Infrared , four-coordinate

Formic acid irradiation of, 3 183 reaction with hydrogen atom, 3 191 Formylium cation, 9 231 Formylmethanofuran dehydrogenase, Methano-bacterium wolfei, 40 73 Fossil fuel, radiocarbon and, 3 311-312 Four-coordinated metal centers, 37 19 Fourier-transform infrared spectroscopy, NiFe hydrogenase, 47 295-298, 299, 303 Fourier-transform ion cyclotron resonance... 

The infrared spectrum shows a strong band at 2370 cm. - characteristic of BH3 coordinated to a donor group, and a band at 1110 cm.-1, characteristic of four-coordinate phosphorus. The entire infrared spectrum is given in Table I. 

HOF/DAR] Hoffmann, M. M., Darab, J. G., Palmer, B. J., Fulton, J. L., A transition in the Ni complex structure from six- to four- coordinate upon formation of ion pair species in supercritical water, an x-ray absorption fine structure, near-infrared, and molecular dynamics study, J. Phys. Chem. A, 103, (1999), 8471-8482. Cited on pages 141, 142. 

There is no universally correct answer to the question, "What are the active sites " In many cases it may be correct to answer that the sites are all the surface platinum atoms in another, all four-coordinated surface aluminum atoms and so forth. For a long time other answers have also been given. As early as 1934 Frost and Shapiro (1 ) concluded in a review that sites are often points of crystal lattice deformation. In this connection, Erbacher showed in 1950 (14) that catalytic sites could be annealed. In 1953 Thon and Taylor (j[5) pointed out that the active site could be a dissociatively adsorbed particle, for example, an adsorbed hydrogen atom. In the 1950 s Eischens and Pliskin carried out their classic work of obtaining the infrared spectrum of adsorbed molecules and published a survey of the subject in 1958 (j ) When they observed the adsorbed molecule, they could conceivably be observing the reacting molecule and, as a result, we could be much closer to knowing the nature of the catalytic site. 

The ionic nitrate group, which has D h symmetry, has four fundamental vibrations, three of which are active in the infrared. Upon coordination as either a monodentate or a bidentate ligand, the symmetry becomes C2, which has six, infrared active normal modes of vibration. As a result of coordination, the doubly degenerate V4 band of the ionic nitrate group in the 700 cm region splits into the V3 and V5 bands of the coordinated nitrato group. 

For four-coordinate C2 complexes the infrared-active fundamental vibrations are... 

A -bis [2-(dimethylamino)ethyl] W -dimethyl-1 -ethanediamine] (thiocya-nato-AOpalladium(II) thiocyanate is a diamagnetic, yellow solid. It is veiy hygroscopic and ould be stored in a moisture-free atmosphere. The palladium atom is four-coordinate in the solid state. The H nmr spectmm in DjO exhibits 2 singlet resonances at 2.56 and 2.63 ppm for the methyl protons (DSS as reference). The electronic spectrum in H2O is characterized by 2 absorption maxima at 263 run (e = 7200 L mole cm ) and 325 nm (e = 1800 L mole cm ). The infrared spectrum (Nujol) exhibits i CN) bands at 2105 and 2060 cm. ... 

Crisp et al. (1978) were able to follow the course of the cement-forming reaction using infrared spectroscopy and to confirm previous observations. They found that the technique could be used to distinguish between crystalline and amorphous phases of the cement. Hopeite shows a number of bands between 1105 and 1000 cm this multiplicity has been explained by postulating a distortion of the tetrahedral orthophosphate anion. (Two-thirds of the zinc ions are tetrahedrally coordinated to four phosphate ions, and the remainder are octahedrally coordinated to two phosphate and four water ligands.)... 

Nb(Et2C c)4X is a 1 1 electrolyte in which the metal is probably eight-coordinated by sulfur atoms from four bidentate dithiocarbamate groups. Infrared data suggest that the ligands are unsymmetrically bonded. 

The harmonic vibrational infrared spectrum of the four bases, as well as of the two base pairs, has been calculated at the DFT and DFT-solvent level of theory by finite differentiation of the forces acting on atoms along the normal coordinates. In the following, we briefly analize the results, which... 

Nickel carbonyl is by far the best-known of these compounds. All the data support a tetrahedral structure with four equivalent, linear Ni—C—0 arrangements. The Raman (3, 62, 61) and infrared spectra (8, 53, 135, 136) have been investigated and various assignments of the fundamental frequencies have been put forward on the basis of Td symmetry (53, 136, 208). Several approximate coordinate analyses have been made using these assignments, but the spectra of isotopically substituted species have not been measured, so exact evaluations of force constants have not yet proved possible. The Ni—C and C—0 stretching force constants are particularly important and the values obtained by workers using various approximations are included in Table I. 

With the development of analytical energy derivative methods135 l67, the calculation of vibrational frequencies (second derivatives of the energy with regard to atomic coordinates) and infrared absorption intensities (derivatives of the energy with regard to components of electronic field and atomic coordinates, i.e. dipole moment derivatives) both at the HF and correlation corrected levels has become routine168. There are six (two a " + four e)... 

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