Solid-state structure calculations

A major goal was to investigate the solid state structures of such compounds by single crystal X-ray diffraction. It was found that Lewis acid-base adducts R3M—ER3 show general structural trends, which allow estimations on the relative stability of the adducts. The experimental results were confirmed by computational calculations, giving even deeper insights into the structural parameters and the thermodynamic stability of simple Lewis acid-base adducts. In addition, their thermodynamic stability in solution was investigated by temperature-dependent NMR spectroscopy. 

The solution structure of [Ir(bpy)H2(PRPh2)2]X, R = Me, Ph, X = PF6, BF4, CF3S04, BPh4, as determined from NMR studies, is compared to solid-state structure.152 The main difference between the two structures is the location of the counter ion X. In solution, X is positioned on the side of the bpy ligand remote from the Ir, whereas in the solid state X is found close to one of the pyridine rings and one hydride ligand. Theoretical calculations at the QM/MM (B3PW91/ UFF) level support the experimental results. 

The solid-state structures of orthorhombic S864 and monoclinic Se866 are shown in Figure 15. As may be seen from the average E-E-E bond and EE EE torsion angles, this structure is almost completely relaxed and consequently lone pair repulsion and ring strain are lowest in this arrangement. Other S8 structures were assessed by quantum chemical calculations.69... 

Numerous X-ray investigations have unravelled the solid state structure of contact and solvent-separated ion pairs. It was therefore considered to be of interest to evaluate also the potential of solid state NMR as a tool for the investigation of this structural problem. In addition to the study of chemical shifts discussed above (Section II.B), the quadrupole coupling constant of the nuclide Li, x( Li), was expected to be an ideal sensor for the bonding situation around the lithium cation because, due to its dependence on the electric field gradient, the quadrupolar interaction for this spin-3/2 nucleus is strongly influenced by local symmetry, as exemplified in Section II.C.3. This is also shown with some model calculations in Section ILF. 

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