Vibrational spectroscopy complexes

Miller R E 1988 The vibrational spectroscopy and dynamics of weakly bound neutral complexes Scianca 240 447-53... 

The high stability of fluoride complexes maintains the configuration and vibration parameters of different compounds in various media. This special feature enables clear distinguishing of different complex ion types using vibration spectroscopy in solid, liquid and molten media. 

Complexes in fluoride melts - vibration spectroscopy of fluoride melts... 

The main problems encountered in the investigation of tantalum- and niobium-containing fluoride and oxyfluoride complexes are related to the tendency of the compounds to undergo hydrolysis, particularly at elevated/high temperatures. In addition, the interpretations of the observed effects are often nontrivial and unclear due to the relatively complicated inter-particular interactions and changes that occur under thermal treatment. From this point of view, vibration spectroscopy methods are of high importance due to the dependence of solid phase spectra on the temperature, which, above all, stems from the nature of such inter-ionic interactions [369]. 

For on-bead analysis vibrational spectroscopy (IR-spectroscopy) can be employed attenuated total reflection is a method allowing fast and nondestructive on-bead analysis of small samples (single bead analysis) without significant sample preparation. Solid phase NMR is the method of choice if complex structural analysis is intended on the support. Spatially resolved analysis on the resin is possible with microscopic techniques. 

Recent advances in the vibrational spectroscopy of metal cluster complexes. I. A. Oxton, Rev. Inorg. Chem., 1982,4, 1-26 (107). 

Most informative in this context is vibrational spectroscopy since the number of signals observed depends on the molecular size as well as on the symmetry of the molecule and, if it is part of a condensed phase, of its environment. In particular, Raman spectroscopy has contributed much to the elucidation of the various allotropes of elemental sulfur and to the analysis of complex mixtures such as hquid and gaseous sulfur. 

Vibrational spectroscopy has generally been applied to Si—M complexes in order to assign Si—M, M—Cl, M—P, or M—CO stretching mode(s). 

The use of computer simulations to study internal motions and thermodynamic properties is receiving increased attention. One important use of the method is to provide a more fundamental understanding of the molecular information contained in various kinds of experiments on these complex systems. In the first part of this paper we review recent work in our laboratory concerned with the use of computer simulations for the interpretation of experimental probes of molecular structure and dynamics of proteins and nucleic acids. The interplay between computer simulations and three experimental techniques is emphasized (1) nuclear magnetic resonance relaxation spectroscopy, (2) refinement of macro-molecular x-ray structures, and (3) vibrational spectroscopy. The treatment of solvent effects in biopolymer simulations is a difficult problem. It is not possible to study systematically the effect of solvent conditions, e.g. added salt concentration, on biopolymer properties by means of simulations alone. In the last part of the paper we review a more analytical approach we have developed to study polyelectrolyte properties of solvated biopolymers. The results are compared with computer simulations. 

Vibrational spectroscopy is of utmost importance in many areas of chemical research and the application of electronic structure methods for the calculation of harmonic frequencies has been of great value for the interpretation of complex experimental spectra. Numerous unusual molecules have been identified by comparison of computed and observed frequencies. Another standard use of harmonic frequencies in first principles computations is the derivation of thermochemical and kinetic data by statistical thermodynamics for which the frequencies are an important ingredient (see, e. g., Hehre et al. 1986). The theoretical evaluation of harmonic vibrational frequencies is efficiently done in modem programs by evaluation of analytic second derivatives of the total energy with respect to cartesian coordinates (see, e. g., Johnson and Frisch, 1994, for the corresponding DFT implementation and Stratman etal., 1997, for further developments). Alternatively, if the second derivatives are not available analytically, they are obtained by numerical differentiation of analytic first derivatives (i. e., by evaluating gradient differences obtained after finite displacements of atomic coordinates). In the past two decades, most of these calculations have been carried... 

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