MIXED-CRYSTALS OF PYRAZOLES AND BENZOIC-ACIDS .1. THE MOLECULAR-STRUCTURE OF 3,5-DIMETHYLPYRAZOLE-2,4,6-TRIMETHYLBENZOIC ACID CO-CRYSTALS

The title compound 4a has been prepared by slow evaporation of an equi molar mixture of 2,4,6-trimethylbenzoic acid (mesitylenecarboxylic aci d) and 3,5-dimethylpyrazole. Two pyrazoles and two benzoic acids form a tetramer unit through N-H ... O and O-H ... N hydrogen bonds, The py razole rings in 4a show standard geometries, Variable temperature N-15 CPMAS NMR experiments showed that no dynamic process takes place in 4 a, which is consistent with results of low temperature (77 K) FTIR spe ctroscopy, This fact can be explained taking into account the acid-bas e properties of both components.