Synthesis,properties, and crystal structures of mononuclear nickel(II) and copper(II) complexes with 2-oximino-3-thiosemicarbazone-2,3-butanedione

The tridentate ligand 2-Oximino-3-thiosemicarbazone-2,3-butanedione (Hotsb) reacts with MCl₂ (M = Ni²⁺ or Cu²⁺) to give rise to the mononuclear complexes [Ni(Hotsb)₂]Cl₂ · H₂O (1) and [Cu(Hotsb)Cl₂] · H₂O (2). These complexes have been characterized by X-ray crystallography, spectroscopy, and cyclic voltammetry. The nickel(II) ion in (1) is in a six-coordinate octahedral environment being bonded to the two protonated tridentate ligands which occupy mer positions. The copper(II) ion in (2) is in a five-coordinate square-pyramidal geometry, in which the basal plane is made up the two nitrogens, sulfur, and chloride atom, while the other chloride atom is coordinated at the axial position. The cyclic voltammogram of the complexes displays two one-electron waves corresponding to M^II/M^III and M^II/M^I processes. The electronic as well as infrared spectral properties of the title complexes are reported and discussed.     

Coordination asymmetry in divanadium(V) compounds containing a V2O3 core: synthesis, characterization, and redox properties

A general protocol for the synthesis of micro-oxo divanadium(V) compounds [LOV(micro-O)VO(Salen)] (1-5) incorporating coordination asymmetry has been developed for the first time. One of the vanadium centers in these compounds has an octahedral environment, completed by tetradentate Salen ligand, while the remaining center has square pyramidal geometry, made up of tridentate biprotic Schiff-base ligands (L2-) with ONO (1-3) and ONS (4, 5) type donor combinations. Single crystal X-ray diffraction analysis, ESI-MS, and NMR (both 1H and 51V) spectroscopy have been used extensively to establish their identities. The V(1)-O(6)-V(2) bridge angle in these compounds, save 3, lie in a narrow range (166.20(9)-157.79(16) degrees) with the V2O3 core having a rare type of twist-angular structure, somewhat intermediate between the regular anti-linear and the syn-angular modes. For 3, however, the bridge angle is sufficiently smaller 117.92(8) degrees that it forces the V2O3 core to adopt an anti-angular geometry. The V(1)...V(2) separations in these molecules (3.7921(7)-3.3084(6) A) are by far the largest compared to their peers containing a V2O3 core. The molecules retain the binuclear structures also in solution as confirmed by NMR spectroscopy. Their redox behaviors appear quite interesting, each undergoing a one-electron reduction in the positive potential range (E1/2, 0.42-0.45 V vs Ag/AgCl) to generate a trapped-valence mixed-oxidation products [LVVO-(micro-O)-OVIV(salen)]1-, confirmed by combined coulometry-EPR experiments. The bent V-O-V bridge in these molecules probably prevents the symmetry-constrained vanadium d xy orbitals, containing the unpaired electron, to overlap effectively via the ppi orbitals of the bridging oxygen atom, thus accounting for the trapped-valence situation in this case.     

Targeted synthesis of mu-oxo divanadium(V) compounds with asymmetry in coordination environments

Isovalent mu-oxo divanadium(V) compounds [L1VO(mu-O)VO(salen)] (1) and its bromo derivative [L2VO(mu-O)VO(salen)].CH3CN (2) (both H2L1 and H2L2 are tridentate dithiocarbazate-based ONS ligands) with ligands providing donor set and coordination number asymmetry in tandem have been synthesized for the first time; confirmations in favor of these unsymmetrical molecular structures have come from single-crystal X-ray diffraction analysis, as well as from NMR (both 1H and 51V) spectroscopy.     

Oxadiazole-metal interface: from isolated molecules to pi-stacking

Derivatives of 2,5-diaryl-1,3,4-oxadiazole are used widely for electron transport in organic light emitting diodes (OLED). This study addresses the structure of 2,5-diphenyl-1,3,4-oxadiazole (PPD) molecules on Cu(111) using scanning tunneling microscopy (STM) and density function theory (DFT): at incomplete coverage, PPD molecules are found horizontally on the surface; once the surface area is insufficient to accommodate all adsorbates in this fashion, a pi-stacked film of vertically arranged molecules is formed. In contrast to bulk PPD, in this film, the molecules are arranged face-to-face at a separation of square root(3a0) = 4.4 A as imposed by the substrate interatomic spacing along the [-2 1 1] direction.     

Primordial curvature perturbation during and at the end of multi-field inflation

We study the generation of the primordial curvature perturbation in multi-field inflation. Considering both the evolution of the perturbation during inflation and the effects generated at the end of inflation, we present a general formula for the curvature perturbation. We provide the analytic expressions of the power spectrum, spectral tilt and non-Gaussianity for the separable potentials of two inflaton scalars, and apply them to some specific models.     

Synthesis and Crystal Structure of 2,13-Bis(acetamido)-3,14-dimethyl-2,6,13,17-tetraazatricyclo[14,4,0<Superscript>1.18</Superscript>,0<Superscript>7.12</Superscript>]docosane Tetrachlorocobalt(II)dihydrate

Abstract The novel ionic compound [H₂bdtd][CoCl₄] · 2H₂O (1) was prepared by the reaction between CoCl₂ and 2,13-bis(acetamido)-3,14-dimethyl-2,6,13,17-tetraazatricyclo[14,4,0^1.18,0^7.12]docosane (bdtd) in adjusted to pH 3.0 by 1.0 M HCl and structurally characterized. The crystals are monoclinic C2/c with a = 18.7777(9), b = 9.7356(4), c = 20.0884(9) ?, β = 109.6340(10)°, V = 3458.9(3) ?³, Z = 4. The dication H₂bdtd occupies a special position about an inversion center. The cobalt(II) atom in the anion is in a distorted tetrahedral environment with four chloride ligands. The crystal structure is stabilized by a variety of hydrogen-bonding contacts involving the dication, chloride anions and solvent water molecules. Cyclic voltammetry of [CoCl₄]²⁻ anion in 1 undergoes irreversible one-electron reduction to the Co^II/Co^I. Graphical abstract The crystal structure of the ionic compound [H₂bdtd][CoCl₄] · 2H₂O (1) consists of [H₂bdtd]²⁺ cation, [CoCl₄]²⁻ anion and water molecules joined together by ionic interaction and hydrogen bonds. Electronic supplementary material The online version of this article (doi:) contains supplementary material, which is available to authorized users.     

Synthesis,characterization, and crystal structure of cobalt(II) complex with 2-oximino-3-thiosemicarbazone-2,3-butanedione

The reaction of cobalt(II) chloride with the tridentate ligand 2-oximino-3-thiosemicarbazone-2,3-butanedione [Hotsb (1)] leads to the formation of the novel six-coordinated complex [Co(otsb)₂]·2H₂O (2). This complex has been synthesized and characterized by X-ray crystallography, spectroscopic and cyclic voltammetric measurements. The ligand Hotsb (1) obtained by the condensation of 2,3-butanedione monoxime and thiosemicarbazide is used for the preparation of complex 2. The Hotsb (1) crystallizes into a monoclinic lattice with space group P2₁/c. The crystal structure of 2 shows a distorted mer-octahedral geometry in which the ligands are coordinated as uninegatively charged tridentate chelating agents via the hydrazine nitrogen atoms, the azomethine nitrogen atoms, and the thiolate sulfur atoms. The cyclic voltammogram of 2 undergoes two irreversible one-electron waves corresponding to Co^II/Co^III and Co^II/Co^I processes.     

Preparation, characterization and crystal structures of copper(II) hexaazamacrotetracyclic complexes with organic ligands

The reaction of [Cu(L)](ClO₄)₂ · H₂O (L=1,3,10,12,16,19-hexaazatetracyclo[17,3,1,1^12.16,0^4.9]tetracosane) with NaN₃ and Na₂tp yields mononuclear and dinuclear copper(II) complexes, [Cu(L)(N₃)](ClO₄) (1) and [Cu(L)(μ-tp)](ClO₄) · 2H₂O (2). These complexes have been characterized by X-ray crystallography, electronic absorption, cyclic voltammetry and magnetic susceptibility. The crystal structure of (1) shows that the copper(II) ion has a distorted square-pyramidal geometry with the two secondary and two tertiary amines of the macrocycle and one nitrogen atom from the azide group coordinating the axial position. The copper(II) ions in (2) are bridged by the terephthalate anion to form a dinuclear complex, in which each copper(II) ion reveals a distorted square-pyramid with four nitrogen atoms of the macrocycle and the oxygen atom of bridging tp ligand. Cyclic voltammetry of the complexes gives two one-electron waves corresponding to Cu^II/Cu^III and Cu^II/Cu^I processes. The magnetic susceptibility measurement for (2) exhibits a weak antiferromagnetic interaction between copper(II) centers with a 2J value of −2.21 cm⁻¹ (H = −2JΣS₁ · S₂). The electronic spectra and electrochemical behavior of the complexes are significantly affected by the nature of the organic ligands.     

Synthesis and characterization of copper(II) tetraaza macrocyclic complex with 2- benzimidazolepropionate ligand

A mononuclear complex [Cu(L)(bip)₂] (1) (L = 3,14-dimethyl-2,6,13,17-tetraazatricyclo [14,4,0^1.18, 0^7.12]docosane; bip = 2-benzimidazolepropionate) has been synthesized and structurally characterized by X-ray crystal structure analysis. The crystals are monoclinic P2 ₁/n with a = 10.2990(2), b = 15.9400(3), c = 11.991(14) Å, = 101.92(7)°, V = 1926(2) ų, Z = 2. The copper(II) coordination geometry exhibits an axially elongated octahedron with four nitrogen atoms from the macrocycle and two oxygen atoms from the bip ligands. The cyclic voltammogram of 1gives 2 one-electron waves corresponding to Cu^II/Cu^III and Cu^II/Cu^I processes.     

Two-dimensional nickel(II) tetraaza macrocyclic complex linked by hydrogen bonds

The complex [Ni(L)](PDC) 2H₂O (L = 3,14-dimethyl-2,6,13,17-tetraazatricyclo[16,4, 0^1.18,0^7.12]docosane; PDC = 3,5-pyrazoledicarboxylate) has been synthesized and characterized by X-ray crystallography. It crystallizes in the monoclinic system P2₁/c with a = 9.739(4) Å, b = 10.491(3) Å, c = 16.884(3) Å, = 97.17(2)°, V = 1711.5(8) ų, Z = 4. The coordination environment around the nickel(II) ion exhibits a slightly distorted square-plane with four secondary amines of the macrocycle. The title compound is interconnected to give a two-dimensional network through the hydrogen-bonding interactions.