Intermolecular interaction studies in ammonium squarate: crystal structure and vibrational spectra

详细信息    查看全文

• 作者：Sté ; fanos L. Georgopoulos ; Renata Diniz ; Bernardo L. Rodrigues ; Maria I. Yoshida and Luiz Fernando C. de Oliveira
• 关键词：Squarate ion ; Crystal structure ; Vibrational spectroscopy ; Oxocarbon ion
• 刊名：Journal of Molecular Structure
• 出版年：2005
• 出版时间：2005
• 年：2005
• 卷：753
• 期：1-3
• 页码：147-153
• 全文大小：229 K

文摘

Ammonium squarate salt [(NH₄)₂C₄O₄] crystallizes in the monoclinic space group P2₁/c. The crystal presents the squarate ions displayed in layers parallel to a crystallographic axis and forming hydrogen bonds interactions with ion=1&_userid=10&md5=28329f410d4a644e1372a3c39fcb6db7""> cations, localized between squarate anions layers. The squarate anion presents similar CC and CO bond distances which indicate a degree of electronic delocalization in the rings. A π-stacking interaction is observed between squarate rings separated by interplanar distance and centroid ring distance of respectively 3.41 and 3.71 . The electron delocalization was also observed in the vibrational spectra. The infrared spectrum shows a narrow band around 1530 cm⁻¹, assigned to a coupled stretching mode of CO and CC groups, indicating the high symmetry of the squarate ion. The Raman spectrum also shows this effect in the 1000 to 1200 cm⁻¹ region (related to CC stretching mode), where it is expected a decrease of the number of bands if compared to squarate ion in aqueous solution, where the symmetry is actually D_4h; in the (NH₄)₂C₄O₄ Raman spectrum just one strong band is observed at 1120 cm⁻¹. All the vibrational results indicate the symmetry is very close to the one observed for the solvated ion in aqueous solution; once again the vibrational analysis appears as an important tool in recognizing the oxocarbon ion geometry in the solid state.