Crystalline solids atomic coordinates

Table 8.53 shows the main features of XAS. The advantages of EXAFS over diffraction methods are that the technique does not depend on long-range order, hence it can always be used to study local environments in amorphous (and crystalline) solids and liquids it is atom specific and can be sensitive to low concentrations of the target atom (about 100 ppm). XAS provides information on interatomic distances, coordination numbers, atom types and structural disorder and oxidation state by inference. Accuracy is 1-2% for interatomic distances, and 10-25 % for coordination numbers. 

The zwitterionic A5S7-fluorosilicates 4-22 were isolated as crystalline solids. Compounds 4-8, 13, and 17-22 were structurally characterized in the solid state by single-crystal X-ray diffraction. In contrast to the achiral zwitterions 4-16, the zwitterions 17-22 are chiral, the respective crystals consisting of pairs of enantiomers [(A)- and (C)-enantiomers]. In all cases, the /-coordination polyhedron was found to be a somewhat distorted trigonal bipyramid, with fluorine atoms in the two axial sites. This is illustrated for 6 and 19 in Fig. 1. Selected geometric parameters for compounds 4-8, 13, and 17-22 are listed in Table I. As can be seen from these data, the axial Si-F distances [1.647(2)-1.743(1) A] are significantly longer than the equatorial ones [1.589(2)-1.638(1) A]. The Si-Cl distances amount... 

Because the heat capacities of crystalline solids at various T are related to the vibrational modes of the constituent atoms (cf section 3.1), they may be expected to show a functional relationship with the coordination states of the various atoms in the crystal lattice. It was this kind of reasoning that led Robinson and... 

A similar reaction of i -Bu2Mg with 2,6-di-fert-butylphenol in the presence of 18-crown-6 affords i-BuMgOC6H3Bu-r-2,6(18-crown-6) (209) as a crystalline solid. An X-ray crystal-structure determination showed that this compound in the solid state also exists as a monomer with a a-bonded i-butyl group and a a-bonded phenoxy oxygen atom. Three adjacent oxygen atoms of the crown-ether are involved in coordination to magnesium, resulting in penta-coordination. 

When 2-cyanoethylzinc iodide is recrystallized from THF, a crystalline material is obtained. This material appeared to be the mono-THF adduct of 2-cyanoethylzinc iodide which exists in the solid state as a coordination polymer via coordination of the cyanide functionality to an adjacent zinc atom. Coordination saturation at zinc is reached by the coordination of an additional THF molecule. No further structural data have been given for this compound . 

Bis[l,2-phenylenebis(dimethylarsine)]gold(I) bis(pentafluorophenyl)aurate(I) is a white crystalline solid that melts at 178°C. It is soluble in acetone and dichloromethane, slightly soluble in diethyl ether, and insoluble in hexane. Its IR spectrum shows, along with those due to the pentafluorophenyl group (see Section B), strong absorptions at 745,590,435,365, and 350 cm "1 arising from the bis(arsine). In the cation the bis(arsine) acts as a chelate and therefore the cation contains a tetrahedral four-coordinated gold(I) atom.9... 

The white crystalline solids are readily soluble in organic solvents (even alkanes) but are insoluble in water and the lower alcohols. They are inert to water but are hydrolyzed by dilute acid. In solution they are monomeric and non-ionized. An X-ray crystallographic study of Be40(0Ac)6 shows the O to be centrally coordinated to four Be atoms in a tetrahedral geometry each of the Be atoms is tetrahedrally surrounded by four O donors from bridging acetates and the central oxygen (62).322... 

The heavier atoms of Group 13 appear not to form p -p bonds. Five- and six-coordinate structures (schemes (4) and (5)) are almost entirely restricted to the heavier atoms, although at least one complex containing five-coordinate boron is known. According to VSEPR theory, scheme (4) structures should be trigonal bipyramidal. However, InClf- and TlClf are found to be square pyramidal in crystalline solids. As noted in Section 8.2, this shape (also adopted by MnClf-) is possibly favoured by crystal packing requirements. 

If the immediate neighbor atoms (coordination number) m is known such as in a crystalline solid, the question can be answered readily by invoking the binomial theorem. Since in the liquid state the coordination number m varies dynamically throughout the system, the answer to this question requires more thought. We know that for a given P (the atomic composition of B), there exists an average number of B s surrounding A and that the number n (P) can be written as ... 

Compound 65f was isolated as a sky-blue crystalline solid which is highly soluble in nonpolar organic solvents. The molecular structure of 65f was determined by a single crystal X-ray analysis. It showed the neodymium atom in a distorted octahedral coordination environment (Fig. 20) [78]. Dark red crystalline [Me2Si(OtBu)(NrBu)]3Eu was prepared analogously. 

Titanium Trifluoride. The trifluoride (121) is a blue crystalline solid, density 2980 kg/m3, in which the titanium atoms are six-coordinate at the center of a slightly distorted octahedron, where the mean Ti—F distance is 197 pm. Titanium trifluoride [13470-08-1] is stable in air at room temperature but decomposes to titanium dioxide when heated to 100°C. It is insoluble in water, dilute acid, and alkalies but decomposes in hot concentrated acids. The compound sublimes under vacuum at ca 900°C but disproportionates to titanium and titanium tetrafluori.de [7783-63-3] at higher temperatures. 

The solid-state structure for stannocene has not been determined the crystal structure for the orthorhombic crystalline form of plumbocene is shown in Fig. 2 (17), Plumbocene is associated in the solid state, with each lead atom coordinated to three cyclopentadienyl rings, one of them terminal and two of them bridging to other lead atoms. 

Using a different metal salt, Cd(NOj)2, instead of CdClj oxidation reaction results in a slightly higher yield of the cadmium texaphyrin complex [60, 65]. However, upon purification, the product is obtained as a mixture of crystalline and non-crystalline solids. A single crystal X-ray diffraction study of the crystalline portion of the sample gave an unexpected result. The structure obtained (Fig. 20) revealed a six-coordinate pentagonal pyramidal cadmium (II) complex 156 (c.f. Scheme 20) where one of the two possible axial ligation sites is occupied by a benzimidazole [65]. The five donor atoms of the pentadentate texaphyrin macrocycle complete the coordination sphere about the cadmium with the cadmium... 

A highly unusual mixed oxidation state compound, (FgGe4)GeF4, is formed from GeF4 and Ge at 350 °C as a colorless crystalline solid. The overall structure is polymeric with fluorine bridges the Ge atom is octahedrally coordinated by fluorines and four Ge atoms fall into two groups, both with distorted square pyramidal coordination by F and active lone pairs. 

Halides with the stoichiometry Ti7Xie (X = Cl, Br) have also been prepared. They are black crystalline solids sensitive to both oxidation and hydrolysis. They consist of octahedrally coordinated Ti and tF atoms in the ratio 1 6 (i.e. TiCU bTiCU). 

Alkylzinc thio- and selenocarbamate derivatives are coimnonly air-sensitive white crystalline solids, with the thiocarbamate derivatives being more soluble in organic solvents than the selenocarbamate derivatives. They have been found to be dimers of general formula [RZnE2CNRy2, in which each carbamate chelates one metal atom and bridges to the next one (Figure 41). The zinc atoms are four-coordinate with a distorted tetrahedral geometry. 

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