Crystals of the dihydrates of guanosine (C10H13NsOs) and inosine (C10H12N4Os) are nearly isostructural. They are monoclinic, space group P2~, with cell dimensions a= 17.518, b= 11.502, c= 6.658/~, ,0=98"17 ° (guanosine) and a= 17-573, b= 11.278, c=6.654 A, ,8=98.23 ° (inosine). There are two nucleoside molecules and four water molecules per asymmetric unit. Data were collected on an automated diffractometer; the structures were solved by Patterson and trial-and-error methods and refined to R indices of about 0.035. The structure features hydrogen bonding between purine bases to form ribbons parallel to b and parallel stacking of purine bases along c; the separation between adjacent rings within a stack is 3-3 A,. The conformations about the glycosidic C-N bond and the puckerings of the sugar rings are quite different for the two molecules in the asymmetric unit. IntroductionGuanosine (I) and inosine (II) are constituents of the ribonucleic acids (RNA). Guanosine is a major component of most types of RNA; inosine is a minor constituent of the transfer RNA's in which it is believed to occupy the 5' terminal position (the 'wobble' position) in a number of the anticodon triplets.Several tautomeric forms of the purine ring can be formulated for guanosine and for inosine. Since the possible existence of rare tautomers has important implications regarding base pairing and the corresponding biological properties of the nucleic acids, we felt that the detailed crystal structures of these compounds should be determined. Knowledge of the crystal structures of these nucleosides would also furnish additional information about nucleoside conformation, hydrogen bonding capabilities, and the forces which govern parallel stacking of purine rings in the solid state. We were particularly interested in obtaining structural data which might help explain the mechanism of self association of guanine derivatives in aqueous solution (Gellert, Lipsett & Davies, 1962;Sarkar & Yang, 1965;Michelson, 1958), and the unusually stable secondary structures of oligo-and polyguanylic acids (Lipsett, 1964; Pochon & Michelson, 1965;Radding, Josse & Kornberg, 1962; Fresco & Massouli6, 1963;Ralph, Connors, Schaller & Khorana, 1963).We report here the crystal structures of guanosine and inosine which demonstrate that these compounds are in their normal tautomer form in the solid state and support the importance of parallel stacking of purine bases as a stabilizing force in the interactions between nucleic acid constituents.A preliminary report of this work has been published (Bugg, Thewalt & Marsh, 1968). ExperimentalCrystals of guanosine, in the form of thin elongated plates, were obtained by slowly cooling a hot saturated solution; inosine was crystallized as thin needles from water by evaporating a saturated solution at room temperature. Crystals of the two compounds were cleaved and fragments were mounted in several different orientations for X-ray study.Weissenberg and oscillation photographs showed the Laue symmetries to be Czh-2/m. The space g...

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The (C5H5 - n Me n )2Zr[η2-C2(SiMe3)2] (n = 2−5; 1,3-dimethyl, 1,2,3-trimethyl) (2C−F) complexes were prepared by the reduction of corresponding zirconocene dichlorides with magnesium in THF in the presence of bis(trimethylsilyl)acetylene (BTMSA). All of them are stable in the absence of THF. Crystal structures of (C5HMe4)2Zr[η2-C2(SiMe3)2] (2E) and (C5Me5)2Zr[η2-C2(SiMe3)2] (2F) and of the analogous titanium complexes are isomorphous. The red shift of the ν(C⋮C) vibration and the downfield shift of 13C δ(C⋮C) indicate that BTMSA in 2C−F is more strongly coordinated than in analogous titanocene complexes. The nonisolated complex (C5H4Me)2Zr[η2-C2(SiMe3)2](THF) (2 B·THF) rearranges after the loss of THF to give the dimer [(η5-C5H4Me)(η1-C(SiMe3)CH(SiMe3)Zr(μ-η1:η5-C5H3Me)]2 (3B).

chemical shifts. However, the effect we see is too large to have such an origin.5(5) (a) G.

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Thermally induced elimination of bis(trimethylsilyl)acetylene from its titanocene complex [{η5-C5Me4(SiMe3)}2Ti(η2-Me3SiC⋮CSiMe3)] (1) afforded the stable titanocene [{η5-C5Me4(SiMe3)}2TiII] (2) in high yield under mild conditions. Compound 2 exhibits paramagnetic line broadening of 1H NMR signals, although it is silent in EPR spectra down to −196 °C. The solid-state structure determination revealed an exactly parallel arrangement of the cyclopentadienyl rings in 2 due to crystallographically imposed symmetry. Complex 2 smoothly reacts with ethylene to give the yellow η2-ethylene complex [{η5-C5Me4(SiMe3)}2Ti(η2-CH2CH2)] (3). The structures of 1 and 3, determined by single-crystal X-ray diffraction, show the bent-titanocene moieties with the η2-coordinated Me3SiC⋮CSiMe3 and CH2CH2 ligands, respectively.

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