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Chromium-53 is a spin-3/2 nucleus with a relatively small magnetic moment, low natural abundance, and large quadrupole moment. These properties have severely hampered the development of 53Cr NMR, especially in the solid state. In this Communication, the first 53Cr solid-state NMR spectra of prototypal diamagnetic chromium(0) and chromium(VI) compounds are presented. Specifically, analyses of 53Cr NMR spectra of solid hexacarbonylchromium(0), caesium chromate(VI), and potassium chromate(VI) have allowed for the determination of 53Cr quadrupolar coupling parameters and the first chromium chemical shift (CS) tensors. This work demonstrates the potential of 53Cr solid-state NMR, in particular the extreme sensitivity of the 53Cr quadrupolar coupling constant to the local chromium environment. Comparisons are made to known 53Cr NMR parameters available from solution studies, and to the 95Mo solid-state NMR parameters of analogous molybdenum compounds. The influence of crystal symmetry present in isomorphic Cr(CO)6 and Mo(CO)6 is strongly reflected in the magnitudes of the metal nuclei CS tensors and in their orientation with respect to their corresponding electric field gradient tensors.

This work presents performance data after ultrasonic extraction (UE) for the elemental analysis of a number of metal species in samples of interest in environmental and occupational health. In this study, several National Institute of Standards and Technology (NIST) Standard Reference Materials® (SRMs) were subjected to UE in various acid solutions. The extraction solutions employed were 25% nitric acid (v/v), 25% nitric–hydrochloric acids (v/v) and concentrated nitric–hydrochloric acids (1∶1). NIST SRMs 1648, 1579a, 2583, 2704, 2710, 3087a, and 8074 were subjected to these acid conditions and ultrasonic energy (about 1 W cm−2), and elemental recoveries were determined following analysis by inductively coupled plasma atomic emission spectrometry (ICP-AES). Observed recoveries were higher overall with HNO3–HCl mixtures than with nitric acid alone, and recoveries were generally higher for concentrated acid mixtures. Recoveries of >80% could be achieved for some elements (As, Cd, Cu, Mn, Pb, Zn) when using acidic ultrasonic treatment with no deliberately added heating, even under diluted acid conditions. However, several elements (Ba, Co, Cr, Fe, Mg, Ni, V) yielded 90%) dissolution of hexavalent chromium (CrVI) from both soluble (potassium chromate) and insoluble (lead chromate) CrVI reference sources. Sonication in HNO3–HF was used to extract Cd, Fe, Pb and Zn from aerosol filters, water rinsates and aerosol samplers alone; ICP-AES was used for elemental measurement. Sample losses were found for these four elements from rinsates and samples following removal of the aerosol filter, thereby demonstrating the utility of carrying out sonication directly within the aerosol sampler containing the filter. It is hypothesized that UE will be increasingly used for analytical sample preparation purposes.

New phases of composition MIGa(CrO4)2 (MI=Na, K or Rb) have been synthesized by solid state reaction in air. The crystallograhic data of the three compounds have been refined by the Rietveld method. They all show a layer structure, the layer being formed of GaO6 octahedra linked to CrO4tetrahedra by sharing corners. Alkali metal ions lie in the interlayer space. The three compounds are thermally stable up to 300 °C, but above this temperature they decompose evolving oxygen. Impedance measurements show that they are ion conductors, the ionic conductivity being highest for the Na compound.

Base catalyzed aldol condensation reactions and selective partial oxidation of sulfides are very important classes of reactions in synthetic organic chemistry. We have prepared a new alkali exchanged form of mesoporous polytriallylamine, OH-MPTA-1 and a Cr-grafted material Cr-MPTA-1 via the simple and facile in situ radical polymerization of a triallylamine template by organic–organic self-assembly of anionic surfactant systems. The materials have been characterized by elemental analysis, powder X-ray diffraction (XRD), transmission electron microscope (TEM), Fourier transform infrared spectroscopy (FT-IR), UV-vis diffuse reflectance spectroscopy (DRS), thermogravimetric analysis (TGA) and scanning electron microscopy (SEM). Powder XRD and TEM image analyses suggests the presence of mesophase and disordered wormhole-like mesopores in these samples. Our experimental results reveal that the alkali exchanged material OH-MPTA-1 acts as a very efficient base catalyst for the direct aldol reaction of different aromatic aldehydes with acetone. On the other hand, the Cr-grafted material Cr-MPTA-1, obtained through the reaction of potassium chromate with MPTA-1, acts as a very efficient catalyst for the liquid phase partial oxidation of sulfides to sulfoxides. Both OH-MPTA-1 and Cr-MPTA-1 can be recycled more than five times without an appreciable loss in activity for their respective catalytic reactions.

The potentiometric titration of chloride, bromide, iodide and thiocyanate with silver nitrate, using the mineral pyrite as a sensor for the detection of the end-point, is described. The potentials of the pyrite electrode were found to be established rapidly, and accurate and reproducible results were obtained. The pyrite electrode potential showed a sub-Nernstian dependence on the concentration of the ionic species investigated. In addition, lead(II) was determined by titration with potassium chromate and chloride by titration with standard mercury(I) solution. Accurate and reproducible results were also obtained in the reverse titrations.

The kinetics of the oxidation of DL-penicillamine (3-sulfanyl-D-valine) and glutathione (γ-glutamylcysteinylglycine) by potassium chromate has been studied at pH 7 under pseudo-first-order conditions of an excess of thiol, at I= 0.50 mol dm–3(NaClO4). The glutathione reaction is biphasic, while for penicillamine it is monophasic. The first stage of the oxidation of glutathione obeys the simple expression (i). The second stage of the same reaction is slower than the first by a factor of 104 and kobs=k1[RSH]+k–1(i), obeys the rate expression (ii). The biphasic nature is consistent with the formation and decay of a Rate =(k1k2[RSH]2+k1k3[RSH])//(k–1+k3+k2[RSH])[CrVI]T(ii), chromate–glutathione adduct. Parameter k1/k–1 at 25.3 °C has been determined as 184 ± 4 dm3 mol–1. The second-order rate constant, k2, for the decomposition of the intermediate is (1.07 ± 0.04)× 10–2 dm3 mol–1 s–1. The activation parameters were calculated as ΔH‡= 90 ± 7 kJ mol–1 and ΔS‡= 63 ± 29 J K–1 mol–1. The oxidation of DL-penicillamine shows simple first-order kinetics with respect to [DL-penicillamine], and may also be represented by expression (ii). The second-order rate constant, k1, obtained at 25.2 °C for the formation of a chromate–penicillamine intermediate is 0.23 ± 0.01 dm3 mol–1 s–1. The corresponding activation parameters are ΔH‡= 72 ± 7 kJ mol–1 and ΔS‡=–18 ± 28 J K–1 mol–1. A common mechanism which is compatible with the kinetics of both reactions is proposed.

The kinetics of oxidation of L-ascorbic acid (H2A) by potassium chromate has been studied under aerobic and anaerobic conditions over the range 0.002 ⩽[A]T⩽ 0.040 mol dm–3, 3.50 ⩽ pH ⩽ 8.70, 17.8 ⩽T⩽ 35.1 °C, 0.06 ⩽l⩽ 0.50 mol dm–3(NaClO4) and 0.05 ⩽[O2]⩽ 0.12 mmol dm–3. The experimental rate constants obtained in the presence of oxygen are about 10 times smaller than those obtained in its absence. A mechanism involving the formation of a chromium(VI)–ascorbate–oxygen intermediate is discussed in an attempt to explain this. The disappearance of chromium(VI) under aerobic conditions follows the rate law (I) where kf=(k1Ka1[H+]+k2Ka1Kc+k3[H+]2)/(Ka1+[H+])(Kc+[H+]). –d[CrVI]/dt=kf[A]T[CrVI]T(I) At 25 °C and l= 0.50 mol dm–3(NaClO4), k1= 59.4 ± 0.5, k2= 0.10 ± 0.02 and k3= 115 ± 3 dm3 mol–1 s–1.

Cyclizations of the a,c-biladiene salts (3) and (4) to give the porphyrins (5) and (6), respectively, have been studied in the presence of a variety of chelating agents and oxidants. As a standard, the established procedure [copper(II) chloride–boiling dimethylformamide–6 min] gave compounds (5) and (6), in 37 and 20% yields respectively. Using zinc(II) acetate as a chelating agent for the a,c-biladienes, a large number of oxidants have been studied (in place of the copper chloride); best yields of porphyrin were obtained with potassium chromate [31% of (5); 22% of (6)] and silver iodate [35% of (5); 31% of (6)]. Other oxidants [PbO2, K2Cr2O7, Kl, Hg(OAc)2, Ag2O, and AgOAc] gave moderate yields of porphyrin, and others (Table 1 ) gave either a trace of porphyrin, or none at all. In a useful modification of the copper(II) chloride cyclization, a,c-biladienes have been cyclized during 2 h at room temperature to give porphyrins in yields of 34–65% after removal of chelated copper.

The initial retention, the limiting retention after thermal annealing, and the susceptibility to radiation annealing, of thermal neutron-irradiated solid solutions of potassium chromate in potassium fluoberyllate were shown to be linear functions of the composition of the mixed crystals. Such a relation is found to be incompatible with the activated exchange model for the radiation annealing process. The susceptibilities of a number of chromates and dichromates to thermal and radiation annealing were determined and the behavior of ammonium dichromate and anhydrous lithium chromate studied in more detail. No evidence of the epithermal reaction of the fragments with ammonium ions was obtained. Some futher data on mixed crystals of chromates and sulfates are reported. (auth)

Isothermal and isochronal annealing of neutron activated K2CrO4 was investigated by measuring the 51Cr distribution among aqueous 51Cr(VI), 51Cr(III)-monomer, 51Cr(III)-dimer and 51Cr(III)-polymer species following dissolution. Annealing occurring in the temperature range from –8° to 240° is tentatively attributed to a set of reactions involving at least five crystal phase 51Cr-containing species. Electrons, holes or other irradiation produced species in the bulk crystal appear to participate only in reactions occurring below 100° where little annealing to 51Cr(VI) occurs. The principal reaction in this range is a conversion of dimer-forming species to monomer-forming species. Below 180°, 51Cr(III)-monomer-forming species do not produce appreciable 51Cr(VI). Above 180°, part of the 51Cr(III)-monomer-forming species is rapidly converted to 51Cr(VI) while the remainder is converted to 51Cr(VI) at the same relative rate as is the remaining 51Cr(III)-dimer-forming species.

It is shown that the retention and the annealing characteristics following neutron irradiation of potassium chromate are determined to some extent by the treatment of the crystals before irradiation. Crushing or irradiating the crystals with electrons before neutron irradiation reduces the retention but renders the products more susceptible to thermal annealing. A quantitative study of the combination of thermal and radiation annealing is reported. It is suggested that these and other observations reflect the influence of crystal defects on the fate of the recoiling atom and the subsequent annealing reactions. Three possible mechanisms of radiation annealing are discussed and a mechanism involving the defects is found compatible with all the existing data. By a simple development of this model all the other annealing phenomena in potassium chromate crystals can be interpreted. (auth)

Using potassium chromate labeled with Cr/sup 51/, it has been shown that, during immersion of steel in chromate solution, logarithmic growth of an oxide film, containing chromic and iron oxides, proceeds in a manner similar to that of oxide film growth in air. The work also indicates the presence of an adsorbed Cr-containing layer. It is concluded that inhibition is maintained as long as the concentration of chromate ions in the solution (or the presence of the adsorbed layer) can sustain uninterrupted and orderly (logarithmic) growth of the oxide film. The work has also demonstrated the logarithmic growth of the oxide film on steel in air at room temperature. (auth)

Isothermal and isochronal annealing of neutron-activated K2CrO4 were carried out in the presence and in the absence of oxygen. The 51Cr(VI)-retention is unaffected by the presence of oxygen, as previously reported. The 51Cr(III) distribution between 51Cr(III)-monomer and 51Cr(III)-dimer + polymer is insensitive to oxygen at annealing temperatures below 100°C but is affected by the presence of oxygen above 100°C. Experiments with post-irradiation-recrystallized K2CrO4 show a similar effect of oxygen upon the distribution of 51Cr among the 51Cr(III) species after annealing at temperatures greater than 100°C. It is proposed that crystal defects, trapped charge carriers and other species introduced by radiation do not play an essential role in the annealing reactions which occur above 100°C. Oxygen may directly affect the crystal-phase 51Cr(III)-precursor species, rather than act solely as a surface electron trap.

An electromagnetic isotope separator and a 600 kV ion accelarator have been used for the production of energetic beams of radioactive 51Cr ions from 5 to 450 keV. The chemical fate of singly-and doubly-charged chromium ions in KClO4, K2CrO4, K2SO4, Na2MoO4, mixed K2CrO4+K2SO4 crystals, and mixed K2CrO4+K2BeF4 crystals have been studied using a tracer technique. A comparison between the distribution of 51Cr atoms among the possible chemical forms produced with accelerated 51Cr ions and chemical effects of recoils from nuclear reactions in K2CrO4, and in the mixed crystal systems show similar features. Evidence for the presence of chromous ions in KClO4, K2SO4, and the mixed crystal systems is presented. The chemical distribution of the 51Cr atoms depends on the chemical composition of the target, the target preparation method, the energy, and the charge of the accelerated ions, and on the dose received. Further evidence for an electronic annealing mechanism for irradiated potassium chromate is obtained.

In the photochemical reaction of sulphuric acid esters of leuco vat dyes (vat esters), sulphite, sulphate and dithionate are produced, and a spectrophotometric method for the determination of these species in solution has been devised. An aliquot of solution is analysed for sulphite by the method using bleached Fuchsin N and formaldehyde solutions. Another aliquot is treated with hydrogen peroxide in the cold to oxidise sulphite to sulphate. The sulphate due to oxidation of sulphite plus the original sulphate is measured by the barium chloride and potassium chromate solutions method and the original sulphate is calculated by difference. A third aliquot is treated with hydrogen peroxide in the cold, then concentrated hydrochloric acid is added and the resulting solution is boiled. Dithionate is oxidised quantitatively to sulphate. Total sulphate is measured as before and sulphate due to dithionate is calculated by subtraction. Concentrations as low as 0.5 × 10–5M sulphite and 1 × 10–4M sulphate can be determined by this method.

Single-crystal Raman spectra have enabled the identification and assignment to be made of nearly all the predicted factor-group fundamentals derived from internal modes of the anion in potassium chromate. Single-crystal i.r. and Raman methods were also used to study the lattice modes of this compound.

γ-Irradiation of K2CrO4 at 77°K produces two main paramagnetic species which disappear on warming, though the e.s.r. spectra are complicated by spurious lines thought to be from impurities. The first of the two centres is believed to be the electron-deficient species CrO4–, and the following e.s.r. parameters have been obtained for this ion: gxx= 2·0162, gyy= 2·0142, gzz= 2·0080, and Ax [graphic omitted] 3G. A single-crystal study of this ion has indicated four magnetically distinct sites in the unit cell for an arbitrary orientation of the external field, with gxx approximately parallel to the c-axis of the crystal. The electron hole is thought to be in a non-bonding orbital on oxygen, hyperfine coupling with the Cr nucleus occurring via spin-polarisation of the Cr–O bonds. The second of the two centres is thought to be CrO43– which gives an e.s.r. spectrum which can only be measured below about 10°K. The g-values obtained for this ion are: gxx= 1·9776, gyy= 1·9539, gzz= 1·9281. The reaction sequence leading to the formation of these centres, CrO42–+γ→ CrO4–+ e–; CrO42–+ e–→ CrO43–, is apparently reversed on warming.

The radiation and thermal annealing of neutron-activated single crystals and polycrystalline K2CrO4 has been investigated by measuring the 51Cr distribution among aqueous 51Cr(VI), 51Cr(III)-monomer, and 51Cr(III)-dimer species following dissolution. Radiation annealing up to 75 Mrad doses and thermal annealing in the temperature interval –78° to 300°C are attributed to at least seven crystal phase 51Cr-containing species. Six well-separated thermal annealing reactions occur between –78° and 300°C in single crystals receiving a γ-dose less than 1 Mrad during reactor irradiation. The fine structure of the thermal annealing curves is lacking in polycrystalline K2CrO4 and in single crystals receiving more than 3-4 Mrad in pile γ-dose. Three radiation annealing reactions take place in both polycrystalline and single crystals of K2CrO4 for doses up to 75 Mrad, but the reactions are different at low doses (0-5 Mrad) in the two types of crystals. The annealing eactions have been studied both in the presence and absence of air. The influence of the annealing atmosphere depends to a large extent on the crystal perfection.