Salts of the scissor-shaped racemic host 1,1′-binaphthyl-2,2′-dicarboxylic acid with amines: structure and thermal stability

Abstract

The salts formed between racemic 1,1′-binaphthyl-2,2′-dicarboxylic acid (BNDA) and the amines diethylamine (DEA), di-n-butylamine (DBA), cyclohexylamine (CHA) and dicyclohexylamine (DCHA) are reported. Structure 1, (BNDA²⁻)(2DEA⁺), and 2a, (BNDA²⁻)(2DBA⁺), resulted from slow evaporation of a solution of BNDA in the respective amine. A competition experiment whereby BNDA was dissolved in a mixture of 60% DEA and 40% DBA resulted in a polymorph of 2a, namely 2b. Slow evaporation of dilute solutions of BNDA with CHA and DCHA resulted in a mixed salt solvate 3, (BNDA²⁻)(3CHA⁺)(C₇NO₂H₁₁⁻)·CHA·H₂O, and a salt solvate, 4, (BNDA²⁻)(2DCHA⁺)·CH₃OH·H₂O, respectively. For all the experiments methanol was used as a co-solvent due to BNDA insolubility with the amines. In structure 3 one of the CHA guests reacted with carbon dioxide in the atmosphere to form a carbamate anion, C₇NO₂H₁₁⁻. The kinetics of desolvation for salts 1, 2a and 2b were also determined.