Does Higher-Dimensional Hydrogen Bonding Guarantee a Smaller Thermal Expansion? A Thermal Expansion Study of an Interdigitated 1D and Interpenetrated 3D Hydrogen-Bonded Colored Dimorphic System

The 1:1:1 complex of benzene-1,3,5-tricarboxylic acid (BTA), 4,4′-methylenebis­(2,6-dimethylaniline) (MBDA), and methanol has two polymorphic forms that can be regarded as synthon polymorphs. The hydrogen bond dimensionalities in the crystal structure of the two forms are different, and the forms have their own unique colors. The polymorph, with a three-dimensional hydrogen bond topology (3D form), forms an interpenetrated network and is violet in color, whereas the other polymorph, which is bright yellow in color, forms an interdigitated one-dimensional hydrogen bond topology (1D form). The volumetric expansion of the 3D form is comparable to that of the 1D form, but the anisotropy of expansion is found to be significantly higher in the 3D form than in its 1D counterpart. A structure–property correlation study of the dimorphic complex is presented in the context of their thermal expansion behavior and color