Ab initio and density functional theory studies of the structure,gas-phase acidity and aromaticity of tetraselenosquaric acid

• 来源期刊: 中国化学(英文版)
• 年，卷（期）: 2000,（6）
• 所属期刊栏目: Articles
• 页码范围: 808-814
• 页数: 7页
• 语种: 英文

摘要

Results or ab initio selr-consistent-field ( SCF) and denityfunctional theory (DFr) calculations of the gas-phase structure, acidity (free energy of deprotona tion, △G°) and aroma ticity of tetraselenosquaric acid (3, 4-diseleny-3-cyclobutene-1,2-diselenone, H2C4Se4) are reported.The global minimu found on the potenial energy surface of tetraselenosquaric acid presents a planar conformation. The ZZ isomer was found to have the lowest energy among the three planar conformers and the ZZ and ZE is omers are very close in energy. The optimized geometric parameters exhibit a bond length equalization relative to reference compounds, cyclobutanediselenone, and cyclobutenediselenol. The computed aromaic stabilization energy(ASE)by homodesmotic reaction is -77.4 (MP2(fu)/6 - 311 + G* *//RHF/6 - 311 + G* * ) and - 54.8 kJ/mol (B3LYP/6 - 311 + G* * //B3LYP/6 - 311 + G* * ). The aromaticity of tetraselenosquaric acid is indicated by the calculated diamagnetic susceptibility exaltation (A) - 19.13 (CSGT(IGAIM) - RHF/6 - 311 + G**//RHF/6 - 311 + G* * and - 32.91(4π· 10-6 m3/mo l)(CSGT(IGA1M)-B3LYP/6 - 311 + G* *//B3LYP/6 - 311 + G* * ).Thus, tetraselenosquaric acid fulfils the geometric, energetic and magnetic criteria of aromaticity. The calculated gas-phase acidity is △G10(298K) = 1257.7 and △G20(298K) = 1617.1 kJ/mol. Hence, tetraselenosquarc acid is the stronest acid among the three squaric acids (3,4-dihydroxy-3-cyclobutene-1,2-dione, H2C4O4, 3,4-dithiohydroxy-3- cyclobutene-1,2-dithione, H2C4S4, 3,4- diselenyl-3- cyclobutene- 1,2-diselenone, H2C4Se4).