Isostructural Salts Research Articles

Structural insights into supramolecular interactions in isostructural salts of 2,4,6-triaminopyrimidinium with various heterocyclic carboxylates.

2,4,6-Triaminopyrimidine is an interesting and challenging molecule due to the presence of multiple hydrogen-bond donors and acceptors. Its noncovalent interactions with a variety of carboxylic acids provide several supramolecular aggregates with frequently occurring molecular synthons. The present work focuses on the supramolecular interactions of 2,4,6-triaminopyrimidinium 3-(indol-3-yl)propionate-3-(indol-3-yl)propionic acid (1/1), C4H8N5+·C11H10NO2-·C11H11NO2, (I), 2,4,6-triaminopyrimidinium 2-(indol-3-yl)acetate, C4H8N5+·C10H8NO2-, (II), 2,4,6-triaminopyrimidinium 5-bromothiophene-2-carboxylate, C4H8N5+·C5H2BrO2S-, (III), and 2,4,6-triaminopyrimidinium 5-chlorothiophene-2-carboxylate, C4H8N5+·C5H2ClO2S-, (IV). All four salts exhibit robust homomeric and heteromeric R22(8) ring motifs. Salts (I) and (II) develop sextuple [in (I)] and quadruple [in (I) and (II)] hydrogen-bonded arrays through fused-ring motifs. Salt (II) exhibits a rosette-like architecture. Salt (IV) is isostructural and isomorphous with salt (III), exhibiting an identical crystal structure with a different composition and an identical supramolecular architecture. In salts (III) and (IV), a linear hetero-tetrameric motif is formed and, in addition, both salts exhibit halogen-π interactions which enhance the crystal stability. All four salts develop a supramolecular hydrogen-bonded pattern facilitated by several N-H...O and N-H...N hydrogen bonds with multiple furcated donors and acceptors.

Ultrafast Pump–Probe Spectroscopy in Organic Dirac Electron Candidate α-(BETS)2I3

Photo-induced carrier dynamics were measured in the organic Dirac electron candidate α-(BETS)2I3 to investigate why resistivity increases below TMI = 50 K. We found a change in carrier dynamics due to an insulating gap formation below T′ = 50 K. On the other hand, the relaxation time and polarization anisotropy of the observed dynamics differ from those in the charge-ordering (CO) state of the isostructural salt α-(ET)2I3. Based on the difference, it can be concluded that the insulating phase has a different origin than the CO state.

Effect of External Pressure on the Metal–Insulator Transition of the Organic Quasi-Two-Dimensional Metal κ-(BEDT-TTF)2Hg(SCN)2Br

The metal–insulator transition in the organic quasi-two-dimensional metal κ-(BEDT-TTF)2Hg(SCN)2Br at TMI ≈ 90 K has been investigated. The crystal structure changes during this transition from monoclinic above TMI to triclinic below TMI. A theoretical study suggested that this phase transition should be of the metal-to-metal type and brings about a substantial change of the Fermi surface. Apparently, the electronic system in the triclinic phase is unstable toward a Mott insulating state, leading to the growth of the resistance when the temperature drops below TMI ≈ 90 K. The application of external pressure suppresses the Mott transition and restores the metallic electronic structure of the triclinic phase. The observed quantum oscillations of the magnetoresistance are in good agreement with the calculated Fermi surface for the triclinic phase, providing a plausible explanation for the puzzling behavior of κ-(BEDT-TTF)2Hg(SCN)2Br as a function of temperature and pressure around 100 K. The present study points out interesting differences in the structural and physical behaviors of the two room temperature isostructural salts of κ-(BEDT-TTF)2Hg(SCN)2X with X = Br, Cl.

Isostructural hybrid iodometalate(III)/triiodide salts with perovskite-like packing: comparison of physical properties for SbIII and BiIII complexes

Reactions of Sb2O3 or Bi2O3, 1,2-bis(4-pyridyl)ethane (bpe) and diiodine in concentrated HI resulted in isostructural salts (H2bpe)2[MI6](I3) [M = Sb (1), Bi (2)] featuring perovskite-like arrangement of anions in crystal packing. Physical properties, including UV-Vis and Raman spectra, as well as thermal stability, were investigated and compared for this pair of complexes; the optical band gaps for 1 and 2 are 1.32 and 1.57 eV, respectively.

A new strategy to design isostructural salts: The case of the antitumor drug dimethylaminomicheliolide

Isostructural multicomponent crystals provide a promising way for fine-tuning physicochemical properties, whereas their design remains quite challenging. The purpose of this work was to provide a new strategy for obtaining isostructural multicomponent crystals by introducing coformers with functional group positional isomerism. Five isostructural salts of an antitumor drug dimethylaminomicheliolide (DMAMCL) were reported and designed with a series of dihydroxybenzoic acid regioisomers for the first time, which were identified by power and single-crystal X-ray diffractions. Similar lattice parameters suggested these obtained salts may have the same crystal packing mode. The quantitative similarity parameters via XPac, CrystalCMP and Mercury program further proved these crystal structures are 3D isostructural. Hirshfeld surface maps and 2D fingerprint plots show that the isostructural salts have similar intermolecular interactions. Compared with DMAMCL, obvious improvement was observed in the thermal stability, hygroscopicity, and solubility of these isostructural salts. Meanwhile, isostructural crystals may have different physicochemical properties, even though the shape and molecular size are similar and the packing of crystal structures is equally matched.

Crystal structure, theoretical and vibrational analysis of isostructural salts of l-arginine analogue, (S)-2-amino-3-guanidinopropanoic acid

The (S)-2-amino-3-guanidinopropanoic acid (HAGP) is unnatural homologue of l-arginine. Three new isostructural salts were synthesized (H3AGP)Cl2, (H3AGP)Br2 and (H3AGP)I2. They crystallize in orthorhombic symmetry, space group P212121 with Z = 4. Analysis of molecular and crystal structures reveals complexity of hydrogen bonding network. Graph-set approach was used to describe hydrogen bonding patterns. Algebraic juxtaposition of the elementary graph-set descriptors gave all the patterns found in the crystal structures. Infra-red and Raman spectra were interpreted based on theoretical calculations for the [(H3AGP)Cl6]4– cation and further potential energy distribution analysis.

Synthesis and characterization of crystalline niobium and tantalum carbonyl complexes at room temperature.

A variety of homoleptic transition metal carbonyl complexes are known as bulk compounds for group 7-12 metals. These metals typically feature a maximum of 6 CO ligands to form complexes with 18 valence electrons. In contrast, group 3-5 metals, with fewer valence electrons, have been shown to form highly coordinated heptacarbonyl and octacarbonyl complexes-although they were only identified by gas-phase mass spectrometry and/or matrix isolation spectroscopy work. Now we have prepared heptacarbonyl cations of niobium and tantalum as crystalline salts that are stable at room temperature. The [M(CO)7]+ (M = Nb or Ta) complexes were formed by the oxidation of [M(CO)6]- with 2Ag+[Al(ORF)4]- (RF, C(CF3)3) under a CO atmosphere; their experimental characterization was supported by density functional theory calculations. Other unusual carbonyl compounds were also synthesized: two isostructural salts that contained the 84-valence-electron cluster cation [Ag6{Nb(CO)6}4]2+, the piano-stool complexes [(1,2-F2C6H4)M(CO)4]+ and two polymorphs of neutral Ta2(CO)12 with a long, unsupported Ta-Ta bond.

Crystal structures and vibrational spectra of L-argininium(2+) bis(tetrafluoroborate) and L-argininium(2+) bis(perchlorate).

In the present work crystal structures of (L-ArgH2)(BF4)2 (I) and (L-ArgH2)(ClO4)2 (II) isostructural salts have been determined. They crystallize in triclinic system with space group P1 and Z = 1. Structure features of the (I) and (II) were compared with respective data of previously known (L-ArgH)(BF4) and (L-ArgH)(ClO4) salts with singly charged L-argininium(+) cation. Infrared and Raman spectra of the (I) and (II) are compared with spectra of (L-ArgH)(BF4) and (L-ArgH)(ClO4) salts. The presence of cation and anions and hydrogen bonds between them are reflected in the IR and Raman spectra. The crystals (I) and (II) exhibit second harmonic generation activity.

Infrared and Raman spectra of strontium and barium pimelates monohydrates.

The salts of dicarboxylic acids with alkaline earth metals are not very thoroughly studied and only a few such compounds are well known and characterized. In this work a detailed examination of the infrared spectra recorded at room temperature (RT) and at the liquid nitrogen boiling temperature (LNT) and Raman spectra (at room temperature) of the monohydrates of strontium and barium pimelates, [Sr(μ6-C7H10O4)(H2O)]n and [Ba(μ6-C7H10O4)(H2O)]n respectively, has been carried on. These isostructural salts are important nucleating agents for processing of isotactic polypropylene (iPP). The vibrational spectra of the two salts have been interpreted by using factor group analysis. For more correct and unequivocal interpretation of the vibrational spectra, samples containing partially and almost fully deuterated crystallization water have also been prepared and studied. The effect of the metal ion on the vibrations of the pimelic acid ion as well as the strength of the hydrogen bonds formed by the crystallization water molecule has been discussed.

Racemic Salts and Solid Solutions of Enantiomers of the Antihypertensive Drug Carvedilol

The R and S enantiomers of the antihypertensive drug carvedilol (CVD) can display remarkable miscibility in the crystalline state allowing this active pharmaceutical ingredient (API) to form a solid-solution of enantiomers (SSEs) as well as racemic compounds. Although rare and still little explored, these intriguing systems can also be used to design racemic multicomponent crystal forms toward the improvement of undesirable pharmaceutical properties of APIs. In this study, aiming to understand why there is miscibility between the enantiomers during the supramolecular recognition and crystallization processes of the CVD in the presence of salt formers, two SSEs and one racemic salt were prepared from the reaction of CVD with pharmaceutically acceptable HCl, HBr, and oxalic acids. Two monohydrated isostructural salts, hydrochloride (CVD-HCl-H2O) and hydrobromide (CVD-HBr-H2O), crystallize as racemic SSEs. These unique systems are formed from the miscibility of the R···R and S···S homochiral units that propa...

Hydrogen bonding in two benzene-1,2-diaminium pyridine-2-carboxylate salts and a cocrystal of benzene-1,2-diamine and benzoic acid.

The isostructural salts benzene-1,2-diaminium bis(pyridine-2-carboxylate), 0.5C6H10N22+·C6H4NO2-, (1), and 4,5-dimethylbenzene-1,2-diaminium bis(pyridine-2-carboxylate), 0.5C8H14N22+·C6H4NO2-, (2), and the 1:2 benzene-1,2-diamine-benzoic acid cocrystal, 0.5C6H8N2·C7H6O2, (3), are reported. All of the compounds exhibit extensive N-H...O hydrogen bonding that results in interconnected rings. O-H...N hydrogen bonding is observed in (3). Additional π-π and C-H...π interactions are found in each compound. Hirshfeld and fingerprint plot analyses reveal the primary intermolecular interactions and density functional theory was used to calculate their strengths. Salt formation by (1) and (2), and cocrystallization by (3) are rationalized by examining pKa differences. The R22(9) hydrogen-bonding motif is common to each of these structures.

First Mononuclear Lanthanide Imidazolium Carboxylates

The synthesis and structural analysis of six new lanthanide imidazolium carboxylates are discussed. The first mononuclear lanthanide imidazolium carboxylate salts, [{(L)2M}3+{NO3−}3], M=Sm (1), Gd (2), Dy (3) and Y (4), were synthesized from the reaction between zwitterionic tris-imidazolium carboxylate and corresponding metal nitrate salts. The presence of monodentately coordinating carboxylate groups in 1–4 are confirmed by FT-IR spectra. The isostructural salts 1–4 are discrete tricationic monomer. To the best of our knowledge, the ionic salts 1–4 are the first structurally characterized mononuclear lanthanide imidazole carboxylates. The coordination environment of M(III) is fulfilled by six carboxylate oxygen atoms of ligands in distorted octahedron geometry.

Enhancement of Intermolecular Magnetic Exchange through Halogen···Halogen Interactions in Bisadeninium Rhenium(IV) Salts

Two novel ReIV salts of general formula [H2ade]2[ReIVX6]X2·4H2O [H2ade2+ = 9H-adenine-1,7-diium; X = Cl(1) and Br(2)] have been synthesized and magnetostructurally characterized. 1 and 2 are isostructural salts that crystallize in the orthorhombic system with space group Fdd2. Both compounds are made up of discrete mononuclear [ReIVX6]2– and X– anions and doubly protonated adenine cations. The six-coordinate rhenium(IV) ion is bonded to six halide ligands [X = Cl (1) and Br (2)] in an octahedral geometry. Short intermolecular ReIV–X···X–ReIV interactions, as well as ReIV–X···H–N(H2ade) and ReIV–X···H–Ow hydrogen bonds, are present in the crystal lattice of 1 and 2. Magnetic susceptibility measurements on polycrystalline samples of 1 and 2 in the temperature range 2.0–300 K show the occurrence of significant intermolecular antiferromagnetic interactions in both compounds, resulting in the observation of maxima in χM at ca. 6.0 (1) and 12.0 K (2). The larger spin delocalization from the ReIV ion onto the pe...

Synthesis, Crystal Structures, Raman and EPR Studies of Mixed Trihalides in Association with Transition Metal (CoII–ZnII) Tris-chelates

Four new isostructural salts, [M(phen)3](I2Br)2·3CH2Cl2 where, M=Co (1), Ni (2), Cu (3), or Zn (4) have been synthesized by reacting the metal nitrates with 1,10–phenanthroline (phen) in presence of potassium bromide and iodine in a two phase procedure. The [Cu(phen)3]2+ coordination corresponds to tetragonally elongated octahedron while the other three are much more symmetrical. The pure Cu2+ complex as well as other salts doped with Cu2+ give hyperfine resolved EPR spectra in a wide temperature range showing dynamic Jahn–Teller distortion. The trihalide ion is nearly linear with bond distances in the range, I–I (2.786–2.833 A) and I–Br (2.759–2.794 A). Geometry optimization (DFT and MP2 methods) predicts a much more unsymmetrical “gas phase” structure for I2Br− ion. Calculated Raman frequencies are in reasonable agreement with observed values. Electronic spectral results show that the integrity of the trihalide ion is retained in solution. Three new isostructural compounds having the general formula [M(phen)3](I2Br)2 having nearly symmetrical I2Br− ion are synthesized and characterized.

Magnetic and Optical Properties of Layered (Me4P+)[MIVO(Pc•3–)]•–(TPC)0.5·C6H4Cl2 Salts (M = Ti and V) Composed of π-Stacking Dimers of Titanyl and Vanadyl Phthalocyanine Radical Anions

Two isostructural salts with radical anions of titanyl and vanadyl phthalocyanines (Me4P+)[MIVO(Pc•3–)]•–(TPC)0.5·C6H4Cl2 (M = Ti (1), V (2)), where TPC is triptycene, were obtained. These salts contain phthalocyanine layers composed of the {[MIVO(Pc•3–)]•–}2 dimers with strong π–π intradimer interaction. The reduction of metal phthalocyanines was centered on the Pc macrocycles providing the appearance of new bands in the near infrared range and a blue shift of Q- and Soret bands. That results in the alternation of shorter and longer C–Nimine bonds in Pc•3–. Only one S = 1/2 spin is delocalized over Pc•3– in 1 providing a χMT value of 0.364 emu K mol–1 at 300 K. Salt 1 showed antiferromagnetic behavior approximated by the Heisenberg model for isolated pairs of antiferromagnetically interacting spins with exchange interaction of J/kB = −123.0 K. The χMT value for 2 is equal to 0.617 emu K mol–1 at 300 K to show the contribution of two S = 1/2 spins localized on VIV and delocalized over Pc•3–. Magnetic beha...

Crystal structures of bis-[(9S,13S,14S)-3-meth-oxy-17-methyl-morphinanium] tetra-chlorido-cobaltate and tetra-chlorido-cuprate.

(9S,13S,14S)-3-Meth-oxy-17-methyl-morphinan (dextromethorphan) forms two isostructural salts with (a) tetra-chlorido-cobaltate, namely bis-[(9S,13S,14S)-3-meth-oxy-17-methyl-morphinanium] tetra-chlorido-cobaltate, (C18H26NO)2[CoCl4], and (b) tetra-chlorido-cuprate, namely bis-[(9S,13S,14S)-3-meth-oxy-17-methyl-morphinanium] tetra-chlorido-cuprate, (C18H26NO)2[CuCl4]. The distorted tetra-hedral anions are located on twofold rotational axes. The dextromethorphan cation can be described as being composed of two ring systems, a tetra-hydro-naphthalene system A+B and a deca-hydro-isoquinolinium subunit C+D, that are nearly perpendicular to one another: the angle between mean planes of the A+B and C+D moieties is 78.8 (1)° for (a) and 79.0 (1)° for (b). Two symmetry-related cations of protonated dextromethorphan are connected to the tetra-chlorido-cobaltate (or tetra-chlorido-cuprate) anions via strong N-H⋯Cl hydrogen bonds, forming neutral ion associates. These associates are packed in the (001) plane with no strong attractive bonding between them. Both compounds are attractive crystalline forms for unambiguous identification of the dextromethorphan and, presumably, of its optical isomer, levomethorphan.

Crystal structures, magnetic and electrical properties of two new two-dimensional bis(2-thioxo-1, 3-dithiole-4, 5-dithiolato)nickelate salts

Two new salts of bis(2-thioxo-1, 3-dithiole-4, 5-dithiolato) nickelate monoanion with 4-amino-1-heptylpyridinium (1) and 4-amino-1-nonylpyridinium (2) were prepared and characterized. Two isostructural salts with anion/cation=1:1 crystallize in space group P-1 with similar cell parameters and packing structures. The anions and cations form alternating layered arrangements, which are connected via charge-assisted S⋯H H-bonds. Within an anion layered alignment, the magnetic exchange is transmitted between the neighboring anions via three types of pathways (face-to-face π–π stack, lateral-to-lateral and head-to-tail S⋯S contacts), where the stronger antiferromagnetic coupling occurs between the face-to-face stacked anions, owing to π-type magnetic orbitals efficiently overlapped, than others and dominates the magnetic nature of 1 and 2. The dielectric and conducting properties were also investigated for two salts in the temperature range of 175–375K.

Synthesis, Electronic Properties, Thermoelectric Power, and Crystal and Band Structures of Unsymmetrical EDOB-EDT-TTF Salts Composed of PF6 −, AsF6 −, and SbF6 − at Various Temperatures

The synthesis and crystal structure of EDOB-EDT-TTF donor were described. Novel EDOB-EDT-TTF radical salts with different octahedral AsF6 − and SbF6 − were prepared. Based on the electrical conductivity measurements, the newly prepared conductive AsF6 salt underwent a metal-to-semiconductor (MS) transition similar to the previously reported isostructural PF6 salt. The X-ray analyses of the AsF6 and SbF6 salts at various temperatures elucidated their structural characteristics. The AsF6 salt formed a dimer below 330 K with the formation of an O⋅⋅⋅H short contact in the intermolecular intradimer along the stacking column. Simultaneous measurements of the thermoelectric power and the resistivity on a single sample were performed for the PF6, AsF6, and SbF6 salts. The MS transition temperatures of these PF6 and AsF6 salts were also determined from thermoelectric power data. The band structures and Fermi surfaces for the AsF6 salts at 293 and 350 K were calculated.

Variable Magnetic Interactions between S = 1/2 Cation Radical Salts of Functionalizable Electron-Rich Dithiolene and Diselenolene Cp2Mo Complexes

A series of Cp(2)Mo(dithiolene) and Cp(2)Mo(diselenolene) complexes containing N-alkyl-1,3-thiazoline-2-thione-4,5-dithiolate ligand (R-thiazdt, R = Me, Et, CH(2)CH(2)OH) and N-alkyl-1,3-thiazoline-2-thione-4,5-diselenolate ligand (R-thiazds, R = Me, Et) have been synthesized. These heteroleptic molybdenum complexes have been characterized by electrochemistry, spectroelectrochemistry, and single crystal X-ray diffraction. They act as very good electron donor complexes with a first oxidation potential 200 mV lower than in the prototypical Cp(2)Mo(dmit) complex and exhibit almost planar MoS(2)C(2) (or MoSe(2)C(2)) metallacycles. All five complexes formed charge transfer salts with a weak (TCNQ) and a strong acceptor (TCNQF(4)), affording ten different charge-transfer salts, all with 1:1 stoichiometry. Crystal structure determinations show that the S/Se substitution in the metallacycle systematically affords isostructural salts, while the Cp(2)Mo(R-thiazdt) complexes with R equals ethyl or CH(2)CH(2)OH can adopt different structures, depending on the involvement of the hydroxyl group into intra- or intermolecular hydrogen bonding interactions. Magnetic susceptibility data of the salts are correlated with their structural organization, demonstrating that a face-to-face organization of the Me-thiazdt (or Me-thiazds) ligand favors a strong antiferromagnetic interaction, while the bulkier R = Et or R = CH(2)CH(2)OH substituents can completely suppress such intermolecular interactions, with the added contribution of hydrogen bonding to the solid state organization.

Isostructural salts of the same complex showing contrasting thermal spin-crossover mediated by multiple phase changes

Two salts of [FeL2](2+) (L = 2,6-bis[5-methyl-1H-pyrazol-3-yl]pyridine) are isostructural under ambient conditions but show different thermal spin-crossover behaviour, involving a variety of crystallographic phase changes.