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At least 1,081 records · Page 60Linked to original sources
PubMed2002

A highly efficient photochemical bromination as a new method for preparation of mono, bis and fused pyrazole derivatives.

N-Bromosuccinimide (NBS) was found to afford photochemical bromination of N-substituted 3-methyl-2-pyrazolin-5-one in chloroform solution. The nature of the products formed was found to be highly dependent on the photolysis time and on the type of N-substituted 3-methyl-2-pyrazolin-5-one. The reaction of substituted 2-pyrazolin-5-ones with NBS in the absence of light yielded in all cases a mixture of N-substituted 3-methyl-4-bromo- (and -4,4-dibromo-) 2-pyrazolin-5-ones. The mechanism of photobromination was illustrated. Separation of all of the products was achieved using column chromatography. The chemical structure of all of the products was assigned by elemental analysis, IR, 1H NMR and GC-MS measurements.

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PubMed2003

A crystallographic, EPR and theoretical study of the Jahn-Teller distortion in [CuTp2] (Tp- = tris[pyrazol-1-yl]hydridoborate).

Crystals of the title compound (1) contain two independent, centrosymmetric half-molecules per asymmetric unit. While both of these show Jahn-Teller elongated six-coordinate geometries, the lengths of the elongated Cu-N bonds in the two molecules differ by 0.117(2) A at 30 K. The structure of one of these molecules (molecule A) does not vary with temperature below 350 K. The other molecule (molecule B) shows Cu-N bond lengths that are temperature-dependent between 225 and 375 K, but do not vary further at lower temperature. This indicates a fluxional axis of Jahn-Teller elongation in this molecule at these higher temperatures. Consideration of the thermal parameters in these structures implies that the fluxionality in molecule B is frozen out near 150 K. This conclusion is supported by a Q-band powder EPR study. The d-d transition energies of molecules A and B have been calculated by several density function (DF) methods, including a time-dependent DF calculation. The crystallographic data have been reproduced using the vibronic coupling model of Burgi and Hitchman. This has shown that the different fluxionality regimes for molecules A and B are not a consequence of their different static molecular structures, but rather reflect their different local environments in the crystal.

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PubMed2004

Magnetic behavior and Mossbauer spectra of spin-crossover pyrazolate bridged dinuclear diiron(II) complexes: X-ray structures of high-spin and low-spin [(Fe(NCBH3)(py))2(mu-bpypz)2].

The synthesis and characterization of new spin-crossover pyrazolato bridged dinuclear [(FeII(NCS)(py))2(mu-bpypz)2] and the corresponding cyanotrihydroborato-kappaN complexes are described together with the X-ray crystal analysis of the latter in both the high-spin and low-spin states as well as the variable temperature magnetic susceptibility and/or Mossbauer spectra demonstrating the spin-crossover which exhibits an one-step process, but not a two-step one characteristic of the known bpym bridged dinuclear complexes.

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PubMed2006

Design and solvothermal synthesis of luminescent copper(I)-pyrazolate coordination oligomer and polymer frameworks.

Two luminescent coordination compounds, [Cu(Pz)]3 (1) and [Cu2(Bpz)]n (2), were isolated from solvothermal reactions of Cu(NO3)2 with 3,5-dimethylpyrazole (HPz) and 3,3',5,5'-tetra-methyl-4,4'-bipyrazole (H2Bpz) respectively in the presence of NH3, of which 1 was revealed to be a planar trimer and 2 a three-dimensional framework, presenting a rare 3-connected binodal (6(2).10)(6.10(2)) topology and eight-fold interpenetration.

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PubMed2001

4-([(1E)-(2-Hydroxyphenyl)methylidene]amino)-1,5-dimethyl-2-phenyl-2,3-dihydro-1H-pyrazol-3-one.

In the title compound, C18H17N3O2, a strong intramolecular O-H...N hydrogen bond [N...O 2.607 (3), O-H 0.97 (3) and H...N 1.71 (3) A, and O-H...N 153 (2) degrees ] was observed, which leads to a unique phenol-imine tautomerism in the solid state. The C=N imine bond distance and the C-N-C bond angle [1.287 (2) A and 121.7 (1) degrees, respectively] indicate the existence of this phenol-imine tautomer. In solution, the phenol-imine tautomer of the title free Schiff base ligand is dominant in both polar and non-polar solvents, as supported by 1H NMR and UV-visible spectroscopic data.

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PubMed2001

Bis[2-(pyrazol-3-yl)phenolato-kappa2N2,O]copper(II) dimethanol solvate.

The title compound, [Cu(C9H7N2O)2]*2CH3OH, contains a crystallographically centrosymmetric near-regular square planar Cu(II) centre with trans-disposed chelating ligands. The complex molecules associate into a one-dimensional polymeric chain via hydrogen bonding to the solvent molecules.

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PubMed2002

4,5-Dihydro-3-methyl-5-(4-methylphenyl)-1H-pyrazole-1-carboxamidinium acetate acetone hemisolvate.

The X-ray structure analysis of the unexpected product of the reaction between 4-(4-methylphenyl)but-3-en-2-one and aminoguanidine revealed the title compound, C(12)H(17)N(4)(+) x -C(2)H(3)O(2)(-) x 0.5C(3)H(6)O, consisting of a protonated amidine moiety joined to a substituted pyrazoline ring at the N1 atom. The amidine group is protonated and the positive charge is delocalized over the three C[bond]N bonds in a similar manner to that found in guanidinium salts. The amidinium moiety of the cation is linked to the acetate anions through four N[bond]H...O hydrogen bonds, with N...O distances of 2.749 (4), 2.848 (4), 2.904 (4) and 2.911 (4) A. The pyrazoline ring adopts a flattened envelope conformation and the substituted phenyl ring is oriented perpendicular to the attached heterocycle. The acetone solvate molecule lies across a twofold rotation axis.

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PubMed2003

4,5-Dihydro-3-methyl-5-(4-methylphenyl)-1H-pyrazole-1-carboxamide.

The reaction between 4-(4-methylphenyl)but-3-en-2-one and aminoguanidine produced an unexpected product of formula C(12)H(15)N(3)O, consisting of a carboxamide moiety joined to a substituted pyrazoline ring at one of the N atoms. The pyrazoline ring adopts a flat-envelope conformation and the substituted phenyl ring is oriented almost perpendicular to the heterocycle. The carbonyl O atom has partial anionic character as a result of the transfer of pi density from the two adjacent sp(2) N atoms and is involved in an intermolecular hydrogen bond with the amide group.

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