Comparison of DMF and DMSO as Solvents

Research will be limited to:
- Solvents: DMF and DMSO
- Application: Organic Synthesis
- Coordination Target: Metals
- Property: Removal Difficulty

Strategy: I will investigate the comparative coordination chemistry of DMF and DMSO with transition metals, specifically focusing on their relative binding affinities (donor numbers) and the stability of the resulting metal-solvent complexes. Simultaneously, I will research the physical properties and practical methodologies for their removal from reaction mixtures, including boiling points, azeotrope formation, and specialized work-up techniques (e.g., aqueous washing vs. lyophilization). This dual approach will provide the scientific basis for comparing their 'removal difficulty' in the context of metal-catalyzed organic synthesis.
Queries:
- DMF vs DMSO coordination strength transition metal complexes donor number
- removal of DMF and DMSO from organic synthesis reaction mixtures comparison
- stability constants metal-DMF vs metal-DMSO complexes organic synthesis
- azeotropic removal of DMF and DMSO solvents workup
- residual DMF DMSO metal coordination removal difficulty synthesis

Executing 5 concurrent searches:
- DMF vs DMSO coordination strength transition metal complexes donor number
- removal of DMF and DMSO from organic synthesis reaction mixtures comparison
- stability constants metal-DMF vs metal-DMSO complexes organic synthesis
- azeotropic removal of DMF and DMSO solvents workup
- residual DMF DMSO metal coordination removal difficulty synthesis

Found 7 papers. Key excerpts:

Solubility of Hybrid Halide Perovskites in DMF and DMSO. — Andrey A Petrov et al., 2021

Hybrid lead–halide perovskites with a general formula APbX 3 (A = CH 3 NH 3 + , CH(NH 2 ) 2 + ; X = I − , Br − , Cl − ) represent a new perspective class of materials for solar cells and optoelectronics as they possess a set of outstanding properties such as high absorption coefficients, high charge carrier mobility and intense luminescence [ 1 , 2 , 3 ]. Because of their high solubility in polar coordinating solvents, hybrid perovskites can be easily obtained using simple and cheap solutions methods such as spin-coating, slot-die coating, blade-coating, etc. [ 4 , 5 ]. Dimethylformamide (DMF), dimethyl sulfoxide (DMSO) and gamma-butyrolactone (GBL) are the most frequently used solvents to obtain hybrid perovskites, either in a form of polycrystalline films or as single crystals [ 5 , 6 ].
Although perovskite solutions with concentrations >1 M are commonly used, the solubility of single precursors, as well as the perovskites with different compositions, are almost never reported. In particular, only fragmentary data are present such as the solubility behavior of bromide perovskites in DMF and iodide perovskites in GBL, reported by Saidaminov et al. [ 7 ], which raises a question about the character of solubility behavior in other perovskite-solvent systems. Another consequence of the absence of reliable solubility data of perovskites in DMF, DMSO or mixed solvents is neglecting the fact that solutions used for perovskite processing prepared at elevated temperatures are, in fact, often oversaturated when deposited, which leads to reduced reproducibility and weak morphology control when processing light-absorbing layers [ 8 ].
Currently, despite the widespread use of perovskite solutions for almost a decade, almost no systematic studies on the solution chemistry have been reported [ 9 ]. Moreover, particular interactions between solvents and solutes have not been a subject of thorough investigation until very recently. The configurations of solvated iodoplumbate complexes in DMSO and DMF solutions of MAPbI 3 were modeled in [ 10 , 11 ]. In 2020, Tutantsev et al. proposed a

model explaining the interaction and relative solubility of hybrid perovskites in different solvents and showed that it relies on strong donor−acceptor, ion−dipole and hydrogen bonding interactions which can be described by donor numbers, dipole moments and Hansen hydrogen bonding parameters, respectively [ 12 ].
Herein, we present for the first time a complete set of solubility data for MAPbI 3 , FAPbI 3 , MAPbBr 3 and FAPbBr 3 perovskites in DMF and DMSO, and rationalize the observed differences in solubility by analyzing the donor numbers of the solvents and halide anions.
We found that the solubilities of iodide perovskites, MAPbI 3 and FAPbI 3 , in DMF steadily increase upon heating from 30 °C to 90 °C, demonstrating direct solubility behavior ( Figure 1 a). In contrast, the solubilities of bromide perovskites, MAPbBr 3 and FAPbBr 3 , decrease upon heating (so called inverse solubility behavior) [ 7 ] ( Figure 1 a). At temperatures above 90 °C, the solubility of MAPbI 3 in DMF continues to grow, whereas that of FAPbI 3 drops significantly.
In DMSO, the solubilities of three perovskites MAPbI 3 , FAPbI 3 and FAPbBr 3 grow in the whole measured temperature range of 30–120 °C, while the solubility of MAPbBr 3 demonstrate a steep increase upon heating up to 45 °C, reaching 5 M and then slowly decreases above 75 °C ( Figure 1 b).
The observed differences in the solubility behavior on solution composition can be explained by considering the processes associated with the solid–liquid phase equilibrium, which includes: (1) the crystal lattice breakdown of the solid phase that can release the solvent molecules if the solid phase was a solvate, and (2) the formation of haloplumbate complexes with a specific configuration of the first coordinating sphere of Pb 2+ . The latter, in turn, includes a complex equilibrium between halide ions and solvent molecules for the coordination with Pb 2+ ions and entropy change associated with the number of solvent molecules bound to the haloplumbate complexes, such as [Pb(Hal) n

(S) 6−n ] (n−2)− (Hal = I − , Br − , Cl − ; S = GBL, DMSO, DMF).
While the crystal lattice energy of the perovskites increases in the series MAPbI 3 –MAPbBr 3 –MAPbCl 3 according to the experimental thermodynamic data [ 13 ], the intensity of the interaction of solvent molecules with Pb 2+ ions can be described by donor numbers (DN), as it was shown in [ 12 ]. The donor number is determined on the basis of the experimental enthalpies of complexation with a strong electron-pair acceptor SbCl 5 , defined for the chosen solvents as DN(GBL) = 18.0, DN(DMF) = 26.6 and DN(DMSO) = 29.8 [ 14 ]. Similarly, to characterize the intensity of the interaction of halide ions with Pb 2+ in the solutions, the donor numbers of I − , Br − and Cl − can be considered, as determined in the study [ 15 ]: DN(I − ) = 28.9, DN(Br − ) = 33.7 and DN(Cl − ) = 36.2. Although the comparison of the relative donor numbers of the solvents with the donor numbers of the halide anions cannot be carried out directly, the relative changes in DN in the series of solvents or halides clearly elucidates solubility regularities and can explain the character of solubility curves for hybrid perovskites with various compositions, also considering their different crystal lattice energies and their roughly equal-entropy growth after dissolving ( Table 1 ).
The smallest donor numbers among DMSO, DMF and GBL are observed for GBL (DN = 18.0). On the one hand, this value seems to be large enough for the solvent to compete with iodide anions (DN(I − ) = 28.9) and to bind directly with Pb 2+ in haloplumbate complexes. This leads to the solubility of MAPbI 3 and FAPbI 3 > 1.5 M. On the other hand, pure PbI 2 is not soluble in GBL [ 16 ] which indicates that the GBL donor number is not large enough to effectively solvate PbI 2 molecules. Furthermore, GBL cannot

Mol-ecular structure of fac -[Mo(CO) 3 (DMSO) 3 ]. — Benedict J Elvers et al., 2021

[Mo(CO) 6 ] is a commercially available starting material that is easy to handle. It is, however, not particularly reactive. In order to facilitate quicker and/or more complete reactions, it can be activated by replacing some of the CO ligands by solvent ligands. This is often done with aceto­nitrile, which results in fac -[Mo(CH 3 CN) 3 (CO) 3 ] complexes. Other examples comprise, for instance, [Mo(CO) 5 (THF)] (THF = tetra­hydro­furane), [Mo(CO) 4 (nbd)] (nbd = norbornadiene) and fac -[Mo(CO) 3 (DMF) 3 ] (DMF = di­methyl formamide) (Wieland & van Eldik, 1991 ▸ ; Mukerjee et al. 1988 ▸ ; Villanueva et al. , 1996 ▸ ). Depending on the co-ligand, the stability and reactivity of the resultant complex can be fine-tuned. It was, for example, previously emphasized that the pyridine complexes surpass aceto­nitrile complexes in reactivity (Kuhl et al. , 2000 ▸ ). In cases where the carbonyl ligands are supposed to be retained, stronger carbon­yl–metal inter­actions and very weak metal–co-ligand inter­actions are preferred. In cases where the carbonyl ligands shall also be replaced, the opposite is true. The grade of activation is reflected in the C≡O bond lengths and the Mo—C carbon­yl bond lengths. For the former, infrared spectroscopy provides an easy way to probe the strength of the bond between carbon and oxygen with stretching vibration bands in a normally not populated region of the infrared wavenumber range (around 2000 cm −1 ). This bond strength depends directly on the metal–carbon inter­action as the stronger the metal carbon bond, the weaker the carbon–oxygen bond becomes (Elschenbroich, 2003 ▸ ) and these again depend on the strengths of the trans -located co-ligand-to-metal inter­actions. A short and strong C≡O bond is, hence, indicative of only weak carbonyl metal–ligand inter­actions and concomitantly impaired complex stability. FT–IR therefore constitutes a particularly

helpful assessment tool, in particular in cases where no crystal structure is available. On the other hand, it is also quite useful to combine both methods, if possible, for validation purposes and adding reliability to future spectroscopic evaluation of related species. In the course of synthesizing molybdenum–carbonyl complexes as starting materials and in a search for the optimum balance between reactivity and stability, various solvent complexes were tested in our group. During these experiments, DMSO was considered beneficial and the title complex fac -[Mo(CO) 3 (DMSO) 3 ] was prepared and crystallized. This complex was first reported in the literature in 1959 (Hieber et al. , 1959 ▸ ), but its crystal structure remained, apparently, elusive to date. Notably, it also appears that since then the complex has never been mentioned again. As very nice and suitable crystals of the title compound were obtained, an X-ray diffraction structural analysis was carried out. The respective high-quality results, along with the signatory carbonyl FT–IR stretch bands are presented here.
fac -[Mo(CO) 3 (DMSO) 3 ] crystallizes in the triclinic space group P . The asymmetric unit represents the entire mol­ecule (Fig. 1 ▸ ) while Z = 2. The central zero-valent molybdenum is coordinated in a facial fashion by three neutral di­methyl sulfoxide and three neutral carbonyl ligands, i.e. it is embraced by a C 3 O 3 donor set. The coordination geometry of the complex is essentially octa­hedral, showing an almost perfect Bailar twist angle (Wentworth, 1972 ▸ ) of 59.08°. The average cis -donor—Mo—donor angle between the three coordinated DMSO mol­ecules is, at approximately 79°, slightly more acute compared to that of the carbonyl ligands, at approximately 84° despite di­methyl sulfoxide being considerably more bulky. The three trans angles across molybdenum range from 173.76 (16) to 178.08 (18)°, indicating a slight distortion from ideal octa­hedral geometry.
The structures of the title compound and those of chemic­ally very closely related fac -[Mo(CH 3 CN) 3 (CO) 3 ] (

refcode: IZUQAV; Antonini et al. , 2004 ▸ ) and fac -[Mo(CO) 3 (DMF) 3 ] (refcode: WAJWIN; Pasquali et al. , 1992 ▸ ) are, as expected, quite similar in the immediate coordination sphere surrounding molybdenum, which is also evident from the overlaid mol­ecular structures (Fig. 2 ▸ ). Still, some specifics in the metrical parameter details in the individual species are quite notable.
In particular the C—O and Mo—C distances are inter­esting when compared to those of fac -[Mo(CH 3 CN) 3 (CO) 3 ] and fac -[Mo(CO) 3 (DMF) 3 ]. Whereas the average C—O bond length in fac -[Mo(CO) 3 (DMSO) 3 ] is 1.170 (6) Å and the average Mo—C distance is 1.911 (5) Å, in fac -[Mo(CH 3 CN) 3 (CO) 3 ] the average C—O and Mo—C distances are 1.167 and 1.923 Å, respectively. In fac -[Mo(CO) 3 (DMF) 3 ], these values are 1.172 Å (C—O) and 1.909 Å (Mo—C). The complexes with the O-donor solvent coordination exhibit longer C—O and shorter Mo—C distances, which is indicative of stronger bonds between carbonyl and molybdenum than in the case of the N-donor solvent. At the same time, this suggests that the share of electron density between molybdenum and coordinated solvent is decreased in the case of O-donor solvents and increased in the case of the N-donor solvent. This is also reflected in the reported IR data. In the case of aceto­nitrile, two C—O bands are reported, and for the other two complexes, three. In perfectly octa­hedral symmetry, only two bands would be expected (Elschenbroich, 2003 ▸ ). The presence of three bands therefore indicates a distortion of the complex from perfect symmetry. The comparison of the highest energy infrared bands with the shortest observed C—O bond lengths in

Impact of dielectric constant of solvent on the formation of transition metal-ammine complexes — Debashree Manna et al., 2023

1 INTRODUCTION

     Solvents are a critical component in nearly all chemical processes, as they significantly impact the stability of the complexes involved. This influence is commonly determined as the solvation energy (ΔEsolv), defined as


              Δ⁢Esolv=Esolv⁡(D−A)−(Esolv⁡(D)+Esolv(A)),
              (1)where Esolv⁡(D−A),Esolv⁡(D), and Esolv⁡(A) are solvation energies of the complex (D−A) and subsystems (D) and (A), respectively. Its value is determined by (i) the change in the solvent accessible surface area (SASA) and (ii) the change in the charge distribution that occurs during complex formation. While the SASA consistently destabilizes the complex, the effect of charge redistribution depends on the bond type and the extent of the charge redistribution. The destabilizing effect predominates for complexes with small charge redistribution, such as those formed by sharing electrons to create a covalent bond, and most non-covalent complexes.1-3 The dative bond (DB) complexes, which have a dual bonding character combining covalent and ionic contributions (see Equation 2), are an intriguing group in this regard.4, 5



              Ψdative⁡(D+−A−)=a⁢Ψcovalent⁡(D−A)+b⁢Ψionic⁡(D+,A−)
              (2)




     Previous research has indicated that the ionic component of the wavefunction is responsible for the most significant solvent effects.6-9 It reflects the changes in the charge redistribution during complexation due to a charge transfer between the two subsystems. In general, for the neutral DB complexes, the complex stabilizes in polar solvents whenever the dipole moment in the complex increases, leading to the negative value of ΔEsolv. The stability of positively charged DB complexes in a solvent is largely dependent into the solvent's ability to solvate the cations and the ligands, which can modify the ligand binding properties and the cation selectivity.10-15 In these cases, the charge separation reduces in the complex relative to isolated subsystems, leading to destabilization of the complex in the solvent. The destabilization is more pronounced with increasing solvent polarity resulting in the positive ΔEsolv value.16

     The DB complexes formed between metal and ligands are essential in the bio- and environmental-related fields and possible medical applications.17-19 However, there are very limited computational studies that have addressed the solvation effect on the nature of the DB complexes containing transition metal ions and the dependence of the stability of these complex species on the dielectric constant of the solvent.16 Note that the thermodynamic stability of metal–ligand complexes is a crucial factor that determines metal ion selectivity and has tremendous applications in solvent extraction, environmental speciation,20 and more.

     In this work, we have theoretically evaluated the effect of solvents on the stability and thermodynamic properties of complex cations of the [M(NH3)n]2+/3+ type using computational methods. Predominantly, coordination complexes bearing ammine ligands are widely observed in 3d transition metals. Consequently, our focus primarily rested on examining 3d transition metals in this context. Nevertheless, for the sake of comprehensive testing, we have extended our calculations to [Cd(NH3)n]2+ complexes characterized by a [4d10] configuration, as well as [Hg(NH3)n]2+ complexes, which exhibit a [5d10

] configuration. The reasons for the changes in the calculated values of thermodynamic parameters of the complex of several transition metals and ammonia as ligands in solvents with different polarities are discussed. The mathematical correlation of the dependence of the dielectric constant of the solvent (ε) on binding free energies (ΔG) and ΔEsolv is determined, aiming to understand the role of ε on ΔG and ΔEsolv for metal ion–ligand complexes. To the best of our knowledge, no attempt has yet been made to obtain a general trend for predictions of complex stability without performing further quantum chemical calculations. The solvent effect is also discussed regarding changes in the coordination numbers of transition metals in complexes.
2 RESULTS AND DISCUSSION

     Table S1 presents the results of geometry optimizations, particularly the lengths of the MN dative bond in [M(NH3)n]2+/3+ complexes in the gas phase, CS2, acetone, and DMSO. The data show a general MN bond length trend shortening with increasing solvent polarity. More specifically, there is an inverse dependency between MN bond lengths and Ɛ. Therefore, the effect of solvent polarity on MN bond lengths is significant for the solvents with low dielectric constant and almost negligible for the solvents with higher dielectric constant values. Spin states considered for the complexes are also listed in the table.

     Figure 1A,B displays a comparison of the interaction energies in Zn(NH3)4]2+ and Zn(NH3)6]2+ as a function of solvent polarity, calculated for all solvents at the PBE0-D3/def2-TZVPP approach and the CCSD(T)/def2-TZVPP method, which is considered as the “gold standard.” These results justify the use of the PBE0-D3 for further studies. It has been seen that for all the di-cationic complexes T1 diagnostic values are below 0.02 thus single reference methods are acceptable here. Figure 1C shows the behavior of Gibbs free

Electronic Structure and Optical Properties of Tin Iodide Solution Complexes. — Freerk Schütt et al., 2023

Tin halide perovskites are emerging materials
for photovoltaic
and optoelectronic applications, 1 − 3 responding to the pressing quest
for nonpolluting and nontoxic compounds for solar cells. 4 , 5 Like their Pb-based counterparts, these systems are produced via
solution chemistry, and the efficiency of the resulting thin films
crucially depends on the physicochemical properties of the precursors. 6 − 8 The choice of the solvent is a particularly critical point as it
can induce oxidation 9 − 11 and thus contribute to the rapid degradation of the
material in operational conditions. 6 , 12 , 13 As a result of these efforts, it is now common knowledge
that the popular solvent dimethyl sulfoxide (DMSO) is detrimental
for the stability of tin halide perovskite solar cells. 6 , 8 This finding has stimulated the search for guiding principles toward
the choice of optimal solvents for the synthesis of this class of
materials. 14 , 15
The missing piece of the
puzzle is a systematic, first-principles
analysis of the microscopic properties of tin halide solution complexes
as building blocks for corresponding perovskite structures. Similar
studies performed on lead halide counterparts have significantly contributed
to disclosing the characteristics of these compounds 16 − 21 and, hence, to better understanding the evolution process of these
systems from solution precursors to thin films through several intermediate
steps. 22 , 23 In the case of Sn-based halide perovskites,
such efforts have been conducted primarily in conjunction with experiments. 6 A dedicated ab initio study is, to the best of
our knowledge, still missing.
In the framework of time-dependent
density functional theory coupled
to the polarizable continuum model (PCM), we investigate the physical
properties of 14 solution complexes, SnI 2 M 4 ,
where M indicates a common solvent molecule chosen among compounds
previously adopted experimentally in the synthesis of tin halide precursors. 6 In the presented analysis, we focus on the structural,
energetic, electronic, and optical properties of these systems. We
characterize the considered compounds by looking at bond lengths and
angles and by comparing them with their counterparts in PbI 2 M 4 complexes. We assess their formation energy and rationalize
our findings with respect to the donor number of the solvent.

Finally,
we inspect the electronic structure in order to interpret their absorption
spectra and disclose the characteristics of their optical excitations,
including their composition and spatial distribution among the constituents.
All ab initio calculations presented
in this study were performed
using density functional theory (DFT) 24 , 25 as implemented
in the Gaussian 16 software package. 26 The
implicit solvent interactions were simulated with the PCM 27 , 28 adopting the values for the dielectric constants of the solvents
listed in Figure 1 .
van der Waals interactions were accounted for using the semiempirical
Grimme D3 dispersion scheme. 29 Reference
calculations on the isolated SnI 2 complex assumed to be
implicitly solvated in DMSO were performed adopting the PCM.
Overview of
the 14 solvents considered in this study with their
respective Gutmann’s donor number ( D N ) and static dielectric constant (ε): hexamethylphosphoramide
(HMPA), N , N ′-dimethylpropyleneurea
(DMPU), N , N -diethylformamide (DEF),
dimethyl sulfoxide (DMSO), 1,3-dimethyl-2-imidazolidinone (DMI), dimethylacetamide
(DMAC), N -methyl-2-pyrrolidone (NMP), dimethylformamide
(DMF), N -methylacetamide (NMAC), 3-methyl-2-oxazolidinone
(3MOx), γ-butyrolactone (GBL), propylene carbonate (PC), tetramethylurea
(TMU), and acetonitrile (ACN). On the bottom right panel, a sketch
of the SnI 2 M 4 compounds in the solvent cavity
is reported: the numbers label the Sn–I (purple) and the Sn–M
(black) bonds.
The geometries of the SnI 2 M 4 complexes were
optimized through the minimization of the interatomic forces. By means
of additional frequency calculations, we checked that all the obtained
structures represented global minima except for SnI 2 (TMU) 4 and SnI 2 (HMPA) 4 , which exhibited one
and four negative frequencies, respectively. We

argue that this result
does not impact the following analysis of the electronic and optical
properties of the complexes, which is primarily focused on identifying
trends. For these optimizations, we used the generalized gradient
approximation in the Perdew–Burke–Ernzerhof (PBE) parametrization 30 together with the LANL2DZ basis set; pseudopotentials
were adopted for Sn and I atoms and the double-ζ basis set cc-pVDZ
for the remaining lighter species. We checked that the choice of this
functional, which is substantially more efficient than hybrid approximations
and adopted in previous studies on similar systems, 16 − 18 , 20 , 21 did not affect the
electronic structure of the resulting optimized structures. For single-point-geometry
DFT calculations, for the population and natural bond order (NBO)
analysis, as well as for the time-dependent DFT (TDDFT) runs, we adopted
the range-separated hybrid functional CAM-B3LYP 31 in combination with the SDD basis set together with the
corresponding SDD pseudopotentials for Sn and I and the quadruple-ζ
cc-pVQZ basis set for the lighter atoms. The output of (TD)DFT calculations
was postprocessed to obtain relevant information on the systems. The
molecular orbitals (MOs) of the SnI 2 M 4 complexes
were analyzed with the natural atomic orbital (NAO) method as implemented
in the Multiwfn 32 software on the basis
of the NBO calculations performed with Gaussian 16. 33 , 34
The properties of the complexes were analyzed in light of
the Gutmann
donor number ( D N ) of
the solvents as the primary classifier according to their Lewis basicity.
This property is recognized as a determining factor for the effectiveness
of the solvents and specifically for their ability to solvate halide
perovskite precursors. 22 , 35 − 37 The values
of D N adopted in this
work were taken from available references and, in the absence of the
latter, estimated from first-principles from the ionization potential
(IP) and the electron affinity (EA) of the compounds as computed from
DFT 38 , 39 (see Figure 1 and Table

Weak Interactions in Dimethyl Sulfoxide (DMSO)-Tertiary Amide Solutions: The Versatility of DMSO as a Solvent. — Camilla Di Mino et al., 2023

Polar aprotic liquids are widely used
as solvents on both a laboratory
and industrial scale, with important applications across a wide range
of chemistry, biochemistry, and nanoscience. 1 − 3 In this context,
their relevant physicochemical properties include high dipole moments,
high relative permittivities, and high boiling points, along with
broad electrochemical stability windows when compared to their protic
analogues. 4 This combination of attributes
makes these liquids highly effective for solvation of a wide spectrum
of ions, small molecules, polymers, and nanostructures. 1 , 5 − 9 For example, in electrochemistry, their inertness and ability to
solvate both metal ions and polymeric coelectrolytes under highly
reducing conditions are critical for battery function and stability. 2 , 3 , 10 In addition, polar aprotic liquids
provide a unique arena in which to study and tune the fundamental
nature of weak intermolecular interactions, including C–H···O
and C–H···π hydrogen bonds and both cyclic
and acyclic π–π effects.
Dimethylformamide
(DMF, Me 2 NC(=O)H) and dimethylacetamide
(DMAc, Me 2 NC(=O)Me) are the simplest aprotic amides,
in which the proton donor (protic) N–H groups present in formamide
(FA, H 2 NC(=O)H), N -methylformamide
(NMF, MeHNC(=O)H), and N -methylacetamide (NMAc,
MeHNC(=O)Me) are replaced by N–Me ( Figure 1 ). The aprotic nature and the
high dipolar character of these amides make them the ideal candidate
for studying weak competitive interactions in the liquid state. Both
DMF and DMAc are planar acyclic amides, where partial double bond
character in the N–C=O framework arises from π
electron delocalization that enforces the planarity of the molecule. 11 DMF and DMAc have similar dipole moments (μ
= 3.86 and 3.72 D, respectively) and relative permittivities (ϵ r = 36.8 and 37

.8 at 20 °C, respectively, Table 1 ) which lead to strong
dipole–dipole interactions and relative orientational effects
in the liquid structure. 12 Both molecules
are regarded as weak Lewis bases, with donor numbers (DN) of 26.6
kcal mol –1 and 27.8 kcal mol –1 and acceptor numbers (AN) of 16.0 kcal mol –1 and
13.6 kcal mol –1 , respectively, for DMF and DMAc, Table 1 . 13 Furthermore, the presence of a C(=O)–H group
in DMF raises the possibility of hydrogen bonding by a weakly donating
formic H atom. On a practical level, this functionality also means
that while DMF is one of the most heavily used solvents for chemical
synthesis, it can react under highly basic conditions and with strong
reducing and chlorinating agents. DMAc is usually more inert and so
has complementary applications for example in the production of pharmaceuticals
and polymers. 11
DMF, DMAc, and DMSO molecular models. The arrow indicates the direction
of the molecular dipole, while the circle through which it passes
highlights the center-of-mass (CoM) for each species.
Neutron diffraction studies of liquid DMF and DMAc
have shown well-defined
local structures. 12 For both cases, the
coordination number of molecules in the first solvation shell is found
to be around 13, with a clear second shell also present. In DMF, weak
C(=O)–H···O hydrogen bonds are observed
that are thought to be electrostatic in nature. In DMF, the first
solvation shell shows the expected preference for antiparallel dipole
orientation between molecules, while in DMAc, parallel dipoles maximize
dispersion forces between the π-delocalized O=C–N
backbones and methyl groups. 12 These results
are consistent with Raman and IR spectroscopy and molecular dynamics
studies of liquid DMF, all of which reported a highly structured first
solvation shell with weak hydrogen bonding from carbonyl and methyl
H atoms, in line with the “relatively short” C–H···O=C
contacts seen earlier by gas

-phase electron diffraction. 14 − 19
Dimethyl sulfoxide (DMSO, Me 2 S=O) is a pyramidal
molecule with a high dipole moment (μ = 3.96 D), weak Lewis
base character (DN = 29.8 kcal mol –1 and AN = 19.3
kcal mol –1 ), and a remarkably high permittivity
for an aprotic solvent (ϵ r = 47.2
at 20 °C). Its unique properties are due to the combination of
a soft lone pair on the sulfur atom and the strong polarization of
the S=O bond. DMSO, like DMF and DMAc, is miscible with water
and many organic solvents and has a unique ability to solvate a wide
range of chemical species from apolar hydrocarbons to entirely dissociated
salts. DMSO is therefore extremely important in processing and technology. 20 Moreover, DMSO is able to penetrate human skin
with a nondestructive effect on tissues and is a keystone protectant
in cryobiology. 21 Additional theoretical
interest stems from the long-standing question of how to best represent
the sulfoxide bond: S + –O – rather
than a formal S=O double bond. 22 − 24 Structural studies of
liquid DMSO by X-ray and neutron diffraction have reported nearest
neighbor coordination numbers in the range 11.5–13.8 and provided
evidence for short-range antiparallel alignment of dipoles, with head-to-tail
ordering at longer distances. In addition, weak methyl hydrogen to
oxygen intermolecular contacts were observed at distances of approximately
3.4 Å, but as such, these probably do not constitute hydrogen
bonds. 25 − 28
While the bulk physicochemical properties of DMF, DMAc, and
DMSO
are therefore similar ( Table 1 ), the pure liquids exhibit contrasting local structures.
This latter point immediately raises the question as to which interactions
will dominate in mixtures of these molecules, and in particular how,
and to what extent, DMSO is accommodated within the local solvation
environments of DMF and DMAc (and vice versa ).
Previous studies of mixtures of the polar protic solvent NMF in
DMSO

DMSO Deintercalation in Kaolinite–DMSO Intercalate: Influence of Solution Polarity on Removal — Berenger ZOGO MFEGUE et al., 2021

1. IntroductionClays are industrial materials used in many domains, such as paints, inks, rubbers, ceramics, and building materials. When developing eco-friendly plastics, to deal with pollution problems associated with fossil-based plastics, the use of biopolymers has been explored by scientists worldwide. The sensitivity of biopolymers to fluid diffusion and their low mechanical responses requires the use of fillers during the reinforcing phase [1]. Clay materials are among the most explored candidates for such uses. The interest in clays is due to their strong anisotropy and specific surface that influence the filler–matrix interactions [2,3]. Among clays, swelling clays, such as montmorillonite, Laponite, or Hectorite, are widely explored, given that their exfoliation, which favors their dispersion within the polymer matrix, is more easily achieved [4,5,6,7]. Kaolinite, despite its great abundance and purity of deposits [8], remains more scarcely explored [3,9]. However, improving its use is cost-effective, given its abundance.The asymmetric structure of the kaolinite layer, due to the overlay of tetrahedral and octahedral sheets within the layer, induces strong superimposed dipoles that, together with hydrogen bonds between the silica ring and the aluminum surface, give a strong cohesive energy to the mineral [10,11]. This cohesive energy makes the kaolinite layer almost non-expansive, and hence poorly dispersible. To improve its use as fillers in polymer–clay composites, the exfoliation of the kaolinite layer is a key factor [12]. Kaolinite intercalation with small polar molecules, such as dimethyl sulfoxide (DMSO), urea, or formamide, is well known in the literature [13,14,15,16,17]. The intercalated kaolinites are used as intermediates in composite-making [6,9,14,15,18,19]. The development of kaolinite–polymer composites is still challenging, as the dispersion of kaolinite to nano size is not easily achieved. The kaolinite–DMSO intermediate is used in many studies [3]. The preparation of the kaolinite–DMSO intermediate is done in various ways, including solution intercalation [12], homogenization intercalation (

wet mixing) [20], or mechanochemical process [21]. As the intercalation within the kaolinite layer is also variable, Mbey et al. (2020) [22] recently explored the influence of kaolinite crystallinity on the intercalation of DMSO and established that increased crystallinity is favorable for DMSO intercalation.The use of kaolinites in the reinforcing phase in polymer–clay (nano)composites are rare [3,4,5,6,9,23,24]. However, some recent works indicates that the use of kaolinite can be improved if convenient dispersion is achieved [3,9,25]. These studies used kaolinite–DMSO as an intermediate to improve the dispersion of clay within a polymer matrix. The study of kaolinite–DMSO complexes shows that the intercalated molecule influences H-bonding within the kaolinite layer, which results in a less cohesive structure [12]. In the present study, it is proposed that the intercalation–deintercalation process can be of interest to reduce the cohesion of the kaolinite crystallite. Given that the rate of deintercalation may affect the kaolinite structure, the removal of intercalated DMSO is carried out in three solvents including water, ethyl acetate, and acetone. The media were chosen because of their differences in polarity, as the driving out of DMSO is probably dependent on solvent polarity. X-ray diffraction (XRD), Fourier transform infra-red (FTIR), and thermal analysis were used to analyze the kaolinite–DMSO intercalate and the products of deintercalation. 2. Materials and Methods 2.1. MaterialsAn alluvial clay from the Lokoundjé subdivision was used. This was previously characterized in a study by Ndjigui et al., 2018 [26]. The sample was wet-sieved at 75 µm to increase its kaolinite content. The collected cake was dried to constant weigh at ambient temperature for one week before being crushed and kept in polyethylene bags. The sieved sample was named GR375.Analytical grade DMSO by Fluka was used for the preparation of kaolinite–DMSO intermediates.For the deintercalation, three solvents of different pol

arity were selected. The selection was done according to the polarity of the intercalated molecule, here DMSO, whose relative polarity is 0.444. The solvents’ relative polarities as extracted from Reichardt and Welten 2011 [27] are given in Table 1. 2.2. MethodsFor the DMSO intercalated complex, a mixture made of 200 mL of DMSO, 20 mL of distilled water, and 30 g of clay was placed in a glass jar. The resulting suspension was maintained at the ambient temperature of the laboratory (28 ± 1) °C for ten days. A manual shaking of 5 min was applied daily for each jar for ten days. The solid clay was recovered from the suspension by centrifugation at 2000 rpm using a HERAUS MegaFuge 8 centrifuge by Thermo-Scientific. The collected cake was air-dried for five days before being dried at 100 °C in an oven to constant weight. The DMSO intercalated sample was codified GR375-D.Displacement of DMSO from the kaolinite was performed using ethyl acetate, acetone, and distilled water. The products were respectively labeled GR375-AE, GR375-AC, and GR375-E.For the GR375-AE preparation, 3 g of GR375-D was placed in 100 mL of ethyl acetate. The mixture was refluxed at 70 °C (boiling temperature of ethyl acetate) for one hour. The solid phase was collected after centrifugation at 2000 rpm and dried in ambient temperature for 24 h, then at 100 °C, for 24 h, in an oven. For the GR375-AC sample, acetone was used as a replacement for ethyl acetate and the same protocol was applied with the refluxing being done at 57 °C (acetone boiling temperature). For GR375-E preparation, 3 g of GR375-D was dispersed in distilled water and reflux at 95 °C.X-ray diffraction of the various samples was performed at the Laboratory of Bioinorganic Chemistry and Catalyze at the University of Dusseldorf (Germany) using a Bruker D2 Phaser diffractometer operating with a Cu-Kα radiation (λ = 1.54 Å) and under a voltage of 30 kV. The XRD patterns were recorded

Crystallization Pathways of FABr-PbBr 2 -DMF and FABr-PbBr 2 -DMSO Systems: The Comprehensive Picture of Formamidinium-Based Low-Dimensional Perovskite-Related Phases and Intermediate Solvates. — Sergey A Fateev et al., 2022

Organo-inorganic lead halide compounds with a perovskite structure of the general formula ABX 3 [A = CH 3 NH 3 + (MA + ), CH(NH 2 ) 2 + (FA + ); B = Pb 2+ , Sn 2+ ; X = I – , Br – ] as well as their low-dimensional derivatives have recently emerged as a promising new class of materials for solar cells and next-generation light-emitting diodes (LEDs) due to its broadly tunable photoluminescence (PL) (410–700 nm), high PL quantum yield (QYs = 50–90%), small full width at half maximum of PL peaks [ 1 , 2 , 3 , 4 , 5 , 6 , 7 , 8 ] and advantages of solution-processing techniques compatible to organic LEDs [ 9 ]. In particular, lead bromide materials with perovskite and perovskite-derived structures with bright-green PL emission might act as green emitters excited by standard blue-emitting diodes [ 10 , 11 , 12 , 13 ]. Solution methods of crystallization are popular for fabrication of bromide perovskite thin films with a good quality for light-emitting diodes with external quantum efficiency exceeding 20% [ 14 , 15 ]. The recent studies of the solution-processed crystallization of hybrid perovskites confirmed the crucial role of processing solvents and intermediate phases on the properties of final materials [ 16 , 17 , 18 ]. Additionally, it was previously identified that in systems with iodide anions and methylammonium cations, the crystallization of perovskite from DMF and DMSO solutions precedes the crystallization of intermediate solvate phases such as (MA) 2 Pb 3 I 8 ·2Solv, (MA) 3 PbI 5 ·Solv (Solv = DMF or DMSO) and (MA) 2 Pb 2 I 6 ·2DMF, depending of the ratio of precursors [ 16 , 17 ], while in systems with bromide anions ions, it was found that crystallization proceeds without the formation of intermediate phases [ 19 ].
Unlike methylammonium and cesium the flat FA + cation is considered to form plenty of layered two-dimensional (2D) polymorphs in the presence of organic halide excess [ 19 , 20 ]

which can form multiphase heterostructures with FAPbBr 3 3D perovskite with highly tunable and improved optical properties such as enhanced EQE and reversed photochromism [ 21 , 22 , 23 ] of hybrid materials since it can form phases with different inorganic substructure dimensions (3D and 2D) [ 19 , 20 ]. Additionally, two adducts of formamidinium bromoplumbates with DMSO were recently discovered (FA 2 PbBr 4 ·DMSO and FAPbBr 3 ·DMSO) [ 17 , 24 ]. Thus, among the 3D hybrid perovskites FABr-PbBr 2 system in the FABr excessive region is expected to have the most complex chemical equilibria during crystallization from widely used DMF and DMSO solvents because of competition between multiple possible perovskite-like phases and solvates. Understanding of these equilibria is essential for rational chemical engineering of solution-processed FA x PbBr 3+x films and devises. In the present work, we have investigated the phase diversity of the FABr-PbBr 2 -DMF and FABr-PbBr 2 -DMSO solution system for detailed optimization of perovskite film processing.
To identify the equilibrium crystal phases in the FABr-PbBr 2 -DMF/DMSO systems, we observed the process of crystallization by drying drops of solutions of different compositions followed by isolation of the crystals to resolve the crystal structures by single-crystal X-ray diffraction methods. At room temperature (RT), the ternary solution system FABr-PbBr 2 -DMF in equilibrium state reveals five independent phases at different FABr/PbBr 2 ratio ( r ) from 1 to 5 ( Figure 1 ): FAPbBr 3 perovskite, three different polytypes of two-dimensional (110) perovskite-derived structures FA 2 PbBr 4 and FA 3 PbBr 5 phase with one-dimensional perovskite-derived structure which is confirmed by XRD measurements. For FABr-PbBr 2 -DMSO system at RT conditions the crystallization process of 3D and 2D perovskites is accompanied by the appearance of intermediate solvate phases with FAPbBr

3 ∙DMSO and FA 2 PbBr 4 ∙DMSO compositions ( Figure 1 ).
According to the XRD measurements for FABr-PbBr 2 -DMF system in the FABr/PbBr 2 ratio ( r ) from 0 to 0.9 only PbBr 2 phase is crystallized. At r = 0.9 ÷ 1, the PbBr 2 coexist with the FAPbBr 3 perovskite phase. Crystallization of phase-pure 3D perovskite FAPbBr 3 was observed for the FABr/PbBr 2 stoichiometric concentration and FABr-excessive compositions with r = 1.1 ÷ 1.5. An excess of FABr greater than 1.5 results in that the 3D perovskite phase crystallizes first, and crystallization of low-dimensional 2D perovskite FA 2 PbBr 4 phases is observed from the remaining solution. Up to 4 different layered perovskite phases crystallizes directly from mother solution starting from r = 2.1. There are three layered perovskite-derived phases with the FA 2 PbBr 4 stoichiometry corresponding to different crystal structures. The crystal structures of these polymorphs have already been published earlier [ 19 , 20 ]. The t -FA 2 PbBr 4 and m -FA 2 PbBr 4 compounds crystallize from DMF solution [ 19 ] while γ -FA 2 PbBr 4 forms under distinctly different synthetic conditions precipitating under cooling from concentrated aqueous HBr [ 20 ]. Two of the FA 2 PbBr 4 polymorphs have the crystal structure of (110)-oriented layered perovskite with ‘2 × 2’ arrangement of the inorganic layers whereas the third polymorph γ -FA 2 PbBr 4 adopts a ‘3 × 2’ arrangement of the inorganic layers (see Figure 1 ). All structures consist of corner-shared [ P b B r 6 ] ∞ 2 − octahedra forming corrugated layers separated with formamidinium interlayer cations. The main difference between first two polymorphs is the different Layer Shift Factor [ 25 ] (different stacking of adjacent inorganic layers). The m-FA 2 PbBr 4 has a staggered [ 26 ] stacking of layers with LSF (0.5