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The title complex, [Mo(C8F12)(C5H5)(C3H6NS2)], contains both a eta4-C4(CF3)4 cyclobutadienyl ligand with approximate C4v local symmetry and a eta5-C5H5 cyclopentadienyl ring. The centroids of the rings and the S atoms of a chelating dithiocarbamate ligand define the pseudo-tetrahedral coordination of the Mo atom. The Mo-C(cyclobutadienyl) bond lengths [2.189 (2)-2.211 (2) A] are unusually short, probably reflecting strong electron withdrawal by the trifluoromethyl groups. The molecules straddle crystallographic mirror planes.

In the title type B(2) acid salt, Na(LH)(LH(2)).H(2)O [LH(2) = C(2)H(4)C(CO(2)H)(2)] or Na(+).C(5)H(5)O(4)(-).C(5)H(6)O(4).H(2)O, the vertices of a distorted octahedron centred on each Na(+) cation are defined by six O atoms, one from a water molecule, one from an internally hydrogen-bonded LH(-) anion and four from three neutral LH(2) acid molecules. Chains of edge-sharing O(6) octahedra are stabilized by hydrogen bonds, which interconnect the donor H(2)O and LH(2) molecules and LH(-) anions. In particular, the LH(2) molecule donates H atoms to LH(-) and H(2)O and forgoes the internal hydrogen bond which stabilizes the free acid and all of its characterized salts.

In the title compound, hexa-micro-chloro-dichlorotetrakis(N-trimethylammonio-p-toluenesulfonamidate-kappa(2)N,O)tetramercury(II), [Hg[Me(3)N(+)N(-)SO(2)C(6)H(4)CH(3)-p]Cl(2)](4) or [Hg(4)Cl(8)(C(10)H(16)N(2)O(2)S)(4)], four nearly linear and parallel Cl-Hg-Cl units associate through pairwise Hg.Cl interactions of 3.1-3.2 A. Each Hg atom is also coordinated through N and O atoms to a ylide molecule. The available structural data indicate that coordination of a sulfonyl-stabilized nitrogen ylide to a metal atom (Hg or Ag) has no detectable effect on its geometry.

The structure of the cation in the ylide hydrochloride [Me(3)NNHC(O)C(6)H(4)-Cl-p]Cl.H(2)O, or C(10)H(14)ClN(2)O(+).Cl(-).H(2)O, is compared with that of the free ylide. Protonation lengthens the N-C(O) bond but shortens the C=O and N-N bonds by approximately 0.03 A and increases the dihedral angle between the phenyl and ylide planes.

The title disulfonyl-stabilized pyridinium ylide, C(5)H(5)N(+)-C(-)(SO(2)C(6)H(5))(2) or C(18)H(15)NO(4)S(2), contains a near planar NCS(2) core. The structure suggests that the formal negative charge of the ylide C atom is delocalized to the S atoms rather than the N atom. Structural features of pyridinium ylides are briefly discussed.

The racemic form of the title secondary monoalcohol, C(16)H(14)O, forms crystals in which the molecules are linked into chains by hydrogen bonding. The chain architecture is unusual; adjacent molecules are related pseudosymmetrically, by either a pseudo-diad or a pseudo-glide plane, while alternate molecules are related exactly by a crystallographic glide plane.

Crystals of 9-methylfluoren-9-ol, C(14)H(12)O, undergo a reversible phase transition at 176 (2) K. The structure of the high-temperature alpha form at 200 K is compared with that of the low-temperature beta form at 100 K. Both polymorphs crystallize in space group P1 with Z = 4 and contain discrete hydrogen-bonded R(4)(4)(8) ring tetramers arranged around crystallographic inversion centres. The most obvious changes observed on cooling the crystals to below 176 K are an abrupt increase of ca 0.5 A in the shortest lattice translation, and a thermal transition with deltaH = 1 kJ mol(-1).

The title compound, C23H23NO2SSi, at 100 K adopts a boat conformation which brings the C-H bond of an axial phenyl substituent into proximity [C...N = 3.376 (1) A] with the aziridine lone pair. The factors which favour this conformation for bicyclo[3.1.0]hexane systems are considered.