Electrochemical and positron annihilation studies of semicarbazones and thiosemicarbazones derived from ferrocene

A series of six ferrocene derivatives containing a semicarbazone or thiosemicarbazone side chain was investigated by cyclic voltammetry and positron annihilation lifetime measurements. Both the redox and the electron capture processes took place on the Fe atom. Correlations between the two methods were proposed, taking into account the substituents on the side chain of the compounds, their redox potentials and the probabilities of o-positronium (o-Ps).formation.Uma série de seis derivados de ferroceno contendo uma cadeia lateral de semicarbazona ou tiossemicarbazona foi investigada por voltametria cíclica e estudos utilizando medidas de tempo de vida de pósitrons. Ambos os fenômenos, tanto o processo redox como o de captura de elétrons, ocorreram no átomo de ferro. Foram propostas correlações entre os dois métodos, levando em conta os substituintes na cadeia lateral dos compostos, os potenciais redox e as probabilidades de formação de o-positrônio (o-Ps)

Weak C-H...Cl-Pd interactions toward conformational polymorphism in trans-dichloridobis (triphenylphosphane) palladium (II)

A new triclinic polymorph of the title compound, [PdCl2(C18H15P)2], has two independent mol­ecules in the unit cell, with the Pd atoms located on inversion centres. One mol­ecule has an eclipsed conformation, whereas the second mol­ecule adopts a gauche conformation. The mol­ecules with a gauche conformation are involved in weak inter­molecular C-H...Cl-Pd inter­actions with symmetry-related mol­ecules. It is suggested that C-H...Cl-Pd inter­actions are mainly responsible for the existence of conformational differences, which contribute to the polymorph formation. In the crystal, there are layers of eclipsed and gauche mol­ecules separated by normal van der Waals inter­actions.FAPESP (09/08131-1)CNPqCAPESPROE

A Mixed Ligand Platinum(II) Complex: Spectral Analysis, Crystal Structure, Steric Demand of the Ligand, and Bioactivity of cis-[Pt(PPh3)2(L1-O,S)]PF6 (L1-O,S = N,N-Morpholine-N′-benzoylthiourea)

A novel mixed platinum(II) complex with general formula [Pt(PPh3)2(L1-O,S)]PF6 has been synthetized and characterized by elemental analysis, molar conductivity, and by IR and NMR (1H, 13C and 31P) spectroscopic methods. The crystal structure has been determined by single-crystal X-ray crystallography. The molecule presents an almost ideal square-planar geometry, and the crystal is stabilized by weak C?H···O and C?H···F hydrogen bonds, and C?H···π stacking interactions. The steric congestion of ligands is described by ?exact? cone and solid cone angles, and the percentage of metal surface shielded by the ligands. The results are compared to closely related palladium complexes. The X-ray structure revealed the proximity of the ortho phenyl proton of one PPh3 ligand to platinum(II) showing rare intramolecular C?H···Pt anagostic binding interaction. The title complex was determined to be active against tumor cells, and it also showed a moderate inhibitory action against mycobacterium tuberculosis.Fil: Pérez, Hiram. Universidad de La Habana; CubaFil: Ramos, Raúl. Universidad de La Habana; CubaFil: Plutín, Ana M.. Universidad de La Habana; CubaFil: Mocelo, Raúl. Universidad de La Habana; CubaFil: Erben, Mauricio Federico. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - La Plata. Centro de Química Inorgánica "Dr. Pedro J. Aymonino". Universidad Nacional de La Plata. Facultad de Ciencias Exactas. Centro de Química Inorgánica "Dr. Pedro J. Aymonino"; ArgentinaFil: Castellano, Eduardo E.. Universidade de Sao Paulo; BrasilFil: Batista, Alzir A.. Universidade Federal do São Carlos; Brasi

On an accidental degeneracy in the 31P{¹H} NMR chemical shifts in ruthenium diphosphine complexes

The [RuCl(bipy)(dppb)(4-pic)]PF6 complex was prepared and fully characterized. The X-ray crystal structure of this complex was determined in order to make an unambiguous distinction between the two possible positions of the 4-methylpyridine ligand (4-pic) in the compound: trans to phosphorus atom or trans to nitrogen atom. The [RuCl(bipy)(dppb)(4-pic)]PF6 complex exhibits an unusual temperature-dependent accidental degeneracy of the 31P chemical shifts in its solution NMR spectrum

Experimental and theoretical investigation of molecular structure and conformation of the 4-isopropylthioxanthone

In this study, the molecular structure and conformational analyses of the 4-isopropylthioxanthone (4-ITX) are reported according to experimental and theoretical results. The compound crystallizes in the centrosymmetric PView the MathML source space group with only one molecule in the asymmetric unit, presenting the most stable conformation, in which the three fused-rings adopt a planar geometry, and the isopropyl group assumes a torsional angle with less sterical hindrance. The structural and conformational analyses were performed using theoretical calculations such as Hartree–Fock (HF), DFT method in combination with 6-311G(d,p) and 6-31++G(d,p) and the results were compared with infrared spectroscopy (FT-IR) and X-ray diffraction (XRD). The supramolecular assembly of 4-ITX is kept by non-classical C-H⋯O hydrogen bonds and weak interactions such as π-π stacking. 4-ITX was also studied by 1H and 13C NMR spectroscopy. UV-Vis absorption spectroscopic properties of the 4-ITX showed the long-wavelength maximum shifts towards high energy when the solvent polarity increases.FAPESP (09/08131-1)CNPqCAPES/PROE

Understanding the conformational changes and molecular structure of furoyl thioureas upon substitution

1-Acyl thioureas [R1C(O)NHC(S)NR2R3] are shown to display conformational flexibility depending on the degree of substitution at the nitrogen atom. The conformational landscape and structural features for two closely related thioureas having R1 = 2-furoyl have been studied. The un-substituted 2-furoyl thiourea (I) and its dimethyl analogue, i.e. 1-(2-furoyl)-3,3-dimethyl thiourea (II), have been synthesized and fully characterized by spectroscopic (FT-IR, 1H and 13C NMR) and elemental analysis. According to single crystal X-ray diffraction analysis, compounds I and II crystallize in the monoclinic space group P21/c. In the compound I, the trans–cis geometry of the almost planar thiourea unit is stabilized by intramolecular Nsingle bondH ⋯ Odouble bondC hydrogen bond between the H atom of the cis thioamide and the carbonyl O atom. In compound II, however, the acyl thiourea group is non-planar, in good agreement with the potential energy curve computed at the B3LYP/6-31 + G(d,p) level of approximation. Centrosymmetric dimers generated by intermolecular N — H ⋯ O = C hydrogen bond forming R22(8) motif are present in the crystals. Intermolecular interactions have been rationalized in terms of topological partitions of the electron distributions and Hirshfeld surface analysis, which showed the occurrence of S ⋯ H, O ⋯ H and H ⋯ H contacts that display an important role to crystal packing stabilization of both thiourea derivatives.Instituto de Física La PlataCentro de Química Inorgánic

Experimental and theoretical study of the kinetics of dissociation in cis-[Ru'Cl IND.2'(P-P)(N-N)] type complexes

As reações de substituição [RuCl2(P-P)(N-N)] + L → [RuCl(L)(P-P)(N-N)]+ + Cl-, onde P‑P = 1,4-bis(difenilfosfino)butano e N-N = 2,2´-bipiridina, 4,4´-dimetóxi-2,2´-bipiridina, 4,4´-dimetil-2,2´-bipiridina e 4,4´-dicloro-2,2´-bipiridina, L = piridina (py) ou 4-metilpiridina (4-pic), foram estudadas sob condições de pseudo-primeira ordem. As reações ocorrem por um mecanismo dissociativo e as constantes de velocidade nas reações de substituição aumentam com o aumento do pKa dos ligantes N-heterocíclicos e com a diminuição dos potenciais de oxidação do centro metálico. Quanto mais alta é a porcentagem de participação dos orbitais atômicos d do metal na formação do HOMO, conforme calculado pelo método DFT, mais fácil é a dissociação do cloreto da esfera de coordenação do complexo. Nos espectros de 31P{1H} RMN da série de complexos de fórmula geral [RuCl(L)(P-P)(N-N)]PF6, há dois dubletos com Δσ < 1, o que é consistente com produtos formados pela dissociação do cloreto trans ao átomo de fósforo nos precursores.The substitution reactions [RuCl2(P-P)(N-N)] + L → [RuCl(L)(P-P)(N-N)]+ + Cl-, where P‑P = 1,4-bis(diphenylphosphino)butane and N-N = 2,2´-bipyridine, 4,4´-dimethoxy-2,2´-bipyridine, 4,4´-dimethylpyridine-2,2´-bipyridine and 4,4´-dichloro-2,2´-bipyridine, L = pyridine (py) or 4-methylpyridine (4-pic), were studied under pseudo-first order conditions. The reactions proceeded by means of a dissociative mechanism. The rate constants of the substitution reactions increased as the pKa of the N-heterocyclic ligands increased and as the oxidation potential of the metal center decreased. The greater the participation of the atomic d orbitals of the metal in the HOMO, according to DFT calculations, the easier is the dissociation of the chloride from the coordination sphere of the complex. In the 31P{1H} NMR spectra of the series of complexes of general formula [RuCl(L)(P-P)(N-N)]PF6, there are two doublets with Δσ < 1. This is consistent with products formed by dissociation of the chloride trans to one of the phosphorus atoms in the precursors.CNPqFAPESPFAPERJCAPE