A Persistent Preference for Layer Motifs in Self-Assemblies of Squarates and Hydrogen Squarates by Hydrogen Bonding [X−H···O; X = N, O, or C]:  A Crystallographic Study of Five Organic Salts

Abstract

The synthesis and single-crystal X-ray structures of hydrogen squarates of imidazole (1), histidine (2), and 2-aminopyridine (4) and squarates of histidine (3) and 4-aminopyridine (5) are reported. Both hydrogen squarate [HSQ] 1and squarate [SQ] 2ions participate in complementary hydrogen bonding [X-H‚‚‚O; X ) N, O, or C] networks. While the [HSQ] 1ion acts both as a donor and as an acceptor of hydrogen bonds in salts 1, 2, and 4 and creates head-to-tail infinite chains of anions in 1 and head-to-head ten-membered cyclic dimers in 4, the [SQ] 2ion participates as a powerful acceptor of as many as six hydrogen bonds in 3 and 5. In all cases, extensive hydrogen bonding and ionic interactions between the components lead to layered assemblies. In 1, the cross-linking of the [HSQ] 1chains by protonated imidazolium ions through N-H‚‚‚O bonds creates a two-dimensional ionic sheet which is further stabilized by the presence of C-H‚‚‚O bonds resulting from the participation of the imidazolium C-H groups. In 2 and 3, the layered structures are formed by cross-linking of the cationic self-assemblies (His-His infinite helices in 2 and His-His zigzag ribbons in 3) by [HSQ] 1and [SQ] 2-, respectively. A novel feature in 3 is the presence of two C-H‚‚‚O bonds between the more acidic CH group and the O1 in [SQ] 2-. In 4, the cyclic dimers of [HSQ] 1are interwoven into a two-dimensional sheet with a checker-board motif by the participation of 2-aminopyridinium cation in horizontal and vertical N-H‚‚‚O bonds. The two-dimensional layered assembly in 5 arises by extensive participation of water molecules in cross-linking of the alternating anion-cation conjugates both in horizontal and vertical directions. Irrespective of the presence of different types of hydrogen-bonding patterns in the structures of 1-5, the persistent formation of a two-dimensional layered assembly is significant and may be a characteristic of squaric acid salts.

Organic mandelates as promising materials with non-linear optical application

“…Instead that compounds (1) and (4) crystallized in non-centrosymmetric space groups, the properties of these crystals are such as to include some of the most important characteristic desired for practical application in useful for crystal engineering and NLO technology. The compounds are characterized by high solubility in aqueous media, allowing reasonable rate of crystal growth and good properties, particularly in the cases of (1) and (4). The compounds possess high thermal stability at temperatures Table 1 Theoretical UV spectra in aqueous solution of (1)- (3) B3LYP/6-31 ?…”

“…The design of non-linear optical devices incorporating second harmonic generator materials, which produce frequency doubling effect of optical wavelength electromagnetic radiation, is attractive area of modern materials research and crystal engineering [1][2][3][4][5][6][7][8][9][10]. It is known that various organic and inorganic compounds possess the ability to double the frequency of laser light passing through them, this ability is known as SHG and provides the ability to produce laser light of higher energy than that provided by the initial laser light source.…”

“…Hydrogen bonding also tends to increase the thermal stability and mechanical strength of the crystalline material, and to suppress the formation of crystalline hydrates. The corresponding organic base is preferably an amine, imine [1][2][3][4][11][12][13][14][15] or heterocycle with basic nitrogen atoms. For these reasons the current research is focused on design, synthesis and isolation of the organic mandelates (Scheme 1).…”

Crystal structure and spectroscopic properties of ammonium hydrogensquarate squaric acid monohydrate

“…HSq @ exists in at least four different forms. As established in series of systematic crystallographic studies on the self-assembly of squarates and hydrogensquarates [1][2][3][4][5][6]. Detailed studied on the correlation of vibrational spectroscopic properties and structural motifs in squaric acid derivatives have been reported [7][8][9][10][11][12][13][14].…”

Crystal structure of N‐(3,4‐dichlorophenyl)‐N′‐hydroxy‐2‐oxo‐2‐phenylacetamidine

“…Intermolecular hydrogen bonding has received considerable attention among the directional noncovalent intermolecular interactions [1]; it combines moderate strength and directionality [2] in linking molecules to form supramolecular structures.…”