Biomedical subjects
Publications and source records attributed to R E Gerkin.
In the structure of the phthalide form of 2-acetylbenzoic acid, C9H8O3, there is a single type of hydrogen bond. Each molecule donates one and accepts one hydrogen bond. The hydrogen-bonded molecules form sets of puckered ribbons running along the c direction which are not crosslinked to each other. The dihedral angle between the planes of adjacent molecules along a hydrogen-bonded ribbon is 77.4(1) degrees.
In the title compound, C13H10O3, there is a single type of intermolecular hydrogen bond. From this is formed a cyclic dimer about a twofold axis. In addition, there is an intramolecular hydrogen bond which is virtually identical to that observed in salicylic acid.
In the structure of the title compound, C10H6O4, there is a single intramolecular hydrogen bond. In addition, there are a number of significant intermolecular C-H...O attractive interactions. These interactions account in part for the rather high density for an ordinary monocarboxylic acid, 1.522 Mg m(-3).
The structure of 2-naphthoic acid, C11H8O2, has been investigated at 153 K in order to determine the degree of disorder of the carboxylic acid group for comparison with that of the room-temperature structure. Analysis of the anisotropic displacement ellipsoids of the carboxyl-O atoms demonstrated that these parameters are wholly consistent with thermal motion of the O atoms. A model with ordered carboxyl-O atoms, but with the acid-H atom refined at two sites with 0.5 occupancy at each, was found to be statistically significantly better than a model with ordered carboxyl-O atoms and an ordered acid-H atom. Thus, as in the room-temperature study, the best structural description is that the O atoms are ordered and the acid-H atom is disordered. Nonetheless, comparisons of the geometric parameters of the carboxyl groups at 296 and 153 K suggest progress toward a fully ordered structure at the lower temperature. Except for the expected slight overall contraction and the slightly altered geometry of the carboxyl group, the structure is virtually the same as at room temperature.
In biphenyl-3-carboxylic acid, C13H10O2, hydrogen bonding is of the cyclic-dimer type about a center of symmetry. The carboxyl H atom is ordered. The dihedral angle between the planar phenyl rings is 31.78(8) degrees at 296 K and 31.27(6) degrees at 203 K. The data show that the larger-than-average magnitudes of the displacement parameters of the carboxylic O atoms are due to thermal motion rather than static disorder.
Anthracene-1,8-dicarboxylic acid, C16H10O4, crystallized in the noncentrosymmetric space group P2(1)2(1)2(1). The carboxyl H and O atoms are ordered. The carboxyl groups make angles of 13.9 (2) and 21.6 (2) degrees with the best-fit core plane and the average distance of the core atoms from this plane is 0.018 (12) A. The anthracene core displays near twofold symmetry. Each molecule is involved in cyclic-dimer hydrogen bonding with two other molecules so as to form zigzag chains of hydrogen-bonded molecules which are not cross-linked with one another. These discrete chains are separated from each other by C...C, C...H and H...H closest approaches.
In xanthene-9-carboxylic acid, C14H10O3, hydrogen bonding is of the cyclic dimer type but involves two crystallographically inequivalent molecules and does not occur about a center of symmetry. The carboxylic H atoms are ordered. The dihedral angle (fold angle) of the xanthene core is 14.2 (1) degree for molecule A and 11.3 (2) degrees for molecule B. The planes of the carboxyl groups are almost perpendicular to the xanthene cores.
The structures of two phases of fluorene-4-carboxylic acid, C14H10O2, from room-temperature growths have been determined. In the alpha phase, O-H...O hydrogen bonding occurs via cyclic dimers about a center of symmetry; in the beta phase, cyclic dimers with O-H...O hydrogen bonds are formed between two crystallographically inequivalent molecules and do not involve a center of symmetry, though centers of symmetry are present in the crystal. The present evidence strongly suggests that the beta phase is metastable with respect to the alpha phase at room temperature, but the regions of stability have not been determined.
3-Aminopyrazine-2-carboxylic acid, C5H5N3O2, displays an extensive network of intra- and intermolecular hydrogen bonds which are undoubtedly responsible for the modest values of the displacement parameters. H-atom transfer to the ring N atoms did not occur and the carboxy and amino H atoms are ordered. The virtually planar molecules lie very nearly in planes parallel to (102) and are stacked along the a direction with separations of 3.324 (2) A indicating pi-pi interactions.
The central rings of 1,2,3,4,7,8,9,10-octahydrochrysene, C18H20, are essentially planar, with the r.m.s. deviation of the atoms defining the plane from the best-fit plane being 0.013 (2) A. The outer rings are found to be substantially non-planar, contrary to the conclusion of an earlier study based on photographic data [Ferrier & Iball (1958). Acta Cryst. 11, 325-329]. The C-C single-bond distances in the outer rings are quite uniform, with the range of observed values varying by only 0.017 (6) A. There are no notably close intermolecular approaches.
In fluorene-1-carboxylic acid, C14H10O2, the sole hydrogen bond is of the cyclic dimer type about a center of symmetry. The carboxyl H atom is ordered. Distances in the fluorene core are very similar to those in fluorene itself; the fluorene core dihedral angle is, however, larger than in fluorene.
The structure of sodium cerium sulfate monohydrate, NaCeIII(SO4)2.H2O, comprises distorted NaO6 octahedra, CeO9 polyhedra in the form of distorted tricapped trigonal prisms, and slightly irregular tetrahedral sulfate ions. This structure is isomorphic with that of NaLaIII(SO4)2.H2O. All bonds fall within normal limits. The sulfate ion manifested rigid-body behavior but neither of the cation complexes did. As in the previous structural analysis of the La analog [Blackburn & Gerkin (1994). Acta Cryst. C50, 835-838], the water molecule is modelled as having O-atom disorder but with an ordered H atom. Hydrogen bonds involve only sulfate O atoms as acceptors. The anisotropic atomic displacement parameters are found to be in good agreement with the corresponding parameters determined for the La analog, but in poor agreement with those previously reported for the title salt by Lindgren [Acta Chem. Scand. Ser. A, (1977), 31, 591-594]. Taken together, the data establish that the lack of correction for absorption in the previous study of the Ce salt, rather than some intrinsic property of the Ce salt, is responsible for the displacement parameter discrepancies. The absolute structure has been determined.
Lithium tetraoxobromate(1-) monohydrate, LiBrO4.-H2O, whose perchlorate analog has not yet been described, is found to be isomorphic with NaBrO4.H2O and NaClO4.H2O. Each of the two inequivalent Li ions is coordinated by six O atoms, thus forming distorted octahedra, each of which has three inequivalent Li-O distances. At room temperature, the average Li(1)-O and Li(2)-O distances are 2.150 and 2.164 A, respectively. The perbromate ion displays very nearly regular tetrahedral geometry, although it is not subject to symmetry constraints. At 296 K the average observed Br-O distance is 1.610 (4) A and the average O-Br-O angle is 109.5 (6) degrees, while at 173 K the corresponding values are 1.613 (4) A and 109.5 (7) degrees. The perbromate ion shows rigid-body behavior but the lithium coordination polyhedra do not. At 296 K, the average rigid-body corrected Br-O distance in the perbromate ion is 1.624 (3) A, in excellent agreement with the corresponding value reported for NaBrO4.H2O. Refinement of the two inequivalent H atoms allowed detailed analysis of the hydrogen bonding, which is more extensive than in NaBrO4.H2O or in NaClO4.H2O. The average observed B values for the H atoms [2.9 (3) A2 at 296 K and 2.8 (3) A2 at 173 K] are sufficiently small to suggest that dynamic disordering of the H atoms (determined by magnetic resonance methods for NaClO4.H2O) is not significant in the title salt.
The structure of NaLaIII(SO4)2.H2O consists of distorted Na-O6 octahedra, La-O9 complexes in the form of distorted tricapped trigonal prisms, and slightly irregular tetrahedral sulfate ions. All bond distances fall within normal limits. The sulfate ions manifest rigid-body behavior but this is not the case for either of the cation complexes. The single water molecule is modelled as having O-atom disorder but an ordered H atom. Hydrogen bonds involve only sulfate O atoms as acceptors. The absolute structure has been determined.
In the title structure, the 1,4,5,8-naphthalenetetra-carboxylate anion possesses 2/m symmetry with the twofold axis coincident with the central C--C bond of the naphthalene rings. The ten atoms comprising the naphthalene core have a mean deviation of 0.033 A from the best least-squares plane describing these atoms, with the carboxyl C atom 0.395 (2) A removed from the plane. The dihedral angle between the carboxylate plane and the least-squares plane of the naphthalene rings is 46.2 (3) degrees. The O--C--O angle of the carboxylate group, 121.13(12) degrees, is smaller than normally expected, presumably due to the bidentate interaction with the Ca ion. The Ca ion is coordinated by eight O atoms: six carboxylate O atoms and two water O atoms. Because the Ca ion resides on a twofold axis there are only four independent Ca--O distances, which are in the range 2.368 (1)-2.681 (1)A. In this structure, the organic anions are separated by Ca ions and water molecules such that there are no short-range organic-organic interactions. One of the water molecules separating the organic anions is not involved in coordination with Ca, and is disordered.
The structures of 1-naphthoic acid and 2-naphthoic acid have been investigated in order to determine the degree of disorder of the carboxylic acid groups. 1-Naphthoic acid was found to be completely ordered with C--O bond lengths of 1.214 (3) and 1.312 (3) A, and C--C--O bond angles of 124.8 (2) and 114.2 (2) degrees. 2-Naphthoic acid was found to possess a significant degree of disorder with C--O bond lengths of 1.256 (3) and 1.274 (3) A, and C--C--O bond angles of 117.7 (2) and 119.1 (2) degrees. In 2-naphthoic acid, the acid H atom was refined at two sites with 0.5 occupancy at each. Analysis of the anisotropic displacement ellipsoids of the acid O atoms for each structure demonstrated that these parameters are consistent with thermal motion of the O atoms. These results indicated that the proton, but not the O atoms, is disordered in the carboxylic acid group of 2-naphthoic acid. In each structure, the acid molecules form cyclic dimers about inversion centers, with an O...O(acceptor) distance of 2.653 (3) in 1-naphthoic acid and 2.618 (3) A in 2-naphthoic acid. The cyclic dimers form layers in each of these structures wherein lateral closest intermolecular approaches to the acid O atoms are from ring H atoms. The intermolecular O...H close approaches, together with the intramolecular close approaches, are very uniform in distance and angle of approach for the two O atoms in the 2-naphthoic acid structure.(ABSTRACT TRUNCATED AT 250 WORDS)
Diphenanthro[1,2-b;2',1'-d]furan crystallizes in space group Pnma (No. 62) with the mirror plane bisecting the molecule and passing through the furan O atom. Although exhibiting packing similar to that of dibenzofuran, this diphenanthrofuran showed no disorder of the sort found in that close molecular analog. The C atoms of the individual phenanthrene rings of the title compound have a mean deviation of 0.027 (21) A from the best least-squares plane describing the rings. The configuration and conformation of the individual phenanthrene rings in this diphenanthrofuran closely match the theoretical and experimental results for phenanthrene itself. Overall, this diphenanthrofuran molecule adopts a distinct V shape, the dihedral angle between the least-squares best-fit planes of the phenanthrene rings being 11.0 (1.2) degrees.
The structure of the title compound consists of columns of Ca ions surrounded by four columns of perbromate ions and four columns of water molecules alternating in pairs. The CaO8 complex was found to be dimensionally similar to corresponding complexes in other simple tetrahydrated calcium salts. The eight coordinating O atoms form a polyhedron which departs only slightly from a (distorted) square antiprism. Each of the crystallographically inequivalent perbromate ions was found to conform to rigid-body behavior while the CaO8 complex did not. Although the perbromate ions depart moderately from regular tetrahedral geometry, the mean Br--O bond length agrees well with previously determined values. Hydrogen bonds in this structure involve water-oxygen acceptors as well as perbromate-oxygen acceptors.