title: Statistically disordered short hydrogen bonds in (pipzH2)(cdoH)2 and a comparison with (pipzH2)(cdo)·H2O (pipz is piperazine and cdoH2 is chelidonic acid).
abstract: Two related proton-transfer compounds, namely piperazine-1,4-diium 4-oxo-4H-pyran-2,6-dicarboxylate monohydrate, C(4)H(12)N(2)(2+)·C(7)H(2)O(6)(2-)·H(2)O or (pipzH(2))(cdo)·H(2)O, (I), and piperazine-1,4-diium bis(6-carboxy-4-oxo-4H-pyran-2-carboxylate), C(4)H(12)N(2)(2+)·2C(7)H(3)O(6)(-) or (pipzH(2))(cdoH)(2), (II), were obtained by the reaction of 4-oxo-4H-pyran-2,6-dicarboxylic acid (chelidonic acid, cdoH(2)) and piperazine (pipz). In (I), both carboxyl H atoms of chelidonic acid have been transferred to piperazine to form the piperazine-1,4-diium ion. The structure is a monohydrate. All potential N-H donors are involved in N-H···O hydrogen bonds. The water molecule spans two anions via the 4-oxo group of the pyranose ring and a carboxylate O atom. The hydrogen-bonding motif is essentially two-dimensional. The structure is a pseudomerohedral twin. In the asymmetric unit of (II), the anion consists of monodeprotonated chelidonic acid, while the piperazine-1,4-diium cation is located on an inversion centre. The single carboxyl H atom is disordered in two respects. Firstly, the disordered H atom is shared equally by both carboxylic acid groups. Secondly, the H atom is statistically disordered between two positions on either side of a centre of symmetry and is engaged in a very short hydrogen-bonding interaction; the relevant O···O distances are 2.4549 (11) and 2.4395 (11) Å, and the O-H···O angles are 177 (6) and 177 (5)°, respectively. Further hydrogen bonding of the type N-H···O places the (pipzH(2))(2+) cations in pockets formed by the chains of (cdoH)(-) anions. In contrast with (I), the (pipzH(2))(2+) cations form hydrogen-bonding arrays that are perpendicular to the anions, yielding a three-dimensional hydrogen-bonding motif. The structures of both (I) and (II) also feature π-π stacking interactions between aromatic rings.
authors.affiliation: Department of Chemistry, Faculty of Science, University of Kurdistan, Sanandaj, Iran. mghadermazi@yahoo.com
authors.forename: Mohammad
authors.initials: M
authors.lastname: Ghadermazi
authors.forename: Marilyn M
authors.initials: MM
authors.lastname: Olmstead
authors.forename: Jafar
authors.initials: J
authors.lastname: Attar Gharamaleki
authors.forename: Shahideh
authors.initials: S
authors.lastname: Rostami
mesh_terms: D018360:Crystallography, X-Ray; D006860:Hydrogen Bonding; D007477:Ions / Q000737:chemistry*; D008958:Models, Molecular; D015394:Molecular Structure; D000077489:Piperazine; D010879:Piperazines / Q000737:chemistry*; D011714:Pyrans / Q000737:chemistry*; D014867:Water / Q000737:chemistry
chemical_list: D007477:Ions; D010879:Piperazines; D011714:Pyrans; C559204:piperazine-1,4-diium 4-oxo-4H-pyran-2,6-dicarboxylate monohydrate; D014867:Water; D000077489:Piperazine; C046884:chelidonic acid