Crystal Structure of a Proton-Transfer Self-associated Compound Tetrakis(guanidinium)bis(eosinate) hexahydrate

Abstract

Designing the self-assembly of neutral molecules or ions into preordained motifs by non-covalent interactions is an area of current interest, especially in the context of generating new molecular materials. In recent years, many compounds based on cations of guanidine and its derivatives are the object of chemical research owing to their biological role in living organisms, supramolecular structure, function as molecular switches, 1,2 and their interesting physico-chemical properties. Particularly, the guanidinium cation has been proven to be a powerful structure-determining template in the formation of both coordination polymer networks and hydrogen bonded networks.3 In order to explore the interactions between 2¢,4¢,5¢, 7¢-tetrabormofluorescein (eosin) and guanidinium cation, herein we report on the synthesis and crystal structure of the title compound, tetrakis(guanidinium)bis(eosinate) hexahydrate (I).Guanidine carbonate (0.045 g, 0.250 mmol) was dissolved in 2 mL of water and 2¢,4¢,5¢,7¢-tetrabormofluorescein (0.081 g, 0.125 mmol) was dissolved in 5 mL of 1:1 acetone by warming. Then, a clear solution of 2¢,4¢,5¢,7¢-tetrabormofluorescein was slowly added to the guanidine carbonate solution. The mixture was kept at room temperature for slow evaporation. After one week, needle-shaped pink-colored crystals of tetrakis(guanidini um)bis(eosinate) hexahydrate (I) were obtained. Single crystals with dimensions of (0.34 ¥ 0.20 ¥ 0.12) mm 3 were chosen for X-ray diffraction studies. Determinations of the unit-cell parameters and data collections were performed with Mo Ka radiation (l = 0.71073 Å) at 293 K on a Bruker Apex II CCD area-detector diffractometer. The structure was solved using direct methods.All non-hydrogen atoms were refined anisotropically by full matrix least-squares methods on F 2 . Primary non-hydrogen atoms were solved by direct method, and secondary non-hydrogen atoms were solved by a difference maps. The hydrogen atoms were added geometrically. The H- A co-crystal of tetrakis(guanidinium) bis(eosinate) hexahydrate (I) was synthesized, and the molecular and crystal structures of (I) were determined by a single-crystal X-ray diffraction technique. The crystal system is triclinic with a space group of P1 and Z = 4. The unit-cell dimensions are a = 14.4774 (8)

Cocrystals versus Salts of Fluorescein

“…The use of basic nitrogen-containing molecules as partners for cocrystallization offers the theoretical possibility of proton transfer with the formation of organic salts. Such salts were reported for eosin (2 ,4 ,5 ,7tetrabromofluorescein) with 4-aza-1-azoniabicyclo[2.2.2]octane [20] and guanidium cations [21]. In Mannich derivatives of fluorescein, the presence of basic nitrogen atoms attached to the xanthene core allows the intramolecular transfer of the protons with the formation of zwitterions [22].…”

“…In Mannich derivatives of fluorescein, the presence of basic nitrogen atoms attached to the xanthene core allows the intramolecular transfer of the protons with the formation of zwitterions [22]. als 2021, 11, x FOR PEER REVIEW 2 of 17 tetrabromofluorescein) with 4-aza-1-azoniabicyclo[2.2.2]octane [20] and guanidium cations [21]. In Mannich derivatives of fluorescein, the presence of basic nitrogen atoms attached to the xanthene core allows the intramolecular transfer of the protons with the formation of zwitterions [22].…”