Structural Data in the Solid State

The main bond distances found in HNCC are reported in Table II, which has been divided into three sections, corresponding to the three 

Bond Distances in High Nuclearity Metal Carbonyl Clusters 

Polyhedron Circum radius Calculated hole (in A) for d = 1.4 A b Comparison with some covalent radii (A) 

A peculiarity of the three-dimensional clusters, containing more-or-less regular polyhedra of metal atoms, is the existence of a central cavity whose dimensions, as shown in Table III, are a function of the particular geometry of the polyhedron. The existence of such a hole is confirmed by the formation of a large number of carbide derivatives. 

Deformation and other bonding peculiarities are often found in HNCC, and our present ability merely to describe most of these phenomena gives an idea of the present state of the theory. 

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A summary with references of published X-ray structural data in the solid state of purines other than adenine and guanine has been compiled (B-72MI40902. p. 6l). 

The reaction with PPh2CCH leads to the formation of [Au(QF5)(PPh2CCH)[ [53] whose P H NMR spectrum shows a singlet at 17.2ppm, in the H NMR spectrum the resonance of the C = CH proton is observed at 3.46 ppm. The IR spectrum shows, besides the pentafluorophenyl absorptions, a band at 3271 cm due to the V(Csch) and another absorption at 2056 cm for the asymmetric C = C stretch. The structure of this complex was studiedby X-ray diffraction, the Au(I) atom is an almost linearly coordinated and the Au—C and Au—P distances are in the range of the values found for similar complexes. The excitation and the emission data in the solid state at 77 K are 331 and 445 nm. 

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... 

According to X-ray diffraction data, in the solid-state complex 87 adopts a six-membered metallacyclic structure, as the result of P-Pd-Cl-B bridging coordination. The interaction of the borane moiety with the chlorine atom is apparent from the short Cl-B distance (2.165(2) A) and the pyramidalization of the boron environment (EBa = 349.1°). The bridging coordination of the Pd-Cl bond by the PB 7b contrasts with the B-pendant coordination mode adopted by complex 72, deriving from the related ligand 7e featuring mesityl groups at boron (see Section IV.A). This illustrates the role of steric factors in the participation, or not, of the Lewis acid in the coordination assembly. 

The structural parameters, vibrational frequencies, IR and Raman intensities of the vibrational bands were calculated by DFT. The predicted frequencies were compared with experimental data in the solid state. The short M—O distance in Cu(acac)2 suggests a strong metal-ligand bond. 

NMR spectra in CHCIF2 solution indicate that [Zr(acac)2(N03)2] becomes stereochemi-cally rigid on the NMR time scale at temperatures below -144°C, and the spectra in the slow-exchange limit are consistent with the Ci-mmmm structure found in the solid state. Kinetic data for exchange of acetylacetonate methyl groups between the two inequivalent sites of the Ci-mmmm stereoisomer are included in Table 11. 

Freudenberg and co-workers [10] refined the finding of Schardinger [4] and proposed that CD complexes with most of their ligands are of the inclusion type. The first experimental evidence for molecular inclusion by CDs in the solid state came from X-ray crystallography. Hybl et al. [11] determined the structure of the complex of a-CD with potassium acetate by using three-dimensional X-ray diffraction data. In the solid state, the acetate anions are included in the a-CD cavity. 

Speiss used ab initio methods (HF/6-31G ) and the gauge-invariant atomic orbital (GIAO) approach to generate NMR chemical shifts to unravel the behavior of a naphthylene-bridged molecular tweezer and a 1,4-dicyanobenzene guest. The benefit of augmenting experimental NMR data (in the solid-state and solution phase), and the X-ray structure of a 1 1 complex, with computational methods was clear to the authors who stated the following ... 

Physical properties of A-4-thiazoline-2-one and derivatives have received less attention than those of A-4-thiazoline-2-thiones. For the protomeric equilibrium, data obtained by infrared spectroscopy favors fbrm 51a in chloroform (55, 96, 887) and in the solid state (36. 97. 98) (Scheme 23). The same structural preference is suggested by the ultraviolet spectroscopy studies of Sheinker (98), despite the fact that previous studie.s in methanol (36) suggested the presence of both 51a and... 

Pyridazine-3(2//)-thiones exist in the thione form (14), as is evident from an X-ray structure analysis of pyridazine-3(2//)-thione. 6-Mercaptopyridazine-3(2//)-thione is predominantly in the monothiolmonothione form (15) in aqueous solution and in the solid state, 6-hydroxypyridazine-3(2//)-thiones are in the hydroxythione form (16) and 6-aminopyridazine-3(2//)-thiones exist in the aminothione form (17) for further details see (73HC(28)755). Cinnoline-4(l//)-thiones and phthalazine-l(2//)-thione have been shown on the basis of UV data and ionization constants to exist in the thione forms. 

As mentioned in Section II,B, solutions of y9-hydroxypyridines in the nonpolar solvents chloroform and carbon tetrachloride show sharp infrared absorption bands near 3600 cm indicating that they exist in the hydroxy form. Infrared spectral data also led Mason to conclude that -hydroxypyridines probably exist largely as such in the solid state and exhibit O— 0 hydrogen bonding, a conclusion which is contrary to an earlier proposal favoring a zwitterion structure. 

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