Crystal structure and spectroscopic properties of ammonium hydrogensquarate squaric acid monohydrate

Abstract

The structure of ammonium hydrogensquarate squaric acid monohydrate has been determined by single crystal X-ray diffraction. The compound crystallizes in the monoclinic space group C2/c and exhibits a 3D network with molecules linked by intermolecular interactions with participation of the H 2 Sq, HSq @ , NH 4 + , and H 2 O species. The HSq @ anion and the neutral H 2 Sq form a strong headto-tail dimer through O-HÁÁÁO hydrogen bonding with lengths of 2.587 and 2.494 Å (protected space between numeral and unit). The layers are connected by ammonium cations and water molecules in a plane through the OÁÁÁN (2.950, 2.978, 3.036 Å ) and OÁÁÁO (2.953, 2.781 Å ) bonds. Another such layer is connected to the NH 4 + cation in the adjacent plane through bifurcated N-HÁÁÁO hydrogenbonding to form a double layer (NHÁÁÁO bond lengths are 3. 036, 2.978, 2.857, 2.909, 2.958, and 2.742 Å , respectively). The IR-band assignment of the compound was achieved using the polarized IR-spectroscopy of oriented colloids in a nematic host. Theoretical ab initio calculations were performed and achieved with a view to explain the IR-bands of the H 2 Sq.HSq @ motif.

Salts of aromatic amines: Crystal structures, spectroscopic and non-linear optical properties

“…The IR bands at 835, 829 and 800 cm −1 in both compounds are assigned to the corresponding out-of-plane vibrations of the phenyl ring in the cation. These data are in accordance as well with the previouse studies on the tryptammonium salts [47,48]. Compounds (3) and (4), also containing a p-hydroxy-substituted phenyl have the same IR characteristics as the cation, joined by the skeletal in-plane and out-of-plane mode.…”

Self-Assembly of Hydrogensquarates: Crystal Structures and Properties

“…The presence of H 2 Sq and its anions in the solid state leads to the possibility of controlling the assembly of individual molecules in solids, using hydrogen bonding as a powerful noncovalent force for organizing organic molecules. [10][11][12][13][14][15][16][17][18][19][20][21][22][23][24] The following self-assembly patterns of squaric acid itself and its anions HSqand Sq 2have been identified up to now in crystal structures (Scheme 1): (HSq -) individual R-dimers (Ia) and two independent isolated R-dimers (Ib), HSq -R-chains (IIa, IIb), and HSqβ-chains (IIIa, IIIb), differing by the disposition of the anion with respect to the chain. In IIIa, all of the HSqare coplanar, while in IIIb, they are orientated in a mutually perpendicular mannner.…”

Hydrogen-bond landscapes, geometry and energetics of squaric acid and its mono- and dianions: a Cambridge Structural Database, IsoStar and computational study

“…CSD reference code KECYBU11 (Semmingsen, 1973) and others in the KECYBU family (Semmingsen et al, 1977(Semmingsen et al, , 1995Hollander et al, 1977)]. This motif is preserved in SOCLEC (Kolev et al, 2008) and TURPOL (Mathew et al, 2002), which are both ammonium salts of a co-crystal of H 2 SQ with its monoanion (HSQ À ); the ammonium ion, together with an additional water molecule in SOCLEC, serves to link the almost planar R 4 4 ð20Þ rings in these Mean geometry of hydrogen bonds involving O-H donors and terminal-O acceptors in squaric acid (H 2 SQ) and its anions (HSQ À and SQ 2À ).…”