The reaction of oxygen uptake by Co(II) complexes with a group of diastereoisomeric dipeptides, consisting of alanine and leucine in various chiral forms, has been studied in an aqueous solution. The structure of the bridging moiety has been discussed on the basis of spectroscopic results (UV, Vis, near IR, CD, ESR). The effect of stereoselectivity has been confirmed by studies on reversibility of oxygenation. Comparative ESR measurements were done for mixed complexes with imidazole as N-base in the axial position. All of the results were compared with that for glycine dipeptides (containing only one asymmetric atom).

The system LaPO₄-Ba(PO₃)₂-LaP₅O₁₄, a part of the La₂O₃-BaO-P₂O₅ oxide system, has been investigated by differential thermal analysis, X-ray powder diffraction and microscopy in reflected light and its phase diagram was suggested. It was found that in the composition range under investigation, there occurs the quasi-binary section, i.e. La(PO₃)₃-Ba(PO₃)₂ only. Its phase diagram has been determined.

New coordination polychelates of manganese(II), cobalt(II), nickel(II), copper(II), zinc(II) and cadmium(II) with the Schiff base derived from 4,4'-dihydroxydibenzoyl biphenyl and 2,3-butanedionedihydrazone have been synthesized and characterized by elemental analysis, electronic and IR spectra, magnetic susceptibility, thermal analysis and D.C. electrical conductivity. The Schiff base behaves as a dibasic, tetradentate ligand coordinating through an ONNO system and forms chelates with general formula of [ML^.xH₂O]_n (where x =1 or 2). The thermogravimetric studies indicate a two stage decomposition and the presence of water molecules. Using thermal decomposition data, different kinetic and thermodynamic parameters have also been evaluated. D.C. electrical conductivity was measured over a wide range of temperature in a pellet form. The Schiff base and its polychelates have also been tested for their antimicrobial activities.

Trinuclear carboxylate compound [Fe₃O(CH₃COO)₆(H₂O)₃]₂[PtCl₆]• 8H₂O has been studied by Moessbauer spectroscopy, magnetochemistry, thermal analysis and X-ray crystallography. Crystal data: monoclinic, space group P2₁/n, a = 10.505(2), b = 14.278(3), c = 19.885(4) , = 96.00(3)° and Z = 2. The final R-value is 0.027 for 4606 reflections with I2(I). The crystal consists of the complex [Fe₃O(CH₃COO)₆(H₂O)₃]⁺ cations, centrosymmetric [PtCl₆]^2- anions and water molecules. The [Fe₃O(CH₃COO)₆(H₂O)₃]⁺ cation has the typical structure of a trinuclear iron(III) compound with µ₃-O bridge. All crystal components are connected via a system of hydrogen bonds into a 3D network. Moessbauer spectrum displays at room temperature a single quadrupole doublet with an isomer shift of 0.70 mm/s and quadrupole splitting of 0.48 mm/s, consistent with high-spin Fe(III). µ_eff per Fe atom (3.25µ_B at 293 K and 2.23µ_Bat 120 K), indicate the antiferromagnetic coupling between the paramagnetic iron ions with J = -31 cm^-1.

S-Glycosyl O,O-diethyl phosphorodithioates derivatives of L-arabino-, D-ribo- and D-xylofuranose can be conveniently prepared by treatment of reducing monosaccharides with tosyl chloride or diphenyl phosphorochloridate and diethyl phosphorodithioate under phase-transfer conditions. Their ability to act as glycosyl donors was demonstrated.

As part of our investigation on antimicrobial agents, the structure of 5-chloro-2-[p-t-butylphenyl]benzoxazole is reported: C₁₇H₁₆ClNO, mol. mass 285.77, monoclinic, space group: C2/c; a = 32.164(6) , b = 6.756(1) , c = 13.710(3) ; = 92.73(3)° V = 2975.8(10) ³; d_x = 1.276 g cm^-3; Z = 8; F(000) = 1200; µ(CuK) = 2.219 mm^-1. Final R = 0.0658 for 2621 reflections with F > 4(F). Final atomic coordinates for this 2,5-disubstituted benzoxazole were used as a starting point in molecular modelling of remaining 32 derivatives searched as antimicrobial agents. Electronic parameters calculated with quantum chemistry methods and classical Hansch's constants were applied in searching for structure-activity correlation. It was established that geometrical para-
meters (area and volume) and LUMO energy values seem to be most important for the activity.

Cycloadditions of diazoalkanes to thiones take place in two directions furnishing 1,3,4-thiadiazolines and/or their 1,2,3-isomers, depending upon the substituents. Adamantanethione and diazomethane give rise to both regioisomers; a literature report on the high solvent dependence of the isomer ratio is confirmed, and the two regioisomers are isolated. The 1,3,4-thiadiazoline 20 eliminates N₂ at 80°C (t_1/2 55 s) in a 1,3-dipolar cycloreversion; the thiocarbonyl ylide 22 generated undergoes electrocyclization, forming a thiirane, or is intercepted by reactions with HX (thiols, alcohols) or dipolarophilic multiple bonds. The N₂ extrusion from the isomeric 1,2,3-thiadiazoline 21 is at 80°C 600 times slower; the formation of the spirothiirane and homoadamantane-2-thione is explained by a diazonium thiolate as an intermediate.

Infrared results concerning the surface species in MgO catalysts doped with Na⁺ ions are presented. Different surface carbonate structures and hydroxyls groups have been found. It was assumed that created carbonate compounds could be involved in decreasing of MgO specific surface area. Sodium carbonate and unidentate carbonate structures may cause elimination and blockage of low coordination sites of MgO surface, being responsible both for hydrogen detachment from CH₄ molecules and for oxidation of methyl radicals to carbon oxides - the undesired reactions of oxidative coupling of methane (OCM). It was observed that increasing temperature led to decomposition of surface bicarbonate and unidentate carbonate structures. Some of them are being reconverted to more stable bicarbonate structures. Carbon dioxide and water desorptions result in gradual restoration of low coordinated sites of MgO, corresponding to high selectivity to C₂ hydrocarbon formation. Sodium ions may also cause structural changes in MgO lattice. The catalysts were active and selective above 950 K for C₂ hydrocarbon formation, although sodium carbonate is sufficiently stable under the conditions of the OCM process.

Ab-initio gas-phase structure calculation of the geometry of three isomers of the cyanoaniline were determined using the Hartree-Fock level of theory. The optimized molecular structures have been compared with the in-crystal geometry of the molecules. The small differences in the bond lengths and angles were interpreted and analyzed in terms of the distribution of the charge density. The calculated charge density and its Laplacian function were analyzed in terms of the topological properties at the (3,-1) critical points (CPs) of the covalent and polar bonds. The effect of the donor-/acceptor functional groups attached to the phenyl ring is demonstrated especially in the location of the bond critical points and in the charge density at the bond critical points.

Results of high level quantum chemical calculations on thiocarbonyl S-imides of type 4 are reported. Structure and properties of thioformaldehyde S-imide (4b) (CH₂SNH) and its derivatives were calculated by DFT(B3LYP) in conjunction with 6-31+G(d,p) and 6-31+G(3df,3dp) basis sets. For the sake of comparison conventional ab initio quantum chemical calculations were also performed at MP2 and QCISD(T) levels. The calculated geometry and molecular properties of 4b are compared with those of closely related ylidic structures such as thioformaldehyde S-methylide (1, R¹-R⁴ = H), thioformaldehyde S-oxide (2, R¹-R² = H), and thioformaldehyde S-sulfide (3, R¹-R² = H). Differently substituted thiocarbonyl S-imides 4d-i were calculated to show the effect of substitution on their molecular and electronic structure as well as on some physical properties. The parent compound 4b in the molecular ground state is predicted to be most stable in the planar and bent anti-conformation with geometric parameters and electronic characteristics of a predominantly ylidic structure. The IR and UV absorption maxima of 4b were calculated and discussed with respect to the expected structure of this reactive intermediate.

Results of high level quantum chemical calculations on thiocarbonyl S-imides 1 are reported. The reactivity of thioformaldehyde S-imide (1a) (CH₂S⁺NH^-) in pericyclic reactions was calculated by density functional theory using gradient corrected functionals in conjunction with 6-31+G(d,p) and 6-31+G(3df,3dp) basis sets. For the sake of comparison, conventional ab intitio quantum chemical calculations at correlated levels of theory, such as MP2, QCISD(T) G1 and G2(MP2), were also performed. The predicted reactivity of the parent compound is compared with those of some closely related ylides (S-centered 1,3-dipoles), such as thioformaldehyde S-methylide (2a), thioformaldehyde S-oxide (3a) and thioformaldehyde S-sulfide (4a). To show the effect of substitution on structure and reactivity a series of acyclic and cyclic substituted thiocarbonyl S-imides 1b-k was calculated. The 1,3-electrocyclic ring closure of 1a to form thiaziridines 5 is predicted to be exothermic process by about 10 kcal/mol with activation energies of about 30 kcal/mol. The calculated reaction energies are considerably affected by higher angular momentum polarization functions, such as f-functions. In the case of some substituted thiocarbonyl S-imides, such as thiotropone S-imide (1i) and thiofluorenone S-imide (1j), the exothermicity of the ring closure reaction is lower than that of the parent compound. The concerted prototype [3+2]-cycloaddition of 1a with ethylene is strongly exothermic (about 50 kcal/mol) with the activation energy of about 20 kcal/mol. The energetics of both types of the pericyclic reactions of 1a appears closely related to that of 4a but differs more strongly from that of 3a. The contemporary knowledge on thiocarbonyl S-imides 1 is reviewed and discussed in conjunction with theoretical results.

The crystal structures of three pyrazolopyridines, ethyl 4-amino-6-ethyl-1-pentyl-1H-pyrazolo[3,4-b]pyridinium-5-oate chloride hydrate C₁₆H₂₅N₄O₂^{+ .}Cl^-.H₂O (1), ethyl 4-amino-6-isopropyl-1-pentyl-1H-pyrazolo[3,4-b]pyridinium-5-oate chloride C₁₇H₂₇N₄O₂^+.Cl^- (2), and 4-amino-1-pentyl-1H-pyrazolo[3,4-b]pyridine-5-N-(2-propenyl)carboxamide C₁₅H₂₁N₅O (3) have been determined by X-ray structure analysis of single crystals. The ethyl and isopropyl substituents in compounds 1 and 2, respectively, which are in ortho position relative to the ester group, cause a twist of the O=C-O-C plane with respect to the plane of pyrazolopyridine ring system. In the absence of that steric hindrance, in compound 3, the intramolecular N(amine)-H^...O hydrogen bond closes the nearly planar six-membered ring. The coplanarity of the ester or amide plane with the plane of ring system is probably a necessary condition for the significant anxiolytic action. In both cations, the protonation takes place at the pyridine nitrogen atom. In the crystal structures of salts there are separate layers of anions and cations. In the free base, intermolecular hydrogen bonds make infinite chains of molecules.

The low-temperature crystal structures of 4-(1-naphthyl)[2.2]paracyclophane (1), C₂₆H₂₂, orthorhombic, Pca2₁, a = 15.860(3), b = 7.2871(14), c = 30.954(5) , Z = 8 (two independent molecules) and 4-{1-(2'-methyl)naphthyl}[2.2]paracyclophane (2), C₂₇H₂₄, monoclinic, P2₁/c, a = 8.0243(6), b = 14.8073(14), c = 16.239(2) , = 93.868(8)°, Z = 4 have been determined. In both compounds the conformations are such that the hydrogen at the naphthyl 8-position lies above the bridgehead atom C3 in (1) and points into the cyclophanyl cavity in (2) (the methyl group lies above the bridgehead atom C3). The interplanar angles between the naphthyl groups and the cyclophane rings, to which they are bonded, are 49.8 (49.1) and 55.5°, respectively.

Crystals of diaquobis(trans hydrogen pyrazine-2,3-dicarboxylato N,O)nickel(II) - title compound I, contain monomeric molecules. The nickel(II) ion is coordinated by two molecules of pyrazine-2,3-dicarboxylic acid, each donating its heteroring nitrogen [Ni-O 2.0485(15) ] and one oxygen atom, belonging to the nearest monodentate carboxylic group [Ni-O 2.0199(14) ]. Two water molecules [Ni-O 2.0914(17) ] complete the octahedral coordination around the central ion. The second carboxylic group and the heteroring nitrogen do not directly bond to the nickel(II) ion. Monomeric molecules of the composition Ni(II)(APZA)₂(H₂O)₂ - title compound II, have been also found in the crystals of diaquobis(trans 3-amino-2-pyrazinecarboxylato O,N)nickel(II) compound. The coordination of the Ni ion is octahedral. (N,O) bonding moieties of two ligand molecules [Ni-O 2.0395(12) , Ni-N 2.0669(14) ] and the Ni ion are coplanar. The oxygen atoms donated by two water molecules [Ni-O 2.0656(14) ] constitute the vertices of the slightly elongated octahedron. The structures of both title compounds indicate a preference of nickel ion to form monomeric molecules. The monomeric molecules contain strong intramolecular hydrogen bonds. The stability of the crystals is maintained by a system of intermolecular hydrogen bonds.

Crystal and molecular structure of 3-(2,4,6-trimethylphenyl)-8-phenyl-oxo-1,7-dioxa-2-azaspiro[4,4]non-2-ene has been determined by X-ray diffraction technique. Crystal data for C₂₁H₂₁NO₃: monoclinic, C2/c, a = 20.969(4) , b = 10.319(2) , c = 16.601(3) , = 97.5(3)°, Z = 8, R = 0.0658 for 3477 reflections. Contrary to the solution, in the crystalline state only one conformer exists.