Supramolecular structure of the 1:2 complex of 1,4-dimethylpiperazine mono-betaine with squaric acid

The 1: 2 complex of 1,4-dimethylpiperazine mono-betaine (MBPZ) with squaric acid (H(2)SQ) has been characterised by single-crystal X-ray analysis, FTIR and NMR spectroscopies, and by DFT calculations. The crystals are monoclinic, space group P2(1)/c. Two MBPZ cations and four hydrogen squarate anions (HSQ(-)) are linked by strong O(1)=H center dot center dot center dot O(13) (2.525(4) angstrom), O(14)-H center dot center dot center dot O(21) (2.511(4) angstrom) and N(4)-H center dot center dot center dot O(23) (2.607(3)angstrom) hydrogen bonds into a cyclamer R-6(6)(38). In turn, the cyclamers are linked into a helix C-4(4)(20) through two O(24)-H center dot center dot center dot O(11) hydrogen bonds of 2.516(4)angstrom. The piperazinium ring has a chair conformation with N(4)-CH3 and N(1)-CH2COOH substituents in the equatorial positions, and N(1)-CH3 in the axial position. The FTIR spectrum is consistent with the crystal data. Two models of the 1: 2 complex of MBPZ with H(2)SQ have been optimised at the B3LYP/6-311++G(d,p) level of theory and have been used to calculate harmonic IR frequencies. One of the models (2) is dominated by electrostatic attraction between NH(4)(+) and HSQ(-), whereas in the other (3) squaric acid interacts with a zwitterionic MBPZ through the O-H center dot center dot center dot O and O-H center dot center dot center dot N hydrogen bonds

Bis(tetra­ethyl­ammonium) bis­(hydrogen l-tartrate) l-tartaric acid monohydrate

In the title compound, 2C8H20N+·2C4H5O6 −·C4H6O6·H2O, the presence of the two tetra­ethyl­ammonium cations is balanced by two hydrogen l-tartrate anions. Also present in the asymmetric unit are a mol­ecule of l-tartaric acid and a water mol­ecule. The various components are linked by O—H⋯O hydrogen bonds. In the crystal, two-dimensional networks are formed via O—H⋯O hydrogen bonds and C—H⋯O inter­actions involving the water mol­ecule, the hydrogen l-tartrate anions and the l-tartaric acid mol­ecules. These layers, which stack along [001], are separated by tetra­ethyl­ammonium cations. The latter are also involved in C—H⋯O inter­actions with the anions and the l-tartaric acid and water mol­ecules participating in the two-dimensional network

Betaines as proton-acceptors

Ammonium alkanoates (ammonioalkanocarboxylates) are zwitterions (or inner salts, or betaines), because they possess formally charged ammonium and carboxylate groups separated by one or more sp3 carbon atoms. The chemistry of betaines has become a subject of particular interest due to their applications in biological research, especially with regard to their important role in aminoacid synthesis as methyl transfer agents. The crystals of many betaine complexes display interesting physical properties, exhibiting phase transitions with ferroelectric, antiferroelctric and ferroelastic behavior. Betaines containing a hydrophobic chain in the range of 8–20 carbon atoms show the unique properties characteristic for amphoteric surfactants and their current industrial application is in toiletries and personal care products. The conformational structure of zwitterionic molecules depends on several factors. The electrostatic attraction between two charged groups depends strongly on arm flexibility (energy differences between rotational trans and gauche isomers), bulkiness and hydration of charged groups preventing their close approach, solvent and arm electrical properties which control electrostatic attraction between two opposite charged groups, and polarization of solvent around the molecule caused by the dielectric discontinuity between solvent and solute interior (image charge effect). Electrostatic interaction is the common determinant and probably the most important element in structure-reactivity correlation in organic and biological systems. On the other hand, organic compounds are thought to be pure even though they may be a mixture of conformational isomers. This is because the isomers covert rapidly with each other at room temperature and their individual reactivates are little known. Occasionally the conformers may be stabilized in the crystallographic matrixes of polymorphic structures. This article describes structures of seven groups of aliphatic, aromatic and alicyclic betaines and numbers of their new hydrogen-bonded complexes with mineral and organic acids