Crystal Structure of Bis(1-butyl-1-methypyrrolidinium) Perthiodicarbonate Complex

: Bis(1-butyl-1-methypyrrolidinium) perthiodicarbonate was obtained by the reaction of carbon disulfide with 1-butyl-1-methypyrrolidinium acetate ([BmPyrro][Ac]) in the liquid phase. Structural characterization of this original complex was achieved by single-crystal X-ray diffraction (SCXRD) analysis. The asymmetric unit of the title compound, C 2 S 6 · 2C 9 H 20 N, consisted of two crystallographically 1-methyl-1-butyl pyrrolidinium cations and one perthiodicarbonate anion. The complex C 2 S 6 · 2C 9 H 20 N crystallized in the monoclinic space group, C 2/c, and possessed the following cell parameters: a = 16.0970(10) Å, b = 14.7140(9) Å, c = 12.3280(8) Å, α = 90 ◦ , β = 112.3730(12) ◦ , γ = 90 ◦ , V = 2700.11 Å 3 , and Z = 8, Z’ = 0.5.


Introduction
Ionic liquids attract the attention of physical chemists due to their unique characteristics and wide spectrum of applications.As they have very good dissolution properties for most organic and inorganic compounds, they are increasingly used neutrally by chemists as substitutes for traditional organic solvents or as an excellent medium for the synthesis and stabilization of nanoparticles.They also may have a role in trapping small molecules such as CO 2 [1,2].In recent years, they have also been used for new crystallization strategies, including the crystallization of solids with high and low melting points, and they are found as additives in the crystallization conditions of macromolecules such as proteins [3].

Synthesis of Bis(1-butyl-1-methypyrrolidinium) Perthiodicarbonate 4
Upon the dissolution of CS2 in [BmPyrro] [Ac] 1, a blood-red solution was observed, showing that a reaction had occurred.This blood-red color of the CS2-[BmPyrro] [Ac] solution was due to the presence of CS3 2− anions.Previous 1 H, 13 C NMR, and UV-visible investigations conducted by our research team showed that the reaction of [BmPyrro] [Ac] 1 with CS2 led, via coupled complex reactions, to the degradation of this molecule to form several main adducts, namely, CO2, OCS, thioacetate anion (CH3COS − ) 2, and, as a minor species, trithiocarbonate anion (CS3 2− ) 3 (Scheme 1) [4,5].Such products formed in this system have already been found in the solution of CS2 in 1-butyl-3-methylimidazolium acetate ([Bmim] [Ac]) [6].In order to isolate one of these 1-butyl-1-methypyrrolidinium salts, we investigated some crystallographic assays.The different tests made it possible to isolate a single crystalline form.Thus, orange crystals in the shape of a thick diamond were obtained.Surprisingly, the data of their measurement revealed the formation of a complex consisting of two 1-methyl-1-pyrrolidinium cations coupled with a single perthiodicarbonate anion (Scheme 1).This formation of perthiodicarbonate anion from a reaction medium containing CS2 and CS3 2− initially formed has already been described in the literature [7,8].Scheme 1. Synthesis of bis(1-butyl-1-methypyrrolidinium) perthiodicarbonate 4.

Crystallographic Structure
The title compound crystallized in the monoclinic C 2/c space group.The asymmetric unit of the title compound, C2S62C9H20N, consisted of one 1-methyl-1butyl-pyrrolidinium cation and one half perthiodicarbonate anion; the whole anion was obtained by symmetry around a 2-fold rotation axis situated at 0,y,1/4.The cation was disordered into two positions, with the respective occupation of 86/14%, which corresponded approximately to a 90° rotation around the alkyl axis of the molecule.Both conformations were stabilized by different but similar S•••H short contacts; however, a

Results and Discussion
2.1.Synthesis of Bis(1-butyl-1-methypyrrolidinium) Perthiodicarbonate 4 Upon the dissolution of CS 2 in [BmPyrro] [Ac] 1, a blood-red solution was observed, showing that a reaction had occurred.This blood-red color of the CS 2 -[BmPyrro] [Ac] solution was due to the presence of CS 3 2− anions.Previous 1 H, 13 C NMR, and UV-visible investigations conducted by our research team showed that the reaction of [BmPyrro] [Ac] 1 with CS 2 led, via coupled complex reactions, to the degradation of this molecule to form several main adducts, namely, CO 2 , OCS, thioacetate anion (CH 3 COS − ) 2, and, as a minor species, trithiocarbonate anion (CS 3 2− ) 3 (Scheme 1) [4,5].Such products formed in this system have already been found in the solution of CS 2 in 1-butyl-3-methylimidazolium acetate ([Bmim] [Ac]) [6].In order to isolate one of these 1-butyl-1-methypyrrolidinium salts, we investigated some crystallographic assays.The different tests made it possible to isolate a single crystalline form.Thus, orange crystals in the shape of a thick diamond were obtained.Surprisingly, the data of their measurement revealed the formation of a complex consisting of two 1-methyl-1-pyrrolidinium cations coupled with a single perthiodicarbonate anion (Scheme 1).This formation of perthiodicarbonate anion from a reaction medium containing CS 2 and CS 3 2− initially formed has already been described in the literature [7,8].

Synthesis of Bis(1-butyl-1-methypyrrolidinium) Perthiodicarbonate 4
Upon the dissolution of CS2 in [BmPyrro] [Ac] 1, a blood-red solution was observed, showing that a reaction had occurred.This blood-red color of the CS2-[BmPyrro] [Ac] solution was due to the presence of CS3 2− anions.Previous 1 H, 13 C NMR, and UV-visible investigations conducted by our research team showed that the reaction of [BmPyrro] [Ac] 1 with CS2 led, via coupled complex reactions, to the degradation of this molecule to form several main adducts, namely, CO2, OCS, thioacetate anion (CH3COS − ) 2, and, as a minor species, trithiocarbonate anion (CS3 2− ) 3 (Scheme 1) [4,5].Such products formed in this system have already been found in the solution of CS2 in 1-butyl-3-methylimidazolium acetate ([Bmim] [Ac]) [6].In order to isolate one of these 1-butyl-1-methypyrrolidinium salts, we investigated some crystallographic assays.The different tests made it possible to isolate a single crystalline form.Thus, orange crystals in the shape of a thick diamond were obtained.Surprisingly, the data of their measurement revealed the formation of a complex consisting of two 1-methyl-1-pyrrolidinium cations coupled with a single perthiodicarbonate anion (Scheme 1).This formation of perthiodicarbonate anion from a reaction medium containing CS2 and CS3 2− initially formed has already been described in the literature [7,8].Scheme 1. Synthesis of bis(1-butyl-1-methypyrrolidinium) perthiodicarbonate 4.

Crystallographic Structure
The title compound crystallized in the monoclinic C 2/c space group.The asymmetric unit of the title compound, C2S62C9H20N, consisted of one 1-methyl-1butyl-pyrrolidinium cation and one half perthiodicarbonate anion; the whole anion was obtained by symmetry around a 2-fold rotation axis situated at 0,y,1/4.The cation was disordered into two positions, with the respective occupation of 86/14%, which corresponded approximately to a 90° rotation around the alkyl axis of the molecule.Both conformations were stabilized by different but similar S•••H short contacts; however, a Scheme 1. Synthesis of bis(1-butyl-1-methypyrrolidinium) perthiodicarbonate 4.

Crystallographic Structure
The title compound crystallized in the monoclinic C 2/c space group.The asymmetric unit of the title compound, C 2 S 6 •2C 9 H 20 N, consisted of one 1-methyl-1-butyl pyrrolidinium cation and one half perthiodicarbonate anion; the whole anion was obtained by symmetry around a 2-fold rotation axis situated at 0,y,1/4.The cation was disordered into two positions, with the respective occupation of 86/14%, which corresponded approximately to a 90 • rotation around the alkyl axis of the molecule.Both conformations were stabilized by different but similar S•••H short contacts; however, a very short S•••H contact and numerous H•••H interactions, potentially repulsive, were found for the minor conformation.Only the main position is drawn in Figure 2 for clarity.The bond distances and angles of our pyrrolidinium cation were all within normal ranges [9,10], with the butyl substituent adopting the energetically preferred anti conformation with an N1-C6-C7-C8 torsional angle of 173.0(2)°.The pyrrolidine heterocycle adopting the energetically preferred envelope (Cs) ring conformation with an interplanar dihedral angle between the C7A-10A-N1A and C9A-C8A-C10A-C7A planes in the pyrrolidine ring was found at 32.9(3)°.
The network cohesion was ensured by anion-cation interactions through close H•••S contacts involving the methyl group, CH2 of the pyrrole ring of the pyrrolidinium cation, and the four sulfur atoms of the CS2 -moiety of the anion.Each anion interacted with six cations (two with a double S•••H contact with the methyl of the cation, Figure 3a; 2 with a single S•••H contact with the methyl of the cation or the CH2 of the pyrrolidine ring, Figure 3b), whereas the cations interacted with three anions.All these interactions propagated in the three directions to form the crystal network.According to the classification of T. Steiner [13], the S•••H short contacts can be considered weak hydrogen bonding, providing that the distance is close to or below the sum of Van   ORTEP (Oak Ridge Thermal Ellipsoid Plot) drawing of the bis(1-butyl-1methypyrrolidinium) perthiodicarbonate with thermal ellipsoids at the 50% level.The labeling scheme is shown for the asymmetric unit only.The minority part of the disordered cation is removed for clarity.
The bond distances and angles of our pyrrolidinium cation were all within normal ranges [9,10], with the butyl substituent adopting the energetically preferred anti conformation with an N1-C6-C7-C8 torsional angle of 173.0(2) • .The pyrrolidine heterocycle adopting the energetically preferred envelope (Cs) ring conformation with an interplanar dihedral angle between the C7A-10A-N1A and planes in the pyrrolidine ring was found at 32.9(3) • .
The network cohesion was ensured by anion-cation interactions through close H•••S contacts involving the methyl group, CH 2 of the pyrrole ring of the pyrrolidinium cation, and the four sulfur atoms of the CS 2 − moiety of the anion.Each anion interacted with six cations (two with a double S•••H contact with the methyl of the cation, Figure 3a; 2 with a single S•••H contact with the methyl of the cation or the CH 2 of the pyrrolidine ring, Figure 3b), whereas the cations interacted with three anions.All these interactions propagated in the three directions to form the crystal network.According to the classification of T. Steiner [13], the S•••H short contacts can be considered weak hydrogen bonding, providing that the distance is close to or below the sum of Van der Waals radii and that the D-H•••S angle is close to 180 • (>110 • ).As the S•••H short contacts of the title compound fulfilled these requirements, they could be considered as weak hydrogen bonding (S•••H distance around 2.75 A within the 2.2-3.2range found in the CSD data for similar interactions and D-H•••S angle > 140 • ).Nevertheless, the C-S•••H angle was far from the ideal value of 105 • and did not lie within the S-C-S plane, which most probably suggests the mainly electrostatic nature of these interactions.
the very scarce crystal structures containing this perthiodicarbonate moiety, as only five entries were found in the CSD database [11,[14][15][16][17].It is interesting that the conformation of this dianion is quasi-identical within all the published crystal structures as the RMSD (Root Mean Square Deviation) ranged from 0.065 Å to a maximum value of 0.136 Å between our dianion molecular structure and that of the bis(tetraphenylphosphonium) perthiodicarbonate [14].

Materials and Methods
Commercial reagents were used as received, without additional purification.Crystallographic data were collected at 298 K on a Bruker APEX Duo diffractometer (Bruker France S.A.S., Champs-sur-Marne, France) using monochromatic Mo-Kα radiation (λ = 0.71073 Å).

Bis(1-butyl-1-methypyrrolidinium) Perthiodicarbonate
CS2 was dissolved in [BmPyrro][Ac] at a 0.02 mole fraction at room temperature.A slight release of heat was observed as well as a strong red coloring of the sample.The solution was then distributed into drops of different volumes (4 μL to 10 μL) on a siliconized glass slide.The glass plate was then placed in a vacuum desiccator (0.05 mbar) overnight to remove residual water traces and CO2 and OCS forms during the chemical reaction between [BmPyrro][Ac] and CS2 [4][5][6]; then, it was placed at 4 degrees Celsius for 72 h.Suitable green-orange diamond-shaped crystals 300 × 200 × 100 μm long were observed in the drops.The crystals were then preserved in paraton oil before being measured.

Crystal and Refinement Data
The structure of bis(1-butyl-1-methypyrrolidinium) perthiodicarbonate was established using X-ray crystallography (Figure 2) [18].The green-orange crystal of the title compound was obtained by slow evaporation under reduced pressure from the reaction solution mixture, as described above.
The collected data were reduced using SAINT software, version 6.45 (SAINT, Bruker AXS Inc., Madison, WI, USA), and all reflections were used for unit-cell refinement.The crystal structure was solved by direct methods and successive Fourier difference syntheses with the SHELXS program and refined on F 2 by anisotropic full-matrix weighted least square methods using SHELXL within the OLEX2 package [19][20][21].All It is worth noting that the structural description of this original dianion completes the very scarce crystal structures containing this perthiodicarbonate moiety, as only five entries were found in the CSD database [11,[14][15][16][17].It is interesting that the conformation of this molecular dianion is quasi-identical within all the published crystal structures as the RMSD (Root Mean Square Deviation) ranged from 0.065 Å to a maximum value of 0.136 Å between our dianion molecular structure and that of the bis(tetraphenylphosphonium) perthiodicarbonate [14].

Materials and Methods
Commercial reagents were used as received, without additional purification.Crystallographic data were collected at 298 K on a Bruker APEX Duo diffractometer (Bruker France S.A.S., Champs-sur-Marne, France) using monochromatic Mo-Kα radiation (λ = 0.71073 Å).

Bis(1-butyl-1-methypyrrolidinium) Perthiodicarbonate
CS 2 was dissolved in [BmPyrro][Ac] at a 0.02 mole fraction at room temperature.A slight release of heat was observed as well as a strong red coloring of the sample.The solution was then distributed into drops of different volumes (4 µL to 10 µL) on a siliconized glass slide.The glass plate was then placed in a vacuum desiccator (0.05 mbar) overnight to remove residual water traces and CO 2 and OCS forms during the chemical reaction between [BmPyrro][Ac] and CS 2 [4][5][6]; then, it was placed at 4 degrees Celsius for 72 h.Suitable green-orange diamond-shaped crystals 300 × 200 × 100 µm long were observed in the drops.The crystals were then preserved in paraton oil before being measured.

Crystal and Refinement Data
The structure of bis(1-butyl-1-methypyrrolidinium) perthiodicarbonate was established using X-ray crystallography (Figure 2) [18].The green-orange crystal of the title compound was obtained by slow evaporation under reduced pressure from the reaction solution mixture, as described above.
The collected data were reduced using SAINT software, version 6.45 (SAINT, Bruker AXS Inc., Madison, WI, USA), and all reflections were used for unit-cell refinement.The crystal structure was solved by direct methods and successive Fourier difference syntheses with the SHELXS program and refined on F 2 by anisotropic full-matrix weighted least square methods using SHELXL within the OLEX2 package [19][20][21].All non-H atoms except those of the minority disordered part of the cation were refined anisotropically.H-atoms were analyzed according to the riding model and included for structure factor calculation, but not refined.
Molbank 2024, 2024, x FOR PEER REVIEW 3 of 6 very short S•••H contact and numerous H•••H interactions, potentially repulsive, were found for the minor conformation.Only the main position is drawn in Figure 2 for clarity.

Figure 2 .
Figure 2. ORTEP (Oak Ridge Thermal Ellipsoid Plot) drawing of the bis(1-butyl-1methypyrrolidinium) perthiodicarbonate with thermal ellipsoids at the 50% level.The labeling scheme is shown for the asymmetric unit only.The minority part of the disordered cation is removed for clarity.
der Waals radii and that the D-H•••S angle is close to 180° (>110°).As the S•••H short contacts of the title compound fulfilled these requirements, they could be considered as weak hydrogen bonding (S•••H distance around 2.75 A within the 2.2-3.2range found in the CSD data for similar interactions and D-H•••S angle > 140°).Nevertheless, the C-S•••H angle was far from the ideal value of 105°

Figure 2 .
Figure 2.ORTEP (Oak Ridge Thermal Ellipsoid Plot) drawing of the bis(1-butyl-1methypyrrolidinium) perthiodicarbonate with thermal ellipsoids at the 50% level.The labeling scheme is shown for the asymmetric unit only.The minority part of the disordered cation is removed for clarity.

Figure 3 .
Figure 3.View of the anion-cation interaction showing the (a) double S•••H contacts and (b) single S•••H contacts.

Figure 3 .
Figure 3.View of the anion-cation interaction showing the (a) double S•••H contacts and (b) single S•••H contacts.