Ivan Vicković

The stereostructure of trimers of biacetyl

Abstract Structures of two trimers of biacetyl were determined on the basis of chemical and spectroscopic evidence and the single-crystal X-ray analysis. The compounds are shown to be exo-3, endo-7-diacetyl-1- hydroxy-endo-3,5,exo-7-trimethyl-cis-2,4,6-trioxabicyclo[3.3.0]octanc (2) and 11-hydroxy-1,3,5,7,11- pentamethyl-cis-2,4,6,8-tetraoxatricyclo[3.3.3.03.7]undecan-9-one(3).

Structural study of picolinamide complexes of Ni(II), Zn(II), Cd(II), and Hg(II) nitrates in solid state and solution

Three picolinamide complexes of nickel(II) (1), zinc(II) (2), and cadmium(II) (3) have been prepared and their solid state structures were determined by single-crystal X-ray diffraction analysis. Their structures in DMSO solutions as well as the structure of similar mercury(II) complex, [Hg(NO3)(pia)2](NO3) (4), have been elucidated by 1H and 13C NMR spectra. The picolinamide is bound through the N,O-donors in all four complexes in solid state, but only in 4 it is in solution state. In nickel (1), zinc (2), and cadmium (3) complexes the pia-N coordination in solution is suggested. The X-ray analysis revealed that isomorphous nickel (1) and zinc (2) crystal structures comprise the centrosymmetrical trans-[M(H2O)2(pia)2]2+ (M = Ni, Zn; pia = picolinamide) and nitrate. The crystal lattices also contain two non-coordinated H2O molecules. In 3, each cadmium(II) is N,O-chelated by two cis-oriented pia ligands, while remaining coordination sites of the capped pentagonal bipyramid are occupied by three oxygen atoms from two nitrates. Crystal structures are dominated by O/N/C–H···O hydrogen bonds. The carboxamide moieties in 1 and 2 do not form any head-to-head or catemeric supramolecular synthons, but participate in the formation of (12) motifs with solely the amide nitrogen atoms as double hydrogen bond donors. In 3, neighboring molecules are linked into head-to-head amide dimers. The biological effect of picolinamide and [Zn(pia)2(H2O)2](NO3)2 on ingestion and intracellular microbicidal capacities of human peripheral blood phagocytes was also assessed.

Key intermediates in the caffolide pathway for degradation of uric acid. X-ray structure of methylammonium 1-methylcaffolide

Abstract Alloxanic acid ureides ( 3 ) formed by oxidative ring fission at the 3,4-bond of uric acids ( 1 ), undergo a facile rearrangement to isomeric products whose ammonium caffolide structure 5 was established by synthesis and confirmed by X-ray analysis of methylamine salt of 1-methylcaffolide ( 5b ).

Addition compounds of bis(trifluoromethyl)mercury with tetraphenylphosphonium and tetraphenylarsonium halides and thiocyanates

Addition compounds of Hg(CF 3 ) 2 with [Ph 4 P]X and [Ph 4 As]X in the 1:1 ratio for X = Cl, Br, I as well as in the 1:2 ratio for X = SCN, were isolated from aquaeous solution and identified by elemental analysis and infrared spectroscopy. Molar conductance of the thiocyanate compounds in nitrobenzene solution points to its complex-salt nature defined as [Ph 4 P] 2 [Hg(CF 3 ) 2 (SCN) 2 ] and [Ph 4 As] 2 [Hg(CF 3 ) 2 -(SCN) 2 ], but not for the halide compounds. However, in the monoclinic crystals of the chloride ccompound, as shown by X-ray diffractometry, pairs of [Hg(CF 3 ) 2 molecules are bridged over by two chlorides in a centro-symmetrical dimer with the CHgC bond angle of 160.5(8)° and the Hg…Cl bond length of 2.823(3) and 2.837(4) A. The structure was refined to the R factor of 0.053. When X = CN no addition compounds were obtained, the reaction products were HCF 3 and the complex salts [Ph 4 P] 2 - [Hg(CN)] 4 and [Ph 4 As] 2 [Hg(CN)] 4 , not described so far.

Stereoelectronic control in the oxidation of gem-disulphides

The first example of stereospecific oxidation in the gem-disulphide series is reported; chemical, spectral, and X-ray evidence indicated the stereoelectronic discrimination between two modes of approach of electrophile in the conversion to meso-2,2-bis(methylsulphinyl)-1,3-diphenylpropane (2).