Squaric acid, H2C4O4 (H(2)SQ), is a completely flat diprotic acid that can crystallize as such, as well as in three different anionic forms, i.e. H(2)SQ . HSQ(-), HSQ(-) and SQ(2-). Its interest for crystal engineering studies arises from three notable factors: (i) its ability of donating and accepting hydrogen bonds strictly confined to the molecular plane; (ii) the remarkable strength of the O-H . . .O bonds it may form with itself which are either of resonance-assisted (RAHB) or negative-charge-assisted [(-)CAHB] types; (iii) the ease with which it may donate a proton to an aromatic base which, in turn, back-links to the anion by strong low-barrier N-H+. . .O1/2- charge-assisted hydrogen bonds. Analysis of all the structures so far known shows that, while H(2)SQ can only crystallize in an extended RAHB-linked planar arrangement and SQ(2-) tends to behave much as a monomeric dianion, the monoanion HSQ(-) displays a number of different supramolecular patterns that are classifiable as beta -chains, alpha -chains, alpha -dimers and alpha -tetramers. Partial protonation of these motifs leads to H(2)SQ . HSQ(-) anions whose supramolecular patterns include ribbons of dimerized beta -chains and chains of emiprotonated alpha -dimers. The topological similarities between the three-dimensional crystal chemistry of orthosilicic acid, H4SiO4, and the two-dimensional one of squaric acid, H2C4O4, are finally stressed.

Associations of squaric acid and its anions as multiform building blocks of hydrogen-bonded molecular crystals

GILLI, Gastone
Primo
;
BERTOLASI, Valerio
Secondo
;
GILLI, Paola
Penultimo
;
FERRETTI, Valeria
Ultimo
2001

Abstract

Squaric acid, H2C4O4 (H(2)SQ), is a completely flat diprotic acid that can crystallize as such, as well as in three different anionic forms, i.e. H(2)SQ . HSQ(-), HSQ(-) and SQ(2-). Its interest for crystal engineering studies arises from three notable factors: (i) its ability of donating and accepting hydrogen bonds strictly confined to the molecular plane; (ii) the remarkable strength of the O-H . . .O bonds it may form with itself which are either of resonance-assisted (RAHB) or negative-charge-assisted [(-)CAHB] types; (iii) the ease with which it may donate a proton to an aromatic base which, in turn, back-links to the anion by strong low-barrier N-H+. . .O1/2- charge-assisted hydrogen bonds. Analysis of all the structures so far known shows that, while H(2)SQ can only crystallize in an extended RAHB-linked planar arrangement and SQ(2-) tends to behave much as a monomeric dianion, the monoanion HSQ(-) displays a number of different supramolecular patterns that are classifiable as beta -chains, alpha -chains, alpha -dimers and alpha -tetramers. Partial protonation of these motifs leads to H(2)SQ . HSQ(-) anions whose supramolecular patterns include ribbons of dimerized beta -chains and chains of emiprotonated alpha -dimers. The topological similarities between the three-dimensional crystal chemistry of orthosilicic acid, H4SiO4, and the two-dimensional one of squaric acid, H2C4O4, are finally stressed.
Gilli, Gastone; Bertolasi, Valerio; Gilli, Paola; Ferretti, Valeria
File in questo prodotto:
File Dimensione Formato  
gilli2001.pdf

solo gestori archivio

Descrizione: Full text editoriale
Tipologia: Full text (versione editoriale)
Licenza: NON PUBBLICO - Accesso privato/ristretto
Dimensione 862.53 kB
Formato Adobe PDF
862.53 kB Adobe PDF   Visualizza/Apri   Richiedi una copia

I documenti in IRIS sono protetti da copyright e tutti i diritti sono riservati, salvo diversa indicazione.

Utilizza questo identificativo per citare o creare un link a questo documento: https://hdl.handle.net/11392/1679879
Citazioni
  • ???jsp.display-item.citation.pmc??? 2
  • Scopus 59
  • ???jsp.display-item.citation.isi??? 54
social impact