X-ray techniques, and

These salts are soluble in diethyl ether and dichloromethane, but relatively insoluble in petroleum ether. The ethylzinc complex 55b was investigated by single crystal X-ray techniques, and the structure of the cation is shown in Figure 26. 

The number of X-ray structures published since the publication of CHEC-II(1996) has increased, underlining the importance of this technique in structure elucidation. The structure of a number of 1,2,4-thiadiazoles and 1,2,4-thiadiazolidines has been determined by X-ray techniques and they are listed in Table 1. The first preparation of an A7-oxide derivative of a 1,2,4-thiadiazole 2 has been reported. The X-ray structure of compound 2 shows that it has a nearly planar ring this conformation is stabilized by hydrogen bonding with the carboxamide group <1999J(P1)2243>. 

In silicon derivatives, X-ray studies of compound 27 were consistent with a covalently bonded trigonal bipyramidal molecule <2000CC565>. In addition, nucleophilic substitution at silicon for similar compounds was modeled either by NMR or X-ray techniques and both methods correlate in the calculation of % Si-O bond formation <2003JOM66, 2003JOM154>. 

X-ray crystallographic techniques have greatly aided progress in deducing the chemistry of 1,2,4-thiadiazoles. The structures of a number of 1,2,4-thiadiazoles and 1,2,4-thiadiazolidines have been determined by x-ray techniques, and are listed in Table 1. 

Elemental composition (CUSO4) Cu 39.81%, S 20.09%, O 40.10%. Aqueous solution of copper(ll) sulfate may be analyzed for copper by instrumental techniques (see Copper). The sulfate anion may be determined by ion chromatography. The crystal may be characterized by x-ray techniques and other physical tests. 

Elemental composition Pb 68.32%, S 10.57%, O 21.10%. the solid crystalline powder or the mineral anglesite may be characterized by x-ray techniques and physical properties. Lead can be analyzed in the sohd compound or its nitric acid extract by various instrumental techniques (See Lead). 

In a study conducted by the Armour Research Foundation (Ref 41) a-Pb azide crystals wrapped in a thin A1 foil were subjected to fast and thermal neutrons in the heavy water pile at Argonne National Laboratory. With a thermal flux rate of about 10l4n/cm2/sec the crystals were irradiated for 8, 17 and 170 hours. The crystals decompd to a brown powder which was identified as Pb carbonate by X-ray techniques and infrared absorption spectra. From a mass spectrographic analysis of the isotopes of carbon and oxygen in the decompn products, it was determined that the mechanism of carbonate formation is a reaction with the atmosphere by broken surface bands produced by the neutrons. Subsequently, Raney (Ref 60) reported... 

It is to be hoped that with improved three-dimensional x-ray techniques and with ever increasing interest in the coordination chemistry of actinides, more attention from a coordination chemist will be drawn to these fascinating complexes. 

After cooling, the bimetallic specimen obtained was cut along the cy-lindrical axis, ground flat and polished electrolytically. The cross-sections prepared in such a way were examined metallographically, by x-ray techniques and electron probe microanalysis. Microhardness measurements in the transition zone between initial phases were also made. 

Although coordination number 8 cannot be regurded as commer, the number of known compounds has Increased rapidly in recent years, so thai it is now exceeded only hy four- and six-coordiration. The factors important in this increase can be traced largely to improved three-dimen.sional X-ray techniques and to increased interest in Ihe coordination chemistry oflanthanide and actinide elements (see Chapter 14). 

A novel approach is reported for the accurate evaluation of pore size distributions for mesoporous and microporous silicas from nitrogen adsorption data. The model used is a hybrid combination of statistical mechanical calculations and experimental observations for macroporous silicas and for MCM-41 ordered mesoporous silicas, which are regarded as the best model mesoporous solids currently available. Thus, an accurate reference isotherm has been developed from extensive experimental observations and surface heterogeneity analysis by density functional theory the critical pore filling pressures have been determined as a function of the pore size from adsorption isotherms on MCM-41 materials well characterized by independent X-ray techniques and finally, the important variation of the pore fluid density with pressure and pore size has been accounted for by density functional theory calculations. The pore size distribution for an unknown sample is extracted from its experimental nitrogen isotherm by inversion of the integral equation of adsorption using the hybrid models as the kernel matrix. The approach reported in the current study opens new opportunities in characterization of mesoporous and microporous-mesoporous materials. 

The hydrogen atoms in many crystals have since been located using more refined X-ray techniques and particularly by neutron diffraction. Spectroscopic studies (infrared and n.m.r.) have also contributed to our knowledge of hydrogen bonding. 

A combination of X-ray techniques and multinuclear ( H, C, solid-state NMR has been employed to follow the structural... 

In one study, DSC was compared with X-ray powder diffraction for quantifying amorphous nifedipine in mixtures of crystalline nifedipine and compared with FTIR for quantifying polymorphs in pharmaceutical formulations. The DSC gave a limit of determination of 0.06% compared to 5% for the X-ray technique and the DSC gave a limit of determination of 0.02 % compared to 7 % by FTIR. 

The phase diagram between Th and ThC was studied by metallographic and X-ray techniques and by measurements of the electrical resistivity in quenched and slowly-cooled Th-C alloys. The a-p transformation temperature of thorium increased gradually with carbon content up to 2.3 at% C, and rapidly thereafter. Extrapolation to zero carbon content gave Ttrs(Th, cr) = (1633 + 10) K. 

Modern chemistry is aided profoundly by the advancement of x-ray techniques, and crown ether chemistry is no exception. Our understanding of solution coinplexaiion has been augmented by numerous solid-state structures. Among the earliest crown ether complexes to appear were those reported by Truter and Bush. Numerous other contributions to this area were reviewed by Dobler. In brief, many crown ethers are solid and form regular crystals. Because they possess an empty central space, one or more methylene residues typically turns inward to fill the molecular void. When complexation of a cation occurs, the methylene rotates outward so that the bound cation will be accessible to all of the macroring donors. 

The fact that certain structure-related phenomena tend to support one model, whereas others can be explained adequately only in terms of the other, underlines the limiting nature of either of the two concepts. The actual morphological structure of nylon is more complex and may involve paracrystals of any of the possible polymorphic forms, mesomorphic regions, and essentially amorphous domains. This is also indicated by a multiple melting phenomenon [279] that was investigated by high-temperature x-ray techniques and differential scanning calorimetry, and has been explained based on three phases — crystalline, intermediate, and liquid amorphous [280]. 

---