(Nitrato‐κO)bis(pyridine‐2‐carboxamide‐κ2N1,O)mercury(II) nitrate

In the title compound, [Hg(NO₃)(C₆H₆N₂O)₂]NO₃, the Hg^II atom is five‐coordinate. The distorted square‐pyramidal mercury(II) coordination environment is achieved by two N,O‐bidentate picolinamide ligands, with one O‐monodentate nitrate ion in the apical position. A seven‐coordinate extended coordination environment is completed by two additional weak Hg...O interactions, one from the coordinated nitrate ion and one from the other nitrate ion, to give seven‐coordination. The molecules are linked into a two‐dimensional network by N—H...O hydrogen bonds.     

A new coordination mode of 6‐methylnicotinic acid in trans‐tetraaquabis(6‐methylpyridine‐3‐carboxylato‐κO)cobalt(II) tetrahydrate

The title compound, [Co(C₇H₆NO₂)₂(H₂O)₄]·4H₂O, contains a Co^II ion lying on a crystallographic inversion centre. The Co^II ion is octahedrally coordinated by two 6‐methylpyridine‐3‐carboxylate ligands in axial positions [Co—O = 2.0621 (9) Å] and by four water molecules in the equatorial plane [Co—O = 2.1169 (9) and 2.1223 (11) Å]. There are also four uncoordinated water molecules. The 6‐methylpyridine‐3‐carboxylate ligands are bound to the Co^II ion in a monodentate manner through a carboxylate O atom. There is one strong intramolecular O—H...O hydrogen bond, and six strong intermolecular hydrogen bonds of type O—H...O and one of type O—H...N in the packing, resulting in a complex three‐dimensional supramolecular structure.     

Mercury(II) Compounds with 1,3-Benzothiazole-2-thione. Spectral, Thermal, and Crystal Structure Studies

Mercury(II) halides, HgX₂ (X = Cl^–, Br^–, I^–) react with 1,3-benzothiazole-2-thione (btztH) in methanol solutions giving the HgX₂(btztH) and HgX₂(btztH)₂ types of compounds. Mercury(II) acetate gives the thiolato compound Hg(btzt)₂ because of the deprotonation of btztH. Hg(btzt)₂ reacts with 2,2-bipyridine (bipy) giving a 1:1 complex. IR, ¹H, and ¹³C NMR spectral studies indicate that btztH acts as a monodenatate ligand through the S thione donor atom in all complexes. The X-ray crystal structure determinations of [HgI₂(btztH)]₂, HgBr₂(btztH)₂, Hg(btzt)₂, and Hg(btzt)₂(bipy) have been carried out revealing tetrahedrally coordinated mercury atom in [HgI₂(btztH)]₂ and HgBr₂(btztH)₂, while in Hg(btzt)₂(bipy) 2 + 2 coordination is achieved through strong Hg (N(bipy) contacts. A linear coordination in Hg(btzt)₂ is not affected by the Hg N contacts, which are longer than in Hg(btzt)₂(bipy), but still shorter than the van der Waals sum of mercury and nitrogen covalent radii. [HgI₂(btztH)]₂ exists as centrosymmetrical dimer with a Hg₂I₂ bridging core. The dimeric molecules are linked by the intermolecular hydrogen bonds between the terminal iodine atom and the NH group [3.63(1) Å] into infinite chains along the z-axis. There are N–H Br(bridging) intermolecular hydrogen bonds in HgBr₂(btztH)₂ joining molecules into endless chains along the x-axis. The Br(bridging) atom acts as double proton acceptor and two NH groups as proton donors [NH Br(bridging) 3.278(9) and 3.338(7) Å]. The mercury to sulfur and mercury to halogen bond distances in [HgI₂(btztH)]₂ and HgBr₂(btztH)₂ are discussed in relation to the analogous compounds, revealing strong influence of hydrogen bonds on their relative strengths as well as crystal packing requirements of the ligand. The sulfur and halogen atoms are more tightly bound to mercury implicating severe distortion of the coordination polyhedron in the structures in which they do not take part in hydrogen bonds formation. The influence of steric requirements of the ligands in Hg(btzt)₂ and Hg(btzt)₂(bipy) on the distortion of the mercury coordination polyhedra accompanied with the relative strength of Hg N contacts is considered.     

A 1:2 complex of mercury(II) chloride with 1,3‐imidazole‐2‐thione

The Hg atom in the title monomeric complex, di­chloro­bis(3‐imidazolium‐2‐thiol­ato‐S)­mercury(II), [HgCl₂(C₃H₄N₂S)₂], is four‐coordinate having an irregular tetrahedral geometry composed of two Cl atoms [Hg—Cl 2.622 (2) and 2.663 (2) Å] and two thione S atoms [Hg—S 2.445 (2) and 2.462 (2) Å]. The monodentate thione ligand adopts a zwitterionic form and exists as the 3‐imidazolium‐2‐thiol­ate ion. The bond angle S1—Hg—S2 of 130.87 (8)° has the greatest deviation from ideal tetrahedral geometry. Intermolecular hydrogen bonds between two of the four N—H groups and one of the Cl atoms [3.232 (8) and 3.238 (7) Å] stabilize the crystal structure, while the other two N—H groups contribute through the formation of N—H?Cl intramolecular hydrogen bonds with the other Cl atom [3.121 (7) and 3.188 (7) Å].     

Kinetic Spectrophotometric Determination of Ascorbic Acid in Pharmaceutical Samples by Oxidation of Ponceau 4R by Hydrogen Peroxide

A new sensitive and simple kinetic method is developed for determination of traces of ascorbic acid based on its activated effect on oxidation of trisodium‐2‐hydroxy‐1‐(4‐sulphonato‐1‐naphthylazo)naphthalene‐6,8‐disulphonato (red artificial color Ponceau 4R) by hydrogen peroxide, in the presence of Cu(II) as catalyst, in borate buffer. The reaction is followed spectrophotometrically by tracing the oxidation product at 478.4 nm within 1 min after addition of H₂O₂. The optimum reaction conditions are: borate buffer (pH = 11.00), Ponceau 4R (9.6·10^?6 mol/L), H₂O₂ (2·10^?2 mol/L), Cu(II) (8·10^?7 mol/L) at 22 °C. Following this procedure, ascorbic acid can be determined with a linear calibration graph up to 1.76 ng/mL and a detection limit of 0.28, based on 3S criterion. The relative error ranges between 6.77‐1.66% for the concentration interval of ascorbic acid 1.76‐17.61 ng/mL. The effects of certain foreign ions upon the reaction rate were determined for an assessment of the selectivity of the method. The method was applied for determination of ascorbic acid in pharmaceutical samples, and spectrophotometric method was used like an comparative method.     

Synthesis,spectroscopic and structural investigation of Zn(NCS)2(nicotinamide)2 and [Hg(SCN)2(nicotinamide)]n

Zinc(II) and mercury(II) thiocyanate complexes with nicotinamide, bis(nicotinamide-N)-bis(thiocyanato-N)zinc(II) (1) and catena-[nicotinamide-N-(μ-thiocyanato-S,N)(thiocyanato-S)mercury(II)] (2), have been prepared and characterized by spectroscopic, thermal and X-ray crystallographic methods. The vibrational bands of diagnostic value are compared to the values of the free ligand and the data are in good correlation with the X-ray results. Centrosymmetrical hydrogen bonded dimers are found, R₂²(10) in 1 and R₂²(8) in 2.     

Preparation,structural and thermal characterization of cobalt(II) and copper(II) complexes with 3-hydroxypicolinamide

Cobalt(II) and copper(II) complexes of 3-hydroxypicolinamide (3-OHpia), namely [Co(3-OHpia)₂(H₂O)₂](NO₃)₂ (1), [Co(3-Opia)₂(H₂O)₂] (2) and [Cu(3-OHpia)₂(NO₃)₂] (3), were prepared and characterized by IR spectroscopy and TG/DTA methods. The molecular and crystal structures of 1 and 3 were determined by X-ray crystal structure analysis. Complexes 1 and 3 were obtained by reaction of 3-hydroxypicolinamide with cobalt(II) nitrate or copper(II) nitrate, respectively, in a mixture of ethanol and water. Complex 2 was prepared by reaction of cobalt(II) acetate and 3-OHpia in aqueous solution. X-ray structural analysis revealed octahedral coordination polyhedra in both 1 and 3 and the same N,O-chelated coordination mode of 3-OHpia. The coordination sphere of the cobalt(II) center in 1 is completed by two coordinated water ligands and that of the copper(II) center in 3 by two coordinated nitrate anions. There are also two uncoordinated nitrate ions in 1 which compensate the positive charge of cobalt(II). The crystal structures of 1 and 3 are dominated by intermolecular O–H···O and N–H···O hydrogen bonds. The thermogravimetric study indicated the loss of two coordinated water molecules in 1 and 2 and of one 3-OHpia ligand together with N₂ molecule in 3 at lower temperatures (up to 300 °C).     

One-pot synthesis of iodine-substituted 1,4-oxazepines

A facile one-pot method for the synthesis of iodine-substituted 1,4-oxazepines is reported. When reacted with ZnCl₂ and I₂ in DCM at 40?°C, N-propargylic β-enaminones, prepared by the conjugate addition of propargylamine to α,β-alkynic ketones, underwent 7-exo-dig cyclization by zinc chloride and concomitant reaction with molecular iodine to afford 2-(iodomethylene)-2,3-dihydro-1,4-oxazepines in good to high yields. This cyclization was found to occur with broad scope of substrates and high tolerance of functional groups. The resulting iodine-containing 1,4-oxazepines can be further elaborated to more complex structures by subsequent cross-coupling reactions, which may provide a platform for biological studies.