Structural studies bond angles

VSEPR theory can successfully account for many of the fine details in a structure, especially bond angles. However, we will be mainly concerned with the gross geometries of molecules and polyatomic ions. Structural minutiae are of considerable interest to most inorganic chemists, but they are important in the study of descriptive inorganic chemistry only to the extent that they may illuminate details of bonding which are relevant to the very existence of a substance, and to its reactions. 

Precise description of the pyramidal structures would also require that the bond angles be specified. The EPR spectrum of the methyl radical leads to the conclusion that its structure could be either planar or a veiy shallow pyramid. The IR spectrum of the methyl radical has been recorded at very low tempertures in frozen argon. This IR study puts a maximum of 5° on the deviation from planarity. A microwave study has also indicated... 

The preparation and structural characterization of the ions HX2 has been an important feature of such work/ As expected, these H-bonded ions are much less stable than Hp2 though crystalline salts of all three anions and of the mixed anions HXY (except HBrI ) have been isolated by use of large counter cations, typically Cs+ and NR4+ (R = Me, Et, Bu") — see pp. 1313-21, of ref. 23 for further details. Neutron and X-ray diffraction studies suggest that [C1-H - C1] can be either centrosymmetric or non-centrosymmetric depending on the crystalline environment. An example of the latter mode involves interatomic distances of 145 and 178 pm respectively and a bond angle of -168 (Cl- -Cl 321.2pm).( >... 

Structural Studies. X-ray powder diffraction patterns for I indicate that the crystal structure is isomorphous to Zr2(0H)2-(SOO3 (H20)>. Figure 1 depicts the structure of the zirconium compound (5). The structure of I is identical to that of the zirconium analog except for variations in bond distances and angles which do not affect the overall structure. We have as yet been unable to obtain single crystals of I which are suitable for X-ray diffraction studies. 

The fulminate ion, CNO-, probably has a structure intermediate between C N O and C N 6 for since these two bond types have the same bond angles and term symbols ( 2), they can form intermediate structures lying anywhere between the two extremes. Which extreme is the more closely approached could be determined from a study of the bond angles in un-ionized fulminate molecules, such as AgCNO or ONCHgCNO, for the first structure would lead to an angle of 125° between the CNO axis and the metal-carbon bond, the second to an angle of 180°. 

In an extensive ab initio MO study the structures, energies and vibrational spectra of the sulfonium ions H3S with n=l-4 were studied at the MP2/6-311(2df,2pd) level of theory [70]. It was confirmed that HsS is of Csv symmetry with dsH= 134.6 pm and bond angles of 94.2° This cation had previously been isolated as a component of the salt [H3S][SbF6] [71] and had been observed spectroscopically [72]. The experimental gas phase re geometry is dsH= 135.02 pm and 0 hsh=94.189° [72] which agrees well with the ab initio calculated values by Botschwina et ah dsH=135.0 pm, aHsn=94.2° [73]. 

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