Tropolone, C7H602, crystallizes in space group P21/e, with a= 7.135, b---12.178, c= 7.122 A, fl= 99.63 ° and Z= 4. The crystal structure was solved by the symbolic addition procedure and refined by the leastsquares method to give the final R value of 0.054 for the 853 observed reflexions. The molecule is essentially planar and exhibits a slight degree of bond alternation in the seven-membered ring. The hydroxyl group makes a bifurcated hydrogen bond with carbonyl oxygen atoms, of which one branch is intramolecular and the other intermolecular. The latter intermolecular branches form a hydrogenbonded dimer. These characteristic hydrogen bonds seem to play a role in increasing the contribution from the dipolar ionic forms to the ground state of the tropolone molecule.

2,5-Distyrylpyrazine(C20H16N2), which has photo-polymerizability in the crystalline state, crystallizes in the orthorhombic system with cell dimensions of a=20.638, b=9.599, and c=7.655 Å, including four molecules in the unit cell. The space group is Pbca. The structure has been determined by the direct method and refined by the block-diagonal-matrix least-squares method using three-dimensional data. The molecules is not planar; the average plane of the pyrazine ring makes a dihedral angle of 12.09° with that of the benzene ring. The molecules are spaced by the c-translation forming an almost parallel plane-to-plane stack. In this stack, the ethylenic double bonds approach each other at the shortest intermolecular distances of 3.939 Å, since the long axis of the molecule makes an angle of about 30° with the c-axis. Therefore, the polymerization may occur between these double bonds to form a cyclobutane ring.

Two copper complexes containing l-histidine and l-asparagine crystallize from aqueous solution at pH 7.0. Both crystals are monoclinic, space group P21. l-Asparaginato-l-histidinatocopper(II): a=10.913(3), b=12.911(4), c=10.206(3) Å, β=113.83(2)°, Z=4. l-Asparaginato-l-histidinatoaquacopper(II) trihydrate: a=12.654(4), b=11.623(4), c=5.931(2) Å, β=100.47(3)°, Z=2. In both structures, four coordinating atoms in an approximately planar arrangement around copper are the α-amino and imidazole δ-nitrogen atoms of l-histidine and α-amino nitrogen and α-carboxyl oxygen of l-asparagine. The fifth coordination site is occupied by the α-carboxyl oxygen of l-histidine. Difference between the two complex crystals is found at the sixth coordination site; a water molecule is coordinated in the hydrated crystal to complete a distorted octahedral environment, while in the anhydrous crystal this site is unoccupied so that the geometry of the complex is square-pyramidal.

The crystal structure of anhydrous diphenylcyclopropenone was determined and the structural features are compared with those in its monohydrate. The systematic variation of the molecular geometry found is attributable to the contribution from a dipolar ionic form, enhanced by the formation of the hydrogen bond.

Cytosine: N-formylglycine complex crystallizes in the space group Pna21 with cell dimensions of a=8.444(2), b=21.169(5), and c=5.120(1) Å. The structure was solved by the trial-and-error method on the basis of a Patterson map. A full-matrix least-squares refinement led to an R value of 0.035. The difference map revealed the protonation of cytosine by the carboxyl group of N-acylamino acid and the involvement of ionic interaction in complex formation. This mode is the same as proposed for cytosine: N-benzoylglycine complex in spite of different molecular environment. Such arrangement of cytosine and ionized carboxyl group of amino acid may suggest a mutual recognition scheme between nucleic acid and protein.

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Crystals of 8, 8-dicyanoheptafulvene, C10H6N2, are monoclinic, with two molecules in a unit cell with the dimensions a=7.84, b=13.14, c=3.99 Å, and β=97.9°; the space group is P21⁄m. The intensities were recorded on multiple-film equi-inclination Weissenberg photographs and measured visually against a standard scale. A trial structure was constructed from the Patterson projections, P(u, v) and P(u, w), and a Harker section, P(u, 1/2, w). The atomic coordinates and anisotropic temperature factors were refined by the least-squares method. The final R factor for (hkl) reflections is 0.107. A considerable bond alternation in the conjugated seven-membered ring has been observed. The average long and short bond lengths in the ring are 1.44 and 1.34 Å respectively. The shortest C=C bond measures 1.31 Å, which is shorter than that in ethylene. The exocyclic C=C bond length is 1.42 Å, suggesting a considerable dipolar resonance structure, one which may be responsible for the stability of the compound. The C≡N bond length is 1.13 Å. The molecule deviates slightly from being planar; it lies nearly parallel to the (101) plane. All the intermolecular separations correspond to normal van der Waals interactions; the perpendicular distance between the molecular planes is 3.4Å. The thermal motion was interpreted in terms of rigid body vibrations, and the bond lengths and angles were corrected for the rotational oscillations.

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