N,N′-bis(substituted-phenyl)oxamides and their dinuclear pentacoordinate nickel(II) complexes

The preparation, spectroscopic characterization and magnetic study of N,N′-bis(substituted-phenyl)oxamidate-bridged nickel(II) dinuclear complexes of formula {[Ni(N₃-mc)]₂(μ-CONC₆H₄-X)}(PF₆)₂ (N₃-mc = 2,4,4-trimethyl-1,5,9-triazacyclo-dodec-1-ene (Me₃-N₃-mc) or 2,4,4,9-tetramethyl-1,5,9-triazacyclododec-1-ene (Me₄-N₃-mc), X = 2-Cl, 4-Cl, 2-OCH₃, 4-OCH₃) are reported. These paramagnetic nickel(II) complexes have been characterized by both one- and two-dimensional (COSY) ¹H NMR techniques. The COSY spectrum of 5 has allowed to achieve the assignment of the phenyl protons of the N,N′-diphenyloxamidate. The crystal structures of [Ni(Me₃-N₃-mc)(μ-CONC₆H₄-4-Cl)]₂(PF₆)₂ (6), [Ni(Me₃-N₃-mc)(μ-CONC₆H₄-4-OMe)]₂(PF₆)₂ (8) and [Ni(Me₄-N₃-mc)(μ-CONC₆H₄-2-Cl)]₂(PF₆)₂ (9) have been determined and their magnetic properties have been studied. The value of magnetic coupling between the two nickel(II) ions across the oxamidate bridge [J = − 37.6 (6), −39.9 (8) and −39.7 cm⁻¹ (9)] is sensitive to the distortion of the coordination sphere of the metal ions and the topology of the molecular bridge.     

Phase separation in manganites induced by orbital-ordering strains

Doped manganite perovskites AMnO(3) exhibit a rich variety of electronic properties, resulting from the interplay of charge (Mn(3+)/Mn(4+)), spin (Mn magnetic moment) and orbital (Mn(3+) Jahn-Teller distortion) degrees of freedom. Magnetisation measurements and ESR spectra have been used to study a series of eight AMnO(3) perovskites, in which the A cation sites are occupied by a distribution of 70% trivalent lanthanide and 30% divalent Ca, Sr or Ba ions. These all have a mean A cation radius of 1.20 Angstrom but different values of the cation size variance sigma(2). A change from orbital disorder to order (cooperative Jahn-Teller distortions) was previously found in the insulating regime at sigma(2) = approximately 0.005 Angstrom(2). This work has shown that co-existence of the orbitally ordered and disordered phases is found in sigma(2)= 0.0016-0.0040 Angstrom(2) samples, with a difference of 40 K between their Curie temperatures. This is ascribed to competition between orbital ordering and microstructural lattice strains. At larger sigma(2) > 0.005 Angstrom(2), the orbital ordering strains are dominant and only this phase is observed. This intermediate temperature phase segregation is one of many strain-driven separation phenomena in manganites.     

Antioxidant activity of methimazole-copper(II) bioactive species and spectroscopic investigations on the mechanism of its interaction with Bovine Serum Albumin

Free radical-mediated oxidative stress has been implicated in numerous autoimmune disorders including Graves’ disease. Hyperthyroidism results in a marked increase in intracellular antioxidant enzymes including superoxide dismutase. The later activity is significantly increased in untreated Graves’ patients while treatment with methimazole results in normalization of the free radical and antioxidant activity indices. In this context, and considering the findings mentioned above, the aim of the present study was to evaluate unknown biological activities of methimazole and its methimazole-copper(II) complex investigating their superoxide scavenger power. Under the applied experimental conditions, methimazole did not show superoxide dismutase (SOD) activity while the copper complexes exhibited a strong superoxide radical scavenging capacity. Bearing in mind that the capacity of drugs to bind and/or interact with albumin is essential for their pharmacokinetic and pharmacodynamic properties, a complete investigation of the binding ability of both compounds by using Fourier transform infrared (FT-IR), Raman and Fluorescence spectroscopies, and UV-Vis spectrophotometry was included. Besides, in order to probe the copper ligand environment the EPR spectra of such compounds were analyzed.     

A novel organic-inorganic hybrid based on a dinuclear copper complex supported on a keggin polyoxometalate

The autoassembly process of copper-oxalate dimers and Keggin type polyoxometalates leads to the first example of a new family of organic-inorganic hybrids, K(14)[(Cu(2)(bpy)(2)(mu-ox))(SiW(11)O(39)Cu(H(2)O))](2)[SiW(11)O(39)Cu(H(2)O)]. approximately 55H(2)O. This compound crystallizes in the monoclinic space group C2/m, a = 37.932(6) A, b = 21.303(3) A, c = 12.546(2) A, beta = 106.16(1) degrees, Z = 2. The crystal structure reveals the presence of a polymeric hybrid built up of alternating dimer and polyoxometalate entities.     

Experimental and theoretical study of the mechanism for the kinetic of elimination of methyl carbazate in the gas phase

The elimination kinetic of methyl carbazate in the gas phase was determined in a static system over the temperature range of 340–390 °C and pressure range of 47–118 Torr. The reaction is homogeneous, unimolecular, and obeys a first order rate law. The decomposition products are methyl amine, nitrous acid, and CO gas. The variation of the rate coefficients with temperatures is given by the Arrhenius expression: log k₁ (s^?1) = (11.56 ± 0.34) ? (180.7 ± 4.1) kJ mol^?1(2.303 RT)^?1. The estimated kinetics and thermodynamics parameters are in good agreement to the experimental values using B3LYP/6‐31G (d,p), and MP2/6‐31G (d,p) levels of theory. These calculations imply a molecular mechanism involving a concerted non‐synchronous quasi three‐membered ring cyclic transition state to give an unstable intermediate, 1,2‐oxaziridin‐3‐one. Bond order analysis and natural charges implies that polarization of O (alkyl)? C (alkyl) bond of the ester is rate determining in this reaction. Copyright © 2008 John Wiley & Sons, Ltd.     

Kinetics and mechanisms of gas‐phase decarbonylation of α‐methyl‐trans‐cinamaldehyde and E‐2‐methyl‐2‐pentenal under homogeneous catalysis of hydrogen chloride

The kinetics of the gas‐phase elimination of α‐methyl‐trans‐cinamaldehyde catalyzed by HCl in the temperature range of 399.0–438.7 °C, and the pressure range of 38–165 Torr is a homogeneous, molecular, pseudo first‐order process and undergoing a parallel reaction to produce via (A) α‐methylstyrene and CO gas and via (B) β‐methylstyrene and CO gas. The decomposition of substrate E‐2‐methyl‐2‐pentenal was performed in the temperature range of 370.0–410.0 °C and the pressure range of 44–150 Torr also undergoing a molecular, pseudo first‐order reaction gives E‐2‐pentene and CO gas. These reactions were carried out in a static system seasoned reactions vessels and in the presence of toluene free radical inhibitor. The rate coefficients are given by the following Arrhenius expressions:

• Products formation from α‐methyl‐trans‐cinamaldehyde
• α‐methylstyrene :
• β‐methylstyrene :
• Products formation from E‐2‐methyl‐2‐pentenal
• E‐2‐pentene :

The kinetic and thermodynamic parameters for the thermal decomposition of α‐methyl‐trans‐cinamaldehyde suggest that via (A) proceeds through a bicyclic transition state type of mechanism to yield α‐methylstyrene and carbon monoxide, whereas via (B) through a five‐membered cyclic transition state to give β‐methylstyrene and carbon monoxide. However, the elimination of E‐2‐methyl‐2‐pentenal occurs by way of a concerted cyclic five‐membered transition state mechanism producing E‐2‐pentene and carbon monoxide. The present results support that uncatalyzed α‐β‐unsaturated aldehydes decarbonylate through a three‐membered cyclic transition state type of mechanism. Copyright © 2014 John Wiley & Sons, Ltd.     

Pentacoordinate nickel(II) complexes double bridged by phosphate ester or phosphinate ligands: spectroscopic, structural, kinetic, and magnetic studies

The bis(phosphatediester)-bridged complexes [[Ni([12]aneN(3))(mu-O(2)P(OR)(2))](2)](PF(6))(2) [[12]aneN(3)=Me(3)[12]aneN(3), 2,4,4-trimethyl-1,5,9-triazacyclododec-1-ene; R=Me (1), Bu (2), Ph (3), Ph-4-NO(2) (4); [12]aneN(3)=Me(4)[12]aneN(3), 2,4,4,9-tetramethyl-1,5,9-triazacyclododec-1-ene; R=Me (5), Bu (6), Ph (7), Ph-4-NO(2) (8)] were prepared by hydrolysis of the phosphate triester with the hydroxo complex [[Ni([12]aneN(3))(mu-OH)](2)](PF(6))(2) or by acid-base reaction of the dialkyl or diaryl phosphoric acid and the above hydroxo complex. The acid-base reaction was also used to synthesise the phosphinate-bridged complexes [[Ni([12]aneN(3))(mu-O(2)PR(2))](2)](PF(6))(2) [[12]aneN(3)=Me(3)[12]aneN(3), R=Me (9), Ph (10); [12]aneN(3)=Me(4)[12]aneN(3), R=Me (11), Ph (12)]. The molecular structures of complexes 2, 3 and 12 were established by single crystal X-ray diffraction studies. The eight-membered rings defined by the nickel atoms and the bridging ligands show distorted twist-boat, chair and boat-boat conformations in 2, 3 and 12, respectively. The experimental susceptibility data for compounds 2, 3 and 12 were fitted by least-squares methods to the analytical expression given by Ginsberg. The best fit was obtained with values of J=-0.11 cm(-1), D=-9.5 cm(-1) and g=2.20 for 2; J=-0.97 cm(-1), D=-9.3 cm(-1) and g=2.21 for 3; and J=-0.14 cm(-1), D=-11.9 cm(-1) and g=2.195 for 12. The magnetic-exchange pathways must involve the phosphate/phosphinate bridges, because these favour antiferromagnetic interactions. The observation of a higher exchange parameter for compound 3 is a consequence of a favourable disposition of the O-P-O bridges. The kinetics for the hydrolysis of TNP (tris(4-nitrophenyl)phosphate) with the dinuclear nickel(II) hydroxo complex [[Ni(Me(3)[12]aneN(3))(mu-OH)](2)](PF(6))(2) was studied by UV-visible spectroscopy. The proposed mechanism for TNP-promoted hydrolysis can be described as one-substrate/two-product, and can be fitted to a Michaelis-Menten equation.