Two New Structures of 5-Nitrouracil

Abstract

We thank Dr K. Mackenzie who conceived the research programme, executed preparative and kinetic work, and provided excellent quality crystals. Dr R. Siedlecka is thanked for the preparation of compound (2D). CW thanks the Institut Laue-Langevin for a studentship.Supplementary data for this paper are available from the IUCr electronic archives (Reference: CF1209). Services for accessing these data are described at the back of the journal. Strathclyde, Glasgow G1 1XL Scotland. E-mail: a. r. kennedy @ ccsun, strath, ac. uk (Received 17 July 1997; accepted 12 November 1997) AbstractThe structure of monoclinic anhydrous 5-nitrouracil, C4H3N304, and of the solvate 5-nitrouracil dimethyl sulfoxide, C4H3N304.C2H6OS, are presented and compared with the previously known structures of the orthorhombic anhydrous form and the monohydrate. Comment 5-Nitrouracil (5NU) is currently of prime interest to the non-linear optical community (Puccetti et al., 1993; Youping et al., 1992) and is also of relevance to the biological and pharmaceutical sciences (Rao et al., 1995; Perrier & Bym, 1982). Interest in the manufacture and desolvation processes of 5NU led us to investigate the crystal growth and stability of the 5NU system from its favoured industrial solvents, water and dimethyl sulfoxide (DMSO). Two crystalline forms had previously been reported, namely, an optically active orthorhombic anhydrate, (I) (Pierce & Wing, 1986), and a monoclinic monohydrate, (II) (Craven, 1967). We found that aqueous solution growth gave a mixture not only of these known polymorphs but also of a third, a monoclinic anhydrate, (HI). In addition, growth from DMSO and aqueous DMSO solutions gave a DMSO-solvated form, (IV). The structures of these new polymorphs are discussed as are the relationships between all four forms.The crystal structures exhibit extensive hydrogenbonding networks (Tables 3 and 6; Figs. 1 and 2) and it is here that the major differences between the polymorphs lie. In 5NU.DMSO, formal hydrogen bonding exists only between the N--H moieties of 5NU and the sulfoxide of the solvent; there are no 5NU to 5NU bonds, for example. This leads to the layered structure shown in Fig. 2. In contrast, the hydrated structure has dimeric hydrogen-bonded 5NU units linked in sheets by both 5NU---H20 and 5NU...5NU interactions. In (III), hydrogen bonding occurs about inversion centres, such that each 5NU molecule has four individual hydrogen bonds involving two adjacent molecules. This contrasts with (I), where each 5NU molecule is hydrogen bonded to four adjacent molecules. The differing intermolecular interactions seem to have little effect on the molecular structures of the 5NU moiety, with all bond lengths and angles being in good agreement. The main conformational difference is evident in the large twist of the NO2 group away from the plane of the ring in 5NU.DMSO, whereas it approaches coplanarity in the other three forms [dihedral angle between the least-squares planes of the ring and the NO2 group: 4.7, 2.0, 7.0(1) and 16.8 (1) ° f...

Solid-phase molecular recognition of cytosine based on proton-transfer reaction. Part II. supramolecular architecture in the cocrystals of cytosine and its 5-Fluoroderivative with 5-Nitrouracil

“…The molecular geometry of the two components of the cocrystal (Table 1) largely agrees with the already known solvent-free structure of the two units [42,43]. …”

The first polymorph in the family of nucleobases: a second form of cytosine

“…5-Nitrouracil (NIMFOE; Kennedy et al, 1998;Srinivasa Gopalan et al, 2000) has three polymorphic forms. The centrosymmetric form has centrosymmetric R 2 2 (8) dimers (Fig.…”

Study of hydrogen bonds in crystalline 5-nitrouracil. Density functional theory calculations of the O-17, N-14, and H-2 nuclear quadrupole resonance parameters

“…The considered single and cluster models of 5NU representing non-hydrogen bonded and hydrogen bonded systems are created by available X-ray coordinates [13]. However, since hydrogen positions are not accurately located by X-ray, the B3LYP/6-311G** optimization was performed to optimize just the hydrogen coordinates while the other coordinates kept frozen during the process [16].…”

“…E-mail: mirzaei_m@modares.ac.ir; hadipour@modares.ac.ir nucleobase, and its derivatives to HB interactions have been previously studied due to importance of 5-derivatives of uracil in pharmaceutical and biological activities in living systems [5][6][7][8][9][10][11][12]. 5-Nitrouracil (5NU) is the 5-nitro derivative of uracil whose contribution to HB interactions was reported by earlier X-ray study of Kennedy et al [13].…”

“…Present density functional theory (DFT) work studies the properties of N-H … O and C-H … O types of HB interaction of the backbone uracil in the reported crystalline structure of 5NU by Kennedy et al [13]. The EFG tensors are calculated at the sites of oxygen, nitrogen, and hydrogen nuclei of backbone uracil in a four-molecule cluster model of 5NU including the most possible interacting molecules with the target one (Fig.…”