Ferromagnetically Coupled S=1 Chains in Crystals of Verdazyl-Nitronyl Nitroxide Diradicals

Thermally stable organic diradicals with a triplet ground state along with large singlet-triplet energy gap have significant potential for advanced technological applications. A series of phenylene-bridged diradicals with oxoverdazyl and nitronyl nitroxide units were synthesized via a palladium-catalyzed cross-coupling reaction of iodoverdazyls with a nitronyl nitroxide-2-ide gold(I) complex with high yields. The diradicals exhibit high stability and do not decompose in an inert atmosphere up to 180 °C. For the diradicals, both substantial AF (ΔE_ST≈−64 cm⁻¹) and FM (ΔE_ST≥25 and 100 cm⁻¹) intramolecular exchange interactions were observed. The sign of the exchange interaction is determined both by the bridging moiety (para- or meta-phenylene) and by the type of oxoverdazyl block (C-linked or N-linked). Upon crystallization, diradicals with the triplet ground state form unique one-dimensional exchange-coupled chains with strong intra- and weak inter-diradical ferromagnetic coupling.     

Preparation and Crystal Structure of a New Uranyl Sulfate Templated by a Bis-isothiouronium Cation

Crystals of a new uranyl sulfate (C₂N₄H₈S₂)[UO₂(SO₄)₂] · 0.3H₂O ( 1 ) templated by a relatively rare bis-isothiouronium cation, were formed upon evaporation of aqueous solutions containing uranyl acetate, thiourea, and excess sulfuric acid. The new compound is orthorhombic, P2₁2₁2₁, a = 6.928(2) Å, b = 13.398(3) Å, c = 15.225(3) Å, Z = 2. Its crystal structure is comprised of [UO₂(SO₄)₂] moieties linked by hydrogen bonds formed between the template cations and terminal oxygen atoms of the sulfate tetrahedra. The C₂N₄H₈S₂²⁺ template is most likely formed in situ during a redox reaction between uranyl cation and thiourea in a strongly acidic medium, with UO₂²⁺ partially reduced to U⁴⁺.     

Phase transfer of metal cations by induced dynamic carrier agents: biphasic extraction based on dynamic covalent chemistry

In contrast to the classical method where a single molecule is designed to extract metal cations under specific conditions, dynamic covalent chemistry provides an approach based on the implementation of an adaptive dynamic covalent library for inducing the generation of the extractant species. This approach has been applied to the liquid–liquid extraction of copper(ii) nitrate based on a dynamic library of acylhydrazones constituents that self-build and distribute through the interface of a biphasic system. The addition of copper(ii) cations to this library triggers a modification of its composition and the up-regulation of the ligand molecules driven by coordination to the metal cations. Among these, one species has proven to be sufficiently lipophilic to play the role of carrier agent and its formation by component exchange enables the partial extraction of the copper(ii). The study of different pathways to generate the dynamic covalent library demonstrates the complete reversibility and the adaptability of the system. The detailed analytical investigation of the system provides a means to assess the mechanism of the dynamic extraction process.

Phase transfer of Cu(ii) cations is achieved by component exchange in a dynamic covalent library of acylhydrazone ligands. B1/B2 component exchange leads to the generation of a lipophilic carrier agent that extracts Cu(ii) into chloroform.     

Phase transitions in K3AlF6

Phase transitions in the elpasolite-type K₃AlF₆ complex fluoride were investigated using differential scanning calorimetry, electron diffraction and X-ray powder diffraction. Three phase transitions were identified with critical temperatures , and . The α-K₃AlF₆ phase is stable below T₁ and crystallizes in a monoclinic unit cell with a=18.8588(2)Å, b=34.0278(2)Å, c=18.9231(1)Å, β=90.453(1)° (a=2a_c−c_c, b=4b_c, c=a_c+2c_c; a_c, b_c, c_c—the basic lattice vectors of the face-centered cubic elpasolite structure) and space group I2/a or Ia. The intermediate β phase exists only in very narrow temperature interval between T₁ and T₂. The γ polymorph is stable in the T₂<T<T₃ temperature range and has an orthorhombic unit cell with a=36.1229(6)Å, b=17.1114(3)Å, c=12.0502(3)Å (a=3a_c−3c_c, b=2b_c, c=a_c+c_c) at 250 °C and space group Fddd. Above T₃ the cubic δ polymorph forms with a_c=8.5786(4)Å at 400 °C and space group . The similarity between the K₃AlF₆ and K₃MoO₃F₃ compounds is discussed.     

Heteroscedasticity of retention factor and adequate modeling in micellar liquid chromatography

The two concepts of micelle formation (pseudo-phase and mass-action) could be the basis of retention models in micellar liquid chromatography (MLC). The separation of 4-hydroxybenzoic acid esters and seven polyaromatic hydrocarbons were performed to study the repeatability of retention factor in MLC. The full two factor experimental design was used for studying the dependence of retention factor variance on mobile phase composition (sodium dodecylsulfate, 1-butanol). The experimentally observed heteroscedasticity and perturbations after linearization were taken into account by using statistical weights obtained on the basis of errors propagation law and the modeling of retention by non-weighted and weighted least squares method was performed. The mechanistical retention models based on pseudo-phase and mass-action concepts of micelle formation were compared by fitting quality and prediction capability and high robustness of bilogarithmic dependence was observed. The significance of retention factor heteroscedasticity for retention hydrophobicity relationships was shown.     

A Noncatalytic Approach to Hetaryl‐Annulated 1,2,4‐Thiadiazine‐1,1‐dioxides

A set of synthetic procedures was developed to yield functionalized pyrido‐, pyrimido‐, and thiazo‐annulated thiadiazine‐1,1‐dioxides on a preparative scale. In all cases the thiadiazine‐1,1‐dioxide ring closure was carried out through a reaction of hetaryl‐sulfonyl chlorides with amidines under mild noncatalytic conditions. In the case of 2‐chloropyridine‐3‐sulfonyl chloride derivatives and 2,4‐dichlorothiazole‐5‐sulfonyl chloride open‐chain sulfonylated amidine intermediates were isolated and then subjected to the cyclization step. The reaction with 2,4‐dichloropyrimidine‐5‐sulfonyl chloride gave rise to the corresponding thiadiazine‐1,1‐dioxides in one‐pot. Similarly, a reaction of 2‐chloropyridine‐3‐sulfonamide with lactime ethers proceeded in one‐pot readily giving the corresponding thiadiazine‐1,1‐dioxides. Remaining chlorine atoms on the prepared hetaryl‐annulated benzothiadiazine‐1,1‐dioxides readily undergo aromatic nucleophilic displacement reactions serving thus as additional variation points for the design of biologically potent compounds.     

Computer simulation of interactions in the NH3-CO2-H2O system

Computer simulation of interactions in the NH₃-CO₂-H₂O system was performed using a quantum-chemical method B3LYP/6-31G(d,p) for the simulation of the possible routes of the reactions and the estimation of the energy parameters: interaction energy between molecules in complexes, activation energy of forward and reverse reactions, and the heat of the reaction. A new version of termolecular reaction mechanism is proposed and investigated. The probability of realization of various paths of interaction in the NH₃-CO₂-H₂O system was shown to be determined by the temperature: at low temperatures the termolecular mechanism is more probable, while at the temperatures close to the standard conditions carbamate and bimolecular mechanisms are preferable.     

Triangular oxalate clusters [W(3)(mu(3)-S)(mu(2)-S(2))(3)(C(2)O(4))(3)](2)(-) as building blocks for coordination polymers and nanosized complexes

The reaction of aqueous [W3S7(C2O4)3](2-) with Ln(3+) and Th(4+) in a 1:1 molar ratio leads to oxalate-bridged heteropolynuclear molecular complexes and coordination polymers. La(3+) and Ce(3+) give a layered structure with big (about 1.8 nm) honeycomb pores which are filled with water molecules and lanthanide ions, in {[Ln(H2O)6]3[W3S7(C2O4)3]4}Br x xH2O (Ia and Ib). The smaller Pr(3+), Nd(3+), Sm(3+), Eu(3+), and Gd(3+) ions give discrete nanomolecules [(W3S7(C2O4)3Ln(H2O)5)2(mu-C2O4)] (with a separation of about 3.2 nm between the most distant parts of the molecule), which are further united into zigzag chains by specific S2...Br- contacts to achieve the overall stoichiometry K[(W3S7(C2O4)3Ln(H2O)5)2(mu-C2O4)]Br.xH2O (IIa-IId). Th(4+) gives K2[(W3S7(C2O4)3)4Th2(OH)2(H2O)10] x 14.33H2O (III) with a nanosized discrete anion (with a separation of about 2.7 nm between the most distant parts of the molecule), in which two thorium atoms are bound via two hydroxide groups into the Th2(OH)2(6+) unit, and each Th is further coordinated by five water molecules and two monodentate [W3S7(C2O4)](2-) cluster ligands. All compounds were characterized by X-ray structure analysis and IR spectroscopy. Magnetic susceptibility measurements in the temperature range of 2-300 K show weak antiferromagnetic interactions between two lanthanides atoms for compounds IIa, IIb, and IId. The thermal decomposition of Ia, Ib, and IIb was studied by thermogravimetry.     

Synthesis and structures of Mo3Se7Te2Br10, Mo3Se7TeI6, and Mo6Te21I22 containing TeX3- (X=Br, I) ligands coordinated to a triangular cluster core

New ternary and quaternary molybdenum cluster chalcohalides were obtained by high-temperature reactions between Mo, chalcogens, and halogens in evacuated ampules. The crystal structures of [Mo3Se7(TeBr3)Br2]2[Te2Br10] (1), [Mo3Se7(TeI3)I2]I (2), and [Mo3Te7(TeI3)3]2(I)(TeI3) (3) were determined by single-crystal X-ray diffraction. The structures of 1 and 2 consist of positively charged zigzag chains infinity1 [Mo3Se7(TeX3)X4/2] (X=Br, I), with Te2Br102- and I-, respectively, as counterions. The TeI3- and TeBr3- ions function as bidentate ligands in 1 and 2. In 3, TeI3- is not coordinated to the metal but acts as a counterion to the [Mo3Te7(TeI3)3]+ cluster cation.     

One-step synthesis of heterocyclic privileged medicinal scaffolds by a multicomponent reaction of malononitrile with aldehydes and thiols

Heterocyclic privileged medicinal scaffolds involving pyridine, 1,4-dihydropyridine, chromeno[2,3-b]pyridine, and dihydro-1,4-dithiepine frameworks are prepared via a single-step multicomponent reaction of structurally diverse aldehydes with various thiols and malononitrile. Mechanistic studies of the synthetic pathway leading to pyridines reveal that 1,4-dihydropyridines undergo oxidation by the intermediate Knoevenagel adducts rather than by air oxygen. The use of o,o'-disubstituted aromatic aldehydes leads to the corresponding 1,4-dihydropyridines, whereas salicylic aldehydes result in chromeno[2,3-b]pyridines. Reactions of ethanedithiol as a thiol component produce dimeric pyridines with sterically unencumbered aldehydes, while o,o'-disubstituted aromatic aldehydes give dihydro-1,4-dithiepines. Thus, depending on the aldehyde and thiol types, diverse libraries of medicinally relevant compounds can be prepared by a simple one-step process involving no chromatography.