title: 2-(4-Bromophenyl)-1,2-dihydropyrimido[1,2-a]benzimidazol-4(3H)-one and 4-(4-methylphenyl)-3,4-dihydropyrimido[1,2-a]benzimidazol-2(1H)-one form hydrogen-bonded base-paired dimers.
abstract: The title compounds, 2-(4-bromophenyl)-1,2-dihydropyrimido[1,2-a]benzimidazol-4-(3H)-one, C(16)H(12)BrN(3)O, (IVa), and 4-(4-methylphenyl)-3,4-dihydropyrimido[1,2-a]benzimidazol-2-(1H)-one, C(17)H(15)N(3)O, (Vb), both form R(2)(2)(8) centrosymmetric dimers via N-H...N hydrogen bonds. The N...N distance is 2.943(3)A for (IVa) and 2.8481(16)A for (Vb), with the corresponding N-H...N angles being 129 and 167 degree, respectively. However, in other respects, the supramolecular structures of the two compounds differ. Both compounds contain different C-H...pi interactions, in which the C-H...pi(centroid) distances are 2.59 and 2.47A for (IVa) and (Vb), respectively (the latter being a short distance), with C-H...pi(centroid) angles of 158 and 159 degree, respectively. The supramolecular structures also differ, with a short Br...O distance of 3.117(2)A in bromo derivative (IVa), and a C-H...O interaction with a C...O distance of 3.2561(19)A and a C-H...O angle of 127 degree in tolyl system (Vb). The dihydropyrimido part of (Vb) is disordered, with a ratio of the major and minor components of 0.9:0.1. The disorder consists of two non-interchangeable envelope conformers, each with an equatorial tolyl group and an axial methine H atom.
authors.affiliation: Department of Chemistry, University of Aberdeen, Meston Walk, Old Aberdeen AB24 3UE, Scotland. jnlow111@hotmail.com
authors.forename: John Nicolson
authors.initials: JN
authors.lastname: Low
authors.forename: Justo
authors.initials: J
authors.lastname: Cobo
authors.forename: Braulio
authors.initials: B
authors.lastname: Insuasty
authors.forename: Manuel
authors.initials: M
authors.lastname: Nogueras
authors.forename: Angela
authors.initials: A
authors.lastname: Salcedo
authors.forename: Adolfo
authors.initials: A
authors.lastname: Sánchez
mesh_terms: D000894:Anti-Inflammatory Agents, Non-Steroidal / Q000737:chemistry; D000977:Antiparasitic Agents / Q000737:chemistry; D001562:Benzimidazoles / Q000737:chemistry*; D002492:Central Nervous System Depressants / Q000737:chemistry; D018360:Crystallography, X-Ray; D006860:Hydrogen Bonding; D008958:Models, Molecular; D011743:Pyrimidines / Q000737:chemistry*
chemical_list: C454614:2-(4-bromophenyl)-1,2-dihydropyrimido(1,2-a)benzimidazol-4(3H)-one; C454615:4-(4-methylphenyl)-3,4-dihydropyrimido(1,2-a)benzimidazol-2(1H)-one; D000894:Anti-Inflammatory Agents, Non-Steroidal; D000977:Antiparasitic Agents; D001562:Benzimidazoles; D002492:Central Nervous System Depressants; D011743:Pyrimidines