen bonds is a result of the great acceptor ability of the thiocyanate sulfur atom.First, in contrast to coordination compounds containing simple ligands that were previously reported as halogen bond acceptor species (for example, −CN, −Cl), the sulfur atom is more distant from the metal center and other ligands, making it sterically more accessible for halogen bonding.The second advantage of the isothiocyanate group is its flexibility and the ability to bend in order to participate in halogen bonding.
Isothiocyanate groups present in metal−organic units in the prepared cocrystals are bent at distinctly different angles.The isothiocyanate group's bending (Ni−N−C) angles in cocrystals of compound 1 are 137−177°, and in cocrystals of compound 2, they are 150−174°(see Tables S2 and S3).Furthermore, the geometry of the selected coordination compounds is also a relevant factor when it comes to the formation of multiple halogen bonds.The most prominent characteristic of the studied Werner coordination compounds is the rotational freedom of the metal−N(pyridine) bond.This facilitates easy access of the isothiocyanate group to the donor molecules and allows the coordination compound to reshape itself for optimal crystal packing.In all cocrystals, the molecular structure of coordination compounds is in good agreement with those of pure 1 and 2, reported as trans isomers.The Table 1.Halogen Bond Lengths (d), Angles (∠), and Relative Shortenings (R.S.) of X•••A Distances of Compound 1 and 2 Cocrystals

Crystal Growth & Design
Ni(II) atom is coordinated by four nitrogen atoms from pyridine molecules and two isothiocyanate groups, forming a structure with a distorted octahedral geometry.The only significant difference in coordination compounds is in the conformation of the pyridine ligands present on the metal center.In pure compound 1 pyridine ligands are arranged in the so-called propeller conformation (where opposite pyridine rings are orthogonal), while in pure compound 2, the opposite pyridine rings are planar.However, except for the (1)(14tfib) 2 cocrystal, in all other cocrystals of compounds 1 and 2, the pyridine rings adopt a propeller conformation.The rotational freedom of the Ni−N pyr bond allows the pyridine rings in various cocrystals to rotate at different angles.To quantify the flexibility of metal−organic units in the synthesized cocrystals, we analyzed angles between the plane of pyridine rings and the plane parallel to the metal center and the four nitrogen atoms from the pyridine ligands (see Tables S4 and S5).For compound  1).Exceptions are cocrystals with ditopic donor molecules that have donor atoms at a bent angle (13tfib and 12tfib), which form multiple halogen bonds with coordination compound 2 (Table 2).The reason behind this could be the absence of a methyl group on pyridine rings, which geometrically enables bridging two metal coordination compounds with at least one donor molecule (Figure 1c).Thermal analysis revealed that the prepared halogen-bonded cocrystals decompose in two steps upon heating.By evaluating the inflection point temperature for the step of thermal degradation (T d , Table 2; also see the Supporting Information), it was found that thermal stability is correlated with the nature of the halogen bond donor molecule.The cocrystals with halogen bond donors 12tfib, 14tfib, and 135tfib exhibit thermal degradation in the range of ca.90−115 °C, and those with ipfb and 13tfib decompose between 50 and 80 °C (see the Supporting Information).The thermal degradation temperatures are remarkably similar in spite of the different supramolecular architectures and significant differences in halogen bond donor melting points.Ipfb and 13tfib donor molecules are liquids at room temperature with melting points at ∼ −31 and ∼23 °C, while 12tfib, 14tfib, and 135tfib are solids with melting points at ∼50, ∼108, and ∼155 °C, respectively.Pure compound 1 decomposes at ∼90 °C, while compound 2 decomposes at ∼70 °C.Consequently, in most cases, cocrystals of compound 1 show higher degradation temperatures than cocrystals of 2. Cocrystal solvates are an exception to this principle, as they exhibit expectedly much lower temperatures of thermal degradation than nonsolvate forms.
The topologies of the halogen bond networks in most cocrystals are associated with the topicity and geometry of the halogen bond donor.As expected, the monotopic donor (ipfb) forms discrete 1:2 halogen-bonded complexes with both coordination compounds.We also isolated one stoichiomorph with 2:3 stoichiometry that also exhibits discrete halogenbonded units.Cocrystals based on 12tfib, 135tfib, and 14tfib exhibit higher dimensionality, halogen-bonded chains, and layers.In (1)(12tfib), (1)(14tfib) 2 , (2) 2 (14tfib) 3 , and ( 2)-(135tfib) cocrystals, the coordination compound and donor molecules form halogen-bonded chains, whereas in (1)-(135tfib) 2 , (2)(12tfib) 2 , and the obtained cocrystal solvates, the coordination compound and donor molecules form complex halogen-bonded layers.The ditopic donor molecule 13tfib forms cocrystals with both coordination compounds but different halogen bonding topologies.In the cocrystal with compound 1, discrete halogen-bonded units are formed, while with compound 2, donor molecules form complex halogenbonded layers.The crystal packing of all obtained cocrystals is similar, with metal−organic units closely packed together and the donor molecules stacked in another layer.The crystal structures of cocrystals can be described in terms of alternating layers/chains of metal−organic units and donor molecules (Figures 1b,d, 2c, 4b,d, 5b,d, 6b,e).Cocrystallization of ditopic donor 12tfib with compounds 1 and 2 resulted in the formation of cocrystals with different stoichiometries and supramolecular architectures.In the structure of (1)(12tfib), each metal−organic molecule is connected by I•••S halogen bonds between isothiocyanate sulfur atoms and two 12tfib molecules, with 12tfib acting as a ditopic halogen bond donor.This results in halogen-bonded chains (Figure 1a), which are further connected by C−H•••S hydrogen bonds into a 3D network, d(C30•••S2) = 3.826 Å.In the structure of (2)(12tfib) 2 , the asymmetric unit contains four crystallographically independent 12tfib molecules and two metal−organic molecules.Each metal−organic unit participates in halogen bonding, forming four I•••S halogen bonds between isothiocyanate sulfur atoms and 12tfib molecules.This results in a 2D halogen-bonded network (Figure 1c).The layers are further connected to a 3D network by C−H•••F contacts.In comparison with (1)(12tfib), it can be assumed that multiple I•••S halogen bonds of metal−organic units are present due to the different coordination compound periphery, i.e., due to the less sterically complicated geometry of the compound 2.This allows 12tfib molecules with a bent geometry (60°angle of propagation) to have easier access to the isothiocyanate group and the acceptor sulfur atom.
Cocrystallization of the most extensively used ditopic perfluorinated halogen bond donor, 14tfib, with compounds 1 and 2 yielded two cocrystals.Similar to (2)(12tfib) 2 , in (1)(14tfib) 2 , each metal−organic molecule participates in halogen bonding, forming four I•••S halogen bonds between isothiocyanate sulfur atoms and 14tfib molecules.This results in ladder-like halogen-bonded chains (Figure 2a), which are further connected into a 3D network by C−H•••F contacts.The cocrystals of compound 2 and 14tfib molecules exhibit 2:3 acceptor to donor stoichiometry.The asymmetric unit contains three crystallographically independent 14tfib molecules, of which two exhibit similar supramolecular bonding.They participate as ditopic donors in I•••S halogen bonds, with metal−organic molecules acting as ditopic halogen bond acceptors and forming halogen-bonded chains (Figure 2b).Surprisingly, the third crystallographically independent 14tfib molecule is not halogen-bonded at all, neither with neighboring metal−organic units nor with 14tfib molecules.This donor molecule plays the role of a void filler within the crystal packing.Furthermore, cocrystallization experiments from the solution involving compounds 1 and 14tfib additionally resulted in the formation of three solvates of (1)(14tfib) 2 , with nitromethane, acetone, or acetonitrile.Two solvates out of these three (with nitromethane and acetonitrile) were also prepared by liquidassisted grinding.On the other hand, mechanochemical experiments using a small amount of acetone yielded the nonsolvate cocrystal (1)(14tfib) 2 (Figure 3).The reason for that could be explained by solvate instability under milling conditions and the high vapor pressure of acetone.Interestingly, the same cocrystallization experiments using the above solvents with compound 2 did not result in the formation of solvates.
In terms of halogen bonding, the supramolecular architectures of all three solvates are comparable and very similar.In all solvates, each metal−organic molecule participates in halogen bonding forming three I      Finally, due to similar supramolecular architectures of cocrystals with volatile donors, ipfb and 13tfib, we were able to compare the reactivity of compounds 1 and 2 with donors using vapor sorption experiments.Aging of compound 1 in an atmosphere of 13tfib for 6 h at 70 °C and then for 2 days at room temperature afforded the (1)(13tfib) 2 cocrystal, identical to the cocrystal prepared by the solution method and mechanochemical experiments.Likewise, an aging experiment of compound 1 in an atmosphere of ipfb afforded a cocrystal product identical to the one prepared by the mechanochemical experiment, (1) 2 (ipfb) 3 , which is probably thermodynamically more stable than the (1)(ipfb) 2 cocrystal obtained by the solution method (Figures S28 and S29).Interestingly, aging experiments with compound 2 in the atmosphere of the same donor molecules at the same conditions did not result in the formation of cocrystals.A probable explanation for this outcome is the microporosity of the starting compound 1 (β-phase), which enables the incorporation of donor molecules in the structure and the formation of cocrystals (Figure 7).

■ CONCLUSIONS
The family of 14 halogen-bonded cocrystals prepared herein demonstrates that nickel(II) coordination compounds with isothiocyanate ions can be used as reliable halogen bond acceptors.In all cocrystals, the main acceptor atom is the isothiocyanate sulfur atom, which shows great potential for halogen bonding, forming up to three halogen bonds with perhalogenated benzenes.Therefore, as both coordination compounds contain two isothiocyanate groups, they act as multitopic acceptors that can form multiple halogen bonds.In this particular instance, coordination compound 1 participates in more halogen bonds than compound 2 in the majority of cocrystals.Since coordination compound 2 molecules, which contain pyridine ligands, tend to cluster closely in the crystal structure, fewer donor molecules can access the sulfur atom.Only in cocrystals with donor molecules that have donor atoms bent (13tfib and 12tfib) is the situation reversed, with more halogen bonds being formed with coordination compound 2.This may be due to the fact that pyridine rings lack a methyl group, which allows donor molecules to geometrically bridge two metal coordination compounds.By exploiting the geometric properties of the herein-used Werner coordination compounds, different multicomponent systems can also be synthesized (stoichiomorphs and cocrystal solvates).The rotational freedom of pyridine substituents and the flexibility of the isothiocyanate group enable these coordination compounds to adjust their shape to accommodate additional halogen bond donor molecules.By combining the structural properties of coordination compounds with halogen bond acceptor properties, additional ways of synthesis can also be used (vapor sorption experiments for microporous coordination compounds).This family of cocrystals demonstrates the uncovered potential of metal− organic systems, which can be used as building blocks in crystal engineering, providing multiple opportunities for synthesis.
■ EXPERIMENTAL SECTION Synthesis.All substances, except coordination compounds 1 and 2, were purchased from commercial sources and used without further purification.Coordination compounds 1 and 2 were synthesized according to the procedure described by Schaeffer et al. 52 Mechanochemical Synthesis.Cocrystal synthesis was performed by grinding mixtures of coordination compound 1 or 2 with a selected halogen bond donor.A mixture of reactants (up to 100 mg) was placed in a 10 mL stainless steel jar along with 20 μL of methanol or acetone and two stainless steel balls measuring 7 mm in diameter.The reaction mixture was then milled for 60 min in a Retsch MM200 Shaker Mill operating at 25 Hz, under normal laboratory conditions (temperature approximately 25 °C, 40−60% relative humidity).The resulting powders were characterized by powder X-ray diffraction.Details on mechanochemical experiments are given in the Supporting Information.
Vapor Sorption Experiments.For the synthesis of cocrystals containing liquid donor molecules 13tfib and ipfb and coordination compound 1, vapor sorption experiments were performed.The experiments were conducted in closed glass vials with caps.The powder of coordination compound 1 was placed in an open Eppendorf tube, and the liquid (100 μL of selected perhalogenated benzene) was placed at the bottom of the glass vial.The glass vials were left at 70 °C for 6 h and then left at room temperature for 2 days.The resulting powders were characterized by powder X-ray diffraction.The PXRD patterns are given in Figures S28 and S29.
Single Crystal Preparation.Crystals suitable for single-crystal Xray diffraction experiments were prepared by crystallization, mostly from methanol or a mixture of methanol with other solvents.Approximately 20 mg of a mixture of coordination compound 1 or 2 with a selected halogen bond donor was dissolved in 5.00 mL of the chosen solvent or mixture of solvents with heating.The crystals were obtained by the slow evaporation of the solvent at room temperature after a few days.Details of crystallization experiments are given in the Supporting Information.
Powder X-ray Diffraction.PXRD experiments were performed on a Malvern PANalytical Aeris Research Edition X-ray diffractometer with CuK α1 (1.54056 Å) radiation at 15 mA and 40 kV.The scattered intensities were measured with a line detector.The angular range was from 5 to 40°(2θ)) with integrated steps of 0.0054332°(2θ)), and the measuring time was 10.2 s per step.Data analysis was performed using the program package Data Viewer. 63

Crystal Growth & Design
Single-Crystal X-ray Diffraction.The crystal and molecular structures of the prepared cocrystals, cocrystal solvates, and stoichiomorphs were determined by single-crystal X-ray diffraction.Diffraction measurements were made on a Rigaku Synergy XtaLAB Xray diffractometer with graphite-monochromated MoK α (λ = 0.71073 Å) radiation.The data sets were collected using the ω scan mode over a 2θ range up to 64°(Synergy XtaLAB).Programs CrysAlis CCD, CrysAlis RED, and CrysAlisPro were employed for data collection, cell refinement, and data reduction, respectively. 64The structures were solved by direct methods and refined using the SHELXT, SHELXS, and SHELXL programs, respectively. 65,66Structural refinement was performed on F 2 by using all data.Non-hydrogen atoms were refined anisotropically and hydrogen atoms were placed in calculated positions and treated as riding on their parent atoms.All calculations were performed using the WINGX crystallographic suite of programs. 67Molecular structures of compounds and their molecular packing projections were prepared using Mercury 2022.3.0. 68Details of data collection and crystal structure refinement are listed in Table S1.Molecular structures showing the atom-labeling shemes are given in Figures S1−14.
Thermogravimetric Analysis.TGA measurements were performed on a Mettler-Toledo TGA/DSC 3+ module.The samples were placed in open 70 μL alumina pans and heated from 30 to 800 °C for coordination compounds 1, 2, and prepared cocrystals at a rate of 10 °C min −1 under nitrogen flow of 50 mL min −1 .The data collection and analysis were performed using the program package STARe Software 15.00. 69TGA curves are given in Figures S30−S45.

Scheme 1 .
Scheme 1.Molecular Schemes of Halogen Bond Acceptors and Halogen Bond Donors Used in This Study
The chains of halogen-bonded molecules are connected into layers by C−H•••S contacts (d(C14•••S1) = 3.784 Å), which are further linked into a 3D network by C− H•••F contacts.
•••S halogen bonds between isothiocyanate sulfur atoms and 14tfib molecules.One isothiocyanate sulfur atom participates in two I•••S halogen bonds, while the other is an acceptor of only one I•••S halogen bond.This type of halogen bonding connects the metal− organic molecules and 14tfib molecules into 2D layers which are further connected by C−H•••F contacts into a 3D network.Solvent molecules present in the crystal structures are connected to metal−organic units by C−H•••O/N hydrogen bonds (C−H•••O hydrogen bond in the acetone solvate, d(C10•••O1) = 3.396 Å; C−H•••N hydrogen bond in the acetonitrile solvate, d(C27•••N7) = 3.674 Å and C−H•••O hydrogen bond in the nitromethane solvate d(C27•••O1) = 3.312 Å).As with previously described cocrystals, cocrystallization of 135tfib with compounds 1 and 2 resulted in cocrystals with different stoichiometries and significantly different supramolecular architectures.However, in the (1)(135tfib) 2 cocrystal, each metal−organic molecule acts as a pentatopic halogen bond acceptor and, therefore, participates in halogen bonding forming five I•••S halogen bonds between isothiocyanate sulfur atoms and 135tfib molecules.One isothiocyanate sulfur atom participates in three I•••S halogen bonds and the

Figure 3 .
Figure 3. Crystal packing of cocrystal solvates and cocrystal obtained by the crystallization of 1 and 14tfib from (a) acetone, (b) nitromethane, (c) acetonitrile, (d) methanol, and (e) powder patterns obtained by the milling of the same coformers with previously mentioned liquid additives.The coordination compound is colored dark blue, while the solvent molecules are shown in light blue color.

Figure 7 .
Figure 7. Crystal packing of cocrystals obtained from 1 and liquid donor molecules (13tfib and ipfb) by using vapor sorption experiments or mechanochemical synthesis.
1, these angles range from 36 to 77°, and for compound 2, from 43 to 65°.Although compounds 1 and 2 differ only in one methyl group on the pyridine ligand, they nevertheless form very different cocrystals.The topicity and geometry of the donor molecule, as well as the geometric properties of the coordination compound, influence the stoichiometry and crystal packing.Pyridine ligands, which are present in compound 2, have a propensity to cluster closely in the crystal structure.On the other hand, compound 1 has additional torsional flexibility at the methyl substituent and can easily adjust its shape to accommodate different donor molecules.Compound 1 in cocrystals tends to form S•••I halogen bonds with more donor molecules compared to compound 2 (Table

Table 2 .
Decomposition Temperatures (T d ) of Compound 1 and 2 Cocrystals Determined by TGA Experiments