In this work, we call the attention to the ambiguity found in the literature when labeling vibrations and molecular orbitals as B1 and B2 for molecules belonging to the C2v point group as, for example, the water molecule. A survey of several books and some articles shows that this ambiguity comes from a long time ago and persists today, being a source of misunderstanding and a waste of time for students and teachers. It means that, in the case of the point groups Cnv, Dn, and Dnh (n = 2, 4, 6), it is very important to draw students’ attention to this ambiguity that exists in the literature. It is unfortunate that the recommendation made by Mulliken, more than sixty years ago, to always place the water molecule in the yz plane, has not been followed.

The built of qualitative energy-level molecular diagrams for different geometries of simple molecules allow to explain the preferred geometry. The diagrams are built using simple symmetry principles and explain, on basis of the number of nonbonding electrons, for example, why the molecule of water is bent and not linear and ammonia is pyramidal and not planar. This simple energy principle does not need to consider the Valence Shell Electron-Pair Repulsion theory (VSEPR theory) neither hybrid orbitals to explain the geometry of simple molecules. This discussion is more appropriate to inorganic chemistry courses where symmetry is a common topic.

Métodos amperométrico e espectrofotométrico foram desenvolvidos para determinar a concentração do traçador iodeto em água produzida de reservatórios de petróleo marítimos. O método amperométrico exibiu uma resposta linear na faixa de 1 a 10 mg L-1 com limites de detecção e de quantificação de 0,2 e 0,6 mg L-1, respectivamente. O método espectrofotométrico também apresentou uma resposta linear na faixa de 1 a 10 mg L-1 com limites de detecção e de quantificação de 1 e 3 mg L-1, respectivamente. Ambos os métodos mostraram-se precisos, lineares, homocedásticos e suas recuperações foram de 101 ± 2 e 100 ± 3%, respectivamente, enquanto que as recuperações para amostras de água produzida de reservatórios (acrescidas de iodeto) foram de 97 ± 7 e 100 ± 3%, respectivamente. Altos teores de sulfato interferem no método espectrofotométrico. Ambos os métodos são alternativas promissoras, simples e baratas à cromatografia iônica para detecção do traçador iodeto em amostras de água produzida de reservatórios de petróleo.

Amperometric and spectrophotometric methods were developed for measuring iodide tracer concentration in water produced from offshore oil reservoirs. The amperometric method exhibited a linear response from 1 to 10 mg L-1 with limits of detection and of quantification of 0.2 and 0.6 mg L-1, respectively. The spectrophotometric method also exhibited a linear response from 1 to 10 mg L-1 with limits of detection and of quantification of 1 and 3 mg L-1, respectively. Both methods showed to be accurate, linear, homoscedastic and their recoveries were 101 ± 2 and 100 ± 3%, respectively, while the recoveries for produced reservoir water samples (fortified with iodide) were 97 ± 7 and 100 ± 3%, respectively. High amounts of sulfate interfere in the spectrophotometric method. Both methods are promising, simple and inexpensive alternatives to ion chromatography for the detection of iodide tracer in produced water reservoir samples.

Rich and Suter diagrams are a very useful tool to explain the electron configurations of all transition elements, and in particular, the s¹ and s0 configurations of the elements Cr, Cu, Nb, Mo, Ru, Rh, Pd, Ag, and Pt. The application of these diagrams to the inner transition elements also explains the electron configurations of lanthanoids and actinoids, except for Ce, Pa, U, Np, and Cm, whose electron configurations are indeed very special because they are a mixture of several configurations.

O estudo cinético da reação clorato-cloreto foi feito acompanhando-se a formação do ClO2• por espectroscopia UV-Vis. Para permitir comparação com resultados da literatura, a velocidade inicial foi medida após pequeno período de indução. Observou-se o fenômeno especial de perfil de saturação em função da concentração inicial do cloreto, sugerindo a formação do intermediário Cl2O3(2-). Em baixa concentração de cloreto, as ordens de reação obtidas com relação ao clorato, cloreto e H+ foram 1,03 ± 0,05, 1,02 ± 0,03 e 2,80 ± 0,03, respectivamente. Estes valores devem ser considerados com cautela pois foram calculados baseados na velocidade máxima após período de indução. Este período de indução indica, na verdade, que o sistema é complexo. Para explicar os resultados experimentais foi proposto um mecanismo contendo a reação entre dois ClOClO formando ClO2•. Esse mecanismo reproduz as curvas experimentais em diferentes [H+]0 e também em alto e baixo [Cl-]0.

The kinetics of chlorate-chloride reaction was studied following the formation of ClO2• by UV-Vis spectroscopy. For comparison with other results in the literature, the initial rate was measured after small induction period. The results show a special effect of a saturation profile for the initial chloride concentration, suggesting the formation of the intermediate Cl2O3(2-). At low chloride concentration, the reaction orders for chlorate, chloride and H+ were 1.03 ± 0.05, 1.02 ± 0.03 and 2.80 ± 0.03, respectively. These order values must be considered with care because they were calculated using the maximum rate values after induction period. In fact, the presence of this induction period indicates that the system is complex. Then, a mechanism was proposed to explain the experimental results, and includes the reaction between two ClOClO to form ClO2•. It was able to model the experimental curves at different [H+]0 and at low and high [Cl-]0.

Dois ligantes tridentados, HL1, [(2-hidroxibenzil)(2-(imidazol-2-il)etil)]amina, e HL2, [(2-hidroxibenzil)(2-(piridil-2-il)etil]amina, foram usados na síntese dos complexos binucleares [Cu2(L1)2]Cl2•2H2O, complexo 1, e [Cu2(L2)2](ClO4)2•1.5H2O, complexo 2,para serem empregados como catalisadores em processos de oxidação. Os complexos foram caracterizados por análise elementar e espectroscopias na região do infravermelho, ultravioleta-visível e ressonância paramagnética eletrônica. Foram também estudados por voltametria cíclica e titulação potenciométrica, a fim de caracterizar seus comportamentos em solução. A resolução da estrutura cristalina do complexo 1 mostrou um cátion binuclear contendo dois grupos fenóxido em ponte. Este arranjo possui uma distância Cu...Cu de 3.043(10) Å, similar à observada na catecol oxidase (2.90 Å). Os comportamentos catalíticos destes complexos foram investigados nas oxidações de cicloexano e de catecol. Na oxidação de cicloexano observou-se baixa atividade para ambos os complexos, que pode ser atribuída ao estereoimpedimento produzido pela falta de coplanaridade entre os anéis aromáticos do arcabouço dos ligantes, sugerindo que a aproximação entre o substrato e o centro ativo binuclear é uma etapa determinante no mecanismo da reação. Com relação à atividade de catecolase, foram observadas altas eficiências, com o complexo 2 sendo mais ativo que o complexo 1. Isto indica que o ligante piridina é capaz de estabilizar melhor o intermediário proposto para esse processo, que contém o centro CuI CuI. Isto é corroborado pela grande participação da piridina no LUMO (lowest unoccupied molecular orbital) do complexo 2, que pode ajudar a acomodar a carga negativa adicional quando o complexo é reduzido da forma CuII CuII para CuI CuI.

The tridentate ligands HL1, [(2-hydroxybenzyl)(2-(imidazol-2-yl)ethyl)]amine, and HL2, [(2-hydroxybenzyl)(2-(pyridil-2-yl)ethyl]amine, were used to synthesize binuclear CuII complexes, [Cu2(L1)2]Cl2•2H2O, complex 1, and [Cu2(L2)2](ClO4)2•1.5H2O, complex 2, in order to obtain catalysts for oxidative processes. Both complexes were characterized by elemental analysis, IR, UV-Vis and EPR spectroscopies. In addition, they were studied by cyclic voltammetry and potentiometric titration in order to investigate their behavior in solution. The crystal structure of complex 1 revealed a binuclear cation where the metal centers are bridged by two phenoxo groups. This arrangement provides a Cu...Cu distance of 3.043(10) Å, which is similar to the observed for catechol oxidase (2.90 Å). The catalytic reactivities of both complexes were investigated for hydrocarbon and catechol oxidations. Complexes 1 and 2 led to low overall hydrocarbon oxidation conversion values of 6.34 % and 7.15 %, respectively. However, for complex 1, only cyclohexanol (Cy-OH) and cyclohexanone (Cy=O) were isolated as reaction products, with selectivities of 68.1% for Cy-OH. This low overall conversion is tentatively attributed to steric hindrance effects produced by the non-coplanar aromatic rings of the ligand scaffolds, which suggest that the access of the hydrocarbon molecule to the binuclear active center is a determinant step in the reaction mechanism. Investigation of catecholase activities has shown high efficiencies, with complex 2 being more active than complex 1. It indicates that the pyridine-containing ligand is able to stabilize the intermediate CuI CuI center which is proposed to be formed in this process. This is corroborated by the strong participation of pyridine in the LUMO (lowest unoccupied molecular orbital) of complex 2, which can help to accommodate the additional negative charge when the complex is reduced from CuII CuII to CuI CuI.

Starting from zero-, first-, and second-order integrated laws for chemical kinetics, some cases are shown which produce fractional orders. Taking the Michaelis-Menten mechanism as a first example, it is shown that substrate order can go from 1 to zero, depending on relative concentration of enzyme and substrate. Using other examples which show fractional orders higher than one and even negative (inhibition), it is shown that the presence of an equilibrium before or parallel to the rate determining step can be the reason for fractional orders, which is an indication of a more complex mechanism.

The Michaelis-Menten equation is used in many biochemical and bioinorganic kinetic studies involving homogeneous catalysis. Otherwise, it is known that determination of Michaelis-Menten parameters K M, Vmax, and k cat by the well-known Lineweaver-Burk double reciprocal linear equation does not produce the best values for these parameters. In this paper we present a discussion on different linear equations which can be used to calculate these parameters and we compare their results with the values obtained by the more reliable nonlinear least-square fit.

Simulations have been carried out on the bromate - oxalic acid - Ce(IV) - acetone oscillating reaction, under flow conditions, using Field and Boyd's model (J. Phys. Chem. 1985, 89, 3707). Many different complex dynamic behaviors were found, including simple periodic oscillations, complex periodic oscillations, quasiperiodicity and chaos. Some of these complex oscillations can be understood as belonging to a Farey sequence. The many different behaviors were systematized in a phase diagram which shows that some regions of complex patterns were nested with one inside the other. The existence of almost all known dynamic behavior for this system allows the suggestion that it can be used as a model for some very complex phenomena that occur in biological systems.

São relatadas, pela primeira vez, a observação de oscilações periódicas, em reator agitado de fluxo contínuo (CSTR), para o sistema bromato-ácido oxálico-Ce(IV)-acetona-ácido sulfúrico. Identificou-se que a reação entre Ce(IV) e a acetona, até então não descrita na literatura e que ocorre antes dos reagentes serem adicionados ao reator, é um fator decisivo para o aparecimento de oscilações regulares.

Periodic oscillations were observed for the first time, in a CSTR, in the system bromate-oxalic acid-Ce(IV)-acetone-sulfuric acid, in a CSTR. A reaction between Ce(IV) and acetone, until now not described in the literature and occurring before the addition of the reagents to the reactor, was identified as a decisive factor for the appearing of the regular oscillations.

A reação bromato-brometo, em meio de ácido perclórico, foi observada numa faixa de acidez até então não estudada. A reação foi acompanhada através da medida da absorvância no ponto isosbéstico para as espécies Br2 e Br3- (lambda= 446 nm). Observou-se um comportamento de primeira ordem para o bromato e para o brometo e um comportamento de segunda ordem para o H+, levando à lei de velocidade ni = k[BrO3-][Br- ][H+]². Esta lei de velocidade sugere um mecanismo envolvendo duas protonações sucessivas do íon bromato, formando o H2BrO3+, que então reage com o íon brometo.Estes resultados discordam de outros estudos que verificaram um comportamento de segunda ordem para o íon brometo, bem como um comportamento de primeira ordem para o H+, que levaram a propor a existência de intermediários tais como H2Br2O3 e HBr2O3-. O comportamento de segunda ordem observado para o H+ na faixa de concentração 0,005 <= [H+] <= 2,77 mol L-1 permite afirmar que o pKa do ácido brômico, HBrO3, deve ser menor do que -0,5 a 25 °C, diferentemente de todas as propostas existentes até agora na literatura para o valor deste pKa.

The bromate-bromide reaction was investigated in an acidity range not studied yet. The reaction was followed at the Br2/Br3- isosbestic point (lambda = 446 nm). It was observed a first-order behavior for bromate and bromide ions and a second-order behavior for H+ ion that results in the rate law nu = k[BrO3-][Br- ][H+]². This rate law suggests a mechanism involving two successive protonation of bromate followed by the interaction of the intermediate species H2BrO3+ with bromide. These results disagree with the obtained by other authors who observed a second-order behavior for the bromide and first-order for H+, and have proposed intermediate species like H2Br2O3 and HBr2O3-. The second-order for [H+] observed in the range 0.005 <= [H+] <= 2.77 mol L-1 sets down that the pKa of bromic acid, HBrO3, must be lower than -0.5 (T = 25 °C), different from all other values for this pKa proposed in the literature.

O sal pentacianonitrosilrutenato(II) de potássio, em forma amorfa, foi sintetizado e caracterizado por espectroscopias UV, IR, difração de raios X e análise termogravimétrica. Amostras irradiadas por raios X revelam, por espectroscopia de Ressonância Paramagnética Eletrônica, a presença de complexos paramagnéticos de rutênio (I) e de radicais NO2. Os parâmetros do hamiltoniano de spin medidos para o complexo [Ru(CN)5NO]3- ( g<FONT FACE="Symbol">^</FONT > ou = 2.0064, A<FONT FACE="Symbol">^</FONT>(14N) = 60.7 MHz, g||= 1.999, A|| (14N) = 77.3 MHz ) indicam uma captura eletrônica em um orbital molecular pi* do grupo nitrosil com a participação de orbitais d xz and d yz do rutênio, como recentemente previsto por cálculos teóricos. Íons de prata, presentes como impurezas oriundas da rota sintética, são reduzidos a Ag(0) durante a irradiação e interagem com quatro nitrogênios equivalentes em um sítio distorcido, originando um espectro de RPE anisotrópico.

Amorphous potassium pentacyanonitrosylruthenate (II) was synthesized and characterized by UV, IR, X-ray diffraction and thermogravimetric analysis. Electron Spin Resonance spectroscopy reveals the presence of paramagnetic ruthenate (I) complexes and NO2 radicals in the X-irradiated diamagnetic salt. Spin-hamiltonian parameters of the [Ru(CN)5NO]3- complex (g<FONT FACE="Symbol">^</FONT > or = 2.0064, A<FONT FACE="Symbol">^</FONT> (14N) = 60.7 MHz, g|| = 1.999, A|| (14N) = 77.3 MHz ) support an electron capture in a pi* molecular orbital of the nitrosyl group mixed with d xz and d yz ruthenium orbitals as recently predicted by theoretical calculations. Silver ions, present as impurities, are reduced to Ag(0) by X-irradiation and coordinate to four magnetically equivalent nitrogens in a distorted site, giving rise to a well resolved anisotropic ESR powder spectrum.