Cadmium atom

Using this equation, the flow of the reaction was followed by registering the frequency shift as a function of reaction time. Typical dependencies are shown in Figure 38 (Facci et al. 1994). As one can see, the curves tend to come to saturation (saturation time depends on film thickness). On the other hand, the plateau level in all cases corresponds well to the value resulting from simple calculation of the number of cadmium atoms available for the reaction in each sample. Numerical data of such estimates are presented in Table 8. The available amount of cadmium atoms was estimated in this case, taking into ac-... 

Process (3.8) is a total 2e per cadmium atom and indicates that CdS formation occurs via a sulfur atom abstraction from 8203 . This reaction was called for in order to suggest that the reduction of Cd " is the only electrochemical step, whereby charge is consumed, followed by a subsequent chemical step comprising sulfur association to reduced cadmium. Sulfur is generated by the decomposition of thiosulfate. On the other hand, reaction (3.9) corresponds to an overall 4e /Cd process where reduction of S2O3 itself must occur as well as that of Cd ", the former comprising actually the rate-determining step. This route becomes more favorable as pH decreases for it requires additional protons. 

The metal formed is deposited on the colloidal particles and causes the absorption of the solution to increase at all wavelengtlK. The depositel cadmium is very reactive. It is reoxidized when air is admitted to the illuminated solution. Addition of methyl viologen to the illuminated solution under the exclusion of air yields the blue colour of the semi-ceduced methyl viologen, MV". As the absorption coefficient of MV" is known, the concentration of reduced cadmium can be readily calculated. reoxidises cadmium atoms ... 

Carbene adducts of dimethylcadmium 188-190 have been obtained by simple addition of CdMe2 to the corresponding carbene at room temperature.2 9 All the three adducts have similar structures. In the case of 190, the Ccarbene-Cd bond of 2.33 A is 0.15 A longer than the Cmethyi-Cd bonds of 2.18 A (Figure 28). As a result, the cadmium atom is in a distorted trigonal-planar environment with a Cmethy -Cd-Cmethyl angle of 136°. 

Unusual arene-cadmium 7r-complexes have been recently prepared and structurally characterized. For example, the /w /zz-bcn/i porphyrin complex 194, which can be obtained by reaction of the free base with CdCl2, possesses a cadmium atom that is bound to the Mfez-phcnylcnc unit of the ligand in an apparent /-fashion (Figure 32). The resulting Cd-C distance of 2.71 A is shorter than the sum of the van der Waals radii.252 Despite this relatively short contact, DFT calculations and AIM analysis point to the weakness of the interaction. Comparable weak arene-cadmium 7r-interactions are also observed in the /wra-benziporphyrin cadmium chloride complex 195.253... 

The reaction of dabco (l,4-diazobicyclo[2.2.2]octane) with Me2Cd yields a 1 1 adduct 197, which adopts a linear polymeric structure (Figure 34).255 The cadmium atom is coordinated by two dabco units and two methyl carbon atoms giving rise to a distorted tetrahedral environment. Finally, the organocadmium adduct 198 (Figure 35) has been isolated from the reaction of Me2Cd with Cd[(SeP-/-Pr2)2N]2.256 The solid-state structure consists of dimeric units where each methylcadmium unit is coordinated to three selenium atoms. The geometry about the cadmium center is tetrahedral with a Cd-C distance of 2.16 A, which is comparable to that observed in other cadmium alkyl complexes. 

X-Ray structural determinations on [(2,2 6, 2"-terpyridyl)Cd Mn(CO)5 2] and [Hg Mn(CO)5)2] have been reported. The former has distorted trigonal-bipyramidal geometry at the cadmium atom and shows considerable distortion of the octahedral co-ordination around the manganese atoms, and the latter contains a linear Mn—Hg—Mn system, the Mn(CO)5 groups being eclipsed. The complexes [X In Mn(CO)5)3 J (X = Cl or Bf n = 0—2) have been prepared and studied in detail. The indium-manganese bonds are readily... 

Fig. 7-11.—The arrangement of cadmium atoms (small circles) and chlorine atoms (large circles) in the rhombohedral crystal cadmium chloride, CdCl . The atoms are arranged in octahedral layers, as represented m Figure 7-10. These layers are superimposed in the manner indicated in the figure. Repetition in the direction of the trigonal axis (vertical) occurs after three layers.

This brings us to a class of compounds too often overlooked in the discussion of simple ionic compounds the transition metal halides. In general, these compounds (except fluorides) crystallize in structures that are hard to reconcile with the structures of simple ionic compounds seen previously (Figs. 4.1-4.3). For example, consider the cadmium iodide structure (Fig. 7.8). It is true that the cadmium atoms occupy octahedral holes in a hexagonal closest packed structure of iodine atoms, but in a definite layered structure that can be described accurately only in terms of covalent bonding and infinite layer molecules. 

In general, the literature contains fewer references to complexes formed from monofunctional amines than to those formed from ammonia itself or from multidentate amines. However, some clarification of earlier studies is to be found in recent reports, e.g. the complexes [Cd(PhNH2)X2] (X = C1 or Br), and their deuterated derivatives, have been reinvestigated and shown to be octahedral.166 This latter study clarified some of the confusion present in the earlier literature concerning these compounds. Another aniline complex, 3CdCl2-4L, has been studied and it has been shown that there are two types of octahedral environment in which the cadmium atoms are found, one comprising a CdCU unit and the other a CdCL unit.167... 

The crystal structure of Cd(S04) has been redetermined.672 The cadmium atom in Cd(S04) is in a very distorted Cd04 tetrahedron, with the O—Cd—O angles varying from 88.1 to 142.7. In contrast, the structure of Cd2(NH4)2(S04)3 contains two inequivalent octahedral sites for Cd2+, and is essentially isostrubtural with K2Mg(S04)3. It is found that Mn2+ may be preferentially incorporated (82%) into the site with the shorter average cation—oxygen distance.673... 

The crystal structure of cafena-bis[ -(Af-methylpiperidinium-4-thiolato)]cadmium(II) perchlorate dihydrate827 involves infinite chains of cadmium atoms, each of them tetrahedrally coordinated to four sulfur atoms of four different Af-methylpiperidinium-4-thiolato groups. Each sulfur atom bridges two consecutive cadmium atoms, r(Cd—S) = 2.548 A. 

If the corrosion sites are treated as surface states on the CdS (as seems logical since the cadmium atoms that eventually receive the holes are part of the semiconductor surface) the first step corrosion rate constant for holes, S, may be analyzed in a similar fashion S =N 0 v.. 

The calculation of the (001) cadmium-surface-water interface used a hexagonal unit cell with a c lattice constant of 135 a.u., and an a lattice constant of 33.788 a.u., corresponding to 36 cadmium atoms in the surface layer. The Cd slabs were 5 layers thick (perpendicular to the c-axis), for a total of 180 cadmium atoms per unit cell. The region between the slabs was filled with 525 water molecules. The plane wave expansion of the electron eigenstates had a cutoff of 9 Ry, giving 20,209 basis functions. Calculational details are described in reference [52]. 

S2 Cd distance of 2.765(1) A (i.e., a separation shorter that the chelate Cd S4 distance underlying the strength of the bridge). Completing the approximately octahedral coordination geometry about the cadmium atom is the S6 atom of the thione ligand Cd S6 2.641(2) A. The remaining cadmium xanthate adducts contain bidentate Lewis bases. 

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