Structural and spectroscopic parameters

The series AuX (tmpp) shows clear patterns [81] in structure and spectroscopic parameters (Table 4.9) (X = Cl, Br, I). 

Information on the thermodynamic properties (complexation constants, enthalpies of complexation, Gibbs energy of formation, and their relationships with structural and spectroscopic parameters) can be found in refs. 12, 23, and 24. 

Statistical mechanics affords an accurate method to evaluate ArSP, provided that the necessary structural and spectroscopic parameters (moments of inertia, vibrational frequencies, electronic levels, and degeneracies) are known [1], As this computation implicitly assumes that the entropy of a perfect crystal is zero at the absolute zero, and this is one of the statements of the third law of thermodynamics, the procedure is called the third law method. 

Table I. Comparison of Structural and Spectroscopic Parameters of Binuclear Iron Complexes...

In order to estimate and compare the magnitude of the M-B interactions in these isoelectronic complexes, a whole set of structural and spectroscopic parameters determined experimentally and/or computed theoretically were considered. This includes the M - B distance the ratio r between the M -B distance and the sum of covalent radii (to take into account the different sizes of the metals involved), the pyramidaliza-tion of the boron environment XB, the rlB NMR chemical shift <5 11B, the difference AqB between the charge at boron in the metal boratrane and the free ligand TPB, the difference A M between the charge at the metal in the metal boratrane and that in the related borane-free complex [M(i-Pr2PPh)3], and the NBO delocalization energy A NBo associated with the main donor-acceptor M-B interaction found at the second order in the NBO analysis (Table 2). Only the conclusions of this detailed analysis will be recalled here ... 

Given the DCD scheme, one may expect the M-H bond in silane o-complexes to be longer than normal due to its inherent electron-deficiency. Indeed, the elongation of the M-H bond in a-complexes of molecular dihydrogen is a well-defined parameter determined by several structural and spectroscopic methods. 

The topic of low-barrier hydrogen bonds (LBHBs) and the question of how they are involved in enzyme function has been discussed heavily in the literature recently. Hydrogen bonds between two bases of nearly matched proton affinity often exhibit strongly perturbed bond lengths and spectroscopic parameters it remains somewhat unclear exactly how the spectroscopic parameters reflect total energy or reactivity. In this study, we report H NMR chemical shift data and surveys of structural preferences for the well-studied 0-H---0 systems, and also for less studied, but biologically important N-H-0 systems, in particular the imidazole and imidazolium functionality. The H shifts also show interesting trends in comparison with O-H-O motifs, which will require further scrutiny. 

Other means of manipulating ions trapped in the FTMS cell include photodissociation (70-74), surface induced dissociation (75) and electron impact excitation ("EIEIO")(76) reactions. These processes can also be used to obtain structural information, such as isomeric differentiation. In some cases, the information obtained from these processes gives insight into structure beyond that obtained from collision induced dissociation reactions (74). These and other processes can be used in conjunction with FTMS to study gas phase properties of ions, such as gas phase acidities and basicities, electron affinities, bond energies, reactivities, and spectroscopic parameters. Recent reviews (4, 77) have covered many examples of the application of FTMS and ICR, in general, to these types of processes. These processes can also be used to obtain structural information, such as isomeric differentiation. 

Linear amino polymers containing basic nitrogen atoms are critically reviewed with regard to their synthesis, protonation and complex formation in solution with metal ions. Cross linked resins having essentially the same structure as linear polymers, are also mentioned. As far as the proto-nation is concerned, special care has been given to thermodynamic aspects, and to the most probable protonation mechanism. Complexing abilities of these polymers have been evaluated through stability constants and spectroscopic parameters. Practical implications of the properties have been considered. 

With the help of scalar relativistic DKH BP DF calculations, we examined the two structural models of Re(CO)3/MgO complexes at dehydroxylated and hydroxylated MgO surfaces (Fig. 4.8) Re(CO)3 and Re(CO)3 adsorbed on neutral and positively charged Vs centers (Mg defects) [264]. Our aim was (i) to justify the possibility that Re(CO)3/MgO complexes are formed, (ii) to determine their stmctural and spectroscopic parameters, and (iii) to investigate whether the Re-Osurf bonds are similar in strength and nature to common coordination bonds. That work [264] was the first high-level computational study to assess quantitatively stmcture and bonding parameters of an oxide-supported organometallic species. 

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