Theoretical investigation of the weakly dihydrogen bonded dimers H2 − nXnAlHHArF and H2 − nXnAlHHKrF (n = 0–2; X = F, Cl)

An ab initio computational study of the properties of the dihydrogen-bonded complexes of H_{2 − n}X_nAlH (n = 0–2; X = F, Cl) with the rare gas (Rg) compounds HArF and HKrF was carried out at the MP2(full)/6-311++G(2d,2p) level of theory. For all the studied complexes, we found a low zero-point corrected binding energies. Large red shifts of the H–Rg vibrational stretching frequency in both complexes were predicted. Electrostatic interactions between the individual monomers are also predicted.     

Investigation of the interactions between ginsenosides and amino acids by mass spectrometry and theoretical chemistry

In order to evaluate the essence of the interactions of ginsenosides and proteins which are composed by α-amino acids, electrospray ionization mass spectrometry was employed to study the noncovalent interactions between ginsenosides (Rb₂, Rb₃, Re, Rg₁ and Rh₁) and 18 kinds of α-amino acids (Asp, Glu, Asn, Phe, Gln, Thr, Ser, Met, Trp, Val, Gly, Ile, Ala, Leu, Pro, His, Lys and Arg). The 1:1 and 2:1 noncovalent complexes of ginsenosides and amino acids were observed in the mass spectra. The dissociation constants for the noncovalent complexes were directly calculated based on peak intensities of ginsenosides and the noncovalent complexes in the mass spectra. Based on the dissociation constants, it can be concluded that the acidic and the basic amino acids, Asp, Glu, Lys and Arg, bound to ginsenosides more strongly than other amino acids. The experimental results were verified by theoretical calculations of parameters of noncovalent interaction between ginsenoside Re and Arg which served as a representative example. Two kinds of binding forms, “head–tail” (“H–T”) and “head–head” (“H–H”), were proposed to explain the interaction between ginsenosides and amino acids. And the interaction in “H–T” form was stronger than that in “H–H” form.     

Effect of axial anions on the thermal stability of square pyramidal manganese(III) complexes

Summary The effect of the axial anion on the thermal behaviour of square pyramidal Mn^III complexes of [Mn(SB)X] (where SB=tetradentate dibasic Schiff base; X=OAc^–, SCN^–, Cl^–, Br^– or I^–) has been studied. A correlation has been made between the thermal stabilities of the complexes and the electronegativities () of the axial donor atoms. Other solid state phenomena (nature of interaction of the solvent of crystallization and polymorphic transformation) were also studied for the acetato and isothiocyanato complexes.     

New Benzo-15-Crown-5 Ethers Featuring Salicylic Schiff Base Substitutions – Synthesis, Complexes and Structural Study

Condensation reactions between 4'-formyl-5'-hydroxybenzo-15-crown-5and 2-aminopyridine, 2-amino-6-methylpyridine, 2-amino-4-methylpyridine or2-(aminomethyl)furan yielded the new laterally functionalized crown ethers1–4. The crown compounds 1–3 form crystalline 1:1 (Na⁺:ligand) complexes 1a–3a with sodium perchlorate. Ligands and complexes have been characterized by elemental analyses, IR, UV-Vis, ¹H-, ¹³C-NMR and mass spectra. The tautomeric equilibria (phenol-imine, O...H–N and keto-amine, O...H–N forms) have been systematically studied by using UV-Vis absorption spectra. The spectra of the ligands 1–4 and complexes 1a–3a were recorded in polar, non-polar, acidic, and basic media. In solutions of polar solvents, tautomeric interconversion of the Schiff base into the keto-amine form has been observed. A crystal structure [monoclinic, space group P2₁/c,a = 14.292(2), b = 9.449(6), c = 16.059(2) Å, = 114.20(1)°,V = 1978.4(13) ų, Z = 4 and D_x = 1.314 g cm^-3] shows that compound 4 is in the form of phenol-imine in solid state. There is a strong intramolecular [O–H...N 1.78(6), O...N 2.581(7), O–H 0.89(6) Å and N...H–O 148.4(5)°] hydrogen bond between the phenolic oxygen and imine nitrogen atoms. The C=N imine bond reveals a trans planar (1E) configuration. The molecules stack in columns parallel to the a/c plane of the unit cell.     

Energy of formation and structures of monoaquacomplexes of anions: Results of calculations by the MNDO/M method

The MNDO/M method has been used to carry out calculations for a series of complexes A^–...H₂O with hydrogen bonds X...H-O, where X=C, N, O, F, S, Cl, Br, I. The energies of formation and the structural parameters obtained for the complexes agree well with experiment and with the results of rigorous calculations.Translated from Teoreticheskaya i Éksperimental'naya Khimiya, Vol. 26, No. 1, pp. 66–70, January–February 1990.     

Cobalt(III) α-Dimethylglyoximates [Co(DH)2(Py)2]2SiF6 · 10H2O and [Co(DH)2(Thio)2]2SiF6 · 2H2O · C2H5OH: Synthesis and Structure

[Co(DH)₂(Py)₂]₂SiF₆ · 10H₂O and [Co(DH)₂(Thio)₂]₂SiF₆ · 2H₂O · C₂H₅OH complexes are synthesized and characterized by X-ray diffraction analysis. Two radicals of -glyoxime linked by hydrogen O–H···O bonds lie in the equatorial plane of the octahedral Co(III) complexes. Intramolecular (– and N–H···O) and intermolecular (O–H···F, O–H···O, N–H···F, N–H···O, N–H···S) interactions are discovered in the crystal. The influence of nonvalence interactions on the structures is discussed.     

Copper(II) complexes of acid amide derivatives of 2-aminopyridineand an exogenous ligand

The bidentate ligands, 2-[(N-acetyl)aminopyridine] (AAPH, A) and 2-[(N-benzoyl)aminopyridine] (BAPH, B) have been used to synthesize copper(II) complexes including an exogenous ligand X (X = AcO^–, HCO₂ ^–, N₃ ^– and benzimidazole). The complexes were characterized by elemental analysis, electronic and vibrational spectroscopy, magnetic and e.s.r. studies. E.s.r. parameters and visible spectra indicated that all the complexes are monomers and exist in distorted octahedral geometry except for benzimidazole. With benzimidazole as an exogenous ligand, a five coordinate complex is formed.     

Studies on labile chargetransfer complexes between o-chloranil and a series of phenols

The electron donor–acceptor (EDA) interactions between o-chloranil and a series of phenols have been studied in dioxan medium. Except for resorcinol, the EDA complexes are formed instantaneously on mixing the donor and the acceptor solutions and then they decay slowly into secondary products. In case of resorcinol, formation and decay of the EDA complex are slow and simultaneous. The kinetics of all these reactions have been studied spectrophotometrically and the formation constants of EDA complexes have been determined from kinetic data. The hν_CT values change systematically as the number and position of the –OH groups change in the aromatic ring of the phenol moiety. From the trends in the hν_CT values, the Hückel parameters (h_Ö and k_C–Ö) for the –OH group, required for a PMO calculation on phenols, have been obtained in a straightforward way and the values so obtained, viz., 1.8 and 1.0 respectively, are close to the ones (1.8 and 0.8) recommended by Streitwieser on the basis of other evidences.     

Transition metal ion complexes of theS-methyldithiocarbazate prepared from 2-acetylpyridineN-oxide

Summary Metal ion complexes of theS-methyldithiocarbazate of 2-acetylpyridineN-oxide, HONS, have been prepared and characterised by spectral and physical methods. Preparative ethanolic solutions on reflux yield complexes in which the deprotonated form of the ligand, ONS, is complexedvia itsN-oxide oxygen, azomethine nitrogen, and thione sulphur. Representative stoichiometries are as follows: [M(ONS)₂]X (M=Fe³⁺, and X=ClO ₄ ^– , FeCl ₄ ^– or M=Co³⁺ and X=BF ₄ ^– ) and [M(ONS)X] (M=Co²⁺, Ni²⁺ and Cu²⁺ and X=Cl^–, Br^–). The i.r., electronic, and electron spin resonance spectra of the complexes are compared to analogous complexes of theX-methyldithiocarbazate of 2-acetylpyridine as well as the thiosemicarbazones of 2-acetylpyridineN-oxide.     

Complexes of Formaldehyde and α-Dicarbonyls with Hydroxylamine: FTIR Matrix Isolation and Theoretical Study

The interactions of formaldehyde (FA), glyoxal (Gly) and methylglyoxal (MGly) with hydroxylamine (HA) isolated in solid argon and nitrogen were studied using FTIR spectroscopy and ab initio methods. The spectra analysis indicates the formation of two types of hydrogen-bonded complexes between carbonyl and hydroxylamine in the studied matrices. The cyclic planar complexes are stabilized by O–H⋯O(C), and C–H⋯N interactions and the nonplanar complexes are stabilized by O–H⋯O(C) bond. Formaldehyde was found to form with hydroxylamine, the cyclic planar complex and methylglyoxal, the nonplanar one in both argon and nitrogen matrices. In turn, glyoxal forms with hydroxylamine the most stable nonplanar complex in solid argon, whereas in solid nitrogen, both types of the complex are formed.     

Synthesis, characterizations and crystal structures of new organoantimony(V) complexes with various isomers of fluoromethylbenzoate ligands

Six new organoantimony(V) complexes containing various isomers of fluoromethylbenzoate ligands [RC₆H₃COO]₂SbPh₃ and [RC₆H₃COO]SbPh₄ [R = 3-F-4-(CH₃) (1, 4), 4-F-2-(CH₃) (2, 5), 5-F-2-(CH₃) (3, 6)] have been synthesized by the reactions of triphenylantimony(V) dichloride or tetraphenylantimony(V) bromide with various isomers of fluoromethylbenzoate ligands in 1:2 or 1:1 stoichiometries. All the complexes have been characterized by elemental analysis, IR and NMR [¹H, ¹³C and ¹⁹F] studies. The crystal structures of complexes 1, 3, 4, 5 and 6 have been determined by X-ray single crystal diffraction. The structure of complexes show that the five-coordinated antimony(V) atom adopts a distorted trigonal bipyramidal geometry. Furthermore, weak but significant intermolecular C–H···O, C–H···F hydrogen bonds, C–H···pi stacking lead to aggregation and assembly of these complexes into 1D and 2D supramolecular frameworks.     

Untersuchung von Kobalt(II)-Komplexen mit N-Arylthioharnstoffen

The complexes of cobalt(II) chloride with o, m, p-tolyl thiourea (I–III); m, p-nitrophenyl thiourea (IV, V); o, m, p-hydroxy phenyl thiourea (VI–VIII); m, p-bromophenyl thiourea (IX, X); p-iodophenyl thiourea (XI) and o-bromo-p-methyl phenyl thiourea (XII) have been synthesised. The elemental analysis reveals that ligands (I–V) form bis and the rest forms tris complexes with cobalt(II). Infrared and farinfrared spectral measurements prove that sulphur is taking part in co-ordination. All complexes are nonelectrolytes in acetone as revealed by conductivity measurements. The data obtained from magnetic susceptibility measurements, electronic spectra in solution are consistant with a practically tetrahedral symmetry.     

The conformational states of cyclopeptide systems. VIII. Synthesis of cyclohexapeptides containing residues of L-valine, L-norvaline, L-leucine, and glycine

Summary The synthesis of seven cyclic hexapeptides containing the residues of L-valine, L-norvaline, L-leucine, and glycine has been effected.Chemical Faculty of the Polytechnic Institute (Gdansk, Poland).M. M. Shemyakin Institute of Bioorganic Chemistry, Academy of Sciences of the USSR. Translated from Khimiya Prirodnykh Soedinenii, No. 1, pp. 57–63, January–February, 1975.     

Copper(II) complexes of isobutyl methyl ketone semicarbazone

Summary Copper(II) complexes of isobutyl methyl ketone semicarbazone have been prepared and characterised by magnetic moments, i.r., electronic and e.s.r. spectral studies. The complexes were found to have CuL₂X₂ and CuL₂X₂ · 2H₂O compositions. The electronic and e.s.r. spectra suggest a five-coordinated trigonal bipyramidal geometry, for the CuL₂X₂ complexes, (X=Cl^–, Br^–, NO ₃ ^– , and 1/2 SO ₄ ^2– ) and six-coordinate octahedral geometry has been suggested for CuL₂X₂ · 2H₂O (X=Cl^–, Br^–, NO ₃ ^– , SO ₄ ^2– ).     

Metal ion complexes of 2-picolinamineN-oxide

Summary A series of cobalt(II), nickel(II) and copper(II) complexes of 2-picolinamineN-oxide, HA, has been prepared. Solids of formula [M(HA)₃](BF₄)₂ (M=cobalt(II) or nickel(II); [Cu(HA)₂]X₂ (X=BF ₄ ^– , NO ₃ ^– ); [Co(HA)₂X₂] (X=Cl^– or Br^–); [Ni(HA)₂Cl₂] and [Cu(HA)X₂] (X=Cl^– or Br^–] have been isolated and characterized by partial elemental analyses, molar conductivities, magnetic susceptibilities, DSC-TGA, and spectral methods. All complexes were found to be monomeric, and their spectral parameters are compared with those of the metal ion complexes ofN-alkyl-2-picolinamineN-oxides, 2-dialkylaminopyridineN-oxides and 2-picolinamine. The cobalt(II) and nickel(II) halide complexes spectrally show a mixture of octahedral and tetrahedral centres.     

Modeling of the Response of Hydrogen Bond Properties on an External Electric Field: Geometry,NMR Chemical Shift,Spin-Spin Scalar Coupling

The response of the geometric and NMR properties of molecular systems to an external electric field has been studied theoretically in a wide field range. It has been shown that this adduct under field approach can be used to model the geometric and spectral changes experienced by molecular systems in polar media if the system in question has one and only one bond, the polarizability of which significantly exceeds the polarizability of other bonds. If this requirement is met, then it becomes possible to model even extreme cases, for example, proton dissociation in hydrogen halides. This requirement is fulfilled for many complexes with one hydrogen bond. For such complexes, this approach can be used to facilitate a detailed analysis of spectral changes associated with geometric changes in the hydrogen bond. For example, in hydrogen-bonded complexes of isocyanide C≡¹⁵N-¹H⋯X, ¹J(¹⁵N¹H) depends exclusively on the N-H distance, while δ(¹⁵N) is also slightly influenced by the nature of X.     

Characteristic features of decomposition of potassium pentacyano-cobaltates(III) on a bombardment with fast atoms

Mass spectra were obtained of cobalt(III) pentacyanide complexes of the K_n[Co(CN)₅X] type bombarded by fast atoms, where X = H₂O, NO₂ ^–, NO^–. The ligand elimination processes from the coordination sphere of the pentacyanides and the redox reactions of the complexes were studied.Translated from Teoreticheskaya i Éksperimental'naya Khimiya, Vol. 28, No. 2, pp. 173–176, March–April, 1992.     

Metal ion directed synthesis of 14–16 membered tetraimine macrocyclic complexes

A new series of 14–16 membered tetraazatetraimine macrocyclic complexes [ML1X2]-[ML3X2] [M=CoII, NiII and ZnII] and [CuL1]X2-[CuL3]X2 [X=Cl or NO3] have been synthesized by the template condensation of dibenzoylmethane with primary diamines in MeOH. The complexes were characterized by elemental analysis, i.r, 1H-n.m.r., e.p.r. and u.v-vis spectroscopy, as well as by conductivity and magnetic susceptibility measurements. The copper complexes exhibit square planar geometry, whereas an octahedral geometry is suggested for all other complexes.     

Coordination chemistry of poly(1-pyrazolyl)alkanes Part V: Preparation and characterization of cobalt(II) complexes with bis(1-pyrazolyl)methane and bis(3-methylpyrazolyl)propane

Summary Bis(1-pyrazolyl)methane, H₂Cbpz, and bis(3-methylpyrazolyl)propane, Me₂Cbmpz, react with cobalt(II) salts to give the solid complexes: [Co(H₂Cbpz)₂X₂] ·2H₂O (X=Cl^–, Br^–, I^–, NO ₃ ^– or ClO ₄ ^– ) and [Co(Me₂-Cbmpz)X₂] (X=Cl^–, Br^–, or I^–), which were isolated and characterised by elemental analysis, i.r. and electronic spectra and conductance measurements. From spectral data, octahedral and tetrahedral structures have been proposed for the H₂Cbpz and Me₂Cbmpz complexes respectively. The molar conductance of the complexes indicates that they are non-ionic.     

Iron(II) and iron(III) complexes of 2,4-dithiobiuret

Summary Ferrous and ferric complexes of 2,4-dithiobiuret (Dtb) of the type Fe(Dtb)_m Xn where m, n = 1-3, and X = CI^–, Br^–, I^– and SO ₄ ^2– , and a neutral Fe(Dtb-H)2 complex have been synthesized and characterised by elemental analyses, magnetic susceptibility, i.r., electronic and Mössbauer spectroscopic studies. From its i.r. spectrum Dtb was found to act as a S,S-coordinating bidentate chelate. The magnetic moment, electronic and Massbauer spectra are consistent with a low spin distorted octahedral structure for the ferric complexes and a high spin form for ferrous complexes.