Structure and stability of hydrogen fluoride complexes with N,N-dimethylformamide

The structure, stability, and paths of formation of 11 (HF)_m(DMF)_n heterocomplexes (m = 1–4, n = 1, 2) were studied in terms of the B3LYP/6-31++G(d, p) density functional calculation. The results of this calculation suggest that: a) addition of hydrogen fluoride molecules to the (HF)_mDMF cyclic fragment is the basic tendency in complex formation in the HF-DMF system; b) data about the structure and properties of stable molecular forms that prevail in N,N-dimethylformamide solutions of hydrogen fluoride can be obtained by quantum chemical calculations for (HF)_mDMF complexes (m = 5–10).     

On rhodium(III) chloride complexes with N,N-dimethylformamide

A prolonged storage of a solution of RhCl₃·nH₂O in N,N-dimethylformamide (DMF) at room temperature is attended by the consecutive formation of two precipitates, which mainly contain the [(CH₃)₂NH₂][RhCl₅(DMF)] complex (I) and the complex [RhCl₃(DMF)₃] (II) liberates. The addition of PPh₄Cl to an aqueous solution of complex I brings about the precipitation of [PPh₄][RhCl₄(H₂O)₂] (III). Complex II (a mixture of mer-and fac-isomers) can be obtained also by treatment of [RhCl₃(CH₃CN)₃] with DMF. In the course of the latter reaction, the formation of intermediate complex [RhCl₃(CH₃CN)₂(DMF)] (IV) is observed. Complexes I–IV are characterized by elemental analysis; complexes I, II, and IV are characterized by the IR and ¹H and ¹³C NMR spectra. The structures of III and IV are determined by X-ray diffraction analysis.     

A calorimetric study ofN,N-dimethylformamide complexes of copper(II) in acetonitrile

Complex formation of copper(II) with N,N-dimethylformamide(DMF) has been investigated calorimetrically in acetonitrile at 25°C. Calorimetric titration curves obtained are explained in terms of formation of [Cu(dmf) _n ]²⁺ (n=1–4, 6) and their formation constants, enthalpies and entropies were determined. Formation of [Cu(dmf)₅]²⁺ is uncertain. The stepwise enthalpies S ₃ ⁰ and entropies S _n ⁰ at each consecutive step are all negative except for S ₃ ⁰ . The overall enthalpies of formation of [Cu(dmf)₆]²⁺ is –(77.8±5.4) kJ-mol^–1, which is compared with the enthalpy of transfer of copper(II) ion, H _t ^o =–79.7 kJ-mol^–1, from acetonitrile to DMF.     

Structural properties of liquidN,N-dimethylformamide

Monte-Carlo simulation of liquidN,N-dimethylformamide was performed. The influence or electrostatic and van der Waals interactions on regularities of the mutual molecular arrangement was investigated. The spatial structure of liquid DMF is determined by the type of molecular packing and steric factors and is close to a random closely packed system of soft spheres. The electrostatic interactions only affect the mutual orientation of the molecular Translated fromIzvestiya Akademii Nauk. Seriya Khimicheskaya, No. 1, pp. 21–27, January, 1998.     

The structure of complexes of HCl withN,N-dimethylformamide based on polarization measurements in the Raman spectra

The Raman spectra of solutions of HCl in DMF were studied and the degree of depolarization of spectral lines was measured. Complexes of three types, 2DMF·HCl, DMF·HCl, and DMF·2HCl, are formed depending on the ratio of the components. Examination of the structure of the contour of the v(C=O) line showed that the acid-base interactions in the complexes occur through the O atom of the DMF molecule. On the basis of polarization measurements it was established that two DMF molecules in the 2DMF·HCl complex are nonequivalent.     

Cu(I) and Fe(II) complexes with N,N-dimethylthioformamide and Fe(II) complexes with N,N-dimethylformamide

The synthesis of the following Cu(I) and Fe(II) complexes with N,N-dimethylthioformamide (DMTF) and N,N-dimethylformamide (DMF) are described: Cu(DMTF)₄ClO₄, Cu(DMTF)₂Cl, Cu(DMTF)₂Br, Cu(DMTF)₂I, Fe(DMTF)₆(ClO₄)₂, Fe(DMTF)₂Cl₂, Fe(DMTF)₂Br₂, Fe(DMTF)₂I₂, Fe(DMF)₆(ClO₄)₂, Fe(DMF)₂Cl₂, Fe(DMF)Br₂ and Fe(DMF)₃I₂. Electronic absorption spectra, IR spectra, magnetic susceptibilities of the solids and in solution as well as conductivities have been measured of these compounds in order to obtain information on the nature of the interaction between the cations and the ligands, the coordination in the crystalline state, in solution and the dissociation of these compounds in the respective solvents.     

Solubility diagrams of the potassium iodide-water-N,N-dimethylformamide and iodine-iodide-water-N,N-dimethylformamide systems at 25°C

The solubility diagrams of the potassium iodide-water-N,N-dimethylformamide (DMFA) and iodine-iodide-water-N,N-dimethylformamide systems were studied at 25°C by the method of sections. The systems are characterized by three-phase equilibria of the peritonic and eutonic types, respectively. Potassium iodide in the I₂-KI-/H₂O-DMFA (95: 5 wt %)/ system was found to salt in crystalline iodine. The selected composition of the H₂O-DMFA mixed solvent possessed a higher iodine-solving ability compared with pure mixture components.     

Capillary electrophoresis in N,N-dimethylformamide

N,N-Dimethylformamide (DMF) is a dipolar protophilic solvent with physicochemical properties that makes it suitable as solvent for capillary electrophoresis (CE). It is prerequisite for the proper application of CE to adjust and to change the pH of the background electrolyte (BGE) in a defined manner. This was done in the present work using benzoic acid-benzoate by selecting different concentration ratios of acid and salt, and calculating the theoretical pH from the activity-corrected Henderson-Hasselbalch equation. The mobilities of the analytes (chloro- and nitro-substituted phenolates) were found to follow reasonably well the typical sigmoid mobility versus pH curve as predicted by theory. The actual mobilities and pK(a) values (at 25 degrees C) of the analytes were derived from these curves. pK(a) values were in the range of 11.1-11.7, being thus 3-4.4 units higher than in water. This pK(a) shift is caused by the destabilization of the analyte anion and the better stability (solubility) of the molecular analyte acid in DMF, which overcome the higher basicity of DMF compared to water. Absolute mobilities were calculated from the actual mobilities; they were between 32x10(-9) and 42x10(-9) m(2)/Vxs. Slight deviations of the measured mobilities from the theoretical mobility versus pH curve were discussed on the bases of ion pairing and heteroconjugation and homoconjugation of either buffer components or buffer components and analytes. Heteroconjugation was used as a mechanism for the electrically driven separation of neutral analyte molecules in a BGE where salicylate acted as complex forming ion. Rough estimation of the complexation constants for the phenolic analytes gave values in the range of 100-200 L/mol. Addition of water to the solvent decreased the effect of heteroconjugation, but it was still present up to the surprisingly high concentration of 20% water. Electrophoretically relevant parameters like ionic mobilities and pK(a) values, and conjugation and ion pairing are dependent on the water content of the solvent. The water uptake of DMF was measured when exposed to humidity of ambient air. The resulted behavior of the water uptake was found rather similar to that for acetonitrile and methanol.     

Polymerization of styrene in N,N-dimethylformamide

The polymerization of styrene in N,N-dimethylformamide (DMF) at 60°C has been studied both in the presence and absence of 4,4′-azobis-4-cyanopentanoic acid (ACV). Rates of polymerization were measured dilatometrically and gravimetrically, and degrees of polymerization were determined viscometrically. There was some discrepancy in the values of the transfer constant to DMF, C_s, obtained by analysis of the results. The most reliable value appeared to be 9.8 × 10^?6, from experimental data obtained in the absence of added ACV.     

Molar enthalpies of transfer of divalent transition metal lons and their chloro complexes from N,N-dimethylformamide to N,N-dimethylacetamide

The molar enthalpies of transfer _t H ^° of some divalent metal ions (M-Mn, Co, Ni and Zn) and their chloro complexes from N,N-dimethyl-for-mamide (DMF) to N,N-dimethylacetamide (DMA) have been determined using the tetraphenylarsonium-tetraphenylborate (TATB) assumption at 25°C. Although physicochemical properties of DMF and DMA as solvent are similar, the _t H ^°(M ²⁺) value increased significantly in the order Mnt H ^° values for the mono-and dichloro complexes showed also a strong metal dependence, while those for the triand tetrachloro complexes practically do not. These results can be reasonably explained in terms of steric hindrance upon solvation of the metal ions and complexes in DMA.     

Structural peculiarities of particle solvation inN,N-dimethylformamide

Monte Carlo computer simulation of infinitely dilute solutions of Cs⁺ and I⁻ ions and Xe atoms inN,N-dimethylformamide (DMF) was performed. Peculiarities of intermolecular interactions and structural properties of the solutions were investigated. The solvation enthalpies of cations and anions are close, but the energies of the ion-solvent and solventsolvent interactions differ appreciably. The solute particles affect the energy and structural properties of DMF only in spatially localized domains. The second solvation shell of the solute particles was not structurally allocated. Two structurally and energetically differing states of DMF molecules (with normal and anomalous orientation of the dipole moments) exist in solution of Cs⁺ cations. The anomalous orientation of DMF molecules is due to the solvation steric effect, packing, and kinematic factors. Translated fromIzvestiya Akademii Nauk. Seriya Khimicheskaya, No. 4, pp. 584–596, April, 2000.     

Comparative study of mono- and dinuclear complexes of late 3d-metal chlorides with N,N-dimethylformamide in the gas phase

Mono- and binuclear complexes of N,N-dimethylformamide (DMF) with chlorides of the divalent, late 3d metals M = Co, Ni, Cu, and Zn are investigated by means of electrospray ionization (ESI). Specifically, ESI leads to monocations of the type [(DMF)(n)MCl](+) and [(DMF)(n)M(2)Cl(3)](+), of which the species with n = 2 and 3 were selected for in-depth studies. The latter include collision-induced dissociation experiments, gas-phase infrared spectroscopy, and calculations using density functional theory. The mononuclear complexes [(DMF)(n)MCl](+) almost exclusively lose neutral DMF upon collisional activation with the notable exception of the copper complex, for which also a reduction from Cu(II) to Cu(I) concomitant with the release of atomic chlorine is observed. For the dinuclear clusters, there exists a competition between loss of a DMF ligand and cluster degradation via loss of neutral MCl(2) with decreasing cluster stability from cobalt to zinc. For the specific case of [(DMF)(n)ZnCl](+) and [(DMF)(n)Zn(2)Cl(3)](+), ion-mobility mass spectrometry indicates the existence of two isomeric cluster ions in the case of [(DMF)(2)Zn(2)Cl(3)](+) which corroborates parallel theoretical predictions.     

Structure of iron(III) ion and its complexation with thiocyanate ion in N,N-dimethylformamide

Complexation of iron(III) with thiocyanate ions has been calorimetrically and spectrophotometrically investigated in N,N-dimethylformamide (DMF) containing 0.4 mol/dm(3) (C(2)H(5))(4)NClO(4) or 1 mol/dm(3) NH(4)ClO(4) as a constant ionic medium at 25 degrees C. Calorimetric titration data were well explained in terms of the formation of [Fe(SCN)(n)]((3-n)+) (n = 1-5), and their formation constants, reaction enthalpies and entropies were determined. Electronic spectra of individual iron(III) thiocyanato complexes were also determined. The stepwise thermodynamic quantities changed monotonously, i.e. DeltaG degrees (1) < DeltaG degrees (2) < DeltaG degrees (3) < DeltaG degrees (4), < DeltaG degrees (5), DeltaH degrees (1) > DeltaH degrees (2) > DeltaH degrees (3) > DeltaH degrees (4) > DeltaH degrees (5), DeltaS degrees (1) > DeltaS degrees (2) > DeltaS degrees (3) > DeltaS degrees (4) > DeltaS degrees (5). This suggests that no extensive desolvation occurred at any step of complexation. On the basis of these thermodynamic quantities, it is postulated that the [Fe(SCN)(n)]((3-n)+) (n = 1-5) complexes have a six-coordinate octahedral structure as well as the [Fe(dmf)(6)](3+) ion, the octahedral structure of which has been confirmed by the EXAFS (extended X-ray absorption fine structure) method.     

Interaction of basalt with orthophosphoric acid

Physicochemical modeling is used to study the decomposition of basalt by orthophosphoric acid. The equilibrium compositions of the liquid and solid phases of the Al-Fe-Ca-Mg-Na-Si-P-O-H system are calculated. The effects of the acid concentration and solid-to-liquid ratio on the composition of reaction products and the degrees of extraction of iron, aluminum, magnesium, calcium, sodium, and silicon into solution are determined. Conditions for selective extraction of the components into liquid phase are estimated.     

The Instability of Permanganate in orthophosphoric acid

Solutions of potassium permanganate in concentrated phosphoric acid (above 50%) are found to be unstable. The oxidation state of manganese is reduced from (VII) to (III) and oxygen is evolved during this process. The extent of decomposition of permanganate is found to be dependent on the concentration of the acid.