Mechanochemical Preparationof Hydrogen-Bonded Adducts Between the Diamine 1,4-Diazabicyclo[2.2.2]octane and Dicarboxylic Acids of Variable Chain Lenth:An X-ray Diffraction and Solid-State NMR Study

摘要

Mechanical mixing of solid dicarboxylic acids of variable chain length HOOC(CH)_2)_nCOOH (n=1-7)with solid 1,4-Diazabicyclo[2.2.2]octane generates the correspodning salts or cocrystals of the formula [N(CH_2CH_2)_3N]H-[OOC(CH_2)_nCOOH](n=1-7).Preparation of the same systems from solution has been instrumental for a full characterization of the mechanochemical products by means of single-crystal and powder-diffraction X-ray analyses,as well as by solid-state NMR.The acid-base adducts,whether invoving proton transfer from the COOH group to the N-acceptor,that is having O…H-N interactions,or the formation of neutral O-H…N hydrogen bonds,show a metling point alternation phenomenon analogous to that shown by the neutral carboxylic acids.The carbon chemical shift tensors of the COOh group obtained from the sideband intensity of lw speed spinning NMR spectra provide a reliable criterion for assigning the protonation state of the adducts.