The solid-state structures of a series of bithiazole and thiophene oligomers, as well as a series of substituted pentacenes, are rationalized in terms of "pitch and roll" inclinations from an "ideal" cofacial pi-stack. Pitch inclinations translate adjacent molecules relative to one another in the direction of the long molecular axis, whereas roll inclinations translate the molecules along the short molecular axis. Thus, moderately large pitch distortions preserve pi-pi interactions between adjacent molecules, whereas roll translations greater than 2.5 A essentially destroy pi-pi overlap between adjacent molecules. The familiar herringbone packing is characterized by large roll distortions. It is shown that thiophenes tend to exhibit large roll translations, whereas thiazoles have small roll but large pitch translations. Substituted pentacenes tend to have both moderate pitch and roll distances. The relationship of molecular packing to transport properties is discussed.

A series of oxoperoxovanadium(V) complexes (ligands:  H3nta = nitrilotriacetic acid, H3heida = N-(2-hydroxyethyl)iminodiacetic acid, H2ada = N-(2-amidomethyl)iminodiacetic acid, Hbpg = N,N-bis(2-pyridylmethyl)glycine, and tpa = N,N,N-tris(2-pyridylmethyl)amine) were characterized as functional models for the vanadium haloperoxidase enzymes. The crystal structures of K[VO(O2)Hheida], K[VO(O2)ada], [VO(O2)bpg], and H[VO(O2)bpg]2(ClO4) were obtained. These complexes all possess a distorted pentagonal bipyramidal coordination sphere containing a side-on bound peroxide. In the presence of sufficient acid equivalents these complexes catalyze the two-electron oxidation of bromide or iodide by peroxide. Halogenation of an organic substrate was demonstrated by following the visible conversion of Phenol Red to Bromophenol Blue. In the absence of substrate, dioxygen can be generated by the halide-assisted disproportionation of hydrogen peroxide. In addition, some of these complexes can efficiently catalyze the peroxidative halogenation reaction, performing multiple turnovers in minutes. The kinetic analysis of the halide oxidation reaction indicates a mechanism which is first order in protonated peroxovanadium complex and halide. The bimolecular rate constants for both bromide and iodide oxidation were determined, with the iodide rates being approximately 5−6 times faster than the bromide rates. The rate constants obtained for bromide oxidation range from a maximum of 280 M-1 s-1 for the Hheida complex to a minimum of 21 M-1 s-1 for the Hbpg complex. The pK a of activation for each complex in acetonitrile was determined to range from 5.4 to 6.0. On the basis of the chemistry observed for these model compounds, a mechanism of halide oxidation and a detailed catalytic cycle are proposed for the vanadium haloperoxidase enzyme.

The unprecedented polymorphism of the non-steroidal anti-inflammatory drug (NSAID) flufenamic acid (FFA) is described here. Nine polymorphs were accessed through the use of polymer-induced heteronucleation (PIHn) and solid-solid transformation at low temperature. Structural elucidation of six of these forms, in addition to the two previously known forms, makes FFA indisputably octamorphic. Although the structure of at least one other form of FFA remains elusive, the occurrence of most of these polymorphs under one crystallization condition through PIHn illustrates that a fine interplay exists among the kinetic factors that lead to phase selection in this NSAID.

The preparation and characterization of a series of encapsulated-lanthanide 15-metallacrown-5 complexes are reported. Planar ligands such as picoline hydroxamic acid (picha) or nonplanar alpha-amino hydroxamic acids (e.g., glycine hydroxamic acid (glyha)) led to one-step syntheses of metallacrowns in yields as high as 85%. The reaction of the appropriate hydroxamic acid with copper acetate and (1)/(5) equiv of gadolinium(III) or europium(III) nitrates in DMF or water yielded crystals of Gd(NO(3))(3)[15-MC(Cu(II)N(picha))-5], 1, Eu(NO(3))(3)[15-MC(Cu(II)N(picha))-5], 2, and Eu(NO(3))(3)[15-MC(Cu(II)N(glyha))-5], 3. Several other 15-metallacrown-5 complexes were synthesized with (1) Cu(II) or Ni(II) in the metallacrown ring metal position, (2) various lanthanides (La(III), Nd(III), Sm(III), Eu(III), Gd(III), Dy(III), Ho(III), Er(III), and Yb(III)) encapsulated in the center of the ring, and (3) chiral alpha-amino hydroxamic acids (e.g., phenylalanine hydroxamic acid (H(2)pheha), leucine hydroxamic acid (H(2)leuha), and tyrosine hydroxamic acid (H(2)tyrha)). It is believed that all of the complexes containing Cu(II) ions have the ring metals either in four-coordinate, square-planar environments, bound to two tetradentate hydroximate ligands, or in five-coordinate, square-pyramidal geometries if solvent is bound. Spectroscopic and magnetic characterization of the Ni(II) complexes suggests that they are either five- or six-coordinate. The encapsulated lanthanides are generally pentagonal bipyramidal, with five oxygen donors from the metallacrown ring and solvent or bidentate nitrate ions in the axial positions. The circular arrangement of ions results in interesting magnetic behavior. With Dy(III) encapsulated in the center of the ring, a magnetic moment as high as 10.9 &mgr;(B) is achieved. Analysis of the variable-temperature susceptibility of La(NO(3))(3)[15-MC(Cu(II)N(picha))-5] indicates that the five Cu(II) ions are antiferromagnetically coupled, forming an S = (1)/(2) ground spin state with a moment of 1.7 &mgr;(B) at liquid helium temperatures. Complex 1 shows ferromagnetic coupling of the Gd(III) ion to the five Cu ions at temperatures below 15 K. Studies of the metallacrown complexes in solution show that they are stable and soluble in DMF and water. A proton relaxation study on complex 1 has revealed a relaxivity of 9.8 mM(-)(1) s(-)(1) (20 degrees C and 30 MHz), a value that is comparable to those of clinically useful MRI contrast enhancement agents. Complex 1 crystallizes in the triclinic space group P&onemacr;, with a = 12.657(3) Å, b = 14.833(3) Å, c = 17.707(3) Å, alpha = 79.65(2) degrees, beta = 86.06(2) degrees, gamma = 68.69(2) degrees, V = 3046.6(12) Å, and Z = 2 (R1 = 0.0534, wR2 = 0.1289). Complex 2 crystallizes in the monoclinic space group P2(1)/n, with a = 16.319(2) Å, b = 21.863(2) Å, c = 18.410(3) Å, beta = 96.85(1) degrees, V = 6522(2) Å(3), and Z = 4 (R1 = 0.0463, wR2 = 0.0750). Complex 3 crystallizes in the triclinic space group P&onemacr;, with a = 11. 173(6) Å, b = 11.534(6) Å, c = 13.3...