Neutron and x-ray crystallographic studies on metal hydride complexes and organic ring inversion

Chapter 1 gives a brief description about neutron diffraction and how neutrons are used to locate hydrogen atoms, an importance over X-rays, especially in the case of metal hydride complexes. Listed individually are 5 different neutron diffraction instruments that have made my research possible.;Chapter 2 describes our single-crystal neutron diffraction results that unambiguously reveal a four-coordinate H atom located in the center of a soluble organometallic tetrahedral complex [Li(THF)4][(C5Me 4SiMe3)4 Dy4(mu-Cl)(mu-H)8]. The core of the molecule consists of a tetranuclear cluster with one interstitial, two face-bridging and five edge-bridging hydride ligands. Neutron data were collected on the Quasi-Laue diffractometer VIVALDI at Institut Laue-Langevin (ILL) (Grenoble, France). The existence of a 4-coordinate hydrogen reinforces previous results observed with a series of high-connectivity hydride ligands located at the interstitial cavities of molecular clusters. Interestingly, the 4-coordinate yttrium allows us to analyze simultaneously three different types of hydride coordination in the same molecule (M2(mu2 - H), M3(mu 3 - H), and M4(mu4 - H)).;Chapter 3 describes the structures of (Cp'-Y)4H11[Cp*WPMe 3] (1) and (Cp'-Y)4H11[Cp*W]; (2) [Cp'= C 5Me4(SiMe3)] which have been determined by single-crystal neutron diffraction on the monochromatic four-circle diffractometer D19 (for 1) and the quasi-Laue diffractometer VIVALDI (for 2) at ILL. A highly distorted 4-coordinate tetrahedral hydrogen and an unprecedented 5-coordinate trigonal bipyramidal hydrogen have been unambiguously located in the complexes cores, for the first time.;Chapter 4 describes our studies to accurately measure the length of the U-H single bond by single crystal neutron diffraction in the molecular complex [(C5Me5)2U(H)(mu-H2)]2 . Presented here is the first accurate covalent bond measurement between the lightest and heaviest naturally occurring elements. Successful single-crystal neutron diffraction has accurately determined both terminal U-H and bridging U-H-U hydride distances on two instruments, VIVALDI of ILL, and SXD of ISIS.;Chapter 5 describes two chiral tetraphenylenes, 2,15-dideuteriotetraphenylene (7) and 2,7-dimethyltetraphenylene (15). They were synthesized and resolved to address the tetraphenylene inversion barrier problem. Neutron diffraction investigation of enantiopure 7 showed that the molecule retained its chirality integrity during its synthesis from enantiopure precursors and rules out the possibility of tetraphenylene framework possessing a low-energy barrier to inversion.