Monovalent copper

Acetylene has a low solubiHty in Hquid oxygen. Excessive concentrations can lead to separation of soHd acetylene and produce accumulations that, once initiated, can decompose violently, detonating other oxidizable materials. Acetylene is monitored routinely when individual hydrocarbons are determined by gas chromatography, but one of the wet classical methods may be more convenient. These use the unique reaction of acetylene with Ilosvay s reagent (monovalent copper solution). The resulting brick-red copper acetyHde may be estimated colorimetricaHy or volumetricaHy with good sensitivity (30). 

In contrast in presence of calcium or copper the phase separation took place for low values of the added salts and almost in stoichiometric proportion with the COO" concentration. As shown in Figure 1 the addition of monovalent... 

Taking into account the electron density relocation (Table 2.4) two routes of NO adsorption can be distinguished. Thus, the nitric oxide coordinates to the monovalent Cr, Ni, and Cu ions in an oxidative way (A<2M > 0), whereas for the rest of the TMIs in a reductive way (AgM < 0). Although this classification is based on the rather simplified criteria, it is well substantiated by experimental observations. Examples of reductive adsorption are provided by interaction of NO with NinSi02 and NinZSM-5, leading at T > 200 K to a Ni -NOs+ adduct identified by the characteristic EPR signal [71]. At elevated temperatures, similar reduction takes place for ConZSM-5 [63], whereas in the case of Cu ZSM-5 part of the monovalent copper is oxidized by NO to Cu2+, as it can readily be inferred from IR and EPR spectra [72,73], This point is discussed in more detail elsewhere [4,57],... 

Due to relatively high affinity of dioxygen to monovalent copper (A/iads = -20.2kcal/mol), the reaction is expected to be poisoned by oxygen [4],... 

The overlap between 5- and p-bands also occurs for the alkali metals and for the monovalent noble metals copper, silver, and gold, which have face-centered cubic structures. The noble metals differ from the alkalis because of the filled d-shell just below the 5-shell in energy the d-band and the 5-band overlap in the solid. 

The CO-TPD technique together with DFT calculations were previously successfully used to characterize monovalent copper positions in Cu-ZSM-5 and Cu-Na-FER catalysts[4, 5]. Recently it was observed that the CO molecule can also form adsorption complexes, where the CO molecule is bonded between two extra-framework cations [6]. It is likely that the formation of similar species between the Cu+ and K+ ions can also occur. The presence of adsorption complexes on such heterogeneous dual cation site was evidenced by the FTIR experiments [7]. The formation of CO complexes on dual cation sites was not considered in our previous TPD models where three types of Cu+ sites were taken into account. 

Due to the presence of low-temperature desorption peak a new desorption site was included to phenomenological model of TPD experiments previously used for the description of the Cu-Na-FER samples [5], The fit of experimental TPD curves was performed in order to obtain adsorption energies and populations for individual site types sites denoted A (A1 pair), B (sites in P channel (A1 at T1 or T2)), C (sites in the M channel and intersection (A1 at T3 or T4)) [3] and D (newly introduced site). The new four-site model was able to reproduce experimental TPD curves (Figure 1). The desorption energy of site D is cu. 82 kJ.mol"1. This value is rather close to desorption energy of 84 kJ.mol"1 found for the site B , however, the desorption entropy obtained for sites B and D are rather different -70 J.K. mol 1 and -130 J.K. mol"1 for sites B and D , respectively. We propose that the desorption site D can be attributed to so-called heterogeneous dual-cation site, where the CO molecule is bonded between monovalent copper ion and potassium cation. The sum of the calculated populations of sites B and D (Figure 2) fits well previously published population of B site for the Cu-Na-FER zeolite [3], Because the population of C type sites was... 

Cul and CuSCN. Both Cul and CuSCN require copper in the monovalent state. This was achieved by complexing Cu2+ ions with thiosulfate, which also reduces Cu2+ to Cu+. Potassium iodide or thiocyanate served as an... 

It is important that the copper is in the monovalent state and incorporated into the silver hahde crystals as an impurity. Because the Cu+ has the same valence as the Ag+, some Cu+ will replace Ag+ in the AgX crystal, to form a dilute solid solution Cu Agi- X (Fig. 2.6d). The defects in this material are substitutional CuAg point defects and cation Frenkel defects. These crystallites are precipitated in the complete absence of light, after which a finished glass blank will look clear because the silver hahde grains are so small that they do not scatter light. 

Both copper and zinc appear to be stored in many bacteria in cysteine-rich proteins, called metallothioneins, which will be discussed from a structural point of view later in the chapter. The expression of these metal sequestering, low-molecular weight, cysteine-rich proteins, is often induced by both monovalent Cu(I) and divalent Zn(II), as well as by the non-biologically necessary, but potentially toxic, Ag(I) and Cd(II). 

Tab. 3.6-3. Overview of cage compounds of the type [M Om(REH)x(RE)y] of the monovalent atoms M (alkali metals and copper) and the pnictogen atoms E (P, As).

Monovalent copper salts were initially found to be better catalyst precursors than divalent copper salts. The latter needed the addition of base. In the presence of dioxygen the copper(I) salts are oxidised to copper(II) hydroxides forming hydroxide bridged dimers. The hydroxides can be replaced by phenolates, thus producing the key-intermediate [23] (Figure 15.16). From this equilibrium we understand that water concentration should be kept low in order to have a maximum amount of phenoxides coordinated to the copper dimers. 

Monophosphabutadienes, 33 281-283 Monophosphacarbodiimides, 33 322 preparation, 33 323 reactivity, 33 322-325 stereoselective reaction, 33 324 Monophosphahexadienes, 33 305, 307-310 Monoterpyridine complexes of copper, 45 288 Monovalent cations hydration shell properties, 34 203-204 structure, 34 202-205... 

Small monovalent cations such as Li" or Cu" may be mobile in iron oxides at relatively low temperatures. This fact can provide an opportunity to prepare unusual compounds at low temperatures by either chemical or electrochemical insertion or extraction of lithium or copper. However, care must be taken in high-temperature preparations to prevent, for example, loss of Li as Li20 at high temperatures or disproportionation at low temperatures - especially at grain boundaries - into lithium-rich and lithium-poor phases. 

Copper acetate was used in Ref. 38 it was noted that if chloride was used instead of acetate, no deposition occurred, and this was attributed to adsorption of chloride on the substrate (Pt). The berzelianite phase with a small amount of umangite impurity was obtained. The composition and phase of the film could be altered by electrochemical cathodic polarization (in an aqueous K2SO4 solution). Initially, there occurred an increase in lattice parameters and decrease in x (Cu2-A Se). With continued polarization, a phase change occurred until eventually only orthorhombic Cui xSe was present in the film. The umangite phase also disappeared, and it was believed that this impurity phase catalyzed the phase transformation. The change in composition during cathodic polarization was attributed to reduction of zerovalent Se to Se, which was dissolved in the solution. Based on the study of Fohner and JeUinek [41] discussed earlier, this explanation can be interpreted as reduction of Sei ( monovalent Se) to Se (divalent Se). 

Gold has a more marked tendency to form complex salts than either copper or silver, but the ammines of gold arc somewhat unstable. Gold forms two series of salts where the metal is monovalent or divalent respectively from both series of salts ammines have been obtained. 

Figure 14.4 The three forms of the copper-complexed catenane, each species being either a monovalent or a divalent complex, (a) Four-coordinate complex, (b) five-coordinate complex, and (c) six-coordinate complex.

When either the 2(6)2 + solution resulting from this process or a solution prepared from a sample of isolated solid 2(6)2 + (BF4 )2 were electrochemically reduced at — IV, the tetracoordinate catenate was quantitatively obtained. The cycle depicted in Fig. 14.3 was thus completed. The changeover process for the monovalent species is faster than the rearrangement of the Cu(II) complexes, as previously observed for the previously reported simpler catenate.16 In fact, the rate is comparable to the CV timescale, and three Cu species are detected when a CV of a CH3CN solution of 2(6)2 + (BF4 )2 is performed. The waves at + 0.63 V and —0.41V correspond, respectively, to the tetra- and hexacoordinate complexes mentioned above. By analogy with the value found for the previously reported copper-complexed catenane,16 the wave at —0.05 V is assigned to the pentacoordinate couple (Fig. 14.4b). 

Copper Activation. Activation with copper causes an emission in zinc sulfide which consists of a blue (460 nm) and a green band (525 nm) in varying ratios, depending on the preparation. The green band is assigned to monovalent copper ions incorpo-... 

All compounds exhibit a temperature-independent diamagnetism which suggests copper to be monovalent. 

The Cr A and several other zeolites containing transition metal ions, which may exist in two or more valence states, were also found to be oxidation catalysts. One such system of note is the copper containing Type Y zeolite, the redox chemistry of which was studied in several recent investigations (2, 3.4, 5). These studies established the range of conditions at which copper exists in divalent, monovalent, or zerovalent state and in particular determined the reduction conditions in hydrogen and carbon monoxide atmospheres for a complete conversion of Cu Y to Cu Y but no further to Cu°. The Cu ions in type Y zeolite were reported to be specific adsorption centers for carbon monoxide ( 6), ethylene ( 7), and to catalyze the oxidation of CO (8). In the present work the Cu ions were also found to be specific adsorption centers for oxygen. 

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