## LSU Historical Dissertations and Theses

1987

Dissertation

#### Degree Name

Doctor of Philosophy (PhD)

#### Department

Chemistry

Steven F. Watkins

#### Abstract

The crystal and molecular structures of four compounds have been determined by X-ray diffraction. Red crystals of 2,6-bis (1-(2,2-dimethylpropanimino)ethyl) pyridine tetracarbonylmolybdenum(0), Mo(CO)$\sb4$(C$\sb{19}$N$\sb3$H$\sb{31}),$ are orthorhombic, Pbca, Z = 8, a = 16.625(6), b = 17.185(3), c = 17.438(3) A; R = 0.0375 over 317 variables and 1454 observed reflections. Mo coordination is distorted octahedral with the organic ligand bonded to the metal at two of three possible Lewis base sites. Crystals of bis(triphenylphosphine)carbonyl (2,2-dicyanoethylidenamino)iridium(I), Ir(PPh$\sb3$)$\sb2$(CO)(C$\sb4$N$\sb3$), are triclinic, P1, Z = 2, a = 11.615(9), b = 12.562(9), c = 16.976(12) A, $\alpha$ = 91.24(7), $\beta$ = 99.46(5), $\gamma$ = 114.91(6)$\sp\circ$; R = 0.0473 over 185 parameters and 2383 observed reflections. One cyano group of the 2,2-dicyanoethylidenamino (TCM) ligand is disordered. On the basis of least squares refinement and quantum mechanical calculations of several models, it is concluded that the TCM anion, when coordinated to Ir, has an excited state pyramidal geometry. Bright yellow crystals of bis(ethylene)(hexamethylbenzene)osmium(0), OS(C$\sb2$H$\sb4)\sb2$(C$\sb6$Me$\sb6$), are triclinic, P1, a = 7.776(2), b = 9.162(3), c = 12.113(2) A, $\alpha$ = 71.53(2), $\beta$ = 78,72(1), $\gamma$ = 62.46(2)$\sp\circ$; R = 0.028 over 209 variables and 3766 observed reflections. Both the ethylene groups and the hexamethylbenzene are $\pi$-complexed to Os. The symmetry of the hexamethylbenzene has been reduced from D$\sb6$h to C$\sb2$v as a result of d$\pi$-p$\pi$* back bonding. The deformation parameters of the ethylene groups are large indicating strong d$\pi$-p$\pi$* back bonding of these ligands. Black, lustrous crystals of a new non-superconducting phase of bis(bis-ethylenedithiatetrathiafulvalenium)diiodoaurate(I), (BEDT-TTF)$\sb2$AuI$\sb2$, are orthorhombic, Pbcm, Z = 4, a = 6.799(3), b = 14.820(3), c = 32.836(6) A; R = 0.064 over 177 variables and 1638 observed reflections. Short intermolecular S-S contact distances, characteristic of these salts, are observed. However, the packing mode in this orthorhombic salt is different from that in the superconducting phase. The crystal structure of another new phase of (BEDT-TTF)$\sb2$AuI$\sb2$ has been only partially determined due to twinning. The present structural model gives R = 0.120 over 1848 reflections in a triclinic lattice, a = 5.728(2), b = 9.045(3), c = 16.351(9) A, $\alpha$ = 91.91, $\beta$ = 97.56, $\gamma$ = 103.28$\sp\circ$. Ab initio quantum mechanical calculations have been carried out on bis-ethylenedithiatetrathiafulvalene (ET) and tetramethyltetrathselenafulvalene (TMTSF). Orbital coefficients and HOMO density plots are presented as part of a long term study of the band structure of organic superconductors.

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