Structural tautomerism of 4-acylpyrazolone schiff bases and crystal structure of 5-methyl-2-phenyl-4-{1-[(pyridin-2-ylmethyl)-amino]-ethylidene}-2,4-dihydro-pyrazol-3-one

The Schiff base derivatives prepared from 4-acetyl-5-methyl-2-phenyl-2,4-dihydro-pyrazol-3-one and alkyl amines are shown to remain exclusively in the amine-one(I) tautomeric form in chloroform solutions at room temperature using a combination of ¹H, ¹³C, APT, COSY, HMQC, and HMBC NMR spectroscopic methods. The crystal structure of 5-methyl-2-phenyl-4-{1-[(pyridin-2-ylmethyl)-amino]-ethylidene}-2,4-dihydro-pyrazol-3-one showed that this 4-acylpyrazolone Schiff base stays in the amine-one(I) form in the solid state as well, and the solid state structure supports the fact that strong hydrogen bonding between amine hydrogen and the pyrazolone C₃ carbonyl oxygen helps to stabilize the amine-one(I) tautomer.     

Novel structural type of bridged urea derivatives bearing azatricyclo[4.3.1.03,8]decane moiety

Structural Chemistry - In an attempt to synthesize 4-thia-6-azatricyclo[5.3.1.13,9]dodecan-5-imine as putative antihypotensive agent with prolonged effect, a reaction of...     

Luminescence-assisted two-photon spectroscopy (LATS) - a new spectroscopic method applied to biexciton levels in highly excited CdS and ZnO

We present a new “economic” method for performing two-photon spectroscopy using just one exciting dye-laser and taking advantage of the hereby produced broad emission bands of highly excited semiconductors. It is applied to the biexciton ground state in CdS (E_biex = 5.0983 eV, symmetry Γ₁) and to an excited biexciton state in ZnO (6.7407 eV, symmetry Γ₅).     

Reaction of an iron-lithium complex with tolane and the structure of dilithiumtetraphenylbutadiene formed

The crystal structure of 1,4-dilithiumbutadiene 2 obtained in the reaction of tolane with an iron(II) hydridolithium complex shows that 2 is a dimer with four lithium atoms, forming a distorted tetrahedron with short Li---Li and Li---C distances. Implication for the reaction of the iron-lithium complex with dinitrogen is discussed.     

New trigonal tris(phosphine oxides)

The reaction of 1,1,1-tris(chloromethyl)propane with diphenylphosphine under phase-transfer conditions afforded 1,1,1-tris(diphenylphosphinomethyl)propane, whose oxidation gave a previously unknown representative of trigonal tris(phosphine oxides), viz., stable 1,1,1-tris(diphenylphosphorylmethyl)propane. Its analogs, viz., bis(diphenylphosphoryl)diphenylphosphinomethane and tris(diphenylphosphoryl)methane, are unstable in air and decompose with the cleavage of the P-C bond.Published in Russian in Izvestiya Akademii Nauk. Seriya Khimicheskaya, No. 9, pp. 1926–1929, September, 2004.     

Synthesis and structures of boron complexes of acyl hydroxy coumarins

New boron chelates were synthesized by the reactions of 3-acetyl-4-hydroxycoumarin and 8-acyl-7-hydroxy-4-methylcoumarins with boron trifluoride etherate and hydroxybenzodioxaborole. The structure of 3-acetyl-4-difluoroboryloxycoumarin containing an intramolecular C=O...B coordination bond was established by X-ray diffraction. Published in Russian in Izvestiya Akademii Nauk. Seriya Khimicheskaya, No. 11, pp. 2012–2015, November, 2006.     

Novel platinum(II) ammine hydroxamate and hydroximate complexes and the platinum-assisted hydrolysis of hydroxamic acids

The 2-pyridinecarboxylate (2-pyca) platinum(IV) complex [2-pycaH2][PtCl4(2-pyca)].H2O, 1, has been synthesised from K2[PtCl4] following the hydrolysis of 2-pyridinehydroxamic acid (2-pyhaH) in the presence of H2O2, and directly from K2[PtCl6] and picolinic acid. Structural characterisation of 1 reveals octahedral geometry about platinum(IV) consisting of a (N,O)-bidentate pyridinecarboxylate ligand and four chloride ligands. A mechanism for the hydrolysis of 2-pyridinehydroxamic acid to 2-pyridinecarboxylic acid is proposed. Two novel coordination modes of hydroxamic acids to platinum(II) are also reported. The dinuclear platinum ammine hydroximato complex, [{cis-Pt(NH3)2}2(mu-2-pyhaH(-1))](ClO4)2.H2O, 3, has been synthesised where the two platinum(II) centres are bridged via(O,O) and (N,N) coordination. The latter coordination mode is via the hydroximate nitrogen and the pyridine nitrogen. The corresponding mononuclear platinum(II) pyridinehydroxamate complex, [cis-Pt(NH3)2(2-pyha)]ClO4, 4, has been synthesised. Spectroscopic studies indicate that the coordination mode is through the pyridine nitrogen and hydroxamate oxygen atoms (N,O).     

The nature and energy characteristics of intramolecular hydrogen bonds in crystals

The review concerns the results of systematic X-ray diffraction studies of the electron density distribution in the crystals of compounds with strong intramolecular hydrogen bonds N-H...O, O-H...O, O-H...N, and N-H...S. The advantages of the topological analysis of the electron density distribution function in the analysis of the nature and estimation of the H-bond energies directly from experimental data are discussed. Published in Russian in Izvestiya Akademii Nauk. Seriya Khimicheskaya, No. 1, pp. 1–14, January, 2006.