Zora Popović

Mercury(II) complexes of heterocyclic thiones. Part 1. Preparation of 1:2 complexes of mercury(II) halides and pseudohalides with 3, 4, 5, 6-tetrahydropyrimidine-2-thione. X-ray, thermal analysis and NMR studies

A series of complexes HgX_2(H_4pymtH)_2 (X = Cl, Br, I, SCN, CN ; H_4pymtH = 3, 4, 5, 6-tetrahydropyrimidine-2-thione) has been obtained by the reaction of H_4pymtH with mercury(II) halides and pseudohalides in the 2:1 molar ratio. X-ray diffraction studies revealed tetrahedral coordination of mercury with S-bound H4pymtH. The exception is Hg(CN)_2(H_4pymtH)_2 where the coordination is 2+2 with two strongly bound CN� {; ; ; ; ; ligands and weaker Hg� {; ; ; ; ; S bonds with H4pymtH. One- and twodimensional 1^H and 13^C NMR measurements in dimethylsulfoxide solution confirmed the complexation of mercury to sulphur. The greatest complexation effects on chemical shifts were detected for the C-2, C-5 and H-1, 3 atoms i.e. two, four and five bonds away from mercury atom. The complexation effects in Hg(SCN)_2(H_4pymtH)_2 and Hg(CN)_2(H_4pymtH)_2 are in agreement with the strongest intramolecular H-bonding in the former and the weakest Hg-S bonds in the latter as compared to other complexes here.

Mercury(II) compounds with 1,3-imidazole-2-thione and its 1-methyl analogue. Preparative and NMR spectroscopic studies. The crystal structures of di-μ-iodo-bis[iodo(1,3-imidazolium-2-thiolato-S)mercury(II)], bis[bromo(1,3-imidazolium-2-thiolato-S)]mercury(II) and bis[μ-(1-N-methyl-1,3-imidazole-2-thiolato-S)]mercury(II)

Abstract A series of mercury(II) compounds of the empirical formulae HgX2L, and HgX2L2 (X=Cl−, Br−, I−, SCN−; L=imtH2, meimtH; imtH2=1,3-imidazole-2-thione, meimtH=1-methyl-1,3-imidazole-2-thione) has been obtained by the reaction of mercury(II) salts and 1,3-imidazole-2-thione and 1-methyl-1,3-imidazole-2-thione, respectively. Mercury(II) acetate yields HgL2 complexes where L=imtH−, meimt−. The isolated compounds have been characterised by elemental chemical analysis, IR and 1H and 13C NMR spectroscopy. Complexation effects on chemical shifts in 1H and 13C spectra were shown to be a reliable probe for distinguishing HgX2L and HgX2L2 complexes. In the former molecules the thione carbon (C-2) is shielded up to 3.0 ppm and the thioamide protons (NH) are deshielded up to 0.5 ppm, as compared to the corresponding atoms in the latter molecules. In all complexes the 13C complexation shift at C-2 decreases with decreasing electronegativity of the halogen atom (X), indicating the corresponding increase in π-character of the C-2–S bond. The crystal structures of HgI2(imtH2), HgBr2(imtH2)2 and Hg(meimt)2 have been determined by X-ray diffractometry and revealed S-bound imtH2 in the iodo and bromo complex, while in Hg(meimt)2 the ligand acts as bridging with stronger S and weaker N bonds.

The first example of coexistence of the ketoamino–enolimino forms of diamine Schiff base naphthaldimine parts: the crystal and molecular structure of N,N′-bis(1-naphthaldimine)-o-phenylenediamine chloroform (1/1) solvate at 200 K

Abstract The N,N′-bis(1-naphthaldimine)-o-phenylenediamine chloroform (1/1) solvate was prepared from 2-hydroxy-1-naphthaldehyde and 1,2-phenylenediamine in a 2:1 molar ratio and characterized in solution and in the solid state using X-ray single crystal diffractometry, IR and NMR spectroscopy. The structure consists of three structural fragments: two planar, but not coplanar naphthaldimine moieties linked by phenyl ring that derived from o-phenylenediamine. The naphthaldimine fragments contain, along with naphthalene rings, six-membered pseudoaromatic chelate rings, formed by O H⋯N or N H⋯O intramolecular hydrogen bonds that retain planarity of the aldimine fragments. This structure is the first example of the coexistence of two different hydrogen bond types within Schiff base molecule, i.e. the one naphthaldimine part exists in the enolimino form (O H⋯N hydrogen bond of 2.5487(17) A), while the other exists in the ketoamino form (N H⋯O hydrogen bond of 2.5706(19) A). The different hydrogen bond types are related to the different π-electron density distribution within two parts. The amino hydrogen atom forms three-center intramolecular hydrogen bond, which includes the N H⋯O hydrogen bond of 2.5706(19) A within the ketoamino part and also the N H⋯N bond of 2.7238(18) A linking two naphthaldimine fragments of the molecule. IR and 1H and 13C NMR spectral data are consistent with revealed molecular structure in the solid state.

Preparation and characterization of the 1:1 adducts of mercury(II) halides with N-benzyl- and N-p-tolyl-2-oxo-1-naphthylideneamine. The crystal and molecular structures of two isostructural di-μ-halo-bis[halo(N-benzyl-2-oxo-1-naphthylideneamine)mercury(II)] adducts (halo=chloro, bromo)

Abstract A series of adducts of the type HgX2(C18H15NO) [X=Cl−, Br−, I−; C18H15NO=N-benzyl-2-oxo-1-naphthylideneamine (bznapH), N-p-tolyl-2-oxo-1-naphthylideneamine (tolnapH)] was obtained by refluxing the solution of the corresponding mercury(II) salt and the related naphthylideneamine in absolute ethanol in a 1:1 molar ratio. The adducts di-μ-chloro-bis[chloro(N-benzyl-2-oxo-1-naphthylideneamine)mercury(II)], HgCl2(bznapH) (1) and di-μ-bromo-bis[bromo(N-benzyl-2-oxo-1-naphthylideneamine)mercury(II)], HgBr2(bznapH) (2) are isostructural with the effective coordination of mercury being 2+2. The HgX2 moieties are retained in the adducts and contain two covalently linked chlorine [2.321(3) and 2.299(3) A in 1] or bromine atoms [2.446(1) and 2.422(1) A in 2]. These moieties are linked mutually by additional contacts of bridging halogen atoms [Hg⋯μX 3.189(2) and 3.298(1) A in 1 and 2, respectively], forming non-planar dimeric Hg2X4 units. Each Schiff-base ligand has a strong contact with mercury through the oxygen atom [Hg⋯O 2.392(5) and 2.410(5) A in 1 and 2, respectively]. The Schiff-base ligand in 1 and 2 exists as the ketoamino (quinoid) tautomeric structure with an intramolecular hydrogen bond of the NH⋯O type [2.58(1) and 2.59(1) A in 1 and 2, respectively]. On the contrary, in DMSO solution, due to dissociation of adducts 1–6, the enolimino (benzenoid) tautomeric form of the Schiff bases was established by NMR spectroscopy.

Coordination-driven self-assembly of thiocyanate complexes of Co(II), Ni(II) and Cu(II) with picolinamide: a structural and DFT study

The new heteroleptic complexes, [M(NCS)2(pia)2] M = Co(II) (1), Ni(II) (2), and [Cu(SCN)2(pia)2] (3), pia = pyridine-2-carboxamide, were synthesized and characterized. Their single crystal X-ray diffraction structures showed octahedral units, with the two thiocyanate ligands occupying cis-positions and binding through the nitrogen atom in Co(II) and Ni(II). In the Cu(II) complex, they were trans and S-bound. The crystal structures display a 2-d structure with NH⋯S hydrogen bonds for the Co(II) and Ni(II), forming tetrameric units, and are isomorphous with the Zn(II) complex, [Zn(NCS)2(pia)2], and a 2-d structure with NH⋯N for the Cu(II). DFT calculations were performed on the new complexes and the analogous polymorphs of [Zn(NCS)2(pia)2], including a second one containing dimeric motifs. The calculated vibrational modes of the thiocyanate ligands corroborate the experimental ones and reflect the coordination mode of the ligand. A comparison between the two Zn(II) polymorphs showed that the NH⋯S bond in the tetramer is stronger (−7.50 kcal mol−1 per metal) than the NH⋯O bond in the dimer (−4.01 kcal mol−1 per metal), indicating a preference for the formation of tetrameric units. The NH⋯N hydrogen bonds calculated in the Cu(II) crystal are stronger (−9.15 kcal mol−1 per metal) than the NH⋯S ones in Ni(II) and Zn(II).

A Homogeneous Mixture Composed of Vanadate, Acid, and TEMPO Functionalized Ionic Liquids for Alcohol Oxidation by H2O2

The functionalized ionic liquids (ILs) of N‐n‐dodecyl pyridinium vanadate (1), N‐(propyl‐1‐sulfonic acid) pyridinium tetrafluoroborate (2), and 4‐(propanoate‐2,2,6,6,‐tetramethylpiperidine‐1‐oxyl) pyridinium tetrafluoroborate (5) were synthesized. The mixture of 1, 2, and 5 in [Bpy]BF4 yielded the compatible IL compositions (ILCs) as a homogenous mixture, which proved to be an efficient catalytic system for oxidation of a wide range of alcohols using H2O2. With the aid of 2 and 5, 1 in [Bpy]BF4 could easily be recovered and reused for at least six runs without a loss in activity. UV/Vis spectroscopic analysis indicated that the role of 2 was to promote the formation of the active peroxo VV species, which is responsible for substrate activation, and the role of 5 was to oxidize the low‐valent vanadium(II–IV) species to regenerate 1.

Mercury(II) Complexes with Heterocyclic Thiones- Preparation and Characterization of the 1:1 and 1:2 Mercury(II) Complexes with Benzo-1, 3-imidazole-2-thione

A series of complexes HgX2 (bzimtH_2 ) and HgX_2 (bzimtH2)_2 (X =Cl^- , Br^- , I^- , SCN^- ; bzimtH_2 = benzo-1, 3-imidazole-2-thione) was obtained by reaction of the mercury(II) salts with benzo-1, 3-imidazole-2-thione in the appropriate molar ratio(1:1 or 1:2). Hg(bzimtH)_2 was obtained by the deprotonation of bzimtH_2 with mercury(II) acetate (irrespective of the molar ratio of the reactants). The complexes were characterised by chemical and thermal analysis, IR, 1^H, and 13^C NMR spectroscopy, and some [HgX_2(bzimtH_2), X =I^- and HgX_2(bzimtH_2)_2 , X =I^- and SCN^-] by X-ray single crystal diffractometry. 1^H and 13^C NMR spectroscopic measurements in dimethyl sulphoxide revealed that the sulphur atom is coordinated to the mercury centre. The greatest complexation effects on the chemical shifts were observed for the thione carbon atom and thioamide proton. The crystal structures of HgI_2(bzimtH_2)_2 and Hg(SCN)_2 (bzimtH_2)_2 ˇC_2H_5OH consist of discrete monomeric molecules with halide or pseudohalide donor atoms and thione sulphur atoms tetrahedrally coordinated to the mercury atom. The structure of HgI2 (bzimtH2 )is polymeric with a trigonal bipyramidal 3 + 2 coordination geometry around the mercury atom. Polymerisation occurs through HgˇˇˇI interactions with neighbouring molecules. The distribution of the pi-electron density in bzimtH_2 corresponds to the thioketo tautomeric form in the solid state, and also in the DMSO solution of the complexes. Intermolecular hydrogen bonds of the type N-HˇˇˇN, N-HˇˇˇS and N-HˇˇˇI are observed.

Hydrogen Bonding in the 2,2'-Bipyridinium Salt of 1,2,4,5-Benzenetetracarboxylic Acid (Pyromellitic Acid)

The 2,2′-bipyridinium salt of pyromellitic acid (PMA) (1,2,4,5-benzenetetracarboxylic acid), 2,2′-bipyridinium hemi[1,2,4,5-benzenetetracarboxylate(2-)] hemi(1,2,4,5-benzenetetracarboxylic acid), C10H8N2H+.1/2[C6H2(COO)4H2O]2-.1/2[C6H2(COO)4H4], has been prepared and studied by X-ray diffraction and IR spectroscopy. 2,2′-Bipyridine acts as a proton sponge by accepting a proton from pyromellitic acid. The transfer of protons results in strong asymmetric intramolecular hydrogen bonds: H(N)⋯N 2.603 (2) A in the bipyridinium cation which has syn conformation and H(O)⋯O 2.396 (2) A in the pyromellitate anion. The N-H⋯N hydrogen bond is part of a three-centred hydrogen bond with a carbonyl group of the neutral pyromellitic acid: N—H⋯N,O with H(N)⋯O 2.805 (2) A. Each neutral PMA molecule is connected by hydrogen bonds with two cations and four anions forming a two-dimensional network with plane indices (112). The IR spectrum also suggests the presence of strong hydrogen bonds.

Synthesis and characterization of copper(II) complexes with 3-methylpicolinic acid. Crystal and molecular structure of bis (3-methylpicolinato- N , O )(4-picoline)copper(II)

Copper(II) complexes of 3-methylpicolinic acid (3-MepicH), namely [Cu(3-Mepic)2] · 2H2O (1) and [Cu(3-Mepic)2(4-pic)] (2) were prepared and characterized by IR spectroscopy and thermal analysis (TGA/DTA). Crystal structure for 2 was determined by X-ray crystal structure analysis. 1 was prepared by reaction of copper(II) sulfate pentahydrate and 3-methylpicolinic acid in aqueous solution, while 2 was prepared by recrystallization of 1 from 4-picoline solution. Structure analysis revealed square-pyramidal copper(II) coordination and N,O-chelating mode of 3-methylpicolinic acid in 2. Copper(II) is coordinated by two 3-Mepic ligands in the basal plane of a square pyramid and by 4-picoline in the apical position. Crystal packing of 2 is dominated by weak intermolecular C–H ··· O hydrogen bonds and π ··· π stacking interactions forming a complex three-dimensional supramolecular architecture.

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.