Self-Assembly of Hydrogensquarates: Crystal Structures and Properties

Abstract

The self-assembly of the hydrogensquarates is elucidated by means of linear-polarized infrared (IR-LD) spectroscopy of oriented colloids in nematic host and the so-called reducing-difference procedure for polarized IR-LD spectra interpretation. The scopes and limitation are discussed on five novel derivatives of squaric acid and its anions, that is, 2-chloro-3-aminopyridinium hydrogensquarate (1), bis (1,2,3,4-tetrahydroquinolinium) squarate (2), bis hydrogensquarate dihydrate salt of 4-(aminomethyl)pyridine (3), N-(2-ammoniumethyl)-piperazinium monohydrate hydrogensquarate squarate (4), and 3-nitropyridinium hydrogensquarate monohydrate (5), respectively. The structures of these compounds 1-5 were solved by means of single-crystal X-ray diffraction, and the crystallographic data were used for the experimental elucidation of the corresponding IR spectra of crystals with respect to studying Fermi-resonance (FR), Davydov splitting (DS), and Fermi-Davydov (FD) as well as Evans' hole effects. The various motifs for self-assembly of squaric acid and its anions in the organic crystals are discussed together with their IR-spectroscopic properties.

Structural characterization of ambazone salt with niflumic acid

“…3); the FTIR spectrum contains also [13,14] NH stretching band in the 3320-3180 cm −1 spectral range, i.e., 3226 cm −1 [13,24]. The new band which appears at ∼3513 cm −1 in the spectrum of AMB · NIA can be explained by the hydrogen bond breaking between H 2 O molecule and N-H group of AMB after the salt formation.…”

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

“…The geometry of the HSQ 2 anions shows that both anions are non-equivalent. The C(12)ZO(12) and C(22)ZO (22) bond lengths of 1.218(5) and 1.215(6) Å , respectively, indicate location of double bonds. A similar location of the CvC and CvO bonds in the hydrogen squarate ring has been observed in the earlier studies of squaric acid complexes (19, 23-25, 32, 35, 37, 39 -41).…”

“…MBPZ has two different proton -acceptor centres, the carboxylate group (pK 1 ¼ 1.48) and the tertiary nitrogen atom (pK 2 ¼ 4.90) (7), whereas H 2 SQ is a strong acid characterised by two dissociation constants, pK 1 ¼ 1.2 -1.7 and pK 2 ¼ 3.2-3.5 (15 -17). H 2 SQ by transferring one proton to a base generates a hydrogen squarate anion, HSQ 2 , or by transferring two protons it can generate a squarate dianion, SQ 22 . The crystal complexes of H 2 SQ with heterocyclic amino-bases have been a subject of study of several groups; e.g.…”

“…Gilli et al (18 -20), , and Uçar et al (24,27,28), and stored in the Cambridge Crystallographic Database Centre (29). Piperazine itself forms with H 2 SQ a 1:2 hydrated complex, where the centrosymmetric dication of piperazine is linked with SQ 22 . The squarate dianions and water molecules are linked into a chain (30), whereas 1,4-dimethylpiperazine with H 2 SQ forms a 1:2 complex in which the squarate anions are linked into a cyclic dimer through OZH· · ·O hydrogen bond [O· · ·O ¼ 2.548(3) Å ].…”

On the tautomerism and color origin in solid state of Npy-protonated-2-aminopyridine: spectroscopic elucidation

“…The possibilities of the linear-dichroic infrared (IR-LD) spectral analysis of oriented colloid suspensions [19][20][21][22][23][24] are used as a unique method for experimental IR-band assignment of suspended compounds. A comparative characterization by means of 1 H-NMR-and UV-spectroscopy is accomplished.…”